Recent advances in biodegradation of emerging contaminants - microplastics (MPs): Feasibility, mechanism, and future prospects

PM10-bound microplastics and trace metals: A public health insight from the Korean subway and indoor environments

Inhalable airborne microplastics (MPs) presented in indoor and outdoor environments, can deeply penetrate the lungs, potentially triggering inflammation and respiratory illnesses. The present study aims to evaluate human health risks from respirable particulate matter (PM)-bound trace metals and MPs in indoor (SW- subway and IRH- indoor residential houses) and outdoor (OD) environments. This research provides an initial approach to human respiratory tract (HRT) mass depositions of PM10-bound total MPs and nine specific MP types to predict potential human health threats from inhalation exposure. Results indicate that PM-bound trace metals and MPs were around 4 times higher in SW microenvironments compared to OD locations. In IRH, cancer risk (CR) levels were estimated 9 and 4 times higher for PM10 and PM2.5, respectively. Additionally, MP particle depositions per gram of lung cell weight were highest in IRH (23.77), followed by OD and SW. Whereas, lifetime alveoli depositions of MPs were estimated at 13.73 MP/g, which exceeds previously reported respiratory disease fatality cases by 10 to 5 times. Prolonged exposure duration at IRH emerged as a key factor contributing to increased CR and MP lung deposition levels. This research highlights severe lung risks from inhaling PM-bound MPs and metals, offering valuable health insights.

Emerging hazardous chemicals and biological pollutants in Canadian aquatic systems and remediation approaches: A comprehensive status report

Emerging contaminants can be natural or synthetic materials, as well as materials of a chemical, or biological origin; these materials are typically not controlled or monitored in the environment. Canada is home to nearly 7 % of the world's renewable water supply and a wide range of different kinds of water systems, including the Great Lake, rivers, canals, gulfs, and estuaries. Although the majority of these pollutants are present in trace amounts (μg/L - ng/L concentrations), several studies have reported their detrimental impact on both human health and the biota. In Canadian aquatic environments, concentrations of pharmaceuticals (as high as 115 μg/L), pesticides (as high as 1.95 μg/L), bioavailable heavy metals like dissolved mercury (as high as 135 ng/L), and hydrocarbon/crude oil spills (as high as 4.5 million liters) have been documented. Biological threats such as genetic materials of the contagious SARS-CoV-2 virus have been reported in the provinces of Québec, Ontario, Saskatchewan and Manitoba provinces, as well as in the Nunavut territory, with a need for more holistic research. These toxins and emerging pollutants are associated with nefarious short and long-term health effects, with the potential for bioaccumulation in the environment. Hence, this Canadian-focused report provides the footprints for water and environmental sustainability, in light of this emerging threat to the environment and society. Several remediation pathways/tools that have been explored by Canadian researchers, existing challenges and prospects are also discussed. The review concludes with preventive measures and strategies for managing the inventory of emerging contaminants in the environment.

Critical review on unveiling the toxic and recalcitrant effects of microplastics in aquatic ecosystems and their degradation by microbes

Production of synthetic plastic obtained from fossil fuels are considered as a constantly growing problem and lack in the management of plastic waste has led to severe microplastic pollution in the aquatic ecosystem. Plastic particles less than 5mm are termed as microplastics (MPs), these are pervasive in water and soil, it can also withstand longer period of time with high durability. It can be broken down into smaller particles and can be adsorbed by various life-forms. Most marine organisms tend to consume plastic debris that can be accumulated easily into the vertebrates, invertebrates and planktonic entities. Often these plastic particles surpass the food chain, resulting in the damage of various organs and inhibiting the uptake of food due to the accumulation of microplastics. In this review, the physical and chemical properties of microplastics, as well as their effects on the environment and toxicity of their chemical constituents are discussed. In addition, the paper also sheds light on the potential of microorganisms such as bacteria, fungi, and algae which play a pivotal role in the process of microplastics degradation. The mechanism of microbial degradation, the factors that affect degradation, and the current advancements in genetic and metabolic engineering of microbes to promote degradation are also summarized. The paper also provides information on the bacterial, algal and fungal degradation mechanism including the possible enzymes involved in microplastic degradation. It also investigates the difficulties, limitations, and potential developments that may occur in the field of microbial microplastic degradation.

