Microplastic Particle Size Research Articles

Adsorption of As(III) by microplastics coexisting with antibiotics

Although recent studies have been conducted on the pollution and toxicity of microplastics with heavy metals or antibiotics, it is necessary to further investigate the coexistence of antibiotics and heavy metals on the surface of microplastics. In this study, the mechanisms of As(III) adsorption by polystyrene (PS) and polyamide (PA) microplastics in the presence of antibiotics (ciprofloxacin, CIP) were investigated. Adsorption behavior was investigated using kinetic and isotherm models, and the effects of microplastic particle size, aging, ion concentration, pH, xanthic acid (FA), and tannic acid (TA) were considered. Adsorption kinetics and isotherm models showed that the kinetics of As(III) adsorption on PS were consistent with a pseudo-first-order model; the kinetics of adsorption on PA were more consistent with segmented linear regression. The Freundlich model is consistent with the adsorption isotherms of As(III) on PS and PA. The smaller the microplastic particle size and the longer the aging time, the better the adsorption of As(III). Increasing NO3−significantly inhibited the adsorption of As(III) by PS, while it first promoted and then inhibited the adsorption by PA. The effect of pH was similar to that ofNO3−. The adsorption of As(III) by PS was significantly promoted by FA and TA, regardless of the presence of CIP; the adsorption of As(III) by PA was inhibited. Scanning electron microscopy (SEM) was used to characterize microscopic morphology of pristine and aged PS and PA microplastics; Fourier transform infrared (FTIR) and X-ray absorption spectroscopy (XPS) revealed changes in surface functional groups of PS and PA, while demonstrating the importance of different functional groups in exogenous additives (CIP and dissolved organic matter, DOM) in the adsorption of As(III). This study provides new insight into adsorption behaviors and interaction mechanisms between ternary pollutants.

Distribution Characteristics and Risk Assessment of Microplastics in Farmland Soil in Guyuan

The farmland ecosystem faces the emerging risk of microplastic pollution. To investigate the distribution characteristics of microplastics in agricultural soils in Guyuan City, the abundance, type, color, size, and shape of microplastics in Guyuan City agricultural soils were analyzed using field survey, microscopic observation, and Fourier transform infrared spectroscopy. In addition, the risk of microplastic pollution was assessed using the pollution load index method (PLI). The results showed that the microplastic abundance of agricultural soils (0-20 cm) in Guyuan City ranged from 186.32 to 1286.24 n·kg-1, and the microplastic abundance of soils in facility agriculture increased significantly by 35.56% and 228.91% compared with those in non-facility agriculture with and without film, respectively, and the microplastic abundance in the arable layer was 0.31 times higher than that in the plough pan layer. PE (26.42% to 62.83%) and PP (27.64% to 42.62%) were the main microplastic polymer types, and the number of soil polymer species was significantly greater in facility agriculture than that in non-facility agriculture. Microplastics <100 μm accounted for 32.21%-42.52%, whereas >1000 μm accounted for only 0.28%-12.31%. The particle size of microplastics in the arable layer was 47.39% higher than that in the plough pan layer, and the particle size of microplastics was the largest in facility agriculture and the smallest in non-facility film-free planting. Microplastics were mostly in the form of films, fibers, fragments, and microbeads, with the greatest abundance in the form of fibers and the second largest in the form of films. A total of seven colors of microplastics were monitored, mainly white and black. The overall risk of contamination in the study area was low, and the highest risk of microplastic contamination was found in the soil of facility agriculture. The results of the study will provide data reference for the assessment of microplastic contamination in agricultural soils and microplastic soil environmental behavior in China.

