Effects of Microplastics in Soil Ecosystems: Above and Below Ground

Soil properties, microbial diversity, and changes in the functionality of saline-alkali soil are driven by microplastics

With the intensification of microplastic (MP) pollution, the impact of MPs on soil ecosystems has garnered considerable attention. We investigated the effects of two commonly used MPs, polyethylene (PE) and polypropylene (PP), at different sizes and doses, on the properties and microbial communities in saline-alkali soil. We found that MP treatment significantly reduced the electrical conductivity but somewhat enhanced the enzyme activities and effective nutrient content of the soil. Microbial diversity is affected by the type, dose, size and interaction of MPs, with fungi being more sensitive than bacteria. Under high-dose PE treatment, the dominant bacteria and fungi enriched, and the diversity indexes declined significantly. Meanwhile, under high-dose PP treatment, several unique bacteria and fungi with low abundance were observed, which eventually increased the diversity indexes. Moreover, PE exerted a stronger effect on bacterial function than PP. High-dose PE treatment suppressed the nitrogen fixation potential of soil bacteria. However, high-dose PP treatment promoted that. In conclusion, our findings showed that PE exerts a stronger negative effect on saline-alkali soil ecosystems than PP. Our findings help bridge the knowledge gap in the impact of MPs on saline-alkaline soils and provide guidance for the rational use of agricultural plastics in saline-alkaline soils.

Microplastics in biosolids: A review of ecological implications and methods for identification, enumeration, and characterization

Biosolids, or treated sludge, are by-products of the wastewater treatment processes and are commonly used in agricultural applications to enrich soil nutrients. However, it contains microplastics, plastic particles with a diameter below 1 mm. Microplastics exist and accumulate in the environment, which can have major impacts on the ecosystem. Despite their abundance in the environment, there are to date no standardized methods for their enumeration and characterization. A literature review was conducted focusing on the occurrence of microplastics at wastewater treatment plants, particularly in the solid waste stream, and their influence on the soil ecosystem where biosolids is applied. We found a conflicting evidence to which extent microplastics negatively impact the ecosystem. Some reported either a direct negative impact of microplastics or because of microplastic interaction with other soil contaminants. Meanwhile, other studies showed no effect or at certain amount of microplastics on the ecosystem. We also found that microplastics size, shape, type, concentration, and exposure time play a critical role in their ecological impacts. However, currently, there is no unified approach for microplastics identification and characterization in solid waste resulting in a various and incomparable data. Therefore, utilizing standardized methods for microplastics analysis must be considered as the initial step to better understand the impact of microplastics onto the environment. We suggest a method's scaling comparison as a practical approach to select and develop techniques based on cost, time, data obtained, accuracy, and sensitivity criteria. Further research into the ecotoxicity of microplastics and continuous monitoring of biosolid applications are also necessary.

Unaccounted Microplastics in the Outlet of Wastewater Treatment Plants—Challenges and Opportunities

Since the 1950s, plastic production has skyrocketed. Various environmental and human activities are leading to the formation and accumulation of microplastics (MPs) in aquatic and terrestrial ecosystems, causing detrimental effects on water, soil, plants, and living creatures. Wastewater treatment plants (WWTPs) are one of the primary MP management centers meant to check their entry into the natural systems. However, there are considerable limitations in effectively capturing, detecting, and characterizing these MPs in the inlet and outlet of WWTPs leading to “unaccounted MPs” that are eventually discharged into our ecosystems. In order to assess the holistic picture of the MPs’ distribution in the ecosystems, prevent the release of these omitted MPs into the environment, and formulate regulatory policies, it is vital to develop protocols that can be standardized across the globe to accurately detect and account for MPs in different sample types. This review will cover the details of current WWTP adoption procedures for MP management. Specifically, the following aspects are discussed: (i) several processes involved in the workflow of estimating MPs in the outlet of WWTPs; (ii) key limitations or challenges in each process that would increase the uncertainty in accurately estimating MPs; (iii) favorable recommendations that would lead to the standardization of protocols in the workflow and facilitate more accurate analysis of MPs; (iv) research opportunities to tackle the problem of ‘missing MPs’; and (v) future research directions for the efficient management of MPs. Considering the burgeoning research interest in the area of MPs, this work would help early scientists in understanding the current status in the field of MP analysis in the outlet of WWTPs.

The original polyethylene microplastics inhibit the growth of sweet potatoes and increase the safety risk of cadmium

Microplastics (MPs) and heavy metals (HMs) co-exist in sweet potato fields of China. As the main component of agricultural field mulch and one of the most polluting and harmful HMs, the effects of polyethylene microplastics (PE MPs) and cadmium (Cd) on sweet potato and soil environment are remains unclear. Here, pot and hydroponic experiments are used to explore the effects of original and weathered PE MPs on growth and Cd uptake of sweet potatoes. The results of pot experiments reveal that compared with the control (0%), 5% of weathered PE MPs can significantly increase soil electrical conductivity (EC); both 5% of the original PE MPs and weathered PE MPs can significantly reduce the concentration of Olsen phosphorus (P) and Olsen potassium (K) in soil, inhibit plant growth, but significantly increase Cd accumulation and glutathione (GSH) level in tissues of sweet potatoes, and also induce membrane lipid peroxidation. In addition, compared to 5% weathered PE MPs, 5% original PE MPs significantly reduce soil EC, growth and peroxidase level of sweet potatoes, but significantly increase Cd concentration in leaves and stems. The results of hydroponic experiment show that original PE MPs significantly increase the P, K, and Cd adsorption compared with weathered PE MPs, and Cd increases the original PE MPs accumulation in the root cortex but decrease PE MPs accumulation in shoots. To sum up, our study investigates the differences and reasons of the effects of original and weathered PE MPs on growth and Cd absorption of sweet potatoes.

Impact of plastic mulching as a major source of microplastics in agroecosystems

The contamination of agroecosystems by microplastics (MPs) has raised great concerns recently. Plastic mulching has contributed a lot in the building of MP pollution in farmlands. This technique has been in use for decades worldwide because of its immense advantages, preferably in drier and colder regions. The physical extraction of plastic mulches at the end of the growing season is very laborious and ineffective, and thus small pieces of mulches are left in the field which later convert into MP particles after aging, weathering, or on exposure to solar radiation. MPs not only influence physical, chemical, or biological properties of soils but also reduce crop productivity which could be a threat to our food security. They also interact with and accumulate other environmental contaminants such as microbial pathogens, heavy metals, and persistent organic pollutants on their surfaces which increase their risk of toxicity in the environment. MPs also transfer from one trophic level to the other in the food chain and ultimately may impact human health. Because of the ineffectiveness of the recovery of plastic film fragments from fields, researchers are now mainly focusing on alternative solutions to conventional plastic mulch films such as the use of biodegradable mulches. In this review, we have discussed the issue of plastic mulch films in agroecosystems and tried to link already existing knowledge to the current limitations in research on this topic from cropland soils and future prospects have been identified and proposed.

Potential risk assessment and toxicological impacts of nano/micro-plastics on human health through food products

The problem of environmental pollution with plastic is becoming more and more acute every year. Due to the low rate of decomposition of plastic, its particles get into food and harm the human body. This chapter focuses on the potential risks and toxicological effects of both nano and microplastics on human health. The main places of distribution of various toxicants along with the food chain have been established. The effects of some examples of the main sources of micro/nanoplastics on the human body are also emphasised. The processes of entry and accumulation of micro/nanoplastics are described, and the mechanism of accumulation that occurs inside the body is briefly explained. Potential toxic effects reported from studies on various organisms are highlighted as well.

