Microplastics in soil: A review on methods, occurrence, sources, and potential risk

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.

Microbial engineering strategies for synthetic microplastics clean up: A review on recent approaches

Microplastics are the small fragments of the plastic molecules which find their applications in various routine products such as beauty products. Later, it was realized that it has several toxic effects on marine and terrestrial organisms. This review is an approach in understanding the microplastics, their origin, dispersal in the aquatic system, their biodegradation and factors affecting biodegradation. In addition, the paper discusses the major engineering approaches applied in microbial biotechnology. Specifically, it reviews microbial genetic engineering, such as PET-ase engineering, MHET-ase engineering, and immobilization approaches. Moreover, the major challenges associated with the plastic removal are presented by evaluating the recent reports available.

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.

Microplastics occurrence, detection and removal with emphasis on insect larvae gut microbiota

Microplastics have been identified in all living forms including human beings, the present need is to restrain its spread and devise measures to remediate microplastics from polluted ecosystems. In this regard, the present review emphasizes on the occurrence, sources detection and toxic effects of microplastics in various ecosystems. The removal of microplastics is prevalent by various physico-chemical and biological methods, although the removal efficiency by biological methods is low. It has been noted that the degradation of plastics by insect gut larvae is a well-known aspect, however, the underlying mechanism has not been completely identified. Studies conducted have shown the magnificent contribution of gut microbiota, which have been isolated and exploited for microplastic remediation. This review also focuses on this avenue, as it highlights the contribution of insect gut microbiota in microplastic degradation along with challenges faced and future prospects in this area.

The effect of polystyrene microplastic and biosolid application on the toxicity and bioaccumulation of cadmium for Enchytraeus crypticus

Plastics smaller than 5 mm that end up in a soil environment are known as microplastics (MPs). Microplastics have become a common contaminant in agricultural areas in addition to metals. However, the effect of cadmium (Cd) on soil organisms has not been clearly defined in the presence of MPs. In addition to MPs, biosolid application as a soil amendment in agricultural lands is also leading to shifts in soil conditions, such as the concentrations of nutrients and organic matter. Therefore, the aim of this study is to investigate the toxicity and bioaccumulation of Cd for Enchytraeus crypticus in the presence of polystyrene (PS)-MPs and biosolids to provide insight into their possible interactions. The lethal toxic concentration (LC50) for Cd was higher than 650 mg Cd/kg dry soil for all conditions. The presence of PS-MPs increased the toxicity of Cd for which EC50 was 102 and 38 mg Cd/kg dry soil without and with Cd, respectively, which may be the result of an increased exposure rate through adsorption of Cd on PS-MPs. On the contrary, the presence of biosolids decreased the toxicity of Cd where EC50 was 193 and 473 mg Cd/kg dry soil for the sets applied with 0.6 and 0.9 g biosolids, respectively. Coexistence of biosolids and PS-MPs decreased the reproduction toxicity of Cd, which is similar to the biosolid effect (EC50 is 305 mg Cd/kg dry soil). Bioaccumulation of Cd only positively correlated with its initial concentration in soil and was not affected by the presence of PS-MPs or biosolids. Integr Environ Assess Manag 2023;19:489-500. © 2022 SETAC.

Abundance, spatial distribution, and characteristics of microplastics in agricultural soils and their relationship with contributing factors

Agro-ecosystem contamination with microplastics (MPs) is of great concern. However, limited research has been conducted on the agricultural soil of tropical regions. This paper investigated MPs in the agro-ecosystem of Hainan Island, China, as well as their relationships with plastic mulching, farming practices, and social and environmental factors. The concentration of MPs in the study area ranged from 2800 to 82500 particles/kg with a mean concentration of 15461.52 particles/kg. MPs with sizes between 20 and 200 μm had the highest abundance of 57.57%, fragment (58.16%) was the most predominant shape, while black (77.76%) was the most abundant MP colour. Polyethylene (PE) (71.04%) and polypropylene (PP) (19.83%) were the main types of polymers. The mean abundance of MPs was significantly positively correlated (p < 0.01) with all sizes, temperature, and shapes except fibre, while weakly positively correlated with the population (p = 0.21), GDP (p = 0.33), and annual precipitation (p = 0.66). In conclusion, plastic mulching contributed to significant contamination of soil MPs in the study area, while environmental and social factors promoted soil MPs fragmentation. The current study results indicate serious contamination with MPs, which poses a concern regarding ecological and environmental safety.

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.

The spatial distribution of microplastics in topsoils of an urban environment - Coimbra city case-study

Due to their seemingly ubiquitous nature and links to environmental and human health problems, microplastics are quickly becoming a major concern worldwide. Artificial environments, such as those found in urban environments, represent some of the main sources of microplastic. However, very few studies have focused on the occurrence of microplastics in urban soils. The aim of the current research was to evaluate the microplastic contamination in urban soils from artificial and natural land uses throughout Coimbra city, Portugal. Sixty-seven spaces and ten land use areas were evaluated. The artificial land use areas were dumps, landfills, parking lots, industries and construction areas, and the natural land use areas were forests, urban parks, moors (wetlands), pastures and urban agricultural areas. Microplastic extraction was done by density separation. Quantification and size measurements of microplastics was carried out using a microscope. Polymer types were identified by μ-FTIR for 25% of the samples. The microplastic content ranged from 5 × 10³ to 571 × 10³ particles·kg^-1, with a mean of 106 × 10³ particle·kg^-1. The green park was the land use with the highest concentration of microplastics (158 × 10³ particle·kg^-1) and the forest was the one with the lowest concentration (55 × 10³ particle·kg^-1). The landfill (150 × 10³ particle·kg^-1), industry (127 × 10³ particle·kg^-1) and dump (126 × 10³ particle·kg^-1) were the artificial spaces with the highest levels of microplastics. The main polymers detected were polypropylene and polyethylene, followed by polyvinyl chloride and rubber, and the main sizes measured between 50 and 250 μm. Our results indicate that natural spaces can contain higher amounts of microplastics as compared to artificial spaces in the urban environment. This suggests that microplastics are easily transported through the urban landscape and that urban green spaces can retain microplastics in their soils. Land use planning may present an opportunity to better control the levels of microplastics in urban environments.

