First basin-scale assessment of PCB and DDT contamination in Mediterranean zooplankton: a baseline for the central-southern basin.

This study provides the first basin-scale assessment of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) in zooplankton collected from the central-southern Mediterranean Sea. Zooplankton samples (N = 26) were collected along a ∼ 1950 nautical mile transect (May-July 2025) and quantified for 24 PCB congeners and six DDT compounds using gas chromatography-mass spectrometry (GC-MS). QA/QC procedures were validated using certified reference material (recoveries 80-117%). PCBs were ubiquitously detected, with concentrations ranging from below detection limits to 96.5 ng g-1 dry weight (dw) (mean 27.7 ± 20.2 ng g-1 dw) and were dominated by penta- and hexachlorinated congeners. DDTs were detected less frequently (54.5% of samples), with lower concentrations (mean 3.30 ± 5.62 ng g-1 dw), primarily as degradation products (DDE and DDD), indicating legacy inputs. Spatial patterns revealed higher PCB levels in coastal areas affected by industrial and urban pressures (e.g. Athens and eastern Sicily), while DDTs were more associated with regions influenced by historical agricultural use and riverine inputs (e.g., western Greece). Offshore sites showed low contamination levels, highlighting the influence of land-based sources. Comparative analyses revealed significantly lower PCB and DDT concentrations than those reported for the Tyrrhenian Sea (ANOVA, p < 0.0001; Kruskal-Wallis, p = 0.0116), supporting a longitudinal contamination gradient across the Mediterranean basin. This study provides a baseline for the central-southern Mediterranean and confirms zooplankton as an effective POP bioindicator. Future studies should extend monitoring and integrate chemical and eDNA approaches to improve basin-scale assessments of Mediterranean marine ecosystems.