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

Abstract

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 (< 80 m) toward galvanized electricity transmission towers (pylons). The soil total Zn concentrations gradually increased in each transect from background values (25-82 mg Zn/kg) to elevated Zn concentrations near the pylon (226-595 mg Zn/kg). Soil samples taken at the furthest distance from the Zn source were spiked with ZnCl2 to a range of total Zn concentrations similar to those in the transect. Nitrification, respiration, and N-mineralization rates were significantly reduced by added Zn in laboratory-spiked soils and were 9 to 95% (mean 32%) of the control values at largest doses depending on soil type and the microbial process. In contrast, these processes were either unaffected by soil Zn (p > 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.

Assessing Bioavailability of Soil Trace Elements

“…There exist bioassay-derived ecotoxicity/ bioavailability databases for a large number of soil organisms, largely based on the use of soluble metal salts and often with no soil matrix effects. Clearly such measurements overestimate many-fold the risks from soil TEs when compared with field situations [203,204,215]. There is an obvious need to revisit such ecotoxicity database for necessary corrections.…”

“…Often such studies have been carried out using soils freshly spiked with soluble metal salts. This does not represent real contamination situations, and like plants, such approaches overestimate TE bioavailability to soil organisms (for example [203,204]). Short-term bioassays and those involving freshly spiked soils therefore may not help in assessing the risk that TEs pose to soil organisms under real field situations.…”

Nitrification and nitrogen mineralization in agricultural soils contaminated by copper mining activities in Central Chile

“…Regression models are present in Table 3. Dai et al (2004) and Smolders et al (2003), the effects of other metals were not significant.…”

“…For example, Oorts et al (2006) indicated that in field-contaminated soil, toxicity thresholds of Cu for nitrifying microorganisms are higher than in metal-spiked soils. Similarly, the study of Smolders et al (2003) reveals a discrepancy in Zn toxicity to microbial responses between metal-spiked and fieldcontaminated soils.…”

Earthworm Biomarkers as Tools for Soil Pollution Assessment

“…The bioavailability of pollutants in comparable soil types polluted in the field or spiked in the lab is different (Smolders et al, 2003). Soil characteristics, e.g.…”