The Montreal Protocol and the fate of environmental plastic debris

Microplastics (MPs) are an emerging class of pollutants in air, soil and especially in all aquatic environments. Secondary MPs are generated in the environment during fragmentation of especially photo-oxidised plastic litter. Photo-oxidation is mediated primarily by solar UV radiation. The implementation of the Montreal Protocol and its Amendments, which have resulted in controlling the tropospheric UV-B (280-315 nm) radiation load, is therefore pertinent to the fate of environmental plastic debris. Due to the Montreal Protocol high amounts of solar UV-B radiation at the Earth's surface have been avoided, retarding the oxidative fragmentation of plastic debris, leading to a slower generation and accumulation of MPs in the environment. Quantifying the impact of the Montreal Protocol in reducing the abundance of MPs in the environment, however, is complicated as the role of potential mechanical fragmentation of plastics under environmental mechanical stresses is poorly understood.

Neuro- and hepato-toxicity of polystyrene nanoplastics and polybrominated diphenyl ethers on early life stages of zebrafish

Nanoplastics (NPs) are good carriers of persistent organic pollutants (POPs) such as polybrominated diphenyl ethers (PBDEs) and can modify their bioavailability and toxicity to aquatic organisms. This study highlights the single and combined toxic effects of polystyrene nanoplastics (PS-NPs) and 2,2 ',4,4 '-tetrabromodiphenyl ether (BDE-47, one of the major PBDE congeners) on zebrafish embryos after an exposure of up to 120 hpf. Our results showed that PS-NPs and BDE-47 formed larger particle aggregates during co-exposure, which attached to the surface of the yolk membrane and even changed its structure, and these particles also bioaccumulated in the intestine of zebrafish larvae, compared with the PS-NPs single exposure. Further, the co-exposure significantly increased mortality, accelerated voluntary movements, enhanced hatching rate, and decreased heart rate. Hepatoxicity analyses revealed that the mixture exposure induced a darker/browner liver colour, atrophied liver and greater hepatotoxicity in zebrafish larvae. In addition to increased ROS accumulation, the reduced expression of the antioxidant gpx1a gene and increased expression of cyp1a1 were found after co-treatment. Moreover, ache and chrn7α genes associated with neurocentral development, were significantly downregulated, mainly in the co-exposure group. In conclusion, simultaneous exposure to PS-NPs and BDE-47 exacerbated oxidative stress, developmental impacts, hepatotoxicity, and neurodevelopmental toxicity in zebrafish larvae. Therefore, neurotoxic effects of complex chemical interactions between PS-NPs and persistent organic pollutants in freshwater environments should be paid more attention.

Responses of bacterial communities to microplastics: More sensitive in less fertile soils

Recently, the potential impact of microplastics (MPs) on bacterial communities has risen enormously attention due to the increasing amount of plastic waste generated nowadays. However, there is a lack of clarity due to limited studies on the responses of bacterial communities to MPs exposures in various soil ecosystems. Here, we conducted a soil microcosm experiment to analyze the potential impact of MPs on bacterial communities in farmland soil, forest soil, and sandy soil. The changes in alpha/beta diversity and co-occurrence network of bacterial communities were more significant in farmland soil amended with PS MPs (5 g kg^-1), forest soil amended with PP MPs (5 g kg^-1), and sandy soil amended with PP MPs (1 g kg^-1). Particularly, the bacterial communities in sandy soil with the least soil organic carbon content were disturbed most significantly compared to other treatments. LEfSe analysis revealed that specific bacterial taxa such as phylum Proteobacteria, Actinobacteria, Firmicutes, and genus Sphingomonas, Candidatus Udaeobacter, Gemmatimonas, were sensitive to MPs exposures. Functional annotation showed that perturbation of bacterial communities was related to organic carbon decomposition, nitrogen fixation, nitrate reduction/respiration, etc. In sum, MPs may potentially affect bacterial community structure and functions relevant to carbon/nitrogen cycles at long-term realistic field exposure.

Microplastics contamination associated with low-value domestic source organic solid waste: A review

Waste activated sludge and food waste are two typical important domestic low-value organic solid wastes (LOSW). LOSW contains significant organic matter and water content resulting in the transboundary transfer of liquid-solid-gas and other multi-mediums, such that the complexity of microplastics (MPs) migration should be of greater concern. This article provides a review of the literature focusing on the separation and extraction methods of MPs from LOSW. The occurrence and source of MPs are discussed, and the output and impact of MPs on LOSW heat and biological treatments are summarized. The fate and co-effects of MPs and other pollutants in landfills and soils are reviewed. This review highlights the migration and transformation of MPs in domestic source LOSW, and future perspectives focused on the development of a unified extraction and analysis protocol. The objective of this review is to promote the technological development of decontamination of MPs in LOSW by sufficient understanding of the fate of MPs, their interaction with coexisting pollutants and the development of targeted preventive research strategies.

The transport of microplastics by ants cannot be neglected in the soil ecosystem

Microplastics (MPs) are widespread in soils and continue to migrate in response to many abiotic and biotic factors. Although some studies have explored the effects of abiotic factors (e.g., wind and water) on MP migration and distribution, there is little information on the effects of biotic factors, especially soil fauna, on this process. Ants are among the most abundant fauna on Earth and play an important role in ecosystem health. Here, we tested whether ants could transport low-density polyethylene (LDPE) MPs in the field. We also investigated the effects of ants (Pheidole sp.) on the removal rates and distribution of LDPE MPs in the laboratory compared to other potential field materials (leaf fragments and tiny stones). We found that, in the field, two ant species (Pheidole sp. and Paratrechina sp.) could actively carry LDPE MPs; the mean removal distance was 75.34 ± 4.05 cm, and the curve had a long tail extending to 140 cm. In the laboratory, the mean number of removed leaf fragments and LDPE MPs was significantly greater than that of removed tiny stones. After 14 days, the proportions of LDPE MPs, leaf fragments, and tiny stones removed into the nests by ants were 15.8%, 19.15%, and 3.3%, respectively. The proportions of LDPE MPs in the original position (not removed by ants), inside the nests, and outside the nests were 18.4%, 15.8%, and 65.8%, respectively. These results indicate that ants play an important, but neglected, role in the transport and distribution of MPs in soil ecosystems. Given the abundance and diversity of ants worldwide, the ant-mediated transport of MPs may be common in soil ecosystems. We suggest that the transport of MPs by ants may expand the distribution of MPs and influence the exposure of other soil fauna to MPs in soil ecosystems.

