Temperature, phytoplankton density and bacteria diversity drive the biotransformation of micropollutants in a lake ecosystem. LakeMP

For most micropollutants (MPs) present in surface waters, such as pesticides and pharmaceuticals, the contribution of biotransformation to their overall removal from lake ecosystems is largely unknown. Even less information is available on how their biotransformation may vary spatially and seasonally in those systems. This study aims at empirically determining the biotransformation rate constants for 35 MPs at different periods of the year and depths of a meso-eutrophic lake. We then tested statistically the association of environmental parameters and microbial communities with the biotransformation rate constants obtained. Biotransformation was observed for 14 out of 35 spiked MPs for at least one sampling time. Large variations in biotransformation rate constants were observed over the seasons and between compounds, resulting in on order of magnitude difference in half-lives obtained for a same compound. Overall, the transformation of MPs was mostly influenced by the lake’s temperature, phytoplankton density and bacterial composition. However, some individual MPs were not following the general trend or association with microorganism biomass. The antidepressant mianserin, for instance, was transformed in all experiments and depths, but did not show any relationship with measured environmental parameters, suggesting the importance of specific microorganisms in its transformation. These results presented contribute to our understanding of the fate of MPs in surface waters and support improved risk assessment of contaminants in the environment.