1,3-bis(trimethylsilyl)urea

Endpoint summary

Additional information

Short-term aquatic toxicity studies are available for all three trophic levels of the registered (parent) substance 1,3-bis(trimethylsilyl)urea (CAS No. 18297 -63 -7). In addition, one study is available for the toxicity of the substance toward microorganisms.

The substance hydrolyses rapidly in contact with water (DT50 < 10 min, OECD 111) and forms the silanol hydrolysis product trimethylsilanol (TMS, CAS No. 1066-40-6) and urea (CAS No. 57 -13 -6). Therefore, it is highly likely that the test organisms in the aquatic tests were predominantly exposed to the hydrolysis products rather than the parent substance itself. Since urea is generally considered to be of low concern for environmental and human health (OECD SIDS, 2002), the results likely reflect the aquatic hazard of the silanol hydrolysis product trimethylsilanol (TMS).

All the available studies were performed according to standard OECD testing guidelines and GLP.

In all studies, the test organisms were both exposed to the test item itself as well as to the silanol hydrolysis product TMS, which was used as reference item to ensure that if toxicity was observed, it could be related to this constituent and not any other degradant of the registered (parent) substance. Based on the analytical findings and physico-chemical properties of TMS, TMS was considered to be a stable degradant representative of the test item. Chemical analyses of all test media was carried out to verify the test concentrations and stability of the test item and reference item in fresh and aged media. Due to the rapid hydrolysis of the test item to TMS in all test media, the concentrations of the test item in the test samples were quantified by measuring the concentration of the stable hydrolysis product TMS.

Since the registered (parent) substance is insoluble in water, saturated aqueous solutions (100% v/v) of both the test item and reference item were prepared in the exact same way. The dissolved test item concentrations achieved by the saturated solution preparation method in the respective testing media was approximately 91 mg/L in the fish study, 80 mg/L in the aquatic invertebrates study and 60 mg/L in the aquatic algae study, indicating the limit of water solubility of the test item under test conditions.

The aquatic toxicity tests were carried out as limit tests with the single exposure concentration of 100% v/v in a semi-static (fish study and aquatic invertebrates study, renewal rate: daily) and static test design (aquatic algae).

The analytical findings showed that both the test item and reference item were not stable under the experimental conditions of the aquatic toxicity tests. Furthermore, adsorption to algal cells was observed in the aquatic toxicity test to aquatic algae and an increase in ammonia (attributable to urea) was recorded in the fish test. Therefore, the results of all tests were based on the geometric mean measured concentrations.

At the end of the respective exposure periods in all tests, no aquatic toxicity was observed at the limit of solubility of the test item in the respective aqueous testing media and no statistically significant toxic effects > 50% were observed towards microorganisms.