The occurrence of microplastic in Mu Us Sand Land soils in northwest China: Different soil types, vegetation cover and restoration years

Microplastic occurrence in urban and industrial soils of Ahvaz metropolis: A city with a sustained record of air pollution

This study investigates, for the first time, the concentration, distribution, fate and chemical composition of microplastics (MPs) in urban and industrial soils of Ahvaz metropolis, SW Iran. MP concentrations ranged from 100 to 3135 and 80 to1220 unit·kg^-1 in urban and industrial soils, respectively, with corresponding means of 619 and 390 unit·kg^-1. The most contaminated urban sites were located in the city center. Precisely these areas were affected by insufficient sanitation infrastructure including sewer systems, surface runoff collection and sewage treatment, and also high traffic loading in a commercial zone. MPs were found in various shapes, colours and sizes. In particular, microfibres (white-transparent and < 250 μm) were the most abundant MPs found in urban (70%) and industrial (55%) soils. Based on the weathering observed in the MPs, a large number of them originated from the fragmentation of other plastics and could have been photobleached. Polyethylene terephthalate and nylon were the dominant polymers in the MPs found in both industrial and urban soils and they could originate from textiles and tyres.

Distribution Characteristics and Source Analysis of Microplastics in Urban Freshwater Lakes: A Case Study in Songshan Lake of Dongguan, China

Current studies on microplastic pollution mainly focus on marine systems. However, few studies have investigated microplastics in an urban lake. This research intends to use an urban lake (Songshan Lake) as an example to explore the pollution characteristics of microplastics and use the principal component as well as the heat map analysis to discuss the relationships between different shapes of microplastics. According to this study, the average abundance of microplastics in the surface water and surface sediments of Songshan Lake were, respectively, 2.29 ± 0.98 items/m3 and 244 ± 121 items/kg; thin films were the major microplastics in both media; transparent this type of color has the most microplastic content. The particle size of microplastics was mainly 0.18–0.6 mm (43.3%) in surface water and 1–2 mm (48.3%) in surface sediments. The composition included five polymers: polyethylene (PE), polypropylene (PP), polypropylene–polyethylene copolymer (PP–PE copolymer), polystyrene (PS), and polyvinyl chloride (PVC), among which PE (47%) and PP (36%) were the main components. Principal component analysis (PCA) showed that there was a positive correlation among the four shapes of microplastics: films, fragments, foams, and fibers. The heat map analysis showed that the same category of shape distribution features may be similar for each sampling site.

Land-use patterns determine the distribution of soil microplastics in typical agricultural areas on the eastern Qinghai-Tibetan Plateau

Land-use patterns may affect the distribution characteristics of soil microplastics (MPs), but the effects in the agricultural areas of the Qinghai-Tibetan Plateau are still unknown. This study investigated the abundance of MPs in facility, farmland, grassland, and orchard soils in the Qaidam basin and Hehuang valley of Qinghai Province and analyzed its shape, size, color, and polymer composition distribution characteristics from 105 sites. The average abundance of MPs in facility, farmland, and grassland soils in the Hehuang valley were 2795.7, 1860.5, and 910.9 items kg^-1, which were 1.33, 4.84, and 1.50 times higher than those in the Qaidam basin, respectively. Orchard soils had 1322.2 items kg^-1 MPs. Soil MPs abundance in grassland and farmland was positively correlated with precipitation and 0 cm ground temperature; and negatively correlated with average wind speed (p < 0.05). Both the particle size of < 1 mm and pellet-shape MPs abundance showed a positive correlation with SOC (p < 0.05). Land-use patterns had the most significant affecting force (51.35%) on soil MPs abundance (p < 0.0001). Hence, land-use patterns, regional climate, and soil properties influence the distribution characteristics of soil MPs; besides, the land-use patterns were dominant.

The occurrence and effect of altitude on microplastics distribution in agricultural soils of Qinghai Province, northwest China

Microplastic (MPs) is a new type of environmental pollutant that has been widely detected in recent years. It is one of the main environmental problems faced by the global ecosystem and has attracted widespread attention. However, few studies have focused on the occurrence and distribution of MPs in agroecosystems. Therefore, Qinghai Province, a typical northwest region of China, was selected as the research area to study the distribution characteristics of MPs in agricultural soils in the low-altitude areas. The results indicated that MPs were detected in all soil samples. The abundance of MPs in agricultural soils in Qinghai Province ranged from 240 to 3660 items·kg^-1. MPs with size less than 0.5 mm dominated, accounting for 50% of the total MPs. The main types of MPs were film and fiber, accounting for 67% and 29% respectively. It was proved that the use of mulching film and sewage irrigation are the main sources of MPs, and the recovery and treatment of agricultural waste can reduce MPs pollution. At the same time, the spatial distribution characteristics of MPs in the soil of Qinghai Province were analyzed, and the results showed that the heavily polluted areas of MPs were mainly concentrated in the densely populated areas in the east of the province. In addition, the influence of altitude on MPs abundance was investigated, and there was a negative correlation between altitude and MPs abundance, and ultraviolet light may accelerate the aging and degradation of MPs. This study revealed the distribution characteristics of farmland soil pollution in typical northwest China, and provided an important theoretical basis for the subsequent study of MPs in agricultural ecosystems.

