A functional gene-array analysis of microbial communities settling on microplastics in a peat-draining environment

Microbial Ecotoxicology-40 Years on

Although ecotoxicology was emerging as a field through the 1970s, the incorporation of microbial indicators into the framework has been slower to evolve. The exploration of microbes as sensitive toxicity tests began in the late 70s and early 80s (with the emergence of Microtox® and other simple tests). However, the applications have been limited, beyond water and wastewater screening. This opinion piece reflects my own perspective on the field-from my early excitement in the 1990s for its possibilities, to a sense of frustration at the slow pace of new development and applications in the field-despite the surge of "omics" options. While microbiology still fails to lead the field of ecotoxicology, the potential remains.

Compounding one problem with another? A look at biodegradable microplastics

Environmental concerns about microplastics (MPs) have motivated research of their sources, occurrence, and fate in aquatic and soil ecosystems. To mitigate the environmental impact of MPs, biodegradable plastics are designed to naturally decompose, thus reducing the amount of environmental plastic contamination. However, the environmental fate of biodegradable plastics and the products of their incomplete biodegradation, especially micro-biodegradable plastics (MBPs), remains largely unexplored. This comprehensive review aims to assess the risks of unintended consequences associated with the introduction of biodegradable plastics into the environment, namely, whether the incomplete mineralization of biodegradable plastics could enhance the risk of MBPs formation and thus, exacerbate the problem of their environmental dispersion, representing a potentially additional environmental hazard due to their presumed ecotoxicity. Initial evidence points towards the potential for incomplete mineralization of biodegradable plastics under both controlled and uncontrolled conditions. Rapid degradation of PLA in thermophilic industrial composting contrasts with the degradation below 50 % of other biodegradables, suggesting MBPs released into the environment through compost. Moreover, degradation rates of <60 % in anaerobic digestion for polymers other than PLA and PHAs suggest a heightened risk of MBPs in digestate, risking their spread into soil and water. This could increase MBPs and adsorbed pollutants' mobilization. The exact behavior and impacts of additive leachates from faster-degrading plastics remain largely unknown. Thus, assessing the environmental fate and impacts of MBPs-laden by-products like compost or digestate is crucial. Moreover, the ecotoxicological consequences of shifting from conventional plastics to biodegradable ones are highly uncertain, as there is insufficient evidence to claim that MBPs have a milder effect on ecosystem health. Indeed, literature shows that the impact may be worse depending on the exposed species, polymer type, and the ecosystem complexity.

Response of microbial communities and biogeochemical cycling functions to sediment physicochemical properties and microplastic pollution under damming and water diversion projects

Understanding the interactions among flow-sediment, microorganisms, and biogeochemical cycles is crucial for comprehending the ecological response mechanisms of dams and water diversion. This study focused on the spatial patterns of carbon, nitrogen, phosphorus, and sulfur (CNPS) cycle functional genes in the water resource for the middle route of the South-to-North Water Diversion Project in China, specifically the Danjiangkou Reservoir (comprising the Han and Dan reservoirs). The investigation incorporated sediment physicochemical properties and microplastic pollution. Numerous microbial species were identified, revealing that microbial communities demonstrated sensitivity to changes in sedimentary mud content. The communities exhibited greater β diversity due to finer sediment particles in the Han Reservoir (HR), whereas in the Dan Reservoir (DR), despite having higher sediment nutrient content and MPs pollution, did not display this pattern. Regarding the composition and structure of microbial communities, the study highlighted that sediment N and P content had a more significant influence compared to particle size and MPs. The quantitative microbial element cycling (QMEC) results confirmed the presence of extensive chemolithotrophic microbes and strong nitrogen cycle activity stemming from long-term water storage and diversion operations. The denitrification intensity in the HR surpassed that of the DR. Notably, near the pre-dam area, biological nitrogen fixation, phosphorus removal, and sulfur reduction exhibited noticeable increases. Dam construction refined sediment, fostering the growth of different biogeochemical cycling bacteria and increasing the abundance of CNPS cycling genes. Furthermore, the presence of MPs exhibited a positive correlation with S cycling genes and a negative correlation with C and N cycling genes. These findings suggest that variations in flow-sediment dynamics and MPs pollution have significant impact the biogeochemical cycle of the reservoir.

Microplastics supply contaminants in food chain: non-negligible threat to health safety

The occurrence of microplastics (MPs) and organic pollutants (OPs) residues is commonly observed in diverse environmental settings, where their interactions can potentially alter the behavior, availability, and toxicity of OPs, thereby posing risks to ecosystems. Herein, we particularly emphasize the potential for bioaccumulation and the biomagnification effect of MPs in the presence of OPs within the food chain. Despite the ongoing influx of novel information, there exists a dearth of data concerning the destiny and consequences of MPs in the context of food pollution. Further endeavors are imperative to unravel the destiny and repercussions of MPs/OPs within food ecosystems and processing procedures, aiming to gain a deeper understanding of the joint effect on human health and food quality. Nevertheless, the adsorption and desorption behavior of coexisting pollutants can be significantly influenced by MPs forming biofilms within real-world environments, including temperature, pH, and food constituents. A considerable portion of MPs tend to accumulate in the epidermis of vegetables and fruits, thus necessitating further research to comprehend the potential ramifications of MPs on the infiltration behavior of OPs on agricultural product surfaces.

