Combination effects of heavy metals and flouranthene on soil bacteria

The effects of (1) Cd, Cu, Zn, and fluoranthene (FLA), separately applied, and (2) combinations of one of these heavy metals with FLA on the growth of bacteria were studied in agar plate experiments. The bacteria were extracted from A horizons of a Eutric Regosol and a Calcic Chernozem. Significant reductions of bacterial counts were observed for both soils at concentrations > 1.0 mg Cd l(-1), 0.5 mg Cu l(-1), and 0.5 mg Zn l(-1), respectively. Additions of FLA up to 100 mg l(-1) did not result in increasing reductions of bacterial growth in the Regosol. Only 0.5, 2, and 100 mg FLA l(-1) caused significant reductions of 22-27%. Bacterial counts were not affected by 0.2 mg FLA l(-1). Low concentrations of heavy metals which were not affective when added separately were found to reduce bacterial growth when applied in combination with 0.2 mg FLA l(-1). At higher levels of heavy metals up to 2.5 mg l(-1), addition of FLA also increased the toxicity of the metals. It is assumed that the enhancement of toxicity by FLA is due to an alteration of the permeability of bacterial cell membranes.