Plant growth-promoting bacteria improve the Cd phytoremediation efficiency of soils contaminated with PE-Cd complex pollution by influencing the rhizosphere microbiome of sorghum

Composite pollution by microplastics and heavy metals poses a potential threat to the soilplant system and has received increasing attention. Plant growth-promoting bacteria (PGPB) have good application potential for the remediation of combined microplastic and heavy metal pollution, but few related studies exist. The present study employed a pot experiment to investigate the effects of inoculation with the PGPB Bacillus sp. SL-413 and Enterobacter sp. VY-1 on sorghum growth and Cd accumulation under conditions of combined cadmium (Cd) and polyethylene (PE) pollution. Cd+PE composite contamination led to a significant reduction in sorghum length and biomass due to increased toxicity. Inoculation with Bacillus sp. SL-413 and Enterobacter sp. VY-1 alleviated the stress caused by Cd+PE complex pollution, and the dry weight of sorghum increased by 25.7% to 46.1% aboveground and by 12.3% to 45.3% belowground. Bacillus sp. SL-413 and Enterobacter sp. VY-1 inoculation increased the Cd content and accumulation in sorghum and improved the phytoremediation efficiency of Cd. The inoculation treatment effectively alleviated the nutrient stress caused by the reduction in soil mineral nutrients due to Cd+PE composite pollution. The composition of the soil bacterial communities was also affected by the Cd, Cd+PE and bacterial inoculation treatments, which affected the diversity of the soil bacterial communities. Network analyses indicated that bacterial inoculation regulated the interaction of rhizospheric microorganisms and increased the stability of soil bacterial communities. The Mantel test showed that the changes in the soil bacterial community and function due to inoculation with Bacillus sp. SL-413 and Enterobacter sp. VY-1 were important factors influencing sorghum growth and Cd remediation efficiency. The results of this study will provide new evidence for the research on joint plantmicrobe remediation of heavy metal and microplastic composite pollution.

Biochemical and transcriptomic responses of buckwheat to polyethylene microplastics

The ubiquity of microplastic is widely recognized as pollution. Microplastic can affect the growth performances of plants. Buckwheat is a potential model crop to investigate plant responses to hazardous materials. Still, little is known about the response of buckwheat to microplastics. Thus, this study investigated the effect and uptake of polyethylene (PE) in buckwheat plant growth by monitoring the morphological and photosynthetic merits, antioxidant systems and transcriptome analysis of gene expression. Results confirmed that the impacts of PE on buckwheat growth were dose-dependent, while the highest concentration (80 mg/L) exposure elicited significantly negative responses of buckwheat. PE can invade buckwheat roots and locate in the vascular tissues. PE exposure disturbed the processes of carbon fixation and the synthesis of ATP from ADP + Pi in buckwheat leaves. The promotion of photosynthesis under PE exposure could generate extra energy for buckwheat leaves to activate antioxidant systems by increasing the antioxidant enzyme activities at an expense of morphological merits under microplastic stresses. Further in-depth study is warranted about figuring out the interactions between microplastics and biochemical responses (i.e., photosynthesis and antioxidant systems), which have great implications for deciphering the defense mechanism of buckwheat to microplastic stresses.

Polyethylene degradation and heavy metals leaching under realistic tropical marine climate

The study examines the influence of temperature and pH on the leaching of six heavy metals (HMs) species: aluminum (Al), zinc (Zn), chromium (Cr), copper (Cu), lead (Pb) and arsenic (As) from transparent polyethylene pellets into seawater. The idea is to understand the potential influence of intensifying global warming and ocean acidification towards microplastic toxicity in the ocean. HMs leaching was obvious by 24th hours, with most HMs concentration decreased in water by 120th and 240th hours except Al. Nevertheless, we report that temperature and pH do not influence the overall HMs leaching from PE pellets with statistical analysis showing no significance (p < 0.05) between temperature and pH toward HMs concentration. Instead, it is hypothesized that these two parameters may be crucial in promoting heavy metal adsorption onto PE pellets under tropical weathering. However, Field Emission Scanning Electron Microscope (FESEM) revealed that temperature and pH are influential in polymer aging and surficial breakdown where pellets exposed in warm, acidic waters showed the greatest extent of weathering. This study highlights that PE pellets exposed under tropical conditions may accelerate surficial degradation and possibly stimulate HMs adherence to the polymer as a pollution vector. Further consideration of metal behaviour in water and microbial activities is crucial to improve our understanding of microplastic toxicity under tropical weathering.

