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LIQUID NITROGEN

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Classification   |    Detailed evidence-based information

Substances Included Synonyms

Therapeutic Toxic Class

    A) Nitrogen is a colorless, odorless, tasteless gas stored under compression in metal containers. Nitrogen exists in a liquid phase between minus 209.86 C (melting point) and minus 195 C (boiling point).

Specific Substances

    1) Nitrogen
    2) Nitrogen gas
    3) Nitrogen, compressed
    4) Nitrogen, refrigerated liquid
    5) Nitrogen, liquid
    6) Nitrogen, cryogenic liquid
    7) Nitrogenium
    8) Azote
    9) CAS 7727-37-9
    1.2.1) MOLECULAR FORMULA
    1) N2

Available Forms Sources

    A) FORMS
    1) Nitrogen is a colorless, odorless, tasteless gas stored under compression in metal containers. Nitrogen exists in a liquid phase between minus 209.86 degrees Celsius (melting point) and minus 195 degrees Celsius (boiling point) (Rockswold & Buran, 1982).
    B) USES
    1) Employed in cryosurgery
    a) To extend surgical margin of excision in cancer operations (Dwyer et al, 1990)
    b) To treat disseminated superficial actinic porokeratosis, elastosis perforans serpiginosa, acne vulgaris cysts, and verrucae (Rosenblum, 1983; Yaffe et al, 1986; Sawyer & Picou, 1989; JEF Reynolds , 1990)
    2) To relieve pain in trigeminal neuralgia (Nally & Zakrzewska, 1984)
    3) Used in medicine and biology for quick freezing of tissues and microorganisms (Clayton & Clayton, 1994)
    4) Used to euthanize dogs, rabbits, and mink (Booth & McDonald, 1982)
    5) Widely used for chilling metals to alter their physical characteristics (Clayton & Clayton, 1994)
    6) Component of fertilizers (ILO, 1983)
    7) Used as carrier gas in gas chromatography (HSDB , 1998)

Overview

Life Support

    A) This overview assumes that basic life support measures have been instituted.

Clinical Effects

    0.2.1) SUMMARY OF EXPOSURE
    A) USES: Nitrogen is a basic element that exists in a liquid phase between minus 209.86 degrees C (melting point) and minus 195 degrees C (boiling point). Liquid nitrogen has many uses, including cryosurgery, pain relief for patients with trigeminal neuralgia, quick freezing of tissues and microorganisms, animal euthanasia, chilling metals to alter their characteristics, a component in fertilizers, and as a carrier gas for gas chromatography.
    B) TOXICOLOGY: When used in cryosurgery, liquid nitrogen causes microvascular failure with minimal inflammatory response amidst liquefaction necrosis and progressive fibrosis. Topical damage can occur from the extreme cold of liquid nitrogen, while inhalational toxicity can occur from its freezing effects as well as the displacement of oxygen. Another potential method of toxicity is the development of a venous gas embolism when used in surgery.
    C) EPIDEMIOLOGY: Liquid nitrogen is commonly used for many different industrial and laboratory purposes. Severe toxicity and death secondary to exposure is extremely rare but has been reported.
    D) WITH POISONING/EXPOSURE
    1) Inhalation of liquid nitrogen gas may injure the pharynx. It may also displace oxygen from air and cause asphyxia with associated central nervous system (CNS) injury with prolonged exposure. Topical application can result in a variety of dermal injuries (eg, hyperemia, erythema, bullae, edema, burns, and necrosis), neuropathies, and gas embolism. Syncope and cardiac arrest have also been described. Ingestion of liquid nitrogen can injure the oropharynx, esophagus, and gastric mucosa. Perforation may occur in extremely severe cases.
    0.2.20) REPRODUCTIVE
    A) At the time of this review, no reproductive studies were found for nitrogen in humans or experimental animals.
    0.2.21) CARCINOGENICITY
    A) At the time of this review, no studies were found on the possible carcinogenic activity of nitrogen in humans or experimental animals.

Laboratory Monitoring

    A) No specific laboratory studies are needed for liquid nitrogen exposures. Labs should be based on patient's symptoms.
    B) No specific levels of nitrogen are needed.
    C) Monitor vital signs following significant exposure.
    D) Obtain an ECG, and institute continuous cardiac monitoring.
    E) Monitor arterial blood gases, pulse oximetry, and pulmonary function tests, and obtain a chest x-ray in any patient with respiratory symptoms.
    F) Monitor mental status. Patients with an altered mental status may require a head CT.

Treatment Overview

    0.4.3) INHALATION EXPOSURE
    A) MANAGEMENT OF MILD TO MODERATE TOXICITY
    1) Treatment is symptomatic and supportive. Depending on the route of exposure, symptoms may vary widely. The most common type of exposure is likely dermal or inhalational; oral ingestions are relatively rare. Monitor closely for respiratory distress. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required. Direct eye and parenteral exposures are also very uncommon.
    B) MANAGEMENT OF SEVERE TOXICITY
    1) Treatment is symptomatic and supportive. Severe toxicity is very rare, but there have been reports of death. Airway injuries may occur with inhalational exposures and dermal exposures can cause serious direct tissue damage. Monitor closely for respiratory distress. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required. Monitor for complications (eg, gas embolism, syncope, and cardiac arrest) from the use of liquid nitrogen.
    C) DECONTAMINATION
    1) PREHOSPITAL: DERMAL EXPOSURE: Liquid nitrogen will rapidly evaporate at room temperature. Washing the skin may not be beneficial. Rewarming of a localized area should only be considered if the risk of refreezing is unlikely. Refreezing thawed tissue increases tissue damage. Avoid rubbing the frozen area which may cause further damage to the area. ORAL EXPOSURE: There is no indication for the use of prehospital activated charcoal. EYE EXPOSURE: There is no evidence for prehospital decontamination following an eye exposure. Patients with an eye exposure who are symptomatic should undergo ophthalmologic evaluation for treatment. INHALATIONAL EXPOSURE: Severe mucosal injury to the hypopharynx may occur. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required.
    2) HOSPITAL: DERMAL EXPOSURE: Rewarming of a localized area should only be considered if the risk of refreezing is unlikely. Refreezing thawed tissue increases tissue damage. Avoid rubbing the frozen area which may cause further damage to the area. Place affected area in a water bath with a temperature of 40 to 42 degrees C for 15 to 30 minutes until thawing is complete. The bath should be large enough to permit complete immersion of the injured area, avoiding contact with the sides of the bath. A whirlpool bath would be ideal. Some authors suggest a mild antibacterial agent (ie, chlorhexidine, hexachlorophene or povidone-iodine) be added to the bath water. Tissues should be thoroughly rewarmed and pliable; the skin will appear a red-purple color. Rewarming may be associated with increasing acute pain, requiring narcotic analgesics. For information on severe frostbites and wound care, refer to the main treatment section of this document. ORAL EXPOSURE: There is no evidence for the use of activated charcoal, gastric lavage, or whole bowel irrigation. EYE EXPOSURE: There is no evidence for decontamination following an eye exposure. Patients with an eye exposure who are symptomatic should undergo ophthalmologic evaluation for treatment. INHALATIONAL EXPOSURE: Severe mucosal injury to the hypopharynx may occur. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required. Tracheostomy may be indicated to avoid trauma from endotracheal intubation over severely damaged pharyngeal tissues. Corticosteroids may be beneficial in treating mucosal injuries. If prolonged asphyxia has occurred following inhalation of liquid nitrogen gas, evaluate for CNS injury and provide treatment as needed. PARENTERAL EXPOSURE: There is the potential for venous gas embolism from liquid nitrogen used in cryotherapy surgery. Potential treatment includes hyperbaric oxygen.
    D) AIRWAY MANAGEMENT
    1) For inhalational exposures, airway management may become an issue, and if there is severe damage to the hypopharynx, tracheostomy may be preferred over endotracheal intubation to avoid further trauma to damaged tissues.
    E) ANTIDOTE
    1) None.
    F) PATIENT DISPOSITION
    1) HOME CRITERIA: Patients with a minor exposure with no symptoms or minimal symptoms that are improving may stay at home.
    2) OBSERVATION CRITERIA: Patients who are symptomatic and not clearly improving should be sent to a healthcare facility for observation until they are clinically improving. Patients should not be discharged until their symptoms are well-controlled.
    3) ADMISSION CRITERIA: Patients with severe symptoms or symptoms that are getting progressively worse despite treatment should be admitted to the hospital. Depending on the severity of symptoms, patients may require an intensive care admission, especially those with cardiovascular instability or airway damage. Patients with dermal injuries may require a burn unit if their symptoms are severe enough. Patients should not be discharged from the hospital until they are clearly improving or their symptoms are well-controlled.
    4) CONSULT CRITERIA: Patients who require intensive care will likely require the service of an intensivist. Patients with airway injuries may require the aid of a surgeon. Patients with severe or extensive dermal injuries should be evaluated by a burn specialist. Consult a regional poison center or medical toxicologist for assistance in managing patients with severe toxicity or for whom diagnosis is unclear. Patients with an eye injury should be evaluated by an ophthalmologist.
    G) PITFALLS
    1) Since severe toxicity is rare, healthcare providers may miss or not realize severe complications that can result from the use of liquid nitrogen (eg, asphyxiation, airway injuries, gas embolism).
    H) DIFFERENTIAL DIAGNOSIS
    1) Liquid nitrogen topical toxicity can mimic other causes of frostbite (eg, extremely cold weather, other extremely cool substances). Inhalational toxicity may mimic other asphyxiants.
    0.4.5) DERMAL EXPOSURE
    A) OVERVIEW
    1) Liquid nitrogen will rapidly evaporate at room temperatures. Washing the skin may not be beneficial.
    2) PREHOSPITAL
    a) Rewarming of a localized area should only be considered if the risk of refreezing is unlikely. Avoid rubbing the frozen area which may cause further damage to the area (Grieve et al, 2011; Hallam et al, 2010).
    3) REWARMING
    a) Do not institute rewarming unless complete rewarming can be assured; refreezing thawed tissue increases tissue damage. Place affected area in a water bath with a temperature of 40 to 42 degrees Celsius for 15 to 30 minutes until thawing is complete. The bath should be large enough to permit complete immersion of the injured part, avoiding contact with the sides of the bath. A whirlpool bath would be ideal. Some authors suggest a mild antibacterial (ie, chlorhexidine, hexachlorophene or povidone-iodine) be added to the bath water. Tissues should be thoroughly rewarmed and pliable; the skin will appear a red-purple color (Grieve et al, 2011; Hallam et al, 2010; Murphy et al, 2000).
    b) Correct systemic hypothermia which can cause cold diuresis due to suppression of antidiuretic hormone; consider IV fluids (Grieve et al, 2011).
    c) Rewarming may be associated with increasing acute pain, requiring narcotic analgesics.
    d) For severe frostbite, clinical trials have shown that pentoxifylline, a phosphodiesterase inhibitor, can enhance tissue viability by increasing blood flow and reducing platelet activity (Hallam et al, 2010).
    4) WOUND CARE
    a) Digits should be separated by sterile absorbent cotton; no constrictive dressings should be used. Protective dressings should be changed twice per day.
    b) Perform twice daily hydrotherapy for 30 to 45 minutes in warm water at 40 degrees Celsius. This helps debride devitalized tissue and maintain range of motion. Keep the area warm and dry between treatments (Hallam et al, 2010; Murphy et al, 2000).
    c) The injured extremities should be elevated and should not be allowed to bear weight.
    d) In patients at risk for infection of necrotic tissue, prophylactic antibiotics and tetanus toxoid have been recommended by some authors (Hallam et al, 2010; Murphy et al, 2000).
    e) Non-tense clear blisters should be left intact due to the risk of infection; tense or hemorrhagic blisters may be carefully aspirated in a setting where aseptic technique is provided (Hallam et al, 2010).
    f) Further surgical debridement should be delayed until mummification demarcation has occurred (60 to 90 days). Spontaneous amputation may occur.
    g) Analgesics may be required during the rewarming phase; however, patients with severe pain should be evaluated for vasospasm.
    h) IMAGING: Arteriography and noninvasive vascular techniques (e.g., plain radiography, laser Doppler studies, digital plethysmography, infrared thermography, isotope scanning), have been useful in evaluating the extent of vasospasm after thawing and assessing whether debridement is needed (Hallam et al, 2010). In cases of severe frostbite, Technetium 99 (triple phase scanning) and MRI angiography have been shown to be the most useful to assess injury and determine the extent or need for surgical debridement (Hallam et al, 2010).
    i) TOPICAL THERAPY: Topical aloe vera may decrease tissue destruction and should be applied every 6 hours (Murphy et al, 2000).
    j) IBUPROFEN THERAPY: Ibuprofen, a thromboxane inhibitor, may help limit inflammatory damage and reduce tissue loss (Grieve et al, 2011; Murphy et al, 2000). DOSE: 400 mg orally every 12 hours is recommended (Hallam et al, 2010).
    k) THROMBOLYTIC THERAPY: Thrombolysis (intra-arterial or intravenous thrombolytic agents) may be beneficial in those patients at risk to lose a digit or a limb, if done within the first 24 hours of exposure. The use of tissue plasminogen activator (t-PA) to clear microvascular thromboses can restore arterial blood flow, but should be accompanied by close monitoring including angiography or technetium scanning to evaluate the injury and to evaluate the effects of t-PA administration. Potential risk of the procedure includes significant tissue edema that can lead to a rise in interstitial pressures resulting in compartment syndrome (Grieve et al, 2011).
    l) CONTROVERSIAL: Adjunct pharmacological agents (ie, heparin, vasodilators, prostacyclins, prostaglandin synthetase inhibitors, dextran) are controversial and not routinely recommended. The role of hyperbaric oxygen therapy, sympathectomy remains unclear (Grieve et al, 2011).
    m) CHRONIC PAIN: Vasomotor dysfunction can produce chronic pain. Amitriptyline has been used in some patients; some patients may need a referral for pain management. Inability to tolerate the cold (in the affected area) has been observed following a single episode of frostbite (Hallam et al, 2010).
    n) MORBIDITIES: Frostbite can produce localized osteoporosis and possible bone loss following a severe case. These events may take a year or more to develop. Children may be at greater risk to develop more severe events (ie, early arthritis) (Hallam et al, 2010).

