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Effect of alkaline-thermal pretreatment on biodegradable plastics degradation and dissemination of antibiotic resistance genes in co-compost system
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This study found that pretreating biodegradable plastics with heat and alkaline solutions speeds up their breakdown during composting, but the process releases large numbers of smaller microplastic fragments. These smaller particles can carry microorganisms and antibiotic resistance genes into the environment, raising concerns that even "eco-friendly" plastics may pose risks to public health during disposal.
Biodegradable plastics (BDPs) are an eco-friendly alternative to traditional plastics in organic waste, but their microbial degradation and impact on antibiotic resistance genes (ARGs) transmission during co-composting remain poorly understood. This study examines how alkaline-thermal pretreatment enhances BDPs degradation and influences the fate of ARGs and mobile genetic elements (MGEs) in co-composting. Pretreatment with 0.1 mol/L NaOH at 100℃ for 40 minutes increased the surface roughness and hydrophilicity of BDPs while reducing their molecular weight and thermal stability. Incorporating pretreated BDPs film (8 g/kg-TS) into the compost reduced the molecular weight of the BDPs by 59.70 % during the maturation stage, facilitating compost heating and prolonging the thermophilic stage. However, incomplete degradation of BDPs releases numerous smaller-sized microplastics, which can act as carriers for microorganisms, facilitating the dissemination of ARGs across environments and posing significant ecological and public health risks. Metagenomic analysis revealed that pretreatment enriched plastic-degrading bacteria, such as Thermobifida fusca, on BDPs surfaces and accelerated microbial plastic degradation during the thermophilic stage, but also increased ARGs abundance. Although pretreatment significantly reduced MGEs abundance (tnpA, IS19), the risk of ARGs dissemination remained. Three plastic-degrading bacteria (Pigmentiphaga sp002188465, Bacillus clausii, and Bacillus altitudinis) were identified as ARGs hosts, underscoring the need to address the risk of horizontal gene transfer of ARGs associated with pretreatment in organic waste management.
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This study found that biodegradable microplastics actually pose a higher risk for spreading antibiotic resistance than conventional non-biodegradable plastics. As biodegradable plastics break down, they appear to promote stress responses in bacteria that encourage the sharing of antibiotic resistance genes. This is concerning because biodegradable plastics are often marketed as safer alternatives.
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