Effects of microplastics and cadmium on the soil-wheat system as single and combined contaminants

Two types of microplastics (MPs) (micro polyethylene (mPE) and micro polypropylene (mPP)) were studied alongside and cadmium (Cd) to determine how they affected soil-wheat systems, both individually and in mixed combinations. This was accomplished by carrying out a pot experiment to reveal their respective interaction effects. Results showed that in different Cd pollution levels soils (0, 1, and 5 mg kg^-1), chlorophyll concentrations in wheat leaves decreased markedly with rising levels of mPE/mPP. In the single mPE treatment, as the mPE content in the soil increased, the aboveground and root biomass improved. By contrast, in the single mPP treatment, when the mPP content was low, the aboveground biomass of wheat increased and with the mPP content increased, the aboveground biomass of wheat decreased. This result was also shown in the combined contamination of mPE/mPP and Cd (1 mg kg^-1) in the root biomass. With an increase in Cd concentration (that is, at 5 mg kg^-1) in the combined contamination, this phenomenon continued in the aboveground biomass while in the roots, there was a promotion effect. At Cd contaminated soil (1 mg kg^-1), MPs inhibited Cd enrichment in aboveground wheat, but at 5 mg kg^-1, Cd enrichment was promoted instead, in both aboveground and roots. Adding mPE/mPP diminished pH and the Cd effective state concentration in soil. The combined contamination of mPE/mPP and Cd affected the Cd biological enrichment in the wheat to some extent, which was influenced by the types of MP and pollution levels of Cd in the soil.

Microplastics in composts, digestates, and food wastes: A review

Diverting food waste from landfills to composting or anaerobic digestion can reduce greenhouse gas emissions, enable the recovery of energy in usable forms, and create nutrient-rich soil amendments. However, many food waste streams are mixed with plastic packaging, raising concerns that food waste-derived composts and digestates may inadvertently introduce microplastics into agricultural soils. Research on the occurrence of microplastics in food waste-derived soil amendments is in an early phase and the relative importance of this potential pathway of microplastics to agricultural soils needs further clarification. In this paper, we review what is known and what is not known about the abundance of microplastics in composts, digestates, and food wastes and their effects on agricultural soils. Additionally, we highlight future research needs and suggest ways to harmonize microplastic abundance and ecotoxicity studies with the design of related policies. This review is novel in that it focuses on quantitative measures of microplastics in composts, digestates, and food wastes and discusses limitations of existing methods and implications for policy.

Responses of maize (Zea mays L.) seedlings growth and physiological traits triggered by polyvinyl chloride microplastics is dominated by soil available nitrogen

As a burgeoning pollutant, microplastics (MPs) has elicited global concern. However, ecological effects and mechanisms of MPs on plant-soil system are still poorly understood. In the present study, the impacts of polyvinyl chloride microplastics (PVC-MPs) on maize (Zea mays L.) seedlings growth and physiological traits and soil properties were discussed through a 30-day pot experiment. Results showed that PVC-MPs had greater toxicity effect on seedlings shoot biomass than root biomass. To defense the impact of PVC-MPs, the superoxide dismutase and catalase activities in seedlings leaf were stimulated. Moreover, the adhesion of MPs on soil particles increased, and soil microorganism, enzymes, and nutrients were altered significantly with increasing content of PVC-MPs. Notably, soil nitrate nitrogen decreased significantly with increasing content of PVC-MPs, whereas soil ammonium nitrogen was promoted under lower contents (0.1% and 1%) of PVC-MPs. Redundancy analysis indicated that soil nitrate nitrogen and ammonium nitrogen can explain 87.4% and 7.7% of variation in maize seedlings growth and physiological traits, respectively. These results display that maize seedlings shoot is more susceptible to the impact of PVC-MPs and soil available nitrogen is the primary limiting factor on maize seedlings growth and physiological traits triggered by PVC-MPs. Impacts of PVC-MPs on maize seedlings growth and physiological traits by nitrogen depletion lead to the possible yield and economic loess and potential risks due to the over use of nitrogen fertilizers.

Understanding the underestimated: Occurrence, distribution, and interactions of microplastics in the sediment and soil of China, India, and Japan

Microplastics (MPs) are non-biodegradable substances that can sustain our environment for up to a century. What is more worrying is the incapability of modern technologies to annihilate MPs from om environment. One ramification of MPs is their impact on every kind of life form on this planet, which has been discussed ahead; that is why these substances are surfacing in everyday discussions of scholars and researchers. This paper discusses the overview of the global occurrence, abundance, analysis, and remediation techniques of MPs in the environment. This paper primarily reviews the event and abundance of MPs in coastal sediments and agricultural soil of three major Asian countries, India, China, and Japan. A significant concentration of MPs has been recorded from these countries, which affirms its strong presence and subsequent environmental impacts. Concentrations such as 73,100 MPs/kg in Indian coastal sediments and 42,960 particles/kg in the agricultural soil of China is a solid testimony to prove their massive outbreak in our environment and require urgent attention towards this issue. Conclusions show that human activities, rivers, and plastic mulching on agricultural fields have majorly acted as carriers of MPs towards coastal and terrestrial soil and sediments. Later, based on recorded concentrations and gaps, future research studies are recommended in the concerned domain; a dearth of studies on MPs influencing Indian agricultural soil make a whole sector and its consumer vulnerable to the adverse effects of this emerging contaminant.

Atrazine sorption on biodegradable microplastics: Significance of microbial aging

The study of the environmental sorption behavior of typical biodegradable microplastics (BMPs) during biodegradation is essential given the different characteristics of BMPs and conventional microplastics (MPs) and the knowledge gap on the sorption capacity of BMPs for pollutants during degradation. In this study, polylactic acid (PLA) and poly (butylene-adipate-co-terephthalate) (PBAT) were chosen as research objects, and the effects of soil microbial aging on their surface properties and atrazine (ATZ) sorption were investigated. The structural composition of the bacterial community was essentially similar between B-PLA and B-PBAT. Microbial aging action created new pores and cavities in PLA, forming microbial films that led to the agglomeration of PLA particles. The microbial aging action destroyed the amorphous regions of PLA and PBAT, resulting in higher crystallinity, and the ester groups broke to form carboxyl groups. The equilibrium sorption (Q_e) of B-PLA increased by 11.12 % compared with PLA, while the Q_e of B-PBAT decreased by 4.95 % compared to PBAT. These results show that soil microbes change the surface properties of PLA and PBAT, thus affecting the sorption mechanism of ATZ, and provide a theoretical premise for the behavior and ecological risk assessment of ATZ in the presence of BMPs.

Microfluidics as a Ray of Hope for Microplastic Pollution

Microplastic (MP) pollution is rising at an alarming rate, imposing overwhelming problems for the ecosystem. The impact of MPs on life and environmental cycles has already reached a point of no return; yet global awareness of this issue and regulations regarding MP exposure could change this situation in favor of human health. Detection and separation methods for different MPs need to be deployed to achieve the goal of reversing the effect of MPs. Microfluidics is a well-established technology that enables to manipulate samples in microliter volumes in an unprecedented manner. Owing to its low cost, ease of operation, and high efficiency, microfluidics holds immense potential to tackle unmet challenges in MP. In this review, conventional MP detection and separation technologies are comprehensively reviewed, along with state-of-the-art examples of microfluidic platforms. In addition, we herein denote an insight into future directions for microfluidics and how this technology would provide a more efficient solution to potentially eradicate MP pollution.

Molecular mechanisms of toxicity and detoxification in rice (Oryza sativa L.) exposed to polystyrene nanoplastics

Nanoplastics (NPs) are an emerging threat to higher plants in terrestrial ecosystems. However, the molecular of NP-related phytotoxicity remains unclear. In the present study, rice seedlings were exposed to polystyrene (PS, 50 nm) NPs at 0, 50, 100, and 200 mg/L under hydroponic conditions to investigate the induced physiological indices and transcriptional mechanisms. We found that 50, 100, and 200 mg/L PS significantly reduced root (53.05%, 49.61%, and 57.58%, respectively) and shoot (54.63%, 61.56%, and 62.64%, respectively) biomass as compared with the control seedlings. The activities of antioxidant enzymes, including catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and ascorbate peroxidase (APX), were significantly activated in all PS treatment groups, indicating that PS inhibited plant growth and induced oxidative stress. Transcriptome analyses showed that PS modulated the expression of the genes involved in cell detoxification, active oxygen metabolism, mitogen-activated protein kinase (MAPK), and plant hormone transduction pathways. Our study provides new insights into phytotoxicity by demonstrating the potential underlying toxicity of PS NPs in higher plants.

