River sediment metal contamination from a coal-fired thermal power plant: Spatio-seasonal variability, ecological...

A comprehensive analysis of metal pollution in river sediments is fundamental to maintain ecosystem health. Located in the Euphrates Basin, the Tohma River in Türkiye is potentially contaminated with metals due to significant anthropogenic activities, including a coal-fired thermal power plant and mining operations. This study presents a systematic evaluation of the spatio-seasonal variations, pollution levels, controlling factors, ecological risks and potential sources of 10 metals in the sediments of the Tohma River. The results showed significant spatial variation in metal concentrations, with sites T1-T4, located near the power plant and mining facilities, exhibiting significantly higher levels. Seasonal fluctuations in metal concentrations were not statistically significant. Cluster analysis categorized sites T1-T4 as polluted, while sites T5-T13 were considered less polluted. Pollution indices (EF, Igeo, Cf) identified Ni, Cd, and Cr as the most prevalent contaminants. Ecological risk index revealed that Cd and Ni posed moderate to significant risks. Other indices (NPI, PLI, NRI, RI, TRI and mPEC-Q) further confirmed high contamination levels at sites T1-T4. Notably, Cr and Ni surpassed the probable effect concentrations in 33 % and 92 % of sediment samples, respectively, indicating potential harm to benthic organisms. Sediment organic matter content emerged as a principal factor influencing the accumulation of metals. Source apportionment using the APCS-MLR receptor model traced the pollution to two primary sources: mixed origins, accounting for 56.69 % of the contamination, and direct anthropogenic sources, contributing 43.31 %, with the latter closely associated with the coal-fired power plant and mining operations.