Dissolved metal contamination, source identification and health risk evaluation in the Tohma River (Turkiye): A spatial-seasonal study

The Tohma River, an important water source in the Euphrates Basin of T & uuml;rkiye, faces potential metal pollution from human activities including industrial discharges, agricultural runoff, mining operations and emissions from a coal-fired thermal power plant. Consequently, the water quality of the Tohma River could impact the ecological integrity of the transboundary Euphrates River. In this study, spatial and seasonal changes, pollution levels, ecological and health risks, and sources of ten dissolved metals (As, Zn, Cd, Pb, Co, Ni, Cr, Mn, Cu, Fe) in the river were comprehensively assessed. Water samples were gathered seasonally from 13 sites between 2023 and 2024 and analyzed using ICP-MS. The average metal levels (mu g/L) were ranked as follows: Fe (80.37) > Zn (27.15) > Cu (11.9) > Mn (7.3) > Ni (5.06) > As (1.72) > Pb (0.61) > Cr (0.129) > Co (0.028) > Cd (0.026). These levels were below the international safety thresholds, which are suitable for aquatic life, drinking, and irrigation. However, spatial analysis detected higher levels of Fe, Zn, and Cu at sites (T9, T13) near industrial discharge points and increased levels of Co, Ni, Cr, and Mn at sites (T1-T3) impacted by the Kangal Thermal Power Plant. Pollution indices (HPI, CD, NPI) and ecological risk index (ERI) confirmed low overall pollution, with Ni and As being identified as the primary metals contributing to pollution. The health risk assessments showed no significant carcinogenic or non-carcinogenic risks for both children and adults, although children were noted to be more vulnerable. Multivariate statistical methods (PCA/FA, cluster analysis) traced the origins of the metals: Co, Cr, Mn, and Ni from anthropogenic sources, Fe, Zn, Cu, Pb and Cd from mixed sources and As from natural sources. These findings highlight the need for targeted pollution control measures to protect the ecosystem and water quality of the Tohma River, ensuring sustainable management of water resources in the region.