Distribution and characteristics of microplastics in the basin of Chishui River in Renhuai, China

Characteristics, drivers and ecological risk assessment of microplastics in the surface water of urban rivers in Guangdong-Hong Kong-Macao Greater Bay Area cities - A case study of Dongguan city

In the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), microplastic pollution in urban rivers is a prominent problem due to the developed economy and high industrial intensity. Using the Xiaohai River, Hanxi River and Dongguan Canal in Dongguan City, an important node city in the GBA, as an example, microplastic characteristics, drivers and ecological risks in the surface water of three rivers were investigated. Results showed that the average abundance of rivers in the wet period (1646.22 ± 154.73 items/m3) was 4.7 times higher than that in the dry period (351.09 ± 34.2 items/m3). Microplastics were mainly in the form of fragments and fibers, with a size range of 30-500 μm, and appeared transparent with white color. The microplastic polymer types PE, PP, PET and PA accounted for more than 70%. There are large differences in the characteristics of microplastic pollution during different hydrological periods. Redundancy analysis showed that the distribution of plastics, chemical materials, packaging and printing industries along the rivers dominated the differences in microplastic abundance. The electronic information industry contributed most to the composition of microplastic polymer types. The polymer hazard index, pollution load index, and potential ecological risk index for rivers indicate a medium-high risk classification or higher. Therefore, the industrial layout along the urban rivers should be rationalized, the disposal of microplastics in wastewater should be increased, and the use of green plastic products should be promoted. This study provides support for the management of microplastic pollution in urban surface water in the GBA.

Gut microbiota, a key to understanding the knowledge gaps on micro-nanoplastics-related biological effects and biodegradation

Micro-nanoplastics (MNPs) pollution as a global environmental issue has received increasing interest in recent years. MNPs can enter and accumulate in the organisms including human beings mainly via ingestion and inhalation, and large amounts of foodborne MNPs have been frequently detected in human intestinal tracts and fecal samples. MNPs regulate the structure composition and metabolic functions of gut microbiota, which may cause the imbalance of intestinal ecosystems of the hosts and further mediate the occurrence and development of various diseases. In addition, a growing number of MNPs-degrading strains have been isolated from organismal feces. MNPs-degraders colonize the plastic surfaces and form the biofilms, and the long-chain polymers of MNPs can be biologically depolymerized into short chains. In general, MNPs are gradually degraded into small molecule substances (e.g., N2, CH4, H2O, and CO2) via a series of enzymatic catalyses, mainly including biodeterioration, fragmentation, assimilation, and mineralization. In this review, we outline the current progress of MNPs effects on gut microbiota and MNPs degradation by gut microbiota, which provide a certain theoretical basis for fully understanding the knowledge gaps on MNPs-related biological effect and biodegradation.

Unraveling the characteristics of microplastics in agricultural soils upon long-term organic fertilizer application: A comprehensive study using diversity indices

Microplastics negatively impact soil health and productivity. Organic fertilizers constitute significant contributors of microplastics in agricultural soils. Nevertheless, comprehensive data on the diversity of microplastics in long-term fertilized soils remain unavailable. In this study, we assessed the presence of microplastics in soils subjected to application of three different organic fertilizers (pig manure, chicken manure, and sludge composts) over 12 years, and evaluated the potential ecological risks posed by microplastic accumulation. The average microplastic abundance in soil was 368.88 ± 207.97 (range: 90-910) items/kg. Microplastic abundance differed among fertilization treatments, with substantial increases of 16.67%, 71.67%, and 61.43% upon low to high application of the three treatments, respectively. Overall, the microplastics predominantly comprised fibers (70.94%) and fragments (25.25%), of which a substantial proportion constituted light-colored microplastics (transparent and white). The size of microplastics was mainly concentrated in the 1-2 mm range (39.96%), with rayon, polypropylene, polyester, and polyethylene being identified as the major types. The risk assessment indices of the three treatments were 229.38, 257.64, and 175.89, respectively, and were all classified as level 4 (high risk). The microplastic diversity integrated index and principal component analysis revealed that microplastics were uniformly distributed throughout the 0-20 cm soil depth consequent to tillage activity. Together, these findings provide a comprehensive assessment of microplastic pollution in long-term fertilized soils and serve as a scientific basis for reducing microplastic contamination in agricultural soils.

Occurrence, potential sources, and ecological risk assessment of microplastics in the inland river basins in Northern China

Microplastics (MPs) are the pollutants, found widely across various environmental media. However, studies on the MP pollution in urban rivers and the necessary risk assessments remain limited. In this study, the abundance and characteristics of microplastics in a typical urban river were examined to evaluate their distribution, sources, and ecological risks. It was observed that the abundance of MPs in sediments (220-2840 items·kg-1 dry weight (DW)) was much higher than that in surface water (2.9-10.3 items·L-1), indicating that the sediment is the "sink" of river MPs. Surface water and sediment were dominated by small particle size MPs (< 0.5 mm). Fiber and debris were common shapes of MPs in rivers and sediments. The microplastics in river water and sediments were primarily white and transparent, respectively. Polypropylene (PP) and polyethylene (PE) were the major polymers found.

Investigation of microplastics in urban rivers of Eastern China in summer: abundance, characteristics and ecological risk assessment

Microplastics (MPs) are increasingly becoming recognized as worldwide environmental contaminants, exerting a substantial impact on the safety of city rivers. This study explored the abundance and characteristics of MPs in summer 2023, including June and August, representing plum rain and typhoon rain seasons. The Qinhuai River exhibits more spatial fluctuations in six sampling sites with average concentrations of 470 ± 119.56 items per L, and the abundance increases with the water flows in the river. Downstream had the highest MP abundance of 484 ± 121.34 items per L, which were positive with the concentration of suspended solids (SS). Transparent and green MPs were more even in the sampling sites, and the shapes of fragments were predominant in the summer. Interestingly, the proportion of fiber and small-sized (38-75 μm) microplastics was predominant in the plum rain seasons, while the percentage of large-sized (270-5000 μm) and polymers of PE occurred in the typhoon rain seasons. The index of hazard scores of plastic polymers (H) revealed that the studied river had a severe pollution level (IV), which was highly influenced by PVC and PC. Besides, the pollution load index PLI value of different rain seasons was slightly polluted (I), while the PLI in autumn rain seasons was relatively higher than that in other seasons due to the higher variance of MPs. Therefore, the ecological risk of microplastics of PVC and PC in the Qinhuai River during varying seasons should be seriously considered. Our research is expected to provide valuable assistance in improving the management of urban rivers.

Seasonal variation, spatial distribution and risk assessment of microplastics in surface waters of Periyar River, Kerala, India

Microplastics, an emerging contaminant, are widespread in oceans around the world, and rivers are the key conveyors of these pollutants into the oceans. There exists a dearth of available data pertaining to seasonal fluctuation, spatial distribution and risk assessment of microplastics in rivers extending from upper reaches to the lower reaches. The collection of such data is of utmost importance for the purpose of formulating beneficial management strategies for riverine microplastics. In order to bridge this research gap, an investigation was made in the Periyar River in Kerala, India, which is exposed to anthropogenic stress and is at risk of microplastic pollution. A total of eighteen sites (six sites each from downstream, midstream and upstream) along the 244 km of the river were investigated across three seasons in a year. The study revealed a discernible pattern in the spatial distribution of microplastic concentrations, wherein there was a rise in abundance from the upstream to midstream and then a sudden increase of abundance along the downstream regions towards the lower reaches. The highest mean microplastic abundance of 124.95 items/L was obtained during the monsoon season followed by post-monsoon season i.e. 123.21 items/L and pre-monsoon i.e. 120.50 items/L. The predominant forms of microplastics were found to be fibres, fragments and filaments. Most prevalent polymer types acquired were polyethylene (PE) and polypropylene (PP). Pollution hazard index (PHI) and pollution load index (PLI) were also evaluated to assess the water quality of this river. The findings of this study conclude that the Periyar River is polluted with microplastics throughout its course and offer significant insights into the detection of microplastic origins in river systems and lend support to the implementation of potential measures aimed at mitigating their impact.