Groundwater systems under siege: The silent invasion of microplastics and cock-tails worldwide

Microplastics (MPs) contamination is one of the significant escalating environmental concerns worldwide, and this stems from the increasing production and unlawful disposal of plastic materials. Regretfully, the synthesis of plastic materials is expected to triple in the upcoming years. Nevertheless, MPs pollution in marine, aquatic, and terrestrial settings has received much attention, unlike in groundwater systems. This study exhaustively reviewed varying degrees of recent publications in various search engines and provided a detailed state of current knowledge and research progress vis-à-vis MPs and cock-tail pollution in groundwater systems. Evidently, groundwater sources are severely contaminated as a result of growing anthropogenic activities and vertical movement of MPs and cock-tails from the atmospheric, terrestrial, and aquatic environments, however, fewer researchers have fixated their attention on estimating the occurrence of MPs in groundwater resources, while sufficient information regarding their sources, sampling methods, abundance, transport pathways, fate, modeling techniques, appropriate and adequate data, sorption properties, separation from other environmental media, toxicity, and remedial measures are extensively lacking. In addition, MPs may combine with other toxic emerging contaminants to improve migration and toxicity; however, no research has been conducted to fully understand cock-tail migration mechanisms and impacts in groundwater systems. Over time, groundwater may be regarded as the primary sink for MPs, if effective actions are neglected. Overall, this study detected a lack of concern and innumerable voids in this field; hence, vital and nascent research gaps were identified for immediate, advanced, and interdisciplinary research investigations.

Evidence of interspecific plasmid uptake by pathogenic strains of Klebsiella isolated from microplastic pollution on public beaches

Microplastic beads are becoming a common feature on beaches, and there is increasing evidence that such microplastics can become colonised by potential human pathogens. However, whether the concentrations and pathogenicity of these pathogens pose a public health risk are still unclear. Therefore, the aim of this study was to determine realistic environmental concentrations of potential pathogens colonising microplastic beads, and quantify the expression of virulence and antimicrobial resistance genes (ARGs). Microplastic beads were collected from beaches and a culture-dependent approach was used to determine the concentrations of seven target bacteria (Campylobacter spp.; E. coli; intestinal enterococci; Klebsiella spp.; Pseudomonas aeruginosa; Salmonella spp.; Vibrio spp.). All seven target bacteria were detected without the need for a pre-enrichment step; urban sites had higher bacterial concentrations, whilst polymer type had no influence on bacterial concentrations. Klebsiella was the most abundant target bacteria and possessed virulence and ARGs, some of which were present on plasmids from other species, and showed pathogenicity in a Galleria melonella infection model. Our findings demonstrate how pathogen colonised microplastic beads can pose a heightened public health risk at the beach, and highlights the urgency for improved monitoring and enforcement of regulations on the release of microplastics into the environment.

Plastisphere microbiome: Methodology, diversity, and functionality

Broad topics of the plastisphere in various environments are reviewed, including its methodologies, diversity, functionality, and outlook.

Comparison of learning models to predict LDPE, PET, and ABS concentrations in beach sediment based on spectral reflectance

Microplastic (MP) contamination on land has been estimated to be 32 times higher than in the oceans, and yet there is a distinct lack of research on soil MPs compared to marine MPs. Beaches are bridges between land and ocean and present equally understudied sites of microplastic pollution. Visible-near-infrared (vis-NIR) has been applied successfully for the measurement of reflectance and prediction of low-density polyethylene (LDPE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) concentrations in soil. The rapidity and precision associated with this method make vis-NIR promising. The present study explores PCA regression and machine learning approaches for developing learning models. First, using a spectroradiometer, the spectral reflectance data was measured from treated beach sediment spiked with virgin microplastic pellets [LDPE, PET, and acrylonitrile butadiene styrene (ABS)]. Using the recorded spectral data, predictive models were developed for each microplastic using both the approaches. Both approaches generated models of good accuracy with R² values greater than 0.7, root mean squared error (RMSE) values less than 3 and mean absolute error (MAE) < 2.2. Therefore, using this study's method, it is possible to rapidly develop accurate predictive models without the need of comprehensive sample preparation, using the low-cost option ASD HandHeld 2 VNIR Spectroradiometer.

