European environmental scenarios of chemical bioavailability in freshwater systems

The goal of environmental risk assessment (ERA) is to quantify the risk that a given chemical would impair the structure and function of natural ecosystems by assessing its environmental exposure and the expected ecological aspects. However, the environmental realism, ecological relevance and methodological accuracy of the currently used exposure and effect assessment approaches have been questioned for years. The issue has been recently underlined in a joint opinion from the three scientific committees of the European Commission, in which the major challenges for risk assessment were devised. Concerning exposure assessment, the transition to more dynamic and realistic modelling approaches and scenarios was suggested, since it would allow a more accurate prediction of bioavailable concentrations and their variations in space and time. In this work, an improved dynamic multimedia model (ChimERA fate), including a phytoplankton compartment and equations to calculate phytoplankton, detritus and dissolved organic matter variations in time, was developed. The model was parameterized to simulate five dynamic scenarios for shallow meso-eutrophic phytoplankton-dominated water bodies based on a latitudinal gradient (in Europe); such scenarios include seasonal profiles of water temperature, autochthonous phytoplankton biomass, detritus, and dissolved organic matter. Model runs were performed for a number of chemicals with increasing hydrophobicity (8 PCBs), with the aim of investigating the influence of scenario characteristics and compound properties on bioavailable concentrations. The key processes were adsorption/uptake by phytoplankton and deposition to sediment of detritus-bound chemicals. The northern scenarios (“Scandinavia” and “UK”) showed the highest bioavailable concentrations, with max/min ratios up to 25; in contrast, for example, maximum concentrations in the “Mediterranean” scenario were lower by a factor of 2 to 9 with respect to the northern ones (depending on chemical hydrophobicity), due to the generally higher biomass and carbon levels, and showed only limited seasonal variability (up to a factor of 4). These results highlight the importance of including biomass and organic carbon dynamics in both modelling approaches and scenarios for the evaluation of exposure concentrations in aquatic environments. Acknowledgement - The ChimERA project is financed by the Long-range Research Initiative of CEFIC (www.cefic-lri.org) (project code: LRI-ECO19).