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(70-73) The use of PICT to quantify the effects of metals at polluted sites on microbial processes . Van Beelen, Patrick*,1, Wouterse, Marja1, 1 Antonie van Leeuwenhoeklaan 9, Bilthoven, The Netherlands ABSTRACT- Pollution-Induced Community Tolerance (PICT) is probably the only method to distinguish the toxic effects caused by a specific pollutant apart from effects of other (natural) factors at polluted sites. For the PICT method, microorganisms are removed from their natural environment and exposed to a specific metal under controlled conditions in the laboratory. When a metal is bioavailable it will have toxic effects on the microorganisms in the polluted soil and the most sensitive microorganisms will be eliminated from that soil. The absence of microorganisms sensitive to a specific metal at a polluted site is a clear indication that the metal is toxic and bioavailable at that site. An improved method was developed using Biolog microtiter plates. The microorganisms were exposed to specific metals in BisTris buffer at pH 7. This avoids the precipitation of metals by phosphate buffer which made earlier methods less sensitive and only suited for metals which have a relatively high solubility in phosphate buffer. The remaining activity of the exposed microorganisms was tested in Biolog plates. For each metal and soil combination, 31 different substrates were tested to obtain EC50 and EC10 values for each substrate. These values are listed in a Processes Sensitivity Distribution (PSD) and different PSDs were compared between soils. It was shown that slightly elevated zinc and nickel levels in soil lead to a significantly decreased sensitivity for zinc and nickel. An increased copper concentration, even up to 1494 mg/kg, did not lead to an decreased sensitivity to copper. An increased chromium concentration, up to 3935 mg/kg, did not lead to a decreased chromium III sensitivity but it did lead to a decreased chromium VI sensitivity. Key words: metal, pollution, soil, processes |
