Decontamination of soil polluted with DDTs and HCH by nano zerovalent iron

Abstract

Nano zerovalent iron, encapsulated in poly-N-vinylpyrrolidone (nZVI/PVP) was used for the decontamination of soil long-term polluted with persistent organic pollutants, organochlorine pesticides: DDTs (dichlorodiphenyltrichloroethane and its metabolites) – 4.2 mg/kg dry soil, HCHs (isomers of hexachlorocyclohexane) – 1.2 mg/kg dry soil. The experiment was established ex situ and it was designed in oxic and cycled anoxic/oxic conditions. HCHs, mostly represented by the persistent beta-HCH isomer, disappeared completely after the first cycle of soil remediation. The concentration of DDTs decreased by 14 times, mostly due to transformation of p,p′-DDT isomer, in the soil amended with nZVI/PVP nanoparticles. By the end of the third cycle of soil remediation, the concentration of p, p′-DDT amounted to only 4–6% of the initial concentration. The transformation of DDT took place both in aerobic and anaerobic pathways, with the formation of DDE and DDD metabolites correspondingly. Analysis of soil microbiome involved in nitrogen transformation processes demonstrated that, in soil supplemented with nZVI/PVP and soy extract, the number of ammonifying bacteria has increased, resulting in a population that was more than 4.5 times higher, compared to soil without amendments. The additives did not affect the growth of oligotrophic bacteria and bacteria assimilating mineral forms of nitrogen, and the application of soy extract to the soil restored the number of micromycetes, suppressed under the anoxic conditions. This integrated approach offering a solution for remediating soils contaminated with highly persistent organochlorine pesticides.