Determination of the biologically relevant sampling depth for terrestrial ecological risk assessments

To estimate the risks to soil organisms from soil contaminants, assessors need to relate the vertical distribution of contaminants to the vertical distribution of the organisms. Paramount to this objective is appropriate sampling strategies. While methodologies have been proposed that focus on optimizing the spatial scale of sampling efforts, sampling depths for ecological risk assessments (ERAs) are usually dictated by the vertical distribution of soil contamination or default to a generic constant. However, these approaches may not adequately reflect site-specific exposures to soil biota. This study uses a meta-analysis approach to quantify the zone of highest biological activity, for soil-dwelling ecological receptors commonly utilized in ERAs. Results suggest sampling strategies should be adaptive allowing for variable depths. If constant depths are utilized, our results suggest that samples should be collected to a depth of approximately 25–30 cm as opposed to shallower depths.