Solar radiation may increase the environmental toxicity of titanium dioxide nanoparticles, according to tests on water fleas as part of a study by Germany's environment agency (UBA). As a result, the UBA is calling for more ecotoxicity tests to be carried out in the presence of simulated solar radiation.
Researchers at Aachen University carried out a series of the tests on two types of titanium dioxide nanomaterials for the UBA. They exposed a range of organisms, from water fleas to earthworms, to the nanoparticles. They found that earthworm tests are suitable for studying the materials. However, the tendency of the particles to agglomerate and to sediment can cause problems with water flea (Daphnia) and fish embryo acute toxicity tests, they add.
The researchers also looked at the applicability of OECD guidelines for testing nanomaterials. In the study report, the UBA calls for guidance to adapt current aquatic ecotoxicity test guidelines to define particle stability. Ecotoxicology tests on titanium dioxide materials should always include possible effects of sunlight, recommends the report. “Neglecting the influence of sunlight results in a clear underestimation of the environmental risk, associated with titanium dioxide materials,” it cautions.
Given the high diversity of nanomaterials, the report also suggests establishing a screening tool for photoactive substances. Moreover, it should be “mandatory” to test the potential to form reactive oxygen species for all nanomaterials, before conducting ecotoxicity tests, it adds.