Biodegradation of polyvinyl chloride (PVC) microplastics in superworms (Zophobas atratus larvae): High biodegradation rate with limited mineralization and elevation of oxidative stress

Abstract

Polyvinyl chloride (PVC) has been an environmental concern due to its persistence and potential toxicity of degraded chlorinated intermediates and plasticizers. Although previous evidence indicates that plastivorous mealworms (Tenebrio molitor) can biodegrade PVC, present study demonstrates that superworms (Zophobas atratus), another member in Tenebrionidae family, are capable of degrading high-purity, rigid PVC microplastics (MPs), addressing critical gaps in the mechanistic understanding of insect-mediated PVC biodegradation. Biodegradation was unequivocally confirmed via a multi-analytical framework: mass reduction of ingested PVC, gel permeation chromatography (GPC) characterized by broad depolymerization (reduction in Mw, Mn, and Mz of the residual polymers by 18.03%, 24.04%, and 10.26%, respectively), and biological metabolism by δ13C analysis. Furthermore, Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) confirmed extensive chemical oxidation and dechlorination, while thermogravimetric analysis (TGA) demonstrated reduced thermal stability. The larvae achieved a specific PVC removal rate (SPRR) of 13.2 ± 0.8 mg/100 larvae·day, while removal efficiency reached 40.5% ± 1.2%, mainly converting to chlorinated organic intermediates and releasing 1.29% as chloride. This study provides crucial insights into PVC biodegradation, revealing that the PVC/wheat bran (WB) co-dieting ratio (100%, 80%, 50%, 30%, 20%, and 10%) alters the degradation efficiency and depolymerization pattern of PVC. Furthermore, this degradation process induces elevated reactive oxygen species (ROS), such as •OH and H2O2, driven by synergistic gut microbial activities and host responses. These findings clarify the complex host–microbe interplay governing PVC biodegradation and provide new, verifiable insights into insect- and gut microbe-mediated plastic biodegradation.