Understanding plastic degradation and microplastic formation in the environment: A review

Size fractionation of high-density polyethylene breakdown nanoplastics reveals different toxic response in Daphnia magna

Plastic litter is a growing environmental problem. Recently, microplastics and nanoplastics, produced during breakdown processes in nature, have been in focus. Although there is a growing knowledge concerning microplastic, little is still known about the effect of nanoplastics. We have showed that mechanical breakdown of high-density polyethylene (HDPE), followed by filtration through 0.8 µm filters, produces material toxic to the freshwater zooplankton Daphnia magna and affected the reproduction in life-time tests. However, further size fractionation and purification reveals that the nanoplastics fraction is non-toxic at these concentrations, whereas the fraction with smaller sizes, below ~ 3 nm, is toxic. The HDPE nanoplastics are highly oxidized and with an average diameter of 110 nm. We conclude that mechanical breakdown of HDPE may cause environmental problems, but that the fraction of leached additives and short chain HDPE are more problematic than HDPE nanoplastics.

Microplastics retained in stormwater control measures: Where do they come from and where do they go?

Stormwater control measures (SCM) can remove and accumulate microplastics and may serve as a long-term source of microplastics for groundwater pollution because of their potential for downward mobility in subsurface. Furthermore, the number of microplastics accumulated in SCM may have been underestimated as the calculation typically only accounts for microplastics accumulated via episodic stormwater loading and ignores microplastic accumuation via continuous atmospheric deposition. To evaluate the source pathways of accumulated microplastics and their potential for downward mobility to groundwater, we analyzed spatial distributions of microplastics above ground on the canopy around SCM and below ground in the subsurface in and outside the boundaries of fourteen SCM in Los Angeles. Using an exponential model, we link subsurface retardation of microplastics to the median particle size of soil (D₅₀) and land use. Despite receiving significantly more stormwater, microplastic concentrations in SCM at surface depth or subsurface depth were not significantly different from the concentration at the same depth outside the SCM. Similar concentration in and outside of SCM indicates that stormwater is not the sole source of microplastics accumulated in SCM. The high concentration of microplastics on leaves of vegetation in SCM confirms that the contribution of atmospheric deposition is significant. Within and outside the SCM boundary, microplastics are removed within the top 5 cm of the subsurface, and their concentration decreases exponentially with depth, indicating limited potential for groundwater pollution from the microplastics accumulated in SCM. Outside the SCM boundary, the subsurface retardation coefficient decreases with increases in D₅₀, indicating straining of microplastics as the dominant removal mechanism. Inside the boundary of SCM, however, the retardation coefficient was independent of D₅₀, implying that microplastics could have either moved deeper into the filter layer in SCM or that compost, mulch, or organic amendments used in the filter media were pre-contaminated with microplastics. Overall, these results provide insights on microplastics source, accumulation, and downward mobility in SCM.

Plastic mulch debris in rhizosphere: Interactions with soil-microbe-plant systems

Large amounts of plastic mulch debris (PMD) accumulated in the soil can endanger agroecosystems. However, little is known about the interactions between PMD and soil-microbe-plant systems. In this study, a pot experiment (four replicates) in tropical greenhouse was conducted to investigate the effects of PMD (polyethylene) at different concentrations (0, 0.4, 0.8, 4.0, 6.0 g kg^-1) on soil nutrients, rhizosphere bacterial communities and rice growth. This study further explored the interactive mechanisms between PMD and environmental factors based on correlation analysis and previous studies. The results showed that PMD continuously reduced the soil capabilities to store nutrients (C, N, P, humic-like substances) and increased the proportion of P and biodegradable dissolved organic matter (DOM). At the full ripening stage of rice growth, total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in all PMD treatments significantly decreased by 60.86, 52.51 and 34.83% respectively as compared to CK (p < 0.05). Furthermore, PMD increased the total abundance of bacteria but reduced the diversity and evenness of bacterial communities, which further affected microbial metabolic functions. Total OTUs and Shannon decreased 0.02-17.05% and 0.69-7.55% in treatments. At harvest-time, PMD reduced the biomass and yield of rice with 11.34 and 19.24% (all treatments on average) lower than CK. Under the influence of PMD, the order of correlation size between PMD and one environmental factor was PMD-soil > PMD-microbe > PMD-plant, and the order of correlation between two environmental factors was soil-microbe > microbe-plant > soil-plant. Over all, PMD had the most significant negative effects on soil nutrients storage, followed by the change of microbial community structure and microbial metabolic functions. The negative effects of PMD on crops were relatively weak.

Environmental behaviors of microplastics in aquatic systems: A systematic review on degradation, adsorption, toxicity and biofilm under aging conditions

Microplastics (MPs, < 5 mm) in the environment have attracted worldwide attention due to their wide distribution and difficulty in handling. Aging processes such as UV irradiation, biodegradation, physical abrasion and chemical oxidation can affect the environmental behavior of MPs. This review article summarizes different aging processes of MPs and subsequent effects on the adsorption of pollutants, the leaching of additives, and the toxicity of MPs. In addition, the formation process of biofilm on the surface of MPs and the interactions between biofilm and aged MPs are revealed. MPs can accumulate different environmental pollutants (organic pollutants, heavy metals, microorganisms, etc.) through surface adsorption, pore filling and distribution. Moreover, the aging of MPs affects their adsorption performance toward these pollutants due to a series of changes in their specific surface area and oxygen-containing functional groups. The release of some toxic additives such as phthalates after aging can enhance the toxic effects of MPs. Aging also changes the shape and size of MPs, which can affect the eating habits of the organisms and further increase the potential toxicity of MPs. This article conducts a systematical analysis and summary of the environmental behavior and physicochemical properties of MPs as well as the changes due to MPs aging, which helps to better understand the impact of aging on MPs in the environment. Future research on MPs aging should reduce the knowledge gap between laboratory simulation and actual conditions and increase the environmental relevance.