Adsorption and desorption characteristics of heavy metals onto conventional and biodegradable plastics

Biodegradable plastics have been widely used to replace conventional plastics to minimize environmental impacts of plastic packaging. However, before biodegradable plastics decompose in the environment, they could pose a threat to terrestrial and aquatic creatures by acting as vectors of contaminants in the food chain. In this study, conventional plastic bags (CPBs) made of polyethylene and biodegradable plastic bags (BPBs) made of polylactic acid were examined for their heavy metal adsorption. Effects of solution pHs and temperatures on adsorption reactions were investigated. Because of a larger BET surface area, presence of oxygen-containing function groups, and smaller crystallinity, the heavy metal adsorption capacities of BPBs are significantly larger than those of CPBs. Among Cu (up to 791.48 mg⋅kg^-1), Ni (up to 60.88 mg⋅kg^-1), Pb (up to 1414.58 mg⋅kg^-1), and Zn (up to 295.17 mg⋅kg^-1), Pb and Ni show the largest and the lowest extents of adsorption onto the plastic bags, respectively. In the different waterbodies in nature, Pb adsorption on the CPBs and the BPBs were 318.08-379.91 and 528.41-764.22 mg⋅kg^-1, respectively. Consequently, Pb was selected as the target contaminant in the desorption experiments. After Pb was adsorbed onto the CPBs and the BPBs, Pb could be completely desorbed and released into simulated digestive systems in 10 h. In conclusion, BPBs could be potential vectors of heavy metals, and their suitability as a substitute for CPBs must be thoroughly investigated and confirmed.

Gravimetric analysis of stability of polymeric materials during exposure to chemical disinfectants at different temperatures

The goal of this study was to evaluate the impact of thermal and chemical aging processes on high-density polyethylene (HDPE), low-density polyethylene (LDPE), unplasticized polyvinyl chloride (U-PVC), and high-impact polyvinyl chloride (Hi-PVC) pipes. The materials were exposed to 1-10 ppm chemical disinfectants [chlorine dioxide (ClO₂) and hypochlorite (HOCl)] at 40-80 °C for 1200 h. The diffusion properties of the materials were systematically analyzed based on the change in their sorption characteristics and activation energies according to the Arrhenius model. Moreover, the structural changes were analyzed with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) radiation, and thermogravimetric analysis (TGA). The results show that the materials have Fickian characteristics in the aging environment. Specifically, the water sorption rates of HDPE and LDPE increase first and then decrease after reaching saturation (Ms); those of U-PVC and Hi-PVC its increasing continuously with different rate. This behavior of materials was prominent for ClO₂ at high temperature and disinfectant dose because of polymeric chains crosslinking and rearrangement, extraction of monomers, and stable compounds removal during aging under exposed conditions. The deleterious effects decreased the activation energies of the materials and increased the concentrations of carbonyl groups [CO] via the formation of ketones, aldehydes, and carboxylic acids. The decomposition temperature increased with the changes in the material morphology and elemental contents under the investigated conditions. Moreover, LDPE and Hi-PVC were more severely affected in the thermal aging process with 10 mg.L^-1 ClO₂ at 80 °C.

