First evidence for covalent linkage of acidic metabolites of metalaxyl and DDT as non-extractable pesticide residues in soil and sediment

Abstract

Soils and sediments are a major sink for lipophilic organic pollutants. The remobilization potential of non-extractable residues is an important aspect of the environmental risk assessment and is directly linked to the binding modes of xenobiotics to macromolecular geopolymers. For instance, weak binding will favour rapid release of toxic metabolites, whereas strong binding will favour release in the long run. So far there is few strong evidence on the precise nature and strength of pollutant binding to organic matter. We used 1,1,1-trichloro-2,2-bis(chlorophenyl)ethane (DDT) contaminated sediment and metalaxyl spiked microbial active soil for alkaline hydrolysis reaction with ¹⁸O-sodium hydroxide (Na¹⁸OH). Gas chromatography–mass spectrometry analyses showed 2 Da shifts in molecule ions of 2,2-bis(chlorophenyl)acetic acid methylester (DDA-methylester) and additionally in fragment ions of ¹⁸O-metalaxyl indicating monolabeled derivatives of both pesticide metabolites.¹⁸O-labeling of the carboxyl moiety during hydrolysis proved the cleavage of the metabolites from organic macromolecules. This is the first concrete evidence for stable ester linkage of acidic metabolites of DDT and metalaxyl in soil and sediment matrices.