EFFECTS OF LEAD ON THE DECOMPOSITION OF ORGANIC-MATTER

As part of a study on the effect of lead on the soil microflora, its influence on the decomposition of glucose, starch, cellulose, glutamic acid, casamino acids and on the excrements of the millepede Glomeris marginata in a sandy soil were investigated. Lead (PbCl2) considerably increased the lag period of the oxidation of starch and cellulose, and reduced the maximum rates of oxidation of glucose, starch, glutamic acid and casamino acids. The number of viable bacteria on dilution plates was found to be even more affected by the addition of Pb than the respiration rate. The occurrence of a Chromohacterium species during the decomposition of casamino acids, and its absence in the presence of Pb, indicated a shift in the composition of the soil microflora caused by Pb pollution. A delay in the decomposition of Glomeris excrements by Pb could still be measured 200 days after mixing the soil with the excrements. Two years after the addition of Pb, a retarded decomposition of glutamic acid could still be measured when this compound was added to Pb-amended soil, even though the retardation effect had decreased. Repeated addition of glutamic acid to the Pb-polluled soil shortened the time until the maximum oxidation rate occurred, but it did not affect the rate of maximum oxidation. It was concluded that the dissimilation of organic compounds in Pb polluted sandy soil may be seriously affected. © 1979.