Application of biological indicators to assess recovery of hydrocarbon impacted soils

Remediation programmes are considered complete when human risk-based criteria are met. These targets are unrelated to the ecological parameters that may be important with regard to future soil uses. As a consequence, there has been a move towards the consideration of biological indicators for hazard assessment in conjunction with the remediation of contaminated soils. This study uses a range of biological assays to assess the ecological health of soils from a former gas works site undergoing various remediation treatments. The indicators that optimally differentiated the extent of soil remediation were biomass-C, respiration, dehydrogenase activity, earthworm toxicity and mustard seed germination. Although they had different end-points, once robust and sensitive biological indicators were incorporated into a quantitative soil quality index, they gave a clearer representation of ecological health than chemical data alone by their integration of contamination effects at a number of trophic levels.