The retention of plastic particles by macrophytes in the Amazon River, Brazil

This study evaluated the presence of plastics and microplastics in macrophytes in an urbanized sector of the Amazon River. A total of 77 quadrats in 23 macrophyte banks were sampled during the dry (September 2020) and rainy (June 2021) season. Five species were identified: Paspalum repens, Pontederia rotundifolia, Pistia stratiotes, Salvinia auriculata and Limnobium laevigatum, with P. repens being dominant during the dry season (47.54%) and P. rotundifolia during the rainy season (78.96%). Most of the plastic particles accumulated in Paspalum repens (49.3%) and P. rotundifolia (32.4%), likely due to their morphological structure and volume. The dry season showed a higher accumulation of plastic particles than the rainy season. Microplastics were found in most samples, during both the dry (75.98%) and rainy seasons (74.03%). The upstream macrophyte banks retained more plastic particles compared to the downstream banks. A moderate positive correlation was observed between the presence of plastic particles and macrophyte biomass, and a weak positive correlation between the occurrence of microplastics and mesoplastics. White and blue fragments, ranging from 1 to 5 mm were the most common microplastics found in the macrophyte banks. Green fragments and green and blue fibers were identified as polypropylene, blue and red fragments as polyethylene, and white fragments as polystyrene. Therefore, the results of this study highlight the first evidence of the retention of plastic particles in macrophytes of the Amazon and highlight a significant risk due to the harmful effects that this type of plastic can cause to the fauna and flora of aquatic ecosystems.

Microplastics in Asian rivers: Geographical distribution, most detected types, and inconsistency in methodologies

Microplastics pose a significant environmental threat, with potential implications for toxic chemical release, aquatic life endangerment, and human food chain contamination. In Asia, rapid economic growth coupled with inadequate waste management has escalated plastic pollution in rivers, positioning them as focal points for environmental concern. Despite Asia's rivers being considered the most polluted with plastics globally, scholarly attention to microplastics in the region's freshwater environments is a recent development. This study undertakes a systematic review of 228 scholarly articles to map microplastic hotspots in Asian freshwater systems and synthesize current research trends within the continent. Findings reveal a concentration of research in China and Japan, primarily investigating riverine and surface waters through net-based sampling methods. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) emerge as the predominant microplastic types, frequently observed as fibers or fragments. However, the diversity of sampling methodologies and reporting metrics complicates data synthesis, underscoring the need for standardized analytical frameworks to facilitate comparative analysis. This paper delineates the distribution of microplastic hotspots and outlines the prevailing challenges and prospects in microplastic research within Asian freshwater contexts.

Natural organic small molecules promote the aging of plastic wastes and refractory carbon decomposition in water

Microplastics and nanoplastics are ubiquitous in rivers and undergo environmental aging. However, the molecular mechanisms of plastic aging and the in-depth effects of aging on ecological functions remain unclear in waters. The synergies of microplastics and nanoplastics (polystyrene as an example) with natural organic small molecules (e.g., natural hyaluronic acid and vitamin C related to biological tissue decomposition) are the key to producing radicals (•OH and •C). The radicals promote the formation of bubbles on plastic surfaces and generate derivatives of plastics such as monomer and dimer styrene. Nanoplastics are easier to age than microplastics. Pristine plastics inhibit the microbial Shannon diversity index and evenness, but the opposite results are observed for aging plastics. Pristine plastics curb pectin decomposition (an indicator of plant-originated refractory carbon), but aging plastics promote pectin decomposition. Microplastics and nanoplastics undergoing aging processes enhance the carbon biogeochemical cycle. For example, the increased carbohydrate active enzyme diversity, especially the related glycoside hydrolase and functional species Pseudomonas and Clostridium, contributes to refractory carbon decomposition. Different from the well-studied toxicity and aging of plastic pollutants, this study connects plastic pollutants with biological tissue decomposition, biodiversity and climate change together in rivers.

Intelligent classification and pollution characteristics analysis of microplastics in urban surface waters using YNet

Microplastics (MPs, ≤ 5 mm in size) are hazardous contaminants that pose threats to ecosystems and human health. YNet was developed to analyze MPs abundance and shape to gain insights into MPs pollution characteristics in urban surface waters. The study found that YNet achieved an accurate identification and intelligent classification performance, with a dice similarity coefficient (DSC) of 90.78%, precision of 94.17%, and recall of 89.14%. Analysis of initial MPs levels in wetlands and reservoirs revealed 127.3 items/L and 56.0 items/L. Additionally, the MPs in effluents were 27.0 items/L and 26.3 items/L, indicating the ability of wetlands and reservoirs to retain MPs. The concentration of MPs in the lower reaches of the river was higher (45.6 items/L) compared to the upper reaches (22.0 items/L). The majority of MPs detected in this study were fragments, accounting for 51.63%, 54.94%, and 74.74% in the river, wetland, and reservoir. Conversely, granules accounted for the smallest proportion of MPs in the river, wetland, and reservoir, representing only 11.43%, 10.38%, and 6.5%. The study proves that the trained YNet accurately identify and intelligently classify MPs. This tool is essential in comprehending the distribution of MPs in urban surface waters and researching their sources and fate.

Innovative overview of the occurrence, aging characteristics, and ecological toxicity of microplastics in environmental media

Microplastics (MPs), pollutants detected at high frequency in the environment, can be served as carriers of many kinds of pollutants and have typical characteristics of environmental persistence and bioaccumulation. The potential risks of MPs ecological environment and health have been widely concerned by scholars and engineering practitioners. Previous reviews mostly focused on the pollution characteristics and ecological toxicity of MPs, but there were few reviews on MPs analysis methods, aging mechanisms and removal strategies. To address this issue, this review first summarizes the contamination characteristics of MPs in different environmental media, and then focuses on analyzing the detection methods and analyzing the aging mechanisms of MPs, which include physical aging and chemical aging. Further, the ecotoxicity of MPs to different organisms and the associated enhanced removal strategies are outlined. Finally, some unresolved research questions related to MPs are prospected. This review focuses on the ageing and ecotoxic behaviour of MPs and provides some theoretical references for the potential environmental risks of MPs and their deep control.

Characteristics of bacterial community structure in the sediment of Chishui River (China) and the response to environmental factors

Sediment microorganisms performed an essential function in the biogeochemical cycle of aquatic ecosystems, and their structural composition was closely related to environmental carrying capacity and water quality. In this study, the Chishui River (Renhuai section) was selected as the research area, and the concentrations of environmental factors in the water and sediment were detected. High⁃throughput sequencing was adopted to reveal the characteristics of bacterial community structures in the sediment. In addition, the response of bacteria to environmental factors was explored statistically. Meanwhile, the functional characteristics of bacterial were also analyzed based on the KEGG database. The results showed that the concentration of environmental factors in the water and sediment displayed spatial differences, with the overall trend of midstream > downstream > upstream, which was related to the wastewater discharge from the Moutai town in the midstream directly. Proteobacteria was the most dominant phylum in the sediment, with the relative abundance ranged from 52.06% to 70.53%. The distribution of genus-level bacteria with different metabolic activities varied in the sediment. Upstream was dominated by Massilia, Acinetobacter, and Thermomonas. In the midstream, Acinetobacter, Cloacibacterium and Comamonas were the main genus. Nevertheless, the abundance of Lysobacter, Arenimonas and Thermomonas was higher in the downstream. Redundancy analysis (RDA) showed that total nitrogen (TN) and total phosphorus (TP) were the main environmental factors which affected the structure of bacterial communities in sediment, while total organic carbon (TOC) was the secondary. The bacterial community was primarily associated with six biological pathway categories such as metabolism. Carbohydrate metabolism and amino acid metabolism were the most active functions in the 31 subfunctions. This study could contribute to the understanding of the structural composition and driving forces of bacteria in the sediment, which might benefit for the ecological protection of Chishui River.

Abundance and risk assessment of microplastics in water, sediment, and aquatic insects of the Nile River

Microplastics (MPs) are a serious threat in freshwater environments. The ecological risk and abundance level of MPs in abiotic and biotic compartments of the Nile River haven't been systematically reported. Thus, these issues were highlighted in the present study during different seasons of the sampling year. The results showed that MP concentrations in the river ranged from 2.24 ± 0.6 to 3.76 ± 1.1 particles/L, 298 ± 63 to 520 ± 80 particles/kg dry weight, and 0.081 ± 0.051 to 4.95 ± 2.6 particles/individual in surface water, sediment, and different species of aquatic insects, respectively. All the extracted MPs are colored blue, red, and black. Fiber-shaped polyesters (<500-1500 μm) were the most common MPs in all the river compartments. MPs' dominance was observed during the summer in comparison with that in the other seasons. Environmental risk indicators indicate the high ecological risk of MPs, which are widely distributed in the Nile River. In conclusion, MP consumption by aquatic insects may not only be related to levels of environmental contamination, since other variables, such as taxon size, weight, and particular feeding behavior, may also be significant. Additionally, the presence of MPs in insects (at lower trophic levels) creates the potential for predation-based inter-trophic level transmission. Thus, higher trophic-level investigations of various feeding groups should be carried out to identify any possible harm that MPs cause to various aquatic organisms.

