Remediation of highly contaminated soils from an industrial site by employing a combined treatment with exogeneous humic substances and oxidative biomimetic catalysis

Remediation of two polluted soils from a northern Italian industrial site heavily contaminated with organic contaminants was attempted here by subjecting soils first to addition with an exogenous humic acid (HA), and, then, to an oxidation reaction catalyzed by a water-soluble iron-porphyrin (FeP). An expected decrease of detectable organic pollutants (>50%) was already observed when soils were treated only with the H2O2 oxidant. This reduction was substantially enhanced when oxidation was catalyzed by iron-porphyrin (FeP + H2O2) and the largest effect was observed for the most highly polluted soil. Even more significant was the decrease in detectable pollutants (70-90%) when soils were first amended with HA and then subjected to the FeP + H2O2 treatment. This reduction in extractable pollutants after the combined HA + FeP + H2O2 treatment was due to formation of covalent CC and COC bonds between soil contaminants and amended humic molecules. Moreover, the concomitant detection of condensation products in soil extracts following FeP addition confirmed the occurrence of free-radical coupling reactions catalyzed by FeP. These findings indicate that a combined technique based on the action of both humic matter and a metal-porhyrin catalyst, may become useful to quantitatively reduce the toxicity of heavily contaminated soils and prevent the environmental transport of pollutants.