Occurrence Characteristics and Risk Assessment of Microplastics in Water and Sediments of Anhui Section of Huaihe River Basin

The occurrence characteristics and ecological risk level of microplastics in the water and sediments of the Anhui section of Huaihe River Basin were analyzed via field sampling, stereomicroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), risk index (H), and pollution load index (PLI) model. The current situation of microplastics in the water and sediments of the basin was analyzed, and the ecological risk assessment of microplastics was conducted. The results showed that the detection rate of microplastics at each site in the basin was 100%. The average abundance of microplastics in surface water and sediments was (39800±3367) n·m-3 and (5078±447) n·kg-1, respectively. The average abundance of microplastics in the downstream was higher than that in the upstream and midstream. The particle size of microplastics in water and sediments was primarily 20-150 μm, accounting for 82.96% and 80.77%, respectively. The microplastics were primarily fiber (water 76.05%, sediment 84.53%), film (water 21.83%, sediment 15.43%), and debris (water 2.12%, sediment 0.04%). The microplastics in water and sediments were primarily transparent, accounting for 63.31% and 83.69%, respectively. Polyethylene (65.74% in water and 80.62% in sediment) and polypropylene (18.43% in water and 9.71% in sediment) were the major components of water and sediments. Microplastics were primarily derived from agricultural films, abandoned fishing gear and nets, and artificially abandoned plastic bags in ports. The microplastic risk index (H) model assessment revealed that the risk index of some sites was high, and the risk level of microplastics in the Anhui section of Huaihe River Basin was grade II. The pollution load index (PLI) model assessment revealed that the ecological risk of surface water and sediments in the basin was generally low.

Ethanol, not water, should be used as the dispersant when measuring microplastic particle size distribution by laser diffraction

Size distribution is a crucial characteristic of microplastics (MPs). A typical method for measuring this property is wet laser diffraction. However, when measuring size distributions of MPs, despite it being a poor dispersant for many MPs, water is commonly selected, potentially limiting the reliability of reported measurements. To evaluate dispersant suitability, different aqueous concentrations of ethanol (0, 10, 20, 30, 40, 50, 75, 100 wt%) and aqueous solutions of 0.001 wt% Triton X-100 and a mixture comprising 10 wt% sodium pyrophosphate and 10 wt% methanol were used as dispersants in a laser granulometer (Mastersizer 2000) to determine particle size distributions (PSDs) of granular polyethylene MP35, MP125 and MP500 particles (nominally <35, <125 and, < 500 μm in size). The reliability of the PSDs depended on the dispersant used and size of primary MPs. With increasing ethanol concentrations, PSD curves of MP35 particles shifted from multi-modal to mono-modal distributions. The measured size distribution reduced from 1588.7 to 4.5 μm in water to 39.9 to 0.1 μm in 100 wt% ethanol. Generally, as ethanol concentration increased, uncertainty associated with the PSD parameters decreased. Although Triton X-100 and the mixed solution also showed better dispersion than water, measured particle sizes and coefficient of variation (COV, %) were notably larger than those for 100 wt% ethanol. Similar trends were observed for larger-sized MP125 and MP500 particles, but differences in PSD curves, PSD parameters, and COV (%) among dispersants were less pronounced. In all dispersants, the volume weighted mean diameters (VWMD) in 100 wt% ethanol (MP35: 14.1 μm, MP125: 102.5 μm, MP500: 300.0 μm) were smallest and close to diameters determined from microscope observations (MP35: 14.6 μm, MP125: 109.0 μm, MP500: 310.6 μm). Therefore, for accurate determinations of the PSDs of MP by wet laser diffraction, ethanol rather than water should be used as the dispersant.

Novel Insights into the Dermal Bioaccessibility and Human Exposure to Brominated Flame Retardant Additives in Microplastics.

In this study, we optimized and applied an in vitro physiologically based extraction test to investigate the dermal bioaccessibility of polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD), incorporated as additives in different types of microplastics (MPs), and assess human dermal exposure to these chemicals. The dermal bioaccessibility of PBDEs in polyethylene (PE) MPs was significantly higher (P < 0.05) than in polypropylene (PP) MPs. Both log Kow and water solubility influenced the dermal bioaccessibility of PBDEs. For HBCDDs in polystyrene MPs, the dermally bioaccessible fractions were 1.8, 2.0, and 1.6% of the applied dose for α-, β-, and γ-HBCDDs, respectively. MP particle size and the presence of cosmetic formulations (antiperspirant, foundation, moisturizer and sunscreen) influenced the bioaccessibility of PBDEs and HBCDDs in MP matrices at varying degrees of significance. Human exposure to ∑PBDEs and ∑HBCDDs via dermal contact with MPs ranged from 0.02 to 22.2 and 0.01 to 231 ng (kg bw)-1 d-1 and from 0.02 to 6.27 and 0.2 to 65 ng (kg bw)-1 d-1 for adults and toddlers, respectively. Dermal exposure to PBDEs and HBCDDs in MPs is substantial, highlighting for the first time the significance of the dermal pathway as a major route of human exposure to additive chemicals in microplastics.

