Essential, trace and toxic elements content, their distribution and risk assessment in Karaagach river, Bulgarian Black Sea region

Abstract

In the southeastern part of the Bulgarian Black Sea coast, the Veleka River and the Burgas Lake Vaya have been studied, but there is still no comprehensive study of the Karagach River. In order to monitor changes in concentrations of essential, trace and toxic elements and their distribution in the surface waters in the Black Sea region, sampling points along the Karaagach river length were selected. Monthly surface water sampling was conducted from June 2021 to June 2022 at selected points and analyzed for 22 elements (Al, As, Cu, Cr, Mn, Zn, Ni, Cd, Pb, B, Ba, Co, Na, Se, Ag, Be, Mg, K, Bi, Li, Sr, V). The annual average concentrations of Al and Mn where found at the five monitoring points were 27.5 ± 8.0 µg L–1 and 89.7 ± 40.1 µg L–1, respectively, categorize these metals as major pollutants. Exceedances above the permissible concentrations of Ni (5.2 ± 1.3 µg L–1), Cd (0.30 ± 0.08 µg L–1) and Pb (3.0 ± 0.5 µg L–1) were only recorded in urbanized sites, therefore they are classified as point contaminants. Based on Pearson's correlation statistical analysis the non-identical origin of the major pollutants and a presumed anthropogenic source of the point contaminants were identified. Heavy contamination of the Karagach River with Al and Mn was recorded in autumn at three of the monitored sites, assessed by calculating different contamination indexes.