A critical review of microplastics in the soil-plant system: Distribution, uptake, phytotoxicity and prevention

Microplastics (MPs) are creating an emerging threat on the soil ecosystems and are of great global concern. However, the distribution in soil-plant system, as well as the phytotoxicity and impact mechanisms of MPs remain largely unexplored so far. This study introduced the diverse sources of MPs and showed the significant spatial variation in the global geographic distribution of MPs contamination based on data collected from 116 studies (1003 sampling sites). We systematically discussed MPs phytotoxicity, such as plant uptake and migration to stems and leaves, delaying seed germination, impeding plant growth, inhibiting photosynthesis, interfering with nutrient metabolism, causing oxidative damage, and producing genotoxicity. We further highlighted the alterations of soil structure and function by MPs, as well as their self and load toxicity, as potential mechanisms that threaten plants. Finally, this paper provided several preventive strategies to mitigate soil MPs pollution and presented research gaps in the biogeochemical behavior of MPs in soil-plant systems. Meanwhile, we recommended that methods for the quantitative detection of MPs accumulated in plant tissues should be explored and established as soon as possible. This review will improve the understanding of the environmental behavior of MPs in soil-plant systems and provide a theoretical reference to better assess the ecological risk of MPs.

The aging behavior of polyvinyl chloride microplastics promoted by UV-activated persulfate process

Microplastics (MPs) experienced different aging processes in environment. Literatures about effect of artificially-accelerated aging on MPs behavior are still insufficient. The accelerated process induced by ultraviolet(UV)-activated persulfate (PS) is a promising technology for obtaining different aged MPs to understand long-term aging behavior. In the work, the aging behavior of polyvinyl chloride (PVC) accelerated by UV/PS system were investigated. It exhibited a dechlorination with 58.495 ± 6.090 mg/L Cl^- release after 35 h UV-activated PS (0.01 M) process. The treatment led to significant alternations on surface morphology and chemical feature of PVC. The crystallinity was increased, and average size was reduced from 154.11 µm to 119.28 µm with aging time. Subsequently, many smaller size particles were produced. Furthermore, the process induced the breaking of backbone. Simultaneously, more oxygen-containing functional groups were identified. The oxidation reaction accelerated by sulfate radical (SO₄^•-) and reactive oxygen species (ROS) was predominant, which immensely promoted aging process. Sustained high levels of free radical contributed to production of alcohols and carboxylic acids short chain organics. The study explored aging behavior of PVC accelerated by UV/PS system, which could be helpful for understanding environmental behavior and providing further information to assess potential risks of MPs.

Seeking for a perfect (non-spherical) microplastic particle - The most comprehensive review on microplastic laboratory research

In recent decades, much attention has been paid to microplastic pollution, and research on microplastics has begun to grow exponentially. However, microplastics research still suffers from the lack of standardized protocols and methods for investigation of microplastics under laboratory conditions. Therefore, in this review, we summarize and critically discuss the results of 715 laboratory studies published on microplastics in the last five years to provide recommendations for future laboratory research. Analysis of the data revealed that the majority of microplastic particles used in laboratory studies are manufactured spheres of polystyrene ranging in size from 1 to 50 µm, that half of the studies did not characterize the particles used, and that a minority of studies used aged particles, investigated leaching of chemicals from microplastics, or used natural particles as a control. There is a large discrepancy between microplastics used in laboratory research and those found in the environment, and many laboratory studies suffer from a lack of environmental relevance and provide incomplete information on the microplastics used. We have summarized and discussed these issues and provided recommendations for future laboratory research on microplastics focusing on (i) microplastic selection, (ii) microplastic characterization, and (iii) test design of laboratory research on microplastics.

