Solubility of Tin in Aqueous Media: Implications for Regulatory Ecotoxicity Testing?

Effects caused in ecotoxicity tests by physical factors due to precipitated particles cannot be used for classification in Europe under the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH). For tin (Sn), results from ecotoxicity tests have been observed to be difficult to interpret in regard to exposures of dissolved Sn. Experiments were undertaken with Sn(IV) chloride at 2-2000 µg L^-1 in aquatic test media of differing pHs and hardness. A predictive Sn precipitation model was derived using these data and speciation modelling. Previous ecotoxicity tests assessed with the model indicated that organisms were exposed to Sn precipitates. It was therefore not possible to establish the dissolved Sn doses in the tests, invalidating the results for use in risk assessment. Developing an understanding of the speciation and precipitation behaviour of trace elements should be considered a priority before conducting ecotoxicity testing.