Ecotoxicological evaluation of soil quality criteria.

To implement the Soil Protection Act of 1986, the Dutch Ministry of Housing, Physical Planning, and Environment has recently proposed a list of soil quality reference values. These values are, as yet, insufficiently based on ecotoxicological evidence. In this paper, a three-step procedure of risk assessment for soil contaminants is proposed. Arguing from experimental results concerning no observed effect concentrations for a set of selected soil organisms, the method aims at protecting a certain fraction of soil life, taking factors such as soil organic matter and clay content into account. When applied to cadmium, a concentration protecting 95% of soil invertebrates is estimated as 0.16 micrograms/g for a standard soil. The value of 0.8 micrograms/g, as proposed by the Dutch authorities, may, given the present variation and uncertainty of toxicity data, protect about 85% of the soil invertebrate fauna. It is concluded that even low levels of cadmium in soil may endanger the functioning of some sensitive soil animal species.