Soil microbial activities and heavy metal mobility in long-term contaminated soils after addition of EDTA and EDDS

A 40-day incubation experiment was carried out in order to evaluate the microbial activities and heavy metal availability in long-term contaminated arable and grassland soils after addition of EDTA (ethylenediaminetetraacetic acid) or EDDS ([S,S]-ethylenediaminedisuccinic acid). Soils with similar contamination of heavy metal from the vicinity of a lead smelter were used in the experiment. The soil microbial carbon (Cmic) decreased significantly after addition of EDTA in the arable soil (CM1); lesser effects were observed in the grassland soil (CM2). Addition of EDDS caused a decrease of Cmic during the first 10 days of incubation. In the later phases of the experiment, Cmic increased, and even exceeded the amounts found in the control soils. Respiratory activities and metabolic quotients (qCO2) increased after the addition of the chelating agents into the soils. Higher respiratory activities and qCO2 were observed in the EDTA-treated soils. The readily available heavy metal fractions were extracted with NH4NO3 solution. Readily mobilizable heavy metal fractions of Cd, Pb, Zn, and (in part) Cu increased during the first 3–10 days of incubation in the presence of EDTA. The addition of EDDS particularly increased concentrations of available Cu. Significant correlations between NH4NO3-extractable metals, soil respiratory activities, and qCO2 were found in both soil treatments with EDTA and EDDS. This indicates that enhanced metal mobility seriously affects the microbial processes in experimental soils. In addition, the relationships between NH4NO3-extractable Cd, Cu, and the microbial biomass were found in the CM1 soil amended with EDTA.