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Possible hazards from biodegradation of soil plastic mulch: Increases in microplastics and CO2 emissions
Summary
Researchers conducted an 18-month experiment to study whether biodegradable plastic mulches actually break down fully in soil or leave behind microplastic fragments. They found that the biodegradable mulches did generate microplastics and also increased soil carbon dioxide emissions compared to conventional mulch. The study raises questions about whether biodegradable mulches are truly more environmentally friendly than standard plastic film when microplastic generation and carbon release are considered.
Biodegradable mulches are widely recognized as ecologically friendly substances. However, their degradation percentage upon entering soils may vary based on mulch type and soil microbial activities, raising concerns about potential increases in microplastics (MPs). The effects of using different types of mulch on soil carbon pools and its potential to accelerate their depletion have not yet well understood. Therefore, we conducted an 18-month experiment to investigate mulch biodegradation and its effects on CO emissions. The experiment included burying soil with biodegradable mulch made of polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT), and control treatments with traditional mulch (PE) and no mulch (CK). The results indicated that PE did not degrade, and the degradation percentage of PLA and PBAT were 46.2% and 88.1%, and the MPs produced by the degradation were 6.7 × 10 and 37.2 × 10 items/m, respectively. Biodegradable mulch, particularly PLA, can enhance soil microbial diversity and foster more intricate bacterial communities compared to PE. The CO emissions were 0.58, 0.74, 0.99, and 0.86 g C/kg in CK PE PLA, PBAT, respectively. A positive correlation was observed between microbial abundance and diversity with CO emissions, while a negative correlation was observed with soil total organic carbon. Biodegradable mulch enhanced the transformation of soil organic C into CO by stimulating microbial activity.