The Effect of Microplastics-Plants on the Bioavailability of Copper and Zinc in the Soil of a Sewage Irrigation Area

It is essential to understand the occurrence from and plant bioavailability of soil microplastics to heavy metals in soils to assess their environmental fate and risk. The purpose of this study was to evaluate the effect of different microplastic concentrations on the bioavailability of copper and zinc in soil. The relationship between the availability of heavy metals in soil assessed by chemical methods (soil fractionation) and the bioavailability of copper and zinc assessed by biological methods (accumulation in maize and cucumber leaves) in relation to the concentration of microplastics. The results showed that copper and zinc in soil shifted from stable to effective fraction with increasing polystyrene concentrations, which would increase the toxicity and bioavailability of heavy metals. When the concentration of polystyrene microplastics increased, copper and zinc accumulation in plants increased, chlorophyll a and chlorophyll b decreased, and malondialdehyde increased. It is shown that the addition of polystyrene microplastics promoted the toxicity of copper and zinc and inhibited plant growth.

Personal protective equipment (PPE) disposal during COVID-19: An emerging source of microplastic and microfiber pollution in the environment

Waste generated by healthcare facilities during the COVID-19 pandemic has become a new source of pollution, particularly with the widespread use of single-use personal protective equipment (PPE). Releasing microplastics (MPs) and microfibers (MFs) from discarded PPE becomes an emerging threat to environmental sustainability. MPs/MFs have recently been reported in a variety of aquatic and terrestrial ecosystems, including water, deep-sea sediments, air, and soil. As COVID-19 spreads, the use of plastic-made PPE in healthcare facilities has increased significantly worldwide, resulting in massive amounts of plastic waste entering the terrestrial and marine environments. High loads of MPs/MFs emitted into the environment due to excessive PPE consumption are easily consumed by aquatic organisms, disrupting the food chain, and potentially causing chronic health problems in humans. Thus, proper management of PPE waste is critical for ensuring a post-COVID sustainable environment, which has recently attracted the attention of the scientific community. The current study aims to review the global consumption and sustainable management of discarded PPE in the context of COVID-19. The severe impacts of PPE-emitted MPs/MFs on human health and other environmental segments are briefly addressed. Despite extensive research progress in the area, many questions about MP/MF contamination in the context of COVID-19 remain unanswered. Therefore, in response to the post-COVID environmental remediation concerns, future research directions and recommendations are highlighted considering the current MP/MF research progress from COVID-related PPE waste.

Promising Agromaterials Based on Biodegradable Polymers: Polylactide and Poly-3-Hydroxybutyrate

Electrospun fabrics have unique properties due to their uniform morphology and high surface area to volume ratio. Ultrathin nonwoven fabrics are produced for many applications: biomedical, nanosensors, tissue engineering and filtration systems. In this work, nonwoven polylactide, polylactide/natural rubber, poly-3-hydroxybutyrate, and poly-3-hydroxybutyrate/nitrile butadiene rubber fabrics were prepared by electrospinning methods. The obtained fabric samples were used as substrates for the growth of winter wheat seeds "Yubileinaya 100" (Triticum aestivum L.). The stimulating effect of polymer substrates on seed germination and plant growth was shown. The structure and properties of nonwoven agromaterials were controlled by differential scanning calorimetry, IR-spectroscopy, and optical microscopy. The mechanical properties of the obtained fabrics before and after their utilization as substrates were studied. After the wheat growing experiment, the degree of crystallinity of PHB and PHB/NBR samples decreased by 12% and they completely lost their mechanical properties. It is shown that the main factors providing the efficiency of seed growth technology on polymer substrates are the chemical nature and structure of the biodegradable matrix.

Potential of Advanced Oxidation as Pretreatment for Microplastics Biodegradation

In the last two decades, microplastics (MP) have been identified as an emerging environmental pollutant. Due to their small size, MP particles may easily enter the food chain, where they can have adverse effects on organisms and the environment in general. The common methods for the removal of pollutants from the environment are not fully effective in the elimination of MP; thus, it is necessary to find a more suitable treatment method(s). Among the various approaches tested, biodegradation is by far the most environmentally friendly and economically acceptable remediation approach. However, it has serious drawbacks, generally related to the rather low removal rate and often insufficient efficiency. Therefore, it would be beneficial to use some of the less economical but more efficient methods as pretreatment prior to biodegradation. Such pretreatment would primarily serve to increase the roughness and hydrophilicity of the surface of MP, making it more susceptible to bioassimilation. This review focuses on advanced oxidation processes (AOPs) as treatment methods that can enhance the biodegradation of MP particles. It considers MP particles of the six most commonly used plastic polymers, namely: polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate and polyurethane. The review highlights organisms with a high potential for biodegradation of selected MP particles and presents the potential benefits that AOP pretreatment can provide for MP biodegradation.

Metal Release from Microplastics to Soil: Effects on Soil Enzymatic Activities and Spinach Production

Microplastics (MPs) represent emergent pollutants in terrestrial ecosystems. Microplastics can cause the release of metal and damage to crop quality. The present research aimed to evaluate the effects of Mater-bi (Bio-MPs) and polyethylene (PE-MPs) MPs at different concentrations on soil properties and on the growth of Spinacia oleracea L. Plants were grown in 30 pots filled with soil mixed with 0.5, 1 and 2% d.w. of Bio-MPs and PE-MPs and in 5 pots filled only with soil, considered as controls (K). At the end of the vegetative cycle, the spinach plants were evaluated for the epigeal (EPI) and hypogeal (HYPO) biomasses and the ratio of HYPO/EPI was calculated. In the soil, the total and the available fractions of Cr, Cu, Ni and Pb and the hydrolase (HA), β-glucosidase (β-glu), dehydrogenase (DHA) and urease (U) activities were evaluated. The results revealed that the addition of Bio-MPs increased soil total Cr, Cu and Pb and available Cu concentrations, and the addition of PE-MPs increased Pb availability. In soil contaminated by both Bio-MPs and PE-MPs, HA and β-glu activities were stimulated, whereas DHA activity was reduced. The HYPO and HYPO/EPI biomasses were reduced only in soils contaminated by the 2% Bio-MPs.

Phytotoxic Effects of Polystyrene and Polymethyl Methacrylate Microplastics on Allium cepa Roots

Plastic contamination has become one of the most pressing environmental issues due to rapidly increasing production of disposable plastic products, their fragmentation into smaller pieces, and long persistence in the environment, which affects all living organisms, including plants. In this study, Allium cepa roots were exposed to 0.01, 0.1, and 1 g L^-1 of commercial polystyrene (PS-MPs) and polymethyl methacrylate microparticles (PMMA-MPs) for 72 h. Dynamic light scattering (DLS) analyses showed high stability of both types of MPs in ultrapure water used for A. cepa treatment. Morphometric analysis revealed no significant change in root length compared to control. Pyrolysis hyphenated to gas chromatography and mass spectrometry (Py-GC-MS) has proven PS-MPs uptake by onion roots in all treatments, while PMMA-MPs were recorded only upon exposure to the highest concentration. Neither MPs induced any (cyto)toxic effect on root growth and PMMA-MPs even had a stimulating effect on root growth. ROS production as well as lipid and protein oxidation were somewhat higher in PS-MP treatments compared to the corresponding concentrations of PMMA-MP, while neither of the applied MPs induced significant damage to the DNA molecule assayed with a Comet test. Significantly elevated activity of H₂O₂ scavenging enzymes, catalase, and peroxidases was measured after exposure to both types of MPs. Obtained results suggest that onion roots take up PS-MPs more readily in comparison to PMMA-MPs, while both types of MPs induce a successful activation of antioxidant machinery in root cells that prevented the occurrence of toxic effects.

Leaching of phthalate acid esters from plastic mulch films and their degradation in response to UV irradiation and contrasting soil conditions

Phthalate acid esters (PAEs) are commonly used plastic additives, not chemically bound to the plastic that migrate into surrounding environments, posing a threat to environmental and human health. Dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) are two common PAEs found in agricultural soils, where degradation is attributed to microbial decomposition. Yet the impact of the plastic matrix on PAE degradation rates is poorly understood. Using ¹⁴C-labelled DBP and DEHP we show that migration from the plastic matrix into soil represents a key rate limiting step in their bioavailability and subsequent degradation. Incorporating PAEs into plastic film decreased their degradation in soil, DBP (DEHP) from 79% to 21% (9% to <1%), over four months when compared to direct application of PAEs. Mimicking surface soil conditions, we demonstrated that exposure to ultraviolet radiation accelerated PAE mineralisation twofold. Turnover of PAE was promoted by the addition of biosolids, while the presence of plants and other organic residues failed to promote degradation. We conclude that PAEs persist in soil for longer than previously thought due to physical trapping within the plastic matrix, suggesting PAEs released from plastics over very long time periods lead to increasing levels of contamination.

