Contact Us    Contact Us     |     Feedback
MOBILE VIEW  | 

UREA

Export To Excel

Classification   |    Detailed evidence-based information

Substances Included Synonyms

Therapeutic Toxic Class

    A) Urea is formed in normal metabolic processes. It is also used in fertilizers, as a diuretic, anti-neoplastic, aid in wound healing, in the processing of plastics, paper, animal feed, resins, barbituric acid and toothpaste, and in bakeries.

Specific Substances

    1) AQUADRATE
    2) B-I-K
    3) CARBAMIDE
    4) CARBAMIDE RESIN
    5) CARBAMIMIDIC ACID
    6) CARBONYL DIAMIDE
    7) CARBONYLDIAMINE
    8) ISOUREA
    9) MOCOVINA (Czech)
    10) Molecular Formula: C-H4-N2-O
    11) NCI-c 02119
    12) OHM/TADS NUMBER: 7216943
    13) PRESPERSION, 75 UREA
    14) PSEUDOUREA
    15) NIOSH/RTECS YR 6250000
    16) STCC 4960131
    17) SUPERCEL 3000
    18) UREA
    19) UREACIN 10, 20, 40
    20) UREAPHIL
    21) UREOPHIL
    22) UREUM
    23) UREVERT
    24) VARIOFORM II
    25) WISWESSER NOTATION: ZVZ
    26) CAS 57-13-6
    27) AQUDRATE
    1.2.1) MOLECULAR FORMULA
    1) CH4N2O
    2) (NH2)2CO

Available Forms Sources

    A) FORMS
    1) PHARMACEUTICAL -
    a) A sterile USP formulation containing 40 and 90 grams (HSDB , 2001).
    b) Available in various creams.
    2) CHEMICAL GRADES -
    a) ACS & USP grades
    b) Solid and liquid complex forms
    c) Urea is pelletized or pilled to avoid caking and ease handling.
    d) Available as commercial, technical and fertilizer grade (HSDB , 2001).
    3) PRODUCTS CONTAINING UREA -
    a) Ureacin-20 Creme contains urea at 20%; Ureacin-40 contains urea at 40%; Ureacin-10 lotion contains urea 10%.
    b) Urea-Ammonium Nitrate Liquor (typically contains 6% urea)
    c) UAL-37 contains 35% urea
    d) UF Concentrate-85 contains 26% urea
    e) A normal epoxy-amine ratio for epoxy-urea resins is 70:30 (HSDB , 2001).
    B) SOURCES
    1) NATURAL SOURCES -
    a) Occurs in urine and other body fluids (HSDB , 2001). It is the diamide of carbonic acid and is the most important metabolic product of protein catabolism in man. It is formed in the liver and is excreted in the urine (Bergmeyer, 1974).
    b) EXPOSURES: Occupational exposure to urea occurs via dermal contact and inhalation of dust, especially to workers applying urea fertilizers.
    2) NATURAL POLLUTION SOURCES -
    a) Urea is a natural product of nitrogen and protein metabolism, occurring in urine and animal waste. Urea can be formed in natural waters (HSDB , 2001).
    b) Urea is released into the environment through direct application to soil as a nitrogen-release fertilizer. Small amounts of urea can be released in waste water effluents from manufacturing sites (Mavrovic & Shirley, 1983).
    C) USES
    1) Uses of urea include fertilizers, plastics, paper, hospital and veterinary use, bakeries, animal feed, resins, barbituric acid production, toothpaste manufacture, mosquito repellent, and as a deicing compound on airport runways (HSDB , 2001).
    2) Urea was formerly used as a diuretic, but has since been replaced by more efficacious agents (HSDB , 2001).
    3) Urea has been used topically in the treatment of ichthyosis and hyperkeratotic skin disorders, and has been used intra-amniotically for the termination of pregnancy (S Sweetman , 2001).

Overview

Life Support

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

Clinical Effects

    0.2.1) SUMMARY OF EXPOSURE
    A) ANIMAL STUDIES - In sheep and cattle, clinical effects included pronounced muscle fasciculations, trembling, grinding teeth, dysrhythmias, ataxia, lateral recumbency, anuria, dry mouth, frothy salivation, dyspnea, bloating, abdominal pain, regurgitation, hyperesthesia, mydriasis and convulsions. The primary cause of death was respiratory arrest. Laboratory examination showed increased glucose, ammonia and urea levels.
    B) WITH THERAPEUTIC USE
    1) Adverse effects include nausea, vomiting, dizziness, disorientation, drowsiness, diuresis, hyponatremia, hypokalemia, and confusion. Urea's systemic toxicity is similar to that of mannitol.
    C) WITH POISONING/EXPOSURE
    1) Urea is considered a mild to moderate intoxicant and a mild irritant. Exposure causes erythema of eyes and skin. Urea's systemic toxicity is similar to that of mannitol. Massive occupational exposure to carbamide produced persistent respiratory insufficiency.
    0.2.4) HEENT
    A) WITH POISONING/EXPOSURE
    1) Eye damage is expected only when concentrations are high or duration of exposure is extended. Rebound increases in intraocular pressure have been seen.
    0.2.5) CARDIOVASCULAR
    A) WITH THERAPEUTIC USE
    1) Therapeutic administration of intravenous solutions may cause a fall in blood pressure.
    0.2.6) RESPIRATORY
    A) ANIMAL STUDIES have shown dyspnea and respiratory arrest.
    B) WITH POISONING/EXPOSURE
    1) Massive occupational exposure to carbamide produced chronic respiratory insufficiency in one adult.
    0.2.7) NEUROLOGIC
    A) ANIMAL STUDIES: Animals have developed trembling, fasciculations, hyperreflexia, convulsions, ataxia, and lethargy.
    B) WITH THERAPEUTIC USE
    1) Therapeutic administration of intravenous solution has caused intracranial hemorrhage, headache, and confusion.
    0.2.8) GASTROINTESTINAL
    A) ANIMAL STUDIES: Grinding teeth, dry mouth, bloating, and regurgitation were observed in animals.
    B) WITH THERAPEUTIC USE
    1) Nausea and vomiting have occurred following oral or intravenous administration.
    0.2.10) GENITOURINARY
    A) WITH THERAPEUTIC USE
    1) High urea levels will produce diuresis and should not be used in patients with severely impaired renal function.
    0.2.13) HEMATOLOGIC
    A) WITH THERAPEUTIC USE
    1) Thrombosis and leukocytosis are possible. Rapid intravenous administration may cause hemolysis.
    0.2.14) DERMATOLOGIC
    A) WITH POISONING/EXPOSURE
    1) Is a mild skin irritant.
    0.2.15) MUSCULOSKELETAL
    A) WITH THERAPEUTIC USE
    1) Urea is irritating to tissues. Extravasation may lead to pain and necrosis.
    0.2.16) ENDOCRINE
    A) WITH THERAPEUTIC USE
    1) An intolerance to carbohydrates may develop with high urea concentrations.
    0.2.20) REPRODUCTIVE
    A) Intraplacental and intrauterine administration of urea to humans has produced abortions.
    0.2.21) CARCINOGENICITY
    A) Carcinogenicity data are questionable. Both negative and positive studies have been reported.

Laboratory Monitoring

    A) Follow blood urea nitrogen (BUN) to detect urea increases.
    B) When diuresis is extensive, follow fluids and electrolytes.

