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Non-Homogeneous Toxicity of Polyvinyl Chloride Microplastics on Microalgal Cells Regulated by Nutrient Availability
Summary
Scientists found that tiny PVC plastic particles can either harm or actually boost the growth of algae — tiny organisms at the base of aquatic food chains — depending on how many nutrients are available in the water. This matters because it helps explain why microplastic pollution doesn't affect ecosystems the same way everywhere, which is important since these algae-based food webs ultimately connect to the seafood and water systems humans rely on. While this study focused on algae rather than direct human health effects, understanding how microplastics behave differently in nutrient-poor versus nutrient-rich waters (like polluted lakes versus open ocean) could
Microplastics (MPs) have been shown to exert time-dependent toxic effects on microalgae, with toxicity either intensifying or alleviating over prolonged exposure. However, the underlying mechanisms driving this phenomenon remain unclear, particularly regarding the role of external nutrient depletion in the surrounding medium. Herein, we performed bioassays and computational modeling to evaluate the effects of polyvinyl chloride microplastics (mPVC, 10, 50, and 100 mg L−1) on the growth and physiology of Desmodesmus sp. under varying initial medium nutrient levels (100%, 25%, 8%, and 4%) for 96 h. The results demonstrated that nutrient levels in the culture medium modulated the toxic impact of mPVC. Under a 25% nutrient concentration, exposure to 100 mg L−1 mPVC significantly inhibited algal growth by 6.5%, whereas at a 4% nutrient level, the growth of Desmodesmus sp. was significantly enhanced by 7.0%. Consistently, mPVC exposure at 25% nutrient concentration led to a sharper decline in intracellular pigment content (13.1–15.5%), soluble sugars content (8.2–27.0%), and photosynthetic efficiency (4.3–20.5%). In contrast, exposure to mPVC at 4% nutrient level improved the light use efficiency (11.9–15.4%) and electron transport rate (9.2–13.9%) of the algal cells. Independent action modeling revealed that as medium nutrient levels decreased, the interaction effects of mPVC exposure shifted from a synergistic to an antagonistic relationship. Overall, our findings identify medium nutrient availability as a critical regulatory factor influencing the toxic effects of mPVC on microalgae, potentially providing different insights into understanding the time-dependent toxicity of MPs.