Adsorptive behavior of micro(nano)plastics through biochar: Co-existence, consequences, and challenges in contaminated ecosystems

The abundance of micro(nano)plastics in natural ecosystems is a crucial global challenge, as these small-sized plastic particles originate from land-based and marine-based activities and are widely present in marine, freshwater, and terrestrial ecosystems. Micro(nano)plastics can significantly be reduced through various methods, such as biological, chemical, and physical techniques. Biochar is a low-cost adsorbent and is considered an efficient material and its application is ecologically effective carbon-negative for remediation of organic and inorganic pollutants. Therefore, this review critically discusses the fate and transport of micro(nano)plastics and their interactions with different biochar in aqueous and column porous media. This review outlines the implications of biochar with the co-existence of micro(nano)plastics in efforts to understand their coupled effects on soil physicochemical properties, microbial communities, and plant growth, along with the removal of heavy metals and other toxic contaminants. In batch experiments, biochar synthesized from various biomasses such as corn straw, hardwood, pine and spruce bark, corncob, and Prosopis juliflora had shown high level of removal efficiency (>90 %) for microplastic adsorption under varying environmental conditions viz., pH, temperature, ionic strength, particle size, and dose due to chemical bonding and electrostatic attractions. Increased temperature of the aqueous solutions encouraged higher adsorption, while higher pH and dissolved organic matter and nutrients may show decreased adsorption capacities for micro(nano)plastics using biochar. Compared to other available physical, chemical, and biological methods, biochar-amended sand filters in column experiments have been very efficient in removing micro(nano)plastics. In saturated column porous media, various microplastics could be inhibited using biochar due to decreased electrostatic repulsion, steric hindrance, and competitive sorption due to humic acid, ionic strength, and cations. Finally, this review provides in-depth insights on further investigations and recommendations for overall micro(nano)plastics removal using biochar-based materials.

Smallholder vegetable farming produces more soil microplastics pollution than large-scale farming

Microplastics (MPs) accumulation in farmland has attracted global concern. Smallholder farming is the dominant type in China's agriculture. Compared with large-scale farming, smallholder farming is not constrained by restrictive environmental policies and public awareness about pollution. Consequently, the degree to which smallholder farming is associated with MP pollution in soils is largely unknown. Here, we collected soil samples from both smallholder and large-scale vegetable production systems to determine the distribution and characteristics of MPs. MP abundance in vegetable soils was 147.2-2040.4 MP kg^-1 (averaged with 500.8 MP kg^-1). Soil MP abundance under smallholder cultivation (730.9 MP kg^-1) was twice that found under large-scale cultivation (370.7 MP kg^-1). MP particle sizes in smallholder and large-scale farming were similar, and were mainly <1 mm. There were also differences in MP characteristics between the two types of vegetable soils: fragments (60%) and fibers (34%) were dominant under smallholder cultivation, while fragments (42%), fibers (42%), and films (11%) were dominant under large-scale cultivation. We observed a significant difference in the abundance of fragments and films under smallholder versus large-scale cultivation; the main components of MPs under smallholder cultivation were PP (34%), PE (28%), and PE-PP (10%), while these were PE (29%), PP (16%), PET (16%), and PE-PP (13%) under large-scale cultivation. By identifying the shape and composition of microplastics, it can be inferred that agricultural films were not the main MP pollution source in vegetable soil. We show that smallholder farming produces more microplastics pollution than large-scale farming in vegetable soil.

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.

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.

Occurrence and distribution of microplastics in coastal plain soils under three land-use types

Microplastic pollution is an issue of major environmental concern worldwide. Land-use type may affect the abundance, polymer types, and distribution characteristics of soil microplastics but their distribution remains unknown on the coastal plain of east China. Here, the abundance of microplastics in farmland (FL), plantation (P), and orchard/secondary forest (OSF) soils was determined on the east China coastal plain, and characteristics of the microplastics (shape, size, colour, and polymer composition) were analysed in soil samples collected from 33 sites. The average abundances of microplastics in FL, P, and OSF soils on the coastal plain of the east China coast were 185, 109, and 150 items kg^-1, respectively. Small particles, fibres and transparent particles were the main characteristics of the microplastics observed. The polymer types were mainly PP and PET. The abundance of microplastics in farmland was positively correlated with population density in the study area. Therefore, agricultural activities associated with high population density are the main factors leading to the high abundance of microplastics in farmland soil.

The neglected potential source of microplastics from daily necessities: A study on protective mobile phone cases

Microplastics (MPs) pollution has become a serious global environment problem. It is therefore of practical significance to investigate the MP pollution caused by using plastic materials on a daily basis. In this study, different protective mobile phone cases (PMPCs) were selected as a representative plastic commodity that are in contact with the human body for long periods to explore the generation and transportation of MPs during 3 months of actual use. The average abundances were 1122 particles cm^-2 on the PMPC and 314 particles cm^-2 on the palm, respectively. There were four main kinds of MPs produced during the use of different PMPCs, which indicated that waste plastics may be recycled and used as raw materials, resulting in a complex PMPC composition. The median sizes of MPs on the surfaces of PMPCs and palms were 28 and 32 µm, respectively, which were smaller than the sizes reported in other studies. The combined effect of ultraviolet ageing and friction was the main reason for MP generation during daily PMPC use. Based on the results of a fitted regression equation and Monte Carlo simulation, the sharply generation of MPs may occur when PMPC was used for approximately 33 days.

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.

Influence of aged and pristine polyethylene microplastics on bioavailability of three heavy metals in soil: Toxic effects to earthworms (Eisenia fetida)

