Abiotic and biotic degradations of a LDPE blend in soil of South Brazil landfill

LPDE biodegradation promoted by a novel additive based on silica nanoparticles: Structural, microbial and ecotoxicological characterization

This study developed a biodegrading additive based on nanosilica and modified by cellulase enzyme in the presence of citric acid and sodium citrate. The additive was tested as a facilitator for biodegradation of the commercial low-density polyethylene (LDPE) in soil. Enzyme immobilization was confirmed by enzymatic assays. Moreover, additive and nanocomposites were characterized by spectroscopic and microscopic techniques. To assess the role of additive in biodegradation, CO2 production in soil was measured at 30 °C for 83 days. Biodegraded nanocomposites were cultivated to isolate possible LDPE-biodegrading microorganisms. Ecotoxicity of the studied materials was evaluated on cucumber (Cucumis sativus L.). CO2 production from LDPE/additive sample was similar to the starch (1055 ± 14 mg and 1078 ± 28 mg, respectively), and higher than pure LDPE (882 ± 34 mg) and LDPE/nanosilica (992 ± 30 mg). Although the presence of LDPE/nanosilica and LDPE/additive led to root length reduction of 24.3 ± 2.3% compared to the control (soil), the accumulation of root biomass was not affected. Furthermore, the nanocomposites did not cause harmful effects on seedling growth. Nine microbial isolates were recovered from biodegraded samples and identified by molecular techniques. It was demonstrated for the first time the LDPE biodegradation potential by four bacterial isolates (Bacillus safensis FO-36b, Lysinibacillus capsici, Bacillus albus N35-10-2 and Bacillus paranthracis Mn5) and two fungal isolates (Cladosporium halotolerans clone EF_526 and Cladosporium sp. MV-2018B isolate MLT-27). Our study sheds light on the biodegradation of commercial LDPE by soil microorganisms using a novel LDPE-biodegrading additive nanocomposite.

The impact of arbuscular mycorrhizal fungi and endophytic bacteria on peanuts under the combined pollution of cadmium and microplastics

It remains unclear how symbiotic microbes impact the growth of peanuts when they are exposed to the pollutants cadmium (Cd) and microplastics (MPs) simultaneously. This study aimed to investigate the effects of endophytic bacteria Bacillus velezens SC60 and arbuscular mycorrhizal fungus Rhizophagus irregularis on peanut growth and rhizosphere microbial communities in the presence of Cd at 40 (Cd40) or 80 (Cd80) mg kg-1 combined without MP or the presence of low-density polyethylene (LDPE) and poly butyleneadipate-co-terephthalate (PBAT). This study assessed soil indicators, plant parameters, and Cd accumulation indicators. Results showed that the application of R. irregularis and B. velezens significantly enhanced soil organic carbon and increased Cd content under the conditions of Cd80 and MPs co-pollution. R. irregularis and B. velezens treatment increased peanut absorption and the enrichment coefficient for Cd, with predominate concentrations localized in the peanut roots, especially under combined pollution by Cd and MPs. Under treatments with Cd40 and Cd80 combined with PBAT pollution, soil microbes Proteobacteria exhibited a higher relative abundance, while Actinobacteria showed a higher relative abundance under treatments with Cd40 and Cd80 combined with LDPE pollution. In conclusion, under the combined pollution conditions of MPs and Cd, the co-treatment of R. irregularis and B. velezens effectively immobilized Cd in peanut roots, impeding its translocation to the shoot.

Hydrocarbon-based plastics: Progress and perspectives on consumption and biodegradation by insect larvae

The obvious contrast between the remarkable durability and the high consumption of plastic products leads to the deposition of at least 100 million tons of plastics per year in nature. Since 2010, several studies have shown the potential of insect larvae to biodegrade different types of plastics, at higher rates than those reported for microorganisms. This review discusses a compilation of studies about the consumption and biodegradation of hydrocarbon-based plastics, particularly PE, PS, PP and PVC, by lepidopteran and coleopteran larvae. Insects of the Coleoptera order seem to have a better adaptation for PS biodegradation, while those of the Lepidoptera order can better biodegrade PE. Tenebrio molitor biomineralize PE and PS into CO₂, and PVC into HCl; while Tenebrio obscurus and Zophobas atratus converts PE and PS into CO₂, respectively. Plastic biodegradation by T. molitor has been shown to be dependent on microbiota, exception for PE. Similar PS and PE biodegradation profile has been shown for T. obscurus. PS, PP and PE biodegradation by Z. atratus is also reported to be microbial-dependent. For Galleria mellonella, microbial role on PE biodegradation is still controversial, but the PS metabolism was proved to be microbiota-independent. Advances in this field has stimulated new studies with other insect species, which need to be better explored. Uncovering and understanding the chemical processes behind the innate plastic biodegradation by insect larvae will open the perspective to new eco-friendly innovative biotechnological solutions for the challenge of plastic waste.

Effect of different polymers of microplastics on soil organic carbon and nitrogen - A mesocosm experiment

Agricultural microplastic pollution has become a growing concern. Unfortunately, the impacts of microplastics (MPs) on agricultural soil carbon and nitrogen dynamics have not been sufficiently reported. In an attempt to remedy this, we conducted a 105-day out-door mesocosm experiment in a soil-plant system using sandy soils amended with two types of MPs, low-density polyethylene (LDPE-MPs) and biodegradable (Bio-MPs), at concentrations of 0.0% (control), 0.5%, 1.0%, 1.5%, 2.0% and 2.5% (w/w, weight ratio of microplastics to air-dry soil). Soil organic matter (SOM), dissolved organic carbon (DOC), permanganate oxidizable carbon (POXC), available nitrogen (AN) of N-NH₄⁺ and N-NO₃^-, and dissolved organic nitrogen (DON) were measured on day 46 (D46) and 105 (D105) of the experiment. SOM was also measured after microplastics were mixed into soils (D0). For LDPE-MPs treatments, SOM on D0, D46 and D105 showed no significant differences, while for Bio-MPs treatments, SOM significantly (p < 0.05) decreased from D0 to D46. Compared to the control, soil POXC was significantly (p = 0.001) lowered by 0.5%, 1.0% and 2.5% LDPE-MPs and ≥ 1.0% Bio-MPs on D105. LDPE-MPs showed no significant effects on soil DOC and nitrogen cycling. 2.0% and 2.5% Bio-MPs showed significantly higher (p < 0.001) DOC and DON (on D46 and D105) and ≥1.5% Bio-MPs showed significantly lower (p = 0.02) AN (on D46). Overall, Bio-MPs exerted stronger effects on the dynamics of soil carbon and nitrogen cycling. In conclusion, microplastics might pose serious threats to agroecosystems and further research is needed.