Photo-transformation of microplastics and its toxicity to Caco-2 cells

In recent years, microplastics (MPs) pollution, as a global environmental problem, has been widely concerned by countries all over the world. However, the research on the impact of MPs on human health is still limited. In this study, we studied the photo-transformation behavior of polystyrene microplastics (PS-MPs) under ultraviolet light and its toxicity to Caco-2 cells. Our results showed that the surface of PS-MPs was roughened by light, and cracks and pits appeared. UV-vis spectra showed that the opening of phenyl ring and the formation of carbonyl group might exist in this process. Based on FTIR and 2D-COS analysis, we observed the formation of carbonyl group and hydroxyl group, and preliminarily determined that the order of photo-transformation of PS-MPs was 698 (CH) > 752 (CH) > 1030 (CO) > 3645 (OH/OOH) > 1740 (CO). XPS showed that the photo-transformation of PS-MPs was a process in which carbon-containing functional groups were gradually partially transformed into oxygen-containing functional groups. Finally, the toxicity results showed that with the increase of PS-MPs concentration and the extension of light irradiation time, the survival rate of Caco-2 cells gradually decreased and the integrity of cell membrane was destroyed. The increased cytotoxicity can be explained at least in part by the fact that the toxicity of oxygen-containing functional groups is greater than that of carbon-containing functional groups, but how these functional groups affect the cytotoxicity of cells still needs sustained research in the future. This study can provide new insights for understanding the environmental behavior and ecological effects of PS-MPs in the environment.

Warming, temperature fluctuations and thermal evolution change the effects of microplastics at an environmentally relevant concentration

Microplastics are sometimes considered not harmful at environmentally relevant concentrations. Yet, such studies were conducted under standard thermal conditions and thereby ignored the impacts of higher mean temperatures (MT), and especially daily temperature fluctuations (DTF) under global warming. Moreover, an evolutionary perspective may further benefit the future risk assessment of microplastics under global warming. Here, we investigated the effects of two generations of exposure to an environmentally relevant concentration of polystyrene microplastics (5 μg L^-1) under six thermal conditions (2 MT × 3 DTF) on the life history, physiology, and behaviour of Daphnia magna. To assess the impact of thermal evolution we thereby compared Daphnia populations from high and low latitudes. At the standard ecotoxic thermal conditions (constant 20 °C) microplastics almost had no effect except for a slight reduction of the heartbeat rate. Yet, at the challenging thermal conditions (higher MT and/or DTF), microplastics affected each tested variable and caused an earlier maturation, a higher fecundity and intrinsic growth rate, a decreased heartbeat rate, and an increased swimming speed. These effects may be partly explained by hormesis and/or an adaptive response to stress in Daphnia. Moreover, exposure to microplastics at the higher mean temperature increased the fecundity and intrinsic growth rate of cold-adapted high-latitude Daphnia, but not of the warm-adapted low-latitude Daphnia, suggesting that thermal evolution in high-latitude Daphnia may buffer the effects of microplastics under future warming. Our results highlight the critical importance of DTF and thermal evolution for a more realistic risk assessment of microplastics under global warming.

Impact of waste of COVID-19 protective equipment on the environment, animals and human health: a review

During the Corona Virus Disease 2019 (COVID-19) pandemic, protective equipment, such as masks, gloves and shields, has become mandatory to prevent person-to-person transmission of coronavirus. However, the excessive use and abandoned protective equipment is aggravating the world's growing plastic problem. Moreover, above protective equipment can eventually break down into microplastics and enter the environment. Here we review the threat of protective equipment associated plastic and microplastic wastes to environments, animals and human health, and reveal the protective equipment associated microplastic cycle. The major points are the following:1) COVID-19 protective equipment is the emerging source of plastic and microplastic wastes in the environment. 2) protective equipment associated plastic and microplastic wastes are polluting aquatic, terrestrial, and atmospheric environments. 3) Discarded protective equipment can harm animals by entrapment, entanglement and ingestion, and derived microplastics can also cause adverse implications on animals and human health. 4) We also provide several recommendations and future research priority for the sustainable environment. Therefore, much importance should be attached to potential protective equipment associated plastic and microplastic pollution to protect the environment, animals and humans.

Photodegradation of microplastics mediated by different types of soil: The effect of soil components

Microplastics (MPs) have attracted considerable attention due to its worldwide distribution, environmental persistence, and ecological risks. In this work, the photodegradation of MPs mediated by five different types of soils were investigated. The results showed: after 20 d of xenon lamp irradiation, significant degradation of MP was observed on Harbin (S1), Huainan (S2), Jiangxi (S3), Shaanxi (S4) and Hainan (S5). The order of photodegradation rate of MP was S2 > S5 > S4 > S1 > S3. The components of the soil have some correlations with MPs photodegradation. The photodegradation of MP mediated by soil components (specifically, the clay, the iron oxides and MnO₂) displayed positive effect, while the photodegradation of MPs mediated by organic carbon showed inhibition trend. It is worth noting that electrostatic interaction may be the dominant factor affecting the interaction between MPs photodegradation rate and different soils surfaces. This study is helpful to deepen the understanding of the photochemical behavior of MP in soil, and is of great significance to evaluate the environmental fate and mechanism mediated by MP in soil.

