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Polylactic acid (PLA) is biodegraded rapidly under composting or thermophilic temperature but slowly under natural conditions with substantial microplastics generated. In this study, we examined the feasibility of PLA biodegradation and developed a novel approach for PLA waste management using yellow mealworms (Tenebrio molitor larvae) to achieve biodegradation and resource recovery simultaneously. Results confirmed PLA biodegradation in mealworms as sole PLA and PLA-bran mixtures (10%, 20%, 30% and 50% PLA, wt/wt). Feeding PLA-bran mixtures supported the larval development with higher survival rates and lower cannibal rates than feeding PLA only at ambient temperature. The PLA conversion efficiency was 90.9% with 100% PLA diet and was around 81.5–86.9% with PLA-bran mixtures. A peak insect biomass yield was achieved at a PLA ratio of 20%. PLA biodegradation was verified via detection of chemical and thermal modifications. Gut microbial community analysis indicated that intestinal communities shifted with PLA biodegradation, resulting in clusters with OTUs unique to the PLA diet. Based on these findings, we propose a circular approach for PLA waste management via resource recovery of used PLA as the feedstock for insect biomass production, management of mealworm excrement waste as fertilizer, and utilization of agricultural products for PLA production. [Display omitted] • Mealworms digested polylactic acid (PLA) to support their life activities. • Biodegradation of PLA in mealworms was confirmed via FTIR and TGA. • A peak biomass yield was achieved at 20% PLA with a co-diet bran (wt/wt). • The removal efficiency of PLA ingested was more than 81.5% in mealworms. • The gut microbiome significantly shifted due to PLA biodegradation. [ABSTRACT FROM AUTHOR]

It is widely understood that microplastics (MPs) can induce various biological stresses in macroinvertebrates that are incapable of biodegrading plastics. However, the biodegradation and physiological responses of plastic-degrading macroinvertebrates toward MPs of different degradability levels remain unexplored. In this study, Tenebrio molitor larvae (mealworms) were selected as a model of plastics-degrading macroinvertebrate, and were tested against three common plastics of different degradability rankings: polyvinyl chloride (PVC), polystyrene (PS), and polylactic acid (PLA) MPs (size <300 μm). These three MPs were biodegraded with the rate sequence of PLA > PS > PVC, resulting in a reversed order of negative physiological responses (body weight loss, decreased survival, and biomass depletion) of mealworms. Simultaneously, the levels of reactive oxygen species (ROS), antioxidant enzyme activities, and lipid peroxidation were uniformly increased as polymer degradability decreased and intermediate toxicity increased. PVC MPs exhibited higher toxicity than the other two polymers. The oxidative stresses were effectively alleviated by supplementing co-diet bran. The T. molitor larvae fed with PLA plus bran showed sustainable growth without an increase in oxidative stress. The results provide new insights into the biotoxicity of MPs on macroinvertebrates and offer comprehensive information on the physiological stress responses of plastic-degrading macroinvertebrates during the biodegradation of plastics with different degradability levels. [Display omitted] • Microplastics (MPs) degradation rate by mealworms with sequence of PLA > PS > PVC. • Physiological responses were dependent on polymer degradability and intermediate toxicity. • Supplementing nutrient-rich co-diets alleviated oxidative stress by MPs. • Nanoplastics were not detected in frass after microplastics biodegradation. [ABSTRACT FROM AUTHOR]

