Acute and Chronic Toxicity of Sediments Containing Platinum and Palladium on Freshwater Benthic Organisms <scp> <i>Chironomus riparius</i> </scp> and <scp> <i>Hyalella azteca</i> </scp>

The expanding demand for platinum group elements (PGEs) in industrial and medical applications has led to their increasing accumulation in aquatic sediments. However, their ecological impacts remain poorly understood, particularly for sediment-dwelling invertebrates. This study assessed the toxicity of platinum (Pt) and palladium (Pd) across a concentration range of 29-1214 μg·g^-1 dw in two freshwater benthic species, Chironomus riparius (C) and Hyalella azteca (H), under both acute and chronic exposures. Pt was more toxic (LC₅₀ in μg·g^-1 dw; H: 289 ± 28; C: 84 ± 7) than Pd (H: 1192 ± 356; C: 209 ± 44) for acute survival, whereas Pd caused more pronounced sublethal effects on growth. Bioaccumulation patterns showed that H. azteca accumulated more Pt, whereas C. riparius retained more Pd. In C. riparius, chronic exposure to Pd impacted survival, emergence, and female adult weight, indicating developmental disruption. Compared with other sediment-associated metals, Pd and Pt showed moderate to high toxicity: more toxic than uranium, nickel, arsenic, and molybdenum; comparable with copper; and less toxic than cadmium and lead. Although biological responses varied across metals, species, and endpoints, a consistent pattern of toxicity emerged. This study addresses a significant knowledge gap and reinforces the need to include PGEs in sediment quality guidelines. Although current environmental concentrations remain below toxicity thresholds, growing industrial use raises concerns for future ecological risk. Our findings support regulatory efforts by providing essential toxicity benchmarks and call for further research on mixture toxicity and mechanisms of action.