Derivation of soil quality criteria using predicted chemical speciation of Pb2+ and Cu2+

Abstract
A review is made of soil toxicological data that report soil total lead or copper in combination with soil pH. Using these data, free metal activities in the soil solution of those tests are estimated using published regressions that describe the relationships between metal activities and the total metal content, pH, and soil organic matter content. The toxicological significance of the predicted free metal activities is compared to that of total metal contents. In a majority of cases, estimated free metal activity improves the prediction for toxic effects on crops, soil organisms, or soil microbial processes. The free metal activity level corresponding to a defined level of risk can be used to derive a pH‐dependent soil criterion for total metal content that should generate a soil solution‐free metal activity below the determined critical level.