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 HO 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 HO 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.