Range Of Toxicity

    A) TOXICITY: Signs of asphyxia may occur when liquid nitrogen gas displaces the oxygen in air to 15% or less. Prolonged asphyxia leading to death may happen when oxygen concentration falls to 6% or less.

Clinical Effects

Summary Of Exposure

    A) USES: Nitrogen is a basic element that exists in a liquid phase between minus 209.86 degrees C (melting point) and minus 195 degrees C (boiling point). Liquid nitrogen has many uses, including cryosurgery, pain relief for patients with trigeminal neuralgia, quick freezing of tissues and microorganisms, animal euthanasia, chilling metals to alter their characteristics, a component in fertilizers, and as a carrier gas for gas chromatography.
    B) TOXICOLOGY: When used in cryosurgery, liquid nitrogen causes microvascular failure with minimal inflammatory response amidst liquefaction necrosis and progressive fibrosis. Topical damage can occur from the extreme cold of liquid nitrogen, while inhalational toxicity can occur from its freezing effects as well as the displacement of oxygen. Another potential method of toxicity is the development of a venous gas embolism when used in surgery.
    C) EPIDEMIOLOGY: Liquid nitrogen is commonly used for many different industrial and laboratory purposes. Severe toxicity and death secondary to exposure is extremely rare but has been reported.
    D) WITH POISONING/EXPOSURE
    1) Inhalation of liquid nitrogen gas may injure the pharynx. It may also displace oxygen from air and cause asphyxia with associated central nervous system (CNS) injury with prolonged exposure. Topical application can result in a variety of dermal injuries (eg, hyperemia, erythema, bullae, edema, burns, and necrosis), neuropathies, and gas embolism. Syncope and cardiac arrest have also been described. Ingestion of liquid nitrogen can injure the oropharynx, esophagus, and gastric mucosa. Perforation may occur in extremely severe cases.

Heent

    3.4.3) EYES
    A) WITH POISONING/EXPOSURE
    1) CORNEAL ABRASIONS: When rabbit eyes were exposed to liquid nitrogen for 5 seconds, reversible corneal abrasions were demonstrated by fluorescein staining. However, no discernible injury was demonstrated following a one to two seconds exposure (Grant & Schuman, 1993).
    3.4.6) THROAT
    A) WITH POISONING/EXPOSURE
    1) PHARYNGEAL INJURY: Inhalation of liquid nitrogen gas may result in dysphonia, swollen epiglottis, bullae formation on the hard palate and posterior pharynx with eventual sloughing and ulceration in areas of greatest involvement, and a potential for postinjury stricture and stenosis (Rockswold & Buran, 1982).

Cardiovascular

    3.5.2) CLINICAL EFFECTS
    A) CARDIAC ARREST
    1) Cardiac arrest has been reported following cryotherapy utilizing topical liquid nitrogen (Wingfield & Fraunfelder, 1979; Epstein & Shupack, 1977; Finelli, 1975; Goldstein, 1979; Caravati et al, 1969).
    B) THROMBOEMBOLIC DISORDER
    1) CASE REPORT: Venous gas embolism was reported in a man who underwent curettage and cryotherapy for a suspected chrondrosarcoma of the humerus (Dwyer et al, 1990).

Neurologic

    3.7.2) CLINICAL EFFECTS
    A) NEUROPATHY
    1) Neuropathies and syncope have been reported following topical application of liquid nitrogen for cryotherapy (Wingfield & Fraunfelder, 1979; Epstein & Shupack, 1977; Finelli, 1975; Goldstein, 1979; Caravati et al, 1969).
    B) CENTRAL NERVOUS SYSTEM DEFICIT
    1) Prolonged hypoxia from inhalation of evolved nitrogen gas can result in CNS injury (Proctor & Hughes, 1988).
    2) Nitrogen gas at standard temperature and pressure is nontoxic, but may act as a simple asphyxiant by displacing oxygen from the air, particularly in enclosed spaces (AAR, 1987) (NFPA, 1986) (Sax & Lewis, 1996). Dizziness, fatigue, decreased vision, mood disturbances, numbness of extremities, headache, confusion, decreased coordination and judgment, cyanosis, and loss of consciousness may occur from asphyxia (CHRIS , 1985; Kizer, 1984).
    C) DROWSY
    1) NARCOSIS: At high concentrations and pressures (such as in deep-sea diving), nitrogen has a narcotic action (Sax & Lewis, 1989).

Gastrointestinal

    3.8.2) CLINICAL EFFECTS
    A) FROSTBITE
    1) Ingestion of liquid nitrogen can cause injury to the oropharyngeal, esophageal and gastric mucosa. In severe cases perforation may occur.

Dermatologic

    3.14.2) CLINICAL EFFECTS
    A) FROSTBITE
    1) Direct dermal contact with the liquid nitrogen may result in frostbite (NFPA, 1986) (CHRIS , 1985).
    B) DERMATITIS
    1) Hyperemia has been reported following topical application of liquid nitrogen (Wingfield & Fraunfelder, 1979; Epstein & Shupack, 1977; Finelli, 1975; Goldstein, 1979; Caravati et al, 1969).
    C) BULLOUS ERUPTION
    1) ONYCHODYSTROPHIES: Erythema, bullae formation, and edema have been reported following topical application of liquid nitrogen (Wingfield & Fraunfelder, 1979; Epstein & Shupack, 1977; Finelli, 1975; Goldstein, 1979; Caravati et al, 1969).
    D) CHEMICAL BURN
    1) Inhalation of liquid nitrogen gas results in burns to the lips with charring, inflammation, and edema (Rockswold & Buran, 1982).
    E) SKIN NECROSIS
    1) Cryogenic necrosis with liquid nitrogen cryotherapy does not usually extend beyond 2 mm when topically applied with cotton swabs, with an average maximum depth of about 1.5 mm. Application under pressure has been noted to increase the extent of necrosis (Caravati et al, 1969; Finelli, 1975).
    2) Gangrene of the foot and lower leg due to cold injury was described following exposure to liquid nitrogen (Leu & Clodius, 1989). Thrombotic occlusions were revealed on histology.
    F) SUBCUTANEOUS EMPHYSEMA
    1) CASE REPORT: Subcutaneous emphysema has developed after spray application of liquid nitrogen to facial actinic keratoses in 2 elderly patients with fragile skin (Cook & Georgouras, 1993).
    G) GRANULOMA
    1) CASE REPORT: Pyogenic granuloma developed on the palm of a patient treated for verruca vulgaris with liquid nitrogen followed by daily application of salicylic acid for 5 days (Kolbusz & O'Donoghue, 1993).
    H) KARYOPYKNOSIS
    1) Karyopyknosis and vacuolation were evident in the epidermis on post-mortem histological examination in 2 patients with liquid nitrogen contact and death due to asphyxiation. Hyperemia and edematous changes in the dermis were also reported. The skin lesion was determined to be the result of antemortem cryo-injury from liquid nitrogen (Tabata et al, 1995).