Treatment Overview

    0.4.2) ORAL/PARENTERAL EXPOSURE
    A) Urea is not highly toxic, and extensive decontamination and treatment is seldom necessary. Gastric decontamination is not indicated in high concentrations due to possible strong irritant effects. Gastric decontamination may be of value with high volumes of lower concentrations. Activated charcoal has not been tested.
    B) Urea is effectively eliminated by the kidney. If normal renal function exists, diuresis will ensue. Patients should have adequate hydration. If diuresis is extensive, monitor electrolytes.
    0.4.3) INHALATION EXPOSURE
    A) INHALATION: Move patient to fresh air. Monitor for respiratory distress. If cough or difficulty breathing develops, evaluate for respiratory tract irritation, bronchitis, or pneumonitis. Administer oxygen and assist ventilation as required. Treat bronchospasm with an inhaled beta2-adrenergic agonist. Consider systemic corticosteroids in patients with significant bronchospasm.
    B) Urea would be a mild to moderate irritant if inhaled in an aerosol. After the exposure has been terminated, patients should be evaluated for respiratory distress. Dyspnea and respiratory failure has been seen in poisoned animals, respiratory support should be available in severe cases.
    0.4.4) EYE EXPOSURE
    A) DECONTAMINATION: Remove contact lenses and irrigate exposed eyes with copious amounts of room temperature 0.9% saline or water for at least 15 minutes. If irritation, pain, swelling, lacrimation, or photophobia persist after 15 minutes of irrigation, the patient should be seen in a healthcare facility.
    B) Urea may be mild to moderately irritating to the eye. Most exposures may be handled by irrigation and observation for prolonged pain or erythema (not expected).
    1) HIGH CONCENTRATIONS - or prolonged exposures may produce more significant irritation and should be seen by an ophthalmologist for evaluation.
    0.4.5) DERMAL EXPOSURE
    A) OVERVIEW
    1) DECONTAMINATION: Remove contaminated clothing and jewelry and place them in plastic bags. Wash exposed areas with soap and water for 10 to 15 minutes with gentle sponging to avoid skin breakdown. A physician may need to examine the area if irritation or pain persists (Burgess et al, 1999).

Range Of Toxicity

    A) As with all irritants, concentration is not the only factor which affects the extent of tissue damage. The concentrations below should only be used as an estimate, with each patient examined individually.
    1) INHALATION: Concentrations under 50% are not likely to cause tissue damage.
    2) SKIN/MUCOUS MEMBRANES: 25% to 50% concentrations did not produce toxicity in the ear.
    3) INJECTION: Subcutaneous injections of a 6% to 30% solution did not produce toxicity.
    4) UTERINE MYOMETRIUM/CERVIX: Injection of a 58% solution in the uterus produced necrosis, while a 10% injection into the cervix did not.

Clinical Effects

Respiratory

    3.6.1) SUMMARY
    A) ANIMAL STUDIES have shown dyspnea and respiratory arrest.
    B) WITH POISONING/EXPOSURE
    1) Massive occupational exposure to carbamide produced chronic respiratory insufficiency in one adult.
    3.6.2) CLINICAL EFFECTS
    A) RESPIRATORY INSUFFICIENCY
    1) WITH POISONING/EXPOSURE
    a) CASE REPORT: A 34-year-old previously healthy man developed chronic respiratory insufficiency (up to one year later) after falling into a reloading wagon containing granulated carbamide (99.6% carbamide and 0.4% bicarbamide). He was completely covered in the formula for 10 minutes, and arrived at the hospital in a deep coma (Glasgow Coma Scale =4) along with hypotension and a chest X-ray showing signs of acute lung injury. Physical exam demonstrated multiple burns in the mouth and on the vocal cords, epiglottis and mucous membranes. Dermal burns were also present on exposed skin. The patient gradually recovered, but developed a persistent nonproductive cough and dyspnea. CT of the chest showed evidence of allergic alveoli reaction likely of a toxic origin. Spirometry was consistent with obstructive respiratory insufficiency, along with a persistent cough and dyspnea on exertion which were present one year later (Anand & Kabata, 2009).
    3.6.3) ANIMAL EFFECTS
    A) ANIMAL STUDIES
    1) APNEA
    a) SHEEP: The primary cause of death was respiratory arrest in one study (Edjtehadi et al, 1978).
    2) DYSPNEA
    a) COWS poisoned with urea fertilizer experienced dyspnea (Hoque & Dey, 1998; Caldow & Wain, 1991).

Neurologic

    3.7.1) SUMMARY
    A) ANIMAL STUDIES: Animals have developed trembling, fasciculations, hyperreflexia, convulsions, ataxia, and lethargy.
    B) WITH THERAPEUTIC USE
    1) Therapeutic administration of intravenous solution has caused intracranial hemorrhage, headache, and confusion.
    3.7.2) CLINICAL EFFECTS
    A) CLOUDED CONSCIOUSNESS
    1) WITH THERAPEUTIC USE
    a) Therapeutic administration of intravenous solutions have caused headache and confusion (JEF Reynolds , 1993; Osol & Hoover, 1975).
    B) INTRACRANIAL HEMORRHAGE
    1) WITH THERAPEUTIC USE
    a) CASE REPORT: Fatal intracranial hemorrhage was noted in an adult hypertensive man suffering from cerebrovascular disease after being given 90 grams of urea in 1 liter of normal saline by slow intravenous infusion (Marshall & Hinman, 1962).
    C) COMA
    1) WITH POISONING/EXPOSURE
    a) CASE REPORT: A 34-year-old previously healthy man fell into a reloading wagon containing granulated carbamide (99.6% carbamide and 0.4% bicarbamide). He was completely covered in the formula for 10 minutes, and arrived at the hospital in a deep coma (Glasgow Coma Scale =4) along with hypotension and a chest X-ray showing signs of acute lung injury. Physical exam demonstrated multiple burns in the mouth and on the vocal cords, epiglottis and mucous membranes. Dermal burns were also present on exposed skin. The patient gradually recovered, but developed a persistent nonproductive cough and dyspnea (Anand & Kabata, 2009)
    3.7.3) ANIMAL EFFECTS
    A) ANIMAL STUDIES
    1) CNS EFFECTS
    a) Pronounced muscle fasciculations, trembling, ataxia, lethargy, hyperreflexia, aggressiveness, and convulsions were observed (Edjtehadi et al, 1978; Caldow & Wain, 1991).
    2) SEIZURES
    a) MOUSE: Intraperitoneal injection of 6608 mg/kg produced convulsions or affected the seizure threshold (RTECS , 2001).
    3) TREMOR
    a) COWS: Muscular tremors, lethargy, hyperreflexia, and aggressiveness were seen in cows poisoned with urea fertilizer (Hoque & Dey, 1998; Caldow & Wain, 1991).
    4) SOMNOLENCE
    a) DOGS: Chronic urea intoxication (300 to 700 mg/mL) of dogs resulted in drowsiness similar to that seen with tranquilizing drugs (Balestri et al, 1971).

Summary Of Exposure

    A) ANIMAL STUDIES - In sheep and cattle, clinical effects included pronounced muscle fasciculations, trembling, grinding teeth, dysrhythmias, ataxia, lateral recumbency, anuria, dry mouth, frothy salivation, dyspnea, bloating, abdominal pain, regurgitation, hyperesthesia, mydriasis and convulsions. The primary cause of death was respiratory arrest. Laboratory examination showed increased glucose, ammonia and urea levels.
    B) WITH THERAPEUTIC USE
    1) Adverse effects include nausea, vomiting, dizziness, disorientation, drowsiness, diuresis, hyponatremia, hypokalemia, and confusion. Urea's systemic toxicity is similar to that of mannitol.
    C) WITH POISONING/EXPOSURE
    1) Urea is considered a mild to moderate intoxicant and a mild irritant. Exposure causes erythema of eyes and skin. Urea's systemic toxicity is similar to that of mannitol. Massive occupational exposure to carbamide produced persistent respiratory insufficiency.

