Soil quality criteria derived from critical body concentrations of metals in soil invertebrates

Abstract

Statistical methods that have been developed to estimate critical (or maximum acceptable) levels of toxic chemicals in soils use as input data external threshold concentrations (ETC), which are usually estimated by “no observed effect concentrations” derived from laboratory experiments. These experiments often do not reflect the bioavailability of the chemical for an organism as experienced in the field. This may cause deviations between laboratory ETC and the ‘real’ ETC in the field. In this paper it is proposed to base the calculation of soil quality criteria on ETC in the field, derived from internal threshold concentrations in soil invertebrates and field concentration factors. An example for cadmium shows that this approach leads to a higher variance in threshold concentrations for the field compared with the variance in laboratory ETC. This is explained by large differences in the rate at which soil invertebrates take up chemicals from their environment, i.e. the bioavailability. The calculation of critical levels is influenced strongly by variance in the data; as a result the critical level based on threshold concentrations in the field is lower than the critical level based on laboratory threshold concentrations. This demonstrates clearly the importance of a good estimate of the variation in ETC caused by differences in bioavailability.