Assessment of the dynamics of polluting and toxic substances in surface waters and bottom sediments of river ecosystems is one of the indicators of an integrated load of the Dniester river basin, Dniester estuary and the Black Sea. In the current work, joint data from the section of the Middle and Lower Dniester are presented. On the territory of Moldova, samples were collected downstream of Dniester hydroelectric station 2- at villages Naslancea, Valcinet, Soroca, Camenca, Erjova, Goieni, Cocieri, Vadu-lui-Voda, Varnița, Sucleia, Palanca, in Ukraine - at village Mayaki, from a distance of 15.4 km away, from the flowing of Dniester river in Dnestrovsk estuary, during the period December 2018 to August 2019. Chemical analysis was carried out by methods adapted to ISO standards using modern equipment (Agilent 7890B and others), certified in Ukraine and Moldova, part of material was analyzed in Sweden as part of the Visby Project Scholarship for PhD exchange studies, 2018-2019 year at University of Agricultural Sciences (SLU), Uppsala, Sweden (1). The studied organochlorine pesticides (OCPs) (α, β, and γ isomers of HCH, DDT and its metabolites DDE, DDD, aldrin, dieldrin, heptachlor, hexachlorobenzene, etc.) belong to a particularly dangerous group of compounds of persistent organic pollutants (POPs). The most toxic of this group are dichlorodiphenyltrichloroethane DDT and HCH (Lindane), μg/kg),DDD (9.68 μg /kg) was almost 4 times higher than EQS. The concentrations of dieldrin and heptachlor of 5.4 and 6.13 μg/kg, exceeded EQS by 10, 8 and 2.5 times respectively. References 1. Anastasia Ivanova, Lutz Ahrens, Karin Wiberg, Anna-Karin Dahlberg "Persistent Organic Pollutants in sediments from rivers in Moldova "In Session: Contaminated Sediments: an Understudied Environmental SETAC Europe 29th Annual Meeting in Helsinki, Finland on 26-30 May 2019, pp. 341-342. 2. Handbook of pesticides. Organochlorine compounds (ChOC)– http://www.pesticidy.ru/group_substances/organochlorines which ranked on top list in terms of production and use in agriculture even until the 1980s [2]. The widespread use of OCP in the last century has led to the accumulation of these compounds in water bodies and in the streams, soils, animals, and plants. One of the fundamental physicochemical processes in aquatic ecosystems that reduce the migration of pesticides is the adsorption of pesticides by suspended solids, their deposition and accumulation in bottom sediments. Over the past 2 years, the γ-HCH isomer (Lindane) has not been detected in the middle section of the Dniester, but was found in all samples in the lower Dniester - near Mayaki in the range of 0.17 to 2.12 ng /l, and during February its concentration was 10 times higher and exceeded the environmental quality standard (EQS = 0.20 ng / l). The concentrations of the β - HCH isomer varied from analytical zero <0.05 ng / l to 1.55 ng/l, the average value was 0.55 ng/l. No content of the α - HCH isomer was detected in all water samples. The total content of DDT and its metabolites in the lower Dniester was in the range of 3.28- 19.42 ng/l and did not exceed EQS. In the silts of the Middle Dniester, the highest concentration of HCB was found at Soroca (0.98 ng g-1 dw). DDT and its transformation products were found in all samples of silts. The concentrations of Σ6DDT ranged from 1.1 to 52 ng g-1dw with maximum values at Goieni p, p'- DDE and p, p'-DDD were the predominant compounds and constituted 56% and 26% of Σ6DDTs in the Middle and Lower Dniester River within the Moldova [1]. In the bottom sediments in the lower Dniester, the concentration of the γ -HCH isomer was 0.25-1.02 μg/kg, which exceeded the environmental quality standard by 5 and 20 times (EQS = 0.05 μg /kg), β- isomer HCH (was detected only in March -0.24 μg/kg of the α-HCH isomer, not detected. DDT content in the silts varied in the range of 1.52-10.90 μg/kg), which exceeds 4 times the EQS (EQS = 2.5 μg/kg),DDD (9.68 μg /kg) was almost 4 times higher than EQS. The concentrations of dieldrin and heptachlor of 5.4 and 6.13 μg/kg, exceeded EQS by 10, 8 and 2.5 times respectively. References 1. Anastasia Ivanova, Lutz Ahrens, Karin Wiberg, Anna-Karin Dahlberg "Persistent Organic Pollutants in sediments from rivers in Moldova "In Session: Contaminated Sediments: an Understudied Environmental SETAC Europe 29th Annual Meeting in Helsinki, Finland on 26-30 May 2019, pp. 341-342. 2. Handbook of pesticides. Organochlorine compounds (ChOC)– http://www.pesticidy.ru/group_substances/organochlorines
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