Vital Signs

    3.3.4) BLOOD PRESSURE
    A) WITH THERAPEUTIC USE
    1) Therapeutic administration of intravenous solutions may cause a fall in blood pressure (JEF Reynolds , 1993).

Heent

    3.4.1) SUMMARY
    A) WITH POISONING/EXPOSURE
    1) Eye damage is expected only when concentrations are high or duration of exposure is extended. Rebound increases in intraocular pressure have been seen.
    3.4.3) EYES
    A) ANIMAL STUDIES
    1) RABBITS given intravitreal injection of 0.2 mL of a 10 molar solution, caused inflammation, chorioretinitis, and degeneration of the retina (Grant & Schuman, 1993).
    2) MYDRIASIS has been reported in poisoned sheep (Edjtehadi et al, 1978).
    3) When beef cornea were exposed to a 1 molar solution for an hour, the epithelium became loosened from the stroma. When tested on rabbit eyes, contact for 5 minutes with a saturated solution caused loss of corneal epithelium, moderate grayness of the stroma and subsequent slow regeneration of the epithelium (Grant & Schuman, 1993).
    4) Intracarotid injection of concentrated urea has done significant damage to the retina and the ciliary body. Retinal pigment epithelial cells are affected and the blood-retina barrier broken down.
    a) Intraocular pressure is significantly reduced and the aqueous outflow system rapidly shows swelling of the connective tissue of the inner wall of Schlemm's canal, followed by edema of the trabecular meshwork.
    b) Within several weeks there is return to normal, except for failure of pigmented ciliary epithelium to regenerate (Grant & Schuman, 1993; HSDB , 2001).
    B) WITH POISONING/EXPOSURE
    1) Eye damage is expected only when concentrations are high or duration of exposure is extended (Grant & Schuman, 1993).
    2) The eye is permeable to urea, so rebound elevation in intraocular pressure and vitreous volume may occur 8 to 12 hours after ocular hypotensive effects have ended (HSDB , 2001).

Gastrointestinal

    3.8.1) SUMMARY
    A) ANIMAL STUDIES: Grinding teeth, dry mouth, bloating, and regurgitation were observed in animals.
    B) WITH THERAPEUTIC USE
    1) Nausea and vomiting have occurred following oral or intravenous administration.
    3.8.2) CLINICAL EFFECTS
    A) NAUSEA AND VOMITING
    1) WITH THERAPEUTIC USE
    a) Nausea and vomiting may be seen after oral administration, presumably due to gastric irritation. These symptoms may also occur after intravenous administration (JEF Reynolds , 1993).
    3.8.3) ANIMAL EFFECTS
    A) ANIMAL STUDIES
    1) MOUTH DRY
    a) SHEEP: Grinding teeth, dry mouth, bloating, and regurgitation were observed in poisoned sheep (Edjtehadi et al, 1978).
    2) SALIVA INCREASED
    a) COWS: Frothy salivation, grinding teeth, bloating, and abdominal pain were reported in an urea-poisoned heifer (Hoque & Dey, 1998).

Genitourinary

    3.10.1) SUMMARY
    A) WITH THERAPEUTIC USE
    1) High urea levels will produce diuresis and should not be used in patients with severely impaired renal function.
    3.10.2) CLINICAL EFFECTS
    A) ABNORMAL RENAL FUNCTION
    1) WITH THERAPEUTIC USE
    a) Because urea is primarily eliminated by the kidneys, it should not be used in patients with severely impaired renal function (AMA, 1977). High urea levels will promote diuresis (Balestri et al, 1971).
    B) DISORDER OF MENSTRUATION
    1) Two Russian studies reported reproductive effects in women occupationally exposed to urea-formaldehyde resins (pp 87-91; Shumilina, 1975). In the first, female workers in a veneer factory complained of more vascular and digestive problems than did male workers. They also reported increased menstrual disorders, compared to female controls (pp 87-91). These workers were also exposed to formaldehyde, noise, and heat.

Hematologic

    3.13.1) SUMMARY
    A) WITH THERAPEUTIC USE
    1) Thrombosis and leukocytosis are possible. Rapid intravenous administration may cause hemolysis.
    3.13.2) CLINICAL EFFECTS
    A) LEUKOCYTOSIS
    1) WITH THERAPEUTIC USE
    a) Leukocytosis has been seen after intra-amniotic urea injection (Burnett et al, 1975).
    B) THROMBOEMBOLUS
    1) WITH THERAPEUTIC USE
    a) Superficial and deep thrombosis may occur if urea is given into the veins of the lower extremities (HSDB , 2001). Thrombosis may occur independently of any extravasation (S Sweetman , 2001).
    C) HEMOLYSIS
    1) WITH THERAPEUTIC USE
    a) Hemolysis has been seen experimentally and therapeutically. Rapid administration of intravenous solutions may cause hemolysis. Using glucose or invert sugar solutions as diluent will reduce the risk (S Sweetman , 2001).
    b) CASE SERIES: An infusion of 6 molar urea (in 10% invert sugar) was given to healthy adults. It caused intravascular hemolysis similar to that seen with sickle-cell anemia (Bensinger, 1973).
    c) CASE REPORT: An adult woman given urea and oxytocin for termination of pregnancy developed intravascular coagulation attributed to urea (Grundy & Craven, 1976).
    d) Hemorrhage due to coagulopathy was reported in 2 women during midtrimester termination of a pregnancy (Burkman, 1977a)
    e) An iso-osmotic (with serum) aqueous urea solution (1.63%) caused 100% hemolysis of erythrocytes cultured in this solution for 45 minutes (JEF Reynolds , 1993).

Dermatologic

    3.14.1) SUMMARY
    A) WITH POISONING/EXPOSURE
    1) Is a mild skin irritant.
    3.14.2) CLINICAL EFFECTS
    A) ERUPTION
    1) WITH POISONING/EXPOSURE
    a) In the standard Draize test on humans, a dose of 22 mg/3D on skin provoked a mild reaction (RTECS , 2001).
    1) May cause erythema after skin exposure (HSDB , 1993).
    B) BURN
    1) WITH POISONING/EXPOSURE
    a) CASE REPORT: A 34-year-old previously healthy man developed dermal burns to exposed skin after falling into a reloading wagon containing granulated carbamide (99.6% carbamide and 0.4% bicarbamide). He was completely covered in the formula for 10 minutes, and arrived at the hospital in a deep coma. Physical exam demonstrated multiple burns on the vocal cords, epiglottis, mucous membranes and exposed skin. Burning sensation of the skin and mucous membranes of the mouth were reported (Anand & Kabata, 2009).

Musculoskeletal

    3.15.1) SUMMARY
    A) WITH THERAPEUTIC USE
    1) Urea is irritating to tissues. Extravasation may lead to pain and necrosis.
    3.15.2) CLINICAL EFFECTS
    A) EXTRAVASATION INJURY
    1) WITH THERAPEUTIC USE
    a) Urea is irritating to tissues. Extravasation may lead to pain and necrosis (HSDB , 2001).