Spatial distribution and vertical characteristics of microplastics in the urban river: The case of Qinhuai River in Nanjing, China

Microplastics (MPs) are emerging as global environmental pollutants, significantly influencing the safety of city rivers. This study investigated six sampling sites in the Qinhuai River of Nanjing, which explored the distribution and characteristics of MPs and the microbial structure in 2023. The studied river contained various levels of MPs with average concentrations of 667.68 items/L, whose abundance firstly decreased midstream and then increased downstream. The MPs abundance upstream was higher in surface water column, microplastics midstream and downstream accumulated more in deep water column. Black and blue are prevalent in the color distribution, while the polymers of PC, PP and PS changed with increasing depth, with a proportion of 74 % ∼ 97 % in the dominant shapes of granules. Furthermore, the water with higher MPs may stimulate the growth of MPs-related bacteria in sediments, including the genus of Pseudoxanthomonas and Dechloromonas. Our research will provide constructive support for enhancing urban river management strategies.

Differences in Chemical Composition, Polyphenol Compounds, Antioxidant Activity, and In Vitro Rumen Fermentation among Sorghum Stalks

The aim of the study was to examine the differences in the chemical composition, polyphenol compounds, antioxidant activity, and in vitro rumen fermentation among six varieties of sorghum stalks. The results show that maoliangnuo 1 (M1) contained a higher (p < 0.05) level of dry matter, and jinzhong 405 (J4) contained a higher (p < 0.05) level of crude protein content. The concentrations of neutral detergent fiber, acid detergent fiber, and cellulose were significantly higher (p < 0.05) in stalk jinliangnuo (JN). The levels of chlorogenic acid, homoorientin, isovitexin, vitexin, rhoifolin, genistin, quercetin, apigenin, aloe emodin, emodin, and total polyphenols were all significantly (p < 0.05) higher in maohongnuo 6 (M6) than in the other stalks. Moreover, stalk M6 contained higher (p < 0.05) levels of total antioxidant capacity (TAC), glutathione peroxidase (GPX), catalase (CAT), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging capacity. There were significant (p < 0.05) positive correlations between total polyphenols and TAC, superoxide dismutase, GPX, CAT, and DPPH free-radical scavenging capacity. The total gas production was significantly (p < 0.05) influenced by the sorghum stalk variety and incubation time. Stalk J4 displayed higher values for the (p < 0.05) immediately soluble fraction and the potential extent of gas production, while stalk M6 exhibited a significantly lower (p < 0.05) insoluble fraction level. Furthermore, stalk M6 exhibited a significantly higher level of (p < 0.05) ruminal fluid propionic acid, but its level of butyric acid and its ratio of acetic acid to propionic acid were both significantly lower (p < 0.05). Taken together, the results reported in this paper indicate that the chemical composition, polyphenol compounds, antioxidant activity, and in vitro rumen fermentation all vary greatly among different varieties of sorghum stalks.

Monthly variation and transport of microplastics from the Soan River into the Indus River

The presence of plastic and microplastic pollution in freshwater systems receives extensive concerns for its accumulative trend and potential ecological impacts. This is the first annual study that investigated the monthly profile of plastic pollution in the mouth of the Soan River. Plastic pollutants comprising microplastic content up to 91.7 % were abundantly found during different seasons around the year, ranging from 132.7 items/m3 to 641.3 items/m3. The average abundance of plastics was significantly higher in August (641.3 ± 23.7 items/m3) than in other months. Overall, fibers, large microplastics (L-MPs), and transparent items were dominant by shape (57.7 %), size (61.9 %), and color (24.6 %), respectively. The highest average number of fibers (374.3/m3) and L-MPs (396 items/m3) were recorded during May and remained higher in the surface water from December to May. Fragments (432.3/m3) and S-MPs were observed higher (362.3 items/m3) during the peak rainy month of the summer monsoon season (August). Variations in the abundance and morphotypes were seemingly not only influenced by the seasonal change but also might be due to hydromorphological characteristics of the river, especially riverbed morphology, and the flow of the water. Only 5.2 % of the total items found were identified using μ-FTIR (micro-Fourier Transformed Infrared Spectroscope) which consisted of 70.7 % plastic items. Spectroscopy revealed that polyethylene terephthalate was an abundantly found polymer that largely prevailed in the form of fibers, followed by polypropylene and polyethylene. Most of the fragments, foams, and films were composed of polypropylene, polystyrene, and rayon respectively. Being an urban river, the polymeric profile demonstrated that anthropogenic activities had a significant impact on polluting the river. These findings are a very important source to understand the profile of plastic pollution in the Soan River and also a significant reference for policy-making in controlling plastic pollution among the riverine networks.

Investigation of microplastics and microplastic communities in selected river and lake basin soils of Thiruvananthapuram District, Kerala, India

Riparian areas are highly dynamic bio-geophysical settings with a surge of waste deposition predominantly including land-based plastic discards. These polymer discards are destined to be the prime constitution of marine "plastisphere." The polymer fate is determined by waterbodies, where the chances of plastic retention are higher, eventually mediating the formation of microplastics (MPs) in years or decades. Such formed MPs are a potential threat to the aqua bio-regime. A systematic investigation of three waterbody basin soils (Karamana River, Killiyar, and Akkulam-Veli Lake) showed the presence of MPs in all the samples analyzed with varying sizes, shapes, colors, and compositions. MPs of the shapes flakes, fragments, filaments, sheets, foams, and fibers were observed with dimensions 0.3-4.7 mm. Most of the particles were white in hue (WT), followed by colorless (CL), light yellow (L.Y), light brown (L.B), orange (OR), red (RD), and blue (BL), respectively. The polymer communities were identified as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and nylon. The highest average MP density was identified in the basin of Killiyar (799 ± 0.09 pieces/kg) followed by Karamana River (671 ± 3.45 pieces/kg), indicating the closeness of the sampling station to the city center compared to Akkulam-Veli Lake (486 ± 58.55 pieces/kg). The majority of the sampling sites belonged to the slopy areas and came under the highly urbanized land category. A close association was observed between particle abundance and urban activity. The study foresees possible threats inflicted by MP abundance upon the area-wide hydro-biological system.

Distribution and characteristics of microplastics in an urban river: The response to urban waste management

The rivers have been proven to be potential sources and the major transport pathways of microplastic (MP) in natural aquatic eco-systems, yet there is an absence of understanding the provenances and distribution dynamics of MP in fluvial water body of urban regions. The present investigation aimed to characterize the distribution and accumulation of MPs in both surface water and riverine bed sediments in a typical urban river (Nanming River, southwest China), during the dry and wet seasons of 2021. MP were detected throughout the entire sample set, with average surface water abundances of 750 ± 53 n/m3 and 693.3 ± 40 n/m3 in dry and wet seasons, respectively, and 2250 ± 496.7 n/kg (dw) in surface sediments. Furthermore, the composition of 25 polymer types MPs were analyzed. The sediment of the Nanming River is a sink for MPs, recording their long-term accumulation. Multivariate statistical analysis-based results indicated that urban littering and agricultural input were the major contributors of non-point MP in the Nanming River, while the discharged effluent was another factor influencing the distribution of MPs in urban fluvial system. The average abundance of MPs was negatively correlated with purchase power parity (PPP), demonstrating that the poorly waste management results in a higher abundance of MPs in municipal river systems. The present study systematically characterized the distribution of MPs in medium-sized urban rivers systems in Southwest China. These findings can inform policy and management decisions to reduce MPs pollution in urban rivers and protect aquatic ecosystems.

Occurrence of microplastic pollution in rivers globally: Driving factors of distribution and ecological risk assessment

Microplastics, as global emerging pollutants, have received significant attention worldwide due to their ubiquitous presence in the rivers. However, there is still a lack of clarity on the occurrence, driving factors, and ecological risks of microplastics in rivers worldwide. In this study, a global microplastic dataset based on 862 water samples and 445 sediment samples obtained from 63 articles was constructed, which revealed the temporal and spatial distribution of abundance and morphological characteristics of microplastics in rivers across the globe. In global rivers, the abundance of MPs in both water and sediment spans across 10 and 4 orders of magnitude, respectively. The MP comprehensive diversity index based on the physical morphological characteristics of MPs indicated a significant positive correlation between the pollution sources of MPs in different environmental media. Based on the data was aligned to the full-scale MPs, a novel framework was provided to evaluate the ecological risk of MPs and the interaction effects between the influencing factors driving the distribution characteristics of MPs in rivers around the world. The results obtained demonstrated a wide variation in the key driving factors affecting the distribution of microplastics in different environmental media (water and sediment) in rivers globally. The diversity indices of the morphological characteristics of MPs in densely populated areas of lower-middle income countries in Asia were significantly higher, implying that the sources of microplastics in these regions are more complex and extensive. More than half of the rivers are exposed to potential ecological risks of MPs; however, microplastics may pose only immediate risks to aquatic species in Burigang River, Bangladesh. This can provide valuable insights for formulating more effective scientific strategies for the management of MP pollution in rivers.

