Urea

Endpoint summary

Additional information

Urea is of very low acute toxicity to aquatic organisms.

Toxicity to fish

The 48 hour LC₅₀of urea in golden orfe is reported to be >10000 mg/l. This can also be considered as the NOEC. The results reported by the two laboratories were identical. The effects of urea on survival, food utilization and oxygen consumption of the fresh water fish Oreochromis mossambicus were studied. The percentage survival of O. mossambicus when exposed to different concentrations of urea at 24, 48, 72 and 96 h exposures was noted and it was found that 22000 and 38000 mg/L urea concentration were sublethal and lethal, respectively. The median lethal concentration, which killed 50% of the fish during 96 h exposure, was 28000 mg L−1. Rearing the fish in increasing sublethal concentrations of urea, it was found that the feeding rate decreased from 34.341 ± 7.067 mg g live fish−1 d−1(control) to 13.921 ± 2.315 mg g live fish−1 d−1at the highest concentration of urea (22,000 mg L−1). Growth rate was drastically reduced. The consumption of oxygen in O. mossambicus diminished from 0.962 ± 0.208 to 0.645 ± 0.118 mg g live fish−1 h−1 when reared in the highest sublethal concentration of urea. The 96 hour LC₅₀of urea to B. barnawas > 9100 mg/l. The NOEL was 4961 ppm. The 96 hour acute LC₅₀of urea to golden orfe fish is reported in a further study to be >6810 mg/l. No long-term toxicity data are available: a waiver is proposed for this endpoint. Urea is of inherently low toxicity to fish species: it is a normal product of protein catabolism and therefore fish have evolved effective excretion mechanisms. Additionally, exposure will be limited by the action of microorganisms and incorporation of urea into the nitrogen cycle.

 

Toxicity to aquatic 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 LC50 values for freshwater snail eggs, juveniles and adults were reported to be 14241 mg/l, 18255 mg/l and 22998 mg/l. Following 48 hours 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 LC50 in mosquito (Aedes aegypti) larvae is reported to be 60000 mg/l. No long-term toxicity data are available: a waiver is proposed on exposure grounds. Urea is of inherently low toxicity to species of aquatic invertebrates and exposure will be limited by the action of microorganisms and incorporation of urea into the nitrogen cycle

 

Toxicity to algae

The 192 hour toxicity threshold of blue-green algae urea was 47 mg/l. To some extent urea exhibits toxic action to Microcystis aeruginosa. The 7 day toxicity threshold of urea to Scenedesmus quadricauda was >10000 mg/l. The 72 hour toxicity threshold of Entosiphon sulcatum to urea was 29 mg/l, and the 16 hour toxicity threshold of urea to Pseudomonas putida was > 10000 mg/l.