Biodegradability and ecological impacts of polyethylene-based mulching film at agricultural environment

Polyethylene and sulfa antibiotic remediation in soil using a multifunctional degrading bacterium

To obtain a multifunctional bacterium that can effectively degrade polyethylene (PE) and sulfonamide antibiotics (SAs), PE and SAs were selected as the primary research objects. Multifunctional degrading bacteria were isolated and screened from an environment in which plastics and antibiotics have existed for a long time. An efficient degrading strain, Raoultella sp., was screened by measuring the degradation performance of PE and SAs. We analyzed the changes in the microbial community of indigenous bacteria using 16S rRNA. After 60 d of degradation at 28 °C, the Raoultella strain to PE degradation rate was 4.20 %. The SA degradation rates were 96 % (sulfonathiazole, (ST)), 86 % (sulfamerazine, (SM)), 72 % (sulfamethazine, (SM2)) and 64 % (sulfamethoxazole, (SMX)), respectively. This bacterium increases the surface roughness of PE plastic films and produces numerous gullies, pits, and folds. In addition, after 60 d, the contact angle of the plastic film decreased from 92.965° to 70.205°, indicating a decrease in hydrophobicity. High-throughput sequencing analysis of the degrading bacteria revealed that the Raoultella strain encodes enzymes involved in PE and SA degradation. The results of this study not only provide a theoretical basis for further study of the degradation mechanism of multifunctional and efficient degrading bacteria but also provide potential strain resources for the biodegradation of waste plastics and antibiotics in the environment.

Biodeterioration of polyethylene by Bacillus cereus and Rhodococcus equi isolated from soil

Polyethylene (PE), a non-biodegradable plastic, is widely used in agriculture as a mulch material, which causes serious plastic pollution when it is discarded. Recent studies have described the biodeterioration of PE by bacteria, but it is difficult for a single bacterial species to effectively degrade PE plastic. We isolated two strains with PE-degrading ability, Bacillus cereus (E1) and Rhodococcus equi (E3), from the soil attached to plastic waste on the south side of Mount Tai, China, using a medium with PE plastic as the only carbon source. By clear zone area analysis, we found that E1 mixed with E3 could improve the degradation of PE plastics. The mixture of E1 and E3 was incubated for 110 days in a medium containing PE and mulch film as the only carbon source, respectively. After 110 days, a decrease in pH and mass was observed. Obvious slits and depressions were observed on the surface of the PE film and the mulch films using scanning electron microscopy. The surface hydrophobicity of both films decreased, and FTIR revealed the formation of new oxidation groups on their surfaces during the degradation process and the destruction of the original CH2 long chains of PE. Besides, we found that surface of the mulch films contained more viable bacteria than the liquid medium. In conclusion, we identified two PE-degrading strains whose mixture can effectively degrade mulch film than pure PE film. Our results provide a reference for understanding PE plastic degradation pathways and their associated degradation processes.

Deep insights into biodegradability mechanism and growth cycle adaptability of polylactic acid/hyperbranched cellulose nanocrystal composite mulch

The widespread use of petroleum-based plastic mulch in agriculture has accelerated white and microplastic pollution while posing a severe agroecological challenge due to its difficulty in decomposing in the natural environment. However, endowing mulch film with degradability and growth cycle adaptation remains elusive due to the inherent non-degradability of petroleum-based plastics severely hindering its applications. This work reports polylactic acids hyperbranched composite mulch (PCP) and measured biodegradation behavior under burial soil, seawater, and ultraviolet (UV) aging to understand the biodegradation kinetics and to increase their sustainability in the agriculture field. Due to high interfacial interactions between polymer and nanofiler, the resultant PCP mulch significantly enhances crystallization ability, hydrophilicity, and mechanical properties. PCP mulch can be scalable-manufactured to exhibit modulated degradation performance under varying degradation conditions and periods while concurrently enhancing crop growth (wheat). Thus, such mulch with excellent performance can reduce labor costs and the environmental impact of waste mulch disposal to replace traditional mulch for sustainable agricultural production.

Advancing agriculture through bioresource technology: The role of cellulose-based biodegradable mulches

Agriculture plays a pivotal role in meeting the world's ever-growing food demands. However, traditional agricultural practices often have negative consequences for the environment, such as soil erosion and chemical runoff. Recently, there has been a pressing need for advance agricultural practices. Cellulose-based mulches offer a solution by optimizing agricultural productivity while minimizing harm. These mulches are made from renewable bioresources derived from cellulose-rich materials. Compared to plastic mulches, cellulose-based alternatives show potential in improving nutrient retention, soil health, weed suppression, water conservation, and erosion mitigation. The article investigates the characteristics and application methods of cellulose-based mulches, highlighting their biodegradability, water retention, crop protection, and weed suppression capabilities. It also evaluates their economic feasibility, emphasizing their potential to transform sustainable farming practices. Overall, cellulose-based mulches have the potential to revolutionize agriculture, addressing environmental concerns while optimizing productivity. They represent a significant step toward a more sustainable and resilient agricultural system.