Endocrine

    3.16.1) SUMMARY
    A) WITH THERAPEUTIC USE
    1) An intolerance to carbohydrates may develop with high urea concentrations.
    3.16.2) CLINICAL EFFECTS
    A) ABNORMAL GLUCOSE TOLERANCE TEST
    1) WITH THERAPEUTIC USE
    a) Intolerance to carbohydrates has been observed in patients with chronic uremia, mild to severe renal failure, and in normal volunteers (Giovannetti & Barsotti, 1975).
    3.16.3) ANIMAL EFFECTS
    A) ANIMAL STUDIES
    1) ABNORMAL GLUCOSE TOLERANCE TEST
    a) DOGS: Intolerance to carbohydrates has been observed in intoxicated dogs (Giovannetti & Barsotti, 1975).

Reproductive

    3.20.1) SUMMARY
    A) Intraplacental and intrauterine administration of urea to humans has produced abortions.
    3.20.2) TERATOGENICITY
    A) BIRTHWEIGHT SUBNORMAL
    1) In a study of 130 trim shop finishers and 316 warehouse inspectors, a 47.5% incidence of menstrual disorders was reported. Neonatal anemia and low birth weight were also mentioned (Shumilina, 1975). Significantly, these women were also exposed to formaldehyde and occasionally had to lift over 100 pounds. In both of these studies, adverse reproductive effects could not be attributed to urea alone because of mixed and poorly documented exposures.
    B) ANIMAL STUDIES
    1) Urea was not teratogenic in rats (Seipelt, 1969), pigs (Ehrentraut, 1969), or sheep (Krisanov, 1969). Large doses (120 grams) of urea have been used, together with prostaglandin F2 alpha, to induce abortions when injected into the amniotic cavity (Haning & Peckham, 1985; Burkman, 1977). In these cases, urea was probably acting as an osmotic agent and may have had the effect of rupturing the amniotic membrane. This route of exposure is not relevant to the workplace.
    3.20.3) EFFECTS IN PREGNANCY
    A) PLACENTAL BARRIER
    1) Urea has also been studied for its ability to cross the human placenta, but the results were not available at the time of this review (Dancis, 1981).
    B) ABORTION
    1) Intraplacental administration of 1400 to 1600 mg/kg in women in their 16th week of pregnancy produced abortion (RTECS , 2001).
    C) PREGNANCY CATEGORY
    UREAC
    Reference: Briggs et al, 1998
    D) ANIMAL STUDIES
    1) MONKEY - Intrauterine administration of 6 gm/kg in an 18 week pregnant female resulted in abortion (RTECS , 2001).
    2) RATS/MICE - Teramoto et al (1981) gave 2 grams/kg orally to rats on day 12 and to mice on day 10 of pregnancy and found no greater defect or resorption rates.

Carcinogenicity

    3.21.1) IARC CATEGORY
    A) IARC Carcinogenicity Ratings for CAS57-13-6 (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) Carcinogenicity data are questionable. Both negative and positive studies have been reported.
    3.21.3) HUMAN STUDIES
    A) LACK OF INFORMATION
    1) Carcinogenicity data are questionable (Lewis, 1992). Both negative and positive studies have been reported.
    3.21.4) ANIMAL STUDIES
    A) CARCINOMA
    1) RODENTS/POSITIVE EFFECTS - Rats given an oral dose of 821 gm/kg/1Y-C showed tumorigenic effects. In the blood, there was lymphoma, including Hodgkin's disease (RTECS , 2001).
    a) Mice given an oral dose of 394 gm/kg/1Y-C showed tumorigenic effects. In the blood, there was lymphoma, including Hodgkin's disease (RTECS , 2001).
    2) Urea has not been listed as an animal carcinogen by IARC (1987) or the National Toxicology Program (USDHHS, 1994).
    B) LACK OF EFFECT
    1) RODENTS/NEGATIVE STUDIES - As a part of the National Cancer Institute's effort to screen environmental and occupational chemicals for chronic toxicity and carcinogenicity, urea (0.45%, 0.9%, and 4.5%) was fed to mice and rats for 12 months. Urea was considered to be non-carcinogenic (Fleischman et al, 1980).

Genotoxicity

    A) Human mutation data have been reported.

Cardiovascular

    3.5.1) SUMMARY
    A) WITH THERAPEUTIC USE
    1) Therapeutic administration of intravenous solutions may cause a fall in blood pressure.
    3.5.2) CLINICAL EFFECTS
    A) HYPOTENSIVE EPISODE
    1) WITH THERAPEUTIC USE
    a) Therapeutic administration of intravenous solutions may cause a fall in blood pressure (JEF Reynolds , 1993).
    2) WITH POISONING/EXPOSURE
    a) CASE REPORT: A 34-year-old previously healthy man fell into a reloading wagon containing granulated carbamide (99.6% carbamide and 0.4% bicarbamide). He was completely covered in the formula for 10 minutes, and arrived at the hospital in a deep coma (Glasgow Coma Scale =4) along with hypotension (100/40 mmHg) and a chest X-ray showing signs of acute lung injury. Physical exam demonstrated multiple burns in the mouth and on the vocal cords, epiglottis and mucous membranes. Dermal burns were also present on exposed skin. The patient gradually recovered, but developed a persistent nonproductive cough and dyspnea(Anand & Kabata, 2009)
    3.5.3) ANIMAL EFFECTS
    A) ANIMAL STUDIES
    1) DYSRHYTHMIA
    a) COWS: Dysrhythmias were reported in a heifer following urea poisoning (Hoque & Dey, 1998).

Laboratory Monitoring

Monitoring Parameters Levels

    4.1.1) SUMMARY
    A) Follow blood urea nitrogen (BUN) to detect urea increases.
    B) When diuresis is extensive, follow fluids and electrolytes.
    4.1.2) SERUM/BLOOD
    A) BLOOD/SERUM CHEMISTRY
    1) Measure blood urea nitrogen (BUN) to detect urea increases. This is a standard test in most clinical laboratories. Other clinical laboratory abnormalities have not been reported in humans. See animal studies below.
    2) Extensive diuresis may provoke fluid and electrolyte imbalances.
    3) ANIMALS - Laboratory examination showed increased plasma glucose, ammonia, and urea levels in sheep (Edjtehadi et al, 1978).
    4.1.3) URINE
    A) URINALYSIS
    1) A number of chemicals produce abnormalities of the hematopoietic system, liver, and kidneys. Monitoring urinalysis is suggested for patients with significant exposure.

Methods

    A) MULTIPLE ANALYTICAL METHODS
    1) Colorimetric, enzymatic, and Merckognost urea test are available for testing serum urea. All three provide acceptable results for clinical use (Ivanovic, 1981).
    2) AQUEOUS SOLUTION - Thin-layer chromatography has been used (Thielemann, 1979).
    3) CREAMS - A technique for hydrolyzing urea using 78% w/w sulfuric acid and refluxing for 20 minutes has been used for estimating urea content in creams (Dreyer-van der Glas & Dingjan, 1983).
    4) ANIMAL FEEDS - Both a colorimetric and urease method have been used to determine urea content in animal feeds (HSDB. 1993).

Treatment

Life Support

    A) Support respiratory and cardiovascular function.

Monitoring

    A) Follow blood urea nitrogen (BUN) to detect urea increases.
    B) When diuresis is extensive, follow fluids and electrolytes.