Micro and nanoplastics ravaging our agroecosystem: A review of occurrence, fate, ecological impacts, detection, remediation, and prospects

Micro-and nanoplastics (MNPs) are particles that are smaller than a millimeter in size and have infiltrated both terrestrial and aquatic ecosystems. MNPs pollution have become a widespread problem causing severe adverse effects on human health and the environment worldwide. Once in the environment, these polymers are not easily degradable due to their recalcitrant nature and small size and are easily consumed by aquatic organisms and transported through the food chain, at great risk to human health. Substantial evidence demonstrates the negative effects of MNPs residues on aquatic organisms' reproductive and developmental defects. Similarly, soil flora, soil quality, and plant height have been severely impacted by their presence in the agroecosystem. This is evident in the inhibition of water absorption by blocked seed pores, delayed germination, and the dramatic decline in transpiration rates and growth of plant roots, inevitably leading to drop in biomass and crop production, posing an overall threat to global food security. In this review, we present the impact of MNPs in agroecosystems around the globe, including their sources, occurrence, distribution, transport, and ultimate fate. We recommend using bio-based plastics, eco-friendly remediation strategies, reformed agricultural practices, non-single-use synthetic plastic legislation, and increased plastic waste disposal awareness campaigns as effective tools to mitigate this problem.

A discussion of microplastics in soil and risks for ecosystems and food chains

Microplastics are among the major contaminations in terrestrial and marine environments worldwide. These persistent organic contaminants composed of tiny particles are of concern due to their potential hazards to ecosystem and human health. Microplastics accumulates in the ocean and in terrestrial ecosystems, exerting effects on living organisms including microbiomes, fish and plants. While the accumulation and fate of microplastics in marine ecosystems is thoroughly studied, the distribution and biological effects in terrestrial soil call for more research. Here, we review the sources of microplastics and its effects on soil physical and chemical properties, including water holding capacity, bulk density, pH value as well as the potential effects to microorganisms and animals. In addition, we discuss the effects of microplastics in combination with other toxic environmental contaminants including heavy metals and antibiotics on plant growth and physiology, as well as human health and possible degradation and remediation methods. This reflect is an urgent need for monitoring projects that assess the toxicity of microplastics in soil and plants in various soil environments. The prospect of these future research activities should prioritize microplastics in agro-ecosystems, focusing on microbial degradation for remediation purposes of microplastics in the environment.

Environmental microplastics: Classification, sources, fates, and effects on plants

Microplastic (MP) pollution has become a global concern due to the generation of extensive plastic waste and products (370 million metric tons in 2020) that are difficult to biodegrade. Therefore, MPs have attracted a great deal of research attention, and many new findings regarding MPs (over 9000 papers published in the last 3 years) have been reported. MPs generally exert adverse effects on plants. As MPs accumulate in agricultural ecosystems, many studies have sought to understand the sources and fates of MPs and their effects on various plants. However, there have been few reviews of the properties of MPs, their effects on plants, and their interactions with other factors (e.g., drought, heat, ultraviolet light, plant hormones, heavy metals, and other pollutants) remain poorly understood. In this review, we performed scientometrics analyses of research papers (January 1, 2019, to September 30, 2022) in this field. We focused on the recent progress in the classification of MPs and their sources, circulation, and deposition in agricultural ecosystems. We review MP uptake and transport in plants, as well as factors (size, type, and environmental factors) that affect MP uptake, the positive and negative effects of MPs on plants, and the mechanisms of MP impacts on plants. We discuss current issues and future perspectives concerning research into plant interactions with MPs, along with some promising methods to manage the MP issue.

Environmental risk of microplastics after field aging: Reduced rice yield without mitigating yield-scale ammonia volatilization from paddy soils

Microplastics (MPs, <5 mm) are enriched in paddy ecosystems as emerging environmental pollutants. Biochar (BC) is a controversial recalcitrant carbon product that poses potential environmental risks. The presence of these two exogenous organic substances has been demonstrated to have impacts on soil nitrogen cycling and crop production. However, the after-effects of MPs and BC on soil ammonia (NH₃) volatilization and rice yield after field aging remain unexplored. In this study, two common MPs, including polyethylene (PE) and polyacrylonitrile (PAN), and BC were selected for rice growing season observations to study the impacts on soil NH₃ volatilization and rice yield after field aging. The results showed that the reduction of cumulative soil NH₃ losses by MPs was around 45% after one-year field aging, which was within the range of 40-57% in the previous rice season. Abatement of NH₃ volatilization by MPs mainly occurred in basal fertilization and was related to floodwater pH. Besides, the reduction rate of NH₃ volatilization by BC and MPs + BC was enhanced after field aging (63% and 50-57%) compared to that in the previous rice season (5% and 11-19%), with the abatement process occurring in the first supplementary fertilization. There was a significant positive correlation between cumulative NH₃ volatilization and soil urease activity. Notably, field aging removed the positive effect of MPs and MPs + BC in reducing yield-scale NH₃ losses in the previous rice season (∼62%). Furthermore, despite BC affecting rice yield insignificantly after field aging, the presence of MPs led to a significant 17-19% reduction in rice yield. Our findings reveal that differences in the after-effects of BC and MPs in field aging emerge, where the negative impacts of MPs on soil NH₃ abatement and crop yield are progressively becoming apparent and should be taken into serious consideration.

Global Research Activities on Micro(nano)plastic Toxicity to Earthworms

Micro(nano)plastics are emerging contaminants that have been shown to cause various ecotoxicological effects on soil biota. Earthworms, as engineers of the ecosystem, play a fundamental role in soil ecosystem processes and have been used as model species in ecotoxicological studies. Research that evaluates micro(nano)plastic toxicity to earthworms has increased greatly over the last decade; however, only few studies have been conducted to highlight the current knowledge and evolving trends of this topic. This study aims to visualize the research status and knowledge structure of the relevant literature. Bibliometrics and visualization analyses were conducted using co-citations, cooperation networks and cluster analysis. The results showed that micro(nano)plastic toxicity to earthworms is an emerging and increasingly popular topic, with 78 articles published from 2013 to 2022, the majority of which were published in the last two years. The most prolific publications and journals involved in this topic were also identified. In addition, the diversity of cooperative relationships among different countries and institutions confirmed the evolution of this research field, in which China contributed substantially. The high-frequency keywords were then determined using co-occurrence analysis, and were identified as exposure, bioaccumulation, soil, pollution, toxicity, oxidative stress, heavy metal, microplastic, Eisenia foetida and community. Moreover, a total of eight clusters were obtained based on topic knowledge clustering, and these included the following themes: plastic pollution, ingestion, combined effects and the biological endpoints of earthworms and toxic mechanisms. This study provides an overview and knowledge structure of micro(nano)plastic toxicity to earthworms so that future researchers can identify their research topics and potential collaborators.

Analysis of microplastics in soils on the high-altitude area of the Tibetan Plateau: Multiple environmental factors

Microplastics (MPs), a class of emerging contaminants, are ubiquitous in the environment, but limited information is known about them in remote terrestrial environment at high-altitude areas with inconvenient traffic and sparsely populated. In this study, 54 soil samples were collected from various land use patterns (greenhouse, ordinary farmland, grassland, and bare land) in western area of the Tibetan Plateau to determine the influence of land use type, altitude, meteorological parameters, and distance from the road edge on MP distribution. The MP abundance ranged from 0 (not detected) to 190 items/kg, with an average number of 64.8 items/kg. The concentration of MPs was slightly negatively correlated with altitude because of less human activities in high-altitude areas (especially agricultural activities). The random forest (RF) models showed that altitude was the most important driving factor that affected the MP distribution. Small-sized MPs were more abundant at higher altitudes than at low ones, and the special natural environment of the high-altitude areas (tall vegetation scarcely, UV, and strong wind speed) may be conducive to the degradation of MPs in surface soils. The special source of MPs in non-agricultural soils was associated with traffic behavior: parking and rest behavior beside roads at high altitude areas, which filled an important source of MPs in the plateau area. This study emphasized the need to investigate the effects of traffic activities on MPs in remote areas at high altitudes.

