Seasonal Geochemical Analysis of Toxic Metal Contamination and Ecological Risk Assessment in Sediments of the Değirmendere River Basin and Estuary, Türkiye

Abstract This study investigates toxic metal contamination in the sediments of the Değirmendere River Basin (riverbed and estuary) in Türkiye, with the aim of assessing pollution levels, ecological risks, and the seasonal variability of metal concentrations. Sediment samples were collected from 20 stations during the summer and winter of 2022 and analyzed using geochemical and statistical methods. The metals evaluated include Cu, Pb, Zn, Ni, As, Co, V, and La. The findings reveal that Cu (79.46 ± 20.17 μg g -1 ) and Pb (63.83 ± 15.11 μg g -1 ) exceeded pollution thresholds, with the highest concentrations observed in winter, particularly in estuarine areas affected by industrial and urban activities. Seasonal variations were significant for As, Pb, V, and Zn (Mann-Whitney U, p < 0.05), with higher concentrations of As, Pb, and Zn in winter, likely due to increased runoff and erosion. The Geoaccumulation Index (I geo ) and Sediment Enrichment Factor (SEF) indicated moderate to significant contamination for Cu, Pb, and As. The ecological risk index (RI) categorized the estuary as a moderate to considerable ecological risk area, with RI values ranging from 150 to 319.2. These findings highlight significant anthropogenic impacts on sediment quality in the Değirmendere River Basin, emphasizing the urgent need for continuous monitoring and targeted mitigation measures.