Respiratory

    3.6.2) CLINICAL EFFECTS
    A) INJURY DUE TO ASPHYXIATION
    1) Liquid nitrogen gas may displace oxygen from the air and result in hypoxia or asphyxia (Proctor & Hughes, 1988).
    2) Nitrogen gas at standard temperature and pressure is nontoxic, but may act as a simple asphyxiant, particularly in enclosed spaces, by displacing oxygen from the air (AAR, 1987) (NFPA, 1986) (Sax & Lewis, 1996). Dizziness, fatigue, decreased vision, mood disturbances, numbness of extremities, headache, confusion, decreased corrdination and judgment, cyanosis, and loss of consciousness may occur from asphyxia (CHRIS , 1985; Kizer, 1984).
    3) Simple asphyxiants displace oxygen from the breathing atmosphere primarily in enclosed spaces and result in hypoxemia (Kizer, 1984). Air hunger, fatigue, decreased vision, mood disturbances, numbness of extremities, headache, confusion, decreased coordination and judgment, cyanosis, and unconsciousness may be noted (Kizer, 1984).
    4) CASE REPORT: Two young researchers died from asphyxia. They had been working in a closed, cool room and were found with 3 opened Dewar flasks containing liquid nitrogen. It was speculated that the liquid nitrogen was being used to cool the room. The liquid nitrogen quickly evaporated, displacing the oxygen in the air with nitrogen gas (Tabata et al, 1995).
    B) ACUTE RESPIRATORY INSUFFICIENCY
    1) CNS depression may lead to respiratory depression resulting in hypoventilation and apnea (Briantseva, 1982).
    C) DISORDER OF RESPIRATORY SYSTEM
    1) NARCOSIS: At high concentrations and pressures (such as in deep-sea diving), nitrogen has a narcotic action (Sax & Lewis, 1989). Bubbles of nitrogen gas are the cause of compressed air illnesses (bends, caisson disease) (Sax & Lewis, 1989). The narcotic and compressed air illness effects are not seen with exposure to nitrogen under normal atmospheric pressure.
    D) INJURY OF UPPER RESPIRATORY TRACT
    1) Inhalation of liquid nitrogen gas may result in dysphonia, swollen epiglottis, bullae formation on the hard palate and posterior pharynx with eventual sloughing and ulceration in areas of greatest involvement, and a potential for postinjury stricture and stenosis (Rockswold & Buran, 1982).

Reproductive

    3.20.1) SUMMARY
    A) At the time of this review, no reproductive studies were found for nitrogen in humans or experimental animals.

Carcinogenicity

    3.21.1) IARC CATEGORY
    A) IARC Carcinogenicity Ratings for CAS7727-37-9 (International Agency for Research on Cancer (IARC), 2016; International Agency for Research on Cancer, 2015; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2010; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2010a; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2008; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2007; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2006; IARC, 2004):
    1) Not Listed
    3.21.2) SUMMARY/HUMAN
    A) At the time of this review, no studies were found on the possible carcinogenic activity of nitrogen in humans or experimental animals.

Laboratory Monitoring

Monitoring Parameters Levels

    4.1.1) SUMMARY
    A) No specific laboratory studies are needed for liquid nitrogen exposures. Labs should be based on patient's symptoms.
    B) No specific levels of nitrogen are needed.
    C) Monitor vital signs following significant exposure.
    D) Obtain an ECG, and institute continuous cardiac monitoring.
    E) Monitor arterial blood gases, pulse oximetry, and pulmonary function tests, and obtain a chest x-ray in any patient with respiratory symptoms.
    F) Monitor mental status. Patients with an altered mental status may require a head CT.

Treatment

Life Support

    A) Support respiratory and cardiovascular function.

Patient Disposition

    6.3.3) DISPOSITION/INHALATION EXPOSURE
    6.3.3.1) ADMISSION CRITERIA/INHALATION
    A) Patients with severe symptoms or symptoms that are getting progressively worse despite treatment should be admitted to the hospital. Depending on the severity of symptoms, patients may require an intensive care admission, especially those with cardiovascular instability or airway damage. Patients with dermal injuries may require a burn unit if their symptoms are severe enough. Patients should not be discharged from the hospital until they are clearly improving or their symptoms are well-controlled.
    6.3.3.2) HOME CRITERIA/INHALATION
    A) Patients with a minor exposure with no symptoms or minimal symptoms that are improving may stay at home.
    6.3.3.3) CONSULT CRITERIA/INHALATION
    A) Patients who require intensive care will likely require the service of an intensivist. Patients with airway injuries may require the aid of a surgeon. Patients with severe or extensive dermal injuries should be evaluated by a burn specialist. Consult a regional poison center or medical toxicologist for assistance in managing patients with severe toxicity or for whom diagnosis is unclear. Patients with an eye injury should be evaluated by an ophthalmologist.
    6.3.3.5) OBSERVATION CRITERIA/INHALATION
    A) Patients who are symptomatic and not clearly improving should be sent to a healthcare facility for observation until they are clinically improving. Patients should not be discharged until their symptoms are well-controlled.

Monitoring

    A) No specific laboratory studies are needed for liquid nitrogen exposures. Labs should be based on patient's symptoms.
    B) No specific levels of nitrogen are needed.
    C) Monitor vital signs following significant exposure.
    D) Obtain an ECG, and institute continuous cardiac monitoring.
    E) Monitor arterial blood gases, pulse oximetry, and pulmonary function tests, and obtain a chest x-ray in any patient with respiratory symptoms.
    F) Monitor mental status. Patients with an altered mental status may require a head CT.

Oral Exposure

    6.5.1) PREVENTION OF ABSORPTION/PREHOSPITAL
    A) DERMAL EXPOSURE
    1) Liquid nitrogen will rapidly evaporate at room temperature. Washing the skin may not be beneficial.
    2) PREHOSPITAL
    a) Rewarming of a localized area should only be considered if the risk of refreezing is unlikely. Avoid rubbing the frozen area which may cause further damage to the area (Grieve et al, 2011; Hallam et al, 2010).
    3) REWARMING
    a) Do not institute rewarming unless complete rewarming can be assured; refreezing thawed tissue increases tissue damage. Place affected area in a water bath with a temperature of 40 to 42 degrees Celsius for 15 to 30 minutes until thawing is complete. The bath should be large enough to permit complete immersion of the injured part, avoiding contact with the sides of the bath. A whirlpool bath would be ideal. Some authors suggest a mild antibacterial (ie, chlorhexidine, hexachlorophene or povidone-iodine) be added to the bath water. Tissues should be thoroughly rewarmed and pliable; the skin will appear a red-purple color (Grieve et al, 2011; Hallam et al, 2010; Murphy et al, 2000).
    b) Correct systemic hypothermia which can cause cold diuresis due to suppression of antidiuretic hormone; consider IV fluids (Grieve et al, 2011).
    c) Rewarming may be associated with increasing acute pain, requiring narcotic analgesics.
    d) For severe frostbite, clinical trials have shown that pentoxifylline, a phosphodiesterase inhibitor, can enhance tissue viability by increasing blood flow and reducing platelet activity (Hallam et al, 2010).
    4) WOUND CARE
    a) Digits should be separated by sterile absorbent cotton; no constrictive dressings should be used. Protective dressings should be changed twice per day.
    b) Perform twice daily hydrotherapy for 30 to 45 minutes in warm water at 40 degrees Celsius. This helps debride devitalized tissue and maintain range of motion. Keep the area warm and dry between treatments (Hallam et al, 2010; Murphy et al, 2000).
    c) The injured extremities should be elevated and should not be allowed to bear weight.
    d) In patients at risk for infection of necrotic tissue, prophylactic antibiotics and tetanus toxoid have been recommended by some authors (Hallam et al, 2010; Murphy et al, 2000).
    e) Non-tense clear blisters should be left intact due to the risk of infection; tense or hemorrhagic blisters may be carefully aspirated in a setting where aseptic technique is provided (Hallam et al, 2010).
    f) Further surgical debridement should be delayed until mummification demarcation has occurred (60 to 90 days). Spontaneous amputation may occur.
    g) Analgesics may be required during the rewarming phase; however, patients with severe pain should be evaluated for vasospasm.
    h) IMAGING: Arteriography and noninvasive vascular techniques (e.g., plain radiography, laser Doppler studies, digital plethysmography, infrared thermography, isotope scanning), have been useful in evaluating the extent of vasospasm after thawing and assessing whether debridement is needed (Hallam et al, 2010). In cases of severe frostbite, Technetium 99 (triple phase scanning) and MRI angiography have been shown to be the most useful to assess injury and determine the extent or need for surgical debridement (Hallam et al, 2010).
    i) TOPICAL THERAPY: Topical aloe vera may decrease tissue destruction and should be applied every 6 hours (Murphy et al, 2000).
    j) IBUPROFEN THERAPY: Ibuprofen, a thromboxane inhibitor, may help limit inflammatory damage and reduce tissue loss (Grieve et al, 2011; Murphy et al, 2000). DOSE: 400 mg orally every 12 hours is recommended (Hallam et al, 2010).
    k) THROMBOLYTIC THERAPY: Thrombolysis (intra-arterial or intravenous thrombolytic agents) may be beneficial in those patients at risk to lose a digit or a limb, if done within the first 24 hours of exposure. The use of tissue plasminogen activator (t-PA) to clear microvascular thromboses can restore arterial blood flow, but should be accompanied by close monitoring including angiography or technetium scanning to evaluate the injury and to evaluate the effects of t-PA administration. Potential risk of the procedure includes significant tissue edema that can lead to a rise in interstitial pressures resulting in compartment syndrome (Grieve et al, 2011).
    l) CONTROVERSIAL: Adjunct pharmacological agents (ie, heparin, vasodilators, prostacyclins, prostaglandin synthetase inhibitors, dextran) are controversial and not routinely recommended. The role of hyperbaric oxygen therapy, sympathectomy remains unclear (Grieve et al, 2011).
    m) CHRONIC PAIN: Vasomotor dysfunction can produce chronic pain. Amitriptyline has been used in some patients; some patients may need a referral for pain management. Inability to tolerate the cold (in the affected area) has been observed following a single episode of frostbite (Hallam et al, 2010).
    n) MORBIDITIES: Frostbite can produce localized osteoporosis and possible bone loss following a severe case. These events may take a year or more to develop. Children may be at greater risk to develop more severe events (ie, early arthritis) (Hallam et al, 2010).
    B) ORAL EXPOSURE
    1) There is no indication for the use of prehospital activated charcoal.
    C) EYE EXPOSURE
    1) There is no evidence for prehospital decontamination for eye exposures. Patients with eye exposures who are symptomatic should undergo ophthalmologic evaluation for treatment.
    D) INHALATIONAL EXPOSURE
    1) Severe mucosal injury to the hypopharynx may occur. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required.

