DETERMINATION OF HEAVY METALS AND PERSISTENT ORGANIC POLLUTANTS IN SEDIMENT CORES FROM SOUTH ETHIOPIA

The determination of heavy metals and persistent organic pollutants present in lacustrine sediments is of interdisciplinary interest, supplementing the information on environmental history of a lake’s drainage basin derived from mineralogical, geochemical and paleontological proxy-data. The distribution of the elements in lacustrine sediments can be used for the determination of the relative atomic variation to determine areas of higher contamination and give information on industrial and civilizational influences on the environment. Sources of environmental contamination can still be identified after a long period of time. Additionally to these purposes, the distribution of contaminants in lacustrine sediments can be used to determine the age of the respective sediment layer. A special aim of the case study shown the use of persistent organic pollutants e.g. DDT and its derivatives for age determination of most recent sediment layers (less than 50 years). The analysis of lacustrine sediments is also a challenge for scientists in chemical respect, because analytical methods well suited for the analysis of lacustrine sediments derived from sediment cores have to be designed. Thus, advanced sample preparation methods for the analysis of very different chemical pollutants, like lead, zinc, DDT, Lindane, etc. have to deal with low amounts of sample, highly contaminated sample matrices and a very high number of samples. They have to be sensitive, reliable and fast. Automation of measurements should be used when possible. In the case study shown methods well suited for all these needs were developed and applied to lacustrine sediments derived from plumb line cores from Lake Abaya (South Ethiopia). Using these high-resolution data on organic and inorganic pollutants it is possible to identify trends in the depth distribution of chemical pollutants in the lacustrine sediments extracted across the lake area (80*20 km). Consequently, pollutants allow a kind of chemical fingerprinting that allows chronological classification of lacustrine deposits and, thus, to correlate sediment sequences also beyond large distances. Next to this, from the analysis especially of organic pollutants and their derivatives data on the age of the deposits can be derived, focusing the period of the past 50 years, which, in general, comprises many uncertainties in dating.