• PVC ingested in Tenebrio molitor larvae was broadly depolymerized within 12–15 h. • Biodegradation of PVC was confirmed by polymer modification. • PVC was partially mineralized with about 3% to chloride. • Depolymerization was inhibited by gentamicin thus gut microbe dependent. • Gut microbiome shifted significantly after feeding PVC. Tenebrio molitor larvae (Coleoptera: Tenebrionidae) are capable of depolymerizing and biodegrading polystyrene and polyethylene. We tested for biodegradation of Polyvinyl Chloride (PVC) in T. molitor larvae using rigid PVC microplastic powders (MPs) (70–150 μm) with weight-, number-, and size-average molecular weights (M w , M n and M z) of 143,800, 82,200 and 244,900 Da, respectively, as sole diet at 25 °C. The ingestion rate was 36.62 ± 6.79 mg MPs 100 larvae-1 d-1 during a 16-day period. The egested frass contained about 34.6% of residual PVC polymer, and chlorinated organic carbons. Gel permeation chromatography (GPC) analysis indicated a decrease in the M w , M n and M z by 33.4%, 32.8%, and 36.4%, respectively, demonstrating broad depolymerization. Biodegradation and oxidation of the PVC MPs was supported by the formation of O C and O C functional groups using frontier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (1H NMR), and by significant changes in the thermal characteristics using thermo-gravimetric analysis (TGA). Chloride released was counted as about 2.9% of the PVC ingested, indicating limited mineralization of the PVC MPs. T. molitor larvae survived with PVC as sole diet at up to 80% over 5 weeks but did not complete their life cycle with a low survival rate of 39% in three months. With PVC plus co-diet wheat bran (1:5, w/w), they completed growth and pupation as same as bran only in 91 days. Suppression of gut microbes with the antibiotic gentamicin severely inhibited PVC depolymerization, indicating that the PVC depolymerization/biodegradation was gut microbe-dependent. Significant population shifts and clustering in the gut microbiome and unique OTUs were observed after PVC MPs consumption. The results indicated that T. molitor larvae are capable of performing broad depolymerization/biodegradation but limited mineralization of PVC MPs. [ABSTRACT FROM AUTHOR]

Evidence for plastic degradation by mealworms has been reported. However, little is known about the residual plastics derived from incomplete digestion during mealworm-mediated plastic biodegradation. We herein reveal the residual plastic particles and toxicity produced during mealworm-mediated biodegradation of the three most common microplastics, i.e., polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC). All three microplastics are effectively depolymerized and biodegraded. We discover that the PVC-fed mealworms exhibit the lowest survival rate (81.3 ± 1.5%) and the highest body weight reduction (15.1 ± 1.1%) among the experimental groups by the end of the 24-day experiment. We also demonstrate that the residual PVC microplastic particles are more difficult to depurate and excrete for the mealworms compared to the residual PE and PS particles by using laser direct infrared spectrometry. The levels of oxidative stress responses, including reactive oxygen species, antioxidant enzyme activities, and lipid peroxidation, are also highest in the PVC-fed mealworms. Sub-micron microplastics and small microplastics are found in the frass of mealworms fed with PE, PS, and PVC, with the smallest particles detected at diameters of 5.0, 4.0, and 5.9 µm, respectively. Our findings provide insights into the residual microplastics and microplastic-induced stress responses in macroinvertebrates under micro(nano)plastics exposure. [Display omitted] • PE, PS, and PVC microplastics were rapidly ingested and efficiently biodegraded by mealworms. • The PVC-fed mealworms had the worst physiological performance during the 24-day test. • Undigested microplastics remained in mealworm intestines for a longer time than normal food. • Oxidative stress responses were discovered in the mealworms fed with PE, PS, and PVC microplastics. • Sub-micron microplastics and small microplastics were found in the frass of the mealworms. [ABSTRACT FROM AUTHOR]