Insight into the effect of microplastics on the adsorption and degradation behavior of thiamethoxam in agricultural soils

Thiamethoxam and microplastics are both common pollutants in farmland soil; however, few studies have focused on the interaction between thiamethoxam and microplastics in soil. Here, a batch experiment and soil incubation experiment were performed to explore the mechanism and effects of microplastics on the adsorption and degradation behaviors of thiamethoxam in soil, respectively. First, the batch experimental results indicated that the adsorption process of thiamethoxam on the microplastic/soil mixtures and soil-only systems mainly relies on chemical interactions. All sorption processes had moderate intensities of adsorption, and the sorption process occurred on the heterogeneous surface. In addition, the particle size and dose of microplastics could both affect the adsorption behavior of thiamethoxam onto microplastics/soil systems. The sorption capacity of thiamethoxam in soil decreases as the particle size of microplastics increases, but the sorption capacity increases as the dose of microplastics increases. Second, the results of the soil incubation experiment showed that the half-lives of thiamethoxam ranged from 57.7 d to 86.6 d, from 86.6 d to 173.3 d, and 115 d in the biodegradable microplastic/soil systems, nondegradable microplastic/soil systems, soil-only systems, respectively. These results indicate that biodegradable microplastics promoted the degradation of thiamethoxam, while nondegradable microplastics delayed the degradation process of thiamethoxam in soil. Overall, microplastics could change the degradation behaviors, sorption capacity and adsorption efficiency, and then affect the mobility and persistence of thiamethoxam in the soil environment. These findings contribute to understanding the influence of microplastics on the environmental fate of pesticides in the soil environment.

Spatial Distribution of Microplastics in Water and Sediments of Main Rivers in Taihu Lake Basin

Contemporary research on microplastic pollution has mainly focused on the ocean as a large sink, with a few studies involving relatively small sinks such as inland rivers and lakes. Taihu Lake is a typical inland lake and is the third largest freshwater lake in China. In this study, the spatial and temporal distribution, abundance, particle size, polymer composition, and ecological risk indices of microplastics in the water and sediments of 15 major inlet rivers in the Taihu Lake basin were investigated. The abundance of fibrous microplastics was the highest among the four characterized microplastic types. The particle size of microplastics in the water column and sediment was mainly in the range of 20–200 μm. The main component of microplastics in the water column was polyurethane, while in the sediment the main component of microplastics was polyurethane. Fibrous microplastics with a principal size of 20–100 μm are the main component of microplastics in landscape river sediments. The navigable rivers had the highest abundance of microplastics. All three river types have an environmental risk rating of III, which is at a medium to high level. The results of this study provide a reliable basis for the study of this sink in inland lakes.

A method to study the effects of combined stress of cadmium and microplastics on the acute toxicity of Eisenia fetida.

The compound pollutants formed by microplastics and cadmium present a significant potential threat to the soil-based ecosystem, and it is urgent to carry out relevant ecotoxicological studies. However, the lack of appropriate test methods and scientific mathematical analysis models has restricted the progress of research. Based on an orthogonal test design, a ternary combined stress test was performed to study the effect of microplastics and cadmium on earthworms. This study used the particle size and concentration of microplastics as well as the concentration of cadmium as test factors. Using the improved factor analysis model and the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method, a new model was constructed according to the response surface methodology to analyze the acute toxic effects on earthworms under the combined stress of microplastics and cadmium. In addition, the model was tested in a soil-polluted environment. The results show that the model can perfectly integrate the spatiotemporal cross effects of the concentration and time of the applied stress, and the scientific data analysis process ensures the efficient development of ecotoxicological research in the actual compound pollution environment. Moreover, the results of the filter paper test and soil test showed that the equivalent toxicity ratio of cadmium concentration, microplastic concentration, and microplastic particle size to earthworms as 26:35:39 and 23:36:41, respectively. In terms of the interaction effect, a certain positive interaction was observed between the cadmium concentration and that of the microplastics and their particle size, while a negative interaction was observed between the concentration of microplastics and their particle size. This research provides a test basis and model reference for early monitoring of the health of contaminated soils and assessments of ecological safety and security.