Nano/micro-plastic, an invisible threat getting into the brain

Due to weather and working/operational conditions, plastic degradation produces toxic and non-biodegradable nano and microplastics (N/M-Ps, ranging from 10 nm to 5 mm), and over time these N/M-Ps have integrated with the human cycle through ingestion and inhalation. These N/M-Ps, as serious emerging pollutants, are causing considerable adverse health issues due to up-taken by the cells, tissue, and organs, including the brain. It has been proven that N/M-Ps can cross the blood-brain barrier (via olfactory and blood vessels) and affect the secretion of neuroinflammatory (cytokine and chemokine), transporters, and receptor markers. Neurotoxicity, neuroinflammation, and brain injury, which may result in such scenarios are a serious concern and may cause brain disorders. However, the related pathways and pathogenesis are not well-explored but are the focus of upcoming emerging research. Therefore, as a focus of this editorial, well-organized multidisciplinary research is required to explore associated pathways and pathogenesis, leading to brain mapping and nano-enabled therapeutics in acute and chronic N/M - Ps exposure.

Tapping into fungal potential: Biodegradation of plastic and rubber by potent Fungi

Plastic polymers are present in most aspects of routine daily life. Their increasing leakage into the environment poses a threat to environmental, animal, and human health. These polymers are often resistant to microbial degradation and are predicted to remain in the environment for tens to hundreds of years. Fungi have been shown to degrade complex polymers and are considered good candidates for bioremediation (biological pollutant reduction) of plastics. Therefore, we screened 18 selected fungal strains for their ability to degrade polyurethane (PU), polyethylene (PE), and tire rubber. As a proxy for plastic polymer mineralization, we quantified O2 consumption and CO2 production in an enclosed biodegradation system providing plastic as the sole carbon source. In contrast to most studies we demonstrated that the tested fungi attach to, and colonize the different plastic polymers without any pretreatment of the plastics and in the absence of sugars, which were suggested essential for priming the degradation process. Functional polymer groups identified by Fourier-transform infrared spectroscopy (FTIR), and changes in fungal morphology as seen in light and scanning electron microscopy (SEM) were used as indicators of fungal adaptation to growth on PU as a substrate. Thereby, SEM analysis revealed new morphological structures and deformation of the cell wall of several fungal strains when colonizing PU and utilizing this plastic polymer for cell growth. Strains of Fusarium, Penicillium, Botryotinia cinerea EN41, and Trichoderma demonstrated a high potential to degrade PU, rubber, and PE. Growing on PU, over 90 % of the O2 was consumed in <14 days with 300-500 ppm of CO2 generated in parallel. Our study highlights a high bioremediation potential of some fungal strains to efficiently degrade plastic polymers, largely dependent on plastic type.

Engineered biochar combined clay for microplastic biodegradation during pig manure composting

This study pursued to regulate bacterial community succession pattern and expedited biodegradation of microplastics (MP) during pig manure (PM) composting employing walnut shell biochar (WSB) and montmorillonite (M). The WSB with concentration of 0%, 2.5%, 5%, 7.5%, 10% and 12% along with 10% M participated into PM for 42 days compost to search the optimal solution. The results confirmed the most prosperous bacterial phylum consisted of Firmicutes (3.02%-91.80%), Proteobacteria (2.08%-48.54%), Chloroflexi (0-44.62%) and Bacteroidetes (0.85%-40.93%). The addition of biochar has dramatically arranged bacterial community at different stages of composting. Energy Dispersive Spectrometer (EDS) revealed that carbon element in MPs decreased since the chemical bond fracture, under the intervention of high-temperature composting and WSB, the carbon content of MPs was maximum reduced by 20.25%. Fourier transform infrared spectrum indicated that CC, C-O, C-H and -COOH abundance of MPs in 10% and 12% dose biochar addition sharply reduced, interestingly, explicating WSB and composting made MP biodegradable. This experiment possesses affirmatory practical meaning for elimination of potential hazards by composting.