Biodegradable mulch films improve yield of winter potatoes through effects on soil properties and nutrients

Biodegradable mulch films are recognized as a promising substitute of polyethylene (PE) films to alleviate the "white pollution". Biodegradable mulch films with optimum degradation rates increase crop yield even compared to PE films. However, the mechanisms underlying this yield-increasing effect remains elusive. In this study, three biodegradable film treatments (BFM1, BFM2 and BFM3) and one PE film treatment (PFM) were used to evaluate their effects on soil and winter potatoes, and a partial least squares path model (PLS-PM) was constructed to investigate their relationships. The degradation rates of films under different treatments were ranked as BFM3 > BFM2 >BFM1 > PFM, and presented distinctive effects on soil properties and nutrients, structure of soil bacterial community, and yield traits of winter potatoes. The PLS-PM showed that mulch treatments affected potato yield through effects on soil properties (soil water and temperature) and soil nutrients (TOC, DOC, TN and NO3--N). The disintegration of the biodegradable films decreased soil water content and temperature, and reduced the loss of soil nutrients in the topsoil at the later growth stage of winter potatoes compared to PE films. Additionally, the elevated content of soil TN and NO3--N under treatment BFM1 may play a key role in its yield-increasing effect on potatoes compared to treatments PFM and BFM2. Thus, biodegradable mulch films with proper degradation rates regulate soil TN and NO3--N through their effects on soil water and temperature, and subsequently improve the yield of winter potatoes compared to PE mulch films.

Degradation characteristics of polyethylene film by microorganisms from lake sediments

Polyethylene (PE) exists widely in many habitats as a persistent organic pollution and poses a major threat to the ecological environment. In this study, bacterial communities in freshwater lake sediments were exposed to culture media using PE films as the sole carbon source in aerobic and anaerobic microculture environments, and they were able to adhere and adapt to the PE films for a longer period of time. The results demonstrated that the pH value of the medium in the two cultural conditions was distinct, as were the rates of films weight loss and surface functional group alterations. We also concluded the certain bacterial genera from freshwater lake sediments who may be able to degrade PE films under either aerobic or anaerobic conditions. Simultaneously, the dominating bacterial communities between the medium and the film differed significantly under two cultural settings, as did the community composition, while metabolism was the primary function.

Polyethylene degradation and assimilation by the marine yeast Rhodotorula mucilaginosa

Ocean plastic pollution is a severe environmental problem but most of the plastic that has been released to the ocean since the 1950s is unaccounted for. Although fungal degradation of marine plastics has been suggested as a potential sink mechanism, unambiguous proof of plastic degradation by marine fungi, or other microbes, is scarce. Here we applied stable isotope tracing assays with 13C-labeled polyethylene to measure biodegradation rates and to trace the incorporation of plastic-derived carbon into individual cells of the yeast Rhodotorula mucilaginosa, which we isolated from the marine environment. 13C accumulation in the CO2 pool during 5-day incubation experiments with R. mucilaginosa and UV-irradiated 13C-labeled polyethylene as a sole energy and carbon source translated to degradation rates of 3.8% yr-1 of the initially added substrate. Furthermore, nanoSIMS measurements revealed substantial incorporation of polyethylene-derived carbon into fungal biomass. Our results demonstrate the potential of R. mucilaginosa to mineralize and assimilate carbon from plastics and suggest that fungal plastic degradation may be an important sink for polyethylene litter in the marine environment.

A computational approach to optimising laccase-mediated polyethylene oxidation through carbohydrate-binding module fusion

Plastic pollution is a major global concern to the health and wellbeing of all terrestrial and marine life. However, no sustainable method for waste management is currently viable. This study addresses the optimisation of microbial enzymatic polyethylene oxidation through rational engineering of laccases with carbohydrate-binding module (CBM) domains. An explorative bioinformatic approach was taken for high-throughput screening of candidate laccases and CBM domains, representing an exemplar workflow for future engineering research. Molecular docking simulated polyethylene binding whilst a deep-learning algorithm predicted catalytic activity. Protein properties were examined to interpret the mechanisms behind laccase-polyethylene binding. The incorporation of flexible GGGGS(x3) hinges were found to improve putative polyethylene binding of laccases. Whilst CBM1 family domains were predicted to bind polyethylene, they were suggested to detriment laccase-polyethylene associations. In contrast, CBM2 domains reported improved polyethylene binding and may thus optimise laccase oxidation. Interactions between CBM domains, linkers, and polyethylene hydrocarbons were heavily reliant on hydrophobicity. Preliminary polyethylene oxidation is considered a necessity for consequent microbial uptake and assimilation. However, slow oxidation and depolymerisation rates inhibit the large-scale industrial implementation of bioremediation within waste management systems. The optimised polyethylene oxidation of CBM2-engineered laccases represents a significant advancement towards a sustainable method of complete plastic breakdown. Results of this study offer a rapid, accessible workflow for further research into exoenzyme optimisation whilst elucidating mechanisms behind the laccase-polyethylene interaction.

