Influences of copper forms on the toxicity to microorganisms in soils

Soil samples with wide ranges of pH (4.9 to 8.1), organic carbon (0.1 to 77 %), and total Cu contents from 32 to 11700 mg kg(-1), collected near a copp er mine, were used to investigate the relationships between microbial featu res and Cu speciation in order to clarify the form(s) of Cu adversely affec ting microorganisms, The effects of Cu on soil microorganisms were evaluate d by tno indicators: the ratio of microbial biomass carbon to soil organic carbon (C-mic/Org-C) and Cu tolerance level of bacterial community (IC50), The sequential extraction scheme of McLaren and Crawford (1973) was used to quantify the different Cu forms (soluble and exchangeable, specifically ad sorbed, and organically bound). These influences were investigated using si mple correlation analysis, multiple regression analysis, and principal comp onent analysis, The IC50 was positively correlated with the log concentrati on of soluble and exchangeable Cu (Ex-Cu) (r = 0.757, P<0.01), The IC50 val ue was also influenced by the amount of specifically adsorbed Cu, The C-mic /Org-C ratio was not significantly correlated with any Cu forms. Thus, othe r soil properties had more influence on the size of microbial biomass carbo n in the soils used. The amount of Eu-Cu exerting high toxicity was affecte d by pH and the amount Of total Cu. (C) 1999 Academic Press.