Measurement, quantification, and potential risk of microplastics in the mainstream of the Pearl River (Xijiang River) and its estuary, Southern China

Landscape and risk assessment of microplastic contamination in farmed oysters and seawater along the coastline of China

Microplastic (MP) pollution poses a significant threat to marine ecosystem and seafood safety. However, comprehensive and comparable assessments of MP profiles and their ecological and health in Chinese farming oysters are lacking. This study utilized laser infrared imaging spectrometer (LDIR) to quantify MPs in oysters and its farming seawater at 18 sites along Chinese coastlines. Results revealed a total of 3492 MPs in farmed oysters and seawater, representing 34 MP types, with 20-100 µm MP fragments being the dominant. Polyurethane (PU) emerged as the predominant MP type in oysters, while polysulfones were more commonly detected in seawater. Notably, oysters from the Bohai Sea exhibited a higher abundance of MPs (13.62 ± 2.02 items/g) and estimated daily microplastic intake (EDI, 2.14 ± 0.26 items/g/kg·bw/day), indicating a greater potential health risk in the area. Meanwhile, seawater from the Yellow Sea displayed a higher level (193.0 ± 110.7 items/L), indicating a greater ecological risk in this region. Given the pervasiveness and abundance of PU and its high correlation with other MP types, we proposed PU as a promising indicator for monitoring and assessing the risk MP pollution in mariculture in China. These findings provide valuable insights into the extent and characteristics of MP pollution in farmed oysters and seawater in China.

Occurrence and fate of microplastics from a water source to two different drinking water treatment plants in a megacity in eastern China

The widespread presence of microplastics (MPs) contamination in drinking water has raised concerns regarding water safety and public health. In this study, a micro-Raman spectrometer was used to trace the occurrence of MP transport from a water source to a drinking water treatment plant (DWTP)1 with an advanced treatment process and DWTP2 with a conventional treatment process and the contributions of different processes to the risk reduction of MPs were explored. Six types of MPs were detected: polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyamide, and polyvinyl chloride. 2-5 μm (35.8-41.2%) and polyethylene terephthalate (27.1-29.9%) were the most frequently detected MP sizes and types of water source samples, respectively. The abundance of MPs in treated water decreased by 72.7-83.0% compared to raw water. Ozonation and granular activated carbon (52.7%), and sand filtration (47.5%) were the most effective processes for removing MPs from DWTP1 and DWTP2, respectively. Both DWTPs showed significant removal effects on polyethylene terephthalate, with 80.0-88.1% removal rates. The concentrations of polystyrene increase by 30.0-53.4% after chlorination. The dominant components in the treated water of DWTP1 and DWTP2 were polypropylene (24.7%) and polyethylene 27.7%, respectively, and MPs of 2-5 μm had the highest proportion (55.3-64.3%). Pollution load index and potential ecological risk index of raw water treated by DWTPs were reduced by 48.0-58.7% and 94.5-94.7%, respectively. The estimated daily intake of MPs in treated water for infants was 45.5-75.0 items/kg/d, respectively, approximately twice that of adults. This study contributes to the knowledge gap regarding MP pollution in drinking water systems.

Evaluation of microplastic pollution and risk assessment in a tropical monsoonal estuary, with special emphasis on contamination in jellyfish

Estuaries, which serve as vital links between land and coastal ecosystems, play a significant part in facilitating the transfer of plastic waste from the land to the ocean. In this research, we examined the prevalence, characteristics, and ecological risks of microplastics (MPs) in the extensively urbanized Cochin Estuarine System (CES), India. Additionally, it represents one of the initial evidence-based examinations of MPs ingestion by jellyfish in Indian waters, focusing on Acromitus flagellatus, Blackfordia virginica, and Pleurobrachia pileus species. The abundance of MPs found in the surface water of the Cochin Estuarine System (CES) varied between 14.44 ± 9 to 30 ± 15.94 MP/m3, with an average of 21.6 ± 11 MP/m3. In both surface waters and jellyfish from the Cochin Estuarine System (CES), fibers were the most prevalent type of MPs, with polyethylene (PE), polypropylene (PP), and polyamide (PA) being the most common polymer varieties. To evaluate the current levels of MPs and their effect on the CES, the Pollution Load Index (PLI), Potential Ecological Risk Index (PERI), and Polymeric Risk Index (H) were utilized. The high PLIestuary values (20.33), high Hestuary values (234.02), and extreme PERIestuary value (1646.06) indicate that the CES is facing an extreme ecological risk. Among the 280 jellyfish individuals examined, 118 (42.14%) were recognized to contain MPs with an average of 1.54 ± 2.68 MPs/individual. Pearson bivariate analysis revealed a significant correlation between the jellyfish bell size and number of plastics per individual. Comparison between jellyfish species revealed, the majority (66%) of the MPs identified in jellyfish were from A. flagellatus and 44 among the 50 jellyfish examined (88%) had MPs. These findings suggest that A. flagellatus may be a potential sink for MPs and may be utilized to be a bioindicator for monitoring MPs contamination in estuarine systems, aiding in future plastic pollution mitigation efforts.