Polyethylene mulching film degrading bacteria within the plastisphere: Co-culture of plastic degrading strains screened by bacterial community succession

As an ecological niche close to the polymer, microorganisms in the plastisphere possess the advantage of degrading plastics. This study aims to investigate the bacterial community succession and obtain degrading bacteria in the plastisphere, as well as identify the most efficient degradation combination by co-culture of multiple strains. The findings demonstrate the alpha-diversity indices of the plastisphere bacterial community are significantly lower, and the community structure is regularly and significantly altered. With the time of culture, the plastisphere community composition alters regularly, and the hydrocarbon-degrading genera become the core members. Functional prediction of community reveals the potential for Xenobiotics Biodegradation and Metabolism of plastisphere, and the apparent variations detections of polyethylene mulching film (PMF) indicating the PMF degrading ability of plastisphere. Besides, three PMF-degrading bacterial strains, Rhodopseudomonas sp. P1 (P), Rhodanobacter sp. Rs (R) and Microbacterium sp. M1 (M), are screened for co-culture with PMF degrading strain Bacillus aryabhattai 5-3 (B). By considering bacterial growth, biofilm adhesion, and apparent degradation of different samples, RB (R. sp. Rs + B. aryabhattai 5-3) is ultimately selected as the best PMF degradation combination. This study provides a new possibility for plastisphere-related research from the perspective of mitigating plastic pollution on agricultural land.

Polymers Use as Mulch Films in Agriculture-A Review of History, Problems and Current Trends

The application of mulch films for preserving soil moisture and preventing weed growth has been a part of agricultural practice for decades. Different materials have been used as mulch films, but polyethylene plastic has been considered most effective due to its excellent mechanical strength, low cost and ability to act as a barrier for sunlight and water. However, its use carries a risk of plastic pollution and health hazards, hence new laws have been passed to replace it completely with other materials over the next few years. Research to find out about new biodegradable polymers for this purpose has gained impetus in the past few years, driven by regulations and the United Nations Organization's Sustainable Development Goals. The primary requisite for these polymers is biodegradability under natural climatic conditions without the production of any toxic residual compounds. Therefore, biodegradable polymers developed from fossil fuels, microorganisms, animals and plants are viable options for using as mulching material. However, the solution is not as simple since each polymer has different mechanical properties and a compromise has to be made in terms of strength, cost and biodegradability of the polymer for its use as mulch film. This review discusses the history of mulching materials, the gradual evolution in the choice of materials, the process of biodegradation of mulch films, the regulations passed regarding material to be used, types of polymers that can be explored as potential mulch films and the future prospects in the area.

Path Deconstruction of Agricultural Environmental Sustainable Development Policy in the Process of International Agricultural Trade Liberalization

Agriculture is particularly essential in the equilibrium between man and nature because of its intimate contact with nature. So the cornerstone for the sustainable development of the human economy and society is the sustainable development of agriculture. When it comes to global trade, agricultural trade has always been in a very special position. The basic situation of agriculture involves food safety, environmental protection, Chinese politics, and many other issues. In order to overcome the problems of overlapping, repetitive, and too many indicators in the evaluation method of agricultural environmental sustainable development and unfavorable for practical operation, this paper proposes an ecological footprint model based on emergy. The model can effectively evaluate the ability of sustainable development of agricultural environment and solve the problem that traditional evaluation methods cannot comprehensively evaluate. This makes agricultural development sustainable and is conducive to the liberalization of international agricultural trade. The experimental results of this paper show that from 2014 to 2018, the degree of damage to the agricultural environment has increased from 21% to 45%, which has led to a decline in the quality of agricultural products, and the output and sales are not as good as before. It can be seen that only by ensuring the sustainable development of the agricultural environment can we ensure the smooth progress of the international agricultural trade liberalization and make China’s economy flourish.

