Effects comparison between the secondary nanoplastics released from biodegradable and conventional plastics on the transfer of antibiotic resistance genes between bacteria

Anaerobic Degradation of Aromatic and Aliphatic Biodegradable Plastics: Potential Mechanisms and Pathways

Biodegradable plastics (BDPs) have been widely used as substitutes for traditional plastics, and their environmental fate is a subject of intense research interest. Compared with the aerobic degradation of BDPs, their biodegradability under anaerobic conditions in environmental engineering systems remains poorly understood. This study aimed to investigate the degradability of BDPs composed of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactide acid) (PLA), and their blends, and explore the mechanism underlying their microbial degradation under conditions of anaerobic digestion (AD). The BDPs readily depolymerized under thermophilic conditions but were hydrolyzed at a slow rate under conditions of mesophilic AD. After 45 days of thermophilic AD, a decrease in the molecular weight and significant increase in the production of methane and carbon dioxide production were observed. Network and metagenomics analyses identified AD as reservoirs of plastic-degrading bacteria that produce multiple plastic-degrading enzymes. PETase was identified as the most abundant plastic-degrading enzyme. A potential pathway for the anaerobic biodegradation of BDPs was proposed herein. The polymers of high molecular weight were subjected to abiotic hydrolysis to form oligomers and monomers, enabling subsequent microbial hydrolysis and acetogenesis. Ultimately, complete degradation was achieved predominantly via the pathway involved in the conversion of acetic acid to methane. These findings provide novel insight into the mechanism underlying the anaerobic degradation of BDPs and the microbial resources crucial for the efficient degradation of BDPs.

Absence of synergistic effects between microplastics and copper ions on the spread of antibiotic resistance genes within aquatic bacteria at the community level

Microplastics and copper ions (Cu2+) are favorable in accelerating the propagation of antibiotic resistance genes (ARGs) in the plastisphere, however, their combined effects on the ARG spread within the bacterial community of the natural environment were less understood. The influence of microplastic types and Cu2+ concentrations on the horizontal gene transfer (HGT) of ARGs mediated by RP4 plasmid within natural bacterial communities in aquatic environments was investigated. Both biodegradable polybutylene succinate (PBS) and non-biodegradable polyvinyl chloride (PVC) microplastics significantly enhanced the transfer of ARGs, with PBS showing a significant higher effect compared to PVC. Cu2+ also increased transconjugation rates at environmentally relevant concentrations (5 μg L-1), but higher levels (50 μg L-1) lead to decreased rates due to severe bacterial cell membrane damage. The transconjugation rates in the presence of both microplastics and Cu2+ were lower than the sum of their individual effects, indicating no synergistic effects between them on transconjugation. Proteobacteria dominated the composition of transconjugates for all the treatment. Transmission electron microscope images and reactive oxygen species production in bacterial cells indicated that the increased contact frequency due to extracellular polymeric substances, combined with enhanced membrane permeability induced by microplastics and Cu2+, accounted for the increasing transconjugation rates. The study provides valuable insight into the potential effects of microplastics and heavy metals on the spread of ARGs from donors to bacterial communities in natural environments.

How micro-/nano-plastics influence the horizontal transfer of antibiotic resistance genes - A review

Plastic debris such as microplastics (MPs) and nanoplastics (NPTs), along with antibiotic resistance genes (ARGs), are pervasive in the environment and are recognized as significant global health and ecological concerns. Micro-/nano-plastics (MNPs) have been demonstrated to favor the spread of ARGs by enhancing the frequency of horizontal gene transfer (HGT) through various pathways. This paper comprehensively and systematically reviews the current study with focus on the influence of plastics on the HGT of ARGs. The critical role of MNPs in the HGT of ARGs has been well illustrated in sewage sludge, livestock farms, constructed wetlands and landfill leachate. A summary of the performed HGT assay and the underlying mechanism of plastic-mediated transfer of ARGs is presented in the paper. MNPs could facilitate or inhibit HGT of ARGs, and their effects depend on the type, size, and concentration. This review provides a comprehensive insight into the effects of MNPs on the HGT of ARGs, and offers suggestions for further study. Further research should attempt to develop a standard HGT assay and focus on investigating the impact of different plastics, including the oligomers they released, under real environmental conditions on the HGT of ARGs.

