Urea

Endpoint summary

Description of key information

The handling of urea by the human body is well characterised as it is a normal product of protein catabolism and is normally produced in large quantities.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

60

Absorption rate - dermal (%):

10

Absorption rate - inhalation (%):

10

Additional information

Absorption of Urea as follows based on physicochemical/toxicological data following ECHA guidance 7c (2017). The substance isa solid material with molecular weight of 60.0556 g/mol and water solubility of 624000 mg/L at 20°C. The log Pow is around -1.73 at 20°C and the mean particle size is 0.1-5 mm. The vapour pressure is 1.2 x 10^-5mmHb or 0.0016 Pa at 25°C. The substance has no ionizable groups.

-         Oral/GI absorption: The molecular weight below 500g/mol, the absence of ionisable groups, the hydrophilic properties and the particle size, are in favor of oral absorption. When SC (subcutaneous) versus oral LD₅₀values were compared, a factor of 0.57-0.63 was reached. Based on these data, an oral absorption of 60% is considered.

-         Respiratory absorption: Based upon the solid state with high particle size (not reaching the thoracic airways), low vapor pressure and high water solubility, deposition in the lower airways is assumed most unlikely and absorption by inhalation is considered to be negligible. From a conservative viewpoint, a 10 % inhalation absorption is considered.

-         Dermal absorption: Based upon the low molecular weight, solid state and low vapor pressure (not evaporating), and the fact that the structure is not binding to skin molecules, dermal absorption is possible. However, the high water solubility, log P <0 and absence of irritation are not in favour of dermal absorption. Experimental data on the absorption of urea across normal human skinin vitrois reported to be up to 9.5%.From a realistic conservative viewpoint, a 10 % dermal absorption is considered.

Urea is produced in the body (liver) of mammals as a consequence of normal physiological processes, primarily by the detoxification of ammonia resulting from protein catabolism, via the urea cycle.