Virgin microplastics (MPs) would undergo aging process when entering environment, the adsorption capability of pollutants onto MPs may change during the aging process. To better understand the influence of aged polyethylene microplastics (PE-MP) on the bioavailability of three heavy metals (Zn, Pb, and Cd) in soil, hydrogen peroxide exposure (3% H₂O₂) and ultraviolet irradiation methods were employed to simulate the aging process. After aging process, different amount (0.1%, 1%, 10%) of PE-MP (pristine or aged) was added into soil to assess the ability of soil (containing PE-MP) adsorbing heavy metal. Moreover, different amount (0.01%, 0.1%, 1%) of PE-MP (pristine or aged) was added into soil to cultivate the earthworms to assess the impact of PE-MP on bioavailability of three heavy metals. Results indicated that the aged and virgin PE-MP had similar capability to adsorb heavy metal, the adsorption ability of Zn²⁺, Pb²⁺, and Cd²⁺ to pristine PE-MP were 2.42, 7.47, and 7.76 mg/g, respectively. The concentration of Zn or Pb in earthworms in treatments of metal +1% PE-MP was slightly higher than that in single metal (Zn or Pb) treatment, moreover, the concentration of Cd in earthworms in treatment of Cd + 1% PE-MP was significantly (p < 0.05) higher than that in single Cd treatment, exhibiting that 1% of PE-MP enhanced the bioavailability of heavy metals in soil. However, heavy metal concentrations in earthworms in treatments of metal + pristine PE-MP showed insignificant (p > 0.05) difference with those in treatments of metal + aged PE-MP, indicating that the aging process in this study did not change the environmental influence of PE-MP on heavy metals bioavailability. Superoxide dismutase activity, reactive oxygen species level, malondialdehyde content, and related gene expression in earthworms showed that PE-MP and heavy metals would bring toxic synergy to earthworms, therefore, the influence of MPs should be comprehensively considered when determining the environmental risk of heavy metals in soil.

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.

Heavy metal-mediated adsorption of antibiotic tetracycline and ciprofloxacin on two microplastics: Insights into the role of complexation

Microplastics (MPs) have recently become an emerging environmental concern. Nevertheless, limited information is known about the adsorption of MPs for organic contaminants under combined heavy metals pollution, with an emphasis on the role of complexation. Thus, this study aims to comprehensively compare and investigate the adsorption performance of antibiotic tetracycline (TC) and ciprofloxacin (CIP) on two polar MPs (polyamide (PA) and polyvinyl chloride (PVC)) affected by Cu(II) and Cd(II) with contrasting complexation abilities. Batch adsorption experiments were used in combination with speciation calculation, zeta potential determination, FTIR spectroscopy characterization and investigation of the affinity of MPs for heavy metals. Results showed that the sorption kinetics and isotherms of TC and CIP on PA and PVC could be well fitted to pseudo-second-order and Langmuir models, respectively, both in the absence and presence of Cu and Cd, suggesting that multiple interactions and monolayer adsorption played an important role in the adsorption process. The presence of Cu substantially improved TC and CIP adsorption and obviously changed the pH dependence of their adsorption onto both MPs, which may result from the Cu-induced strong complexation with TC and CIP. The presence of Cd slightly enhanced TC adsorption on both MPs while reduced CIP adsorption especially on PVC, which may be ascribed to the Cd-induced cationic bridging effects in TC adsorption and the competitive adsorption of Cd in CIP adsorption. Therefore, the heavy metal-mediated complexation effects may play a dominant role in antibiotic adsorption by MPs only in the presence of heavy metals with strong complexation ability while the adsorption performance in the presence of heavy metals with negligible complexation capacity may be influenced by effects other than complexation. This study helps further understand the heavy metal-mediated adsorption behavior of organic contaminants on polar MPs and the role of complexation reactions therein.

Biodegradable Polyesters and Low Molecular Weight Polyethylene in Soil: Interrelations of Material Properties, Soil Organic Matter Substances, and Microbial Community

Conventional and also biodegradable polymer microplastics have started to be broadly present in the environment, if they end up in soil, they may influence both abiotic and biotic soil properties. In this study, the interactions of polyethylene wax together with three biodegradable polyesters PLA, PHB and PBAT with a soil matrix were investigated over a 1-year incubation period. Soil organic matter content was measured using UV-VIS, the microbial biomass amount was measured using qPCR, the mineralisation of polymers was measured using UGA 3000, the surface of polymers was observed with SEM, live/dead microorganisms were determined by fluorescent microscopy and microbial consortia diversity was analyzed using NGS. The amount of humic substances was generally higher in incubations with slowly degrading polyesters, but the effect was temporary. The microbial biomass grew during the incubations; the addition of PHB enhanced fungal biomass whereas PE wax enhanced bacterial biomass. Fungal microbial consortia diversity was altered in incubations with PHB and PBAT. Interestingly, these two polyesters were also covered in biofilm, probably fungal. No such trend was observed in a metagenomic analysis of bacteria, although, bacterial biofilm was probably formed on the PE520 surface. Different methods confirmed the effect of certain polymers on the soil environment.

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.

Polyethylene microplastics increase extracellular polymeric substances production in aerobic granular sludge

Wastewater treatment plants act as microplastic (MPs) sinks and secondary MP pollution sources. Little is known about the effect of MPs on biomass and the efficiency of biological wastewater treatment. This study assessed the impact of polyethylene (PE) MPs concentrations (1, 10, 50 mg/L) in wastewater on biological conversions and extracellular polymeric substances (EPS) production (including alginate) in aerobic granular sludge (AGS). PE MPs did not worsen the efficiency of biological treatment but stimulated the production of EPS and alginate in AGS. The alginate content increased from 238.7 ± 4.4 mg/g MLSS in control to 441.6 ± 13.8 mg/g MLSS at the highest PE load in wastewater. The presence of MP changed AGS morphology and worsened the settling properties of biomass, causing biomass washout from the reactors. At the highest PE load in wastewater, the biomass concentration in the reactor effluent was over 2.8 times higher than in the control.

Microplastic contamination in terrestrial ecosystems: A study using barn owl (Tyto alba) pellets

Microplastics (MPs) are recognised as an emerging environmental problem that needs to be carefully monitored. So far, MPs have been widely recorded in marine and freshwater ecosystems. Still, few studies have focused on MP occurrence in terrestrial ecosystems, although soils are suspected to be one of the main MP reservoirs. To test a non-invasive method for assessing MP contamination in terrestrial ecosystems, we analysed the pellets of a top terrestrial predator, the barn owl (Tyto alba). Sixty pellets were collected from three agricultural areas (20 pellets each) and analysed to assess both barn owl diet and MP content. Thirty-four MPs were confirmed by micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) analysis in 33% of the pellets (min-max 1-5 MPs per pellet). Most of the detected items were microfibres (88.2%). Polyethylene terephthalate, polyacrylonitrile and polyamide were the most abundant polymers. One of the three sites was significantly less contaminated. In the two sites with the highest MP occurrences, barn owl diet was characterised by predation on synanthropic rodents, particularly brown rats (Rattus norvegicus), which may indicate habitat degradation and increased exposure to MPs. Analyses also suggest that Savi's pine vole (Microtus savii) is the prey least at risk of MP contamination, probably due to its strictly herbivorous diet. We argue that the analysis of barn owl pellets may represent a cost-effective method for monitoring MP contamination in terrestrial ecosystems.

