Estrogenicity patterns in the Swiss midland river Lützelmurg in relation to treated domestic sewage effluent discharges and hydrology

Sewage treatment works (STW) discharge estrogenic effluent into rivers, which leads to variable estrogenicity of river water. Here, we characterize how the factors effluent and hydrology influence the estrogenicity of river water. We selected a river for which good hydrological data are available and collected water samples upstream and downstream from a STW discharge; effluent was sampled as well. Sampling took place during four 12-d periods, associated with the seasons, and always occurred in the morning. We also investigated the estrogenicity along the river, both by grab sampling and by passive sampling. Estrogens were analyzed by a recombinant yeast assay (YES); the estrogenicity of a sample was equated to the 17beta-estradiol standard of the YES (ng/L). Estrogenicity upstream from the STW was mostly close to the detection limit of the YES (maximum, 0.4 ng/L). Estrogenicity of effluent ranged between 0.2 and 7.7 ng/L; lower estrogenicity was associated with higher hydraulic retention times. Downstream from the STW, estrogenicity exceeded 1 ng/L on 25% of the days (maximum, 2.1 ng/L). Measured river water estrogenicity correlated positively and significantly with predicted estrogenicity based on effluent estrogenicity and effluent dilution factor. Grab samples taken along the river indicate that no significant sources of estrogens were upstream from the STW; downstream from the STW, the pattern of estrogenicity was highly variable. However, passive sampling showed that the estrogenicity of river water downstream from the STW decreased continuously with increasing distance from the STW, which is largely explained by dilution.