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Effects of different size polylactic acid on arsenic migration and rhizosphere microorganisms in soil-rice system
Summary
Researchers found that polylactic acid (PLA), a common biodegradable microplastic, increased the availability of toxic arsenic in rice paddies by changing soil chemistry and promoting bacteria that convert arsenic into more dangerous forms. Nano-sized PLA particles were particularly harmful, promoting arsenic uptake into rice plants, while larger particles actually blocked it. This study is important for food safety because it shows that even biodegradable plastics in agricultural soil can increase toxic contamination in rice, a staple food for billions of people.
The impact of microplastics on arsenic biogeochemical cycles within the plant-soil system holds critical importance for food safety and public health, yet remains largely underexplored, particularly concerning biodegradable microplastics. This study investigated the influence of polylactic acid (PLA), a representative biodegradable microplastic, on arsenic migration and transformation in rice-soil systems. Our findings indicated that PLA enhanced arsenic bioavailability in soil through acidification and increased dissolution of iron and manganese minerals. Moreover, bacteria enriched by PLA exhibited the ability to reduce and methylate arsenic in the rhizosphere, promoting its transformation into bioavailable and toxic trivalent forms. Notably, PLA with 150 μm and 50 μm inhibited arsenic uptake in rice seedlings, consequently reducing migration from soil to plants, while 150 nm particles promoted arsenic uptake. Furthermore, PLA addition induced oxidative stress and diminished photosynthetic efficiency in plants, exacerbating the detrimental effects of arsenic on plant growth. Overall, the combined presence of PLA and arsenic increased the risk of arsenic migration in rice-soil systems, with nanoplastics posing a more significant threat to rice food safety. Our research findings improve our current understanding of the effects of micro(nano)plastics on the arsenic biogeochemical cycle and identify the ecological and health risks associated with their combined pollution.