Dose-dependent toxicity of polyethylene microplastics (PE-MPs) on physiological and biochemical response of blackgram and its associated rhizospheric soil properties

Microplastic contamination in terrestrial ecosystem is emerging as a global threat due to rapid production of plastic waste and its mismanagement. It affects all living organisms including plants. Hence, the current study aims at understanding the effect of polyethylene microplastics (PE-MPs) at different concentrations (0, 0.25, 0.50, 0.75, and 1.00% w/w) on the plant growth and yield attributes. With blackgram as a test crop, results revealed that a maximum reduction in physiological traits like photosynthetic rate; chlorophyll a, b; and total chlorophyll by 5, 14, 10, and 13% at flowering stage; and an increase in biochemical traits like ascorbic acid, malondialdehyde, proline, superoxide dismutase, and catalase by 11, 29.7, 16, 22, and 30% during vegetative stage was observed with 1% PE-MP application. Moreover, a reduction in growth and yield attributes was also observed with increasing concentration of microplastics. Additionally, application of 1% PE-MPs decreased the soil bulk density, available phosphorus, and potassium, whereas the EC, organic carbon, microbial biomass carbon, NO3-N, and NH4-N significantly increased. Moreover, the presence of PE-MPs in soil also had a significant influence on the soil enzyme activities. Metagenomic analysis (16 s) reveals that at genus level, Bacillus (19%) was predominant in control, while in 1% PE-MPs, Rubrobacter (28%) genus was dominant. Microvirga was found exclusively in T5, while the relative abundance of Gemmatimonas declined from T1 to T5. This study thus confirms that microplastics exert a dose-dependent effect on soil and plant characteristics.

Study of soil microplastic pollution and influencing factors based on environmental fragility theory

Soil microplastics (MPs) pollution is a global concern, but the distribution of MPs and the factors affecting the distribution of MPs in different ecologically fragile karst areas remain poorly understood. Here, we investigated the spatial distribution, characteristics, and composition of MPs in different ecologically fragile karst areas of Guizhou Province and explored the relationship between ecosystem fragility and MPs. Structural equation models combined with robust random forest (RF) models were used to clarify the effects of karst soil properties on MPs and quantify their relative contributions. The abundance of soil MPs in ecologically fragile karst areas was 2949 item kg-1, and the risk of MPs contamination was highest in medium-fragile areas. The robust RF models precisely predicted the abundance of soil MPs in different fragile areas, and the mean root mean square error and R2 were 0.21 and 0.93, respectively. The contribution of karst soil properties to the abundance of MPs was estimated. Some soil chemical properties had a significant effect (p < 0.05) on MPs pollution in ecologically fragile karst areas. The results of our study suggest that the fragile ecological environment may exacerbate MPs pollution. Our study also contributes to establish a scientific theoretical foundation for the utilization of plastics and the prevention and control of microplastics pollution in karst ecosystems.

Benthic biofilms in riverine systems: A sink for microplastics and the underlying influences

Rivers are known as major pathways for transporting microplastics from terrestrial areas to the marine environment. However, the behavior of microplastics in terms of retention and transport within riverine systems remains unclear. While considerable efforts have been made to investigate the water column and sediment, limited attention has been given to understanding the interplay between microplastics and benthic biofilms. Therefore, this study aimed to examine the distribution of biofilm-trapped microplastics along the CaoE River and identify the factors influencing the immobilization of microplastics by benthic biofilms. The findings of this study revealed that benthic biofilms served as a sink of microplastics in the CaoE River, with an average abundance of 575 items/m2 in tributaries and 894 items/m2 in the main stream. The dominant shape of microplastics was fiber, while the primary polymer type was polyethylene terephthalate. The distribution of microplastics exhibited significant spatial heterogeneity, as indicated by their abundance and characteristics. In order to reveal the intriguing phenomenon, variations of influencing factors were estimated, including physicochemical characteristics of water, extracellular polymeric substances of benthic biofilms, and microbial communities of benthic biofilms. A partial least squares path modeling analysis was performed using these variables, revealing that water velocity and microbial diversity of benthic biofilms were the key factors influencing the interaction between microplastics and benthic biofilms. In summary, this study provides substantial evidence confirming the crucial role of benthic biofilms in the immobilization of microplastics, which expands concerns about microplastic pollution in the riverine systems. Furthermore, uncovering the underlying influences of microplastic-biofilm interactions will facilitate the development of effective strategies for the control and management of microplastic pollution.

Microplastic pollution in typical seasonal rivers in northern China: temporal variation and risk assessment

Rivers are important channels for the transport of microplastics (MPs) from land to sea. In this work, the temporal variation and risk assessment of MP pollution in the surface water of the Wei River, a typical seasonal river in northern China, were quantified. The number abundance of MPs in the dry season was significantly higher than that in the wet season (p < 0.05). Fiber was the most abundant type of MP in both dry and wet seasons. Infrared spectrometer and Raman spectroscopy identification showed that polypropylene (PP) and polyethylene (PE) were the major polymers found in both dry and wet seasons, and the mixture of different MP polymers was more diverse in the dry season. The risk assessment showed that the average pollution load index (PLI) and risk quotient (RQ) were 2.10 and 1.19 in the dry season, which significantly decreased to 1.25 and 0.74, respectively, in the wet season (p < 0.05). In total, the results from this study highlight the characteristics of seasonal rivers that influence the temporal distribution and risk assessment of microplastics, providing scientific reference for policymakers and river managers to effectively deal with MP pollution.

Polystyrene and low-density polyethylene pellets are less effective in arsenic adsorption than uncontaminated river sediment

The adsorption process of inorganic arsenic (As) plays an important role in its mobility, bioavailability, and toxicity in the river environment. In this work, the adsorption of dissolved arsenite (As(III)) and arsenate (As(V)) by microplastics (MPs) pellets (polystyrene (PS) and low-density polyethylene (LDPE)), river sediment, and their mixture were investigated to assess the adsorption affinities and mechanism. The adsorption kinetics showed slow and mild rising zones from the natural behavior of the chemical adsorption. The results indicated that both MP characteristics and water properties played a significant role in the adsorption behavior of inorganic As species. The As adsorption equilibrium was modeled well by both Langmuir and Freundlich isotherms and partly fitted with the Sips model suggesting that both mono-layer and multi-layer adsorption occurred during adsorption The spontaneous adsorption process for both As(III) and As(V) was evidenced by the adsorption thermodynamics. The maximum adsorption capacities of As(III) and As(V) reached 143.3 mg/kg and 109.8 mg/kg on PS in deionized water, which were higher than those on sediment-PS mixture (119.3 mg/kg, 99.2 mg/kg), which were all lower than on sediment alone (263.3 mg/kg, 398.7 mg/kg). The Fourier transform infrared spectroscopy analysis identified that As(III) and As(V) interaction with sediment surface functional groups was the main adsorption mechanism from surface complexation and coordination. Two functional groups of polystyrene (-NH2, -OH) were mainly involved in the adsorption of inorganic As species on PS, while -COO- and -OH functional groups contributed to the adsorption mechanism of inorganic As species on LDPE. The findings provide valuable insight on the adsorption behavior and mechanisms of As(III) and As(V) in river systems in the presence of MPs particles. Both PS and LDPE were shown to be less effective than river sediment in the adsorption of As species from water, which provides a different perspective in understanding the scale of MPs impact in pollutant transport in the aquatic environment.

Homogenization of microplastics in alpine rivers: Analysis of microplastic abundance and characteristics in rivers of Qilian Mountain, China

Microplastics in remote areas has received increasing concern in recent years. However, studies on microplastics in alpine rivers and their affecting factors are still limited. In this study, we investigate the abundance and characteristics of microplastic in the surface water of five alpine rivers in Qilian Mountain, China. Utilizing sieve collection, digestion and density separation, along with microscopy and Raman spectroscopy analyses, microplastics were observed in all the water samples and the average abundance of microplastics was 0.48 ± 0.28 items/L, which was lower than in other freshwaters. Transparent (37.3%) and fibrous (72.1%) microplastics were predominant. Polypropylene (53.8%) was the most frequently identified polymer type. Analysis of similarities (ANOSIM) and linear discriminant analysis (LDA) based on microplastic shape, color, and polymer type showed that there was no significant difference in the microplastic characteristics among rivers of Qilian Mountain. The distance decay models revealed that the similarity in microplastics characteristics was not affected by changes in watershed characteristics, such as geographical distance, elevation, water quality, and land use. This finding suggests that the primary source of microplastics in Qilian Mountain rivers could be from dispersed origins. The results of this study indicated that despite remote alpine rivers suffering limited anthropogenic impacts, they were not immune to microplastics. However, in watersheds with lower intensity of human activity, the abundance and characteristics of microplastics in water bodies may be more uniformly distributed and controlled by diffusion conditions such as atmospheric transport or riverine transport. Our investigation unveils novel understanding of microplastic dispersion in secluded alpine territories, emphasizing the crucial need for managing atmospheric transport of microplastics within conservation areas.