Biodegradation of thermo-oxidative pretreated low-density polyethylene (LDPE) and polyvinyl chloride (PVC) microplastics by Achromobacter denitrificans Ebl13

Microplastics pretreatment of prior to biodegradation is an efficient approach for their bioremediation. We isolated Achromobacter denitrificans from compost and used it for biodegradation of thermo-oxidative pretreated polyvinyl chloride (PVC) and low-density polyethylene (LDPE). About 12.3 % and 6.5 % weight loss, and 326.4 and 112.32 mg L^-1 extracellular protein were observed in bacterial flasks with PVC and LDPE, respectively. The pH in treated PVC reached to 5.12 and the thermal stability increased by 29 °C. The chemical modification in LDPE was demonstrated through oxidation of antioxidants (Phenol group), formation of new groups (Aldehyde group), and chain fracture in the main backbone by Fourier transform infrared spectroscopy. Formation of peaks at the range of 1700-1850 cm^-1 in LDPE attributed to formation of carbonyl groups as the degradation result. Scanning electron microscopy confirmed LDPE and PVC degradation by surface alterations. Consequently, thermo-oxidative pretreatment can be considered as a suitable strategy for improving microplastics biodegradation.

Biodegradable Films Prepared from Pulp Lignocellulose Adhesives of Urea Formaldehyde Resin Modified by Biosulfonate

Traditional low-density polyethylene (LDPE) film causes environmental pollution; there is a pressing need to make new bio-based polymers for alternative products, to meet agricultural production needs and for sustainable ecological development. In this study, urea-formaldehyde resin (UF) was modified with polyvinyl alcohol (PVA) and 1-2.5% bio-based sulfonate (BBS). The influence of BBS inducing on the functional groups, microstructure, and thermal behavior was evaluated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). A biodegradable film was prepared with modified UF resin as adhesive and pulp lignocellulose as raw material. The biodegradable mulch film samples were tested for biodegradability, water retention, and cooling soil temperature characters using LDPE and no mulching (NM) as a control. The results showed that with the increase of BBS content, the viscosity and reactivity of modified PUF resin increased, and the free formaldehyde content decreased. A 2%BBS modified PUF resin (2.0BBS/PUF) accelerated the curing process of the PUF resin, formed a flexible macromolecular network structure, and enhanced the toughness of the resin. The biodegradable mulch prepared with PUF, BBS, and 2.0BBS/PUF as adhesives had good water retention. BBS modification increased the degradation rate of mulch by 17.53% compared to the PUF. Three biodegradable films compared with LDPE and NM significantly reduced the soil temperature under summer cucumber cultivation, and the 2.0BBS/PUF coating had the lowest diurnal temperature difference, which provided a suitable soil environment for crop growth.

Substitute for polyethylene (PE) films: A novel cow dung-based liquid mulch on silage cornfields

To prevent soil pollution caused by polyethylene (PE) films in the central region of Gansu, China, liquid mulching made from cow dung (CDLM) was trailed in silage maize fields. The degradation of CDLM and PE films, soil temperature, soil organic matter content, silage maize yield and water use efficiency (WUE) were evaluated for three years (2018–2020). The degradability of CDLM has been found to be much stronger than the one of PE films, with CDLM degrading 40–60 days after sowing and finishing around 100 days. CDLM had a lower insulating impact than PE films but a higher insulating effect than non-mulching films as the control (CK); CDLM could successfully increase soil organic matter, with a total increase of 1.01% over three years. CDLM increased silage maize yield by 6.2% compared to PE films and 17.2% compared to CK. Consequently, CDLM may be an interesting alternative to PE films for enhancing silage maize yield while decreasing soil contamination.

Does bacterial community succession within the polyethylene mulching film plastisphere drive biodegradation?

Agricultural fields are severely contaminated with polyethylene mulching film (PMF) and this plastic in the natural environment can be colonized by biofilm-forming microorganisms that differ from those in the surrounding environment. In this study, we investigated the succession of the soil microbial communities in the PMF plastisphere using an artificial micro-ecosystem as well as exploring the degradation of PMF by plastisphere communities. The results indicated a significant and gradual decrease in the alpha diversity of the bacterial communities in the plastisphere and surrounding liquid. The community compositions in the plastisphere and surrounding liquid differed significantly from that in agricultural soil. Phyla and genera with the capacity to degrade polyethylene and hydrocarbon were enriched in the plastisphere, and some of these microorganisms were core members of the plastisphere community. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis detected increases in metabolism pathways for PMF plastisphere Xenobiotics Biodegradation and Metabolism, thereby suggesting the possibility of polyethylene degradation in the plastisphere. Observations by scanning electron microscopy (SEM) and confocal laser scanning microscopy demonstrated the formation of biofilms on the incubated PMF. SEM, atomic force microscopy, Fourier transform infrared spectroscopy and water contact angle detected significant changes in the surface microstructure, chemical composition and hydrophobicity change of the films, thereby suggesting that the plastisphere community degraded PMF during incubation. In conclusion, this study provides insights into the changes in agricultural soil microorganisms in the PMF plastisphere and the degradation of PMF.

What will polyethylene film mulching bring to the root-associated microbial community of Paeonia ostii?

