Unveiling Fragmentation of Plastic Particles during Biodegradation of Polystyrene and Polyethylene Foams in Mealworms: Highly Sensitive Detection and Digestive Modeling Prediction

Abstract

It remains unknown whether plastic-biodegrading macroinvertebrates generate microplastics (MPs) and nanoplastics (NPs) during the biodegradation of plastics. In this study, we utilized highly sensitive particle analyzers and pyrolyzer-gas chromatography mass spectrometry (Py-GCMS) to investigate the possibility of generating MPs and NPs in frass during the biodegradation of polystyrene (PS) and low-density polyethylene (LDPE) foams by mealworms (Tenebrio molitor larvae). We also developed a digestive biofragmentation model to predict and unveil the fragmentation process of ingested plastics. The mealworms removed 77.3% of ingested PS and 71.1% of ingested PE over a 6-week test period. Biodegradation of both polymers was verified by the increase in the δ13C signature of residual plastics, changes in molecular weights, and the formation of new oxidative functional groups. MPs accumulated in the frass due to biofragmentation, with residual PS and PE exhibiting the maximum percentage by number at 2.75 and 7.27 μm, respectively. Nevertheless, NPs were not detected using a laser light scattering sizer with a detection limit of 10 nm and Py-GCMS analysis. The digestive biofragmentation model predicted that the ingested PS and PE were progressively size-reduced and rapidly biodegraded, indicating the shorter half-life the smaller plastic particles have. This study allayed concerns regarding the accumulation of NPs by plastic-degrading mealworms and provided critical insights into the factors controlling MP and NP generation during macroinvertebrate-mediated plastic biodegradation.

Generation and Fate of Nanoplastics in the Intestine of Plastic-Degrading Insect (Tenebrio molitor Larvae) during Polystyrene Microplastic Biodegradation

“…This observation substantiated that nanosized plastics did not accumulate beyond the detection limit in the excrements following the biodegradation of PS MPs. This finding aligns with earlier research findings involving the biodegradation of commercial PS and PE foam products in T. molitor larvae, 48 and the biodegradation of PS MPs in plastic-degrading G. mellonella larvae. 59 This absence of NPs in the frass can be attributed to the ultrafast PS biodegradation along the intestinal tract of plastic-degrading invertebrates, leading to the final elimination of nanosized plastics in excrements before reaching the anus.…”

“…The increase in the size of the smallest-sized PS particles in the frass was associated with the enhanced PS-degrading ability of the T. molitor larvae, as demonstrated by δ 13 C analysis. Similar to the results of the biodegradation of PS and PE foams, 16,18,42,48 it takes 2 to 3 weeks for T. molitor larvae to reach their stable PS biodegradation, resulting in the smallest particles being larger in size than they were initially. Consequently, their effectiveness in completely removing submicron plastic particles (e.g., particle sizes < 5 μm) within the limited intestinal retention time (approximately 12 h) was compromised.…”

“…This finding aligns with earlier research findings involving the biodegradation of commercial PS and PE foam products in T. molitor larvae, and the biodegradation of PS MPs in plastic-degrading G. mellonella larvae .…”

“…The residue was rinsed thoroughly three times and cleaned with Milli-Q ultrapure water in preparation for the δ 13 C analysis. An elemental analyzer isotope ratio mass spectrometer (EA-IRMS, Vario EL cube-IsoPrime 100, Elementar, Germany) was utilized to detect modifications in the δ 13 C stable isotope signatures of the residual plastics from the frass, in comparison to pristine PS MPs. , The analysis was performed in triplicate to ensure reliability. The precision of the δ 13 C measurements was ±0.10‰, with a data repeatability exceeding 99.9%.…”

Molecular-Weight-Dependent Degradation of Plastics: Deciphering Host–Microbiome Synergy Biodegradation of High-Purity Polypropylene Microplastics by Mealworms

“…To date, only a limited number of microorganisms have been reported to degrade PP, typically requiring pretreatment and exhibiting a slow degradation rate. , Recent researchers have identified certain macroinvertebrates capable of biodegrading major plastics, such as insect larvae belonging to darkling beetles (Coleoptera: Tenebrionidae) including Tenebrio molitor (T. molitor), − Tenebrio obscurus, Zophobas atratus, , Uloma sp., and Plesiophthalmus davidis ; pyralid moths (Lepidoptera: Pyralidae) including Plodia interpunctella, , Galleria mellonella, − and Achroia grisella ; as well as other macroinvertebrates e.g ., land snails Achatina Fulica . Among these, T.…”