Method for rapid biofilm cultivation on microplastics and investigation of its effect on the agglomeration and removal of microplastics using organosilanes

Since microplastics were recognized as a global environmental problem in the early 2000s, research began on possible solutions such as the removal of microplastics from waters. A novel and promising approach for this purpose is microplastics agglomeration-fixation using organosilanes. In this study, it is investigated how biofilm coverage of microplastics affects this process. The biofilm was grown on the microplastics by cultivating it for one week in a packed bed column operated with biologically treated municipal wastewater enriched with glucose. The biofilm was characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and Fourier-Transform infrared spectroscopy (FT-IR). The results show a partial coverage of the microplastics with attached bacteria and extracellular polymeric substances (EPS) after 7 days of incubation. Comparing five polymer types (polyethylene, polypropylene, polyamide, polyester, and polyvinyl chloride) and three organosilanes, the biofilm coverage caused a reduced removal efficiency for all combinations tested as it changes the surface chemistry of the microplastics and therefore the interaction with the organosilanes tested in this study. Treatment of biofilm covered microplastic with ultrasound partly recovers the removal. However, the results underline the importance of simulated environmental exposure when performing experiments for microplastic removal.

Characteristics and influencing factors of airborne microplastics in nail salons

Airborne microplastic particles (MPs) are emerging contaminants. Although some studies have investigated the characteristics of indoor MPs in homes or offices, information regarding MPs in nail salons with potentially higher MP pollution is unavailable. In this study, we collected indoor and outdoor air samples from nail salons to analyze the concentrations, physical characteristics, and polymers of MPs and further assessed the exposure through inhalation and influencing factors. Our data displayed that the average indoor MP concentration was 46 ± 55 MPs/m³. The estimated average annual exposure to indoor MPs was 67,567 ± 81,782 MPs/year. The predominant shape and size of indoor MPs were fragment and <50 μm, respectively. The predominant polymer in indoor air was acrylic (27%), followed by rubber (21%), and polyurethane (13%). Air conditioner, nail treatment, ceiling and flooring with plastic materials, and number of occupants were factors affecting indoor MP concentrations. We concluded that MP pollution was more severe in nail salons and the physical characteristics and polymer compositions differed between nail salons and other indoor spaces reported in other studies. Air conditioner usage induced higher MP emission, and higher MP concentrations were observed in nail salons with plastic ceiling and flooring or more occupants.

Macro problems from microplastics: Toward a sustainable policy framework for managing microplastic waste in Africa

Microplastic pollution is a ubiquitous and emerging environmental and public health concern in Africa due to increased plastic production, product and waste importation, and usage. While studies on the environmental monitoring and characterization of microplastics demonstrated the urgent need for a drastic reduction in plastic waste generation, the effectiveness of the various regulatory and policy interventions implemented or proposed in Africa countries remains poorly understood. We critically examined policies, legislations, and regulations enacted to control microplastic pollution in Africa to develop a sustainable, harmonized framework for the coordinated reduction of plastic waste generation across Africa. Analysis of the interventions revealed most African countries employed traditional perspective (i.e., command-and-control) approaches, whereby state instruments such as plastic ban, production and importation levies, and consumer taxes were enacted. However, the continued increase in microplastic waste generation suggests traditional perspective approaches might not be effective in Africa. Although rarely used in Africa, market-oriented approaches such as private-public waste management are often effective in controlling plastic pollution. Hence, we proposed a bottom-up hybrid regulatory approach for managing microplastics pollution in Africa, involving price-based, right-base, legislation and behavioral frameworks based on best practices in microplastic waste management.

Informal landfill contributes to the pollution of microplastics in the surrounding environment

A large amount of plastic waste is generated yearly worldwide, and landfills are commonly used for the disposal of plastic waste. However, burying in landfill does not get rid of the plastic waste but leave the problem to the future. Previous works have showed that microplastics are presented in the landfill refuse and leachate, which might be potential sources of microplastics. In this work, characteristics of microplastic pollution in an informal landfill in South China were studied. Landfill refuse, underlying soil, leachate, and groundwater samples were collected from different sites within and around the landfill. Results show that microplastics in the landfill refuse and underlying soil varied from 590 to 103,080 items/kg and from 570 to 14,200 items/kg, respectively. Most of the microplastics are fibrous, small sized, and transparent. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are major polymer types. Scanning electron microscope (SEM) images and Fourier Transform Infrared (FTIR) spectra of the microplastic samples indicate varying degree of weathering. Microplastic abundances in the landfill leachate and groundwater ranged from 3 to 25 items/L and from 11 to 17 items/L, respectively. Microplastics detected in the landfill leachate and groundwater are even smaller compared with those in the refuse and underlying soil and their polymer types are more diverse. This work demonstrated that microplastics presented in an informal landfill without sufficient protection can leak out to the surrounding environment. The microplastic pollution originated from informal landfills should receive more attentions.

Environmental Policy for the Restriction on the Use of Plastic Products in Taiwan: Regulatory Measures, Implementation Status and COVID-19’s Impacts on Plastic Products Recycling

In response to international trends regarding the reduction in plastic waste (or plastic pollution), this work used the official statistics that were recently released, focusing on regulatory actions restricting the use of plastic products and/or the increase in recycling in Taiwan. In addition, the impacts of the COVID-19 pandemic on plastic waste generation and plastic products’ recycling were also addressed in the present study. The results showed that the plastic compositions in the garbage slightly increased in recent years, suggesting that the effect of restrictions on the use of plastic products in Taiwan was not significant, even though the regulatory measures have been implemented since 2002. However, chlorine contents in the garbage were significantly increased in 2020. The increase could be attributed to the fact that kitchen waste (containing salt), household waste containing disinfectant (e.g., chlorine dioxide, sodium hypochlorite) or PVC-made products were generated more during the COVID-19 pandemic. Furthermore, the data also indicated that the monthly quantities of recycled plastic containers and other plastic products had no significant change since January 2020, especially in the outbreak period from May 2021 to July 2021.

Chemical composition of microplastics floating on the surface of the Mediterranean Sea

The Mediterranean Sea is one of the most studied regions in the world in terms of microplastic (MP) contamination. However, only a few studies have analysed the chemical composition of MPs at the Mediterranean Sea surface. In this context, this study aims to describe the chemical composition as a function of particle size, mass and number concentrations of MPs collected in the surface waters of the Mediterranean Sea. The chemical composition showed a certain homogeneity at the Mediterranean Sea scale. The main polymers identified by Fourier Transform Infra-Red (FTIR) spectroscopy were poly(ethylene) (67.3 ± 2.4%), poly(propylene) (20.8 ± 2.1%) and poly(styrene) (3.0 ± 0.9%). Nevertheless, discrepancies, confirmed by the literature, were observed at a mesoscale level. Thus, in the North Tyrrhenian Sea, the proportion of poly(ethylene) was significantly lower than the average value of the Mediterranean Sea (57.9 ± 10.5%). Anthropic sources, rivers, or polymer ageing are assumed to be responsible for the variations observed.

