Assessing of the Spatiotemporal Distribution of DDT, Its Metabolites, and Caesium-137 in the Bottom Sediments of the Salgir River (Crimea)

The spatial and temporal changes of the concentration and distribution of an organochlorine pesticide p,p'-dichlorodiphenyltrichloroethane (DDT) and its metabolites and caesium-137 in bottom sediments of the longest Crimean river Salgir were studied. The spatial distribution of ∑DDT and caesium-137 concentrations has uneven focal nature. Maximal concentration of ∑DDT, exceeding the estimated permissible levels in bottom sediments by more than 10 times was detected in the middle reaches of the river in areas near the villages of Krasnaya Zorka and Pyatikhatka (270 and 256 ng/g dry mass, respectively). In these areas, the share of DDT in its total concentration with metabolites was >40%. The ratio of the metabolite DDE and DDT indicates a “fresh” share entry of the source pesticide into the river ecosystem. The activity of ¹³⁷Cs in the surface layer of bottom sediments varied from 4.4 to 69 Bq/kg dry weight. Using the geochronology of ¹³⁷Cs distribution in the bottom sediments cores from the middle reaches of the river, the sedimentation rate was determined, the sediment dating was carried out and the influx of ∑DDT into river sediments from the 1950s to the present was reconstructed. In the middle reaches of the river, a period of maximum DDT pollution of bottom sediments corresponding to the 1950−1960s was identified. The detection of high levels of banned pesticides in the surface layers of bottom sediments indicates local sources of their entry into the river. This requires taking measures to identify them and to protect the river ecosystem against pollution.