Stress response to oxytetracycline and microplastic-polyethylene in wheat (Triticum aestivum L.) during seed germination and seedling growth stages

Much efforts have been devoted to clarify the phytotoxicity of individual contaminants in plants, such as individual antibiotic and microplastic; however, little is known about the phytotoxicity of their combined exposure. Here, we investigated the effects of individual and combined exposure of wheat (Triticum aestivum L.) (Xiaoyan 22) to oxytetracycline (OTC) and polyethylene (PE) microplastics using physiological and metabolic profilings. During the seed germination stage, OTC induced phytotoxicity, as observed through the changes of root elongation, sprout length, fresh weight and the vitality index, with significant effect at the 50 and 150 mg·L^-1 levels; the effect of PE microplastics depended on the OTC level in the combined exposure groups. During seedling cultivation, catalase (CAT) and ascorbate peroxidase (APX), as antioxidant enzyme indices, were sensitive to OTC exposure stress, although OTC was not determined in leaves. Untargeted metabolomics of wheat leaves revealed OTC concentration-, metabolite class- and PE-dependent metabolic responses. Dominant metabolites included carboxylic acids, alcohols, and amines in the control group and all treatment groups. Compared to only OTC treatment, PE reprogrammed carboxylic acid and alcohol profiles in combined exposure groups with obvious separation in PLS-DA. Combined exposure induced fewer metabolites than OTC exposure alone at the 5 and 50 mg·L^-1 levels. The shared metabolite numbers were higher in the OTC groups than in the PE-OTC groups. Pathway enrichment analysis showed a drift in metabolic pathways between individual and combined exposure to OTC and PE, which included glyoxylate and dicarboxylate metabolism, amino acid metabolism and isoquinoline alkaloid biosynthesis. Among metabolites, aromatic acids and amino acids were more sensitive to combined exposure than individual exposure. These results contribute to clarifying the underlying mechanisms of phytotoxicity of individual and combined exposure to OTC and PE.

Adsorption behavior and mechanism of five pesticides on microplastics from agricultural polyethylene films

Polyethylene (PE) agricultural soil films are easily embrittled and decomposed to microplastics (MPs) in environment. As widely used pesticides in vegetable farmland, carbendazim, dipterex, diflubenzuron, malathion, difenoconazole have potential environmental and human safety risks. They are often coexisting with MPs in the environment, and may cause consequential pollution to the ecosystem. Studying the adsorption behavior between pesticides and PE agricultural soil films MPs would be helpful for the risk assessment of co-exposure of pesticides and MPs. Herein, a systematic study on batch adsorption experiments was performed to determine the adsorption process of pesticides on MPs, the environmental factors on adsorption capacity were evaluated, and the adsorption mechanisms were discussed. Results suggested that all these five pesticides can adsorb on MPs, especially for diflubenzuron and difenoconazole. The adsorption kinetics and isotherm fitted to the Pseudo-second-order and Freundlich model, respectively, indicating that besides the adsorption onto surface sites, mass transfer and intraparticle diffusion were involved in the adsorption process, and the adsorption process was mostly controlled by physical and chemical interactions. The adsorption amounts of 5 pesticides on PE MPs follow the order of DIF > DIFE > MAL > CAR > DIP with K_F correlated positively with octanol-water partition coefficients (LogK_ow). The thermodynamic study indicates the adsorption of all pesticides as spontaneous and exothermic processes. The results of this study illustrated that PE MPs can be a good carrier of pesticides in agricultural field.

Biodegradation of mixture of plastic films by tailored marine consortia

This work sheds light on the physicochemical changes of naturally weathered polymer surfaces along with changes of polymer buoyancy due to biofilm formation and degradation processes. To support the degradation hypothesis, a microcosm experiment was conducted where a mixture of naturally weathered plastic pieces was incubated with an indigenous pelagic community. A series of analyses were employed in order to describe the alteration of the physicochemical characteristics of the polymer (FTIR, SEC and GPC, sinking velocity) as well as the biofilm community (NGS). At the end of phase II, the fraction of double bonds in the surface of microbially treated PE films increased while changes were also observed in the profile of the PS films. The molecular weight of PE pieces increased with incubation time reaching the molecular weight of the virgin pieces (230,000 g mol^-1) at month 5 but the buoyancy displayed no difference throughout the experimental period. The number-average molecular weight of PS pieces decreased (33% and 27% in INDG and BIOG treatment respectively), implying chain scission; accelerated (by more than 30%) sinking velocities compared to the initial weathered pieces were also measured for PS films with biofilm on their surface. The orders Rhodobacterales, Oceanospirillales and Burkholderiales dominated the distinct platisphere communities and the genera Bacillus and Pseudonocardia discriminate these assemblages from the planktonic counterpart. The functional analysis predicts overrepresentation of adhesive cells carrying xenobiotic and hydrocarbon degradation genes. Taking these into account, we can suggest that tailored marine consortia have the ability to thrive in the presence of mixtures of plastics and participate in their degradation.

