Soil type-specific environmental quality standards for zinc in Dutch soil.

Abstract

The heavy metal zinc is an element of natural origin. Adverse effects of chemicals on soil ecosystems depend on the soil type. Therefore, soil type-specific variation in natural background concentration and toxicity data should be taken into account in the derivation of environmental quality standards for zinc. In this paper, a methodology is presented, taking the specific features of natural occurrence and soil type into account by deriving soil type-specific background concentrations as well as soil type-specific maximum permissible additions (MPAs) for zinc in Dutch soil. The strategy used to perform a soil type-specific risk assessment for zinc consisted of 6 steps: identification of soil types, determination of characteristic background concentrations, selection of characteristic organisms, determination of no-observed-effect concentrations (NOECs), and derivations of the MPA and the maximum permissible concentration (MPC). Differences in background concentrations between different Dutch soil types were up to a factor of 7.5, whereas the MPA between the soil types varied by up to a factor of 3. This resulted in MPCs for the 3 predominant soil types that vary from 44 mg/kg dry weight (dry wt) to 208 mg/kg dry wt. Although large differences in MPC were observed, the uncertainties in background concentrations hinder setting more accurate environmental quality standards for zinc. Additional measurements on remote background concentrations of zinc in Dutch soil are needed to reduce the uncertainties in the calculated MPCs. The risk assessment approach discussed here is widely applicable to naturally occurring and anthropogenic substances.