Transcriptome alterations in zebrafish gill after exposure to different sizes of microplastics.

Most studies on microplastics (MPs) focused on gut, liver, and brain, and MPs toxicity was size-dependent, but less has been reported on gill. Here, zebrafish were exposed to three sizes of MPs (45-53 µm, 90-106 µm, and 250-300 µm). Next, comparative transcriptome analysis and determination of physiological indices were performed in zebrafish gills to elucidate the size-associated toxicity of MPs to fish gills. Compared with the control, 60, 344, and 802 differentially expressed genes (DEGs) were identified after exposure to 45-53 µm, 90-106 µm, and 250-300 µm MPs for 5 days, respectively. More DEGs in treatment with bigger MPs suggested that bigger MPs might induce more changes in zebrafish gills than smaller ones. These DEGs were significantly enriched in the FoxO signaling, cellular senescence, circadian rhythm and p53 signaling pathways. Besides, 90-106 µm and 250-300 µm MPs treatments inhibited the cell cycle and prevented the apoptosis. The GSH content significantly increased after MPs exposure, suggesting the induction of oxidative stress. AChE and Na+/K+-ATPase activities were significantly lowered in all MPs treatments than in the control, suggesting the inhibition of neurotransmission and ion regulation. These changes might negatively influence the normal functioning of gills, such as osmoregulation, ion regulation, and respiration.

The time-dependent variations of zebrafish intestine and gill after polyethylene microplastics exposure.

Microplastics (MPs) are common environmental contaminants that present a growing health concern due to their increasing presence in aquatic and human systems. However, the mechanisms behind MP effects on organisms are unclear. In this study, zebrafish (Danio rerio) were used as an in vivo model to investigate the potential risks and molecular mechanisms of the toxic effects of polyethylene MPs (45-53 µm). In the zebrafish intestine, 6, 5, and 186 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In the gills, 318, 92, and 484 genes showed differential expression after MP treatment for 1, 5, and 10 days, respectively. In both the intestine and the gills, Gene Ontology (GO) annotation showed that the main enriched terms were biological regulation, cellular process, metabolic process, cellular anatomical entity, and binding. KEGG enrichment analysis on DEGs revealed that the dominant pathways were carbohydrate metabolism and lipid metabolism, which were strongly influenced by MPs in the intestine. The dominant pathways in the gills were immune and lipid metabolism. The respiratory rate of gills, the activity of SOD and GSH in the intestine significantly increased after exposure to MPs compared with the control (p < 0.05), while the activity of SOD did not change in the gills. GSH activity was only significantly increased after MP exposure for 5 days. Also, the MDA content was not changed in the intestine but was significantly decreased in the gills after MP exposure. The activity of AChE significantly decreased only after MPs exposure for 5 days. Overall, these results indicated that MPs pollution significantly induced oxidative stress and neurotoxicity, increased respiratory rate, disturbed energy metabolism and stimulated immune function in fish, displaying an environmental risk of MPs to aquatic ecosystems.

Toxic effects of microplastics and nanoplastics on plants: A global meta-analysis.

Microplastics (MPs) and nanoplastics (NPs) pervade and accumulate within the soil, exerting influences not only on plant growth and development but also on human health through the food chain. However, recent studies on the effects of MPs/NPs on plants yield diverse results. Thus, this study conducts a meta-analysis of 101 recent publications to summarize the influence of type, size, and concentration of MPs/NPs on physiological responses, photosynthetic pigments, and biochemical reactions in various plant species. The findings indicate that the effects of MPs/NPs on plants vary depending on the specific plant species. The impact of different polymer types of MPs/NPs on plants does not show a clear trend, possibly due to variations in polymer functional groups. However, it is noteworthy that polyethylene terephthalate with phenyl groups exhibits the most significant effect on plant fresh weight, chlorophyll a and b, and H2O2 content among all microplastic types. Moreover, MPs exhibit stronger inhibition on most physiological, photosynthetic pigments, and biochemical indicators of plants compared to NPs, although root length, chlorophyll, and H2O2 demonstrate opposite effects. The concentration of MPs/NPs elicits different responses on plant indicators, each with specific trends. Notably, exposure to MPs/NPs stimulates an increase in plant biochemical enzyme indicators. Finally, this study identifies current knowledge gaps and offers insights for future research directions.

Long-term mulching of biodegradable plastic film decreased fungal necromass C with potential consequences for soil C storage.

The use of biodegradable plastic film mulching as a replacement for polyethylene plastic film has gained recognition due to its reduced environmental pollution. However, its impact on soil environment is not yet fully understood. Here, we compared the effects of different plastic film mulching on the accumulation of microbial necromass carbon (C) and its contribution to soil total C in 2020 and 2021. Results showed that biodegradable plastic film mulching decreased the accumulation of fungal necromass C compared to no plastic film mulching and polyethylene film mulching. However, the bacterial necromass C and soil total C were not affected by the plastic film mulching. Biodegradable plastic film mulching decreased the soil dissolved organic carbon content after maize harvest. Random forest models suggested that soil dissolved organic C, soil pH and the ratio of soil dissolved organic C to microbial biomass C were important factors in regulating the accumulation of fungal necromass C. The abundance of the fungal genus Mortierella was also found to have a significant positive contribution to the accumulation of fungal necromass C. These findings suggest that biodegradable plastic film mulching may decrease the accumulation of fungal necromass C by changing substrate availability, soil pH, and fungal community composition, with potential implications for soil C storage.

Algal density affects the influences of polyethylene microplastics on the freshwater rotifer Brachionus calyciflorus.

Most previous researches focused on the toxicity of polystyrene microplastics (MPs) to marine organisms, but less on polyethylene MPs and freshwater zooplanktons. The present study aims to elucidate the toxicity of polyethylene (PE) MPs (diameter = 10-22 µm) to the typical freshwater rotifer Brachionus calyciflorus. Firstly, fluorescent microscope observation showed that rotifers could ingest PE MPs and accumulate them in their digestive tracts. Life-table experiments revealed that exposure to 0.5 × 103, 2.5 × 103, and 1.25 × 104 particles/mL PE MPs significantly reduced net reproductive rate and intrinsic rate of pollution increase of rotifers under algal densities (Scenedesmus obliquus) of 0.1 × 106, and 0.5 × 106 cells/mL, but no significant effects were observed under 2.5 × 106 cells/mL algal density. These results showed that PE MPs suppressed the reproduction of rotifer and this negative effect could be alleviated by increasing food supply. The swimming linear speed of rotifers significantly decreased with increasing MP concentrations. The activities of superoxide dismutase and Na+-K+-ATPase significantly decreased in treatments with high concentration of PE MPs under 0.1 × 106 cells/mL algal density, but did not change significantly in MP treatments under 0.5 × 106 and 2.5 × 106 cells/mL, compared to the control. Glutathione peroxidase activity significantly increased in treatments with 1.25 × 104 particles/mL and 2.5 × 103 particles/mL under 0.1 × 106 and 0.5 × 106 cells/mL algal density, respectively, but did not change significantly in all MP treatments under 2.5 × 106 cells/mL. Exposure to PE MPs might lower the gathering capacity of algae, induce oxidative stress, trigger cell membrane damages and disturb energy metabolism in rotifers, which can explain the PE MPs toxicity to rotifer reproduction.