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Particle size of polyethylene microplastics dictates synergistic-antagonistic switching in arsenic toxicity to Ipomoea aquatica
Summary
Tiny plastic particles in soil can make arsenic contamination worse, while larger plastic particles can actually help crops cope with arsenic exposure better, according to a study on water spinach (a leafy vegetable). This matters because it shows that not all microplastic pollution behaves the same way—the size of the plastic bits matters for how much toxic arsenic ends up affecting the food crops we eat, which has implications for both farming safety and our understanding of what we might be consuming.
The composite pollution of microplastics (MPs) and arsenic poses an increasingly severe threat to farmland ecosystems, but their joint toxic effects, especially the key role of MPs particle size, remain unclear. The combined effects of polyethylene microplastics (PE-MPs) with different particle sizes (0.5 μm, 5 μm, 50 μm, 500 μm) and arsenic on Ipomoea aquatica were revealed through hydroponic and pot experiments. It was found that the interaction between PE-MPs and arsenic exhibited a significant particle size-dependent transformation of synergistic-antagonistic effects. Specifically, small particle size PE-MPs (0.5 μm) were observed to act as a toxicity amplifier, with seed germination efficiency significantly inhibited (reduction >40%) even at low arsenic concentrations, and arsenic-induced inhibition of aboveground biomass was synergistically exacerbated (up to 35%) by intensifying oxidative stress (MDA content increased by up to 45.52%) and disrupting the photosynthetic system (lowest chlorophyll a content). In contrast, large particle size PE-MPs (500 μm) were found to play the role of a toxicity mitigator, particularly with antagonistic effects exhibited at higher arsenic concentrations by partially restoring belowground biomass (10-20% increase compared to single arsenic treatment) and alleviating oxidative damage. These findings demonstrate that PE-MPs particle size serves as a key switch regulating the direction and intensity of its combined toxicity with arsenic, which can provide a crucial theoretical basis for accurately assessing the ecological risks of MPs-metals/metalloids composite pollution.