Hidden threat in turbid waters: Quantifying and modeling the bioaccumulation and risks of particulate metals to clams

A major proportion of metal contaminants in aquatic environments is bound to suspended particulate matter (SPM), yet environmental monitoring typically focuses on dissolved metals, with the filtration step removing SPM. This step may inadvertently hide the potential risks posed by particulate metals. In this study, we used stable isotope tracers to quantify the contributions of SPM-bound metals to the bioaccumulation of nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in Ruditapes philippinarum, a widely distributed clam crucial to global aquaculture. A microporous hollow-fiber filter system was employed to maintain consistent dissolved metal concentrations across treatments, enabling precise assessment of elevated bioaccumulation due to particle ingestion. Our results demonstrated that particulate metals contributed negligible Cd, but accounted for 21.1% of Ni, 67.3% of Zn, 69.5% of Pb, and 73.6% of Cu bioaccumulation in the presence of 10-68 mg L^-1 SPM. Assimilation efficiencies varied among metals, with Pb at 1.5%, Ni at 14.7%, Zn at 48.4%, and Cu at 85.8%. Toxicokinetic modeling further revealed that the bio-uptake of particulate metals can surpass the dissolved metal, challenging the assumption that particulate metals are less bioavailable. Field sampling validated the model's predictive capacity for metal bioaccumulation. These findings underscore the need to reconsider environmental monitoring protocols and revise water quality criteria, especially in turbid coastal waters where aquaculture is prevalent.