Plastic film mulching can increase crop yield and is widely used in agricultural production, but long-term mulching could adversely affect plant growth. To investigate the related mechanism, we studied the bacterial communities in different root-associated compartments of Paeonia ostii, a perennial oil crop, under polyethylene film mulching for three years by full-length 16S rDNA sequencing technology, and measured the soil physicochemical properties and enzyme activities. We found that enzyme activities and available nutrients in the soil tended to decrease after long-term mulching. Analysis of bacterial community composition revealed that the endosphere may be another potential source of the root-associated microbiome of P. ostii, and the rhizoplane plays a selective gating role in the enrichment processes for P. ostii microbiome assembly. Long-term mulching affected the abundance of dominant bacterial communities in different root-associated compartments and reduced the bacterial richness in the endosphere, but increased bacterial interactions in each compartment, as well as between different compartments. We speculate that this is mainly related to the decrease of litter content and the serious degradation of polyethylene film after long-term mulching, which resulted in microplastics and other harmful substances entering the soil. Our study further explained the reasons for the harm of long-term film mulching on plants to guide the rational use of plastic film. KEY POINTS: •Soil enzyme activities and available nutrients decreased after long-term mulching. •Mulching affected the dominant bacterial abundance in different root-associated compartments. •Mulching increased bacterial interactions among compartments.

Effects of microplastics on the terrestrial environment: A critical review

Microplastics are emerging contaminants and there has been growing concern regarding their impacts on aquatic and terrestrial environments. This review provides a comprehensive overview of the current knowledge regarding the sources, occurrences, fates, and risks associated with microplastic contamination in terrestrial environments. This contamination occurs via multiple sources, including primary microplastics (including synthetic materials) and secondary microplastics (derived from the breakdown of larger plastic particles). Microplastic contamination can have both beneficial and detrimental effects on soil properties. Additionally, microplastics have been shown to interact with a wide array of contaminants, including pesticides, persistent organic pollutants, heavy metals, and antibiotics, and may act as a vector for contaminant transfer in terrestrial environments. Microplastics and their associated chemicals can be transferred through food webs and may accumulate across multiple trophic levels, resulting in potential detrimental health effects for humans and other organisms. Although several studies have focused on the occurrence and impacts of microplastic contamination in marine environments, their sources, fate, transport, and effects in terrestrial environments are less studied and not well understood. Therefore, further research focusing on the fate, transport, and impacts of microplastics in relation to soil properties, polymer composition and forms, and land-use types is needed. The development of standardized and harmonized methods for analyzing microplastics in soil-plant ecosystems is essential. Future work should also consider the many interactions of microplastics with soil quality and ecotoxicological impacts on biota in the context of global environmental change.

Anaerobic soil disinfestation, amendment-type, and irrigation regimen influence Salmonella survival and die-off in agricultural soils

AIMS

This study investigated Salmonella concentrations following combinations of horticultural practices including anaerobic soil disinfestation (ASD), soil amendment type and irrigation regimen.

METHODS AND RESULTS

Sandy-loam soil was inoculated with a five-serovar Salmonella cocktail (5.5 ± 0.2 log CFU per gram) and subjected to one of six treatments: (i) no soil amendment, ASD (ASD control), (ii) no soil amendment, no-ASD (non-ASD control) and (iii-vi) soil amended with pelletized poultry litter, rye, rapeseed or hairy vetch with ASD. The effect of irrigation regimen was determined by collecting samples 3 and 7 days after irrigation. Twenty-five-gram soil samples were collected pre-ASD, post-soil saturation (i.e. ASD-process), and at 14 time-points post-ASD, and Salmonella levels enumerated. Log-linear models examined the effect of amendment type and irrigation regimen on Salmonella die-off during and post-ASD. During ASD, Salmonella concentrations significantly decreased in all treatments (range: -0.2 to -2.7 log CFU per gram), albeit the smallest decrease (-0.2 log CFU per gram observed in the pelletized poultry litter) was of negligible magnitude. Salmonella die-off rates varied by amendment with an average post-ASD rate of -0.05 log CFU per gram day (CI = -0.05, -0.04). Salmonella concentrations remained highest over the 42 days post-ASD in pelletized poultry litter, followed by rapeseed, and hairy vetch treatments. Findings suggested ASD was not able to eliminate Salmonella in soil, and certain soil amendments facilitated enhanced Salmonella survival. Salmonella serovar distribution differed by treatment with pelletized poultry litter supporting S. Newport survival, compared with other serovars. Irrigation appeared to assist Salmonella survival with concentrations being 0.14 log CFU per gram (CI = 0.05, 0.23) greater 3 days, compared with 7 days post-irrigation.

CONCLUSIONS

ASD does not eliminate Salmonella in soil, and may in fact, depending on the soil amendment used, facilitate Salmonella survival.

