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Toxicity to soil microorganisms

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Due to the low solubility of C.I. Pigment Yellow 34 and C.I.Pigment Red 104, significant exposure of soil microorganisms to the substance is not expected. However, since a small fraction of the substance may dissolve and chromium and lead ions may dissociate from the substance, the toxicity of these two ions to soil microorganisms is considered here. The toxicity of chromium to soil microorganisms was evaluated by measuring CO2 evolution of soil exposed to Potassium chromate for 28 days. Furthermore the composition of the microbial community was determined. Chromium did not affect total numbers but caused a shift towards a fungi dominated microbial community. CO2 evolution was decreased by chromium addition. The reduction was detectable at a concentration of 20 mg/l and increased further at higher concentrations (Ueda et al. 1987). A study investigating the community composition of microorganisms in increasing distance from a secondary Pb smelter detected a notable decrease in the total numbers of Bacteria, Actinomycetes and Fungi with decreasing distance from the smelter (Bisessar 1982). Thus both ions trigger a decrease in total numbers and in the overall community composition of soil microorganisms.