Extensive abundances and characteristics of microplastic pollution in the karst hyporheic zones of urban rivers

Cities are potential areas for microplastic pollution due to large-scale production and the use of plastic products. The karst ecosystem in southwestern China is fragile, and pollutants are more likely to be transported over long distance, resulting in higher pollution risks. Understanding the abundance and composition of microplastics in karst urban water systems is crucial for microplastic pollution management in a karst region. This study investigates the abundances and characteristics of microplastics typically found in river sediments in 10 cities in karst regions of Southwest China. The results show that the abundance of microplastics in sediments ranged from 800 items·kg^-1 to 4400 items·kg^-1, with an average of 2273 ± 775 items·kg^-1 (n = 30), indicating high abundance. Polyamide (PA) was the most common plastic polymer types in all sediment samples. The abundance of microplastics in the downstream (2527 ± 698 items·kg^-1) was higher than that in the midstream (2350 ± 999 items·kg^-1) and upstream areas (1943 ± 370 items·kg^-1), indicating a gradual accumulation effect in the karst water systems. Microplastic abundance in cities (2119 ± 838 items·kg^-1) was lower than in counties (2427 ± 671 items·kg^-1). No significant correlation was found between microplastic abundance in rivers of urban areas and the level of regional population and economy, but significantly negatively correlated with the efficiency of urban sewage treatment. The results obtained from this study provided insights into the management of microplastic pollution in urban river of a karst region.

Impact of starch-based bioplastic on growth and biochemical parameters of basil plants

The recent use of bioplastics in agriculture is considered an ecological choice, aimed at limiting the environmental impact of plastics, in line with the Sustainable Development Goals of the United Nations. However, the impact of bioplastic residues on the environment is unclear as knowledge is lacking. This is the first study investigating the effect of a starch-based bioplastic on the growth and biochemical parameters of basil. Bioplastic was experimentally prepared and added to the soil at 2.5 % (w/w), corresponding to twice the concentration of plastic mulch film residues currently found in cultivated soils, in view of the increasing agricultural use of bioplastics. Basil plants were grown without (controls) and with bioplastic addition for 35 days, under controlled experimental conditions. Compared to the control, plants exposed to bioplastic showed stunted growth (in terms of shoot fresh weight, height, and number of leaves). Significant reductions in the content of chlorophyll, protein, ascorbic acid, and glucose were also observed. Finally, the treatment caused oxidative stress, as evidenced by the increased content of malondialdehyde in the shoots. The addition of bioplastic increased the electrical conductivity and reduced the cation exchange capacity of the cultivation soil. These results suggest that bioplastic in soil may promote the onset of stressful conditions for plant growth in a similar manner to plastic. They will be complemented by further investigations to unravel the mechanisms underlying these responses, involving different doses and types of bioplastics and other crop species.

Effects of microplastics on cadmium accumulation by rice and arbuscular mycorrhizal fungal communities in cadmium-contaminated soil

Both microplastics (MPs) and cadmium (Cd) are common contaminants in soil-rice systems, but their combined effects remain unknown. Thereby, we explored the effects of three MPs, i.e., polyethylene terephthalate (PET), polylactic acid (PLA), and polyester (PES), on Cd accumulation in rice and the community diversity and structure of arbuscular mycorrhizal fungi (AMF) in soil spiked with or without Cd. Results showed that 2% PLA decreased shoot biomass (-28%), but PET had a weaker inhibitive effect. Overall, Cd alone did not significantly change shoot and root biomass and increased root biomass in combination with 0.2% PES. MPs generally increased soil Cd availability but decreased Cd accumulation in rice tissues. Both MPs and Cd improved the bioavailability and uptake of Fe and Mn in rice roots. MPs altered the diversity and community composition of AMF, depending on their type and dose and co-existing Cd. Overall, 2% PLA caused the most distinct changes in soil properties, plant growth and Cd accumulation, and AMF communities, but showed no synergistic interactions with Cd. In conclusion, MPs can mediate rice performance and Cd accumulation via altering soil properties, nutrient uptake, and root mycorrhizal communities, and biodegradable PLA MPs thought environment-friendly can exhibit higher phytotoxicity than conventional MPs.

The long-term uncertainty of biodegradable mulch film residues and associated microplastics pollution on plant-soil health

Biodegradable mulch film potentially offers an encouraging alternative to conventional (petroleum-based) plastic films. Since biodegradable films are more susceptible to rapid degradation, more microplastics (MPs) are likely to be generated than conventional films within the same time frame, probably leading to more severe MPs pollution and associated effects. However, the effect of biodegradable mulch film residues and associated MPs pollution on plant-soil health remains uncertainty. Here, we evaluated the potential effect of bio-MPs pollution on soil carbon (C) and nutrient (i.e., N and P) cycling, soil biology (microorganisms and mesofauna), and plant health, as these are crucial to agroecosystem functioning and the delivery of key ecosystem services. Unlike the inert (and therefore recalcitrant) C contained within petroleum-based MPs, at least 80% of the C from bio-MPs is converted to CO₂, with up to 20% immobilized in living microbial biomass (i.e., < 0.05 t C ha^-1). Although biodegradable films are unlikely to be important in promoting soil C storage, they may accelerate microbial biomass turnover in the short term, as well as CO₂ production. Compared to conventional MPs, bio-MPs degradation is more pronounced, thereby inducing greater alterations in microbial diversity and community composition. This may further alter N₂O and CH₄ emissions, and ultimately resulting in unpredictable consequences for global climate warming. The extent to which this may occur, however, has yet to be shown in either laboratory or field studies. In addition, bio-MPs have a large chance of forming nanoplastics, potentially causing a stronger toxic effect on plants relative to conventional MPs. Consequently, this would influence plant health, crop productivity, and food safety, leading to potential health risks. It is unclear, however, if these are direct effects on key plant processes (e.g. signaling, cell expansion) or indirect effects (e.g. nutrient deficiency or acidification). Overall, the question as to whether biodegradable mulch films offer a promising alternative to solve the conventional plastic legacy in soil over the long term remains unclear.

Impact of buried debris from agricultural biodegradable plastic mulches on two horticultural crop plants: Tomato and lettuce

Biodegradable mulches (BDM) are increasingly valued and used for substituting non-biodegradable plastic mulches polluting agricultural soils. They are tilled into soil, where they fragment and release compounds throughout their biodegradation. The consequences of BDM use on the plant-soil environment have been partially studied with pristine and with artificially-weathered BDM fragments. However, to guarantee safety use of BDM, studies on the BDM debris effects are required. For this, to determine potential effects of the field-weathering BDM on plants, a mesocosm experiment was performed by sowing seeds from two major plant species commonly cultivated with BDM, tomato (Lycopersicon esculentum) and lettuce (Lactuca sativa), in plant pots containing pristine and field-weathered pieces from seven different BDM formulations, one paper mulch, a polyethylene (PE) mulch, and no-mulch control pots. Germination of both plant species was unaffected by any of the mulch treatments; however, PHB (polyhydroxybutyrate)-based BDM fragments severely inhibited tomato and lettuce plant growth, 90 and 95 %, respectively. Moreover, all pristine and field-weathered BDM significantly delayed lettuce plant development. Tomato plant growth progressed better, but growth retardation was also evidenced with most field-weathered BDM treatments. Overall, field-weathered fragments caused stronger effects on plants than the pristine unused ones. No effects were found for PE mulch, either pristine or field-weathered. The obtained results highlight that BDM debris may alter plant development depending on their nature and on their weathering, rather than on their physical presence, and evidence the need to conduct further experiments on the impact of field-weathered BDM on the plant-soil environment.