Anthropogenic and biological activities elevate microplastics pollution in headwater ecosystem of Yangtze tributaries in Hindu Kush-Himalayan region

Microplastic (MP) pollution is widely spread in oceans, freshwater, and terrestrial environments but MPs in mountainous headwater ecosystem are rarely reported. This study focuses on the headwater of Yangtze tributaries of the Hindu Kush-Himalayan (HKH) region. Five streams at elevations of 900 to 3300 m were selected to investigate the distribution of MPs in water and sediments across altitudes. MPs were found in all water and sediment samples from top stream zone nearly in absence of anthropogenic activity, low anthropogenic zone, and high anthropogenic zone, increased from 12-54, 81-185 to 334-847 items/L, and 2-35, 26-84 to 124-428 items/kg, respectively. This elevation-dependent MP distribution indicated that as elevation decreased, anthropogenic activities intensified and increased MPs input and their abundance, size, and diversity. Notably, hydraulic projects, such as damming, were identified as potential barriers to the migration of MPs downstream. Microbiome analyses revealed the presence of bacterial genes associated with plastic biodegradation in all sediment samples. The study indicates that Shangri-la mountainous streams have been polluted with MPs for years with potential risk of generation of nano-sized particles via natural fragmentation and biodegradation, and thus raises concern on MPs pollution in headwaters streams in mountainous regions.

Biodegradation of polyethylene (PE), polypropylene (PP), and polystyrene (PS) microplastics by floc-forming bacteria, Bacillus cereus strain SHBF2, isolated from a commercial aquafarm

The ubiquitous proximity of the commonly used microplastic (MP) particles particularly polyethylene (PE), polypropylene (PP), and polystyrene (PS) poses a serious threat to the environment and human health globally. Biological treatment as an environment-friendly approach to counter MP pollution has recent interest when the bio-agent has beneficial functions in their ecosystem. This study aimed to utilize beneficial floc-forming bacteria Bacillus cereus SHBF2 isolated from an aquaculture farm in reducing the MP particles (PE, PP, and PS) from their environment. The bacteria were inoculated for 60 days in a medium containing MP particle as a sole carbon source. On different days of incubation (DOI), the bacterial growth analysis was monitored and the MP particles were harvested to examine their weight loss, surface changes, and alterations in chemical properties. After 60 DOI, the highest weight loss was recorded for PE, 6.87 ± 0.92%, which was further evaluated to daily reduction rate (k), 0.00118 day-1, and half-life (t1/2), 605.08 ± 138.52 days. The OD value (1.74 ± 0.008 Abs.) indicated the higher efficiency of bacteria for PP utilization, and so for the colony formation per define volume (1.04 × 1011 CFU/mL). Biofilm formation, erosions, cracks, and fragments were evident during the observation of the tested MPs using the scanning electron microscope (SEM). The formation of carbonyl and alcohol group due to the oxidation and hydrolysis by SHBF2 strain were confirmed using the Fourier transform infrared spectroscopic (FTIR) analysis. Additionally, the alterations of pH and CO2 evolution from each of the MP type ensures the bacterial activity and mineralization of the MP particles. The findings of this study have confirmed and indicated a higher degree of biodegradation for all of the selected MP particles. B. cereus SHBF2, the floc-forming bacteria used in aquaculture, has demonstrated a great potential for use as an efficient MP-degrading bacterium in the biofloc farming system in the near future to guarantee a sustainable green aquaculture production.

Cetyltrimethylammonium Bromide-Modified Laponite@Diatomite Composites for Enhanced Adsorption Performance of Organic Pollutants

This work aims to enhance the adsorption performance of Laponite @diatomite for organic pollutants by modifying it with cetyltrimethylammonium bromide (CTAB). The microstructure and morphology of the CTAB-modified Laponite @diatomite material were characterized using SEM, XRD, FTIR, BET, and TG. Furthermore, the influences of key parameters, containing pH, adsorbent dosage, reaction time, and reaction temperature, on the adsorption process were investigated. The kinetics, thermodynamics, and isotherm models of the adsorption process were analyzed. Finally, potential adsorption mechanisms were given based on the characterization. The research findings indicate that CTAB-La@D exhibits good adsorption performance toward Congo red (CR) over a broad pH range. The maximum adsorption capacity of CR was 451.1 mg/g under the optimum conditions (dosage = 10 mg, contact time = 240 min, initial CR concentration = 100 mg/L, temperature = 25 °C, and pH = 7). The adsorption process conformed to the pseudo-second-order kinetic model, and the adsorption isotherms indicated that the adsorption process of CR was more in line with the Langmuir model, and it was physical adsorption. Thermodynamic analysis illustrates that the adsorption process is exothermic and spontaneous. Additionally, the mechanisms of electrostatic adsorption and hydrophobic effect adsorption of CR were investigated through XPS and FTIR analysis. This work provides an effective pathway for designing high-performance adsorbents for the removal of organic dye, and the synthesized materials hold great capability for practical utilization in the treatment of wastewater.

