Time evolution of estrogen contamination in the Scheldt estuary

Estrogens are contaminants in the Scheldt estuary due to a dense population and intense industrial and anthropogenic activities, but their levels and evolution in this estuary are not well studied. Here we investigated estrogenic activity (EA) in the dissolved, particulate and sediment compartments of the estuary using the Estrogen Responsive Elements (ERE)-Chemical Activated Luciferase Gene Expression (CALUX) bioassay, in recent and historical samples. EA ranges between 7-168, 2.16-22.5 and 1.8-38.2 pg E₂-equivalents g^-1 in the dissolved, particulate and sediment phases of the Scheldt, respectively. The partitioning coefficient (K_d) between the particulate and dissolved phases is about 2000 L kg^-1. EA levels in the estuarine sediments decreased during the last 40 years, but the strongest decrease, from 112 to 28 pg E₂-equivalents g^-1, is observed in the upper estuary. The mass loadings of dissolved and particulate estrogens discharged into the North Sea amount to 7.5 and 1.6 μg s^-1, respectively. Future monitoring of the estrogen levels in various compartments of the Scheldt is necessary considering its strong environmental impact on living organisms and human beings.