Oral Exposure

    6.5.1) PREVENTION OF ABSORPTION/PREHOSPITAL
    A) SUMMARY
    1) Urea is not highly toxic, and extensive decontamination and treatment is seldom necessary. Gastric decontamination is not indicated in high concentrations due to possible strong irritant effects.
    6.5.2) PREVENTION OF ABSORPTION
    A) SUMMARY
    1) Urea is not highly toxic, and extensive decontamination and treatment is seldom necessary. Gastric decontamination is not indicated in high concentrations due to possible strong irritant effects.
    B) ACTIVATED CHARCOAL
    1) Activated charcoal has not been tested. Effectiveness is unknown. Due to low toxicity, activated charcoal would usually not be indicated.
    2) CHARCOAL ADMINISTRATION
    a) Consider administration of activated charcoal after a potentially toxic ingestion (Chyka et al, 2005). Administer charcoal as an aqueous slurry; most effective when administered within one hour of ingestion.
    3) CHARCOAL DOSE
    a) Use a minimum of 240 milliliters of water per 30 grams charcoal (FDA, 1985). Optimum dose not established; usual dose is 25 to 100 grams in adults and adolescents; 25 to 50 grams in children aged 1 to 12 years (or 0.5 to 1 gram/kilogram body weight) ; and 0.5 to 1 gram/kilogram in infants up to 1 year old (Chyka et al, 2005).
    1) Routine use of a cathartic with activated charcoal is NOT recommended as there is no evidence that cathartics reduce drug absorption and cathartics are known to cause adverse effects such as nausea, vomiting, abdominal cramps, electrolyte imbalances and occasionally hypotension (None Listed, 2004).
    b) ADVERSE EFFECTS/CONTRAINDICATIONS
    1) Complications: emesis, aspiration (Chyka et al, 2005). Aspiration may be complicated by acute respiratory failure, ARDS, bronchiolitis obliterans or chronic lung disease (Golej et al, 2001; Graff et al, 2002; Pollack et al, 1981; Harris & Filandrinos, 1993; Elliot et al, 1989; Rau et al, 1988; Golej et al, 2001; Graff et al, 2002). Refer to the ACTIVATED CHARCOAL/TREATMENT management for further information.
    2) Contraindications: unprotected airway (increases risk/severity of aspiration) , nonfunctioning gastrointestinal tract, uncontrolled vomiting, and ingestion of most hydrocarbons (Chyka et al, 2005).
    6.5.3) TREATMENT
    A) SUPPORT
    1) There is no specific antidote. Care is symptomatic and supportive. Respiratory support may be required in severe intoxications. Patients with renal dysfunction are more susceptible to toxicity.
    2) Urea is effectively eliminated by the kidney. If normal renal function exists, diuresis will ensue. Patients should have adequate hydration. If diuresis is extensive monitor electrolytes.
    B) EXPERIMENTAL THERAPY
    1) PROTEIN -
    a) SHEEP - Short-term feeding of protein concentrates to sheep before giving urea supplements can increase their urea tolerance (Payne & Laws, 1976).
    2) WEAK ACIDS
    a) Have been used as an antidote in animals. A dose of 2.5 to 5 liters of 5% acetic acid has been used effectively in cattle. When used in animals, acids such as acetic and propionic acid offer some protection (Hoque & Dey, 1998; Humphreys, 1988).
    b) Poisoned cattle that are not too ill are given 19 to 38 liters cold water and 3.8 liters 5% acetic acid (vinegar) orally. Ammonia absorption from the rumen is decreased due to dilution and a slowed rate of hydrolysis. It also promotes urine flow (Booth & McDonald, 1982).

Inhalation Exposure

    6.7.1) DECONTAMINATION
    A) Move patient from the toxic environment to fresh air. Monitor for respiratory distress. If cough or difficulty in breathing develops, evaluate for hypoxia, respiratory tract irritation, bronchitis, or pneumonitis.
    B) OBSERVATION: Carefully observe patients with inhalation exposure for the development of any systemic signs or symptoms and administer symptomatic treatment as necessary.
    C) INITIAL TREATMENT: Administer 100% humidified supplemental oxygen, perform endotracheal intubation and provide assisted ventilation as required. Administer inhaled beta-2 adrenergic agonists, if bronchospasm develops. Consider systemic corticosteroids in patients with significant bronchospasm (National Heart,Lung,and Blood Institute, 2007). Exposed skin and eyes should be flushed with copious amounts of water.
    6.7.2) TREATMENT
    A) IRRITATION SYMPTOM
    1) Urea would be a mild to moderate irritant if inhaled in an aerosol. After the exposure has been terminated, patients should be evaluated for respiratory distress. Respiratory support should be available in severe cases.
    2) If respiratory tract irritation is present, monitor arterial blood gases and chest x-ray.
    B) BRONCHOSPASM
    1) If bronchospasm and wheezing occur, consider treatment with inhaled sympathomimetic agents.
    C) Treatment should include recommendations listed in the ORAL EXPOSURE section when appropriate.

Eye Exposure

    6.8.1) DECONTAMINATION
    A) EYE IRRIGATION, ROUTINE: Remove contact lenses and irrigate exposed eyes with copious amounts of room temperature 0.9% saline or water for at least 15 minutes. If irritation, pain, swelling, lacrimation, or photophobia persist after 15 minutes of irrigation, an ophthalmologic examination should be performed (Peate, 2007; Naradzay & Barish, 2006).
    6.8.2) TREATMENT
    A) IRRITATION SYMPTOM
    1) Urea may be mild to moderately irritating to the eye. Most exposures may be handled by irrigation with tepid water or saline and observation for prolonged pain or erythema (not expected).
    2) HIGH CONCENTRATIONS - or prolonged exposures may produce more significant irritation and should be seen by an ophthalmologist for evaluation.
    B) Treatment should include recommendations listed in the ORAL EXPOSURE section when appropriate.

Dermal Exposure

    6.9.1) DECONTAMINATION
    A) DERMAL DECONTAMINATION
    1) DECONTAMINATION: Remove contaminated clothing and wash exposed area thoroughly with soap and water for 10 to 15 minutes. A physician may need to examine the area if irritation or pain persists (Burgess et al, 1999).

Enhanced Elimination

    A) EXTRACORPOREAL ELIMINATION
    1) Urea is picked up during dialysis by sodium hydrogen zirconium phosphate (an ion exchange material) (Kirk-Othmer, 1986).

Range Of Toxicity

Summary

    A) As with all irritants, concentration is not the only factor which affects the extent of tissue damage. The concentrations below should only be used as an estimate, with each patient examined individually.
    1) INHALATION: Concentrations under 50% are not likely to cause tissue damage.
    2) SKIN/MUCOUS MEMBRANES: 25% to 50% concentrations did not produce toxicity in the ear.
    3) INJECTION: Subcutaneous injections of a 6% to 30% solution did not produce toxicity.
    4) UTERINE MYOMETRIUM/CERVIX: Injection of a 58% solution in the uterus produced necrosis, while a 10% injection into the cervix did not.

Therapeutic Dose

    7.2.1) ADULT
    A) ROUTE OF ADMINISTRATION
    1) ORAL - A single dose of 20 grams taken 2 to 5 times daily is usually given in fruit juices or syrups to disguise the taste (Osol & Hoover, 1975).
    2) IV (USUAL INFUSION) - 500 milligrams to 1.5 grams/kilogram as a 30% solution in dextrose injection at a rate not exceeding 4 milliliters per minute (S Sweetman , 2001). The maximum dose is 2 grams/kilogram daily.
    3) INTRA-AMNIOTIC INJECTION - For the termination of pregnancy, Urea solutions of 40% to 50% have been given intra-amniotically (S Sweetman , 2001).

