Assessment of DDTs decontamination in polluted soil by Magnetite and Zerovalent Iron nanoparticles

Abstract

The ratio between the concentration of dichlorodiphenyltrichloroethane (DDT) and its

metabolites, dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) provides an approximate indication of the timing of both the introduction and degradation of pesticide residues in contaminated soils. Analyses of soil samples collected from an orchard site located in the Calarasi district of the Republic of Moldova revealed the presence of obsolete organochlorine pesticides contamination, with concentrations exceeding the maximum residue levels (MRLs) by several tens of times. The detected pollutants included DDTs (DDT isomers and related compounds) and HCHs (hexachlorocyclohexane isomers). Experimental soil remediation trials were conducted ex situ, under both aerobic conditions and cyclic anaerobic/aerobic conditions. For the cyclic anaerobic/aerobic treatments, different amendments, such as Fe3O4 nanoparticles (NPs), zero-valent iron (Fe0) NPs, in a form of a colloidal aqueous solution, and soybean extract was introduced into the soil. The experimental results demonstrated that the initial DDT / (DDE + DDD) ratio was 11.58, indicating a relatively recent input of DDT. Anaerobic degradation appeared to predominate, as evidenced by the DDD / DDE ratio of 2.43, signifying a greater accumulation of DDD relative to DDE. The analysis of the DDT / (DDE + DDD) ratio in experimental variants indicates a significant reduction of the parent DDT compound, while the DDD / DDE ratio demonstrates that aerobic degradation remained dominant, though a relative increase in anaerobic transformation products was observed. The DDT / DDD ratio further corroborates the notable accumulation of DDD, underscoring an enhanced contribution of anaerobic pathways in the DDT degradation mechanism.