Evolution of trace metal and organic pollutant concentrations in the Scheldt River Basin and the Belgian Coastal Zone over the last three decades

For the present study, a comprehensive dataset on trace metals (Cd, Cu, Hg, Pb and Zn), PAHs (polycyclic aromatic hydrocarbons), PCBs (polycyclic chlorinated biphenyls) and PCDD/Fs (polycyclic chlorinated dibenzodioxins/furans) in the Scheldt River Basin and the Belgian Coastal Zone was gathered. The resulting time trends for emissions and concentrations measured in the aquatic system itself are presented, discussed and compared to comparable long-term studies.For most of those pollutants atmospheric and aquatic emission data are available from 1985 onward. Earliest studies about pollutants in the Scheldt Estuary go back to 1978 and the general trend observed for their concentrations in the estuary agrees fairly well with the evolution of their emissions. Until the end of the nineties trace metal concentrations decreased at the fluvial and marine end-members of the estuary. However, recent surveys indicate that the dissolved trace metal concentrations particularly in the estuary increased again, while their emissions did not. No historical data about PCDD/Fs' concentrations in the Scheldt River Basin and the Belgian Coastal Zone are available. However, the time trend of the PCDD/F concentrations in human milk corroborates their atmospheric emission reductions.The particulate trace metal concentrations in the Belgian Coastal Zone and in the mouth of the Scheldt Estuary follow the same trend. Nevertheless, Scheldt estuarine inputs to the Greater North Sea decrease slower than those of other estuaries.In sediments of the Upper Scheldt River, a clear decrease for Cd, Pb and Zn, but not for Cu was observed between 1980 and 2007. Also PAH concentrations in those sediments are not decreasing during the last 10 years.A time lag exists between the moment that a reduction in the emission of a given pollutant is realized and the decrease of its concentration in the receiving aquatic environment.

► Trace metal trends in the Scheldt River Basin differ from those of organic pollutants.
► Particulate trace metal concentrations are decreasing since 1978.
► PAH concentrations show no decrease over the past 10 years.
► A time lag exists between emission reductions and their effect on river concentrations.
► Scheldt estuarine inputs to the Greater North Sea decrease slower than those from other estuaries.