Minimum Lethal Exposure

    A) SUMMARY
    1) Information on deaths has come primarily from animal studies. Examples of toxicity are listed below by animal species.
    2) Toxicity and death caused from uremic poisoning are due to a combination of factors, not from urea alone. Urea is one of the less toxic factors seen in uremic poisoning (Giovannetti & Barsotti, 1975).
    B) ANIMAL DATA
    1) COWS
    a) Urea poisoning resulting in death was reported 6 hours after cows drank water contaminated with urea fertilizer. The urea concentration in the water was 86 mmol/L. The ruminal fluid concentrations of ammonia nitrogen in 2 cows which died were 1825 and 957 mg/L (Caldow & Wain, 1991).
    b) The toxic dose in cattle given urea for the first time is approximately 0.45 mg/kg or about 100 to 200 g total. As little is 50 g may cause poisoning in an animal not accustomed to its effects. A tolerance is developed slowly. Unaccustomed animals were killed with as little as 50 g (Clarke & Clarke, 1975).
    2) GOATS
    a) Death occurred in 4 of 5 goats given 50 grams of urea orally (Clarke & Clarke, 1975).
    3) HORSES
    a) Ponies given 450 grams orally died (Clarke & Clarke, 1975).
    4) MONKEYS
    a) Rhesus monkeys had hypertonic urea solutions (58% weight/volume) injected rapidly (IV, IP, intra-amniotic) at a dose of approximately 2 g/kg. This is approximately twice a normal human therapeutic dose. Arterial and cerebrospinal fluid pressures, heart and respiration rates, urine flow, and urea clearance were monitored during the infusion and for 4 hours later. Serum electrolytes, hematocrit and white count, and cumulative urea excretion were measured for 1 week. There were no urea-related deaths and no serious side effects (Blake et al, 1976).
    5) PIGS
    a) Acute, single doses of 16 g/kg and doses of 10% urea in the feed had no apparent effect on 10 week old piglets. Incorporation of 0.4, 0.6 or 1.0 gram of urea per kilogram body weight into the food of 18 month old pigs (weighing 120 to 140 kilograms) failed to produce toxicity (Humphreys, 1988).
    6) SHEEP
    a) Sheep were given 12.5 mL of 3.3 molar urea solution per kilogram, which produced acute ammonia intoxication. Laboratory values which changed beyond acceptable limits were whole blood ammonium-nitrogen, venous blood pH, and serum glucose, lactate dehydrogenase, alkaline phosphatase, creatine kinase, urea nitrogen, inorganic phosphorus, sodium, and potassium (Roller et al, 1982).
    b) Twenty-seven sheep were used to study acute urea toxicity. Groups and survival times are listed below (Edjtehadi et al, 1978):
    GROUPSDOSE (g/kg)SURVIVAL TIME (min)
    Group I0.5165
    Group II0.6109
    Group III0.7560

    c) Lambs died in 90 to 120 minutes after being given 2 grams per kilogram of urea (Clarke & Clarke, 1975).
    d) Sheep can consume up to 100 grams of urea a day as long as the concentration does not exceed 6%. Liver dysfunction increases animal susceptibility (Clarke & Clarke, 1975).
    e) Sheep given a dose of 2 g/kg developed continuous convulsions after 165 minutes (Clarke & Clarke, 1975).

Maximum Tolerated Exposure

    A) SUMMARY
    1) As with all irritants, concentration is not the only factor which affects the extent of tissue damage. The concentrations below should only be used as an estimate, with each patient examined individually.
    2) INHALATION: Concentrations under 50% are not likely to cause tissue damage.
    3) SKIN/MUCOUS MEMBRANES: 25% to 50% concentrations did not produce toxicity in the ear.
    4) INJECTION: Subcutaneous injection of a 6% to 30% solution did not produce toxicity. Injection of a 58% solution in the uterus produced necrosis, 10% injected in the cervix did not.
    B) CASE REPORTS
    1) OCCUPATIONAL EXPOSURE: A 34-year-old previously healthy man developed chronic respiratory insufficiency after falling into a reloading wagon containing granulated carbamide (99.6% carbamide and 0.4% bicarbamide). He was completely covered in the formula for 10 minutes, and arrived at the hospital in a deep coma (Glasgow Coma Scale =4) along with hypotension and a chest X-ray showing signs of acute lung injury. Physical exam demonstrated multiple burns in the mouth and on the vocal cords, epiglottis and mucous membranes. Dermal burns were also present on exposed skin. The patient gradually recovered, but developed a persistent nonproductive cough and dyspnea. CT of the chest showed evidence of allergic alveoli reaction likely of a toxic origin. Spirometry was consistent with obstructive respiratory insufficiency along with a persistent cough and dyspnea with exertion, which were present one year later (Anand & Kabata, 2009).
    C) ROUTE OF EXPOSURE
    1) MIDDLE EAR: Administration of a 25% aerosol and a 50% direct injection did not result in damage (Droegemueller et al, 1978).
    2) UTERINE MYOMETRIUM: Injection of a 58% solution has caused extensive necrosis (Droegemueller et al, 1978).
    3) SUBCUTANEOUS TISSUES (RATS): Injections of a 6% to 30% solution subcutaneously did not produced necrosis within 48 hours (Droegemueller et al, 1978).
    4) CERVIX: Injections of a 10% solution in the human cervix produced brown discolorations. Some studies have shown no evidence of cytotoxicity, while others demonstrated focal necrosis. This was also observed if normal saline was administered (Droegemueller et al, 1978).

Workplace Standards

    A) ACGIH TLV Values for CAS57-13-6 (American Conference of Governmental Industrial Hygienists, 2010):
    1) Not Listed

    B) NIOSH REL and IDLH Values for CAS57-13-6 (National Institute for Occupational Safety and Health, 2007):
    1) Not Listed

    C) Carcinogenicity Ratings for CAS57-13-6 :
    1) ACGIH (American Conference of Governmental Industrial Hygienists, 2010): Not Listed
    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 CAS57-13-6 (U.S. Occupational Safety, and Health Administration (OSHA), 2010):
    1) Not Listed

Toxicity Information

    7.7.1) TOXICITY VALUES
    A) Reference: Lewis, 1992; Knudhansen & Pautong, 1993; RTECS, 2001
    1) LD50- (ORAL)MOUSE:
    a) 11 g/kg
    2) LD50- (SUBCUTANEOUS)MOUSE:
    a) 9200 mg/kg
    3) LD50- (ORAL)RAT:
    a) 8471 mg/kg
    4) LD50- (SUBCUTANEOUS)RAT:
    a) 8200 mg/kg

Pharmacology Toxicology

Pharmacologic Mechanism

    A) COLLAGEN - Urea has been used in collagen chemistry to dissociate collagen. It does so by interfering with hydrophobic linkages and hydrogen bonds. This results in changes of properties such as a decrease in tensile strength and an increase in elasticity (Droegemueller et al, 1978).
    B) MITOSIS - Urea concentrations of 1 to 1.4% produce cytokinetic and cytotoxic effects. Mitosis is arrested in metaphase (Glinos et al, 1983).

Toxicologic Mechanism

    A) Ammonia toxicosis appears to inhibit the citric acid cycle. Acidosis may occur, and increases are seen in anaerobic glycolysis, blood glucose, and blood lactate. One theory is that ammonia saturation of the glutamine-synthesizing system causes a back-up in the citrate cycle, a decrease in its intermediates, and a decrease in energy production and cellular respiration. This may lead to convulsions (Booth & McDonald, 1982).

Physicochemical

Physical Characteristics

    A) Urea has been described as colorless to white, tetragonal, prismatic crystals or powder (HSDB, 2005; Budavari, 1996; Lewis, 1992; Sax & Lewis, 1987).
    B) This compound is almost odorless, or with a slight ammonia odor; it possesses a saline taste (HSDB, 2005) .