Ingestion of microplastics by silver carp (Hypophthalmichthys molitrix) larvae: Quantification of ingestion and assessment of microbiota dysbiosis

The adverse effects of microplastics ingested by aquatic organisms have been reported previously. However, most studies are primarily qualitative; therefore, it is challenging to determine the direct interactions between microplastics and organisms. In this study, for the first time, the microplastic intake behavior of silver carp (Hypophthalmichthys molitrix) larvae, a popular fish in China, as well as intestine accumulation and excretion of the microplastics were quantitatively investigated. The results showed that the intake of microplastics by silver carp larvae was negatively correlated with the particle size of microplastics but positively correlated with the exposure concentration. After intaking microplastics of different sizes, small-sized microplastics (≤ 150 μm) were rapidly excreted from the intestine of silver carp, whereas some large-sized microplastics (≥ 300 μm) remained in the intestine for a long time. The presence of food significantly increased the intake of large-sized microplastics, while small-sized microplastics intake was unaffected by the food. More importantly, the ingested microplastics caused specific changes in the diversity of intestinal microflora, potentially leading to abnormal immune and metabolic functions. The results of this study provide a new understanding on the potential impacts of microplastics on aquatic organisms.

New sight of microplastics aging: Reducing agents promote rapid aging of microplastics under anoxic conditions

The aging of microplastics (MPs) occurs extensively in the environment, and understanding the aging mechanisms of MPs is essential to study the properties, fate and environmental impact of MPs. We proposed a creative hypothesis that polyethylene terephthalate (PET) can be aged by reducing reactions with reducing agents. Simulation experiments based on the principle of reduction of carbonyl by NaBH4 were conducted to test the correctness of this hypothesis. The results showed that after 7 days of experiments, physical damage and chemical transformation occurred in the PET-MPs. The particle size of MPs was reduced by 34.95–55.93 %, and the C/O ratio was increased by 2.97–24.14 %. The changing order of surface functional groups (CO > C-O > C-H > C-C) was obtained. The occurrence of reductive aging and electron transfer of MPs was further supported by electrochemical characterization experiments. These results together reveal the reductive aging mechanism of PET-MPs: CO is firstly reduced to C-O by BH4- attack, and then further reduced to ·R. The resulting ·R recombines to form new C-H and C-C. This study is beneficial to deepen the understanding of the chemical aging of MPs, and can provide a theoretical basis for further research on the reactivity of oxygenated MPs with reducing agents.

Abundance and characterization of microplastics in amphipods from the Japanese coastal environment.

Microplastics can be ingested by tiny detritivores such as amphipods, with potential consequences on the food chain. The present study characterizes the abundance, chemical composition, and size of microplastics in amphipods found in the Japan Sea coastal environment, which is a hotspot for microplastic accumulation. High amounts of microplastic ingestion and a large discrepancy by amphipod species, Talorchestia nipponensis, Ampithoe valida, and Trinorchestia trinitatis, were observed (between 0.2 and 76.3 particles/individual) which may be due to differences in habitat preference and background contamination. This result indicates that coastal amphipods in particular may ingest large amounts of microplastics. The average microplastic particle size in amphipods was 59 ± 8.6µm, with 83% of particles smaller than 90µm, and polyethylene was dominant. This study provides insights into microplastic abundance in coastal amphipods and the context for further studies on coastal amphipod microplastic ingestion.

