Organic and inorganic contaminants in surface and subsurface sediments from Bulgarian Black Sea waters

An extensive study of organic and inorganic pollutants in surface sediments from 32 locations and sediment cores from four locations in Bulgarian Black Sea waters has been carried out. The study included metals, hydrocarbons including polycyclic aromatic hydrocarbons (PAHs), legacy chlorinated and brominated contaminants (polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), dichlorodiphenyltrichloroethane (DDT) and its degradation products, hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), trans-nonachlor) and contaminants of emerging concern (per- and polyfluoroalkyl substances (PFAS)). PBDEs and PFAS are reported in marine sediments from this region for the first time. After studying grain size, total organic carbon contents and ²¹⁰Pb-dating of sediment cores, the levels of these pollutants are concluded to be low at most locations. An exception is several coastal locations off the ports of Varna and Burgas and the Kamchia River estuary, where strongly elevated levels of several pollutants were found. Possible sources for these are discussed based on compound or congener composition. Contaminant levels in sediments from the remaining locations were mostly determined by sediment characteristics, the higher levels found in fine-grained sediments in the open sea. Two of the sediment cores demonstrated an increase in pyrogenic PAHs in recent times, attributed to anthropogenic impacts, while the metals were largely at their natural background level determined through core analysis. No apparent impact of the ongoing war in Ukraine upon sediment pollution could be found as per October 2024, two years after the start of the war.