Rapid urbanization affects microplastic communities in lake sediments: A case study of Lake Aha in southwest China

Effective management of pollutants in urban environments is crucial for achieving sustainable cities. Microplastics, as an emerging pollutant widely present in contemporary environments, have received widespread attention in recent years. However, limited studies have reported the impact of rapid urbanization on regional microplastics. In this study, the abundance and composition of microplastic communities in the sediments of Lake Aha were analyzed using a "microplastic community" and slicing the sediments at 5 cm intervals. Results showed that microplastic abundance of sediments in Lake Aha was relatively high (up to 1700 items/kg) and decreased with increasing depth, with the highest abundance found in the surface layer (0-5 cm, 1090 ± 474 items/kg). Hierarchical cluster analysis (HCA), principal component analysis (PCA), and analysis of similarities (ANOSIM) revealed that the different sediment layers could be classified into high and low urbanization level groups based on the composition of microplastic communities. Linear discriminant analysis effect size (LEfSe) indicated that agricultural input was the main source of microplastic pollution during low urbanization levels, characterized by low abundance, large particle size, and high fiber proportion, while urban activities dominated during high urbanization levels, with high abundance, small particle size, high proportion of Polyethylene terephthalate (PET), fragments, and granules, and colorful microplastics. This study clarifies the impact of urbanization on the abundance and composition of microplastics in lake sediments, which has implications for more effective management and control of microplastic pollution in regions undergoing rapid urbanization.

Effects of microplastics on the growth, photosynthetic efficiency and nutrient composition in freshwater algae Chlorella vulgaris Beij

Microplastics, plastic particles and fragments smaller than 5 mm are ubiquitous in various aquatic environments, but the hazards of microplastics with different particle sizes, concentrations and materials are not well understood. This study investigated the toxicity of polyethylene microplastics (PE-MPs) with different concentrations and particle sizes or polystyrene microplastics (PS-MPs) on freshwater algae Chlorella vulgaris Beij (C. vulgaris) for 11 days. Results indicated that the growth, colony formation, photosynthetic pigment contents and soluble intracellular polysaccharides were unaffected, whereas the photosynthetic efficiency and the total soluble protein (TSP) contents were remarkably decreased at 11 d with the increased concentration of PE-MP exposure. The growth, photosynthetic efficiency, soluble intracellular polysaccharides and TSP contents were unaffected after exposure to PE-MPs with different particle sizes or PS-MPs. By contrast, the colony formation and photosynthetic pigment contents were remarkably decreased after exposure to PS-MPs compared with the control or PE-MPs with the same particle size. The C. vulgaris colonization on microplastics was proven by scanning electron microscopy, indicating that the adsorption effects were the main harmful pathways of different microplastics to algal. Our results suggested that microplastics have limited harmful effects on algae, mainly in adsorption and shading.

Effects of tidal action on the stability of microbiota, antibiotic resistance genes, and microplastics in the Pearl River Estuary, Guangzhou, China

In this study, the 16S rRNA gene amplicon sequencing technique was used to explore the microbial diversity and differences in the water environment of the Pearl River Estuary in Nansha District with various land use types such as the aquaculture area, industrial area, tourist area, agricultural plantation, and residential area. At the same time, the quantity, type, abundance, and distribution of two types of emerging environmental pollutants, antibiotic resistance genes (ARGs) and microplastics (MPs), are explored in the water samples from different functional areas. The results show that the dominant phyla in the five functional regions are Proteobacteria, Actinobacteria and Bacteroidetes, and the dominant genera are Hydrogenophaga, Synechococcus, Limnohabitans and Polynucleobacter. A total of 248 ARG subtypes were detected in the five regions, belonging to nine classes of ARGs (Aminoglycoside, Beta_Lactamase, Chlor, MGEs, MLSB, Multidrug, Sul, Tet, Van). Blue and white were the dominant MP colors in the five regions; 0.5-2 mm was the dominant MP size, and cellulose, rayon, and polyester comprised the highest proportion of the plastic polymers. This study provides the basis for understanding the environmental microbial distribution in estuaries and the prevention of environmental health risks from ARGs and microplastics.

Microplastic pollution in riverine ecosystems: threats posed on macroinvertebrates

Microplastics (MPs) are pollutants of emerging concern that have been reported in terrestrial and aquatic ecosystems as well as in food items. The increasing production and use of plastic materials have led to a rise in MP pollution in aquatic ecosystems. This review aimed at providing an overview of the abundance and distribution of MPs in riverine ecosystems and the potential effects posed on macroinvertebrates. Microplastics in riverine ecosystems are reported in all regions, with less research in Africa, South America, and Oceania. The abundance and distribution of MPs in riverine ecosystems are mainly affected by population density, economic activities, seasons, and hydraulic regimes. Ingestion of MPs has also been reported in riverine macroinvertebrates and has been incorporated in caddisflies cases. Further, bivalves and chironomids have been reported as potential indicators of MPs in aquatic ecosystems due to their ability to ingest MPs relative to environmental concentration. Fiber and fragments are the most common types reported. Meanwhile, polyethylene, polypropylene, polystyrene, polyethylene terephthalate (polyester), polyamide, and polyvinyl chloride are the most common polymers. These MPs are from materials/polymers commonly used for packaging, shopping/carrier bags, fabrics/textiles, and construction. Ingestion of MPs by macroinvertebrates can physically harm and inhibit growth, reproduction, feeding, and moulting, thus threatening their survival. In addition, MP ingestion can trigger enzymatic changes and cause oxidative stress in the organisms. There is a need to regulate the production and use of plastic materials, as well as disposal of the wastes to reduce MP pollution in riverine ecosystems.

A plastic world: A review of microplastic pollution in the freshwaters of the Earth's poles

Microplastic (MP) pollution is of great environmental concern. MPs have been found all over the Earth, including in the poles, which is indicative for the important threat they constitute. Yet, while the ocean is object of major interest, the data available in the literature about MP pollution in the freshwaters of the Earth's poles are still limited. Here, we review the current knowledge of MP pollution in the freshwaters of the Arctic, Antarctica and Third Pole, and we assess its ecological implications. This review highlights the presence of MPs in the lakes, rivers, snow, and glaciers of the investigated sites, questions the transport patterns through which MPs reach these remote areas, and illustrates that MP pollution is a real problem not only in marine systems, but also in the freshwater environments of the Earth's poles. MPs can indeed be ingested by animals and can physically damage their digestive tracts, as well as escalate the trophic levels. MPs can also alter microbial communities by serving as surfaces onto which microbes can grow and develop, and can enhance ice melting when trapped in glaciers. Hence, considered the limited data available, we encourage more research on the theme.

Distribution and risk assessment of microplastics in Liujiaxia Reservoir on the upper Yellow River

Microplastics (MPSs) distribution in global freshwater systems is extensively reported, but the distribution of MPSs in reservoirs of the Yellow River has rarely been studied. To fill in this gap, we systematically investigated the distribution of MPSs in surface water and bank sediments gleaned from Liujiaxia Reservoir of the upper Yellow River for the first time and conducted an ecological risk assessment in succession in this work. The results showed that the main polymer types of MPSs in the surface water and bank sediments of Liujiaxia Reservoir were polyethylene terephthalate (PET), polystyrene (PS), and polypropylene (PP), and the abundance of MPSs in the reservoir surface water and bank sediments ranged from 4.48 to 12.09 item/L and 447.27 to 1543.80 item/kg (dry weight), respectively. Further physical morphology analysis of MPSs in the samples revealed that MPSs in the surface water and bank sediments of Liujiaxia Reservoir were predominantly fibrous with small particle sizes (<1 mm), and there was abundant color, mainly exhibiting transparent, black, and blue. The results of the MPS pollution load index (PLI>1) and the hazard ranking of MPSs (H_Zone = 10.20 for surface water and H_Zone = 14.06 for bank sediments) yielded a hazard class II for MPS pollution in Liujiaxia Reservoir, the combined pollution risk index (PRI_Zone = 17.05 for surface water and PRI_Zone = 31.25 for bank sediments) stated clearly the potential ecological risk in the Liujiaxia Reservoir. Briefly, this study supplemented and enriched the data on the distribution of MPSs in the reservoirs of the Yellow River basin, and provide a benchmark for future pollution control and management in the reservoir area.

