TRENDS OF PRIORITY POLLUTANTS IN THE RHINE DURING THE LAST 50 YEARS

Sediment cores from Lake Ketelmeer, a sedimentation area of the River Rhine were analyzed for priority pollutants (8 metals, 8 polycyclic ar omatic hydrocarbons (PAHs), 7 polychlorinated dibenzo-p-dioxins, 10 po lychlorinated dibenzofurans, 6 planar and mono-ortho polychlorinated b iphenyls and 11 polychlorinated benzenes) in order to determine trends in the last 50 years. Post-depositional changes in pollutant levels w ere verified. Metal and PAH levels reflected the unchanged historical inputs. Concentrations were high in the late 1930s, low during the sec ond world war and reached a maximum between 1955 and 1975. As an examp le, mercury levels changed from 3 to 2 mg/kg and reached 13 mg/kg in t hese successive periods. Levels in recently deposited sediment are ca. 2 mg/kg again. Some chlorinated aromatics proved to be persistent as well. For example, the highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxi n had concentrations less-than-or-equal-to 10 ng/kg in the early 1940s , a maximum of ca. 400 ng/kg in the 1960s and again very low levels (l ess-than-or-equal-to 10) in recently deposited sediment. On the other hand, post-depositional changes were observed for a few higher chlorin ated dioxins and furans and several biphenyls and benzenes. This appea red upon comparison of concentrations in sediment layers collected rec ently and 20 years ago respectively and was possibly caused by microbi al dechlorination. The historical inputs of these pollutants will be u nderestimated by the sediment core data.