Refinement and Validation of the SPEARmetal Index for Assessing Ecological Impacts of Metal Contamination in the Nakdong River, South Korea

The SPEcies-At-Risk index for metals (SPEARmetal) was refined using updated physiological sensitivity data and validated to assess the ecological impact of metal contamination on benthic macroinvertebrate communities in the upper Nakdong River, near a Zn smelter in Korea. Biosurvey and chemical monitoring were collected at 18 sites surrounding the smelter and nearby mines. Acute ecotoxicity tests on 20 indigenous species from the Korean peninsula were conducted and used to update taxon-specific metal sensitivity data. The refined SPEARmetal index, based on this updated sensitivity, was significantly lower than previous versions, with most values below the severe impact threshold (0.5) in the mainstream. The correlation between hazard quotients in water and the SPEAR index improved, with the correlation coefficient increasing from 0.63 to 0.70. Despite consistently high benthic macroinvertebrate indices (BMI) across the study area, generic ecological indices such as total richness, EPT (Ephemeroptera, Plecoptera, Trichoptera), and Shannon diversity showed correlations with metal contamination levels. Principal component analysis identified SPEARmetal as the primary indicator associated with metal contamination in both water and sediment. These findings highlight the improved performance of the refined SPEARmetal index as a more sensitive and specific tool for assessing the ecological status of metal-impacted aquatic ecosystems compared to traditional indices.