Inhalation Exposure

    6.7.2) TREATMENT
    A) SUPPORT
    1) MANAGEMENT OF MILD TO MODERATE TOXICITY
    a) Treatment is symptomatic and supportive. Depending on the route of exposure, symptoms may vary widely. The most common type of exposure is likely dermal or inhalational; oral ingestions are relatively rare. Monitor closely for respiratory distress. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required. Direct eye and parenteral exposures are also very uncommon.
    2) MANAGEMENT OF SEVERE TOXICITY
    a) Treatment is symptomatic and supportive. Severe toxicity is very rare, but there have been reports of death. Airway injuries may occur with inhalational exposures and dermal exposures can cause serious direct tissue damage. Monitor closely for respiratory distress. If inhalation of liquid nitrogen gas has occurred, administer 100% humidified oxygen with assisted ventilation as required. Monitor for complications (eg, gas embolism, syncope, and cardiac arrest) from the use of liquid nitrogen.
    B) MONITORING OF PATIENT
    1) No specific laboratory studies are needed for a liquid nitrogen exposure. Labs should be based on a patient's symptoms.
    2) No specific levels of nitrogen are needed.
    3) Monitor vital signs following a significant exposure.
    4) Obtain an ECG, and institute continuous cardiac monitoring.
    5) Monitor arterial blood gases, pulse oximetry, and pulmonary function tests, and obtain a chest x-ray in any patient with respiratory symptoms.
    6) Monitor mental status. Patients with an altered mental status may require a head CT.
    C) AIRWAY MANAGEMENT
    1) For an inhalational exposure, airway management may be needed, and if there is severe damage to the hypopharynx, tracheostomy may be preferred over endotracheal intubation to avoid further trauma to damaged tissues.
    D) CORTICOSTEROID
    1) May be beneficial.

Dermal Exposure

    6.9.2) TREATMENT
    A) FROSTBITE
    1) PREHOSPITAL
    a) Rewarming of a localized area should only be considered if the risk of refreezing is unlikely. Avoid rubbing the frozen area which may cause further damage to the area (Grieve et al, 2011; Hallam et al, 2010).
    2) REWARMING
    a) Do not institute rewarming unless complete rewarming can be assured; refreezing thawed tissue increases tissue damage. Place affected area in a water bath with a temperature of 40 to 42 degrees Celsius for 15 to 30 minutes until thawing is complete. The bath should be large enough to permit complete immersion of the injured part, avoiding contact with the sides of the bath. A whirlpool bath would be ideal. Some authors suggest a mild antibacterial (ie, chlorhexidine, hexachlorophene or povidone-iodine) be added to the bath water. Tissues should be thoroughly rewarmed and pliable; the skin will appear a red-purple color (Grieve et al, 2011; Hallam et al, 2010; Murphy et al, 2000).
    b) Correct systemic hypothermia which can cause cold diuresis due to suppression of antidiuretic hormone; consider IV fluids (Grieve et al, 2011).
    c) Rewarming may be associated with increasing acute pain, requiring narcotic analgesics.
    d) For severe frostbite, clinical trials have shown that pentoxifylline, a phosphodiesterase inhibitor, can enhance tissue viability by increasing blood flow and reducing platelet activity (Hallam et al, 2010).
    3) WOUND CARE
    a) Digits should be separated by sterile absorbent cotton; no constrictive dressings should be used. Protective dressings should be changed twice per day.
    b) Perform twice daily hydrotherapy for 30 to 45 minutes in warm water at 40 degrees Celsius. This helps debride devitalized tissue and maintain range of motion. Keep the area warm and dry between treatments (Hallam et al, 2010; Murphy et al, 2000).
    c) The injured extremities should be elevated and should not be allowed to bear weight.
    d) In patients at risk for infection of necrotic tissue, prophylactic antibiotics and tetanus toxoid have been recommended by some authors (Hallam et al, 2010; Murphy et al, 2000).
    e) Non-tense clear blisters should be left intact due to the risk of infection; tense or hemorrhagic blisters may be carefully aspirated in a setting where aseptic technique is provided (Hallam et al, 2010).
    f) Further surgical debridement should be delayed until mummification demarcation has occurred (60 to 90 days). Spontaneous amputation may occur.
    g) Analgesics may be required during the rewarming phase; however, patients with severe pain should be evaluated for vasospasm.
    h) IMAGING: Arteriography and noninvasive vascular techniques (e.g., plain radiography, laser Doppler studies, digital plethysmography, infrared thermography, isotope scanning), have been useful in evaluating the extent of vasospasm after thawing and assessing whether debridement is needed (Hallam et al, 2010). In cases of severe frostbite, Technetium 99 (triple phase scanning) and MRI angiography have been shown to be the most useful to assess injury and determine the extent or need for surgical debridement (Hallam et al, 2010).
    i) TOPICAL THERAPY: Topical aloe vera may decrease tissue destruction and should be applied every 6 hours (Murphy et al, 2000).
    j) IBUPROFEN THERAPY: Ibuprofen, a thromboxane inhibitor, may help limit inflammatory damage and reduce tissue loss (Grieve et al, 2011; Murphy et al, 2000). DOSE: 400 mg orally every 12 hours is recommended (Hallam et al, 2010).
    k) THROMBOLYTIC THERAPY: Thrombolysis (intra-arterial or intravenous thrombolytic agents) may be beneficial in those patients at risk to lose a digit or a limb, if done within the first 24 hours of exposure. The use of tissue plasminogen activator (t-PA) to clear microvascular thromboses can restore arterial blood flow, but should be accompanied by close monitoring including angiography or technetium scanning to evaluate the injury and to evaluate the effects of t-PA administration. Potential risk of the procedure includes significant tissue edema that can lead to a rise in interstitial pressures resulting in compartment syndrome (Grieve et al, 2011).
    l) CONTROVERSIAL: Adjunct pharmacological agents (ie, heparin, vasodilators, prostacyclins, prostaglandin synthetase inhibitors, dextran) are controversial and not routinely recommended. The role of hyperbaric oxygen therapy, sympathectomy remains unclear (Grieve et al, 2011).
    m) CHRONIC PAIN: Vasomotor dysfunction can produce chronic pain. Amitriptyline has been used in some patients; some patients may need a referral for pain management. Inability to tolerate the cold (in the affected area) has been observed following a single episode of frostbite (Hallam et al, 2010).
    n) MORBIDITIES: Frostbite can produce localized osteoporosis and possible bone loss following a severe case. These events may take a year or more to develop. Children may be at greater risk to develop more severe events (ie, early arthritis) (Hallam et al, 2010).

Abstracts

Case Reports

    A) ACUTE EFFECTS
    1) A 58-year-old man with a suspected chondrosarcoma of the left humerus underwent curettage and liquid nitrogen infiltration into the tumor bed. Anesthesia was induced with intravenous thiopental and inhaled 60% N2O in O2 supplemented with isoflurane. The PET-N2 (end-tidal nitrogen tension) increased from 0 to a maximum of 380 mmHg which prompted immediate aspiration of the already-instilled 38 mL of liquid nitrogen. However, no bubbles were recovered from the central venous catheter. There was no change in audible heart sounds, oxygen saturation, blood pressure, or ECG. The precipitous drop in the arteriovenous CO2 gradients suggest that gas bubbles caused pulmonary vascular obstruction and wasted ventilation. Otherwise, the intraoperative and postoperative course were uneventful and the patient recovered with no neurological sequelae (Dwyer et al, 1990).
    B) ADULT
    1) A 29-year-old man accidentally inhaled liquid nitrogen vapor and developed burns of lips and oropharynx, large mucosal ulcers of the hard palate, and upper airway distress within an hour of the injury (Rockswold & Buran, 1982). He required tracheostomy and antibiotics and was discharged 4 days later with no sequelae.

Range Of Toxicity

Summary

    A) TOXICITY: Signs of asphyxia may occur when liquid nitrogen gas displaces the oxygen in air to 15% or less. Prolonged asphyxia leading to death may happen when oxygen concentration falls to 6% or less.

Minimum Lethal Exposure

    A) Asphyxia leading to death may occur when the oxygen concentration in the air is reduced to 6% or less (Kizer, 1984).

Maximum Tolerated Exposure

    A) Signs of asphyxia may evident when the liquid nitrogen gas displaces oxygen in the air such that the oxygen concentration is 15% or less (Kizer, 1984; Sax & Lewis, 1996).

Serum Plasma Blood Concentrations

    7.5.2) TOXIC CONCENTRATIONS
    A) TOXIC CONCENTRATION LEVELS
    1) CONCENTRATION LEVEL
    a) Asphyxia leading to death may occur when the oxygen concentration in the air is reduced to 6% or less. Signs of asphyxia may be evident when the liquid nitrogen gas displaces oxygen in the air such that the oxygen concentration is 15% or less (Sax & Lewis, 1996; Kizer, 1984).