Structural breakdown and phytotoxic assessments of PE degradation through acid hydrolysis, starch addition and Pseudomonas aeruginosa bioremediation

Vast amounts of plastic waste are causing serious environmental issues and urge to develop of new remediation methods. The aim of the study is to determine the role of inorganic (nitric acid), organic (starch addition), and biological (Pseudomonas aeruginosa) soil amendments on the degradation of Polyethylene (PE) and phytotoxic assessment for the growth of lettuce plant. The PE-degrading bacteria were isolated from the plastic-contaminated soil. The strain was identified as Pseudomonas aeruginosa (OP007126) and showed the highest degradation percentage for PE. PE was pre-treated with nitric acid as well as starch and incubated in the soil, whereas P. aeruginosa was also inoculated in PE-contaminated soils. Different combinations were also tested. FTIR analysis and weight reduction showed that though nitric acid was efficient in degradation, the combined application of starch and bacteria also showed effective degradation of PE. Phytotoxicity was assessed using morphological, physiological, and biochemical parameters of plant. Untreated PE significantly affected plants' physiology, resulting in a 45% reduction in leaf chlorophyll and a 40% reduction in relative water content. It also had adverse effects on the biochemical parameters of lettuce. Bacterial inoculation and starch treatment mitigated the harmful impact of stress and improved plants' growth as well as physiological and biochemical parameters; however, the nitric treatment proved phytotoxic. The observed results revealed that bacteria and starch could be effectively used for the degradation of pre-treated PE.

Nanoplastics in the soil environment: Analytical methods, occurrence, fate and ecological implications

Soils play a very important role in ecosystems sustainability, either natural or agricultural ones, serving as an essential support for living organisms of different kinds. However, in the current context of extremely high plastic pollution, soils are highly threatened. Plastics can change the chemical and physical properties of the soils and may also affect the biota. Of particular importance is the fact that plastics can be fragmented into microplastics and, to a final extent into nanoplastics. Due to their extremely low size and high surface area, nanoplastics may even have a higher impact in soil ecosystems. Their transport through the edaphic environment is regulated by the physicochemical properties of the soil and plastic particles themselves, anthropic activities and biota interactions. Their degradation in soils is associated with a series of mechanical, photo-, thermo-, and bio-mediated transformations eventually conducive to their mineralisation. Their tiny size is precisely the main setback when it comes to sampling soils and subsequent processes for their identification and quantification, albeit pyrolysis coupled with gas chromatography-mass spectrometry and other spectroscopic techniques have proven to be useful for their analysis. Another issue as a consequence of their minuscule size lies in their uptake by plants roots and their ingestion by soil dwelling fauna, producing morphological deformations, damage to organs and physiological malfunctions, as well as the risks associated to their entrance in the food chain, although current conclusions are not always consistent and show the same pattern of effects. Thus, given the omnipresence and seriousness of the plastic menace, this review article pretends to provide a general overview of the most recent data available regarding nanoplastics determination, occurrence, fate and effects in soils, with special emphasis on their ecological implications.

Microplastics Derived from Food Packaging Waste-Their Origin and Health Risks

Plastics are commonly used for packaging in the food industry. The most popular thermoplastic materials that have found such applications are polyethylene (PE), polypropylene (PP), poly(ethylene terephthalate) (PET), and polystyrene (PS). Unfortunately, most plastic packaging is disposable. As a consequence, significant amounts of waste are generated, entering the environment, and undergoing degradation processes. They can occur under the influence of mechanical forces, temperature, light, chemical, and biological factors. These factors can present synergistic or antagonistic effects. As a result of their action, microplastics are formed, which can undergo further fragmentation and decomposition into small-molecule compounds. During the degradation process, various additives used at the plastics' processing stage can also be released. Both microplastics and additives can negatively affect human and animal health. Determination of the negative consequences of microplastics on the environment and health is not possible without knowing the course of degradation processes of packaging waste and their products. In this article, we present the sources of microplastics, the causes and places of their formation, the transport of such particles, the degradation of plastics most often used in the production of packaging for food storage, the factors affecting the said process, and its effects.

Micro- and nano-plastics pollution and its potential remediation pathway by phytoremediation

This review proposed that phytoremediation could be applied for the decontamination of MPs/NPs. Micro- and nano-plastics (MPs < 5 mm; NPs < 100 nm) are emerging contaminants. Much of the recent concerns have focused on the investigation of their pollution and their potential eco-toxicity. Yet little review was available on the decontamination of MPs/NPs. Recently, the uptake of MPs/NPs by plants has been confirmed. Here, in view of the current knowledge, this review introduces MPs/NPs pollution and highlights the updated information about the interaction between MPs/NPs and plants. This review proposed that phytoremediation could be a potential possible way for the in situ remediation of MPs/NPs-contaminated environment. The possible mechanisms, influencing factors, and existing problems are summarized, and further research needs are proposed. This review herein provides new insights into the development of plant-based process for emerging pollutants decontamination, as well as the alleviation of MPs/NPs-induced toxicity to the ecosystem.

Microplastics in soil ecosystems: soil fauna responses to field applications of conventional and biodegradable microplastics

Although biodegradable plastics are considered an environmentally-friendly alternative to conventional plastics, the effects of biodegradable microplastics (BMPs) on soil faunal communities are poorly understood, especially under field conditions. Here, we investigated the loading impacts of two conventional low-density polyethylene (LDPE) and polypropylene (PP) MPs as well as two biodegradable polylactic acid (PLA) and polybutylene succinate (PBS) MPs at concentrations of 0, 5, 10, and 15 g/m² on soil fauna communities. After 40 d, all MP types did not affect the soil fauna communities. After 130 d, conventional MPs (LDPE-15 and PP-5) significantly increased the abundance of overall soil fauna-attributed mainly to changes in the abundance of Collembola; however, BMPs did not affect the soil fauna communities. Interestingly, MP-induced changes in the abundance and diversity of soil fauna showed a strong tendency to increase over time. Overall, these results indicate that the short-term effects of all MP types on soil faunal communities are inapparent, while soil fauna responses to conventional MPs and BMPs showed slight differences over time. Given these time-dependent soil fauna responses to MPs, we recommend an evaluation of the long-term effects of MPs on soil organisms to gain a comprehensive understanding of their effects on soil ecosystems.

Effects of microplastics and chlorpyrifos on earthworms (Lumbricus terrestris) and their biogenic transport in sandy soil

Although microplastics (MPs) are ubiquitous in agricultural soil, little is known about the effects of MPs combined with pesticides on soil organisms and their biogenic transport through the soil profile. In this study, we conducted mesocosm experiments to observe the effects of microplastics (polyethylene (LDPE-MPs) and biodegradable microplastics (Bio-MPs)) and chlorpyrifos (CPF) on earthworm (Lumbricus terrestris) mortality, growth and reproduction, as well as the biogenic transport of these contaminants through earthworm burrows. The results showed that earthworm reproduction was not affected by any treatment, but earthworm weight was reduced by 17.6% and the mortality increased by 62.5% in treatments with 28% Bio-MPs. Treatments with 28% LDPE-MPs and 7% Bio-MPs combined with CPF showed greater toxicity while the treatment with 28% Bio-MPs combined with CPF showed less toxicity on earthworm growth as compared to treatments with only MPs. The treatments with 1250 g ha^-1 CPF and 28% Bio-MPs significantly decreased the bioaccumulation of CPF in earthworm bodies (1.1 ± 0.2%, w w^-1), compared to the treatment with CPF alone (1.7 ± 0.4%). With CPF addition, more LDPE-MPs (8%) were transported into earthworm burrows and the distribution rate of LDPE-MPs in deeper soil was increased. No effect was observed on the transport of Bio-MPs. More CPF was transported into soil in the treatments with LDPE-MPs and Bio-MPs, 5% and 10% of added CPF, respectively. In addition, a lower level of the CPF metabolite 3,5,6-trichloropyridinol was detected in soil samples from the treatments with MPs additions than without MP additions, indicating that the presence of MPs inhibited CPF degradation. In conclusion, Bio-MPs caused significant toxicity effects on earthworms and the different types of MPs combined with CPF affected earthworms differently, and their transport along the soil profile. Thus, further research is urgently needed to understand the environmental risks of MPs and MP-associated compounds in the soil ecosystem.