Environmental fate of microplastics in an urban river: Spatial distribution and seasonal variation

Rivers are recognized as an important pathway for transport of microplastics (MPs) from land to sea, but limited information is available on the spatial distribution and seasonal variation of riverine MPs from upper reaches to estuaries. Such information is critical for source apportionment and development of effective management measures for riverine MPs. To fill the knowledge gap, we investigated the occurrence of MPs in surface water along an urban river in Guangzhou, southern China in wet and dry seasons. The abundances of MPs from 16 sampling sites in the wet and dry seasons varied from 0.123 to 1.84 particles m^-3 and from 0.046 to 4.21 particles m^-3, respectively. The spatial distribution of MP abundances showed an increasing trend from upstream to midstream and a decreasing trend from midstream to downstream and estuaries. The abundances of MPs peaked at the midstream, which is surrounded by a highly urbanized region with high population density (∼2530 persons per km²). The large surface water runoff during the wet season elevated the MP abundance in riverine water, except for that flowing through the central urban area where the abundance of MPs collected in the dry season was higher than that in the wet season. This was mainly ascribed to the large input from extensive anthropogenic activities and slow water flow rate in urban areas. The estimated monthly riverine MP fluxes from Humen, Hongqili, and Jiaomen were 7.42, 2.38, and 2.3 billion particles, respectively, in the wet season, and 0.86, 0.71, and 0.19 billion particles, respectively, in the dry season. An increase of riverine MP fluxes from Humen, Hongqili, and Jiaomen in the past three years was evident. The results from the present study provide valuable information for source apportionment of riverine MPs and support the initialization of possible MPs controlling measures.

Quantifying environmental emissions of microplastics from urban rivers in Melbourne, Australia

This study aims to understand the amount and type of microplastics flowing into Port Phillip Bay from urban rivers around Melbourne. Water samples were collected from the Patterson, Werribee, Maribyrnong, and Yarra Rivers, which contribute 97 % to the total flow into Port Phillip Bay. On average, the rivers contained a mean of 9 ± 15 microplastics/L and ranged from 4 ± 3 microplastics/L (Patterson) to 22 ± 11 microplastics/L (Werribee). Of the eight polymers investigated, polyamide and polypropylene were the most frequently detected polymers. Using the mean concentration of each river, the flow of microplastics into Port Philip Bay was estimated to be 7.5 × 10⁶ microplastics per day and 3.7 × 10¹⁰ microplastics per year. To fully understand the fate and transport of microplastics into Port Phillip Bay, this study would be the foundation for a more in-depth investigation. Here, further samples will be collected at more points along the river and at the midpoint of each season.

Microplastic contamination in the freshwater shrimp Macrobrachium amazonicum in Itacoatiara, Amazonas, Brazil

The present study analyzed the presence of microplastics (MPs) in the shrimp Macrobrachium amazonicum, which is an economically important food that is consumed in several regions of the Brazilian Amazon. A total of 600 specimens of M. amazonicum were captured at two sampling sites (urban and rural area). A total of 2597 MP particles were recorded in the shrimps, with a significant difference between the two sites. The presence of MPs in the body parts also differed significantly. No significant difference was found between MPs abundance and sex of the shrimps. The size of the MPs did not differ significantly between the collection sites and between the body parts. Dark blue fiber-type MPs were the most abundant. A positive correlation was observed between the abundance of MPs and the total weight of shrimps. Raman spectroscopy identified the dark blue fibers as polypropylene and the FTIR technique identified the light blue fragments as nylon. The results indicate that the presence of MPs in the M. amazonicum shrimp is associated with the capture sites near the urban area and is present in the diet of the Amazonian population that regularly consumes this crustacean in traditional dishes.

Occurrence and risk assessment of microplastics in the Lhasa River-a remote plateau river on the Qinghai-Tibet Plateau, China

Microplastics (MPs) are ubiquitous in the aquatic environment and have received widespread attention worldwide as emerging pollutants. Urbanization and anthropogenic activities are the main sources of MPs in rivers; however, the MPs in plateau rivers with less human activities are not well understood. In this study, the pollution of MPs in the surface water and shore sediment of the Lhasa River from the Qinghai-Tibet Plateau was investigated, and a risk assessment was conducted. The abundance of MPs in the surface water and shore sediment of Lhasa River were 0.63 n/L and 0.37 n/g, respectively. MPs in surface water were mainly dominated by films (43.23%) and fibers (31.12%) in shape, transparent (54.25%) in color, and 0-0.5 mm (75.83%) in size, while MPs in the shore sediment were mainly fibers (43.69%) and fragments (36.53%), transparent (71.91%), and 0-0.5 mm (60.18%). PP and PE were the predominant polymer types, accounting for 44.55% and 30.79% respectively in the surface water and 32.51% and 36.01% respectively in the shore sediment. More notably, the polymer pollution index (H) of MPs in the Lhasa River was at hazard level III due to the high risk caused by PVC, but the pollution load index (PLI) was low at hazard level I. This study reveals that the remote river in the Qinghai-Tibet Plateau are polluted by MPs, and their potential risks to the vulnerable ecosystem deserve attention.

Occurrence of microplastics pollution in the Yangtze River: Distinct characteristics of spatial distribution and basin-wide ecological risk assessment

The widespread presence of microplastics (MPs) in the Yangtze River, the third longest river in the world, has drawn increasing attention. Although numerous studies have been conducted recently to investigate and analyze the MPs exposure to the surface water of the river, most merely focus on a certain part of the Yangtze River, and knowledge of MPs based on the basin-wide is still scattered. This article reveals the spatial distribution characteristics of MPs in the Yangtze River from the whole watershed scale. Among the five areas in the basin, the upstream and the midstream were demonstrated to contain more MPs (3598.6 particles/m³ and 3226.8 particles/m³). The obtained results suggested the MP presented in the entire watersheds was uneven and the 'hotspots' occurred, where the MPs concentrations were relatively higher than the surrounding. The discharging of the wastewater treatment plants along the river, the locations of dams, and the stability and fragment of MPs, were demonstrated to be the important driving factors in the spatial distribution of MPs and leading to the appearance of the MP 'hotspots' in the Yangtze River, but were previously overlooked. It is the first study to evaluate the ecological risk of MPs exposure to the surface water of the Yangtze River with multiple assessment methods, taking not only abundance but also morphological characteristics, polymer composition and toxic effect into account. More importantly, based on the multiple individual MPs risk assessment methods, we developed the BetaMP method which achieves a comprehensive assessment of MP risk in basin-wide by taking multiple MP characteristics into account for the first time. This is conducive to better understanding the environmental impacts of MPs pollution in the different regions of the river.

Dual regulatory effects of microplastics and heat waves on river microbial carbon metabolism

Rivers play a critical role in the global carbon cycle, but the processes can be affected by widespread microplastic (MP) pollution and the increasing frequency of heat waves (HWs) in a warming climate. However, little is known about the role of river microbes in regulating the carbon cycle under the combined action of MP pollution and HWs. Here, through seven-day MP exposure and three cycles of HW simulation experiments, we found that MPs inhibited the thermal adaptation of the microbial community, thus regulating carbon metabolism. The CO₂ release level increased, while the carbon degradation ability and the preference for stable carbon were inhibited. Metabonomic, 16 S rRNA and ITS gene analyses further revealed that the regulation of carbon metabolism was closely related to the microbial r-/K- strategy, community assembly and transformation of keystone taxa. The random forest model revealed that dissolved oxygen and ammonia-nitrogen were important variables influencing microbial carbon metabolism. The above findings regarding microbe-mediated carbon metabolism provide insights into the effect of climate-related HWs on the ecological risks of MPs.

