Enhanced bioavailable contaminant stripping to remediate metal contaminated soil. A case study of Hg contaminated site

The Enhanced Bioavailable Contaminant Stripping (EBCS) is an innovative approach to phytoremediation with the aim of removing metal bioavailable fractions from a contaminated soil. This remediation approach has been tested on a Hg contaminated soil: total concentration 25.6 mg kg-1; bioavailable fractions 0.5% of the total. The experiment was carried out with Brassica juncea plants at greenhouse scale using ammonium thiosulphate (NH4)2S2O3 as strong mobilizing agent to increase Hg bioavailability. In this specific case, after two growing cycles nearly all bioavailable Hg was removed. The metal remained in the soil can be considered inert since it was neither extractable by (NH4)2S2O3, nor uptaken by plants from a further growing cycle. This strategy should be carefully checked by a risk assessment to control the residual Hg. The EBCS is promising: it removes the most dangerous metal forms, reducing cleanup time with high environmental safety.