Linking (Poly)Tungstate Speciation to Toxicity and Bioaccumulation in Daphnia magna

Tungsten is an emerging pollutant commonly assumed to occur as the simple oxyanion tungstate, yet it often condenses into a suite of polytungstates in polluted waters. Despite growing recognition that tungstate polymerization modulates tungsten's environmental fate, its effects on toxicity remain largely unexplored. Here, we tracked the (de)polymerization behavior of three representative (poly)tungstates and examined its associations with multiple measures of acute toxicity to Daphnia magna, including the median lethal concentration (LC₅₀), toxicokinetics, reactive oxygen species (ROS) content, metabolomics, and histology. While tungstate remained stable, W₁₂ metatungstate and phosphotungstate depolymerized to different extents, yielding three distinct polymerization regimes in the exposure media. Monomeric tungstate exhibited high LC₅₀, rapid uptake and efficient excretion, weak ROS signals, and minimal disruption of intestinal integrity. Oligomeric tungstates displayed lower LC₅₀ than tungstate, consistent with slow depuration that generated high internal burdens, ROS accumulation, and suppression-oriented metabolic responses. High-order polytungstates, despite limited uptake and low ROS levels, were associated with structural disruption including irreversible gut barrier damage and mitochondrial collapse and displayed the lowest LC₅₀. Together, these results suggest that tungstate polymerization not only amplifies tungsten toxicity but also alters its mode of action, supporting mechanistic interpretation and prediction of its ecotoxicological dynamics.