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.