Source determination of endocrine activity in the Zenne River, Brussels. Combining flux modelling with in vitro endocrine activity measurements.

Increasing awareness concerning endocrine disrupting chemicals (EDCs) and endocrine active chemicals (EACs) in waterways is prevalent as evidenced by the WFD (2013/39/EU) who prioritized some estrogenic chemicals into their watch list and recommended to EU member states to monitor these substances. During our study we combined water fluxes with EDC distributions in the Zenne River, Brussels, to obtain a mass budget of the pollutant load and track the (highly dynamic) interaction along the river to assess sources and sinks otherwise hidden by classical discrete sampling. This pollutant load was based on the total endocrine activity following in vitro reporter gene analyses, rather than at the individual compound level. Samples were collected from the river (4 locations), in the WWTPs (effluent and influent), and from hospital effluent (envisioned as the most concentrated source of endocrine activity) on a monthly basis over the period of one year. Extractions using Oasis HLB were carried out on the same day of sampling, extracts were analysed (using VM7Luc4E2 CALUX cells) within 4 days of sampling and results are expressed as biological equivalents (BEQs) relative to estradiol (ng E2-eq./L). By applying simple plug-flow/box models (3 boxes in total) between the 4 river sampling locations in water budget assessment, we were able to select 4 sampling events that meet our eligibility criteria (<25% error in water fluxes due to uncertainty, spatial variation in rainfall, CSO events…). The BEQ loadings (g/day) calculated for these events indicate that the most upstream box can be considered closed, whereas the middle and most downstream box are either closed or show unaccounted loads that could be explained by point discharges of endocrine activity. Endocrine activities ranged from 0.7 to 16.5 ng E2-eq./L at individual locations within the Zenne River, comparable to WWTP effluent values. WWTP influent levels and hospital effluent ranged from 17.6 to 359ng E2-eq./L. In total, 9-57% of the BEQ contribution to the Zenne River downstream of Brussels was accounted for by the WWTPs. These results indicate that domestic (treated) wastewater is the largest contributor of BEQs in the Zenne River and would act conservative during transport in the river; furthermore, higher contributions are possible when CSO events occur whereby untreated portions of waste water are released into the river resulting in the highest river BEQs (16.5ng E2-eq./L) measured during this study.