Ph

    A) 7.2 (10% water solution) (Budavari, 1996)

Molecular Weight

    A) 60.06

Other

    A) ODOR THRESHOLD
    1) Odorless (CHRIS, 2005)

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) AIHA: 2006 Emergency Response Planning Guidelines and Workplace Environmental Exposure Level Guides Handbook, American Industrial Hygiene Association, Fairfax, VA, 2006.
    14) AMA: American Medical Association, AMA Department of Drugs, AMA Drug Evaluations, 3rd ed, PSG Publishing Co, Inc, Littleton, MA, 1977.
    15) 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.
    16) Anand JS & Kabata P: Acute exposure to urea. Przegl Lek 2009; 66(6):335-336.
    17) Balestri PL, Rindi P, & Biagini M: Chronic urea intoxication in dogs. Experientia 1971; 27:811-812.
    18) Bensinger TA: Blood 1973; 41:461.
    19) Bergmeyer HW: Methods of Enzymatic Analysis, 2nd English ed, Academic Press, New York, NY, 1974, pp 1791.
    20) Beverley DW & Wheeler D: Arch Dis Child 1986; 61:696.
    21) Blake DA, Burnett LS, & Miyasaki BC: Comparative effects of hyperosmolar urea administered by intra-amniotic, intravenous, and intraperitoneal routes in rhesus monkeys. Am J Obstet Gyn 1976; 124:239-244.
    22) Booth NH & McDonald LE: Veterinary Pharmacology and Therapeutics, 5th ed, Iowa State University Press, Ames, IA, 1982.
    23) Budavari S: The Merck Index, 11th ed, Merck & Co, Inc, Rahway, NJ, 1989.
    24) Budavari S: The Merck Index, 12th ed, Merck & Co, Inc, Whitehouse Station, NJ, 1996.
    25) Burgess JL, Kirk M, Borron SW, et al: Emergency department hazardous materials protocol for contaminated patients. Ann Emerg Med 1999; 34(2):205-212.
    26) Burkman RT: Coagulopathy with midtrimester induced abortion: Association with hyperosmolar urea administration. Am J Obstet Gyn 1977; 127:533.
    27) Burkman RT: Coagulopathy with midtrimester induced abortion: Association with hyperosmolar urea administration. Am J Obstet Gyn 1977a; 127:533.
    28) Burnett LS, King TM, & Atienza MF: Am J Obstet Gynecol 1975; 121:7.
    29) CHRIS : CHRIS Hazardous Chemical Data. US Department of Transportation, US Coast Guard. Washington, DC (Internet Version). Edition expires 1993; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    30) CHRIS: CHRIS Hazardous Chemical Data. US Department of Transportation, US Coast Guard. Washington, DC (Internet Version). Edition expires 2005; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    31) Caldow GL & Wain EB: Urea poisoning in suckler cows. Vet Rec 1991; 128:489-91.
    32) Chaurasia OP: Randomness of chromosome breaks in bone marrow cells of fertilizer-fed mice, Mus musculus. Cytobios 1991; 67:7-12.
    33) Chyka PA, Seger D, Krenzelok EP, et al: Position paper: Single-dose activated charcoal. Clin Toxicol (Phila) 2005; 43(2):61-87.
    34) Clarke EG & Clarke ML: Veterinary Toxicology, The Williams and Wilkins Company, Baltimore, MD, 1975.
    35) 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.
    36) Dancis J: Am J Obstet Gynecol 1981; 141:677-681.
    37) Dreyer-van der Glas SM & Dingjan HA: Pharm Weekbl 1983; 118:575-576.
    38) Droegemueller W, Chvapil M, & Vining J: Urea and dilatation of the cervix. Am J Obstet Gyn 1978; 132:775-782.
    39) 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/.
    40) 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.
    41) Edjtehadi M, Szabuniewicz M, & Emmanuel B: Acute urea toxicity in sheep. Canad J Comp Med 1978; 42:63-68.
    42) Ehrentraut W: Arch Geschwulstforsch 1969; 33:31-38.
    43) Elliot CG, Colby TV, & Kelly TM: Charcoal lung. Bronchiolitis obliterans after aspiration of activated charcoal. Chest 1989; 96:672-674.
    44) FDA: Poison treatment drug product for over-the-counter human use; tentative final monograph. FDA: Fed Register 1985; 50:2244-2262.
    45) Fleischman RW, Baker JR, & Hagopian M: Carcinogenesis bioassay of acetamide, hexanamide, adipamide, urea and P-tolylurea in mice and rats. J Environ Pathol Toxicol 1980; 3:149-170.
    46) Giovannetti S & Barsotti G: Uremic intoxication. Nephron 1975; 14:123-133.
    47) Glinos AD, Bardi GN, & Dermitzaki KC: Cytokinetic and cytotoxic effects of urea on HeLa cells in suspension cultures. J Nat Cancer Inst 1983; 71:1211-1219.
    48) Golej J, Boigner H, Burda G, et al: Severe respiratory failure following charcoal application in a toddler. Resuscitation 2001; 49:315-318.
    49) Graff GR, Stark J, & Berkenbosch JW: Chronic lung disease after activated charcoal aspiration. Pediatrics 2002; 109:959-961.
    50) Grant WM & Schuman JS: Toxicology of the Eye, 4th ed, Charles C Thomas, Springfield, IL, 1993.
    51) Grant WM: Toxicology of the Eye, 3rd ed, Charles C Thomas, Springfield, IL, 1986, pp 965.
    52) Grundy MFB & Craven ER: Br Med J 1976; 2:677.
    53) HSDB : Hazardous Substances Data Bank. National Library of Medicine. Bethesda, MD (Internet Version). Edition expires 1993; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    54) HSDB : Hazardous Substances Data Bank. National Library of Medicine. Bethesda, MD (Internet Version). Edition expires 2001; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    55) HSDB : Hazardous Substances Data Bank. National Library of Medicine. Bethesda, MD (Internet Version). Edition expires 2005; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    56) HSDB : Hazardous Substances Data Bank. National Library of Medicine. Bethesda, MD (Internet Version). Edition expires 4/30/1997; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    57) Haning RV Jr & Peckham BM: Am J Obstet Gynecol 1985; 151:92-96.
    58) Hansch C & Leo A: Substituent Constants for Correlation Analysis in Chemistry and Biology, John Wiley and Sons, New York, NY, 1979.
    59) Harris CR & Filandrinos D: Accidental administration of activated charcoal into the lung: aspiration by proxy. Ann Emerg Med 1993; 22:1470-1473.
    60) Hayes WJ Jr: Toxicology of Pesticides, Williams & Wilkins, Baltimore, MD, 1975.
    61) Hoque M & Dey S: Management of urea poisoning in a heifer. Indian Vet J 1998; 279-280.
    62) Humphreys DJ: Veterinary Toxicology, 3rd ed, Bailliere Tindell, London, England, 1988.
    63) 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.
    64) 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.
    65) 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.
    66) 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.
    67) 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.
    68) 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.
    69) ICAO: Technical Instructions for the Safe Transport of Dangerous Goods by Air, 2003-2004. International Civil Aviation Organization, Montreal, Quebec, Canada, 2002.
    70) 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.
    71) 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.
    72) Ivanovic I: Arch Farm 1981; 31:101-106.
    73) JEF Reynolds : Martindale: The Extra Pharmacopoeia, (CD-ROM version). The Pharmaceutical Press. Englewood, CO (Internet Version). Edition expires 1993; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    74) Knight CW & Sparrow SD: Urea nitrogen budget for a subarctic agricultural soil. Soil Sci Soc Am J 1993; 57:1138-1144.
    75) Krisanov AF: Uch Zap Mord Gos Univ 1969; 77:53-59.
    76) LaDu BN, Mandel HG, & Way EL: Fundamentals of Drug Metabolism and Disposition, Williams and Wilkins, Baltimore, MD, 1971.
    77) Lemiere C, Malo JL, & Garbegalanti L: Bronchial irritation syndrome following inhalation of urea - histological and immuno-histochemical evaluation. Rev Mal Respir 1996; 13:595-597.
    78) Lewis RJ: Sax's Dangerous Properties of Industrial Materials, 8th ed, Van Nostrand Reinhold Company, New York, NY, 1992, pp 3470-3471.
    79) Marshall S & Hinman F: JAMA 1962; 182:813.
    80) Mavrovic I & Shirley AR Jr: Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed, 23, John Wiley and Sons, New York, NY, 1983, pp 548-75.
    81) Mortelmans K: Environ Mutagen 1986; 8:1-119.
    82) NFPA: Fire Protection Guide to Hazardous Materials, 10th ed, National Fire Protection Association, Quincy, MA, 1991.
    83) NFPA: Fire Protection Guide to Hazardous Materials, 13th ed., National Fire Protection Association, Quincy, MA, 2002.
    84) 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.
    85) 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.
    86) 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.
    87) 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.
    88) Naradzay J & Barish RA: Approach to ophthalmologic emergencies. Med Clin North Am 2006; 90(2):305-328.
    89) 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.
    90) 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.
    91) 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.
    92) 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.
    93) 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.
    94) 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.
    95) 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.
    96) 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.
    97) 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.
    98) 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.
