Role of Suspended Particulate Matter for the Transport and Risks of Organic Micropollutant Mixtures in Rivers: A Comparison between Baseflow and High Discharge Conditions.

The partition dynamics of organic micropollutants between water and suspended particulate matter (SPM) in riverine ecosystems differs between dry and wet weather, as demonstrated at two sites at the Ammer River, Germany. One site was impacted by a wastewater treatment plant (WWTP) and the other by runoff of a mixed agricultural/urban area. Liquid and gas chromatography coupled to high-resolution mass spectrometry were used to quantify 415 organic chemicals, and their mixture effects were characterized with three in vitro bioassays indicative of the activation of the aryl hydrocarbon (AhR) and peroxisome proliferator-activated (PPARγ) receptors and the oxidative stress response. During wet weather, the total chemical concentrations and bioactivities in the water increased, but the concentrations in SPM did not change. As SPM levels increased, the SPM-bound chemicals contributed 6-16% to the overall concentrations in the water column during wet weather but only 0.1-0.9% during dry weather. The mixture effects were more strongly associated with SPM under wet conditions, particularly for AhR activity, where SPM accounted for over 90% of the observed effects. The AhR activity may therefore serve as an indicator for assessing the risks of SPM-related pollution in rivers. The high SPM-bound mixtures' activation of AhR and oxidative stress response during rain were primarily caused by polycyclic aromatic hydrocarbons, indicating a major contribution of road runoff.