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EC number: 200-315-5
CAS number: 57-13-6
12-month carcinogenicity screening studies in the rat and mouse demonstrate that urea is of very low chronic toxicity by the oral route. Similarly, no evidence of local or systemic toxicity was seen in 4-week and 25-week dermal toxicity studies in the rat. No clear toxicity was seen in dogs administered high doses of urea by subcutaneous injection over a period 45 days.
Repeated dose oral toxicity
In 12 -month carcinogenicity screening assays (Fleischman et al, 1980),
F-344 rats and C57BL/6 mice (50/sex/group) were exposed to urea in the
diet at concentrations of 4500, 9000 or 45000 ppm for 12 months. Five
animals/sex/group were sacrificed at the end of the 365-day exposure
period and a comprehensive list of tissues was investigated
histopathologically; interim deaths were similarly investigated. All
remaining animals were sacrificed after the 4-month recovery period and
investigated histopathologically. There were no signs of toxicity.
Survival and bodyweights were unaffected by treatment. Gross and
microscopic pathology did not reveal any treatment-related effects. It
is concluded that urea is of very low chronic toxicity. Using default
conversion factors, the dose level of 45000 ppm is calculated to be
equivalent to approximately 2250 mg/kg bw/d in the rat and 6750 mg/kg
bw/d in the mouse.
Repeated dose dermal toxicity
In 4 -week and 25 -week dermal toxicity studies, urea (formulated as an
ointment) was applied to the shorn dorsal skin of groups of male and
female Wistar rats. Bodyweights were measured; food and water
consumption were assessed. Clinical chemistry, urinalysis and
haematological parameters were investigated. At necropsy, organ weights
were recorded; gross necropsy and histopathology were performed. No
dose-dependent toxicity was observed. Bodyweights, food and water
consumption were unaffected by treatment. Clinical chemistry,
haematology and urinalysis parameters were comparable in all groups.
There was no effect of treatment on organ weights or pathology (Sato et
Repeated exposure inhalation toxicity
Urea is demonstrated to be of very low toxicity by the oral and
subcutaneous routes. The substance is a non-volatile solid produced as
crystals with particle sizes of >0.1 mm. There is therefore no potential
for inhalation exposure. The data requirement is therefore waived on
scientific grounds and on exposure considerations. Testing is
additionally not justified on animal welfare grounds.
Repeated dose toxicity by other routes of exposure
Twelve unilaterally nephrectomised dogs were injected subcutaneously
with 10% urea solution (3000-4000 mg/kg bw) every 8 hours over a period
of 45 days. Administration led to increased diuresis, plasma urea levels
were 200 - 700 mg/100ml. The dogs displayed mild drowsiness.
Haematocrit, platelet counts and EEG were not affected. The study
indicates that urea is of very low toxicity in the dog following
repeated administration (Balestri et al, 1971).
classification is proposed. Urea only showed signs of very low chronic toxicity.
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