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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.
Research has already demonstrated the toxic effects of microplastics (MPs) on different biota. However, the underlying toxic mechanism of MPs remains to be elucidated, especially the effect of particle size and the presence of dissolved organic matter in water. This study investigated the impact on Scenedesmus obliquus exposed in five types of polystyrene particle suspensions with different sizes and surface charges, in the presence and absence of humic acid (HA). Results indicated that the 50% growth inhibition rate of S. obliquus showed no significant difference between the five types of MPs, but the toxic mechanism varied with particle size. Larger size MPs caused adverse effects by blocking the light transport and affecting photosynthesis, while smaller ones destroyed the cell wall by adsorbing onto the algae surface. Also, the addition of HA significantly alleviated the toxicity of smaller size MPs, but not of the larger ones. Scanning electron microscopy images and the reactive oxygen species assay demonstrated that the HA could form a corona on the surface of MPs, reduce the affinity to microalgae, and minimize the adverse effect. Together, these findings identified important factors in determining the toxicity of MPs, providing valuable data for risk assessment of MPs.
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Researchers exposed the green microalga Chlorella vulgaris to amino-functionalized polystyrene nanoplastics and found significant toxicity to biomass and chlorophyll, but adding humic acid — a natural organic matter component — substantially reduced toxicity by coating the nanoplastics' positively charged surfaces and preventing their electrostatic attraction to algal cell walls.
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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.
Toxicity Effects of Polystyrene Nanoplastics with Different Sizes on Freshwater Microalgae Chlorella vulgaris
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Researchers tested how two sizes of polystyrene nanoplastics (50 nm and 70 nm) affected the common freshwater microalgae Chlorella vulgaris. Both sizes reduced algae growth, chlorophyll content, and photosynthetic activity in a dose-dependent manner, with the smaller particles causing more damage. Since microalgae form the base of aquatic food chains, their sensitivity to nanoplastics could have cascading effects on entire freshwater ecosystems.
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Researchers investigated the toxic effects of polystyrene microplastics on the freshwater microalgae Euglena gracilis. The study found that microplastic exposure at 1 mg/L induced vacuole formation within 24 hours and significantly disrupted photosynthesis, with smaller particles (0.1 micrometers) causing more severe cellular damage than larger ones (5 micrometers), suggesting size-dependent toxicity mechanisms.
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