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Size matters either way: Differently-sized microplastics affect amphibian host and symbiotic microbiota discriminately
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Researchers exposed toad tadpoles to two sizes of polystyrene microplastics and found both caused growth delays, but through different mechanisms. Larger particles disrupted gut bacteria, while smaller ones triggered stronger gene expression changes in tissues related to brain function and energy metabolism. The study suggests microplastic size matters for how toxicity manifests in amphibians.
Concerns about the implications of microplastics (MPs) on aqueous animals have gained widespread attention. It has been postulated that the magnitude of MPs can influence its toxicity. However, little is known about how MPs toxicity changes with particle size. Amphibians are reliable bioindicators of ecosystem health due to their complex life cycles. In this study, we compared the influences of two sizes nonfunctionalized polystyrene microspheres (1 and 10 μm) on the metamorphosis of Asiatic toad (Bufo gargarizans). Acute exposure to MPs at high concentrations led to bioaccumulation in the digestive track and internal organs (i.e., liver and heart) of tadpoles. Long-term exposure to either size, at environmentally-related concentrations (1 and 4550 p/mL), led to growth and development delay in pro-metamorphic tadpoles. Remarkably, developmental plasticity mitigated these deleterious effects prior to the onset of metamorphic climax without compromising survival rate in later stages. MPs with a diameter of 10 μm dramatically altered the gut microbiota (e.g., abundance of Catabacter and Desulfovibrio) of pro-metamorphic tadpoles, whereas MPs with a diameter of 1 μm induced much more intensive transcriptional responses in the host tissues (e.g., upregulation of protein synthesis and mitochondrial energy metabolism, and downregulation of neural functions and cellular responses). Given that the two MPs sizes induced similar toxic outcomes, this suggests that their principal toxicity mechanisms are distinct. Small-sized MPs can travel easily across the intestinal mucosa and cause direct toxicity, while large-sized MPs accumulate in gut and affect the host by changing the homeostasis of digestive track. In conclusion, our findings indicate that MPs can affect the growth and development of amphibian larvae, but their developmental plasticity determines the ultimate detrimental effects. Multiple pathways of toxicity may contribute to the size-dependent toxicity of MPs. We anticipate that these findings will increase our understanding of the ecological effects of MPs.
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Size-dependent adverse effects of microplastics on intestinal microbiota and metabolic homeostasis in the marine medaka (Oryzias melastigma)
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Researchers exposed marine medaka fish to different sizes of polystyrene microplastics for 60 days and found that particle size was a key factor in determining health effects. Larger particles (200 micrometers) caused weight gain and fat accumulation, while smaller particles (2 and 10 micrometers) led to liver inflammation and damage. The study also revealed that microplastics disrupted the balance of gut bacteria, particularly with larger particle exposure.
Size over substance: Microplastic particle size drives gene expression and fitness loss in a freshwater insect
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Researchers exposed freshwater midge larvae to polyamide and polyvinyl chloride microplastics of different sizes and found that particle size mattered more than plastic type in determining harm. Smaller microplastics triggered stronger stress responses at the gene level, including oxidative stress and immune activation, and caused greater reductions in reproduction and survival. The findings suggest that size should be a primary consideration when assessing microplastic risks to aquatic life.
Size-dependent toxicological effects of polystyrene microplastics in the shrimp Litopenaeus vannamei using a histomorphology, microbiome, and metabolic approach
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Researchers exposed white leg shrimp to polystyrene microplastics of four different sizes and found that toxicity was strongly size-dependent, with smaller particles causing greater tissue damage to guts and gills. Smaller microplastics were also more readily ingested and bioavailable to the shrimp. However, larger particles triggered different responses in gut microbiome diversity and metabolic pathways, indicating that microplastic size influences the type and severity of biological effects.
Differential effects of microplastic exposure on anuran tadpoles: A still underrated threat to amphibian conservation?
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Researchers found that microplastic exposure affects amphibian tadpoles differently depending on the species, with Italian agile frog tadpoles showing reduced survival at high concentrations while green toad tadpoles were more resilient.
Differentiation in the expression of toxic effects of polyethylene-microplastics on two freshwater fish species: Size matters
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Researchers exposed zebrafish and perch to two sizes of polyethylene microplastics for 21 days and found that smaller particles were more toxic, accumulating primarily in the liver while larger ones concentrated in the gills. Both sizes triggered oxidative stress, DNA damage, and activated cell death pathways in both species. The study demonstrates that microplastic particle size is a key factor in determining where the particles end up in fish tissues and how severely they cause harm.
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