Distribution and potential ecological risks of heavy metals in water, sediments, and fish in the main rivers and reservoirs in Rizhao, China†

Aquatic environments have long been threatened by heavy metal pollution, which poses potential risks to human health. Rizhao City, in a typical coastal area, has witnessed increasingly severe heavy metal contamination in its aquatic systems. To comprehensively assess the status of heavy metal pollution in the aquatic environment and formulate effective mitigation strategies, this study focused on the water, sediments and Pseudorasbora parva from the major rivers and reservoirs in Rizhao City. The distribution characteristics and potential sources of Cr, Ni, Cu, As and Pb were systematically analysed. Ecological risks were evaluated using indices such as the water quality index (WQI), geoaccumulation index (I_geo), bioconcentration factor (BCF), estimated daily intake (EDI), target hazard quotient (THQ) and incremental lifetime cancer risk (ILCR). The results revealed that the average concentrations of heavy metals in water followed the order Cr > Ni > Cu > As > Pb, with variations across different rivers and reservoirs. In sediments, Cr and Ni exhibited higher concentrations in the Chaobai River (CR), reaching 45.21 and 34.87 mg kg⁻¹, respectively. Cr and Ni showed higher enrichment in the gills and viscera of P. parva compared to muscle tissues, while the distribution patterns of Cu, As and Pb were more complex. WQI assessments indicated that all sampling sites had WQI values <0, suggesting negligible heavy metal pollution levels in water. However, the I_geo values for Ni and Cu in CR sediments were −0.52 and −0.21, respectively, approaching the threshold and warranting attention to potential contamination risks. BCF results demonstrated stronger enrichment capabilities in gills and viscera. Health risk assessments revealed that EDI was correlated with heavy metal concentrations in fish tissues, with THQ > 1 and ILCR > 1.0 × 10⁻⁴ for gills, indicating potential health threats to frequent consumers from long-term ingestion.