Are you drowned in microplastic pollution? A brief insight on the current knowledge for early career researchers developing novel remediation strategies

Microplastics (MPs) composed of different polymers with various shapes, within a vast granulometric distribution (1 μm - 5 mm) and with a wide variety of physicochemical surface and bulk characteristics spiral around the globe, with different atmospheric, oceanic, cryospheric, and terrestrial residence times, while interacting with other pollutants and biota. The challenges of microplastic pollution are related to the complex relationships between the microplastic generation mechanisms (physical, chemical, and biological), their physicochemical properties, their interactions with other pollutants and microorganisms, the changes in their properties with aging, and their small sizes that facilitate their diffusion and transportation between the air, water, land, and biota, thereby promoting their ubiquity. Early career researchers (ERCs) constitute an essential part of the scientific community committed to overcoming the challenges of microplastic pollution with their new ideas and innovative scientific perspectives for the development of remediation technologies. However, because of the enormous amount of scientific information available, it may be difficult for ERCs to determine the complexity of this environmental issue. This mini-review aims to provide a quick and updated overview of the essential insights of microplastic pollution to ERCs to help them acquire the background needed to develop highly innovative physical, chemical, and biological remediation technologies, as well as valorization proposals and environmental education and awareness campaigns. Moreover, the recommendations for the development of holistic microplastic pollution remediation strategies presented here can help ERCs propose technologies considering the environmental, social, and practical dimensions of microplastic pollution while fulfilling the current government policies to manage this plastic waste.

Exploring biodegradative efficiency: a systematic review on the main microplastic-degrading bacteria

Introduction

Microplastics (MPs) are widely distributed in the environment, causing damage to biota and human health. Due to their physicochemical characteristics, they become resistant particles to environmental degradation, leading to their accumulation in large quantities in the terrestrial ecosystem. Thus, there is an urgent need for measures to mitigate such pollution, with biological degradation being a viable alternative, where bacteria play a crucial role, demonstrating high efficiency in degrading various types of MPs. Therefore, the study aimed to identify bacteria with the potential for MP biodegradation and the enzymes produced during the process.

Methods

The methodology used followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol.

Results and Discussion

The research yielded 68 eligible studies, highlighting bacteria from the genera Bacillus, Pseudomonas, Stenotrophomonas, and Rhodococcus as the main organisms involved in MP biodegradation. Additionally, enzymes such as hydrolases and alkane hydroxylases were emphasized for their involvement in this process. Thus, the potential of bacterial biodegradation is emphasized as a promising pathway to mitigate the environmental impact of MPs, highlighting the relevance of identifying bacteria with biotechnological potential for large-scale applications in reducing MP pollution.

Distribution and risk assessment of microplastic pollution in a rural river system near a wastewater treatment plant, hydro-dam, and river confluence

Rivers are the natural drainage system, transporting anthropogenic wastes and pollution, including microplastics (plastic < 5 mm). In a riverine system, microplastics can enter from different sources, and have spatial variance in concentration, physical and chemical properties, and imposed risk to the ecosystem. This pilot study presents an examination of microplastics in water and sediment samples using a single sample collection from the rural Raquette River, NY to evaluate a hypothesis that distinct locations of the river, such as downstream of a wastewater treatment plant, upstream of a hydro-dam, and river confluence, may be locations of higher microplastics concentration. In general, our results revealed the presence of high microplastic concentrations downstream of the wastewater treatment plant (in sediments), upstream of the hydro dam (both water and sediment), and in the river confluence (water sample), compared to other study sites. Moreover, the risk assessment indicates that even in a rural river with most of its drainage basin comprising forested and agricultural land, water, and sediment samples at all three locations are polluted with microplastics (pollution load index, PLI > 1; PLIzone = 1.87 and 1.68 for water and sediment samples respectively), with risk categories between Levels I and IV ("minor" to "danger"). Overall, the river stands in a "considerable" risk category (PRIzone = 134 and 113 for water and sediment samples respectively). The overall objective of this pilot study was to evaluate our hypothesis and advance our understanding of microplastic dynamics in rural river systems, elucidating their introduction from a point source (wastewater treatment plant), transit through an impediment (hydro-dam), and release into a vital transboundary river (confluence of Raquette-St. Lawrence Rivers).