A reference methodology for microplastic particle size distribution analysis: Sampling, filtration, and detection by optical microscopy and image processing

AbstractMicroplastic (MP) contamination in natural water circulation is a concern for environmental issues and human health. Various types of polymer materials have been identified and were detected in MP analytic test procedures. Beyond MP polymer type, particle size and form play a major role in water analysis due to possible negative toxicologic effects on flora and fauna. However, the correct quantitative measurement of MP size distribution over several orders of magnitude is strongly influenced by sample preparation, filtration materials and processes, and microanalytical techniques, as well as data acquisition and analysis. In this paper, a reference methodology is presented aiming at an improved quantitative analysis of MP particles. An MP analysis workflow is demonstrated including all steps from reference materials to sample preparation, filtration handling, and MP particle size distribution analysis. Background‐corrected particle size distributions (1–1000 µm) have been determined for defined polyethylene (PE) and polyethylene terephthalate (PET) reference samples. Microscopically measured particle numbers and errors have been cross‐checked with the total initial mass. In particular, defined reference MP samples (PE, PET) are initially characterized and applied to filtration experiments. Optical microscopy imaging on full‐area Si filters with subsequent image analysis algorithms is used for statistical particle size distribution analysis. To quantify the effects of handling and filtration, several blind tests with distilled water are carried out to determine the particle background for data evaluation. Particle size distributions of PE and PET reference samples are qualitatively and quantitatively reproduced with respect to symmetry, and maximum and cut‐off diameter of the distribution. It is shown that especially MP particles with a radius of &gt;50 µm can be detected and retrieved with high reliability. For particle sizes &lt;50 µm, a significant interference with background contamination is observed. Data from blank samples allows a correction of background contaminations. Furthermore, for enhanced sampling statistics, the recovery of the initial amount of MP will be qualitatively shown. The results are intended as an initial benchmark for MP analytics quality. This quality is based on statistical MP particle distributions and covers the complete analytic workflow starting from sample preparation to filtration and detection. Microscopic particle analysis provides an important supplement for the evaluation of established spectroscopic methods such as Fourier‐transform infrared spectroscopy or Raman spectroscopy.

Experimental Investigation of Water-Retaining and Unsaturated Infiltration Characteristics of Loess Soils Imbued with Microplastics

Microplastics are abundant in agricultural soils and have significant impacts on rainfall infiltration and soil water-retaining capacity. To explore the effect of microplastics on agricultural soil permeability by simulating the rainfall irrigation process, a one-dimensional vertical soil column rainfall infiltration test device was used to study the unsaturated infiltration characteristics of loess soil imbued with microplastics under rainfall conditions. The following conclusions could be obtained: the microplastic content (q), the microplastic particle size (p), and the soil density (γ) have effects on rainfall infiltration; the soil water-retaining capacity would be weakened owing to the existence of microplastics; and intermittent rainfall is preferred in agricultural irrigation. Finally, the permeability coefficient (k) and average flow rate (V) of the unsaturated soil are deduced together, and the relationship between the permeability coefficient (k) and the matrix suction (ψ) of the unsaturated loess soil containing microplastics is calculated by an example, proving good consistency between the experimental results and theoretical calculations. Microplastics represent negative effects on rainfall infiltration and soil water retention, so it is recommended to dispose of them.

Three typical microplastics affect the germination and growth of amaranth (Amaranthus mangostanus L.) seedlings

Microplastics (MPs) have been a global emerging contaminant and have aroused wide public concern. Currently, it is still unknown the phytotoxicity effect of MPs on amaranth (Amaranthus mangostanus L.). This study investigated the early responses of amaranth by exposing its seeds to suspensions of polystyrene (PS), polyethylene (PE), and polypropylene (PP) MPs. We observed the effects of MPs on seed germination and growth of amaranth, especially on the oxidative damage in amaranth roots. Impacts of MPs on the germination and growth of amaranth varied with the type, concentration, and particle size of MPs. PE MPs and PP MPs inhibited the shoot extension of amaranth, while the root length under PP MPs treatment was generally shorter than that under PS MPs and PE MPs. The accumulation of H2O2 in amaranth roots increased with the rising of MPs concentration. Compared with the control, a little number of dead cells were found in the roots of amaranth under high MPs treatment. It is noteworthy that only under 100 mg/L PP treatment, the amaranthus seedlings root cells were disorganized, due to the reactive oxygen species (ROS) damage in the roots. These findings provide essential information to assess the phytotoxicity of MPs in agricultural products, and provide insights into the underlying mechanisms of the observed phytotoxicity.

