Environmental pollution and ecological risk assessment of total mercury and other potentially toxic elements in the Azzaba Fendek wadi sediments, Algeria

Background Mercury (Hg) contamination in aquatic ecosystems poses serious ecological and public health risks due to its persistence, bioaccumulation, and potential transformation into methylmercury. The Fendek River and nearby quarries in the Algerian Azzaba district are potential hotspots of trace element pollution, where quarrying and industrial activities may significantly influence sediment quality. Objectives and methods This study evaluated total Mercury (THg) contamination in sediments from the Fendek River and adjacent quarries and analyzed associated physicochemical parameters (pH, electrical conductivity, organic matter). Sediment samples were collected across 14 sites and analyzed in triplicate. Total mercury concentrations were determined using cold vapor atomic absorption spectrophotometry (CVAAS) with certified reference materials for quality assurance. The geo-accumulation index (I_geo) was applied to assess contamination levels and identify anthropogenic contributions. Results Total mercury concentrations ranged from 0.37 to 35.11 mg.kg⁻¹, with the highest values near quarry sites. Sediments were slightly alkaline (pH 7.71–8.18), with electrical conductivity ranging from 326.75 to 3824 µS·cm⁻¹ and organic matter content between 1.65% and 9.07%. The I_geo values indicated moderate to heavy THg contamination, particularly in sediments adjacent to quarries. Compared with natural background values (0.4 µg·kg⁻¹) and international sediment quality guidelines (170 µg·kg⁻¹; CCME), the studied sites show significant anthropogenic influence and ecological risk. Conclusion This study highlights substantial THg pollution in the Fendek River basin, mainly linked to quarrying activities. These findings underscore the need for regular monitoring, risk assessment, and remediation measures to safeguard aquatic ecosystems and human health.