SIGNIFICANCE AND IMPACT OF THE STUDY

Synergistic and antagonistic effects on food safety hazards of implementing horticultural practices should be considered.

Combined effects of degradable film fragments and micro/nanoplastics on growth of wheat seedling and rhizosphere microbes

Multiple sources of microplastics (MPs) in farmland could result in the changing of microbial community and the plant growth. Most studies of MPs in agricultural system have focused on the effects of single types of MPs on growth of plants, while neglect interactions between multiple types of MPs. In this study a pot-experiment was conducted to investigate the effects of multiple types of MPs, including polystyrene beads: M1, 5 μm, M2, 70 nm and degradable mulching film (DMF) fragments on growth of wheat seedlings and associated rhizosphere microbial community. CKD (adding DMF) significantly reduced plant height and base diameter of wheat seedlings. DMF in combination with M2, significantly increased plant height and aboveground biomass, but decreased the base diameter. Actinobacteria was the dominant taxa in the rhizosphere bacterial community in various treatments. PCoA analysis showed that the bacterial composition in M2HD (100 mg kg^-1 M² with DMF) was significantly different from that of CKD and M2LD (10 mg kg^-1 M² with DMF). At the level of genera, the dominant fungi in CKD and M2LD were in the genus Fusarium, which is the cause of wheat fusarium blight and Alternaria, which results in decreased base diameter. In CK (control group) and M2HD, Blastobotrys exhibited the greatest abundance, which assisted wheat seedlings in resisting Verticillium disease. Cluster and PCoA analysis showed the fungal composition in CKD was significantly different from CK, M2LD and M2HD. These findings suggest MPs potentially have selective effects on pathogens that affect growth of plants and potentially safety of the food.

Biodegradability of polyethylene mulching film by two Pseudomonas bacteria and their potential degradation mechanism

Wasted polyethylene (PE) products caused pollution has become a global issue. Researchers have identified PE-degrading bacteria which have been considered as a sustainable alleviation to this crisis. However, the degradation mechanism employed by currently isolated bacteria is unclear and their degradation efficiencies are insufficient. More importantly, there is little research into bacteria capable of degrading PE mulching film to solve "white" pollution in agriculture. We determined the PE degradation efficiency of two Pseudomonas, identified by 16S rDNA analysis, and elucidated their potential mechanisms through whole genome sequencing. During an 8-week period, PE mulch lost 5.95 ± 0.03% and 3.62 ± 0.32% of its mass after incubated with P. knackmussii N1-2 and P. aeruginosa RD1-3 strains, respectively. Moreover, considerable pits and wrinkles were observed on PE.The hydrophobicity of PE films also decreased, and new oxygenic functional groups were detected on PE mulch by Fourier Transform Infrared Spectrometry (FTIR). Complete genome sequencing analysis indicated that two Pseudomonas strains encode genes for enzymes and metabolism pathways involved in PE degradation. The results provide a theoretical basis for further research that investigates the mechanism driving the degradation and metabolism of discarded PE in the environment.

Transcriptomic analysis of Rhodococcus opacus R7 grown on polyethylene by RNA-seq

Plastic waste management has become a global issue. Polyethylene (PE) is the most abundant synthetic plastic worldwide, and one of the most resistant to biodegradation. Indeed, few bacteria can degrade polyethylene. In this paper, the transcriptomic analysis unveiled for the first time Rhodococcus opacus R7 complex genetic system based on diverse oxidoreductases for polyethylene biodegradation. The RNA-seq allowed uncovering genes putatively involved in the first step of oxidation. In-depth investigations through preliminary bioinformatic analyses and enzymatic assays on the supernatant of R7 grown in the presence of PE confirmed the activation of genes encoding laccase-like enzymes. Moreover, the transcriptomic data allowed identifying candidate genes for the further steps of short aliphatic chain oxidation including alkB gene encoding an alkane monooxygenase, cyp450 gene encoding cytochrome P450 hydroxylase, and genes encoding membrane transporters. The PE biodegradative system was also validated by FTIR analysis on R7 cells grown on polyethylene.

Assessment of the Decomposition of Oxo- and Biodegradable Packaging Using FTIR Spectroscopy

The strength and resistance of plastics at the end of their service life can hinder their degradation. The solution to this problem may be materials made of biodegradable and oxo-biodegradable plastics. The aim of this research was to determine the degree and nature of changes in the composition and structure of composted biodegradable and oxo-biodegradable bags. The research involved shopping bags and waste bags available on the Polish market. The composting of the samples was conducted in an industrial composting plant. As a result of the research, only some of the composted samples decomposed. After composting, all samples were analysed using FTIR (Fourier Transformation Infrared) spectroscopy. Carbonyl index and hierarchical cluster analysis method was used to detect similarities between the spectra of the new samples. The analysis of the obtained results showed that FTIR spectroscopy is a method that can be used to confirm the degradation and detect similarities in the structure of the analysed materials. The analysis of spectra obtained with the use of FTIR spectroscopy indicated the presence of compounds that may be a potential source of compost contamination. Plastics with certificates confirming their biodegradability and compostability should be completely biodegradable, i.e., each element used in their production should be biodegradable and safe for the environment.