Adverse effects of microplastics on earthworms: A critical review

Microplastics are widely distributed in terrestrial environments and have been known to adversely affect earthworms. Based on 65 publications, we summarized the effects of microplastics on the growth, behavior, oxidative responses, gene expression, and gut microbiota of earthworms. Since microplastics are often present simultaneously with other pollutants, especially heavy metals and hydrophobic organic chemicals (HOCs), the interactions and combined effects of microplastics and these pollutants on earthworms have also been discussed. It has been shown that earthworms can selectively ingest microplastics, preferring to those with smaller particle size (especially smaller than 50 μm) and biodegradable compositions. Generally, microplastics with higher concentrations (especially those > 0.5%, w/w) and smaller sizes (e.g., 100 nm) have greater adverse effects on earthworms. Additionally, microplastics can facilitate the accumulation of heavy metals and organic pollutants by earthworms and pose severer damages. Current knowledge gaps and perspectives for future work are pointed out.

Effects of ionic strength and particle size on transport of microplastic and humic acid in porous media

As an emerging pollutant, the transport behavior of colloidal microplastic particles (CMPs) in saturated porous media may be affected by the simultaneous presence of other substances in the natural environment. In this study, colloidal polystyrene microplastic particles (PSMPs) were selected as the representative of CMPs to investigate the cotransport behaviors of CMPs in the presence of humic acid (HA) under varied environmental conditions (ionic strength: 1, 100 mM KCl; HA concentration: 0, 5, 10, 20 mg⋅L^-1) in porous media. The presence of HA with different concentrations was found to increase the mobility of 1.0-μm and 0.2-μm CMPs in porous media in a non-linear and non-monotonic manner. Furthermore, the HA-facilitated transport of CMPs occurred under both electrostatically unfavorable and favorable attachment conditions (limited to the conditions examined in this study, corresponding to 1 and 100 mM KCl, respectively). The transport behavior of the smaller-sized CMPs (0.2-μm CMPs) was more sensitive to the change of ionic strength and the presence of HA than that of the larger-sized CMPs (1.0-μm CMPs). The cotransport process of CMPs and HA was affected by many factors. Modeling results showed that a small amount of competitive blocking occurred during the cotransport process. Moreover, both the presence of HA and change in ionic strength could affect the surface properties of CMPs. Thus, the cotransport behavior of CMPs with HA was different from the transport of individual CMPs in porous media. Experimental results revealed that HA induced complexity in the transport behavior of CMPs in the aqueous environment. Therefore, undeniably, a lot more systematic explorations are further demanded to better comprehend the CMPs cotransport mechanism in the presence of other substances.

Recent advances on the effects of microplastics on elements cycling in the environment

Microplastics (<5 mm) are an emerging pollutant which have received increasing concern in recent years. Microplastics pose a serious hazard and potential risk to the environment due to their migration, transformation, adsorption and degradation properties. The effects of different types of microplastics on the elemental cycles (carbon, nitrogen and phosphorus cycles) in ecosystems were comprehensively summarized. The impacts of microplastics on the element cycle occur mainly in the soil environment and to less extent in other environments. Microplastics affect carbon sources, carbon dioxide (CO₂) emissions, and carbon conversion processes, mainly by affecting plant and animal activities, changing gene abundance, enzyme activity, and microbial community composition. Microplastics can affect nitrogen sources, nitrogen fixation, ammonification, nitrification and denitrification processes by changing gene abundance, enzyme activity and microbial community composition. Microplastics can also influence phosphorus content and phosphorus conversion processes by stimulating enzyme activity and changing the composition of microbial communities. Future research needs to analyze the coupling of multiple microplastics and influencing factors on elemental cycling processes. This work provides a better view of the impacts of microplastics on element cycles and the interaction between microplastics and organisms.

Deciphering the Fingerprint of Dissolved Organic Matter in the Soil Amended with Biodegradable and Conventional Microplastics Based on Optical and Molecular Signatures

Biodegradable polymers are promoted as promising alternatives for conventional non-degradable plastics, but they may also negatively impact soil ecosystems. Here, we estimated the effects of biodegradable (polylactide (PLA) and polybutylene succinate (PBS)) and non-biodegradable (polyethylene (PE) and polystyrene (PS)) microplastics at a concentration of 1% (w/w) on dissolved organic matter (DOM) in two soil types, a black soil (BS) and a yellow soil (YS), by using fluorescence excitation-emission matrix spectroscopy and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). PBS significantly increased the contents of soil dissolved organic carbon (DOC) and the relative intensities of protein-like components. The turnover rates of soil DOM were statistically higher in PBS treatments (0.106 and 0.196, p < 0.001) than those in other microplastic groups. The FT-ICR-MS results indicated that more labile-active DOM molecules were preferentially obtained in biodegradable microplastic treatments, which may be attributed to the polymer degradation. The conventional microplastics showed no significant effects on the optical characteristics but changed the molecular compositions of the soil DOM. More labile DOM molecules were observed in BS samples treated with PE compared to the control, while the conventional microplastics decreased the DOM lability in YS soil. The distinct priming effects of plastic-leached DOM may trigger the DOM changes in different soils. This study provided important information for further understanding the impact of microplastics on soil carbon processes.

Microplastics profile in constructed wetlands: Distribution, retention and implications

Wastewater and stormwater are both considered as critical pathways contributing microplastics (MPs) to the aquatic environment. However, there is little information in the literature about the potential influence of constructed wetlands (CWs), a commonly used wastewater and stormwater treatment system. This study was conducted to investigate the abundance and distribution of MPs in water and sediment at five CWs with different influent sources, namely stormwater and wastewater. The MP abundance in the water samples ranged between 0.4 ± 0.3 and 3.8 ± 2.3 MP/L at the inlet and from 0.1 ± 0.0 to 1.3 ± 1.0 MP/L at the outlet. In the sediment, abundance of MPs was generally higher at the inlet, ranging from 736 ± 335 to 3480 ± 4330 MP/kg dry sediment and decreased to between 19.0 ± 16.4 and 1060 ± 326 MP/kg dry sediment at the outlet. Although no significant differences were observed in sediment cores at different depth across the five CWs, more MPs were recorded in silt compared to sandy sediment which indicated sediment grain size could be an environmental factor contributing to the distribution of MPs. Polyethylene terephthalate (PET) fibres were the dominant polymer type found in the water samples while polyethylene (PE) and polypropylene (PP) fragments were predominantly recorded in the sediment. While the size of MPs in water varied across the studied CWs, between 51% and 64% of MPs in the sediment were smaller than 300 μm, which raises concerns about the bioavailability of MPs to a wider range of wetland biota and their potential ecotoxicological effects. This study shows that CWs can not only retain MPs in the treated water, but also become sinks accumulating MPs over time.