Spatial distribution and potential sources of microplastics in the Songhua River flowing through urban centers in Northeast China

Microplastics (MPs) have elicited increasing concerns in freshwater systems worldwide. However, little information is available on the MP pollution in the Songhua River, the third largest river in China. And the understanding of the sources and pathways of MPs is limited. In this study, MPs were sampled from river water and wastewater treatment plants in five cities along the Songhua River to investigate the occurrence, spatial distribution, characteristics, and potential sources of MPs. Polyethylene, polypropylene and polystyrene accounted for more than 95% of the total MPs. MP pollution was determined to be spatially heterogeneous. The concentration of MPs in the urban center was always considerably higher than that in the upper reach, and irregular variation was observed from the urban center to the lower reach for each city. Urbanization was one of the primary driving forces of spatial variability. Statistically significant positive correlations (p-value < 0.05) were noted between the average concentration of MPs in river water and population density (p = 0.0023) and number of industrial enterprises above designated size (p = 0.0042) of each city. Line and fiber were the major shapes, and white was the most dominant color. Large (1-5 mm) and small (≤ 1 mm) MP particles accounted for 50% each. Multiple correspondence analysis as a new methodological approach was conducted to elucidate the sources of MPs for the first time. The potential sources of MPs included daily use, fishing, agricultural, and industrial productions. This work provides information about MP contamination for future studies on freshwater systems and new insights into the source apportionment of MPs.

Modeling the Conditional Fragmentation-Induced Microplastic Distribution

Microplastics (MPs) are drawing increasing attention from the international community due to their potential threats to the ecosystem and human health. Although their occurrence and spatial distribution have been extensively studied in recent years, the relationship between their abundance and sizes remains unclear. Moreover, the underlying mechanisms dominating their size distribution have rarely been explored. In the present study, we developed a novel conditional fragmentation model to describe MP size distribution in the soil environment. It is proposed that the distribution of MPs is not a coincidence but controlled by conditional aging. The applicability of this model was tested using data collected from different land use settings in Beijing, China. A distinct downsizing phenomenon from fibers, films, and fragments to granules is observed. Undisturbed land use types accumulated larger sized MPs with higher stability, while human interference accelerated the fragmentation of MPs. Both morphological analysis and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) observations provided direct evidence for the conditional fragmentation process. Furthermore, the model has proven to be suitable for describing the size distribution of MPs from various sources (including atmospheric deposition, transportation, and agriculture) and aging processes (such as mechanical abrasion, chemical oxidation, and photochemical transformation). It is proposed that this model can be used for various purposes in MP-related studies, especially source identification, transport modeling, and risk assessment.

Sorption and leaching behaviors between aged MPs and BPA in water: The role of BPA binding modes within plastic matrix

Due to the hydrophobicity and large specific surface area microplastics (MPs) have become the vector for the migration of environmental organic pollutants. Environmental aging process affects the physiochemical structure of MPs and their corresponding environmental behaviors, in which the effect of bisphenol A (BPA) binding mode within plastic matrix on aging behaviors of MPs is not reported. In this work, the structural properties and BPA sorption behaviors of low density polyethylene (LDPE) MPs with BPA additives and polycarbonate (PC) MPs with BPA monomers exposed to three types of artificial accelerated aging processes including UV/H₂O, UV/H₂O₂, and UV/Cl₂ systems were comparatively investigated. Virgin LDPE and PC exhibited obvious leakage of BPA additives or monomers. Aged LDPE had stronger sorption ability towards BPA in water environment with no observed leakage of BPA additives. While, aged PC had extremely high leakage of BPA monomers, which is similar to virgin PCs and was proved to be a persistent source of BPA release. The BPA sorption on aged LDPE or leaching from aged PC was influenced by aging processes, water pH, salinity, co-existing estradiol (E2), and water sources. This study reveals the potential ecological and environmental risks of MPs containing toxic additives/monomers during aging processes from a new perspective.

The occurrence and abundance of microplastics in surface water and sediment of the West River downstream, in the south of China

Microplastic pollution has aroused great concern in inland waters. Freshwater is the transport routes and potential sources for plastic fragments to the oceans. However, information especially about the occurrence of microplastics in freshwater systems is unclear in certain key areas. This work studied the distribution and characteristics for microplastics in the downstream area of West River. Both sediment and surface water detected microplastics with abundance ranging from 2560 to 10,240 items/kg and 2.99 to 9.87 items/L, respectively. Small size (<0.5 mm) and fiber were the main size and type in both surface waters and sediments. Polypropylene, polyethylene, polyethylene, polyvinyl chloride and polyethylene terephthalate were the polymer types of microplastics, as identified using a Fourier transform infrared spectrometer. In addition, findings here might be in consideration of studying about the distribution of microplastics and the degree to which they were influenced by the use of land. In descending order, the highest microplastics abundance was observed in commercial/public/recreational > residential > industrial > natural areas. Our results indicate the occurrence of high abundance microplastics in river impacted by human activities, and suggest that spatial distribution of microplastics varies between different land use areas.