Curcumin Inhibits Polyethylene-Induced Osteolysis via Repressing NF-κB Signaling Pathway Activation

BACKGROUND/AIMS

Aseptic loosening is a common reason for failed artificial hip replacement after total hip arthroplasty. Aseptic loosening is mostly the result of wear debris that causes osteolysis and weakens the structures that support the prosthesis. Wear debris plays a crucial role in osteolysis during the loosening process, and polyethylene (PE) particles are found as wear debris more frequently than any other type of particle. In the absence of effective therapeutic agents, osteolysis has been hard to treat. Previous studies have demonstrated that curcumin influences signalosome-associated kinases and the proteasome-ubiquitin system during osteoclastogenesis. The aims of this study were to explore the anti-osteolysis effect of curcumin and if possible to identify the signaling pathway involved in a model of PE-induced osteolysis.

METHODS

Differentiation of osteoclasts was induced in vitro by PE particles in RAW264.7 (monocyte/macrophage) cells and in vivo by calvarial and air pouch models of osteolysis established by PE stimulation in mice. We performed a set of TRAP staining, realtime polymerase chain reaction (PCR), and Western blot experiments to evaluate the anti-osteolytic effect of curcumin by comparing specimens that were exposed and not exposed to curcumin.

RESULTS

Curcumin had a promising inhibitory effect on osteolysis induced by wear debris and suppressed the RANK/c-Fos/NFATc1 signaling pathway.

CONCLUSION

Curcumin can prevent PE-induced osteolysis and bone loss. An inhibitory effect on the RANK/c-Fos/NFATc1 signaling pathway may explain the anti-osteolysis activity of curcumin.

Characterization and inventory of PBDD/F emissions from deca-BDE, polyethylene (PE) and metal blends during the pyrolysis process

The thermal treatment of waste electrical and electronic equipment (WEEE) is regarded as the largest potential contributor to the environmental release of polybrominated dibenzo-p-dioxins/dibenzofurans (PBDD/Fs). Herein, the pyrolysis of decabromodiphenyl ether (deca-BDE), polyethylene (PE) and metal blends was conducted to investigate the emission characteristics of PBDD/Fs at different thermal treatment conditions. The total yield of polybrominated dibenzo-p-dioxins (PBDDs) was less than that of polybrominated dibenzofurans (PBDFs) during the pyrolysis of the PE matrix and metal blends. 2,3,7,8-TBDF and 1,2,3,7,8-PBDF were the dominant congeners emitted from the pyrolysis. Temperature, presence of oxygen and type of added metal were the critical influencing factors for the PBDD/F formation rates and speciation in the pyrolysis process.

Supramacroparticulate PE in 6 different joint endoprostheses localisations: An indicator for PE damage?

In the histopathological particle algorithm polyethylene (PE) particles with maximum lengths of more than 100μm - called PE supramacroparticles - are identified exclusively for knee joint and hip prostheses. However, a definitive characterisation, detection in all joint localisations and a causal clarification of the pathogenesis are lacking. In this study a total of 175 SLIM (synovial-like interface membrane) cases with PE supramacroparticles of knee joint prostheses (n=89), hip joint prostheses (n=44), ankle joint prostheses (n=36) and prostheses in three localisations of the upper extremities (n=6) were systematically investigated. The arithmetic mean of the particle length varied greatly within the prosthesis types. This had a significant positive correlation with the prosthesis lifetime and negative correlation with the date of implantation. It can be concluded that both the lifetime and the time of implantation have an influence on the particle length. The prostheses with supramacroparticulate damage moreover showed a clearly reduced survival rate compared with other data published on the prosthesis lifetime. The material wear therefore could not be attributed solely to the usual fatigue factors. Since loosening of the prostheses, decentring of the PE components or damage to the PE inlay existed in all cases, mechanical dysloading seems to be the most probable cause of PE supramacroparticle genesis. Due to the striking length and for demarcation from PE macroparticles, the term supramacroparticulate PE is proposed for a length of more than 100μm. In the extended histopathological particle algorithm supramacroparticulate PE has been included in the macroparticles category and should be taken into account and interpreted causally in histopathological diagnostics of joint prosthesis failure.

