Combining in vitro reporter gene bioassays with chemical analysis to assess changes in the water quality along the Ammer River, Southwestern Germany.

Background: Rivers receive water and associated organic micropollutants from their entire catchment, including from urban, agricultural and natural sources, and constitute an important environmental component for catalyzing pollutant turnover. Environmental removal processes were extensively investigated under laboratory conditions in the past but there is still a lack of information on how organic micropollutants attenuate on the catchment scale. The aim of this study was to describe the chemical and toxicological profile of a 4th order river and to characterize in-stream processes. We propose indicator chemicals and indicator in vitro bioassays as screening methods to evaluate micropollutant input and transport and transformation processes of the chemical burden in a river. Carbamazepine and sulfamethoxazole were selected as indicators for dilution processes and the moderately degradable chemicals tramadol and sotalol as indicators for potential in-stream attenuation processes. The battery of bioassays covers seven environmentally relevant modes of action, namely estrogenicity, glucocorticogenic activity, androgenicity progestagenic activity and oxidative stress response, as well as activation of the peroxisome proliferator-activated receptor and the aryl hydrocarbon receptor, using the GeneBLAzer test battery and the AhR-CALUX and AREc32 assays.

Results: Both approaches, targeted chemical analysis and in vitro bioassays, identified a wastewater treatment plant (WWTP) as a major input source of organic micropollutants that dominantly influenced the water quality of the river. Downstream of the WWTP the amount of detected chemicals and biological effects decreased along the river flow. The organic indicator chemicals of known degradability uncovered dilution and potential loss processes in certain river stretches. The average cytotoxic potency of the river water decreased in a similar fashion as compounds of medium degradability such as the pharmaceutical sotalol.

Conclusions: This study showed that the indicator chemical/indicator bioassay approach is suitable for identifying input sources of a mixture of organic micropollutants and to trace changes in the water quality along small rivers. This method forms the necessary basis for evaluating the natural attenuation processes of organic micropollutants on a catchment scale, especially when combined with enhanced sampling strategies in future studies.