Biodegradation of petroleum-derived plastics in mealworms has been identified with different plastic products. To date, however, the responses of mealworm larvae to plastic biodegradation have received comparatively little attention. Herein, we tested the physiological responses of mealworm larvae after biodegradation of polyethylene (PE) microplastics and evaluated the impact of supplementing co-diet bran on the PE biodegradation and mealworm homeostasis. Significant weight loss, biomass reduction, and decreased survival rates were found for the PE-fed larvae after the six-week test. The efficient removal of PE, molecular weight reduction of residual polymers, and thermal decomposition signals demonstrated the depolymerization and biodegradation. Supplementing bran significantly enhanced the biomass levels and the survival of larvae but disturbed the PE removal in the intestinal tracts. The frass (excrement) from the larvae fed with PE and PE + bran feedstocks both contained undigested residual microplastics of different sizes with no accumulation of nanoplastics. Additionally, higher levels of reactive oxygen species, antioxidant enzyme activities, and lipid peroxidation were detected for larvae fed with pure PE, whereas the oxidative stress levels could be mitigated by supplementing co-diet bran. These results provide methodological insights into assessing the physiological responses of invertebrates after plastic ingestion or under micro(nano)plastic exposure. [Display omitted] • The physiological function and growth of mealworms were negatively influenced by PE degradation. • Oxidative stress and damage were induced in mealworms after PE degradation. • Supplementation of co-diet bran can improve the physiological performance of mealworms. • The levels of oxidative stress and damage in mealworms could be mitigated by supplementing bran. • Nanoplastics could not be accumulated in the frass of mealworms after PE degradation. [ABSTRACT FROM AUTHOR]

In this study, biodegradation of polystyrene (PS) and low-density polyethylene (LDPE) by Zophobas atratus larvae was characterized to investigate fragmentation of ingested polymers, larval physiology, gut microbiota, and microbial functional enzymes over a 28-day test. The larvae maintained high survival rates and low cannibal rates, but their body fat content decreased when fed with PS or LDPE with respective consumption rates of 43.3 ± 1.5 and 52.9 ± 3.1 mg plastics/100 larvae per day. The larvae biodegraded PS via broad depolymerization and LDPE via limited-extent depolymerization. The ingested PS and LDPE were fragmented into microplastics with a mean size of 174 and 185 μm on a volume basis, and the particles with a size of 6.3 and 5.9 μm reached a maximum number, respectively, with no nanoplastics generated. Chemical modifications of the polymers were confirmed. Significant shifts and clustering in the gut microbiota were detected with the relative abundance of Citrobacter sp. increasing when PS and LDPE were fed, as reported for other species of Tenebrionidae. Microbial functional enzymes, possibly associated with plastic degradation, including arylesterase and serine-hydrolase, were upregulated in both PS-fed and PE-fed larvae. This work provides new insights into insect-mediated biodegradation of persistent plastics for future investigations. [Display omitted] • Zophobas atratus biodegraded PS and LDPE in different depolymerization patterns. • Digestive fragmentation into microplastics occurred with no nanoplastics generated. • Significant clustering in the gut microbiota was attributed to PS and LDPE digestion. • Expression levels of functional enzymes were upregulated during plastic degradation. [ABSTRACT FROM AUTHOR]

Abstract: Due to the large diameter and small surface, the contaminant degradation by conventional calcium peroxide (CaO2) is slow with high dosage required. The aggregation of conventional CaO2 also makes it difficult to operate. Nanoscale CaO2 was therefore synthesized and applied to remove toluene in this study. Prepared from nanoscale Ca(OH)2 and H2O2 in the ratio of 1:7, the finely dispersed nanoscale CaO2 particles were confirmed by the scanning electron microscope to be in the range of 100–200nm in size. Compared to their non nanoscale counterparts, the synthesized nanoscale CaO2 demonstrated a superior performance in the degradation of toluene, which could be eliminated in 3d at pH 6. The oxidation products of toluene were analyzed to include benzyl alcohol, benzaldehyde and three cresol isomers. With the addition of 2-propanol, hydroxyl radicals were indicated as the main reactive oxygen species in the oxidation of toluene by nanoscale CaO2. Superoxide radicals were also investigated as the marker of nanoscale CaO2 in the solution. Our study thus provides an important insight into the application of nanoscale CaO2 in the removal of toluene contaminants, which is significant, especially for controlling the petroleum contaminations. [Copyright &y& Elsevier]