Atmospheric deposition of microplastics in the megalopolis (Shanghai) during rainy season: Characteristics, influence factors, and source

Urban areas are the hardest hit by microplastic pollution, and deposition is an important part of microplastic migration and transport in the atmosphere, therefore, the study of microplastics in an urban atmospheric deposition is of great significance. This study aims to investigate the deposition characteristics of atmospheric microplastics in megapolis, to clarify the influence of meteorological and anthropogenic factors, and to analyze the sources of atmospheric microplastics. Six sampling sites in Shanghai were selected to collect atmospheric deposition samples during the rainy season. The mean deposition flux of microplastics was 3261.22 ± 2847.99 P·m^-2·d^-1 (median: 2559.70 P·m^-2·d^-1), and the types were mainly polyamide (PA, 27.79 %), polyethylene terephthalate (PET, 27.29 %), polypropylene (PP, 16.95 %), and polyvinyl fluoride (PVF, 12.88 %). The microplastic with the particle size of <1000 μm accounted for 88.23 %, and the shape was mainly fiber (73.55 %). The results of correlation analysis and variance analysis of microplastic characteristics with meteorological and anthropogenic factors (land-use, atmospheric pollutants, and urban indicators) showed that wind and precipitation had effects on deposition flux, size and shape, and were more significant at small scales (individual cities), while at large scales, the population was the main influence of microplastics. Atmospheric microplastics in Shanghai may be dominated by exogenous sources, through a combination of microplastic characteristics, wind and backward trajectories. This study further reveals the fate of urban atmospheric microplastics, which has implications for the study of global microplastic pollution.

Effects of land use and landscape on the occurrence and distribution of microplastics in soil, China

Microplastic pollution in the soil environment has gathered widespread attention. However, little is known about the effects of land use and landscape patterns on the occurrence and distribution of microplastics in the soil. Herein, the microplastic pollution in different land uses (facility farmland, traditional farmland, orchard, grassland, and woodland) in Yuanmou County, Yunnan Province was investigated. The results showed that the abundance of microplastic ranged from 50.000 to 3450.0 items·kg^-1, with an average abundance of 595.00 ± 740.00 items·kg^-1 and a median of 375.00 items·kg^-1. Microplastics were found to primarily be green-coloured (28.4 %), fragment (72.7 %) in shape, <1 mm (75.7 %) in size, and composed of polypropylene (51.4 %). There were significant differences in the abundance and characteristics of the microplastics between different land use types. Microplastic abundance in facility farmlands, traditional farmlands, and orchard lands was significantly higher than that of grasslands and woodlands (p < 0.05). The main shape of the microplastics in facility farmlands, traditional farmlands, and orchards was fragments and it was fibers in grasslands and woodlands. The median particle size of microplastics in facility farmlands (539.50 μm) and traditional farmlands (574.00 μm), was smaller than those in the orchard (737.60 μm), grasslands (697.60 μm), and woodlands (1239.4 μm). Discrepancies among different land uses may be due to various reasons, such as different pollution sources and the weathering degree of microplastics. The results of the redundancy analysis showed that the microplastic abundance was negatively correlated with the largest patch index. It also showed that microplastic pollution was closely related to human activities. This study provides an important basis for further research on microplastic ecosystem risks that are associated with land use and provides a data basis for formulating effective prevention and control strategies and measures to mitigate soil microplastic pollution.

A critical review on interaction of microplastics with organic contaminants in soil and their ecological risks on soil organisms

The pollution of microplastics (MPs) in soil has become a global environmental problem. Due to high sorption capacity and persistence in environment, the MPs exhibit combined effects with organic pollutants in soil, thereby posing a potential risk to soil ecology and human health. However, limited reviews are available on this subject. Therefore, in response to this issue, this review provides an in-depth account of interaction of MPs with organic contaminants in soil and the combined risks to soil environment. The sorption of organic contaminants onto MPs is mainly through hydrophobic and π-π interactions, hydrogen bonding, pore filling and electrostatic and van der Waals forces. The intrinsic characteristics of MPs, organic contaminants and soil are the key factors influencing the sorption of organic pollutants onto MPs. Importantly, the presence of MPs changes the sorption, degradation and transport behaviors of organic contaminants in soil, and affects the toxic effects of organic contaminants on soil organisms including animals, plants and soil microorganisms through synergistic or antagonistic effects. Source control, policy implementation and plastic removal are the main preventive and control measures to reduce soil MPs pollution. Finally, priorities for future research are proposed, such as field investigations of co-pollution, contribution of plastisphere to organic contaminant degradation, and mechanisms of MPs effects on organic contaminant toxicity.

Riverine microplastics derived from mulch film in Hainan Island: Occurrence, source and fate

Mulch film (MF) residues is an important source of microplastics (MPs) in farmland, but its transportation risk to the wider environment was still unknown. Some researches have pursued the sources of MPs found in exorheic rivers. Even so, a systematic study depicting the occurrence, source and fate of microplastics derived from mulch films (MPMF), the crucial component of MPs in farmlands, in exorheic rivers still lacking. Here, the combination of UV-Vis Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) was used to identify the full-size MPMF (1-5000 μm) in field sediment samples collected by single-diagonal systematic sampling. This study verified that MPMF, a polyethylene-matrix composite doped with additives, contributed a considerable part of MPs detected in upstream farmland soil and riverine sediments, and even had an abundance of 38 ± 11 items/kg to 82 ± 15 items/kg, accounting for 9.0%-13.7% of the total MPs in estuary sediments. Notably, upstream farmland was identified to the main source of the riverine MPMF by partial least square path modeling (PLS-PM), contributing to 94.7% of MPMF in riverside sediments and 85.0% of MPMF in estuary sediments. Our study first demonstrates that MPMF constitutes a non-negligible component of MPs in estuarine sediments and underlines the urgency of strengthening the management of MPs pollution in drainage areas with a high agricultural intensity.

