Comparison of temporal trends (1940s-1990s) of DDT and PCB in Baltic sediment and biota in relation to eutrophication

Comparative temporal trend studies of Sigma DDT and PCB on the Baltic pollu tion, using matrices from Baltic biota and dated lamina from sediment cores in anoxic sediment areas of the Baltic (no bioturbation) have been carried out. Chemical analyses of consecutive laminas of the cores representing in dividual years were compared to long-term temporal trend monitoring of Balt ic biota based on annual sampling and analyses. Earlier studies of sediment cores from the Baltic have often indicated increasing concentrations of ha logenated organic compounds in recent time whereas monitoring of Baltic bio ta showed decreasing concentrations from the 1970s and onwards. In the pres ent study two sediment cores from the northwestern Baltic proper indicate a concentration (dry weight basis) peak in the same time period as for biota , but the decrease during recent decades is slower than for biota. In lamin a representing the period 1940-1950 remarkably high concentrations of both PCB and Sigma DDT were found. Interestingly also a high proportion of nonme tabolized DDT was found in these old lamina, whereas lamina representing 19 60-1970 showed a low portion of nonmetabolized DDT and high portions of the metabolites DDE and DDD during the period 1970-1998. The results are discu ssed in relation to resuspension of sediments, diffusion and interstitial t ransport of halogenated organic compounds in the sediment cores. The result s indicate the importance of resuspension of sediment and that carbon norma lized data are inappropriate for interpretation of temporal trends. The res ults also show that we have no appropriate model to interpret the pollution of the Baltic by halogenated organic compounds, retrospectively, by using lamina from anoxic sediment cores, but that we urgently need more knowledge on the important retention mechanisms in sediment.