Stable Isotopic and Metagenomic Analyses Reveal Microbial-Mediated Effects of Microplastics on Sulfur Cycling in Coastal Sediments

Microplastics are readily accumulated in coastal sediments, where active sulfur (S) cycling takes place. However, the effects of microplastics on S cycling in coastal sediments and their underlying mechanisms remain poorly understood. In this study, the transformation patterns of different S species in mangrove sediments amended with different microplastics and their associated microbial communities were investigated using stable isotopic analysis and metagenomic sequencing. Biodegradable poly(lactic acid) (PLA) microplastics treatment increased sulfate (SO₄^2-) reduction to yield more acid-volatile S and elementary S, which were subsequently transformed to chromium-reducible S (CRS). The S isotope fractionation between SO₄^2- and CRS in PLA treatment increased by 9.1‰ from days 0 to 20, which was greater than 6.8‰ in the control. In contrast, recalcitrant petroleum-based poly(ethylene terephthalate) (PET) and polyvinyl chloride (PVC) microplastics had less impact on the sulfate reduction, resulting in 7.6 and 7.7‰ of S isotope fractionation between SO₄^2- and CRS from days 0 to 20, respectively. The pronounced S isotope fractionation in PLA treatment was associated with increased relative abundance of Desulfovibrio-related sulfate-reducing bacteria, which contributed a large proportion of the microbial genes responsible for dissimilatory sulfate reduction. Overall, these findings provide insights into the potential impacts of microplastics exposure on the biogeochemical S cycle in coastal sediments.

Priorities to inform research on marine plastic pollution in Southeast Asia

Southeast Asia is considered to have some of the highest levels of marine plastic pollution in the world. It is therefore vitally important to increase our understanding of the impacts and risks of plastic pollution to marine ecosystems and the essential services they provide to support the development of mitigation measures in the region. An interdisciplinary, international network of experts (Australia, Indonesia, Ireland, Malaysia, the Philippines, Singapore, Thailand, the United Kingdom, and Vietnam) set a research agenda for marine plastic pollution in the region, synthesizing current knowledge and highlighting areas for further research in Southeast Asia. Using an inductive method, 21 research questions emerged under five non-predefined key themes, grouping them according to which: (1) characterise marine plastic pollution in Southeast Asia; (2) explore its movement and fate across the region; (3) describe the biological and chemical modifications marine plastic pollution undergoes; (4) detail its environmental, social, and economic impacts; and, finally, (5) target regional policies and possible solutions. Questions relating to these research priority areas highlight the importance of better understanding the fate of marine plastic pollution, its degradation, and the impacts and risks it can generate across communities and different ecosystem services. Knowledge of these aspects will help support actions which currently suffer from transboundary problems, lack of responsibility, and inaction to tackle the issue from its point source in the region. Being profoundly affected by marine plastic pollution, Southeast Asian countries provide an opportunity to test the effectiveness of innovative and socially inclusive changes in marine plastic governance, as well as both high and low-tech solutions, which can offer insights and actionable models to the rest of the world.

Critical review of microplastics removal from the environment

Globally, microplastics pollution has become a serious environmental threat due to their multitude sources, widespread occurrence, persistence, and adverse effects to ecosystem and the human health. Addressing this multifaceted threat requires innovative technologies that can efficiently remove microplastics from the environment. In this review, we first overviewed the source, occurrence, and potential adverse impacts of microplastics to human health. We then identified promising technologies for microplastics removal, including physical, chemical, and biological approaches. A detailed analysis of the advantages and limitations of different techniques was provided. We concluded this review with the current challenges and future research priorities, which will guide us through the path addressing microplastics contamination.

The structure and assembly mechanisms of plastisphere microbial community in natural marine environment

The microbial colonization profiles on microplastics (MPs) in marine environments have recently sparked global interest. However, many studies have characterized plastisphere microbiomes without considering the ecological processes that underly microbiome assembly. Here, we carried out a three-timepoint exposure experiment at 1-, 4-, and 8-week and investigated the colonization dynamics for polyethylene, polypropylene, polystyrene, polyvinyl chloride, and acrylonitrile-butadiene-styrene MP pellets in natural coastal water. Using high-throughput sequencing of 16S rRNA, we found diversity and evenness were higher (p < 0.05) in the plastisphere communities than those in seawater, and microorganisms colonizing were co-influenced by environmental factors, polymer types, and exposure duration. Functional potential and co-occurrence network analysis revealed that MP exposure enriched the xenobiotic biodegradation potential and reduced the complexity of the MP microbial network. Simultaneously, null-model analyses indicated that stochastic processes contributed a bigger role than deterministic processes in shaping plastisphere microbial community structure with dispersal limitations contributing to a greater extent to microbial succession trajectories. These results implied the plastic surface had a more important role as a raft onto which microbes attach rather than selectively recruiting plastic-specific microbial colonizers. Our work strengthened the understanding of the ecological mechanisms by which microbial community patterns are controlled during colonization by plastic-associated microbes.