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Size-dependent mitigation by humic acid: rescuing metabolic homeostasis from nano-plastics but not micro-plastics in Microcystis aeruginosa
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Tiny plastic particles polluting our lakes and rivers don't act alone—natural organic matter in water (like decomposed leaves and soil, called humic acid) changes how toxic they are to algae, the base of the aquatic food chain. This study found that humic acid actually helped algae recover from damage caused by nano-sized plastic particles, but didn't offer the same protection against larger microplastic particles, suggesting that plastic pollution's real-world impact depends heavily on both particle size and what else is in the water. Since these algae are a foundation of freshwater ecosystems—and can end up in the water and food we consume—underst
Microplastics (MPs) are ubiquitous freshwater contaminants, yet their combined effects with humic acid (HA) on phytoplankton remain poorly understood. This study investigated the physiological and metabolic responses of Microcystis aeruginosa exposed to polystyrene microplastics (PS) (0.1 µm and 1.0 µm; 0.5–50 mg/L) with or without HA (5 mg/L). PS exposure promoted chlorophyll a (Chl a) synthesis but induced oxidative stress and enhanced extracellular polymeric substance (EPS) secretion. HA modulated these effects in a size-dependent manner: it further enhanced Chl a synthesis under 1.0 μm PS stress but suppressed it under 0.1 μm PS stress. Furthermore, HA effectively mitigated oxidative stress at high-concentration PS exposures. Loosely bound EPS (LB-EPS) was the most sensitive fraction, exhibiting increased humic- and protein-like fluorescence under co-exposure to micro-sized PS and HA. Metabolomics revealed that nano-sized PS disrupted primary metabolism, whereas micro-sized PS triggered defensive secondary metabolism. HA restored metabolic homeostasis specifically under nano-sized PS stress. Ultimately, HA plays a dual, particle-size-dependent role in regulating PS toxicity, clarifying the ecological implications of MP-organic matter interactions.
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Humic acid-cation interactions reshape nanoplastic bioaccessibility and mechanistic toxic pathways toward microalgae
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Nanoplastic pollution doesn't act alone in real water—natural organic matter and dissolved minerals change how toxic these particles are to algae, sometimes making things worse and sometimes better, depending on the combination. This matters because algae sit at the base of aquatic food webs, and this study shows that testing nanoplastics in "clean" lab water can give misleading results about their real-world risk to ecosystems—and ultimately to the food and water systems humans depend on.
Microplastic Impacts on Microalgae Growth: Effects of Size and Humic Acid
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Researchers investigated how different sizes of polystyrene microplastics affect the growth of freshwater microalgae, both with and without naturally occurring humic acid. They found that larger particles blocked light and disrupted photosynthesis, while smaller ones damaged cell walls by adhering to the algae surface. Adding humic acid significantly reduced the toxicity of smaller microplastics by forming a protective coating around the particles.
Humic acid can mitigate or magnify nanoplastic toxicity to freshwater microalgae: what are the factors driving these contrasting effects?
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Researchers explored how humic acid, a natural organic substance found in water, interacts with nanoplastics to either reduce or amplify their toxicity to freshwater microalgae. The study found that humic acid can mitigate nanoplastic toxicity by reducing surface hydrophobicity and improving particle dispersion, but this protective effect diminishes at low humic acid concentrations.
Interplay between micro-nanoplastics and dissolved organic matter in aquatic ecosystems: From eco-corona dynamics to microalgal adaptive resilience
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This review paper looks at what happens when tiny plastic particles (microplastics) mix with natural organic matter in lakes, rivers, and oceans — and finds that this organic matter can actually coat the plastics and reduce their toxic effects on algae, the tiny organisms that form the base of aquatic food chains. This matters because algae health affects everything up the food chain, including the fish and seafood we eat, so understanding what makes microplastics more or less harmful in nature could help us better predict their real-world risks to ecosystems and, ultimately, human food supplies.
The humic acid-like substances released from Microcystis aeruginosa contribute to defending against smaller-sized microplastics
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Researchers studied how the cyanobacterium Microcystis aeruginosa responds to polystyrene microplastic exposure over 17 days at different particle sizes and concentrations. They found that the algae released humic acid-like substances as part of their extracellular secretions, which helped defend against smaller microplastic particles. The study suggests that algae have adaptive mechanisms to cope with microplastic stress, but these defense responses vary depending on particle size.
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