Assessment of the spatial and temporal dstribution of DDT, its metabolites, and cesium-137 in the sediments of the Salgir River (Crimea)

Spatial and temporal changes in the content and distribution of the organochlorine pesticide p,p’-dichlorodiphenyltrichloroethane (DDT), its metabolites, and cesium-137 have been studied in the sediments of the longest river in Crimea, the Salgir. The spatial distribution of ∑DDT and cesium-137 concentrations exhibited an uneven, focal pattern. The highest levels of ∑DDT, exceeding the approximately permissible levels in sediments by more than 10 times, were found in the middle reaches of the river, near the villages of Krasnaya Zorya and Pyatikhata (270 and 256 ng/g of dry mass, respectively). In these areas, DDT accounted for over 40% of the total concentration of DDT and its metabolites. The ratio of the metabolite DDE to DDT suggests recent input of the original pesticide into the river’s ecosystem. The activity of ¹³⁷Cs in the surface layer of sediments ranged from 4.4 to 69 Bq/kg of dry mass. Geochronological analysis of ¹³⁷Cs distribution in sediment cores from the middle reaches of the river enabled the determination of sedimentation rates, sediment dating, and the reconstruction of ∑DDT input into the river’s sediments from the 1950s to the present. A period of maximum DDT contamination in the sediments was identified in the middle reaches of the river, corresponding to the 1950s-60s. The detection of high levels of banned pesticides in the surface layers of sediments points to local sources of contamination, highlighting the need for measures to identify these sources and protect the river ecosystem from further pollution.