Adsorption of perfluoroalkyl substances on polyamide microplastics: Effect of sorbent and influence of environmental factors

Microplastics (MPs) and perfluoroalkyl substances (PFASs) are two types of pollutants coexisting in the environment. Their co-exposure is a source of increasing concern. MPs present in the natural environment suppose an ideal surface for the sorption of hazardous contaminants. This study investigates the adsorption behaviour of six PFASs on polyamide (PA) MPs. Adsorption experiments under various internal (PA and PFASs dosage, PA particle size) and environmental (pH, ionic strength, dissolved organic matter) factors were carried out. Isotherm results (from 0.1 to 25 mg/L of PFASs) showed that the maximum adsorption capacity of the selected PFASs on the PA was as follows: perfluorooctanesulfonic acid (PFOS, 0.873 mg/g) > perfluorooctanoic acid (0.235 mg/g) > perfluoroheptanoic acid (0.231 mg/g) > perfluorohexanoic acid (0.201 mg/g) > perfluoropentanoic acid (0.192 mg/g) > perfluorobutanoic acid (0.188 mg/g) (pH 5.88, 0% salinity and 0% of dissolved organic matter). The PFOS has more tendency to be sorbed onto PA than perfluorocarboxilic acids. The MP characterization by scanning electron microscopy, X ray diffraction and Fourier transform infrared spectroscopy showed changes in the PA surface after adsorption assays. Pore filling, hydrophobic interactions and hydrogen bonds governed sorption process. The sorption capacity of PFASs was crucially affected by the PA size (from 19.6% to 99.9% for 3 mm and 50 μm particle size, respectively). The process was not significantly influenced by salinity while the dissolved organic matter exerted a negative effect (decrease from 100% to 26% for PFOS in presence of 25 mg/L of humic acid). Finally, adsorption rates of PFASs were quantified in real water matrices (influent and effluent wastewater, surface and tap water samples). The results revealed interactions between PA and PFASs and evidenced the role of PA as a vector to transport PFASs in the aquatic environment.

The toxic effects of polystyrene microplastics on freshwater algae Chlorella pyrenoidosa depends on the different size of polystyrene microplastics

Microplastics (MPs) are persistent environmental contaminants. The toxic effects of MPs on aquatic organisms have raised increasing concerns, but their toxic effects on aquatic phytoplankton has not been thoroughly investigated. In the present study, the toxic effects of two sizes MPs (1 μm and 5 μm) on Chlorella pyrenoidosa at 2, 10, 50 mg/L were explored for 1, 5, 10 days. The growth ratio, photosynthetic pigments content, extracellular polymeric substances content, soluble protein content, MDA content and relative expression of genes related to photosynthesis and energy metabolism were measured. These results indicated that 1 μm MP could significantly inhibit the growth of C. pyrenoidosa. Compared with the control group, 1 μm MP significantly reduced the photosynthetic pigment content, induced oxidative stress and disrupted the cell membrane integrity of C. pyrenoidosa. At the molecular level, 1 μm MP altered the transcript levels of genes related to photosynthesis and energy metabolism. Scanning electron microscopy and fluorescent images showed that MPs aggregation with C. pyrenoidosa may be the main reason for the toxic effects of MPs. These results will provide new insight into the toxicity of different MPs on aquatic phytoplankton, and evaluate the risks caused by MPs in aquatic environments.

Distribution characteristics of microplastics in urban rivers in Chengdu city: The influence of land-use type and population and related suggestions

In this study, microplastics (MPs) in urban rivers in the Chengdu eco-zone were systematically studied. Microscopic observations and Fourier-transform infrared spectroscopy were used to determine the microplastic (MP) types. The MPs abundance ranged from 20.92 items/L to 762.95 items/L in water and from 20.92 items/100 g dry weight to 58.57 items/100 g dry weight in sediment. In both the water sample and sediment samples, the dominant MPs morphologies were fibres, lumps, and fragments, and the size of MPs was predominantly distributed in the 50-500 μm rage. The primary polymers were polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET). Locations with large populations and large areas of woodland and construction land tended to exhibit higher concentrations of MPs. Additionally, compared to water samples, sediment exhibited a more reliable correlation fitting data, thus indicating that sediment was more stable in reflecting the presence of MPs in rivers. This study supplemented the gap in MPs pollution in urban rivers in Chengdu city and discussed the impact of land use and population on the distribution of MPs. Suggestions were provided to alleviate MPs pollution in urban rivers from the perspective of urban planning.

New insights into the distribution and interaction mechanism of microplastics with humic acid in river sediments

Information on the distribution and interaction of microplastics (MPs) and humic acids (HAs) in river sediment has not been fully explored. This study assessed the distribution and interaction of MPs with HAs at different depths in river sediments. The results delineated that the average abundance of MPs in the 0-10 cm layer (190 ± 20 items/kg) was significantly lower than that in the 11-20 cm and 21-30 cm layers (211 ± 10 items/kg and 238 ± 18 items/kg, respectively). Likewise, the large MP particles mainly existed in the 0-10 cm layer (31.53%-37.87%), while small MP particles were found in the 21-30 cm layers (73.23%-100%). Moreover, HAs in MPs showed a transformation from low molecular weight to high molecular weight with an increase in depth from 0-10 cm to 21-30 cm, which may contribute to the distribution of MPs in the river sediments. These results provide new insight into the migration of MP pollution in river sediments, but further research needs to assess the interaction of MP with HA for mitigating MP pollution in river sediment.

Occurrence, distribution and sources of microplastics in beach sediments of Miri coast, NW Borneo

Microplastics (MPs) pollution has gained a lot of global interests due to its toxicity to the surrounding ecosystems. The aim of this study is to identify the abundances, physical characteristics, polymer type and elemental composition of MPs in beach sediments of Miri coast, located in Sarawak State, East Malaysia. A total of 1553 particles from 24 sediment samples, collected from eight different beaches along Miri coastline were identified. MPs from the sediments were extracted using density separation method and analyzed through stereoscopic microscope, ATR-FTIR and SEM-EDX. MPs were present most abundant in Lutong Beach, which is the hotspot for the recreational activities. Fragments were identified as the highest abundance type of MPs, followed by fiber, foam and pellet. MPs of size of <1 mm were predominantly present in the samples. Varieties of colors were distinguished in which transparent or no color MPs were the highest quantity studied in the samples. Polymers identified were mainly polyethylene (PE), polyester (PET), polystyrene (PS) and polypropylene (PP), derived from primary and secondary MPs. Carbon and oxygen were dominant and have the highest concentration identified with other elements such as Ca, Al, Ti and Cl. The primary use of these elements as additives are associated with the manufacturing process as they are used to enhance the quality during plastic production. The outcome of this study is to be the first report to identify and characterize the MPs in beach sediments of Miri coast. The occurrence of MPs in Miri beaches may negatively impact marine organisms as this affects their food chain. As consumers, humans are most likely to be affected by the presence of MPs due to their consumption of marine animals, particularly fish present in this region.

Textural characteristics and abundance of microplastics in Tecolutla beach sediments, Gulf of Mexico

Abundance of microplastics in coastal sediments is considered an emerging pollution problem worldwide. In Mexico, studies focused on microplastics in coastal sediments are little. In this study, we analyzed the textural characteristics and investigated the abundance of microplastics in the Tecolutla beach sediments, SW Gulf of Mexico. The extraction of microplastics in sediments was done by density separation. Microplastics were identified by stereomicroscope and scanning electron microscopy, and were classified based on their morphology, color, length, texture, and abundance. Among 181 microplastics, fiber type is predominant (number of microplastics n = 166; 92%) and followed by film (n = 12; 6%) and fragment (n = 3; 2%) types. The most abundant color of microplastics is black (n = 81; 45%) and second dominant color is blue (n = 65; 36%); most of them are fiber type. Based on the textural characteristics of sediments, it was observed that microplastics were derived from the fluvial contribution of the Tecolutla River and were deposited in the coastal environment by ocean currents. This study revealed that the abundance of microplastics was high in fine-grained sediments and was directly proportional to skewness. The results of this study can act as a reference for understanding the abundance of microplastics in the Gulf of Mexico coastal sediments.

Microplastic load in the surface water and Tilapia sparrmanii (Smith, 1840) of the river systems of Okavango Delta, Botswana

Microplastics are 'emerging' contaminants that threatens freshwaters and may have negative impact on the aquatic organisms. However, Botswana has no information on the status of microplastics, including freshwater like the Okavango Delta- the largest, inland wetland hosting wildlife, tourism, and supporting the socio-economic lifestyle of inhabitants. This study assessed the spatial distribution and characterization of microplastics in surface water and in the digestive organs of fish (Tilapia sparrmanii) from the Okavango delta. Surface water samples (156) and whole intact fish (15) were collected and analysed for microplastic contents by wet peroxide oxidation, potassium hydroxide (fish only), density separation, extraction, and stereomicroscope identification. The weight of microplastics for surface water samples varied from 138.18 to 381.67 µg m^-3 and abundance ranged from 10.18 to 22.67 items L^-1 with significant difference observed between sites in both variables. In tilapia, the highest microplastic abundance were found in the intestines then the stomach and the gills from the fish samples. Most prevailing size ranges of microplastics in fish and water samples were 1-2 mm and 2-3 mm while the most abundant shapes were fragments and fibres, respectively. Translucent microplastics were dominant in all samples. The results indicate the presence of microplastics in the Okavango delta even though they are very low (µg m^-3). This baseline information will provide insights on the loads of microplastics in surface water and the quantities ingested by fish in the Okavango delta hence the need for monitoring. It would also guide on the need for effective policies addressing plastic and microplastic pollution.