Application of advanced oxidation processes for the removal of micro/nanoplastics from water: A review

Micro/nanoplastics (MNPs) have been increasingly found in environments, food, and organisms, arousing wide public concerns. MNPs may enter food chains through water, posing a threat to human health. Therefore, efficient and environmentally friendly technologies are needed to remove MNPs from contaminated aqueous environments. Advanced oxidation processes (AOPs) produce a vast amount of active species, such as hydroxyl radicals (·OH), known for their strong oxidation capacity. As a result, an increasing number of researchers have focused on using AOPs to decompose and remove MNPs from water. This review summarizes the progress in researches on the removal of MNPs from water by AOPs, including ultraviolet photolysis, ozone oxidation, photocatalysis, Fenton oxidation, electrocatalysis, persulfate oxidation, and plasma oxidation, etc. The removal efficiencies of these AOPs for MNPs in water and the influencing factors are comprehensively analyzed, meanwhile, the oxidation mechanisms and reaction pathways are also discussed in detail. Most AOPs can achieve the degradation of MNPs, mainly manifest as the decrease of particle size and the increase of mass loss, but the mineralization rate is low, thus requiring further optimization for improved performance. Investigating various AOPs is crucial for achieving the complete decomposition of MNPs in water. AOPs will undoubtedly play a vital role in the future for the removal of MNPs from water.

Research progress on occurrence characteristics and source analysis of microfibers in the marine environment

Synthetic microfiber pollution is a growing concern in the marine environment. However, critical issues associated with microfiber origins in marine environments have not been resolved. Herein, the potential sources of marine microfibers are systematically reviewed. The obtained results indicate that surface runoffs are primary contributors that transport land-based microfibers to oceans, and the breakdown of larger fiber plastic waste due to weathering processes is also a notable secondary source of marine microfibers. Additionally, there are three main approaches for marine microplastic source apportionment, namely, anthropogenic source classification, statistical analysis, and numerical simulations based on the Lagrangian particle tracking method. These methods establish the connections between characteristics, transport pathways and sources of microplastics, which provides new insights to further conduct microfiber source apportionment. This study helps to better understand sources analysis and transport pathways of microfibers into oceans and presents a scientific basis to further control microfiber pollution in marine environments.

Biodegradation of microplastics: Advancement in the strategic approaches towards prevention of its accumulation and harmful effects

Microplastics (MPs) are plastic particles in a size ranging from 1 mm to 5 mm in diameter, and are formed by the breakdown of plastics from different sources. They are emerging environmental pollutants, and pose a great threat to living organisms. Improper disposal, inadequate recycling, and excessive use of plastic led to the accumulation of MP in the environment. The degradation of MP can be done either biotically or abiotically. In view of that, this article discusses the molecular mechanisms that involve bacteria, fungi, and enzymes to degrade the MP polymers as the primary objective. As per as abiotic degradation is concerned, two different modes of MP degradation were discussed in order to justify the effectiveness of biotic degradation. Finally, this review is concluded with the challenges and future perspectives of MP biodegradation based on the existing research gaps. The main objective of this article is to provide the readers with clear insight, and ideas about the recent advancements in MP biodegradation.

Investigating biodegradation of polyethylene and polypropylene microplastics in Tehran DWTPs

Microplastic (MP) pollution is a growing concern and various methods are being sought to alleviate the level of pollution worldwide. This study investigates the biodegradation capacity of MPs by indigenous microorganisms of raw water from Tehran drinking water treatment plants. By exposing polypropylene (PP) and polyethylene (PE) MPs to selected microbial colonies, structural, morphological, and chemical changes were detected by scanning electron microscope (SEM), cell weight measurement, Fourier transform infrared (FTIR), Raman spectroscopy test, and thermal gravimetric analysis (TGA). Selected bacterial strains include Pseudomonas protegens strain (A), Bacillus cereus strain (B), and Pseudomonas protegens strain (C). SEM analysis showed roughness and cracks on PP MPs exposed to strains A and C. However, PE MPs exposed to strain B faced limited degradation. In samples related to strain A, the Raman spectrum was completely changed, and a new chemical structure was created. Both TGA and FTIR analysis confirmed changes detected by Raman analysis of PP and PE MPs in chemical changes in this study. The results of cell dry weight loss for microbial strains A, B, and C were 13.5, 38.6, and 25.6%, respectively. Moreover, MPs weight loss was recorded at 32.6% for PP MPs with strain A, 13.3% for PE MPs with strain B, and 25.6% for PP MPs with strain C.