Microplastic contamination and characteristics spatially vary in the southern Black Sea beach sediment and sea surface water

In this study, the abundance, and characteristics of the microplastics on the southern coast of the Black Sea were assessed. More than 70% of the detected microplastics were smaller than 2.5 mm and mostly consisted of fibers and fragments. The average microplastic abundance in the beach sediment and seawater were 64.06 ± 8.95 particles/kg and 18.68 ± 3.01 particles/m³, respectively. The western coast of the study area (Marmara region) was the most polluted area, and a spatially significant difference was determined in terms of abundance. The composition in the beach sediment (particles/kg) was dominated by styrene acrylonitrile copolymer (SAC) (40.53%), polyethylene terephthalate (PET) (38.75%), and polyethylene (PE) (6.91%), whereas the seawater (particles/m³) was dominated by PET (57.26%), PE (13.52%), and polypropylene PP (11.24%). The results of our study can be a baseline for environmental modeling studies and experimental studies on the marine organisms inhabiting the Black Sea.

Genotoxic effect of microplastics and COVID-19: The hidden threat

Microplastics (MPs) are ubiquitous anthropogenic contaminants, and their abundance in the entire ecosystem raises the question of how far is the impact of these MPs on the biota, humans, and the environment. Recent research has overemphasized the occurrence, characterization, and direct toxicity of MPs; however, determining and understanding their genotoxic effect is still limited. Thus, the present review addresses the genotoxic potential of these emerging contaminants in aquatic organisms and in human peripheral lymphocytes and identified the research gaps in this area. Several genotoxic endpoints were implicated, including the frequency of micronuclei (MN), nucleoplasmic bridge (NPB), nuclear buds (NBUD), DNA strand breaks, and the percentage of DNA in the tail (%Tail DNA). In addition, the mechanism of MPs-induced genotoxicity seems to be closely associated with reactive oxygen species (ROS) production, inflammatory responses, and DNA repair interference. However, the gathered information urges the need for more studies that present environmentally relevant conditions. Taken into consideration, the lifestyle changes within the COVID-19 pandemic, we discussed the impact of the pandemic on enhancing the genotoxic potential of MPs whether through increasing human exposure to MPs via inappropriate disposal and overconsumption of plastic-based products or by disrupting the defense system owing to unhealthy food and sleep deprivation as well as stress. Overall, this review provided a reference for the genotoxic effect of MPs, their mechanism of action, as well as the contribution of COVID-19 to increase the genotoxic risk of MPs.

Sustainable Approach for Synthesis and Completely Recycle of Cyclic CO2-based Polycarbonates

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics. Polycarbonates derived from the copolymerization of CO₂ and epoxides have attracted much attention since they can enable CO₂-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO₂-based polycarbonates have been reported and typically degraded to cyclic carbonates. Here we synthesize a homogeneous dinuclear methyl zinc catalyst ((BDI-ZnMe)₂, 1) to rapidly copolymerize meso-CHO and CO₂ into poly(cyclohexene carbonate) (PCHC) with an unprecedentedly cyclic structure. Moreover, in the presence of trace amounts of water, a heterogeneous multi-nuclear zinc catalyst ((BDI-(ZnMe₂·xH₂O))_n, 2) is prepared and shows up to 99% selectivity towards the degradation of PCHC back to meso-CHO and CO₂. This strategy not only achieves the first case of cyclic CO₂-based polycarbonate but also realizes the complete chemical recycling of PCHC back to its monomers, representing closed-loop recycling of CO₂-based polycarbonates.

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics.

In vitro evaluation of nanoplastics using human lung epithelial cells, microarray analysis and co-culture model

Nanoplastics, including polystyrene nanoplastics (PS-NPs), are widely existed in the atmosphere, which can be directly and continuously inhaled into the human body, posing a serious threat to the respiratory system. Therefore, it is urgent to estimate the potential pulmonary toxicity of airborne NPs and understand its underlying mechanism. In this research, we used two types of human lung epithelial cells (bronchial epithelium transformed with Ad12-SV40 2B, BEAS-2B) and (human pulmonary alveolar epithelial cells, HPAEpiC) to investigate the association between lung injury and PS-NPs. We found PS-NPs could significantly reduce cell viability in a dose-dependent manner and selected 7.5, 15 and 30 μg/cm² PS-NPs as the exposure dosage levels. Microarray detection revealed that 770 genes in the 7.5 μg/cm² group and 1951 genes in the 30 μg/cm² group were distinctly altered compared to the control group. Function analysis suggested that redox imbalance might play central roles in PS-NPs induced lung injury. Further experiments verified that PS-NPs could break redox equilibrium, induce inflammatory effects, and triggered apoptotic pathways to cause cell death. Importantly, we found that PS-NPs could decrease transepithelial electrical resistance by depleting tight junctional proteins. Result also demonstrated that PS-NPs-treated cells increased matrix metallopeptidase 9 and Surfactant protein A levels, suggesting the exposure of PS-NPs might reduce the repair ability of the lung and cause tissue damage. In conclusion, nanoplastics could induce oxidative stress and inflammatory responses, followed by cell death and epithelial barrier destruction, which might result in tissue damage and lung disease after prolonged exposure.

Micro- and nanoplastic transfer, accumulation, and toxicity in humans

Plastics impact our daily lives. Unfortunately, it is the disuse and disposal of these items that may affect us the greatest. Plastic micro- and nanosized particles, likely from bulk degradation, have been identified in air pollution and water sources. Recently, plastic particles have also been identified in consumable products. The purpose of this review is to identify the likely routes of human exposure, the toxicological outcomes and concerns currently reported, and to provide some considerations for future assessments.

