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Blocking the “Trojan Horse” effect: Humic acid alleviates the combined toxicity of amino-modified nanoplastics and tetracycline to microalgae by inhibiting heteroaggregation and oxidative stress
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Tiny plastic particles in water can act like a "Trojan Horse," carrying antibiotics into algae and causing more cell damage than either pollutant alone. This study found that humic acid, a natural substance common in soil and water, can block this effect by preventing the antibiotics from sticking to the plastic in the first place. This is good news because it suggests that in real-world waters rich in natural organic matter, nanoplastic pollution may be less harmful to aquatic ecosystems, and the food chain we depend on, than lab studies alone might suggest.
Given the ever-increasing accumulation of nanoplastics in aquatic environments worldwide, there is concern that plastic pollution will lead to ecological disasters due to the transfer of man-made pollutants, such as antibiotics, into aquatic life by nanoplastics. However, the intensity of this "Trojan Horse" effect may be influenced by natural organic matter that can interact with nanoplastics and antibiotics, possibly affecting their biological impacts. Thus, this study assessed how humic acid (HA, 10 mg L) modulates the combined effects of amino-modified polystyrene nanoplastics (NHPS, 25 mg L) and tetracycline (TC, 5-15 mg L) on microalga Chlorella vulgaris following 96 h exposure. Results showed that exposure to TC and NHPS, especially in combination, elicited various adverse effects on microalgae (e.g., membrane disintegration, mitochondrial dysfunction, growth retardation and impaired synthesis of photosynthetic pigments) due to elevated oxidative stress resulting from heteroaggregation between pollutants and algal cells. This adsorption of TC onto NHPS created a carrier-enhanced delivery system that amplified cellular internalization of both pollutants, leading to persistent disruption of cellular homeostasis. Importantly, HA could ameliorate these toxic effects on microalgae as physicochemical characterization revealed that HA competitively reduced TC adsorption onto NHPS surfaces and enhanced pollutant dispersion stability, thereby reducing the oxidative and membrane damage caused by direct contacts with pollutants. Overall, this study provides a mechanistic understanding of how natural organic matter mitigates the "Trojan Horse" effect of nanoplastics with antibiotics, suggesting that the ecological impacts of nanoplastics may be less severe than anticipated under realistic conditions. Such insights are crucial for refining ecological risk assessment and guiding nanoplastic pollution management.
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Alleviating binary toxicity of polystyrene nanoplastics and atrazine to Chlorella vulgaris through humic acid interaction: Long-term toxicity using environmentally relevant concentrations
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Researchers found that when nanoplastics and the herbicide atrazine were combined in water, they had a synergistic toxic effect on algae that was worse than either pollutant alone. However, adding humic acid, a natural substance found in soil and water, significantly reduced this combined toxicity by coating the nanoplastics and changing their surface properties. This suggests that natural organic matter in the environment may offer some protection against the harmful effects of nanoplastic-chemical mixtures.
Presence of humic acid in the environment holds promise as a potential mitigating factor for the joint toxicity of polystyrene nanoplastics and herbicide atrazine to Chlorella vulgaris: 96-H acute toxicity
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Researchers studied how nanoplastics and the herbicide atrazine together affect freshwater algae, and whether humic acid, a natural organic substance found in water, could reduce their combined harm. They found that both the nanoplastics alone and in combination with atrazine damaged algal growth, photosynthesis, and antioxidant defenses. The presence of humic acid significantly reduced these toxic effects, suggesting it may act as a natural buffer against nanoplastic and pesticide pollution in aquatic environments.
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.
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
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.
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