Towards More Accurate Risk Assessment of Sediment Trace Metals: Integrating Sedimentary Background Determination and Probabilistic Evaluation in Chaohu Lake, China

Accurate ecological risk assessment of trace metals in lake sediments remains a significant challenge due to the widespread use of generalized regional background values, which often fail to capture the spatial and historical heterogeneity of sedimentary environments. This study addresses this gap by establishing sediment-specific background values of heavy metals through high-resolution core sampling from three representative zones (western, central, and eastern) of Chaohu Lake, China. The determined variation depths (36.60 cm, 21.35 cm, and 47.58 cm) allowed for the reconstruction of pre-contamination baselines for key trace metals. These refined background values were then incorporated into enhanced ecological risk assessment frameworks, including the geo-accumulation index (Igeo) and a modified potential ecological risk index (RI), which integrates chemical accumulation with toxicity units (∑TU). A probabilistic risk assessment based on the refined RI was further conducted using a large sediment dataset. The results revealed that 67.0% of the samples posed low ecological risk, while 33.0% fell into the moderate-risk category, with mercury (Hg), arsenic (As), and nickel (Ni) identified as the primary contributors. This study demonstrates that sediment-specific background values, when combined with probabilistic risk modeling, offer a more accurate, site-relevant, and scientifically grounded approach for assessing and managing trace metal contamination in lake systems.