Sorption kinetics, isotherms and molecular dynamics simulation of 17β-estradiol onto microplastics

Microplastic is a new type of pollutant, which can act as a carrier for organic contaminants. It affects the migration and bioavailability of chemicals and potentially threatens the ecology. This work investigated the adsorption kinetics, isotherm and influencing factors of 17β-estradiol (E2) on three dominate microplastics. Then, used molecular dynamics (MD) simulation to analyze the adsorption mechanism. The results showed that E2 adsorption onto microplastics conformed well to the Pseudo-second-order kinetics and Redlich-Petersen isotherm model. The adsorption capacity of E2 on microplastics was polyethylene (PE) > polypropylene (PP) > polystyrene (PS). The small particle size of microplastics was conducive to the adsorption due to its large specific surface area. The thermodynamic parameters demonstrated the adsorption of E2 was a spontaneous and exothermic process, so low temperature was benefit for the adsorption. The MD simulation results indicated the adsorption of E2 on MPs belonged to surface adsorption. The order of E2 adsorption energy by three microplastics obtained by molecular dynamics simulation is consistent with the experimental results. This work may help to understand the molecular adsorption process and provide a theoretical basis for the combined ecotoxicity of microplastics.

The Association Between Microplastics and Microbiota in Placentas and Meconium: The First Evidence in Humans.

Pregnancy and infancy are vulnerable times for detrimental environmental exposures. However, the exposure situation of microplastics (MPs) for mother-infant pairs and the adverse health effect of MPs are largely unknown. Therefore, we explored MP exposure in placentas and meconium samples, and the potential correlation of MP exposure with microbiota in placentas and meconium. A total of 18 mother-infant pairs were effectively recruited from Shanghai, China. The study required pregnant women to provide placentas and meconium samples. An Agilent 8700 laser infrared imaging spectrometer (LDIR) was applied to identify MPs. Microbiota detection was identified by 16S rRNA sequencing. Sixteen types of MPs were found in all matrices, and polyamide (PA) and polyurethane (PU) were the major types we identified. MPs detected in samples with a size of 20-50 μm were more than 76.46%. At the phylum level, both placenta and meconium microbiota were mainly composed of Proteobacteria, Bacteroidota, and Firmicutes. We also found some significant differences between placenta and meconium microbiota in β-diversity and gut composition. Additionally, we found polystyrene was inversely related with the Chao index of meconium microbiota. Polyethylene was consistently inversely correlated with several genera of placenta microbiota. The total MPs, PA, and PU consistently impacted several genera of meconium microbiota. In conclusion, MPs are ubiquitous in placentas and meconium samples, indicating the wide exposure of pregnant women and infants. Moreover, our findings may support a link between high concentration of MPs and microbiota genera in placentas and meconium. Additionally, there were several significant associations between the particle size of MPs in 50-100 μm and meconium microbiota.

Adsorption behavior of azole fungicides on polystyrene and polyethylene microplastics

Agricultural plastic films and triazole fungicides are widely used in agricultural production process. Exposure to natural environment, agricultural plastic films will degrade into micron plastic particles, which will adsorb pesticide molecules and may affect their toxicity, biological activity and persistence. The long-term coexistence of microplastics (MPs) and triazole fungicides will bring potential harms to the agricultural ecological environment. Therefore, two kinds of triazole fungicides flusilazole (FLU) and epoxiconazole (EPO) were selected as cases and the adsorption behaviors of them on polystyrene and polyethylene were investigated. A series of factors which could affect the adsorption behavior were evaluated. Specifically, the particle size of MPs could affect its adsorption capacity, and the smaller the particle size, the stronger the adsorption capacity. Moreover, with the increase of pH value from 6.0 to 9.0, the adsorption capacity of MPs to target compounds gradually increased. The effect of ionic strength was evaluated by NaCl, and 0.05% of NaCl was beneficial to the adsorption process, while the continuous increase of NaCl concentration inhibited the adsorption. Oxalic acid and humic acid decreased the adsorption capacity of flusilazole on PE by 15.99–32.00% and PS by 35.02–48.67%, respectively. In addition, compared with the single pesticide system, the adsorption capacity of MPs for flusilazole and epoxiconazole in the binary pesticides system decreased by 36.13–37.93% and 44.36–51.35%, respectively, indicating that competitive adsorption occurred between the two pesticides. Meanwhile, the adsorption process was evaluated by adsorption kinetics and adsorption isotherms and were consistent with pseudo-second-order kinetic model and Freundlich isotherm model, respectively. Finally, several characterization analyses were conducted to investigated the adsorption mechanism, and hydrogen, halogen bonding and hydrophobic interaction proved to play an important role. The study on the adsorption behavior and mechanism of pesticide on MPs was the basis of assessing the risk of joint exposure.