Urban mangrove ecosystems are under severe threat from microplastic pollution: a case study from Mangalavanam, Kerala, India

The prevalence of microplastics in urban mangrove ecosystems has received little scientific attention despite their immense ecological significance. An investigation was conducted to assess the microplastic abundance and characteristics in three different environmental compartments viz; soil (933 ± 564 particles/kg), sediment (1275 ± 532 particles/kg d.w.), and water (101.6 ± 24 particles/liter) of the Mangalavanam bird sanctuary, a protected mangrove forest in the Cochin city of India. Microplastic fibres were predominant in water, while soil and sediment contained a higher proportion of microplastic fragments. Importantly, surrounding urban features and tidal fluctuation were considered to be influencing microplastic metrics in the area. The colour composition of microplastics was found to be similar in all three environmental compartments and most of the identified polymers were those which are scarcely recycled. Altogether, this study highlights the importance of adopting location-specific measures to protect the area from microplastic pollution and provides the baseline data required for further assessing the impacts of microplastic pollution on mangroves, avifauna, and other components of biodiversity in the region.

Unraveling consequences of the co-exposure of polyethylene microplastics and acid rain on plant-microbe-soil system

Emerging microplastics (MPs) pollution and continuing acid rain (AR) co-exist in terrestrial ecosystems, and are considered as threats to ecosystems health. However, few data are available on MPs-AR interactions in plant-microbe-soil systems. Here, a microcosm experiment was manipulated to elucidate the co-exposure of polyethylene MPs (PE MPs; 1%, 5% and 10%) and AR (pH 4.0) on soil-lettuce system, in which the properties of soil and lettuce, and their links were explored. We found that 10% PE MPs increased soil CO₂ emission and its temperature sensitivity (Q₁₀) in combination with AR, while 1% PE MPs reduced soil CO₂ emission irrespective of AR. PE MPs addition did not influence lettuce production (total biomass) though its photosynthesis was affected. PE MPs exerted negative impact on soil water availability. PE MPs treatments increased NH₄⁺-N content of soil without AR, and dissolved organic carbon content of soil sprayed with AR. 10% PE MPs combined with AR reduced soil microbial biomass, while soil microbial community diversity was not affected by PE MPs or AR. Interestingly, 10% PE MPs addition altered soil microbial community structure, and promoted the complexity and connectivity of soil microbial networks. 5% and 10% PE MPs addition decreased soil urease activity under AR, but this was not the case without AR. These findings highlight the critical role of AR in regulating PE MPs impacts on plant-microbe-soil ecosystems, and the necessity to incorporate other environmental factors when evaluating the actual impacts or risks of MPs pollution in terrestrial ecosystems.

Microplastic-Induced Oxidative Stress in Metolachlor-Degrading Filamentous Fungus Trichoderma harzianum

While there has been intensive research on the influence of microplastics (MPs) on aquatic organisms and humans, their effect on microorganisms is relatively little-known. The present study describes the response of the Trichoderma harzianum strain to low-density polyethylene (LDPE) microparticles. MPs, either separately or with metolachlor (MET), were added to the cultures. Initially, MP was not found to have a negative effect on fungal growth and MET degradation. After 72 h of cultivation, the content of fungal biomass in samples with MPs was almost three times higher than that in the cultures without MPs. Additionally, a 75% degradation of the initial MET was observed. However, due to the qualitative and quantitative changes in individual classes of phospholipids, cell membrane permeability was increased. Additionally, MPs induced the overproduction of reactive oxygen species. The activity of superoxide dismutase and catalase was also increased in response to MPs. Despite these defense mechanisms, there was enhanced lipid peroxidation in the cultures containing the LDPE microparticles. The results of the study may fill the knowledge gap on the influence of MPs on filamentous fungi. The findings will be helpful in future research on the biodegradation of contaminants coexisting with MPs in soil.

Automated identification and quantification of invisible microplastics in agricultural soils

Microplastics in agricultural soils have become the research hotspot in recent years, however, the quantitative methods based on the traditional visual inspection may have a high false detection rate. Here we combined the laser direct infrared (LDIR) and Fourier-transform infrared (FTIR) methods to investigate the microplastics in farmland with long-term agricultural activities. The results showed that the total abundance of microplastics reached 1.98 ± 0.41 × 10⁵, 1.57 ± 0.28 × 10⁵, 1.78 ± 0.27 × 10⁵, and 3.20 ± 0.41 × 10⁵ particles/kg soil in cotton fields with film mulching of 5, 10, 20, and >30 years, respectively. LDIR results indicated that microplastics ranging from 10 to 500 μm accounted for 96.5-99.9 % of the total microplastic amounts in the soils. Additionally, a total of 26 polymer types of microplastics were detected, among which polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), and polytetrafluoroethylene (PTFE) were dominantly observed. For the microplastics detected by FTIR (500 μm-5 mm), PE polymer was majorly observed (88.0-98.9 %). Most microplastics were films (88.2 %), while fibers and pellets were also found. The reclaimed water from sewage treatment plants, the drip irrigation utilities, and the residual plastic film are the potential sources of microplastics in the farmland soils. By using the automated quantitative and identifiable approaches, this study suggested that the commonly used visual counting method may underestimate the microplastic contamination in agricultural soils.

New separation protocol reveals spray painting as a neglected source of microplastics in soils

Microplastics are recently discovered contaminants, yet knowledge on their sources and analysis is limited. For instance, paint microplastics are poorly known because soil separation protocols using flotation solutions cannot separate paint microplastics due to the higher density of paint microplastic versus common microplastics. Here, we designed a new two-step density separation protocol for paint microplastics, allowing paint microplastics to be separated from the soil without digestion. Paint particles were separated from soil samples collected around the graffiti wall at the Mauerpark, Berlin, then quantified according to their shape and color characteristic. The presence of polymers as binders in the paint particles was verified by Fourier transform infrared spectroscopy. Results show concentrations from 1.1 × 10⁵ to 2.9 × 10⁵ microplastics per Kg of dry soil, representing the highest microplastic concentration ever reported in the literature. Particle concentrations decreased and the median size increased with soil depth. Our results provide first evidence that spray painting, a technique with a wide range of applications from industry to art, leaves a legacy of environmental microplastic in soils that has so far gone unnoticed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10311-022-01500-2.