Enhanced aging of polystyrene microplastics in sediments under alternating anoxic-oxic conditions

Aging of microplastics (MPs) (i.e., degradation and weathering) is ubiquitous in the environment. The MP aging process is thought to be limited to light and static areas, while aging in dark and fluctuating anoxic-oxic areas is poorly understood. Here, we provide initial evidence for aging of polystyrene microplastics (PS-MPs) under different anoxic/oxic conditions in sediments, and we further explored these mechanisms using sediment column experiments and pure-culture experiments. The results showed that PS-MPs in alternating anoxic-oxic sediments displayed the highest degree of aging. In the in-situ experiment, both the weight losses and O/C ratios of PS-MPs aged under alternating anoxic-oxic conditions were ∼2 times higher than those aged under static oxic and static anoxic conditions during 2-month experiments. In a 2-month column experiment, the PS-MPs in the alternating anoxic-oxic group showed weight losses and O/C ratios that were, respectively, triple and double the corresponding values for the static oxic and static anoxic groups. Column and pure-culture experiments demonstrated that dark production of ·OH which showed a positive correlation with a Fe redox process could explain enhanced MP aging under the alternating anoxic-oxic conditions. These findings provide a basis for risk assessment and management of MPs in the natural environment, such as in intertidal zones and paddy fields, and also have implications for engineering of optimized MP degradation processes.

Microplastics in vacuum packages of frozen and glazed icefish (Neosalanx spp.): A freshwater fish intended for human consumption

It is widely accepted that human is exposed to microplastics through food consumption, however data occurrence in foodstuffs are still little and basically limited to seafood. In this study, the presence of microplastics was investigated in icefish (Neosalanx spp.) samples sourced from various mass-market retailers in Italy, supplied as frozen, glazed and vacuum-packed product. Icefish is a small freshwater fish widely imported in Europe from China as surrogate of other fish species subjected to commercial restriction, consumed whole after cooking in several culinary preparation. The samples (~10 g of icefish from each of the 40 packs tested) were digested using a solution of 10% potassium hydroxide and filtered through a 5 μm pore-size filter. Filters of the samples were observed under a stereomicroscope and the chemical composition of the items detected were analysed by FTIR spectroscopy. A total of 163 items were counted in 37 (92.5%) samples with a mean value of 0.42±0.28 items/g w.w. Fibers were the most detected morphotype and several plastic polymers, such as polypropylene, polyethylene, polyethylene terephthalate and polystyrene, were identified by FT-IR analysis. As store-bought samples, the sources of microplastics could be substantially related to contamination during food processing. However, an intravital exposure to microplastics present in the surroundings waters cannot be ruled out. More foodstuffs need to be investigated for microplastic presence. In this study, microplastic occurrence was reported in freshwater biota intended for human consumption sampled directly from supermarket contributing to the risk assessment of human exposure to microplastics via food consumption.

Aging assessment of microplastics (LDPE, PET and uPVC) under urban environment stressors

The changes in the chemical structure, surface morphology and crystallinity are reported for three different polymers (LDPE, PET and uPVC) in microplastic form, after being artificially exposed to different aging agents that can affect microplastics in urban environments: ozone, UV-C, and solar radiation. In parallel to the laboratory experiments, the microplastics were exposed to real weathering conditions for three-months in a building rooftop located in the city of Porto (Portugal). By analysing the (virgin and aged) microplastic samples periodically through ATR-FTIR spectroscopy and estimating the Carbonyl Index, it was possible to sketch the aging degree evolution through time and identify the most aggressive agents for each polymer regarding the changes in their chemical structure. SEM and XRD measurements allowed to complement the ATR-FTIR results, giving a more complete picture of the effects of each treatment on each polymer and suggesting that ATR-FTIR measurements are not sufficient to correctly evaluate the aging degree of microplastics. The changes observed in the microplastic particles studied support the theory that microplastics in the environment undergo aging and change their characteristics through time, potentially affecting their behavior and intensifying their impacts.

Generation of nanoplastics during the photoageing of low-density polyethylene

In this work, we studied the hydrolytic and photochemical degradation of three low-density polyethylene (LDPE) materials, within the size range of microplastics (MP). The MPs were exposed to mechanical agitation and UV irradiation equivalent to one year of solar UVB + UVA in a stirred photoreactor. Flow cytometry was used to track the formation of small (1-25 μm) MPs by applying Mie's theory to derive the size of MP particles from scattering intensity readings. The calculation was based on a calibration with polystyrene (PS) beads. The results showed that the generation of 1-5 μm MP reached 10⁴-10⁵ MPs in the 1-25 μm range per gram of LDPE. ATR-FTIR and micro-FTIR measurements evidenced the formation of oxygenated moieties, namely hydroxyl, carbonyl, and carbon-oxygen bonds, which increased with irradiation time. We also found evidence of the production of a high number of nanoplastics (<1 μm, NPs). The Dynamic Light Scattering size of secondary NPs was in the hundreds of nm range and might represent up to 10¹⁰ NPs per gram of LDPE. Our results allowed the unambiguous spectroscopic assessment of the generation of NPs from LDPE under conditions simulating environmental exposure to UV irradiation and used flow cytometry for the first-time to track the formation of secondary MPs.

Microplastics in the environment: Sampling, pretreatment, analysis and occurrence based on current and newly-exploited chromatographic approaches

The omnipresent character of microplastics (MPs) in environmental matrices, organisms and products has recently posed the need of their qualitative as well as quantitative analysis imperative, in order to provide data about their abundance and specification of polymer types in several substrates. In this framework, current and emerging approaches based on the chromatographic separation are of increased relevance in the field of MPs analysis and possess a large number of merits, since most of them are applicable in various complex matrices, sensitive and ideal for the detection of small-sized particles, whereas the common absence of any special pre-treatment step before analysis should also be highlighted. Αnalytical pyrolysis coupled with gas chromatography mass spectrometry (GC-MS) has recently gained ground as a powerful means to deliver information on MPs composition and degradation after their release into environment. Several instrumentations and trends in the area of analytical pyrolysis are thoroughly described within this review, while newly-exploited chromatographic methods in the field of MPs analysis, including Liquid Chromatography (LC) and Gel Permeation Chromatography (GPC) in this line are also investigated. The present review fills the gap of standardization concerning sampling, pre-treatment and chromatographic approaches and gathers all the available methodologies applied inside this area in accordance with the studied substrate, with the most examined environmental matrices being the solid one. After investigating the various works, some development options arise and it appears that chromatographic approaches should focus on improved extraction processes in terms of MPs isolation, since it is a crucial part in plastic items monitoring and is commonly depended on the polymer type and matrix. Special attention is given on the potential of chromatographic techniques for microplastics identification as well as quantification by confirming the current research status and knowledge gaps and highlighting some of the recent trends in this field.

