Persistent organic pollutants in the bottom sediments of rivers in Russia, Syria, and Guinea

This study provides a comparative analysis of concentrations and spatial distribution patterns of DDT (including its metabolites) and polychlorinated biphenyls (PCBs) in bottom sediments from three rivers with contrasting environmental and anthropogenic settings: the Salgir (Russia), the Asi (Orontes, Syrian Arab Republic), and the Fatala (Republic of Guinea). Surface and sediment-core samples collected in 2023 revealed substantial spatial heterogeneity in POPs contamination. In the Salgir River, ∑DDT concentrations reached up to 562 ng/g, with DDT/DDE ratios > 0.79 indicating recent inputs, likely from legacy pesticide storage sites. ∑6PCB concentrations (sum of six indicator congeners) reached 252 ng/g, with evidence of ongoing inputs in industrial zones. The Asi River exhibited the highest ∑6PCB levels (up to 863 ng/g), particularly near industrial facilities, with a congener profile dominated by highly chlorinated forms (hexa- to octachlorobiphenyls), consistent with technical PCB mixtures. The distribution of these contaminants is primarily associated with long-term significant anthropogenic loads of various nature in the Asi River region, although identifying direct sources of PCBs entering the ecosystem of the river requires additional research. The Fatala River showed minimal contamination (∑6PCB < 2.6 ng/g; DDTs below detection limits), reflecting background conditions. Sediment-core profiles confirmed historical PCB contamination peaks in the Salgir River corresponding to the 1960s-1990s, based on established geochronology, and indicated continued PCB accumulation in surface layers of both the Salgir and Asi rivers. Comparison with national and international sediment quality guidelines indicates that the observed contamination levels in the Salgir and Asi rivers substantially exceed ecologically safe values, highlighting their potential impact on the ecosystem.