Urea

Endpoint summary

Description of key information

Reliable and relevant acute and long-term data are available for all three trophic levels, i.e., algae, invertebrates and fish.

Overall, it was demonstrated that urea is not toxic within the normal concentrations outlined in the guidance documents, i.e., all EC50 and EC10 values are > 100 mg urea/L. Hence, there is no rik for the aquatic organisms. However, for the derivation of robust PNECs, the availabe information was assessed.

The most relevant acute data are as follows:

Algae: 72-h ErC50: 24541.9 mg a.s./L

Invertebrates: The 24 hour EC₅₀ for urea in Daphnia was reported to be >10000 mg/l; urea is not acutely toxic to daphnids. The 24 hour LC₅₀values for freshwater snail eggs, juveniles and adults were reported to be 14241 mg/l, 18255 mg/l and 22998 mg/l. Following 48 hour exposure, the LC₅₀value for adults was calculated to be 13477 mg/l.   In another study, the 24 hour LC₅₀values for eggs, juvenile and adult snails were reported to be 13532 mg/l, 24504 mg/l and 26024 mg/l, respectively. Following 48 hours exposure, the LC₅₀value for adults was calculated to be 21412 mg/l. It is concluded that, under normal laboratory conditions, urea displays low molluscicidal activity. The 4 hour LC₅₀in mosquito (Aedes aegypti) larvae is reported to be 60000 mg/l.

Fish: 96 -h LC50 Danio rerio FET: 21060 mg urea/L (result from and inter-laboratory ring test). Further results for various fish species is available.

The most relevant long-term data are as follows:

Algae: 72-h ErC10: 6895.8 mg a.s./L

Daphnids: Daphnia magna reproduction 21-d EC10 140.7 mg/L

Fish EC10 Oreochromis mossambicus: 7247 mg urea/L

Hence, invertebrates are the most sensitive group of organisms. The EC10 -value of 140 mg/L will be used for the risk assessment.

Further information:

Studies with various amphibian species indicate that amphibians are also not sensitive to urea.

Urea is the primary excretion product of fish embryos. In juvenile and adult fish about 10 to 20% of the nitrogen is excreted as urea. Further information on the role of urea in the N-cycle of fish is provided in the section "Biotransformation and kinetics".

Since urea is a natural N-cycle product in fish and especially in embryos and juvenile fish, it is highly unlikely that urea will act as endocrine disruptor.