Workplace Standards

    A) ACGIH TLV Values for CAS7727-37-9 (American Conference of Governmental Industrial Hygienists, 2010):
    1) Editor's Note: The listed values are recommendations or guidelines developed by ACGIH(R) to assist in the control of health hazards. They should only be used, interpreted and applied by individuals trained in industrial hygiene. Before applying these values, it is imperative to read the introduction to each section in the current TLVs(R) and BEI(R) Book and become familiar with the constraints and limitations to their use. Always consult the Documentation of the TLVs(R) and BEIs(R) before applying these recommendations and guidelines.
    a) Adopted Value
    1) Nitrogen
    a) TLV:
    1) TLV-TWA:
    2) TLV-STEL:
    3) TLV-Ceiling:
    b) Notations and Endnotes:
    1) Carcinogenicity Category: Not Listed
    2) Codes: D
    3) Definitions:
    a) D: Simple asphyxiant; see discussion covering Minimal Oxygen Content found in the "Definitions and Notations" section following the NIC tables (in TLV booklet).
    c) TLV Basis - Critical Effect(s): Asphyxia
    d) Molecular Weight: 14.01
    1) For gases and vapors, to convert the TLV from ppm to mg/m(3):
    a) [(TLV in ppm)(gram molecular weight of substance)]/24.45
    2) For gases and vapors, to convert the TLV from mg/m(3) to ppm:
    a) [(TLV in mg/m(3))(24.45)]/gram molecular weight of substance
    e) Additional information:

    B) NIOSH REL and IDLH Values for CAS7727-37-9 (National Institute for Occupational Safety and Health, 2007):
    1) Not Listed

    C) Carcinogenicity Ratings for CAS7727-37-9 :
    1) ACGIH (American Conference of Governmental Industrial Hygienists, 2010): Not Listed ; Listed as: Nitrogen
    2) EPA (U.S. Environmental Protection Agency, 2011): Not Listed
    3) IARC (International Agency for Research on Cancer (IARC), 2016; International Agency for Research on Cancer, 2015; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2010; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2010a; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2008; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2007; IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2006; IARC, 2004): Not Listed
    4) NIOSH (National Institute for Occupational Safety and Health, 2007): Not Listed
    5) MAK (DFG, 2002): Not Listed
    6) NTP (U.S. Department of Health and Human Services, Public Health Service, National Toxicology Project ): Not Listed

    D) OSHA PEL Values for CAS7727-37-9 (U.S. Occupational Safety, and Health Administration (OSHA), 2010):
    1) Not Listed

Pharmacology Toxicology

Toxicologic Mechanism

    A) When used in cryosurgery, liquid nitrogen causes microvascular failure with minimal inflammatory response amidst liquefaction necrosis and progressive fibrosis (Malawer et al, 1988).

Physicochemical

Physical Characteristics

    A) Nitrogen exists in a liquid phase between minus 209.86 degrees Celsius (melting point) and minus 195 degrees Celsius (boiling point) (Rockswold & Buran, 1982).
    B) Nitrogen gas is colorless, odorless, and tasteless (Sax & Lewis, 1996).

Molecular Weight

    A) Nitrogen gas 28.02 (Sax & Lewis, 1996)

Other

    A) ODOR THRESHOLD
    1) Odorless (CHRIS , 2002)

Animal Toxicology

Clinical Effects

    11.1.3) CANINE/DOG
    A) Cardiac arrest followed installation of liquid nitrogen into the mandible marrow cavities of dogs after tooth extraction (Harvey, 1978). Immediate postresuscitative radiographs showed air in the veins of the mediastinum, the right atrium, and the right ventricle.
    B) Marked trabecular necrosis of the cavity developed by three weeks after liquid nitrogen instillation into mature dog bone marrow. Ensuing increased calcification and metaplastic bone formation caused delayed and abnormal reossification (Malawer et al, 1988).