    99) 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.
    100) 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.
    101) 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.
    102) 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.
    103) 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.
    104) 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.
    105) 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.
    106) 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.
    107) 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.
    108) 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.
    109) 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.
    110) 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.
    111) 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.
    112) 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.
    113) 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.
    114) 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.
    115) 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.
    116) 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.
    117) 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.
    118) 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.
    119) 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.
    120) 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.
    121) 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.
    122) 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.
    123) 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.
    124) 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.
    125) 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.
    126) 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.
    127) 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.
    128) 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.
    129) 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.
    130) 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.
    131) 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.
    132) 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.
    133) 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.
    134) 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.
    135) 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.
    136) 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.
    137) 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.
    138) 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.
    139) 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.
    140) 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.
    141) 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.
    142) 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.
    143) 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.
    144) 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.
    145) 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.
    146) 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.
    147) 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.
    148) 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.
    149) 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.
    150) 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.
    151) 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.
    152) 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.
    153) 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.
    154) 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.
    155) 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.
    156) 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.
    157) 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.
    158) 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.
    159) 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.
    160) 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.
    161) 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.
    162) 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.
    163) National Heart,Lung,and Blood Institute: Expert panel report 3: guidelines for the diagnosis and management of asthma. National Heart,Lung,and Blood Institute. Bethesda, MD. 2007. Available from URL: http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.pdf.
    164) 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.
    165) National Research Council : Acute exposure guideline levels for selected airborne chemicals, 5, National Academies Press, Washington, DC, 2007.
    166) National Research Council: Acute exposure guideline levels for selected airborne chemicals, 6, National Academies Press, Washington, DC, 2008.
    167) National Research Council: Acute exposure guideline levels for selected airborne chemicals, 7, National Academies Press, Washington, DC, 2009.
    168) National Research Council: Acute exposure guideline levels for selected airborne chemicals, 8, National Academies Press, Washington, DC, 2010.
    169) None Listed: Position paper: cathartics. J Toxicol Clin Toxicol 2004; 42(3):243-253.
    170) OHM/TADS : Oil and Hazardous Materials/Technical Assistance Data System. US Environmental Protection Agency. Washington, DC (Internet Version). Edition expires 1993; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    171) OHM/TADS: Oil and Hazardous Materials Technical Assistance Data System. US Environmental Protection Agency. Washington, D.C. (Internet Version). Edition expires 2005; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    172) Osol A & Hoover JE: Remington's Pharmaceutical Sciences, 15th ed, Mack Publishing Company, Easton, PA, 1975, pp 864.
    173) Payne E & Laws L: The efficacy of protein supplementation in overcoming urea toxicity in sheep. Br J Nutr 1976; 35:47-54.
    174) Peate WF: Work-related eye injuries and illnesses. Am Fam Physician 2007; 75(7):1017-1022.
    175) Pedersen H, Lomstein BA, & Blackburn TH: Evidence for bacterial urea production in marine sediments. FEMS Microbiol Ecol 1993; 12:51-59.
    176) Phelps AW, Dillingham EO, & Autian J: The influence of urea and cell-surface protein on the behavior of nontumorigenic and chemically transformed cells. J Toxicol Environ Health 1983; 11:783-797.
    177) Pollack MM, Dunbar BS, & Holbrook PR: Aspiration of activated charcoal and gastric contents. Ann Emerg Med 1981; 10:528-529.
    178) Pushkina IK et al: Vopr Gi Tr Nov Tekhnol Protsessami Mamshinostroit Khim Prom-Sti. Mater Mosk Nauchn Konf, 1982.
    179) RTECS : Registry of Toxic Effects of Chemical Substances. National Institute for Occupational Safety and Health. Cincinnati, OH (Internet Version). Edition expires 2001; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    180) RTECS : Registry of Toxic Effects of Chemical Substances. National Institute for Occupational Safety and Health. Cincinnati, OH (Internet Version). Edition expires 4/30/1997; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    181) Rau NR, Nagaraj MV, Prakash PS, et al: Fatal pulmonary aspiration of oral activated charcoal. Br Med J 1988; 297:918-919.
    182) Roller MH, Riedemann GS, & Romkema GE: Ovine blood chemistry values measured during ammonia toxicosis. Am J Vet Res 1982; 43:1068-1071.
    183) S Sweetman : Martindale: The Complete Drug Reference. Pharmaceutical Press. London, UK (Internet Version). Edition expires 2001; provided by Truven Health Analytics Inc., Greenwood Village, CO.
    184) Sax NI & Lewis RJ: Hawley's Condensed Chemical Dictionary, 11th ed, Van Nostrand Reinhold Company, New York, NY, 1987.
    185) Seipelt H: Z Urol Nephrol 1969; 62:623-627.
    186) Shumilina AV: Gig Tr Prof Zabol 1975; 12:18-21.
    187) Tchounwou PB, Englande AJ Jr, & Malek EA: Toxicity evaluation of ammonium sulphate and urea to three developmental stages of freshwater snails. Arch Environ Contam Toxicol 1991; 21:359-364.
    188) Thielemann H: Acta Hydrochim Hydrobiol 1979; 7:125-127.
    189) Trivedi SP, Singh P, & Sethi N: Evaluation of hematotoxic effects of two commonly used fertilizers, diammonium phosphate and urea, on fish Clarias batrachus. Ecotoxicol Environ Safety 1990; 19:135-142.
    190) 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.
    191) 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.
    192) 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-.
    193) 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.
    194) 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.
    195) 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.
    196) 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.
    197) 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-.
    198) U.S. Occupational Safety, and Health Administration (OSHA): Process safety management of highly hazardous chemicals. 29 CFR 2010 2010; 29(1910.119):348-.
    199) USDHHS: Seventh Annual Report on Carcinogens - . (US Department of Health and Human Services, National Toxicology Program), Technical Resources, Inc, Rockville, MD, 1994.
    200) 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.
    201) Wafar MVN, Wafar S, & Kumar RR: Nitrogen uptake kinetics of freshly isolated Zooxanthellae. Indian J Mar Sci 1993; 22:83-88.