Determinants of smallholder farmers' choice on mulch film thickness in rural China

Agricultural mulch film pollution has become a prevailing concern. Studies have shown that the thickness of mulch film is a key factor affecting mulch film recycling, but research about farmers' choice on mulch film thickness is lacking. Based on survey data from 2025 households in five Chinese provinces in 2018, the Heckman two-stage model was used to analyze the influencing factors of farmers' choice on mulch film thicknesses. Mulch film had been used by 21.98% of the sample households, and 41.47% of the used mulch film did not meet the national thickness standard. The econometric results showed that farmers' product cognition and market factors were the two most important factors, and there was a significant negative correlation with the choice of film thickness. In addition, the choice of mulch film with different thicknesses was affected by household characteristics, subjective norms, and farmland property rights. Strengthening and stabilizing farmland property rights is a long-term mechanism to promote farmers to choose thicker mulch film. In addition to strengthening the production and sale of substandard film supervision, farmers' choice of film thickness should be included in village regulations and other rural grass-roots governance systems, especially in the mechanism design between agricultural farmland protective subsidies and the prevention of mulch film pollution, rather than just considering the recycling itself.

Degradation of polyethylene plastic in soil and effects on microbial community composition

Plastics pollution in global soil systems is becoming a severely global issue and potential threat to terrestrial ecosystem serves and human health. Herein, in order to determine the degradability and ecological effects of polyethylene (PE) films, we measured the weight loss and characterization of PE films and analyzed variation in microbial community. The results of weight loss, SEM and FTIR spectra exhibited that PE films had unique degradation performance under different conditions. Simultaneously, we investigated the effects of PE films on the microbial community, and the microbiota colonizing on plastics. PE films may change the soil microbial community composition in soil, and hold the post of unique matrix for microbial colonization. These results indicate that the degradation of PE films and microbial community composition in soil can be affected by different conditions (soil layer, time and plants). By assessing the alteration of microbial community composition and PE films in soil, this work will contribute to enhance our understanding on the potential risks of plastics on soil ecosystems and provide a scientific basis for understanding the ecological effect of plastics on soil functions.

Investigation on the adsorption and desorption behaviors of heavy metals by tire wear particles with or without UV ageing processes

In recent years, tire wear particles (TWP), as the significant proportion of microplastics (MPs), has adsorbed much attention due to its widespread presence in aquatic ecosystem. Compared with typical MPs, TWP exists significant differences in composition, additives, characteristics and so on. With TWP and polypropylene (PP) as target MPs, Cd²⁺ and Pb²⁺ as target pollutants, the adsorption-desorption characteristics of heavy metal ions on original and aged MPs were studied. Compare with the PP, the S_BET of TWP increased more significantly after the UV ageing process. Meanwhile, the zeta potential of TWP increased from -8.01 to -14.6 mV and PP from -5.36 to -9.52 mV, and the surface of the TWP were more negatively-charged. In addition, the hydrophilicity of MPs enhanced due to the increased oxygen-containing functional groups after ageing process. Compared with PP, the physicochemical properties of TWP changed more obviously during UV ageing processes. The adsorption results showed that the pseudo-second-order model could better describe the adsorption processes of Cd²⁺ and Pb²⁺ on MPs. Meanwhile, the orders of adsorption capacity of MPs for Cd²⁺ and Pb²⁺ were aged TWP > aged PP > original TWP > original PP. The phenomenon of adsorption confirmed that TWP had better vector effects for heavy metal ions than PP, and the ageing processes could enhance the adsorption capacity of MPs. Moreover, the desorption results demonstrated that, compared with PP, the TWP (with higher adsorption capacity) also had the better desorption capacity for heavy metal ions in simulated gastric fluid. Compared with PP, the TWP might cause a more serious hazard to aquatic environment and organisms. These investigations would contribute to assessing the potential environmental and biological risk of TWP, especially considering the effect of the ageing process.

