Registration Dossier

Toxicological information

Endpoint summary

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Key value for chemical safety assessment

Additional information

Urea is produced in the body of mammals as a consequence of normal physiological processes, primarily by the detoxification of ammonia resulting from protein catabolism, via the urea cycle. The quantity of urea produced by an adult human is influenced by dietary protein intake but is reported to be typically between 20 -50 g/day. Urea is generated in the liver by the urea (ornithine) cycle by the action of the terminal enzyme arginase I on L-arginine. Reference ranges for urea in human blood are 70 -210 mg/L (7 -21 mg/dL). Therefore assuming a blood volume of 5L (for an adult) and serum proportion of 55%, the quantity of urea present in the blood at any one time is 192.5 -577.5 mg or (assuming a bodyweight of 70 kg), 2.75 -8.25 mg/kg bw.

The urea produced by the urea cycle is removed from the blood by glomerular filtration (as a small, water-soluble molecule), but is largely reabsorbed by the renal tubules. Some urea is transported by specific transport systems back into the urine. The clearance of urea is estimated to be 75 mL/minute, equivalent to approximately 1.5% of the total blood volume/minute. Urea also plays a physiological role in renal countercurrent exchange. Urea is present in saliva in appreciable concentrations (approximately 200 mg/L) and is also present in the epidermis at high levels, where it plays a role in skin hydration.

Dermal absorption

Urea is present at appreciable levels in the human epidermis, where it may play a role as a humectant, maintaining hydration of the stratum corneum. At very high levels of exposure, urea may act as a denaturant and may enhance the dermal absorption of other compounds. Bronaugh et al (1982), report a dermal absorption value of 7.2%, based on the results of a study in the rat in vivo and comparable results in vitro.