Unraveling the effect of micro/nanoplastics on the occurrence and horizontal transfer of environmental antibiotic resistance genes: Advances, mechanisms and future prospects

Microplastics can not only serve as vectors of antibiotic resistance genes (ARGs), but also they and even nanoplastics potentially affect the occurrence of ARGs in indigenous environmental microorganisms, which have aroused great concern for the development of antibiotic resistance. This article specifically reviews the effects of micro/nanoplastics (concentration, size, exposure time, chemical additives) and their interactions with other pollutants on environmental ARGs dissemination. The changes of horizontal genes transfer (HGT, i.e., conjugation, transformation and transduction) of ARGs caused by micro/nanoplastics were also summarized. Further, this review systematically sums up the mechanisms of micro/nanoplastics regulating HGT process of ARGs, including reactive oxygen species production, cell membrane permeability, transfer-related genes expression, extracellular polymeric substances production, and ARG donor-recipient adsorption/contaminants adsorption/biofilm formation. The underlying mechanisms in changes of bacterial communities induced by micro/nanoplastics were also discussed as it was an important factor for structuring the profile of ARGs in the actual environment, including causing environmental stress, providing carbon sources, forming biofilms, affecting pollutants distribution and environmental factors. This review contributes to a systematical understanding of the potential risks of antibiotic resistance dissemination caused by micro/nanoplastics and provokes thinking about perspectives for future research and the management of micro/nanoplastics and plastics.

Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Research advances on the toxicity of biodegradable plastics derived micro/nanoplastics in the environment: A review

The detrimental effects of plastic and microplastic accumulation on ecosystems are widely recognized and indisputable. The emergence of biodegradable plastics (BPs) offers a practical solution to plastic pollution. Problematically, however, not all BPs can be fully degraded in the environment. On the contrary, the scientific community has demonstrated that BPs are more likely than conventional plastics (CPs) to degrade into micro/nanoplastics and release additives, which can have similar or even worse effects than microplastics. However, there is very limited information available on the environmental toxicity assessment of BMPs. The absence of a toxicity evaluation system and the uncertainty regarding combined toxicity with other pollutants also impede the environmental toxicity assessment of BMPs. Currently, research is focused on thoroughly exploring the toxic effects of biodegradable microplastics (BMPs). This paper reviews the pollution status of BMPs in the environment, the degradation behavior of BPs and the influencing factors. This paper comprehensively summarizes the ecotoxicological effects of BPs on ecosystems, considering animals, plants, and microorganisms in various environments such as water bodies, soil, and sediment. The focus is on distinguishing between BMPs and conventional microplastics (CMPs). In addition, the combined toxic effects of BMPs and other pollutants are also being investigated. The findings suggest that BMPs may have different or more severe impacts on ecosystems. The rougher and more intricate surface of BMPs increases the likelihood of causing mechanical damage to organisms and breaking down into smaller plastic particles, releasing additives that lead to a series of cascading negative effects on related organisms and ecosystems. In the case of knowledge gaps, future research is also proposed and anticipated to investigate the toxic effects of BMPs and their evaluation.

Continuous generation and release of microplastics and nanoplastics from polystyrene by plastic-degrading marine bacteria

Plastic waste released into the environments breaks down into microplastics due to weathering, ultraviolet (UV) radiation, mechanical abrasion, and animal grazing. However, little is known about the plastic fragmentation mediated by microbial degradation. Marine plastic-degrading bacteria may have a double-edged effect in removing plastics. In this study, two ubiquitous marine bacteria, Alcanivorax xenomutans and Halomonas titanicae, were confirmed to degrade polystyrene (PS) and lead to microplastic and nanoplastic generation. Biodegradation occurred during bacterial growth with PS as the sole energy source, and the formation of carboxyl and carboxylic acid groups, decreased heat resistance, generation of PS metabolic intermediates in cultures, and plastic weight loss were observed. The generation of microplastics was dynamic alongside PS biodegradation. The size of the released microplastics gradually changed from microsized plastics on the first day (1344 nm and 1480 nm, respectively) to nanoplastics on the 30th day (614 nm and 496 nm, respectively) by the two tested strains. The peak release from PS films reached 6.29 × 106 particles/L and 7.64 × 106 particles/L from degradation by A. xenomutans (Day 10) and H. titanicae (Day 5), respectively. Quantification revealed that 1.3% and 1.9% of PS was retained in the form of micro- and nanoplastics, while 4.5% and 1.9% were mineralized by A. xenomutans and H. titanicae at the end of incubation, respectively. This highlights the negative effects of microbial degradation, which results in the continuous release of numerous microplastics, especially nanoplastics, as a notable secondary pollution into marine ecosystems. Their fates in the vast aquatic system and their impact on marine lives are noted for further study.

