GEOCHRONOLOGY OF PRIORITY POLLUTANTS IN A SEDIMENTATION AREA OF THE RHINE RIVER

Eight sediment cores were taken from Lake Ketelmeer, a sedimentation a rea of the Rhine River, located in the central part of The Netherlands . Priority pollutants (eight metals, six planar and mono-ortho polychl orinated biphenyls, seven polychlorinated dibenzo-p-dioxins, 10 polych lorinated dibenzofurans, and eight polycyclic aromatic hydrocarbons) w ere determined in all or in a selected number of cores. Present-day an d historical levels of pollutants since the late 1930s were establishe d through the use of radionuclide time tracers (Cs-137, Cs-134) and ar ea-specific geological time markers. Postdepositional redistribution o f pollutants and possible transformations were evaluated by analyzing sediment top-layer samples that were taken in 1972. Disappearance in t he anaerobic sediment was observed for several chlorinated biphenyls, dioxins, and furans, Disappearance of the chlorinated compounds may be caused by microbial dechlorination reactions in the anaerobic lake se diment. For the persistent metals and polycyclic aromatic hydrocarbons , as well as for the somewhat changed concentrations of chlorinated ar omatics, trends in the concentration profiles during the last five dec ades are described. Rather low concentrations of almost all studied ch lorinated compounds were observed in the early 1940s. These low levels were in contrast to the metal and PAH concentrations, which were alre ady high in the late 1930s and were lowered during the second world wa r. For all studied compounds, maximum concentrations were found betwee n 1955 and 1975. Cadmium and nickel levels remained high until 1980. T he highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin reached concentrat ions up to 400 ng/kg in the mid-1960s. Recently deposited sediments sh owed lower pollutant levels. The levels of lead, arsenic, and all stud ied PAHs were the lowest observed in the past five decades.