Assessment of Potentially Toxic Element (PTE) Contamination, Source Apportionment and Use of Lead (Pb) Isotope Signatures in Sediments of a Transboundary River

The Tunca River is a transboundary watercourse between Türkiye and Bulgaria. It is the longest tributary of the Meriç River System (MRS) and joins the Meriç River in Türkiye after flowing through Bulgarian territory. In this study, the concentrations of Potentially Toxic Elements (PTEs), including As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, and Zn, as well as lead (Pb) isotope compositions, in sediments from the Turkish section of the Tunca River were investigated. Contamination levels and ecological risk status were evaluated using single and integrated indices and Sediment Quality Guidelines (SQGs). According to the Geoaccumulation Index (Igeo), Enrichment Factor (EF), and Contamination Factor (Cf) values, As, Cd, Mn, and Pb exhibit moderate to considerable levels of contamination. Pollution Load Index (PLI) and Modified Degree of Contamination (mCdeg) values indicate that pollution from total metal loads locally reaches moderate to high levels. PTE concentrations were below Threshold Effect Concentration (TEC) values, suggesting a low probability of adverse biological effects. However, the Potential Ecological Risk Index (PERI) values indicate locally moderate to high ecological risk of total metal loads. Geostatistical analyses suggest that Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn are of geogenic origin, whereas As, Sb, and Mn are associated with anthropogenic sources. The 206Pb/207Pb ratios in the sediments range from 1.18 to 1.25, while the 208Pb/206Pb ratios vary between 2.07 and 2.22. These values deviate slightly from natural isotopic signatures, suggesting anthropogenic influence on Pb concentrations.