Impact of Enzymatic Degradation on the Material Properties of Poly(Ethylene Terephthalate)

With macroscopic litter and its degradation into secondary microplastic as a major source of environmental pollution, one key challenge is understanding the pathways from macro- to microplastic by abiotic and biotic environmental impact. So far, little is known about the impact of biota on material properties. This study focuses on recycled, bottle-grade poly(ethylene terephthalate) (r-PET) and the degrading enzyme PETase from Ideonella sakaiensis. Compact tension (CT) specimens were incubated in an enzymatic solution and thermally and mechanically characterized. A time-dependent study up to 96 h revealed the formation of steadily growing colloidal structures. After 96 h incubation, high amounts of BHET dimer were found in a near-surface layer, affecting crack propagation and leading to faster material failure. The results of this pilot study show that enzymatic activity accelerates embrittlement and favors fragmentation. We conclude that PET-degrading enzymes must be viewed as a potentially relevant acceleration factor in macroplastic degradation.

COVID-19, a double-edged sword for the environment: a review on the impacts of COVID-19 on the environment

This review paper discusses the most relevant impacts of the COVID-19 pandemic on the environment. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) originated in Wuhan, China, in December 2019. The disease has infected 70 million people and caused the death of 1.58 million people since the US Food and Drug Administration issued an Emergency Use Authorization to develop a vaccine to prevent COVID-19 on December 11, 2020. COVID-19 is a global crisis that has impacted everything directly connected with human beings, including the environment. This review discusses the impacts of COVID-19 on the environment during the pandemic and post-COVID-19 era. During the first months of the COVID pandemic, global coal, oil, gas, and electricity demands declined by 8%, 5%, 2%, and 20%, respectively, relative to 2019. Stay-at-home orders in countries increased the concentrations of particles in indoor environments while decreasing the concentrations of PM2.5 and NOX in outdoor environments. Remotely working in response to the COVID-19 pandemic increased the carbon, water, and land footprints of Internet usage. Microplastics are released into our environment from the mishandling and mismanagement of personal protective equipment that endanger our water, soils, and sediments. Since the COVID-19 vaccine cannot be stored for a long time and spoils rapidly, more awareness of the massive waste of unused doses is needed. So COVID-19 is a double-edged sword for the environment.

The life of a plastic butter tub in riverine environments

Plastic pollution in the world's ocean is one of the major environmental challenges that affects the society today, due to their persistence at sea, adverse consequences to marine life and being potentially harmful to human health. Rivers are now widely recognized as being the major input source of land-based plastic waste into the seas. Despite their key role in plastic transportation, riverine plastic pollution research is still in its infancy and plastic sources, hot-spots and degradation processes in riverine systems are to date poorly understood. In this contribution, we introduce a novel concept of following the aging of polypropylene based post-consumer goods placed in known trapping and mobility zones of macroplastics on a fluvial point bar, which was determined through repeated field surveys of macroplastic densities on this bar. As a proof-of-concept, we followed the degradation of 5 identical plastic butter tubs in 5 different locations on a riverbank and significant differences in the aging of the tubs were observed. The degree of aging of the tubs can to some extent be correlated to their proximity to the main river channel, exposure to natural conditions, such as solar radiation, and its storage time on land.

Transport and deposition of microplastic particles in saturated porous media: Co-effects of clay particles and natural organic matter

Natural colloids such as clays and natural organic matter (NOM) are universally present in environments, which could interact with microplastics (MPs) and thus alter the fate and transport of MPs in porous media. The co-effects of clays and NOM on MPs transport in saturated porous media were systematically explored at both low and high ionic strength (IS) conditions. Specifically, bentonite and humic acid (HA) were employed as representative clays and NOM. 5 mM NaCl and 1 mM CaCl₂ solutions were used as low IS conditions, while 25 mM NaCl and 5 mM CaCl₂ solutions were employed as high IS conditions. We found that formation of MPs-bentonite heteroaggregates had great effects on MPs transport under different conditions. Without HA, the small MPs-bentonite heteroaggregates formed under low IS increased MPs transport via serving as mobile carriers, while larger MPs-bentonite heteroaggregates formed at high IS led to the decreased MPs mobility. When both HA and bentonite were copresent in MPs suspension, we found that HA could inhibit the formation of larger sized MPs-bentonite heteroaggregates. Particularly, when the two types of natural colloids copresent in MPs suspensions, MPs transport behaviors were similar to those with only bentonite present in MPs suspensions at low IS, while MPs transport was greatly increased at high IS comparing with those only with bentonite in suspensions. Clearly, without HA in suspensions, bentonite played the dominant role on MPs transport under all examined conditions concerned in this study. Instead, when both HA and bentonite copresent in MPs suspensions, MPs transport was mainly controlled by bentonite at low IS, while both bentonite and HA had major contributions at high IS. The results showed that under solution conditions concerned in present study, MPs mobility in porous media would be greatly affected (either enhanced or inhibited) by the two types of natural colloids.

Evaluation of different packaging methods and storage temperature on MPs abundance and fillet quality of rainbow trout

There are many studies on microplastics (MPs) about the aquatic ecosystems and its components. However, there is limited study on the MPs abundance, identification and sources in processed seafood products which are manufactured for direct human consumption. In this study, rainbow trout (Oncorhynchus mykiss) fillets were packed with different packaging techniques and stored at two different temperatures (+4 and -20°C) for 21 days. The presence, shape, size and polymer type of MPs were determined by ATR-FTIR on certain days (7, 14 and 21 days) in fillets during storage. The chemical quality changes in fillets [with pH, thiobarbituric acid reactive substrate (TBARS), and total volatile basic nitrogen (TVB-N) data] were monitored and the effect of MPs presence was evaluated. At the last step, the estimated MPs intake level in humans was determined with considering the presence of MPs (determined in fillets). The presence of MPs was determined the most in the Polystyrene plate + wrapped film (S) group and the least in the Chitosan film + Polystyrene plate + wrapped film (C) group. When evaluated in terms of chemical parameters, although good results were obtained in all samples stored at - 20°C, the presence of MPs was determined at a high level in fillets which stored at this temperature. As a result of the study, it was determined that the packaging type and storage temperature have significant effects on the presence of MPs and fillet quality.