Selection for antimicrobial resistance in the plastisphere

Microplastics and antimicrobials are widespread contaminants that threaten global systems and frequently co-exist in the presence of human or animal pathogens. Whilst the impact of each of these contaminants has been studied in isolation, the influence of this co-occurrence in driving antimicrobial resistance (AMR)1 in microplastic-adhered microbial communities, known as 'the Plastisphere', is not well understood. This review proposes the mechanisms by which interactions between antimicrobials and microplastics may drive selection for AMR in the Plastisphere. These include: 1) increased rates of horizontal gene transfer in the Plastisphere compared with free-living counterparts and natural substrate controls due to the proximity of cells, co-occurrence of environmental microplastics with AMR selective compounds and the sequestering of extracellular antibiotic resistance genes in the biofilm matrix. 2) An elevated AMR selection pressure in the Plastisphere due to the adsorbing of AMR selective or co-selective compounds to microplastics at concentrations greater than those found in surrounding mediums and potentially those adsorbed to comparator particles. 3) AMR selection pressure may be further elevated in the Plastisphere due to the incorporation of antimicrobial or AMR co-selective chemicals in the plastic matrix during manufacture. Implications for both ecological functioning and environmental risk assessments are discussed, alongside recommendations for further research.

Incomplete degradation of aromatic-aliphatic copolymer leads to proliferation of microplastics and antibiotic resistance genes

Biodegradable plastics (BDPs) have attracted extensive attention as an alternative to conventional plastics. BDPs could be mineralized by composting, while the quality of compost affected by the presence of BDPs and the residual microplastics (MPs) has not been well evaluated. This study aimed to explore the MPs release potential and environmental implications of commercial BDPs (aromatic-aliphatic copolymer) films in uncontrolled composting. Results showed that the molecular weight of BDPs decreased by >60% within 60 d. However, the non-extracted organic matter and wet-sieving measurements indicated that MPs continuously released and accumulated during regular composting. The average MPs release potential (0.1-5 mm) was 134.6 ± 18.1 particles/mg (BDPs), which resulted in 103-104 particles/g dw in compost. The plastisphere of MPs showed a significantly higher (0.95-16.76 times) abundance of antibiotic resistance genes (ARGs), which resulted in the rising (1.34-2.24 times) of ARGs in compost heaps, in comparison to the control groups. Overall, BDPs promote the spread of ARGs through the selective enrichment of bacteria and horizontal transfer from released MPs. These findings confirmed that BDPs could enhance the release potential of MPs and the dissemination of ARGs, which would promote the holistic understanding and environmental risk of BDPs.

Microplastics exposure and immunologic response

OBJECTIVE

To assess the impact of microplastics (MPs) on human health.

DATA SOURCE

The authors conducted a non-systematic review of articles published in English, Portuguese, French, and Spanish in the last decade in the following databases: PubMed, Google Scholar, EMBASE, and SciELO. The keywords used were: microplastics OR nanoplastics OR marine litter OR toxicology OR additives AND human health OR children OR adults.

DATA SUMMARY

MPs are a group of emerging contaminants that have attracted scientific interest and societal attention in the last decade due to their ubiquitous detection in all environments. Humans can primarily be exposed to MPs and nanoplastics via oral and inhalation routes, but dermal contact cannot be overlooked, especially in young children. The possible toxic effects of plastic particles are due to their potential toxicity, often combined with that of leachable additives and adsorbed contaminants.

CONCLUSIONS

Unless the plastic value chain is transformed over the next two decades, the risks to species, marine ecosystems, climate, health, economy, and communities will be unmanageable. However, along with these risks are the unique opportunities to help transition to a more sustainable world.

