Interpretation of bioassay results in the context of the soil quality TRIAD approach.

The recently standardized method ISO 19204 “Soil quality – Procedure for site specific ecological risk assessment of soil contamination (Soil quality TRIAD approach)” describes in a general way the application of three combined lines of evidence (chemistry, ecotoxicology and ecology) along a tiered approach. Regarding the ecotoxicological component, the TRIAD approach consists in carrying out a battery of bioassays on soil samples and to scale the results from all bioassays to calculate an ecotoxicological combined risk score In order to evaluate its applicability and the relevance of the proposed tools, INERIS used the soil quality TRIAD approach on an applied case: an open mine operated for 60 years and which the activities stopped about 100 years ago (the “TRIPLE” project 2016-2017). Among the conclusions, it was noticed that the selection of the control soil may have a significant influence on the expression of the results and therefore on the risk assessment. This impact is particularly obvious for the assessment of a heterogeneous site and for the first TIER (screening level) of the TRIAD method. This statement is illustrated by observing the consequences on the assessment conclusion when the results of bioassays are expressed according different control/reference soils