Cadmium and zinc toxicity to soil microbial biomass and activity

The effects of sewage sludge selectively enriched with zinc at the maximum perrniued level and cadmium at concentration four times the current EU limits on microbial biomass and activity were tested using soils under different management in a laboratory incubation experiment. The microbial biomass and activity and the heavy metal mobility were measured over a period of six months. The resuits showed that neither zinc at the maximum permitted level nor the cadmium at concentrations as high as four times the curent EU limits may have major adverse effects on the microbial biomass and respiration of soils.