Microplastics in the Center of Mediterranean: Comparison of the Two Calabrian Coasts and Distribution from Coastal Areas to the Open Sea

Plastic is everywhere—increasing evidence suggests that plastic pollution is ubiquitous and persistent in ecosystems worldwide. Microplastic pollution in marine environments is particularly insidious, as small fragmentation can increase interaction with biota and food chain access. Of particular concern is the Mediterranean Sea, which has become a large area of accumulation of plastic debris, including microplastics, whose polymeric composition is still largely unknown. In this study, we analyzed the polymeric composition, particle size distribution, shape, and color of small plastic particles (ranging from 50 to 5000 µm) collected from the sea surface in six stations at the center of the Mediterranean Sea. We also described, for the first time, the different distribution of microplastics from coastal areas up to 12 nautical miles offshore. The microplastic density was 0.13 ± 0.19 particles/m², with a marked prevalence of smaller particles (73% < 3 mm) and a peak between 1 and 2 mm (34.74%). Microplastics composition analysis showed that the most abundant material was polyethylene (69%), followed by polypropylene (24%). Moreover, we reported a comparison of the two Calabrian coasts providing the first characterization of a great difference in microplastic concentration between the Tyrrhenian and Ionian sides (87% vs. 13%, respectively), probably due to the complex marine and atmospheric circulation, which make the Tyrrhenian side an area of accumulation of materials originating even from faraway places. We demonstrate, for the first time, a great difference in microplastic concentration between Tyrrhenian and Ionian Calabrian coasts, providing a full characterization and highlighting that microplastic pollution is affected by both local release and hydrography of the areas.

Uncovering the release of micro/nanoplastics from disposable face masks at times of COVID-19

Wearing face masks is a fundamental prevention and control measure to limit the spread of COVID-19. The universal use and improper disposal of single-use face masks are raising serious concerns for their environmental impact, owing to the foregone contribution to plastic water pollution during and beyond the pandemic. This study aims to uncover the release of micro/nanoplastics generated from face mask nonwoven textiles once discarded in the aquatic environment. As assessed by microscopy and flow cytometry, the exposure to different levels of mechanical stress forces (from low to high shear stress intensities) was proved effective in breaking and fragmenting face mask fabrics into smaller debris, including macro-, micro-, and nano-plastics. Even at the low level of fabric deterioration following the first second of treatment, a single mask could release in water thousands of microplastic fibers and up to 10⁸ submicrometric particles, mostly comprised in the nano-sized domain. By contributing to the current lack of knowledge regarding the potential environmental hazards posed by universal face masking, we provided novel quantitative data, through a suitable technological approach, on the release of micro/nanoplastics from single-use face masks that can threaten the aquatic ecosystems to which they finally end-up.

Review of Microplastic Distribution, Toxicity, Analysis Methods, and Removal Technologies

Microplastic contamination has become a problem, as plastic production has increased worldwide. Microplastics are plastics with particles of less than 5 mm and are absorbed through soil, water, atmosphere, and living organisms and finally affect human health. However, information on the distribution, toxicity, analytical methods, and removal techniques for microplastics is insufficient. For clear microplastic analytical methods and removal technologies, this article includes the following: (1) The distribution and contamination pathways of microplastics worldwide are reviewed. (2) The health effects and toxicity of microplastics were researched. (3) The sampling, pretreatment, and analytical methods of microplastics were all reviewed through various related articles. (4) The various removal techniques of microplastics were categorized by wastewater treatment process, physical treatment, chemical treatment, and biological treatment. This paper will be of great help to microplastic analysis and removal techniques.

Plastic pollution during COVID-19: Plastic waste directives and its long-term impact on the environment

Majority of the million tons of plastic produced each year is being disposed after single-use. Plastic bottle, bags, food containers, gloves, and cup that end up in landfills and environment could linger for hundreds to thousands of years. Moreover, COVID-19 pandemic caused by the novel coronavirus (SARS-CoV-2), will also exacerbate the global plastic pollution as the use of personal protective equipment (PPE i.e., gloves, masks) became mandatory to prevent the spread of the virus. Plastic eventually breaking down in micro & nanoscopic bits due to physical or chemical or biological actions in the environment, can enter animal and human food web. So, plastic management programs need to be more robust with a focus on the prevention of the micro and nanoplastics entrance into the environment and food web. In the present pandemic situation, it is even more necessary to know about how much plastic waste is being generated and how different countries are coping up with their plastic waste management. In this review, we have elucidated how global plastic production rise during COVID-19 and how it would contribute to short and long-term impacts on the environment. Plastic pollution during the pandemic will increase the GHS emissions in the incineration facilities. Improper disposal of plastics into the oceans and lands would endanger the marine species and subsequently human lives. We have also assessed how the increased plastic pollution will aggravate the micro and nanoscale plastic problem, which have now become an emerging concern. This review will be helpful for people to understand the plastic usage and its subsequent consequences in the environment in a pandemic like COVID-19.

Micro (nano) plastic pollution: The ecological influence on soil-plant system and human health

Global plastic pollution has been a serious problem since many years and micro (nano) plastics (MNPs) have gained attention from researchers around the world. This is because MNPs able to exhibit toxicology and interact with potentially toxic elements (PTEs) in the environment, causing soil toxicity. The influences of MNPs on the soil systems and plant crops have been overlooked despite that MNPs can accumulate in the plant root system and generate detrimental impacts to the terrestrial environments. The consumption of these MNPs-contaminated plants or fruits by humans and animals will eventually lead to health deterioration. The identification and measurement of MNPs in various soil samples is challenging, making the understanding of the fate, environmental and ecological of MNPs in terrestrial ecosystem is limited. Prior to sample assessment, it is necessary to isolate the plastic particles from the environment samples, concentrate the plastic particles for analysis purpose to meet detection limit for analytical instrument. The isolation and pre-concentrated steps are challenging and may cause sample loss. Herein, this article reviews MNPs, including their fate in the environment and toxic effects exhibited towards soil microorganisms, plants and humans along with the interaction of MNPs with PTEs. In addition, various analysis methods of MNPs and management of MNPs as well as the crucial challenges and future research studies in combating MNPs in soil system are also discussed.

