Biological activity in Cu-contaminated soils: a laboratory experiment

In a laboratory study, soil respiration, catalase and dehydrogenase activities were used as bioindicators of the toxic effects of Cu, added to 6 agricultural soils as copper sulfate (CuSO4) at moderate (100 mg kg(-1)) and high (1000 mg kg(-1)) rates. The samples were kept at 25 degrees C and 50% field capacity during an incubation period of 70 days. The addition of Cu lowered soil pHs, with a general reduction of about 0.5 pH units below control values. The extractable amounts of Cu ranged from 57 to 87% (moderate rate) and 64 to 100% (high rate). The smallest recovery of extractable Cu was observed in soil with the highest pH and in that with the greatest level of organic C. Generally, Cu-contaminated soils showed a significantly reduced respiration rate, dehydrogenase and catalase activities, but the 1000 mg kg(-1) concentration increased CO2 evolution in 4 of the 6 soil samples, and was strongly effective in inhibiting soil respiration, dehydrogenase and catalase activities. Microbial activity changes during incubation could not be totally examined. In the soil with the highest level of organic matter, the microbial parameters were insensitive to Cu addition. On the contrary, in the sandy soil, poor in organic matter, the examined microbial activities were strongly inhibited by Cu application. The results chiefly indicate that alterations of microbial parameters allowed useful quantification of soil disturbance by Cu, and can be recommended for monitoring Cu pollution of soils