Ecological risk assessment – Case studies – Application of the Soil quality TRIAD approach

Different categories of tools are suitable to perform a site specific ecological risk assessment. Most often, a pragmatic combination of these tools will allow a proper risk assessment. The International Standard ISO/FDIS 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). The soil quality TRIAD approach is conceived as a tiered stepwise approach. The risk assessment method described in ISO/FDIS 19204 on a soil contamination has been used on an open mine operated during 60 years and which the activities stopped about 100 years ago. The ground still contains high levels of metallic pollution (Pb, Cd, Zn). In 2016, the soil quality TRIAD approach has been used on five contaminated areas of the old open mine selected for their different profiles with respect to bioavailability or vegetation cover. The Tier one for the three lines of evidence has been applied on every selected locations. The combined use of chemical concentration in soil (Chemistry), plant screening test and earthworm avoidance test (Ecotoxicology) and simple vegetation survey (Ecology) were sufficient to conclude on a potential risk for some of the 5 stations. Individually, the different tools of the first tier of TRIAD were associated with high uncertainties, but used as a whole, they were indeed sufficient to assess the ecological state on some locations. Consequently, some of the expensive and time consuming data collected in these locations were not needed to conclude on an unacceptable risk. For these locations, the use of TRIAD method could have saved financial and time ressources. On other locations, uncertainties were still too great and the implementation of higher tier was needed. The lack of ecotoxicological data among the existing data had been noticed and recommended bioassays (Ecotoxicology approach of TRIAD) were schedulded at the end of 2016. With these complementary results, the TRIAD approach will be reapplied, and as a result, focus will be made on the methodology in order obtain practicable results according to the complexity of the study and, as a consequence, its uncertainties