Insights into the accumulation, distribution and toxicity of pyrene associated with microplastics in rice (Oryza sativa L.) seedlings

Microplastic and polycyclic aromatic hydrocarbons (PAHs) can be introduced into agroecosystems through various agricultural activities and may threaten food safety and human health. However, little research has focused on the behavior of microplastics-associated PAHs and their toxicity effects in agroecosystems, especially in crops. In the present study, we investigated the accumulation, distribution and toxicity of pyrene associated with polyethylene (PE) microplastics in rice (Oryza sativa L.). With quantitative analysis using 14C isotope labelling, the total accumulation efficiency of 14C-pyrene in rice seedlings was 22.4 ± 1.2% and 14.5 ± 0.3% when exposed to freely dissolved pyrene and PE-associated pyrene, respectively. The translocation of 14C-pyrene was significantly decreased by microplastics adsorption even when the amount of pyrene in the rice roots had no significant difference. Subcellular distribution of 14C-pyrene in rice suggested that PE microplastics-associated pyrene located more on cell walls than free dissolved pyrene. Furthermore, results showed free pyrene, but not PE-associated pyrene, significantly decreased the length and biomass of rice roots as well as increased the activities of antioxidant enzymes (superoxide dismutase and catalase). It indicated that the association with microplastics alleviated the phytotoxicity of pyrene in rice seedlings. These findings shed new light on the environmental behavior and effects of PAHs associated with microplastics in crops and will be helpful to its comprehensive risks assessment.

Microplastics in environment: global concern, challenges, and controlling measures

Plastic pollution in various forms has emerged as the most severe environmental threat. Small plastic chunks, such as microplastics and nanoplastics derived from primary and secondary sources, are a major concern worldwide due to their adverse effects on the environment and public health. Several years have been spent developing robust spectroscopic techniques that should be considered top-notch; however, researchers are still trying to find efficient and straightforward methods for the analysis of microplastics but have yet to develop a viable solution. Because of the small size of these degraded plastics, they have been found in various species, from human brains to blood and digestive systems. Several pollution-controlling methods have been tested in recent years, and these methods are prominent and need to be developed. Bacterial degradation, sunlight-driven photocatalyst, fuels, and biodegradable plastics could be game-changers in future research on plastic pollution control. However, recent fledgling steps in controlling methods appear insufficient due to widespread contamination. As a result, proper regulation of environmental microplastics is a significant challenge, and the most equitable way to manage plastic pollution. Therefore, this paper discusses the current state of microplastics, some novel and well-known identification techniques, strategies for overcoming microplastic effects, and needed solutions to mitigate this planetary pollution. This review article, we believe, will fill a void in the field of plastic identification and pollution mitigation research.

Micro(nano)plastic pollution in terrestrial ecosystem: emphasis on impacts of polystyrene on soil biota, plants, animals, and humans

Pollution with emerging microscopic contaminants such as microplastics (MPs) and nanoplastics (NPs) including polystyrene (PS) in aquatic and terrestrial environments is increasingly recognized. PS is largely used in packaging materials and is dumped directly into the ecosystem. PS micro-nano-plastics (MNPs) can be potentially bioaccumulated in the food chain and can cause human health concerns through food consumption. Earlier MP research has focused on the aquatic environments, but recent researches show significant MP and NP contamination in the terrestrial environments especially agricultural fields. Though PS is the hotspot of MPs research, however, to our knowledge, this systematic review represents the first of its kind that specifically focused on PS contamination in agricultural soils, covering sources, effects, and ways of PS mitigation. The paper also provides updated information on the effects of PS on soil organisms, its uptake by plants, and effects on higher animals as well as human beings. Directions for future research are also proposed to increase our understanding of the environmental contamination of PS in terrestrial environments.

Comprehensive Techno-environmental Evaluation of a Pilot-Scale PHA Production from Food Waste in China

Polyhydroxyalkanoates (PHAs), a biodegradable plastic that might replace petroleum-based plastics, can be recovered from organic waste using mixed microbial cultures (MMCs). Research in this field has been ongoing for about 25 years and is now in a critical commercialization period. However, few pilot-scale studies are available to analyze its technical feasibility and environmental impact. We ran an MMC PHA production pilot plant for 6 months using local food waste as the feedstock. The traditional three-stage process achieved PHA content of 47.91 ± 1.91% dry cell weight and volumetric productivity of 9.94 ± 0.01 g/L·d, while a novel rapid proliferation stage was built in, the PHA content and productivity could reach 41.39 ± 2.39% cell dry weight and 20.02 ± 0.01 g/L·d, respectively. Life cycle assessment using field data showed that greenhouse warming potential was much more than five times that of the known literature, and the fossil depletion potential was 10.30 (scenario #1)/7.59 (scenario #2) times higher than petroleum-based polyethylene (PE) plastic. However, establishing a resource-energy-water union instead of an isolated plant could achieve environmental benefits compared to PE plastic. This techno-environmental analysis provides emerging MMC PHA producers worldwide with a valuable reference for further development opportunities and market planning.

Understanding of environmental pollution and its anthropogenic impacts on biological resources during the COVID-19 period

The global outbreak of the COVID-19 pandemic has given rise to a significant health emergency to adverse impact on environment, and human society. The COVID-19 post-pandemic not only affects human beings but also creates pollution crisis in environment. The post-pandemic situation has shown a drastic change in nature due to biomedical waste load and other components. The inadequate segregation of untreated healthcare wastes, chemical disinfectants, and single-use plastics leads to contamination of the water, air, and agricultural fields. These materials allow the growth of disease-causing agents and transmission. Particularly, the COVID-19 outbreak has posed a severe environmental and health concern in many developing countries for infectious waste. In 2030, plastic enhances a transboundary menace to natural ecological communities and public health. This review provides a complete overview of the COVID-19 pandemic on environmental pollution and its anthropogenic impacts to public health and natural ecosystem considering short- and long-term scenarios. The review thoroughly assesses the impacts on ecosystem in the terrestrial, marine, and atmospheric realms. The information from this evaluation can be utilized to assess the short-term and long-term solutions for minimizing any unfavorable effects. Especially, this topic focuses on the excessive use of plastics and their products, subsequently with the involvement of the scientific community, and policymakers will develop the proper management plan for the upcoming generation. This article also provides crucial research gap knowledge to boost national disaster preparedness in future perspectives.

Polyethylene microplastic and biochar interactively affect the global warming potential of soil greenhouse gas emissions

Emerging microplastic pollution and biochar application result in their coexistence in the soil. In this study, a polyethylene microplastic, a straw biochar, and a manure biochar were applied alone or in combination to an agricultural soil to explore their interactive effects on microbial biomass carbon and nitrogen, bacterial community composition, structure and function, and the resultant greenhouse gas emissions in a 45-day laboratory incubation. At the end of incubation, the co-application of microplastic and biochar suppressed the global warming potential of cumulative greenhouse gas emissions compared with the sum of their application alone. Specifically, coexisting with microplastics increased N₂O emissions by 37.5% but decreased CH₄ emissions by 35.8% in the straw biochar added soil, and decreased N₂O, CO₂ and CH₄ emissions by 24.8, 6.2, and 65.2%, respectively, in the manure biochar added soil. A correlation network analysis illustrated that the increased global warming potential was related to the changed bacterial function and microbial biomass carbon and nitrogen in the treatments with straw biochar and/or polyethylene microplastic added, and by the changed bacterial community structure and function in the treatments with manure biochar and/or polyethylene microplastic added. Bacterial functions associated with tricarboxylic acid cycle contributed to CO₂ emissions. Bacterial functions associated with the nitrogen cycle such as nosZ and AOBamoABC were negatively and positively correlated with N₂O emissions, respectively. The interaction between different types of microplastics and soil amendments and the resultant effects on ecosystem function deserve further research.

Interactions of microplastics and soil pollutants in soil-plant systems

In recent years, increasing studies have been reported on characterization and detection of microplastics (MPs), and their interactions with organic pollutants (OPs) and heavy metals (HMs) in soils. However, a comprehensive review on the characteristics and factors that influence MPs distribution in soils, the sorption characteristics and mechanisms of soil contaminants by MPs, especially the interactions of MPs and their complexes with pollutants in the soil-plant systems remains rarely available at present. This review focuses on the sorption features and mechanisms of pollutants by MPs in soil and discussed the effects of MPs and their complexing with pollutants on soil properties, microbe and plants. The polarity of MPs significantly influenced the sorption of OPs, and different sorption mechanisms are involved for the hydrophobic and hydrophilic OPs. The sorption of OPs on MPs in soils is different from that in water. Aging of MPs can promote the sorption and migration of contaminants. The enhanced effects of biofilm in microplastisphere on the sorption of pollutants by MPs are critical, and interactions of soil environment-MPs-microbe-HMs-antibiotics increase the potential pathogens and larger release of resistance genes. The coexistence of HMs and MPs affected the growth of plants and the uptake of HMs and MPs by the plants. Moreover, the type, dose, shape and particle size of MPs have important influences on their interactions with pollutants and subsequent effects on soil properties, microbial activities and plant growth. This review also pointed out some knowledge gaps and constructive countermeasures to promote future research in this field.

