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Combined exposure to tire wear particles and nickel enhances toxicity and mineral nutrient accumulation in aquatic macrophyte Salvinia auriculata Aubl
Summary
Tiny bits of worn tire rubber that wash into rivers and lakes don't just pollute water on their own, this study found that when combined with nickel (a metal common in urban runoff), they team up to harm aquatic plants more than either does alone, stunting growth and disrupting nutrient balance. This matters because it's a reminder that real-world pollution rarely comes from a single source, and the mix of everyday contaminants like tire dust and metals may pose bigger risks to waterways, and the food chains and drinking water they support, than testing pollutants one at a time would suggest.
Tire wear particles (TWPs) are pervasive in urban environments and frequently co‑occur with metals in urban aquatic ecosystems. Nevertheless, interactions between these contaminants and their combined effects on aquatic macrophytes remain insufficiently understood. The aim of this study was to assess the individual and combined effects of untreated (generated from the tread of used tires) and biotically aged TWPs and nickel on growth, photosynthetic pigments, and mineral nutrient concentrations of the floating macrophyte Salvinia auriculata . Plants were exposed to untreated and aged TWPs under relevant environmental concentration (5000 particles/L) and/or Ni (60 µg/L). The results showed that both untreated and aged TWPs released comparable amounts of Zn, while neither released nor adsorbed Ni. A reduction in specific growth rate was observed exclusively under combined exposure to TWPs and Ni, indicating synergistic toxic effects. Alterations in photosynthetic pigments, characterized by reduced chlorophyll and elevated carotenoid contents, suggested stress and activation of non‑enzymatic defence mechanisms, particularly in TWPs and TWPs+Ni treatments. Exposure to TWPs and Ni, applied alone or simultaneously, increased the accumulation of several essential elements (Ca, Cu, Fe, Mg, Mo, and Zn) while decreasing K uptake, which may reflect stress‑induced nutrient reallocation or competitive interactions during metal uptake. Neither untreated nor aged TWPs significantly affected Ni accumulation in plant tissues. Interestingly, the aging only slightly modified TWP‑induced responses, manifested as lower carotenoid, Mg, and Zn contents compared to untreated TWPs. Overall, the results demonstrate that TWPs and Ni interact to exacerbate stress in S. auriculata, emphasizing the ecotoxicological importance of multi-stressor scenarios in aquatic environments.