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.

Addition of polyvinyl pyrrolidone during density separation with sodium iodide solution improves recovery rate of small microplastics (20–150 μm) from soils and sediments

The purpose of this study was to identify a method to accurately separate small microplastics (<100 μm) from soil and sediment. We initially conducted spike-and-recovery tests using polyethylene microbeads and density separation and found that the recovery rate of microplastic particles smaller than 100 μm was less than 60%. This result suggested that previous reports have underestimated the concentrations of microplastics smaller than 100 μm in soil. When polyvinyl pyrrolidone was added and dispersed in a heavy liquid, the recovery rate exceeded 90%, regardless of the microplastic particle size. This improved recovery rate was independent of the type of polymer (polyethylene, polypropylene, polystyrene, polyethylene terephthalate, or nylon 6) and the physicochemical properties of the soil (Andisols, Entisols, or Ultisols), and the method was also effective for marine and lake sediments. Using this method, we measured microplastic concentrations in paddy soil. The results showed that the most common particle size, 20–100 μm, accounted for 64% of all microplastics. Accurate separation from the soil of fractions smaller than 100 μm, which account for the majority of microplastics in soil, will enable an accurate assessment of the impact of microplastics on the soil ecosystem. The method identified in this study can serve as the basic technique for achieving that goal.

Distribution Characteristics of Microplastics and Their Migration Patterns in Xiangxi River Basin

Microplastics as a prevalent pollutant in water bodies have recently attracted widespread attention. To investigate the spatial and temporal distribution characteristics of microplastics in freshwater rivers and their migration patterns, the surface water, sediments, and subsidence zone of the Xiangxi River, a tributary of the Yangtze River, were sampled and analyzed in November 2020 and April 2021, respectively. The results showed that the average abundance of microplastics in the surface water of Xiangxi River was (6.64±1.32) n·L-1 in flat water and (5.00±1.07) n·L-1 in dry water, the average abundance of microplastics in sediments was (0.56±0.13) n·g-1 in flat water and (0.41±0.09) n·g-1 in dry water, and the average abundance of microplastics in the subsidence zone was (0.53±0.15) n·g-1 in flat water and (0.68±0.18) n·g-1in dry water. There were significant differences in the abundance distribution of microplastics in the surface water, sediments, and subsidence zone (P<0.05). In the surface water and sediments, the particle size of microplastics was mainly distributed in the range of 0.1-0.5 mm, and in the subsidence zone, it mainly ranged from 1-5 mm. The color of microplastics was mainly transparent in the surface water and subsidence zone and blue in sediments. The morphology of microplastics in the Xiangxi River basin was mainly fiber, and the materials were mainly polyethylene (PE) and polypropylene (PP). There were many factors affecting the distribution of microplastics. The analysis results showed that the abundance of microplastics in the surface water was negatively correlated with the flow rate of the water body. The abundance of microplastics in the sediment was related to the substrate type of the riverbed and negatively correlated with the substrate particle size. Combined with the microplastic abundance data of each sampling site, it was found that there was a significant migration process of microplastics in the spatial distribution of the Xiangxi River in the watershed. Along the river longitudinal direction, the longitudinal migration of microplastics in the surface water was along the river direction, and in the vertical direction, it showed the mutual migration between the water body and the subsidence zone and the water body and sediments.