Analysis of DDT and Hg in the Toce River (North Italy): sediment contamination and bioaccumulation in benthic invertebrates

Lake Maggiore is a southern subalpine lake located across the border between Italy and Switzerland. It is well studied since 1972 thanks to a monitoring program funded by the International Commission for the Protection of Italian-Swiss Waters (CIPAIS; https://www.cipais.org/web/). This program comprises the analysis of trace elements and persistent organic pollutants (POPs) in sediments of the lake and of the main tributaries and in different bioindicators: zooplankton, lake molluscs, riverine benthic invertebrates, and fish. This lake is characterized by legacy DDT and mercury contamination deriving from industrial activities carried out in a site located along the Toce River, one on the main tributary of the lake. At this site, remediation operations of contaminated industrial soil are ongoing. The present dataset (on excel file) consists of data regarding the analysis of mercury and DDT in sediments and in different taxa of benthic invertebrates collected in the Toce River at four sampling stations: Domo, the most upstream station; Prata, which is upstream of the industrial area; Bosco Tenso, a site downstream the industrial area, and considered a hotspot of contamination; and Ornavasso, the most downstream station. Samples of freshly deposited sediments and of benthic invertebrates were collected seasonally in the pool areas of each site in 2022-2024. As regards sediment, analyses were carried out on the < 63 µm grain size fraction, for comparison between sampling sites and dates. For benthic invertebrates, different taxa were sorted on site and then analysed separately. The reported contaminant concentrations comprise: - total mercury (THg), methylmercury (MeHg); - Dichlorodiphenyltrichloroethane (DDT): 6 congeners and isomers (o,p' DDD, p,p' DDD, o,p' DDE, p,p' DDE, o,p' DDT and p,p' DDT) and total DDT. - Total Organic Carbon (TOC) in sediments; - lipid content in invertebrates. The dataset enables the detection of changes in pollutant concentrations over time and along a longitudinal gradient - from the most upstream site, considered a reference site, to the downstream sites, which are affected by legacy contamination from the industrial area. This provides evidence of both spatial and temporal variations in pollutant levels, as well as expected long-term contamination trends (see annual reports on hazardous substances in Lake Maggiore at https://www.cipais.org/web/). Moreover, the analysis of different benthic invertebrate taxa, representing various functional feeding groups, offers insight into the pathways of contaminants through aquatic trophic chains. Different benthic invertebrate taxa - especially insects - occupy different trophic levels and serve as prey for fish (in their pre-imaginal stages) and for terrestrial predators (as adults). This research was funded by the International Commission for the Protection of Italian-Swiss Waters (CIPAIS) as part of the monitoring program 2022-2024 (https://www.cipais.org/web/).