Urea

Endpoint summary

Description of key information

Earthworms were found to be the most sensitive group for the terrestrial environment.

Multiple acute and chronic studies are available for earthworms covering different species, life stages, laboratory and field studies, investigation of the mode of action and behavioural changes.

Information for other ecological groups is present as well and was used together with the information for earthworms for the derivation of the H05 by SSD.

Additional information

Urea is used as fertilizer. It is well known, that long term exposure of urea can significantly reduces soil pH, which in agricultural situations is controlled by liming. In some long-term studies, the pH was not adjusted. Inhibitory effects after repetitive exposure of urea were attributed to the lowering of soil pH, exclusively. Hence, long-term studies with repeated application without pH adjustment need to be carefully reviewed to avoid potential misinterpretation of their results.

 

When used as fertilizer, the toxic effects of urea observed in plants were contributed to the formation of ammonia which damaged the plants. This can be compensated by the addition of urease inhibitors or sterilization of the soil prior to seeding and fertilization.

 

The most sensitive group of organisms are earthworms and especially E. fetida. The mode of action of urea on earthworms is corrosion of the surface and surface close tissue. This has been observed in various earthworm species. Earthworms react with avoidance behaviour on the presence of urea. In a 33-year field study (Murchie et al. 2015) the pH was controlled and positive effects were observed for all 12 investigated earthworm species at a yearly application rate of 429 kg/ha, corresponding to 286 mg urea/kg dw/year.

Based on the avoidance behaviour effects observed in laboratory tests (OECD 222) seems to be worst case when compared to field studies. The PNEC soil was derived by using the earthworm laboratory data as most sensitive group (and data for other taxa) and resulted in a H05 of 242 mg urea/kg dw. 

 

"Generally, it was observed that management practices that encourage earthworm abundance (like mineral fertilization with nitrogen and phosphorous) are the same as those assuring a good support for a large crop productivity necessary for sustainable agroecosystems." cited from M. Iordache, I. Borza 2010 Relation between chemical indices of soil and earthworm abundance under chemical fertilization ( PLANT SOIL ENVIRON., 56, 2010 (9): 401–407)