Long-term aging and degradation of microplastic particles: Comparing in situ oceanic and experimental weathering patterns

Polypropylene, low-density polyethylene, and high-density polyethylene pre-production plastic pellets were weathered for three years in three experimental treatments: dry/sunlight, seawater/sunlight, and seawater/darkness. Changes in chemical bond structures (hydroxyl, carbonyl groups and carbon-oxygen) with weathering were measured via Fourier Transform Infrared (FTIR) spectroscopy. These indices from experimentally weathered particles were compared to microplastic particles collected from oceanic surface waters in the California Current, the North Pacific Subtropical Gyre, and the transition region between the two, in order to estimate the exposure time of the oceanic plastics. Although chemical bonds exhibited some nonlinear changes with environmental exposure, they can potentially approximate the weathering time of some plastics, especially high-density polyethylene. The majority of the North Pacific Subtropical Gyre polyethylene particles we measured have inferred exposure times>18months, with some >30months. Inferred particle weathering times are consistent with ocean circulation models suggesting a long residence time in the open ocean.

Enhanced adherence of mouse fibroblast and vascular cells to plasma modified polyethylene

Since the last decade, tissue engineering has shown a sensational promise in providing more viable alternatives to surgical procedures for harvested tissues, implants and prostheses. Biomedical polymers, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE), were activated by Ar plasma discharge. Degradation of polymer chains was examined by determination of the thickness of ablated layer. The amount of an ablated polymer layer was measured by gravimetry. Contact angle, measured by goniometry, was studied as a function of plasma exposure and post-exposure aging times. Chemical structure of modified polymers was characterized by angle resolved X-ray photoelectron spectroscopy. Surface chemistry and polarity of the samples were investigated by electrokinetic analysis. Changes in surface morphology were followed using atomic force microscopy. Cytocompatibility of plasma activated polyethylene foils was studied using two distinct model cell lines; VSMCs (vascular smooth muscle cells) as a model for vascular graft testing and connective tissue cells L929 (mouse fibroblasts) approved for standardized material cytotoxicity testing. Specifically, the cell number, morphology, and metabolic activity of the adhered and proliferated cells on the polyethylene matrices were studied in vitro. It was found that the plasma treatment caused ablation of the polymers, resulting in dramatic changes in their surface morphology and roughness. ARXPS and electrokinetic measurements revealed oxidation of the polymer surface. It was found that plasma activation has a positive effect on the adhesion and proliferation of VSMCs and L929 cells.

TG/FTIR analysis on co-pyrolysis behavior of PE, PVC and PS

The pyrolysis and co-pyrolysis behaviors of polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) under N2 atmosphere were analyzed by Thermal gravimetric/Fourier transform infrared (TG/FTIR). The volatile products were analyzed to investigate the interaction of the plastic blends during the thermal decomposition process. The TGA results showed that the thermal stability increased followed by PVC, PS and PE. The pyrolysis process of PE was enhanced when mixed with PS. However, PS was postponed when mixed with PVC. As for PE and PVC, mutual block was happened when mixed together. The FTIR results showed that the free radical of the decomposition could combine into a stable compound. When PE mixed with PVC or PS, large amount of unsaturated hydrocarbon groups existed in products while the content of alkynes was decreased. The methyl (-CH3) and methylene (-CH2-) bonds were disappeared while PVC mixed with PE.