Determination of polyoxymethylene (POM) water partition coefficients for DDT and its degradation products, with inter-laboratory comparison of the passive sampling methodology and bioaccumulation in earthworm (Eisenia fetida)

Environmental context The widespread use of the insecticide DDT has left a legacy of pollution that still threatens ecosystems today. This study presents a method to accurately measure the bioavailability of DDT and its breakdown products in contaminated soils. This will improve risk assessments and guide sustainable land management practices, helping to protect both the environment and human health. Rationale The insecticide dichlorodiphenyltrichloroethane (DDT) and its degradation products (collectively DDX) are persistent organic pollutants that pose significant environmental risks due to their persistence and bioaccumulation in ecosystems. Accurate quantification of DDX bioavailability in soil systems is crucial for effective land management and risk assessment. Methodology This study utilised equilibrium passive sampling with polyoxymethylene (POM) to determine the bioavailability of DDX in soil. The sorption dynamics of 10 DDX compounds were investigated (p,p′-DDT, o,p′-DDT, p,p′-dichlorodiphenyldichloroethane (p,p′-DDD), o,p′-DDD, p,p′-dichlorodiphenyldichloroethene (p,p′-DDE), o,p′-DDE, p,p′-dichlorodiphenylmethane (p,p′-DDM), p,p′-dichlorobenzophenone (p,p′-DBP), 1-chloro-2,2-bis(4-chlorophenyl)ethylene (p,p′-DDMU) and dicofol) and their POM–water partition coefficients (KPOM) were determined. The study involved interlaboratory comparisons, using soils from nine historically contaminated sites and ecotoxicology assessments (mortality, reproduction and bioaccumulation in earthworms, Eisenia fetida) to validate the POM method. Results K POM values for 9 of the 10 DDX compounds were successfully determined, allowing for accurate quantification of freely dissolved pore water concentrations of DDX in historically contaminated soils. The interlaboratory study highlighted important considerations in extraction and gas chromatography–mass spectrometry analysis, and the ecotoxicology study demonstrated the potential of POM passive sampling as a reliable tool for assessing DDX bioavailability (bioaccumulation in Eisenia fetida). Discussion The POM method proved to be a robust and reliable approach for quantifying freely dissolved DDX, with implications for improving the accuracy of risk assessments and guiding sustainable land management practices. The study also highlighted the need for careful consideration of analytical challenges, such as the potential degradation of DDX compounds during gas chromatography analysis, to ensure accurate quantification.