Microplastics in the Environment: Intake through the Food Web, Human Exposure and Toxicological Effects

Recently, studies on microplastics (MPs) have increased rapidly due to the growing awareness of the potential health risks related to their occurrence. The first part of this review is devoted to MP occurrence, distribution, and quantification. MPs can be transferred from the environment to humans mainly through inhalation, secondly from ingestion, and, to a lesser extent, through dermal contact. As regards food web contamination, we discuss the microplastic presence not only in the most investigated sources, such as seafood, drinking water, and salts, but also in other foods such as honey, sugar, milk, fruit, and meat (chickens, cows, and pigs). All literature data suggest not-negligible human exposure to MPs through the above-mentioned routes. Consequently, several research efforts have been devoted to assessing potential human health risks. Initially, toxicological studies were conducted with aquatic organisms and then with experimental mammal animal models and human cell cultures. In the latter case, toxicological effects were observed at high concentrations of MPs (polystyrene is the most common MP benchmark) for a short time. Further studies must be performed to assess the real consequences of MP contamination at low concentrations and prolonged exposure.

Microplastic degradation as a sustainable concurrent approach for producing biofuel and obliterating hazardous environmental effects: A state-of-the-art review

As plastics have been omnipresent in society ever since their introduction in 1907, global plastic production has ballooned in the 20th century or the Plasticene Era (Plastic Age). After their useful life span, they deliberately or accidentally, are disposed of in the environment. Influenced by different factors, plastics undergo fragmentation into microplastics (MPs) and present hazardous risks in all life forms including humans. Obliterating MPs from the environment has been a global challenge for the attainment of sustainable development goals (SDGs). This review aims to present MP degradation routes with a great focus on the thermodegradation and biodegradation routes as sustainable routes of MP degradation. These routes can achieve the reduction and obliteration of MPs in the environment, thus reducing their hazardous effects. Moreover, the thermodegradation of MPs can produce fuels that help solve the dilemma of energy security. Overall, continued research and development are still needed, however, these novel approaches and the increased awareness of the microplastics' hazards give us hope that we can achieve sustainable development in the near future.

Microplastics in terrestrial ecosystems: Moving beyond the state of the art to minimize the risk of ecological surprise

Microplastic (plastic particles measuring <5mm) pollution is ubiquitous. Unlike in other well-studied ecosystems, for example, marine and freshwater environments, microplastics in terrestrial systems are relatively understudied. Their potential impacts on terrestrial environments, in particular the risk of causing ecological surprise, must be better understood and quantified. Ecological surprise occurs when ecosystem behavior deviates radically from expectations and generally has negative consequences for ecosystem services. The properties and behavior of microplastics within terrestrial environments may increase their likelihood of causing ecological surprises as they (a) are highly persistent global pollutants that will last for centuries, (b) can interact with the abiotic environment in a complex manner, (c) can impact terrestrial organisms directly or indirectly and (d) interact with other contaminants and can facilitate their transport. Here, we compiled findings of previous research on microplastics in terrestrial environments. We systematically focused on studies addressing different facets of microplastics related to their distribution, dispersion, impact on soil characteristics and functions, levels of biological organization of tested terrestrial biota (single species vs. assemblages), scale of experimental study and corresponding ecotoxicological effects. Our systematic assessment of previous microplastic research revealed that most studies have been conducted on single species under laboratory conditions with short-term exposures; few studies were conducted under more realistic long-term field conditions and/or with multi-species assemblages. Studies targeting multi-species assemblages primarily considered soil bacterial communities and showed that microplastics can alter essential nutrient cycling functions. More ecologically meaningful studies of terrestrial microplastics encompassing multi-species assemblages, critical ecological processes (e.g., biogeochemical cycles and pollination) and interactions with other anthropogenic stressors must be conducted. Addressing these knowledge gaps will provide a better understanding of microplastics as emerging global stressors and should lower the risk of ecological surprise in terrestrial ecosystems.

Are biodegradable plastics an environmental rip off?

While the use of biodegradable polymers is recognized as a global strategy to minimize plastic pollution, the technical standards (TS) used to attest their biodegradability may not be in compliance with most environmental parameters observed aquatic ecosystems. Indeed, through a careful assessment of the TS currently in use, this study evidenced that these guidelines cover only a fraction of the biogeochemical parameters seen in nature and largely disregard those that occur in the deep-sea. Thus, these TS may not be able to ensure the degradation of such polymers in natural environments, where microbial activity, pH, temperature, salinity, UV radiation and pressure are highly variable. This raises environmental concern, since relevant parcel of plastic ends up in the oceans reaching deep zones. Therefore, there is an urgent need to revise these TS, which must consider the actual fate of most plastic debris and include assessments under the challenging conditions found at these types of environment, alongside microplastic formation and ecotoxicology effects. Moreover, the next generation of biodegradability tests must be designed to enable a cost-effective implementation and incorporate accurate analytical techniques to assess polymer transformation. Furthermore, certification should provide information on time scale and degradation rates and, preferably, be globally harmonized.

Photocatalytic Degradation of Plastic Waste: A Mini Review

Plastic waste becomes an immediate threat to our society with ever-increasing negative impacts on our environment and health by entering our food chain. Sunlight is known to be the natural energy source that degrades plastic waste at a very slow rate. Mimicking the role of sunlight, the photocatalytic degradation process could significantly accelerate the degradation rate thanks to the photocatalyst that drastically facilitates the photochemical reactions involved in the degradation process. This mini review begins with an introduction to the chemical compositions of the common plastic waste. The mechanisms of photodegradation of polymers in general were then revisited. Afterwards, a few photocatalysts were introduced with an emphasis on titanium dioxide (TiO2), which is the most frequently used photocatalyst. The roles of TiO2 photocatalyst in the photodegradation process were then elaborated, followed by the recent advances of photocatalytic degradation of various plastic waste. Lastly, our perspectives on the future research directions of photocatalytic plastic degradation are present. Herein, the importance of catalytic photodegradation is emphasized to inspire research on developing new photocatalysts and new processes for decomposition of plastic waste, and then to increase its recycling rate particularly in the current pandemic with the ever-increasing generation of plastic waste.