Microplastics from agricultural plastic mulch films: A mini-review of their impacts on the animal reproductive system

Plastic mulch films (PMFs) are widely used to improve crop quality and quantity. Although they provide a range of benefits, they degrade into widespread microplastics (MPs), which can cause an unavoidable risk of environmental problems. The residue of PMFs is a significant source of MPs in soils, which can then spread into various ecosystems and be easily absorbed by organisms due to their small size, and subsequently transported through food chain. Notably, MPs have been found in the human placenta, stool and blood, raising an urgent reminder of the potential dangers of MPs to human health. This review summarizes recent studies concerning the effects of MPs on the reproductive system in soil invertebrates, aquatic animals and rodents of both sexes and the mechanisms by which MPs affect the animal reproductive system. The studies on females demonstrated that MPs decrease oocyte quantity and quality, and induce ovary fibrosis, pyroptosis and apoptosis of granulosa cells. In addition, disrupted integrity of the blood-testis barrier, damaged spermatogenesis and compromised sperm quality have been shown in most studies on male animals. The studies on the mechanisms of these effects have provided evidence that MPs act on the animal reproductive system through reactive oxygen species-related mechanisms by initiating the Wnt/β-Catenin and NLRP3/Caspase-1 pathways in females, and the Nrf2/HO-1/NF-κB, p38 MAPK and MAPK/Nrf2 pathways in males. Taken together, these studies reveal the reproductive toxicity of MPs from PMF on animals and serve as a reminder to properly dispose of PMF waste.

Impact of simulating real microplastics on toluene removal from contaminated soil using thermally enhanced air injection

This paper investigated the impacts of various real microplastics (MPs), i.e., polyethylene (PE) and polyethylene terephthalate (PET) with different sizes (1000-2000 and 100-200 μm) and different dosages (0.5 and 5% on a dry weight basis), on the toluene removal during the thermally enhanced air injection treatment. First, microscopic tests were carried out to determine the MPs' microstructure and behavior. The PE was mainly a small block, and PET appeared filamentous and sheeted with a larger slenderness ratio. Second, the interactions between MPs and toluene-contaminated soils were revealed by batch adsorption equilibrium experiments and low-field magnetic resonance. The morphological differences and dosage of the MPs impacted soils' total porosity (variation range: 39.2-42.7%) and proportion of the main pores (2-200 μm). Third, the toluene removal during the air injection consisted of compaction, rapid growth, rapid reduction, and tailing stages, and the MPs were regarded as an emerging solid state to affect these removal stages. The final cumulative toluene concentrations of soil-PET mixtures were influenced by total porosity, and those of soil-PE mixtures were controlled by total porosity (influence weight: 0.67) and adsorption capacity (influence weight: 0.33); meanwhile, a self-built comprehensive coefficient of MPs can reflect the relationship between them and cumulative concentrations (correlation coefficient: 0.783).

Seasonal variation in the correlation between beach wrack and marine litter on a sandy beach in West Iceland

Coastal plastic pollution is a global problem, it affects local ecosystems, and can have economic and social implications. Plastic pollution is pervasive at high latitudes but there is a lack of data on the spatial and temporal amount of marine litter entering coastal systems. In this study, a seasonal accumulation survey of anthropogenic debris and beach wrack was conducted for the first time in Iceland. One hundred data collections were performed on a coast in the Snæfellsnes peninsula throughout one year. Of all the debris retrieved, over 9000 items (0.2 to 50 cm), 78.5 % were plastics. Beach wrack correlated strongly with the quantities of plastic debris entering the coastal environment (R² > 0.9; p < 10^-11), with a different slope for each season. The presence of beach wrack informed important daily and spatial fluctuations in the quantities of plastic debris, while seasonal fluctuations demonstrated higher arrival rate of plastic in autumn and winter.

State of knowledge and future research needs on microplastics in groundwater

Microplastics (MPs) are widespread in aquatic and soil environments. This study targets the issue of MPs' transfer from soil to groundwater. Scientific papers were collected and analyzed using a text-mining approach that classifies text segments. This allowed the identification of four research topics and the organization of the results into a summarizing table. Those four topics are sources of groundwater MPs, main types of MPs (physico-chemical properties, polymer units, shapes, and size), human exposure (mainly drinking water), and potential environmental and human effects. Compared to the research of MP on aquatic or soil compartments, scientific data on MP in groundwater are less substantial. Current results show a divergence due to differences in context (alluvial aquifer, fractured rock aquifer, karst aquifer, etc), collecting, sampling, and analytical methods. This divergence requires further research with standardized analytic protocols and reference materials. The associated research gaps were identified by using the same approach. The following five topics emerged: (1) the transfer of MPs from soil to underground, (2) the contribution of groundwater to drinking water microplastic pollution, (3) the interaction with other contaminants, (4) the human and environmental effects, and (5) the protective and remediation solutions.

Polystyrene microplastics-induced cardiotoxicity in chickens via the ROS-driven NF-κB-NLRP3-GSDMD and AMPK-PGC-1α axes

Microplastics (MPs) pollution is getting increasingly prominent, and its dangers have attracted widespread attention. The heart is the central hub of the organism's survival, and the mechanism of MPs-induced heart injury in chickens is unknown. Here, we investigated the effects of 5 μm polystyrene microplastics (PS-MPs) on the heart and primary cardiomyocytes of chickens at varied concentrations. We observed that PS-MPs caused severe pathological damage and ultrastructural changes in heart, induced myocardial pyroptosis, inflammatory cell infiltration and mitochondrial lesions. PS-MPs evoked abnormal antioxidant enzyme content and ROS overproduction. Detailed mechanistic investigation indicated that PS-MPs triggered pyroptosis via NF-κB-NLRP3-GSDMD axis and exacerbated myocardial inflammation (NLRP3, Caspase-1, IL-1β, IL-18, ASC, GSDMD, NF-κB, COX-2, iNOS and IL-6 overexpression). Additionally, PS-MPs induced mitochondrial damage (TFAM, OPA1, MFN1 and MFN2 down-expression, DRP1 and Fis1 overexpression) and energy metabolism disorders (HK2, PKM2, PDHX and LDH up-regulation) by inhibiting AMPK-PGC-1α pathway. Interestingly, NAC alleviated these aberrant manifestations in vitro. We suggested that PS-MPs driven alterations in NF-κB-NLRP3-GSDMD and AMPK-PGC-1α pathways via ROS overload, which in turn triggered oxidative stress, myocardial pyroptosis, inflammation, mitochondrial and energy metabolism dysfunction. This provided theoretical bases for protecting chickens from toxic injury by MPs.