Legacy Dichlorodiphenyltrichloroethane (DDT) Pollution in a River Ecosystem: Sediment Contamination and Bioaccumulation in Benthic Invertebrates

Dichlorodiphenyltrichloroethane (DDT) contamination in the Toce River in northern Italy was studied by collecting data from 2016 to 2021 upstream and downstream of a production factory which in the past had discharged technical DDT. Analysis of sediments and of bioaccumulation in different benthic invertebrate taxa (Gammaridae, Diptera, Ephemeroptera Baetidae and Heptageniidae) was carried out to assess the transfer of DDT from sediments to benthic invertebrates and the environmental risk of this legacy pollutant for the river ecosystem. DDT and its metabolites dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD), here called DDx, were analyzed by isotope dilution gas chromatography–mass spectrometry (GC-MS/MS). DDx values in sediments in upstream stations (1.14–2.25 ng g−1 1% Organic Carbon) were lower than downstream of the industrial site (5.60–7.60 ng g−1 1% Organic Carbon), often exceeding Sediment Quality Guidelines for total DDx. Peak levels derived from new inputs of parental DDT, as confirmed by fingerprint analysis. Bioaccumulation was higher at downstream sites (up to 5107 ng g−1 lipid weight), confirming the bioavailability of residual DDT as well as active metabolism, with the formation of DDD and DDE. The Biota-Sediment Accumulation Factor evidenced the highest values (over 4.2) for Diptera and Gammaridae, highlighting that invertebrates can transfer contamination from sediments to the trophic chain. Linear regression models were developed to estimate DDx concentrations in benthic invertebrates from DDx concentrations in sediments. However, determination coefficients R2 remained in the range of 0.36–0.51, highlighting the necessity of bioaccumulation analysis to fully estimate environmental risk. The results show that DDT contamination, even if residual, may still represent a risk due to its effective transfer to the trophic chain.