Influence of pH on the toxic effects of zinc, cadmium, and pentachlorophenol on pure cultures of soil microorganisms

Abstract

AbstractIn this study the effect of the acidification of soil pore water on the uptake and toxicity of cationic and anionic pollutants was measured in an experimental model system. The influence of pH on the toxic effects of zinc, cadmium, and pentachlorophenol was studied in buffered suspensions of pure cultures of soil microorganisms. In this system the speciation of the toxicant, the pH, and the biomass are defined, constant, and thus easier to study than in a system with the solid soil matrix and pore water. The mineralization of [14C]acetate to14CO2was used to measure the toxic effects of pollutants on a fungus (Aspergillus nigerCBS 121.49), an actinomycete (Streptomyces lividans66), two Gram‐negativePseudomonas putidastrains (MT‐2 and DSM 50026), and a Gram‐positive strain (Rhodococcus erythropolisA177). Large differences in sensitivity were observed between the species. For pentachlorophenol the highest EC50 was 81 mg/L forPseudomonas putidaat pH 8, whereas the lowest was 0.13 mg/L forAspergillus nigerat pH 6.Aspergillus nigerwas not sensitive to 1,000 mg Zn/L, whereasPseudomonas putidaat pH 7.8 showed the lowest EC50, 0.14 mg Zn/L. When pH was increased, pentachlorophenol became less toxic and showed less sorption to the biomass, whereas zinc and cadmium became more toxic and showed more sorption to the biomass. The results indicate that higher pore‐water concentrations due to acidification of zinc‐ and cadmium‐polluted soils may not be accompanied by increased toxic effects on microorganisms because of the relatively low toxicity of these metals in pore water at low pH.