Occurrence status of microplastics in main agricultural areas of Xinjiang Uygur Autonomous Region, China

A large number of plastic products are used in the process of agricultural production, and the recycling efficiency is low, which leads to the production of a large number of microplastics. Therefore, the microplastic contamination in agricultural areas requires being investigated urgently. In addition, the occurrence characteristics of microplastics are also different in agricultural areas with various land use modes. In this study, the main agricultural areas in Xinjiang are taken as the research object. The abundance of microplastics in the main agricultural areas in Xinjiang ranges from 288 to 1452 items/kg. The shape of microplastics is mainly bulks, and white microplastics account for the highest proportion, and the majority of their sizes are less than 0.5 mm. The risk assessment results show that the contamination risk index of microplastics in this area is 108.92 and the risk level is grade III. The research shows that there is little difference in the abundance of microplastics between paddy field and garden land, which may be because there are few sources of microplastics in the land of these two utilization modes, and the potential pollution sources are similar, such as the atmospheric deposition of microplastics, the falling of fibers on people's clothes during farming, and the agricultural use of sludge. This study can provide a reference for further study on the existing circumstances of microplastics in agricultural areas.

New insights on metal ions accelerating the aging behavior of polystyrene microplastics: Effects of different excess reactive oxygen species

Microplastics (MPs) will coexist with various pollutants in the environment, but it is not clear whether these pollutants will affect the aging process of MPs. The aging process of polystyrene microplastics (PS-MPs) mediated by Cu²⁺ and Pb²⁺ was investigated in this study. The results showed that the aging rate of PS-MPs mediated by Cu²⁺ and Pb²⁺ were significantly higher than that of ultrapure water (After 7 days of light irradiation, the CI values of aging PS-MPs mediated by ultrapure water, Cu²⁺ and Pb²⁺ increased from 0.030 of original PS-MPs to 0.034, 0.048 and 0.086 respectively). This process may be related to the generation of a large amount of reactive oxygen species, because OH were detected in PS-MPs suspension mediated by Cu²⁺, which were significantly higher than those in ultrapure water, while ¹O₂ mediated by Pb²⁺ were more. However, these photo-aging effects were significantly inhibited by reactive oxygen species (ROS) quencher, which indicated that excessive ROS production was the main reason for metal ions to promote the photo-aging of PS-MPs. In addition, this study reported that excessive ROS will accelerate the formation of carbonyl group on the surface of PS-MPs, and lead to the change of physical and chemical properties of PS-MPs. This study provides new insights for the environmental behavior of MPs under the condition of combined pollution.

Deposition and Mobilization of Microplastics in a Low-Energy Fluvial Environment from a Geomorphological Perspective

Though microplastic (MP/MiP) pollution of the environment is a popular research topic, a relatively limited number of studies are investigating its geomorphological context. However, site-specific hydrological and morphological parameters fundamentally affect the MP transport, deposition and mobilization. Therefore, we aimed to evaluate the geomorphological influencing factors on MP deposition in the fluvial sediments of the Tisza River (Central Europe). Between the two surveys (in 2019 and 2020), small flood waves rearranged the MP pollution, as in the sediments of the Tisza it decreased by 30% and in the tributaries by 48%. The previously highly polluted upstream and downstream sections became moderately polluted, but the contamination increased in the Middle Tisza, and the hot-spots were rearranged. The increasing longitudinal trend in the MP content exists if the minimum values of the hydrologically uniform sections are considered. The tributaries are important MP sources, as 80% of them had a higher (by 20%) MP content in their sediments than the Tisza had near the confluence, and they increased the MP content of the Tisza by 52% on average. The point-bars were the most polluted in-channel forms, while the side-bars and sediment sheets had less MP content, by 18 and 23%, respectively. The spatial trend of the MP content of these forms was not the same. Therefore, during the planning of sampling campaigns, it is very important to consider the geomorphological setting of a sampling site: we suggest sampling side-bars. No clear connection between the particle size of the sediments and their MP content was found.

Pollution characteristics and source analysis of microplastics in the Qiantang River in southeastern China

Microplastic pollution resulting from industrialization and urbanization is increasingly serious. Hangzhou is a city with high industrial/urban growth in Southeast China. Focusing on the microplastic pollution in the Hangzhou section Qiantang River, six samples were collected and analyzed during different hydrological periods (normal, wet, and dry periods) and the relationship between microplastic pollution and economic development was investigated. Results showed that more microplastics were found during the dry period than that of the wet period (49.8 vs. 13.2%). Microplastic abundance was 1.5-9.4 items L^-1, showing significant spatial differences in sampling sites. Among the collecting microplastics, debris and fibers accounted for 36.4 and 30.9%. Polyethylene terephthalate and polyvinyl chloride were the main polymers, accounting for 48.3 and 31.8%, respectively. Microplastics with size <1 mm accounted for 60% of the microplastics in surface water samples. Spatially, microplastic abundance was the highest in the middle of the river. Redundant analysis revealed that the per capita GDP (p = 0.002), high-end equipment industry (p = 0.028) and fashion manufacturing (p = 0.006) influenced microplastic abundance. Urbanization coupled with rapid economic development led to increase in local microplastic pollution. Our results provide insight into microplastic distribution patterns in urban river systems in China.

Current status of microplastics pollution in the aquatic environment, interaction with other pollutants, and effects on aquatic organisms

Microplastics, as emerging pollutants, have received great attention in the past few decades due to its adverse effects on the environment. Microplastics are ubiquitous in the atmosphere, soil, and water bodies, and mostly reported in aqueous environment. This paper summarizes the abundance and types of microplastics in different aqueous environments and discusses the interactions of microplastics with other contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), antibiotics, and heavy metals. The toxicity of microplastics to aquatic organisms and microorganisms is addressed. Particularly, the combined toxic effects of microplastics and other pollutants are discussed, demonstrating either synergetic or antagonistic effects. Future prospectives should be focused on the characterization of different types and shapes of microplastics, the standardization of microplastic units, exploring the interaction and toxicity of microplastics with other pollutants, and the degradation of microplastics, for a better understanding of the ecological risks of microplastics.

Evolution of prokaryotic colonisation of greenhouse plastics discarded into the environment

Current knowledge on the capacity of plastics as vectors of microorganisms and their ability to transfer microorganisms between different habitats (i.e. air, soil and river) is limited. The objective of this study was to characterise the evolution of the bacterial community adhered to environmental plastics [low-density polyethylene (LDPE)] across different environments from their point of use to their receiving environment destination in the sea. The study took place in a typical Mediterranean intermittent river basin in Larnaka, Cyprus, characterised by a large greenhouse area whose plastic debris may end up in the sea due to mismanagement. Five locations were selected to represent the environmental fate of greenhouse plastics from their use, through their abandonment in soil and subsequent transport to the river and the sea, taking samples of plastics and the surrounding environments (soil and water). The bacterial community associated with each sample was studied by 16S rRNA metabarcoding; also, the main physicochemical parameters in each environmental compartment were analysed to understand these changes. The identification and chemical changes in greenhouse plastics were tracked using Attenuated Total Reflection Fourier Transform Infra-red spectroscopy (ATR-FTIR). Scanning Electron Microscope (SEM) analysis demonstrated an evolution of the biofilm at each sampling location. β-diversity studies showed that the bacterial community adhered to plastics was significantly different from that of the surrounding environment only in samples taken from aqueous environments (freshwater and sea) (p-value p-value > 0.05). The environmental parameters (pH, salinity, total nitrogen and total phosphorus) explained the differences observed at each location to a limited extent. Furthermore, bacterial community differences among samples were lower in plastics collected from the soil than in plastics taken from rivers and seawater. Six genera (Flavobacterium, Altererythrobacter, Acinetobacter, Pleurocapsa, Georgfuchsia and Rhodococcus) were detected in the plastic, irrespective of the sampling location, confirming that greenhouse plastics can act as possible vectors of microorganisms between different environments: from their point of use, through a river system to the final coastal receiving environment. In conclusion, this study confirms the ability of greenhouse plastics to transport bacteria, including pathogens, between different environments. Future studies should evaluate these risks by performing complete sequencing metagenomics to decipher the functions of the plastisphere.