Comparison of toxicity of zinc for soil microbial processes between laboratory-contamined and polluted field soils

Soil microbial processes are readily disturbed by added zinc (Zn) in laboratory ecotoxicity tests. This study compares Zn toxicity between freshly spiked soils and soils that have been contaminated with Zn in the field. Soils were sampled in three transects ( 0.05) or increased significantly with soil Zn concentrations in the transect soils. These increases could not be explained by soil pH or%soil organic carbon. Leaching soils after spiking significantly lowered the toxic effects of Zn on nitrification or on substrate‐induced respiration. The soil solution Zn concentrations of field soils were always smaller than in spiked soils at equivalent total Zn. Highest soil solution Zn concentrations were always lower than the soil‐solution EC50s of spiked soils. It is concluded that there is a large discrepancy in microbial responses to elevated Zn between spiked soils (unleached) and field‐contaminated soils and there is a need to explain this discrepancy in terms of Zn availability, adaptation processes, and additional soil factors controlling the microbial processes.