A systematic review on bioplastic-soil interaction: Exploring the effects of residual bioplastics on the soil geoenvironment

Growing demand for plastic and increasing plastic waste pollution have led to significant environmental challenges and concerns in today's world. Bioplastics offer exciting new opportunities and possibilities where biodegradable and bio-based plastics are expected to be more eco-friendly and rely on renewable resources. With all its promises, evaluating its real impact and fate on the geoenvironment is paramount for promoting bioplastic use. This paper presents a systematic literature review to understand current bioplastic-soil research and the effects of its residues on the geoenvironment. 632 studies related to bioplastic research in soil since 1973 were identified and categorized into different relevant topics. Publication trend showed bioplastic-soil research grew exponentially after 2010 wherein field studies accounted to 33.1 % of the total studies and only about 9.7 % studied the effects of bioplastic residues on the geoenvironment. Majority of the lab studies were on development and subsequent stability of bioplastics in soil. Short-term studies (in months) dominated the longer-term studies and studies over 4 years were almost non-existent. Lab and field experiments often gave inconsistent results with seasonal, climatic and bio-geographical factors strongly influencing the field results and bioplastic stability in soil. Most existing studies reported significant effects for microbioplastic concentrations at or above 1 % w/w. Bioplastic residues were found to substantially affect soil C/N ratio, impact soil microbial diversity by favouring certain microbial taxa and alter soil physical structure by influencing soil aggregates formation. At higher concentrations, plant health and germination success were also negatively affected. Conclusively, the review found it important to focus more on long-term field experiments to better understand the degree and extent of bioplastic residue impact on soil physico-chemical properties, mechanical properties, soil biology, soil-bioplastic-plant response, nutrients and toxicity. There are also very few studies investigating contaminant transport and migration of micro or nano-bioplastics in soil.

Negative impacts of nanoplastics on the purification function of submerged plants in constructed wetlands: Responses of oxidative stress and metabolic processes

Constructed wetlands (CWs) are an important barrier to prevent nanoplastics (NPs) and microplastics (MPs) from entering receiving streams. However, little is known about how the accumulation of NPs affects the growth, photosynthesis, oxidative stress responses, and metabolism of plants, especially submerged plants that are widely used in CWs for water purification. Herein, we adopted Utricularia vulgaris (U. vulgaris), a typical submerged macrophyte as the model plant to address the above knowledge gaps under exposure to polystyrene NPs (PS-NPs, 500 nm, 0∼10 mg·L^-1). Results showed that PS-NPs were absorbed by insect traps and further transported to stems and leaves of U. vulgaris, which limited plant height (6.8∼72.9%), relative growth rate (7.4∼17.2%), and photosynthesis (3.7∼28.2%). U. vulgaris suffered from oxidative stresses, as evidenced by the increase in malondialdehyde, antioxidant enzymes (catalase, peroxidase, and superoxide dismutase), and H₂O₂, especially under 1 and 10 mg·L^-1. Abundances of 548 metabolites were quantified, and 291 metabolites were detected with altered levels after exposure, in which 25∼34% metabolites were up-regulated, and 32∼40% metabolites were down-regulated in metabolite expression. Metabolic pathways of the tricarboxylic acid cycle and amino acid were disrupted, in which citric acid, threonine, and adenine decreased, while amino acids (like serine, phenylalanine, histidine, etc.) increased first and then decreased with increasing PS-NPs concentrations. Moreover, PS-NPs reduced the removal efficiency of total nitrogen and phosphorus from water by U. vulgaris, bringing potential risks to aquatic ecosystems. These findings have greatly enhanced our understanding of the metabolic mechanisms and interactions of aquatic macrophytes that are heavily used in CWs in response to NPs stress, as well as the impact of NPs on CWs functioning.

Impact of “sachet water” microplastic on agricultural soil physicochemistry, antibiotics resistance, bacteria diversity and function

Nigeria's most consumed potable water plastic wastes are indiscriminately dumped into agricultural soil despite their ability to become microplastics. The study evaluates the potential impacts of these microplastics on soil physico-chemical parameters, soil bacterial diversity and functions as well as antibiotic resistance. Soil sample was collected using a sterile hand-held auger and its physico-chemical parameters evaluated. Baseline microplastic concentration was determined via the flotation method while microbial isolates were obtained from the test (enriched with microplastics) and control samples using cultural technique and metagenomics. Metagenomic next-generation sequencing (mNGS) was done using the Illumina Miseq platform. The cluster of orthologous genes (COG) tool was used in the prediction of bacterial functional roles. Replicate readings were analysed using analysis of variance (ANOVA) and means compared using the student’s t test. Observed baseline microplastic concentration was 0.08 particles/g of soil. The addition of the microplastics to the soil sample decreased the concentrations of some metals (iron, zinc, lead and nickel) while cobalt concentration, pH level and microbial counts increased. Microbial count and pH clustered together while iron, magnesium, nitrate, nitrite, chromium, cobalt, total organic carbon, zinc, lead, and nickel showed positive loading values suggesting that the addition of microplastics could alter them. Dominant taxa were proteobacteria, unknown, firmicutes at the phyla level. At the level of species, Pseudomonas species dominated microplastics incubated soil while potential pathogenic species such as Klebsiella dominated the control sample. A higher level of multi-drug resistance and altered metabolisms was observed in the test sample. Sachet water microplastics could have serious implications for public health and food security.

Implication of microplastics on soil faunal communities - identifying gaps of knowledge

There is mounting evidence that plastic and microplastic contamination of soils can affect physico-chemical processes and soil fauna, as has been excellently summarised in many recently published meta-analyses and systematic reviews elsewhere. It has become clear that impacts are highly context dependent on, e.g. polymer type, shape, dose and the soil itself. Most published studies are based on experimental approaches using (semi-)controlled laboratory conditions. They typically focus on one or several representative animal species and their behaviour and/or physiological response - for example, earthworms, but rarely on whole communities of animals. Nevertheless, soil animals are rarely found in isolation and form part of intricate foodwebs. Soil faunal biodiversity is complex, and species diversity and interactions within the soil are very challenging to unravel, which may explain why there is still a dearth of information on this. Research needs to focus on soil animals from a holistic viewpoint, moving away from studies on animals in isolation and consider different trophic levels including their interactions. Furthermore, as evidence obtained from laboratory studies is complemented by relatively few studies done in field conditions, more research is needed to fully understand the mechanisms by which plastic pollution affects soil animals under realistic field conditions. However, field-based studies are typically more challenging logistically, requiring relatively large research teams, ideally of an interdisciplinary nature to maintain long-term field experiments. Lastly, with more alternative, (bio)degradable and/or compostable plastics being developed and used, their effects on soil animals will need to be further researched.

Occurrence of macroplastics and microplastics in biogenic waste digestate: Effects of depackaging at source and dewatering process

Plastic debris, including macroplastics (>5 mm) and microplastics (0.1-5 mm), has proven to be an emerging contaminant. Anaerobic digestion, coupled with energy recovery, can be an effective valorization technology for biogenic waste. But the use of the resulting digestate as a soil conditioner is a source for plastic debris release into the environment. The preprocess and postprocess used could influence the quantity of plastic debris found in the digestate, but the specifics of these effects are relatively unknown. Therefore, we measured the quantity of plastic debris in raw digestate under a variety of preprocessing scenarios. We also investigated the occurrence of plastic debris in solid and liquid digestates resulting from the dewatering of raw digestate. The quantity of plastic debris ranged from 41 to 3298 particles/kg (WW) for raw digestate, 319-3604 particles/kg (WW) for solid digestate and 7-38 particles/kg (WW) for liquid digestate. We observed that depackaging at source by citizens themselves (removing the package of biogenic waste when dropping it into bins), significantly reduced the quantities of plastic debris in raw digestate by an order of magnitude. Furthermore, the number of polymer types in raw digestate, where depackaging occurred at source, were lower than that where this rule was not in place. The average size of plastic debris in solid digestate was significantly smaller than that in raw digestate, which indicated that the process of mechanical dewatering could generate MPs. It is recommended to depackage for biogenic waste at source to reduce the quantities of MPs in digestate.