References

General Bibliography

    1) 40 CFR 372.28: Environmental Protection Agency - Toxic Chemical Release Reporting, Community Right-To-Know, Lower thresholds for chemicals of special concern. National Archives and Records Administration (NARA) and the Government Printing Office (GPO). Washington, DC. Final rules current as of Apr 3, 2006.
    2) 40 CFR 372.65: Environmental Protection Agency - Toxic Chemical Release Reporting, Community Right-To-Know, Chemicals and Chemical Categories to which this part applies. National Archives and Records Association (NARA) and the Government Printing Office (GPO), Washington, DC. Final rules current as of Apr 3, 2006.
    3) 49 CFR 172.101 - App. B: Department of Transportation - Table of Hazardous Materials, Appendix B: List of Marine Pollutants. National Archives and Records Administration (NARA) and the Government Printing Office (GPO), Washington, DC. Final rules current as of Aug 29, 2005.
    4) 49 CFR 172.101: Department of Transportation - Table of Hazardous Materials. National Archives and Records Administration (NARA) and the Government Printing Office (GPO), Washington, DC. Final rules current as of Aug 11, 2005.
    5) 62 FR 58840: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 1997.
    6) 65 FR 14186: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2000.
    7) 65 FR 39264: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2000.
    8) 65 FR 77866: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2000.
    9) 66 FR 21940: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2001.
    10) 67 FR 7164: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2002.
    11) 68 FR 42710: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2003.
    12) 69 FR 54144: Notice of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances - Proposed AEGL Values, Environmental Protection Agency, NAC/AEGL Committee. National Archives and Records Administration (NARA) and the Government Publishing Office (GPO), Washington, DC, 2004.
    13) AH Hall : Tomes Plus(R) Information System (CD-ROM Version). Micromedex, Inc. Englewood, CO. 1992.
    14) AIHA: 2006 Emergency Response Planning Guidelines and Workplace Environmental Exposure Level Guides Handbook, American Industrial Hygiene Association, Fairfax, VA, 2006.
    15) Abeling U & Seyfried CF: Anaerobic-aerobic treatment of high-strength ammonium wastewater -- nitrogen removal via nitrite. Water Sci Technol 1992; 26:1007-1015.
    16) Akunna JC, Bizeau C, & Moletta R: Denitrification in anaerobic digesters -- possibilities and influence of wastewater COD/N-NOx ratio. Environ Tech 1992; 13:825-836.
    17) Aldridge FJ, Schelske CL, & Carrick HJ: Nutrient limitation in a hypereutrophic Florida lake. Arch Hydrobiol 1993; 127:21-37.
    18) American Conference of Governmental Industrial Hygienists : ACGIH 2010 Threshold Limit Values (TLVs(R)) for Chemical Substances and Physical Agents and Biological Exposure Indices (BEIs(R)), American Conference of Governmental Industrial Hygienists, Cincinnati, OH, 2010.
    19) Aspegren H, Andersson B, & Nyberg U: Model and sensor based optimization of nitrogen removal at Klagshamn Wastewater treatment plant. Water Sci Technol 1992; 26:1315-1323.
    20) Avnimelech Y, Mozes N, & Weber B: Effects of aeration and mixing on nitrogen and organic matter transformations in simulated fish ponds. Aquacult Eng 1992; 11:157-169.
    21) Baskaran K, Scott PH, & Connor MA: Biofilms as an aid to nitrogen removal in sewage treatment lagoons. Water Sci Technol 1992; 26:1707-1716.
    22) Baumgartner M & Conrad R: Role of nitrate and nitrite for production and consumption of nitric oxide during denitrification in soil. FEMS Microbiol Ecol 1992; 101:59-65.
    23) Bebout BM, Fitzpatrick MW, & Paerl HW: Identification of the sources of energy for nitrogen fixation and physiological characterization of nitrogen-fixing members of a marine microbial mat community. Appl Environ Microbiol 1993; 59:1495-1503.
    24) Booth NH & McDonald LE: Veterinary Pharmacology and Therapeutics, 5th ed, Iowa State University Press, Ames, IA, 1982.
    25) Bormann BT, Bormann FH, & Bowden WB: Rapid N2 fixation in pines, alder, and locust -- evidence from the Sandbox Ecosystem Study. Ecology 1993; 74:583-598.
    26) Bradley PM & Morris JT: Effect of salinity on the critical nitrogen concentration of Spartina alterniflora loisel. Aquatic Botany 1992; 43:149-161.
    27) Briantseva LA: Potential disturbance in the regulation of respiration during hyperbaric nitrogen narcosis. Kosm Biol Aviakosm Med 1982; 16:59-61.
    28) CHRIS : CHRIS Hazardous Chemical Data. US Department of Transportation, US Coast Guard. Washington, DC (Internet Version). Edition expires 1985; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    29) CHRIS : CHRIS Hazardous Chemical Data. US Department of Transportation, US Coast Guard. Washington, DC (Internet Version). Edition expires 2002; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    30) Cabrera ML: Modeling the flush of nitrogen mineralization caused by drying and rewetting soils. Soil Sci Soc Am J 1993; 57:63-66.
    31) Caravati CM Jr, Wood BT, & Richardson DR: Onychodystrophies secondary to liquid nitrogen cryotherapy. Arch Dermatol 1969; 100:441-442.
    32) Carney HJ, Binford MW, & Marin RR: Nitrogen and phosphorus dynamics and retention in ecotones of Lake Titicaca, Bolivia Peru. Hydrobiologia 1993; 251:39-47.
    33) Carpenter EJ, Oneil JM, & Dawson R: The tropical diazotrophic Phytoplankter trichodesmium -- biological characteristics of 2 common species. Mar Ecol-Progr Ser 1993; 95:295-304.
    34) Chiemchaisri C, Wong YK, & Urase T: Organic stabilization and nitrogen removal in membrane separation bioreactor for domestic wastewater treatment. Water Sci Technol 1992; 25:231-240.
    35) Chour V, Holas J, & Korab J: Zelivka river storage and treatment complex supplying the Prague Agglomeration with drinking water -- addressing point and non-point pollution problems. Water Sci Technol 1993; 28:159-163.
    36) Clayton GD & Clayton FE: Patty's Industrial Hygiene and Toxicology, Vol 2C, Toxicology, 3rd ed, John Wiley & Sons, New York, NY, 1982.
    37) Clayton GD & Clayton FE: Patty's Industrial Hygiene and Toxicology, Volume 2F, Toxicology, 4th ed, John Wiley & Sons, New York, NY, 1994, pp 4563-4565.
    38) Colbourn P: Limits to denitrification in 2 pasture soils in a temperate maritime climate. Agric Ecosyst Environ 1993; 43:49-68.
    39) Cook D & Georgouras K: Nitrogen emphysema: a complication of cryotherapy. Med J Australia 1993; 159:836.
    40) Corbitt RA: Standard Handbook of Environmental Engineering, McGraw-Hill Publishing Co, New York, NY, 1990, pp 5.154.
    41) Coutinho R & Zingmark R: Interactions of light and nitrogen on photosynthesis and growth of the marine macroalga Ulva Curvata (Kutzing) de Toni. J Exp Mar Biol Ecol 1993; 167:11-19.
    42) Crawford DM & Chalk PM: Mineralization and immobilization of soil and fertilizer nitrogen with nitrification inhibitors and solvents. Soil Biol Biochem 1992; 24:559-568.
    43) DFG: List of MAK and BAT Values 2002, Report No. 38, Deutsche Forschungsgemeinschaft, Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, Wiley-VCH, Weinheim, Federal Republic of Germany, 2002.
    44) Dwyer DM, Thorne AC, & Healey JH: Liquid nitrogen instillation can cause venous gas embolism. Anesthesiology 1990; 73:179-181.
    45) EPA: Search results for Toxic Substances Control Act (TSCA) Inventory Chemicals. US Environmental Protection Agency, Substance Registry System, U.S. EPA's Office of Pollution Prevention and Toxics. Washington, DC. 2005. Available from URL: http://www.epa.gov/srs/.
    46) ERG: Emergency Response Guidebook. A Guidebook for First Responders During the Initial Phase of a Dangerous Goods/Hazardous Materials Incident, U.S. Department of Transportation, Research and Special Programs Administration, Washington, DC, 2004.
    47) Epstein AM & Shupack JL: Syncope associated with liquid nitrogen therapy. Arch Dermatol 1977; 113:847.
    48) Faafeng BA & Roseth R: Retention of nitrogen in small streams artificially polluted with nitrate. Hydrobiologia 1993; 251:113-122.
    49) Filippov VD & El-Halfawy KA: Mutat Res 1981; 82:251-261.
    50) Finelli PF: Ulnar neuropathy after liquid nitrogen cryotherapy. Arch Dermatol 1975; 111:1240-1242.
    51) Geyer DJ, Keller CK, & Smith JL: Subsurface fate of nitrate as a function of depth and landscape position in Missouri Flat Creek Watershed, USA. J Contaminant Hydrol 1992; 11:127-147.
    52) Goldstein N: Cardiac arrest following application of liquid nitrogen. J Dermatol Surg Oncol 1979; 5:602.
    53) Grace PR, Macrae IC, & Myers RJK: Factors influencing the availability of mineral nitrogen in clay soils of the Brigalow (Acacia harpophylla) Region of Central Queensland. Aust J Agric Res 1992; 43:1197-1215.
    54) Grant WM & Schuman JS: Toxicology of the Eye, 4TH ed, Charles C. Thomas, Springfield, IL, 1993.
    55) Grieve AW, Davis P, Dhillon S, et al: A clinical review of the management of frostbite. J R Army Med Corps 2011; 157(1):73-78.
    56) Gu B & Alexander V: Estimation of N-2 fixation based on differences in the natural abundance of N-15 among freshwater N-2-fixing and non-N-2-fixing algae. Oecologia 1993; 96:43-48.
    57) HSDB : Hazardous Substances Data Bank. National Library of Medicine. Bethesda, MD (Internet Version). Edition expires 1998; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    58) Hallam MJ, Cubison T, Dheansa B, et al: Managing frostbite. BMJ 2010; 341:c5864-.
    59) Harvey HJ: Fatal air embolization associated with cryosurgery in two dogs. J Am Vet Med Assoc 1978; 173:175-176.
    60) Heath RT: Nutrient dynamics in Great Lakes coastal wetlands -- future directions. J Great Lakes Res 1992; 18:590-602.
    61) Holguin G, Guzman MA, & Bashan Y: 2 new nitrogen-fixing bacteria from the rhizosphere of mangrove trees -- their isolation, identification and in vitro interaction with rhizosphere Staphylococcus sp. FEMS Microbiol Ecol 1992; 101:207-216.
    62) Hunik JH, Meijer HJG, & Tramper J: Kinetics of nitrosomonas europaea at extreme substrate, product and salt concentrations. Appl Microbiol Biotechnol 1992; 37:802-807.
    63) Hunter S: Acta Neuropathol (Berl) 1985; 68:115-121.
    64) IARC Working Group on the Evaluation of Carcinogenic Risks to Humans : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: 1,3-Butadiene, Ethylene Oxide and Vinyl Halides (Vinyl Fluoride, Vinyl Chloride and Vinyl Bromide), 97, International Agency for Research on Cancer, Lyon, France, 2008.
    65) IARC Working Group on the Evaluation of Carcinogenic Risks to Humans : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol, 88, International Agency for Research on Cancer, Lyon, France, 2006.
    66) IARC Working Group on the Evaluation of Carcinogenic Risks to Humans : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Household Use of Solid Fuels and High-temperature Frying, 95, International Agency for Research on Cancer, Lyon, France, 2010a.
    67) IARC Working Group on the Evaluation of Carcinogenic Risks to Humans : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Smokeless Tobacco and Some Tobacco-specific N-Nitrosamines, 89, International Agency for Research on Cancer, Lyon, France, 2007.
    68) IARC Working Group on the Evaluation of Carcinogenic Risks to Humans : IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Some Non-heterocyclic Polycyclic Aromatic Hydrocarbons and Some Related Exposures, 92, International Agency for Research on Cancer, Lyon, France, 2010.
    69) IARC: List of all agents, mixtures and exposures evaluated to date - IARC Monographs: Overall Evaluations of Carcinogenicity to Humans, Volumes 1-88, 1972-PRESENT. World Health Organization, International Agency for Research on Cancer. Lyon, FranceAvailable from URL: http://monographs.iarc.fr/monoeval/crthall.html. As accessed Oct 07, 2004.
    70) ICAO: Technical Instructions for the Safe Transport of Dangerous Goods by Air, 2003-2004. International Civil Aviation Organization, Montreal, Quebec, Canada, 2002.
    71) ILO: ILO Encyclopaedia of Occupational Health and Safety, 3rd ed, Vol II. Parmeggiani L (Ed), International Labour Organization, Geneva, Switzerland, 1983.
    72) International Agency for Research on Cancer (IARC): IARC monographs on the evaluation of carcinogenic risks to humans: list of classifications, volumes 1-116. International Agency for Research on Cancer (IARC). Lyon, France. 2016. Available from URL: http://monographs.iarc.fr/ENG/Classification/latest_classif.php. As accessed 2016-08-24.
    73) International Agency for Research on Cancer: IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. World Health Organization. Geneva, Switzerland. 2015. Available from URL: http://monographs.iarc.fr/ENG/Classification/. As accessed 2015-08-06.
    74) JEF Reynolds : Martindale: The Extra Pharmacopoeia. The Pharmaceutical Press. London, UK (Internet Version). Edition expires 1990; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    75) Jewell WJ, Nelson YM, & Wilson MS: Methanotrophic bacteria for nutrient removal from wastewater -- attached film system. Water Environ Res 1992; 64:756-765.
    76) Joye SB & Paerl HW: Contemporaneous nitrogen fixation and denitrification in intertidal microbial mats -- rapid response to runoff events. Mar Ecol-Progr Ser 1993; 94:267-274.
    77) Kim J & Verma SB: Soil surface CO2 flux in a Minnesota peatland. Biogeochemistry 1992; 18:37-51.
    78) Kizer KW: Toxic inhalation. Emerg Med Clin North Am 1984; 2:649-666.
    79) Koike I & Tupas L: Total dissolved nitrogen in the northern North Pacific assessed by a high-temperature combustion method. Mar Chem 1993; 41:209-214.
    80) Kolbusz RV & O'Donoghue MN: Pyogenic granuloma following treatment of verruca vulgaris with cryotherapy and duoplant. Cutis 1993; 159:836.
    81) Komor SC & Anderson HW: Nitrogen isotopes as indicators of nitrate sources in Minnesota sand-plain aquifers. Ground Water 1993; 31:260-270.
    82) Leu HJ & Clodius L: An unusual cause of gangrene: cold injury caused by liquid nitrogen. Schweiz Med Wochenschr 1989; 119:192-195.
    83) Liao CM, Maekawa T, & Chiang HC: Removal of nitrogen and phosphorus from swine wastewater by intermittent aeration processes. J Environ Sci Health B-Pestic 1993; 28:335-374.
    84) Ljaljevic J: Glas-Srp Akad Nauka Umet, Od Med Nauka 1977; 29:71-75.
    85) Ljaljevic M: Glas-Srp Akad Nauka Umet, Od Med Nauka 1977b; 29:77-81.
    86) Malawer MM, Marks MR, & McChesney D: The effects of cryosurgery and polymethylmethacrylate in dogs with experimental bone defects comparable to tumor defects. Clin Orthop 1988; 226:299-310.
    87) Martin A, Moreno M, & Marin P: Azotobacter and azospirillum as potential nitrogen fertilizers. Commun Soil Sci Plant Anal 1993; 24:255-260.
    88) Martinova MV: Nitrogen and phosphor compounds in bottom sediments -- mechanisms of accumulation, transformation and release. Hydrobiologia 1993; 252:1-22.
    89) Megharaj M, Pearson HW, & Venkateswarlu K: Removal of nitrogen and phosphorus by immobilized cells of Chlorella vulgaris and Scenedesmus bijugatus isolated from soil. Enzyme Microbial Technol 1992; 14:656-658.