Preparation and characterization of an eco-friendly dust suppression and sand-fixation liquid mulching film

An eco-friendly dust suppression and sand-fixation liquid mulching film was prepared via a facile secondary spraying process in this work. Water polyurethane (WPU) was blended with dissolved humic acid (HA) firstly, and then the blend solutions (HWPU) were sprayed on the surface of cationic starch (CS) / sodium lignosulfonate (LS) film to synthesize the liquid mulching film (CLS-HWPU). The effects of liquid mulching film composition on mechanical properties in dry and wet states were investigated. The results showed that the optimal composition of liquid mulching film was: 3% (CS), 0.9 % (LS), 1.5 % (glycerol), 2% (HA), and 30 % (WPU). The CLS-HWPU liquid mulching films were characterized in terms of light transmittance, degradation performance test, contact angle test, scanning electron microscopy (SEM), total reflectance-Fourier transform infrared spectrometer (ATR-FTIR), thermo gravimetric analysis (TGA), and erosion resistance test. The results indicated that the CLS-HWPU film had good UV resistance, thermal stability, anti-erosion, and biodegradation. The CLS-HWPU film meets the demand of dust suppression and sand-fixation in dusty areas and desertification environments, which opens a new application field for liquid mulching film with high safety and environmental protection.

One-Step Synthesis of Eu3+-Modified Cellulose Acetate Film and Light Conversion Mechanism

A CA-Eu(III) complex was synthesized by the coordination reaction of cellulose acetate (CA) and Eu³⁺ to obtain a CA-Eu light conversion film. This product was then doped with Tb(III) to sensitize the luminescence of Eu³⁺, which could functionalize the CA film. FTIR and XPS showed that the oxygen atoms in C=O, C-O (O=C-O), and O-H were involved in the complexation with Eu³⁺ and formed a Eu-O bond. SEM revealed that Eu³⁺ filled in the pores of the CA film. By changing the experimental conditions, the best fluorescence performance was obtained at the CA: Eu³⁺ ratio of 3:1 with a reaction time of 65 min. The energy transfer between Tb³⁺-Eu³⁺ could be realized by doping Tb³⁺ to enhance the luminescence of Eu³⁺. The best fluorescence performance of the CA-Eu-Tb light conversion film was at a Eu³⁺:Tb³⁺ ratio of 3:1. Compared with the CA film, the light conversion film has high transparency, high tensile strength, and good flexibility. It can convert the ultraviolet light harmful to plants into red light that is beneficial to photosynthesis. This offers high efficiency and environmental protection in the field of agricultural films.

Greater Biofilm Formation and Increased Biodegradation of Polyethylene Film by a Microbial Consortium of Arthrobacter sp. and Streptomyces sp

The widespread use of polyethylene (PE) mulch films has led to a significant accumulation of plastic waste in agricultural soils. The biodegradation of plastic waste by microorganisms promises to provide a cost-effective and environmentally-friendly alternative for mitigating soil plastic pollution. A large number of microorganisms capable of degrading PE have been reported, but degradation may be further enhanced by the cooperative activity of multiple microbial species. Here, two novel strains of Arthrobacter sp. and Streptomyces sp. were isolated from agricultural soils and shown to grow with PE film as a sole carbon source. Arthrobacter sp. mainly grew in the suspension phase of the culture, and Streptomyces sp. formed substantial biofilms on the surface of the PE film, indicating that these strains were of different metabolic types and occupied different microenvironments with contrasting nutritional access. Individual strains were able to degrade the PE film to some extent in a 90-day inoculation experiment, as indicated by decreased hydrophobicity, increased carbonyl index and CO₂ evolution, and the formation of biofilms on the film surface. However, a consortium of both strains had a much greater effect on these degradation properties. Together, these results provide new insights into the mechanisms of PE biodegradation by a microbial consortium composed of different types of microbes with possible metabolic complementarities.

Benchmarking the Agronomic Performance of Biodegradable Mulches against Polyethylene Mulch Film: A Meta-Analysis

Growers are interested in biodegradable alternatives to petroleum-based polyethylene mulch film (PEM). However, many growers cite limited knowledge about biodegradable mulch films (BDMs) as a significant barrier to adoption. Agronomic field tests of BDMs are often limited temporally or spatially, and the variability of performance results relative to PEM may be contributing to this perceived knowledge gap. Our objective was to use data available in the scientific literature to provide the first quantitative performance benchmark of BDMs against PEM. We extracted data from 66 articles for meta-analysis. Response ratios were calculated for comparison of BDMs relative to black PEM, and differences among categorical groups were determined using 95% bootstrap confidence intervals. Overall, BDMs reduced soil temperature by 4.5% ± 0.8% (±one standard error) compared to PEM, and temperatures were coolest beneath paper-based BDM. Starch-polyester BDM was less effective than PEM for weed control, but paper-based BDM reduced weed density and biomass by 85.7% ± 9.2%. Paper-based BDMs were particularly useful for controlling Cyperus spp. weeds. Despite differences in soil temperature and weed suppression, crop yields were not different between BDMs and PEM. Future research should focus on reducing costs, adding functional value, and increasing the biodegradability of BDMs.