Recent Advancements in Photocatalytic Valorization of Plastic Waste to Chemicals and Fuels

The continuous rise in plastic waste raises serious concerns about the ensuing effects on the pollution of global environment and loss of valuable resources. Developing efficient approach to recycle the plastic has been an urgent demand for realizing a sustainable circular economy. Photocatalytic valorization directly utilizes solar energy to transform plastic pollutant into chemicals and fuels, which is hardly implemented by traditional mechanical recycling and incineration strategies, thus offering a promising approach to address the contemporary waste and energy challenges. Here, we focus on the recent advances in the high-value utilization of plastic waste through photocatalysis. The basic principle and different reaction pathways for the photocatalytic valorization of plastic waste are presented. Then, the developed representative photocatalyst systems and converted products are elaborately discussed. At last, the review closes with critical thoughts on research challenges along with some perspectives for further development of this emerging and fascinating filed.

The Potential for PE Microplastics to Affect the Removal of Carbamazepine Medical Pollutants from Aqueous Environments by Multiwalled Carbon Nanotubes

Microplastics are ubiquitous in aquatic environments and interact with other kinds of pollutants, which affects the migration, transformation, and fate of those other pollutants. In this study, we employ carbamazepine (CBZ) as the contaminant to study the influence of polyethylene (PE) microplastics on the adsorption of CBZ pollutants by multiwalled carbon nanotubes (MCNTs) in aqueous solution. The adsorption capacity of CBZ by MCNTs in the presence of PE microplastics was obviously lower than that by MCNTs alone. The influencing factors, including the dose of microplastics, pH, and CBZ solution concentration, on the adsorption of CBZ by MCNTs and MCNTs-PE were thoroughly investigated. The adsorption rate of CBZ by MCNTs decreased from 97.4% to 90.6% as the PE microplastics dose increased from 2 g/L to 20 g/L. This decrease occurred because the MCNTs were coated on the surface of the PE microplastics, which further decreased the effective adsorption area of the MCNTs. This research provides a framework for revealing the effect of microplastics on the adsorption of pollutants by carbon materials in aqueous environments.

Polystyrene microplastics induce apoptosis via ROS-mediated p53 signaling pathway in zebrafish

Microplastic (MP) pollution is ubiquitous and has become an emerging threat to aquatic biota. Recent scientific reports have recorded their toxic impacts at the cellular and organism levels, but the underlying molecular mechanism of their toxicity remains unclear. The present study elucidates an array of molecular events underlying apoptosis in the gills of polystyrene microplastics (PS-MPs) exposed zebrafish (Danio rerio). PS-MPs at different concentrations (10 and 100 μg L^-1) induced the reactive oxygen species (ROS) generation, in turn affecting the oxidative and immune defense mechanism. The expression profile of antioxidant genes cat, sod1, gpx1a and gstp1 were altered significantly. PS-MPs also significantly inhibited the neurotransmission in zebrafish. In addition, the PS-MPs exposure upregulated the expression of p53, gadd45ba, and casp3b resulting in apoptosis. We demonstrate that PS-MPs significantly upregulate the transcriptional pattern of tnfa and ptgs2a which are essential gene markers in inflammatory mechanism. Further, the oxidative damage induced by PS-MPs exposure could lead to cytological damage resulting in altered lamellar structures, capillary dilation, and necrosis in gill histomaps. In conclusion, the findings of this work strongly suggest that PS-MPs induce dose-and time-dependent ROS mediated apoptotic responses in zebrafish. Furthermore, the physiological responses observed in the gills correlate with the above observations and helps in unravelling the potential molecular mechanism underpinning the PS-MPs toxicity in zebrafish.

Acute and Sub-Chronic Effects of Microplastics (3 and 10 µm) on the Human Intestinal Cells HT-29

Due to ingestion of contaminated foods, the human gastrointestinal tract is the most likely site of exposure to microplastics (MPs) with gut barrier dysfunction and intestinal inflammation. Aimed to assess the effects induced by MPs with different granulometry (polystyrene (PS) 3 and 10 µm), we performed an in vitro study by using the human intestinal cell line HT29. As a novelty, we assessed the sub-chronic exposure extending the treatment up to 48 days simulating the in vivo situation. In the range of 100–1600 particles mL⁻¹, both the PS suspensions had moderate cytotoxicity after 24 h with percentages of mortality between 6.7 and 21.6 for the 10 µm and 6.1 and 29.6 for the 3 µm PS. Microscopic observation highlighted a more pronounced lysosomal membrane permeabilization in HT29 exposed to PS 3µm. Reactive oxygen species production was higher in cells exposed to PS 10 µm, but sub-chronic exposure highlighted the ability of the cells to partially neutralize this effect. Comet-assay confirmed the temporary oxidative damage that was PS-induced. Overall, considering the very fast turnover of intestinal cells, the increase in cell mortality, equal to 25% and 11% for 3 and 10 µm PS-MPs for each time point, could trigger intestinal disorders due to prolonged exposure.

Weathering of microplastics and interaction with other coexisting constituents in terrestrial and aquatic environments

Weathering of microplastics (MPs, < 5 mm) in terrestrial and aquatic environments affects MP transport and distribution. This paper first summarizes the sources of MPs, including refuse in landfills, biowastes, plastic films, and wastewater discharge. Once MPs enter water and soil, they undergo different weathering processes. MPs can be converted into small molecules (e.g., oligomers and monomers), and may be completely mineralized under the action of free radicals or microorganisms. The rate and extent of weathering of MPs depend on their physicochemical properties and environmental conditions of the media to which they are exposed. In general, water dissipates heat better, and has a lower temperature, than land; thus, the weathering rate of MPs in the aquatic environment is slower than in the terrestrial environment. These weathering processes increase oxygen-containing functional groups and the specific surface area of MPs, which influence the sorption and aggregation that occur between weathered MPs and their co-existing constituents. More studies are needed to investigate the various weathering processes of diverse MPs under natural field conditions in soils, sediments, and aquatic environments, to understand the impact of weathered MPs in the environment.