    90) Merrill AG & Zak DR: Factors controlling denitrification rates in upland and swamp forests. Canad J Forest Res 1992; 22:1597-1604.
    91) Murphy JV, Banwell PE, & Roberts AHN: Frostbite: pathogenesis and treatment. J Trauma 2000; 48:171-178.
    92) Murray L, Dennison WC, & Kemp WM: Nitrogen versus phosphorus limitation for growth of an estuarine population of eelgrass (Zostera marina L). Aquat Bot 1992; 44:83-100.
    93) NFPA: Fire Protection Guide to Hazardous Materials, 13th ed., National Fire Protection Association, Quincy, MA, 2002.
    94) NRC: Acute Exposure Guideline Levels for Selected Airborne Chemicals - Volume 1, Subcommittee on Acute Exposure Guideline Levels, Committee on Toxicology, Board on Environmental Studies and Toxicology, Commission of Life Sciences, National Research Council. National Academy Press, Washington, DC, 2001.
    95) NRC: Acute Exposure Guideline Levels for Selected Airborne Chemicals - Volume 2, Subcommittee on Acute Exposure Guideline Levels, Committee on Toxicology, Board on Environmental Studies and Toxicology, Commission of Life Sciences, National Research Council. National Academy Press, Washington, DC, 2002.
    96) NRC: Acute Exposure Guideline Levels for Selected Airborne Chemicals - Volume 3, Subcommittee on Acute Exposure Guideline Levels, Committee on Toxicology, Board on Environmental Studies and Toxicology, Commission of Life Sciences, National Research Council. National Academy Press, Washington, DC, 2003.
    97) NRC: Acute Exposure Guideline Levels for Selected Airborne Chemicals - Volume 4, Subcommittee on Acute Exposure Guideline Levels, Committee on Toxicology, Board on Environmental Studies and Toxicology, Commission of Life Sciences, National Research Council. National Academy Press, Washington, DC, 2004.
    98) Nally FF & Zakrzewska LM: (Letter). Lancet 1984; 1:1021.
    99) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for 1,2,3-Trimethylbenzene (Proposed). United States Environmental Protection Agency. Washington, DC. 2006k. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d68a&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    100) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for 1,2,4-Trimethylbenzene (Proposed). United States Environmental Protection Agency. Washington, DC. 2006m. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d68a&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    101) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for 1,2-Butylene Oxide (Proposed). United States Environmental Protection Agency. Washington, DC. 2008d. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648083cdbb&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    102) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for 1,2-Dibromoethane (Proposed). United States Environmental Protection Agency. Washington, DC. 2007g. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064802796db&disposition=attachment&contentType=pdf. As accessed 2010-08-18.
    103) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for 1,3,5-Trimethylbenzene (Proposed). United States Environmental Protection Agency. Washington, DC. 2006l. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d68a&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    104) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for 2-Ethylhexyl Chloroformate (Proposed). United States Environmental Protection Agency. Washington, DC. 2007b. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648037904e&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    105) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Acrylonitrile (Proposed). United States Environmental Protection Agency. Washington, DC. 2007c. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648028e6a3&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    106) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Adamsite (Proposed). United States Environmental Protection Agency. Washington, DC. 2007h. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020fd29&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    107) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Agent BZ (3-quinuclidinyl benzilate) (Proposed). United States Environmental Protection Agency. Washington, DC. 2007f. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064803ad507&disposition=attachment&contentType=pdf. As accessed 2010-08-18.
    108) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Allyl Chloride (Proposed). United States Environmental Protection Agency. Washington, DC. 2008. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648039d9ee&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    109) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Aluminum Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005b. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    110) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Arsenic Trioxide (Proposed). United States Environmental Protection Agency. Washington, DC. 2007m. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480220305&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    111) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Automotive Gasoline Unleaded (Proposed). United States Environmental Protection Agency. Washington, DC. 2009a. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7cc17&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    112) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Biphenyl (Proposed). United States Environmental Protection Agency. Washington, DC. 2005j. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064801ea1b7&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    113) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Bis-Chloromethyl Ether (BCME) (Proposed). United States Environmental Protection Agency. Washington, DC. 2006n. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648022db11&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    114) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Boron Tribromide (Proposed). United States Environmental Protection Agency. Washington, DC. 2008a. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064803ae1d3&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    115) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Bromine Chloride (Proposed). United States Environmental Protection Agency. Washington, DC. 2007d. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648039732a&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    116) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Bromoacetone (Proposed). United States Environmental Protection Agency. Washington, DC. 2008e. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064809187bf&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    117) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Calcium Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005d. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    118) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Carbonyl Fluoride (Proposed). United States Environmental Protection Agency. Washington, DC. 2008b. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064803ae328&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    119) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Carbonyl Sulfide (Proposed). United States Environmental Protection Agency. Washington, DC. 2007e. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648037ff26&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    120) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Chlorobenzene (Proposed). United States Environmental Protection Agency. Washington, DC. 2008c. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064803a52bb&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    121) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Cyanogen (Proposed). United States Environmental Protection Agency. Washington, DC. 2008f. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064809187fe&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    122) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Dimethyl Phosphite (Proposed). United States Environmental Protection Agency. Washington, DC. 2009. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7cbf3&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    123) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Diphenylchloroarsine (Proposed). United States Environmental Protection Agency. Washington, DC. 2007l. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020fd29&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    124) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Ethyl Isocyanate (Proposed). United States Environmental Protection Agency. Washington, DC. 2008h. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648091884e&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    125) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Ethyl Phosphorodichloridate (Proposed). United States Environmental Protection Agency. Washington, DC. 2008i. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480920347&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    126) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Ethylbenzene (Proposed). United States Environmental Protection Agency. Washington, DC. 2008g. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064809203e7&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    127) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Ethyldichloroarsine (Proposed). United States Environmental Protection Agency. Washington, DC. 2007j. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020fd29&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    128) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Germane (Proposed). United States Environmental Protection Agency. Washington, DC. 2008j. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480963906&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    129) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Hexafluoropropylene (Proposed). United States Environmental Protection Agency. Washington, DC. 2006. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064801ea1f5&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    130) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Ketene (Proposed). United States Environmental Protection Agency. Washington, DC. 2007. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020ee7c&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    131) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Magnesium Aluminum Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005h. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    132) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Magnesium Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005g. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    133) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Malathion (Proposed). United States Environmental Protection Agency. Washington, DC. 2009k. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064809639df&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    134) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Mercury Vapor (Proposed). United States Environmental Protection Agency. Washington, DC. 2009b. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a8a087&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    135) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Methyl Isothiocyanate (Proposed). United States Environmental Protection Agency. Washington, DC. 2008k. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480963a03&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    136) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Methyl Parathion (Proposed). United States Environmental Protection Agency. Washington, DC. 2008l. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480963a57&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    137) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Methyl tertiary-butyl ether (Proposed). United States Environmental Protection Agency. Washington, DC. 2007a. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064802a4985&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    138) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Methylchlorosilane (Proposed). United States Environmental Protection Agency. Washington, DC. 2005. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5f4&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    139) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Methyldichloroarsine (Proposed). United States Environmental Protection Agency. Washington, DC. 2007i. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020fd29&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    140) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Methyldichlorosilane (Proposed). United States Environmental Protection Agency. Washington, DC. 2005a. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c646&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    141) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Nitrogen Mustard (HN1 CAS Reg. No. 538-07-8) (Proposed). United States Environmental Protection Agency. Washington, DC. 2006a. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d6cb&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    142) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Nitrogen Mustard (HN2 CAS Reg. No. 51-75-2) (Proposed). United States Environmental Protection Agency. Washington, DC. 2006b. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d6cb&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    143) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Nitrogen Mustard (HN3 CAS Reg. No. 555-77-1) (Proposed). United States Environmental Protection Agency. Washington, DC. 2006c. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d6cb&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    144) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Nitrogen Tetroxide (Proposed). United States Environmental Protection Agency. Washington, DC. 2008n. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648091855b&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    145) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Nitrogen Trifluoride (Proposed). United States Environmental Protection Agency. Washington, DC. 2009l. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480963e0c&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    146) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Parathion (Proposed). United States Environmental Protection Agency. Washington, DC. 2008o. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480963e32&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    147) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Perchloryl Fluoride (Proposed). United States Environmental Protection Agency. Washington, DC. 2009c. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7e268&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    148) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Perfluoroisobutylene (Proposed). United States Environmental Protection Agency. Washington, DC. 2009d. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7e26a&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    149) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Phenyl Isocyanate (Proposed). United States Environmental Protection Agency. Washington, DC. 2008p. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648096dd58&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    150) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Phenyl Mercaptan (Proposed). United States Environmental Protection Agency. Washington, DC. 2006d. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020cc0c&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    151) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Phenyldichloroarsine (Proposed). United States Environmental Protection Agency. Washington, DC. 2007k. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020fd29&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    152) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Phorate (Proposed). United States Environmental Protection Agency. Washington, DC. 2008q. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648096dcc8&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    153) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Phosgene (Draft-Revised). United States Environmental Protection Agency. Washington, DC. 2009e. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a8a08a&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    154) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Phosgene Oxime (Proposed). United States Environmental Protection Agency. Washington, DC. 2009f. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7e26d&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    155) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Potassium Cyanide (Proposed). United States Environmental Protection Agency. Washington, DC. 2009g. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7cbb9&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    156) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Potassium Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005c. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    157) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Propargyl Alcohol (Proposed). United States Environmental Protection Agency. Washington, DC. 2006e. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020ec91&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    158) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Selenium Hexafluoride (Proposed). United States Environmental Protection Agency. Washington, DC. 2006f. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020ec55&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    159) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Silane (Proposed). United States Environmental Protection Agency. Washington, DC. 2006g. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d523&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    160) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Sodium Cyanide (Proposed). United States Environmental Protection Agency. Washington, DC. 2009h. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7cbb9&disposition=attachment&contentType=pdf. As accessed 2010-08-15.
    161) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Sodium Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005i. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    162) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Strontium Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005f. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    163) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Sulfuryl Chloride (Proposed). United States Environmental Protection Agency. Washington, DC. 2006h. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020ec7a&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    164) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Tear Gas (Proposed). United States Environmental Protection Agency. Washington, DC. 2008s. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648096e551&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    165) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Tellurium Hexafluoride (Proposed). United States Environmental Protection Agency. Washington, DC. 2009i. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7e2a1&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    166) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Tert-Octyl Mercaptan (Proposed). United States Environmental Protection Agency. Washington, DC. 2008r. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648096e5c7&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    167) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Tetramethoxysilane (Proposed). United States Environmental Protection Agency. Washington, DC. 2006j. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d632&disposition=attachment&contentType=pdf. As accessed 2010-08-17.
    168) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Trimethoxysilane (Proposed). United States Environmental Protection Agency. Washington, DC. 2006i. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d632&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    169) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Trimethyl Phosphite (Proposed). United States Environmental Protection Agency. Washington, DC. 2009j. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=0900006480a7d608&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    170) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Trimethylacetyl Chloride (Proposed). United States Environmental Protection Agency. Washington, DC. 2008t. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648096e5cc&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    171) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for Zinc Phosphide (Proposed). United States Environmental Protection Agency. Washington, DC. 2005e. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020c5ed&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    172) National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances: Acute Exposure Guideline Levels (AEGLs) for n-Butyl Isocyanate (Proposed). United States Environmental Protection Agency. Washington, DC. 2008m. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=09000064808f9591&disposition=attachment&contentType=pdf. As accessed 2010-08-12.
    173) National Institute for Occupational Safety and Health: NIOSH Pocket Guide to Chemical Hazards, U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Cincinnati, OH, 2007.
    174) National Research Council : Acute exposure guideline levels for selected airborne chemicals, 5, National Academies Press, Washington, DC, 2007.
    175) National Research Council: Acute exposure guideline levels for selected airborne chemicals, 6, National Academies Press, Washington, DC, 2008.
    176) National Research Council: Acute exposure guideline levels for selected airborne chemicals, 7, National Academies Press, Washington, DC, 2009.
    177) National Research Council: Acute exposure guideline levels for selected airborne chemicals, 8, National Academies Press, Washington, DC, 2010.
    178) Nordgren A: A method for determining microbially available-N and available-P in an organic soil. Biol Fertil Soils 1992; 13:195-199.
    179) Nugroho SG & Kuwatsuka S: Concurrent observation of several processes of nitrogen metabolism in soil amended with organic materials. 4. Regulatory effects of ammonium-nitrogen and nitrate-nitrogen on denitrification and N-2 fixation. Soil Sci Plant Nutr 1992; 38:611-617.
    180) Nunes MA, Ramalho JDC, & Dias MA: Effect of nitrogen supply on the photosynthetic performance of leaves from coffee plants exposed to bright light. J Exp Bot 1993; 44:893-899.
    181) Pedrozo F, Diaz M, & Bonetto C: Nitrogen and phosphorus in the Parana River floodplain waterbodies. Arch Hydrobiol 1992; 90(Suppl 2):171-185.
    182) Petersen G, Eldin HN, & Bundgaard E: 2nd generation oxidation ditches -- advanced technology in simple design. Water Sci Technol 1993; 27:105-113.
    183) Peterson BJ, Corliss T, & Kriet K: Nitrogen and phosphorus concentrations and export for the upper Kuparuk River on the north slope of Alaska in 1980. Hydrobiologia 1992; 240.
    184) Proctor NH & Hughes JP: Chemical Hazards of the Workplace, 2nd ed, JB Lippincott Co, Philadelphia, PA, 1988.
    185) RTECS : Registry of Toxic Effects of Chemical Substances. National Institute for Occupational Safety and Health. Cincinnati, OH (Internet Version). Edition expires 1989; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    186) Rockswold G & Buran DJ: Inhalation of liquid nitrogen vapor. Ann Emerg Med 1982; 11:553-555.
    187) Rosenblum GA: Liquid nitrogen cryotherapy in a case of elastosis perforans serpiginosa. J Am Acad Dermatol 1983; 8:718-721.
    188) Sawyer R & Picou KA: Facial presentation of disseminated superficial actinic prokeratosis. Ear Nose Throat J 1989; 1:57-59.
    189) Sax NI & Lewis RJ: Dangerous Properties of Industrial Material, 9th ed, Van Nostrand Reinhold Company, New York, NY, 1996.
    190) Sierra J: Relationship between mineral-N content and N-mineralization rate in disturbed and undisturbed soil samples incubated under field and laboratory conditions. Aust J Soil Res 1992; 30:477-492.
    191) Simek M: Biological nitrogen fixation (nitrogenase activity) as a measure of soil biological activity. Rostl Vyroba 1993; 39:789-796.
    192) Smith VH: Effects of nitrogen-phosphorus supply ratios on nitrogen fixation in agricultural and pastoral ecosystems. Biogeochemistry 1992; 18:19-35.
    193) Strelkov RB: Radiobiologica 1984; 24:264-266.
    194) Sveda R, Rechcigl JE, & Nkedikizza P: Evaluation of various nitrogen sources and rates on nitrogen movement, Pensacola Bahiagrass production, and water quality. Commun Soil Sci Plant Anal 1992; 23:879-905.
    195) Tabata N, Funayama M, & Ikeda T: On an accident by liquid nitrogen - histological changes of skin in cold. Forensic Sci Int 1995; 76:61-67.
    196) Thome U, Kuhbauch W, & Stratmann B: Leaching of nitrogen from permanent grassland treated with cattle slurry. J Agron Crop Sci 1993; 170:84-90.
    197) Tietema A, Warmerdam B, & Lenting E: Abiotic factors regulating nitrogen transformations in the organic layer of acid forest soils -- moisture and pH. Plant Soil 1992; 147:69-78.
    198) U.S. Department of Energy, Office of Emergency Management: Protective Action Criteria (PAC) with AEGLs, ERPGs, & TEELs: Rev. 26 for chemicals of concern. U.S. Department of Energy, Office of Emergency Management. Washington, DC. 2010. Available from URL: http://www.hss.doe.gov/HealthSafety/WSHP/Chem_Safety/teel.html. As accessed 2011-06-27.
    199) U.S. Department of Health and Human Services, Public Health Service, National Toxicology Project : 11th Report on Carcinogens. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program. Washington, DC. 2005. Available from URL: http://ntp.niehs.nih.gov/INDEXA5E1.HTM?objectid=32BA9724-F1F6-975E-7FCE50709CB4C932. As accessed 2011-06-27.
    200) U.S. Environmental Protection Agency: Discarded commercial chemical products, off-specification species, container residues, and spill residues thereof. Environmental Protection Agency's (EPA) Resource Conservation and Recovery Act (RCRA); List of hazardous substances and reportable quantities 2010b; 40CFR(261.33, e-f):77-.
    201) U.S. Environmental Protection Agency: Integrated Risk Information System (IRIS). U.S. Environmental Protection Agency. Washington, DC. 2011. Available from URL: http://cfpub.epa.gov/ncea/iris/index.cfm?fuseaction=iris.showSubstanceList&list_type=date. As accessed 2011-06-21.
    202) U.S. Environmental Protection Agency: List of Radionuclides. U.S. Environmental Protection Agency. Washington, DC. 2010a. Available from URL: http://www.gpo.gov/fdsys/pkg/CFR-2010-title40-vol27/pdf/CFR-2010-title40-vol27-sec302-4.pdf. As accessed 2011-06-17.
    203) U.S. Environmental Protection Agency: List of hazardous substances and reportable quantities. U.S. Environmental Protection Agency. Washington, DC. 2010. Available from URL: http://www.gpo.gov/fdsys/pkg/CFR-2010-title40-vol27/pdf/CFR-2010-title40-vol27-sec302-4.pdf. As accessed 2011-06-17.
    204) U.S. Environmental Protection Agency: The list of extremely hazardous substances and their threshold planning quantities (CAS Number Order). U.S. Environmental Protection Agency. Washington, DC. 2010c. Available from URL: http://www.gpo.gov/fdsys/pkg/CFR-2010-title40-vol27/pdf/CFR-2010-title40-vol27-part355.pdf. As accessed 2011-06-17.
    205) U.S. Occupational Safety and Health Administration: Part 1910 - Occupational safety and health standards (continued) Occupational Safety, and Health Administration's (OSHA) list of highly hazardous chemicals, toxics and reactives. Subpart Z - toxic and hazardous substances. CFR 2010 2010; Vol6(SEC1910):7-.
    206) U.S. Occupational Safety, and Health Administration (OSHA): Process safety management of highly hazardous chemicals. 29 CFR 2010 2010; 29(1910.119):348-.
    207) United States Environmental Protection Agency Office of Pollution Prevention and Toxics: Acute Exposure Guideline Levels (AEGLs) for Vinyl Acetate (Proposed). United States Environmental Protection Agency. Washington, DC. 2006. Available from URL: http://www.regulations.gov/search/Regs/contentStreamer?objectId=090000648020d6af&disposition=attachment&contentType=pdf. As accessed 2010-08-16.
    208) Vannoordwijk M & Wadman WP: Effects of spatial variability of nitrogen supply on environmentally acceptable nitrogen fertilizer application rates to arable crops. Netherlands J Agri Sci 1992; 40:51-72.
    209) Villareal TA, Altabet MA, & Culverrymsza K: Nitrogen transport by vertically migrating diatom mats in the North Pacific Ocean. Nature 1993; 363:709-712.
    210) Wakatsuki T, Esumi H, & Omura S: High performance and N-removable & P-removable on-site domestic waste water treatment system by multi-soil-layering method. Water Sci Technol 1993; 27:31-40.
    211) Walker RF, Hixson SE, & Skau CM: Soil denitrification rates in a subalpine watershed of the eastern Sierra-Nevada. Forest Ecol Manag 1992; 50:217-231.
    212) Weekers PHH & Vanderdrift C: Nitrogen metabolizing enzyme activities in the free-living soil amoebae Acanthamoeba castellanii, acanthamoeba polyphaga and Hartmannella vermiformis. J Eukaryot Microbiol 1993; 40:251-254.
    213) Wingfield DL & Fraunfelder FT: Possible complications secondary to cryotherapy. Ophthalmic Surg 1979; 10:47-55.
    214) Yaffe B, Shafir R, & Tsur H: Complications of liquid nitrogen cryosurgery for verrucae over bony prominences. Ann Plast Surg 1986; 16:146-149.
    215) Yang XS, Garuti G, & Tilche A: Denitrification with Thiobacillus denitrificans in the ANANOX(R) process. Biotechnol Lett 1993; 15:531-536.
    216) Yoon WB & Benner R: Denitrification and oxygen consumption in sediments of 2 South Texas estuaries. Mar Ecol-Progr Ser 1992; 90:157-167.