Using integrated biomarkers to assess ecological risk from multi-metal and metalloid soil contamination

Soil contamination with trace metals and metalloids (TMM) can negatively impact biota in ways not captured by chemical analyses alone. This study evaluates the effectiveness of two integrated biological indices (Total Enzyme activity Index - TEI, Integrated Biomarker Response - IBR) in detecting toxicity effects on biota in soils subjected to long-term TMM contamination. An ex situ biotest using soils from Peisey-Nancroix (France), a former Pb-Ag mining site, was conducted with the sensitive plant Arabidopsis thaliana to identify relevant biomarkers and develop key biological indices. The results demonstrate clear TMM toxicity, reflected in decreased microbial functioning (evidenced by reduced TEI) and impaired plant growth (shown by elevated IBR). These indices were then assessed in situ at the same site. Unexpectedly, TEI-despite its status as an early indicator of soil degradation-showed no relationship with long-term TMM toxicity or Pb-mobility, whereas IBR-derived from endogenous plant biomarkers-strongly correlated with TMM contamination and bioavailable Pb levels, particularly in the sensitive species Geranium sylvaticum. These results indicate that IBR is a reliable proxy for ecological risk and TMM bioavailability in chronically contaminated soils.