Microcystins-Loaded Aged Nanoplastics Provoke a Metabolic Shift in Human Liver Cells

Studies concerning the toxicity of pollutant-loaded nanoplastics (NPs) toward humans are still in their infancy. Here, we evaluated the adsorption of microcystins (MCs) by pristine and aged polystyrene nanoplastics (PSNPs), prepared MCs-loaded aged PSNPS (1, 5, 10, 15, and 19 μg/mg), and systematically mapped the key molecular changes induced by aged and MCs-loaded PSNPs to human hepatoblastoma (HepG2) cells. According to the results, MC-LR adsorption is increased 2.64-fold by aging, and PSNP accumulation is detected in HepG2 cells. The cytotoxicity of the MC-LR-loaded aged PSNPs showed a positive relationship with the MC-LR amount, as the cell viability in the 19 μg/mg loading treatment (aPS-MC19) was 10.84% lower than aged PSNPs; meanwhile, more severe oxidative damage was observed. Primary approaches involved stressing the endoplasmic reticulum and reducing protein synthesis that the aged PSNPs posed for HepG2 cells, while the aggravated cytotoxicity in aPS-MC19 treatment was a combined result of the metabolic energy disorder, oxidative damage, endoplasmic reticulum stress, and downregulation of the MC-LR target protein. Our results confirm that the aged PSNPs could bring more MC-LR into the HepG2 cells, significantly interfere with biological processes, and provide new insight into deciphering the risk of NPs to humans.

Augmented dissemination of antibiotic resistance elicited by non-antibiotic factors

The emergence and rapid spread of antibiotic resistance seriously compromise the clinical efficacy of current antibiotic therapies, representing a serious public health threat worldwide. Generally, drug-susceptible bacteria can acquire antibiotic resistance through genetic mutation or gene transfer, among which horizontal gene transfer (HGT) plays a dominant role. It is widely acknowledged that the sub-inhibitory concentrations of antibiotics are the key drivers in promoting the transmission of antibiotic resistance. However, accumulating evidence in recent years has shown that in addition to antibiotics, non-antibiotics can also accelerate the horizontal transfer of antibiotic resistance genes (ARGs). Nevertheless, the roles and potential mechanisms of non-antibiotic factors in the transmission of ARGs remain largely underestimated. In this review, we depict the four pathways of HGT and their differences, including conjugation, transformation, transduction and vesiduction. We summarize non-antibiotic factors accounting for the enhanced horizontal transfer of ARGs and their underlying molecular mechanisms. Finally, we discuss the limitations and implications of current studies.

Oxidative stress and gene expression induced by biodegradable microplastics and imidacloprid in earthworms (Eisenia fetida) at environmentally relevant concentrations

The environmental issues caused by biodegradable microplastics (BMPs) from polylactic acid (PLA) as well as pesticides are of increasing concern nowadays. In this study, the toxicological effects of the single and combined exposure of PLA BMPs and imidacloprid (IMI), a neonicotinoid insecticide, on earthworms (Eisenia fetida) were investigated in terms of oxidative stress, DNA damage, and gene expression, respectively. The results showed that compared with the control, SOD, CAT and AChE activities in the single and combined treatments decreased significantly, and POD activity showed an "inhibition-activation" trend. SOD and CAT activities of combined treatments on day 28 and AChE activity of combined treatment on day 21 were significantly higher than those of the single treatments. For the rest of the exposure period, SOD, CAT and AChE activities in the combined treatments were lower than those in the single treatments. POD activity in the combined treatment was significantly lower than those of single treatments at day 7 and higher than that of single treatments at day 28. MDA content showed an "inhibition-activation-inhibition" trend, and the ROS level and 8-OHdG content increased significantly in both the single and combined treatments. This shows that both single and combined treatments led to oxidative stress and DNA damage. ANN and HSP70 were expressed abnormally, while the SOD and CAT mRNA expression changes were generally consistent with the corresponding enzyme activities. The integrated biomarker response (IBR) values were higher under combined exposures than single exposures at both biochemical and molecular levels, indicating that combined treatment exacerbated the toxicity. However, the IBR value of the combined treatment decreased consistently at the time axis. Overall, our results suggest that PLA BMPs and IMI induce oxidative stress and gene expression in earthworms at environmentally relevant concentrations, thereby increasing the risk of earthworms.