Microplastics research in Nepal: Present scenario and current gaps in knowledge

The topic of microplastics has drawn considerable scholarly interest in recent times. The objective of this study is to provide an overview of the current state of microplastic pollution research in Nepal and to make future research recommendations. To achieve the objective, three popular databases (Web of Science, SCOPUS and Google Scholar) were used. The results showed that the current scenario for microplastic research in Nepal is in its early stage, which commenced in 2020. A total of six papers were recorded over the period from 2020 to 2023. The research conducted in the fields were rivers, lakes, snow, and sediments. Studies have provided evidence of the occurrence of microplastics in diverse aquatic ecosystems. Lakeshore sediments show concentrations of 100.5 ± 58.6 items/kg dry weight, while shoreline sediments of Phewa lake exhibit variability between 55 and 122.5 items/kg. The lake water in winter records 2.96 ± 1.83 Microplastics per Liter (MPs/L), river water indicates 202 ± 100 items/m3, and snow demonstrates 30 MP/L. In freshwater ecosystems, microplastics, specifically fibers, were found to be the prevailing type, while fragments were recorded in road dust. The study conducted in Nepal provided evidence of the presence of a wide range of polymers. The polymers encompassed polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyamide, polystyrene (PS), and polyester. Microplastic research in Nepal, initiated in 2020, covered rivers, lakes, snow, and sediments. Diverse aquatic ecosystems reveal microplastic presence, emphasizing the need for continued study and awareness. Although extensive research has been carried out on the subject of microplastic contamination and its effects on various creatures on a global scale, an examination of the implications of microplastics on animals, plants, and humans in Nepal has not been found in any scholarly publications. There exists a noticeable deficit of research investigating the consumption of microplastics by human.

Temporal and spatial variation of microplastics in the urban rivers of Harbin

This study was to investigate temporal and spatial variation of microplastics in surface water and sediment in the urban rivers of Harbin during dry and wet season. Water samples (n = 25) in Xinyi River (n = 13) and Ashe River (n = 12) were collected from the selected sampling points. Microplastics in urban rivers in Harbin included polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The results show that urban rivers in Harbin had relatively mild microplastic abundance with most fragments in shape and colorless in color. PP and PE were the major polymers in surface water samples, while PVC and PET were the major polymers in sediment, which were dominated by large-size and granulate shape microplastics. Source apportionment demonstrate that the main sources of microplastics in Xinyi River and Ashe River during dry season were domestic wastewater and effluent from rainfall, while the main sources of microplastics in Xinyi River and Ashe River during wet season were wastewater, atmospheric sedimentation, and agricultural source. The morphology of microplastics in surface water and sediment in urban rivers of Harbin was negatively correlated with water velocity and positively correlated with the concentration of suspended matter, dissolved oxygen, and conductivity. Riparian vegetation on the sides of Xinyi and Ashe River decreased migration process of microplastics by vegetal purification and then resulted in low abundance of microplastics. In conclusion, this study highlighted the occurrence characteristics, source apportionment and environmental influencing factors of microplastics in urban rivers of Harbin, which may develop new insights into the reduction of abundance of microplastics in the urban rivers.

Occurrence and correlation of microplastics and dibutyl phthalate in rivers from Pearl River Delta, China

Microplastics have been identified as the novel contaminants in various environments. Phthalates would be released from plasticized microplastics into a riverine environment while transporting to a marine region, but data on their relationship in rivers have been scarce. In this study, the occurrence, distribution and correlation of microplastics and dibutyl phthalate (DBP) in two rivers from the Pearl River Estuary were investigated. The elevated level of DBP in the Qianshan River (2.70 ± 0.20 μg/L) was in alignment with the presence of highest microplastic concentration at the same sampling site (15.8 ± 9.8 items/L). A positive correlation was observed between microplastics and DBP in all sampling sites (p < 0.05). The results showed that UV irradiation from sunlight was a majorly inducing factor of DBP leaching from polyethylene microplastics. The concentrations of chemical additives in some degrees reflect the microplastic pollution, but environmental factors and multidimensionality of microplastics such as residence times and types may cause spatial differences of chemical additives in aquatic systems.

Abundance and characteristics of microplastics in a freshwater river in northwestern Himalayas, India - Scenario of riverbank solid waste disposal sites

Microplastics (MPs) are one of the challenging and established contaminants that have adverse implications on human health. The focus of this study was to quantify and analyze the contribution of unscientific municipal solid waste (MSW) disposal sites to the MPs in the Jhelum River and the risk associated with it. Quantitative analysis of our study showed a mean MP concentration of 1474 ± 1026 particles/m3 for the entire stretch of the river. All the sites confirmed the presence of MPs with the concentration ranging from 600 particles/m3 to 2500 particles/m3. The size distribution of MPs suggested that 34 % of the microplastics ranged between 300 μm to 75 μm while 66 % of the particles varied between 300 μm to 5 mm. The concentrations of MPs downstream of unscientific disposal sites were found to increase threefold to that of upstream. The Fourier Transform Infrared Spectroscopy (FT-IR) confirmed the presence of polyethylene (PE) in the majority followed by polyvinyl chloride (PVC) and polypropylene (PP). The flakes were dominant throughout the river followed by filaments, fragments, and spherules. Count based Pollution level indexing (PLI) estimated 3-14 times MP contamination in the river with respect to contamination in glacial runoffs. The risk assessment study of the MPs indicated an increase of around 10.2 % in ingestion rates of MPs due to the unscientific disposal of MSW on the banks of the freshwater body. The values of polymer hazard index (PHI) and potential ecological risk index (PERI) were in the extreme case of pollution (PHI>1000 and PERI>1200). This study manifests the adversities of unscientific municipal solid waste disposal for timely waste management.

Impact of persistent rain on microplastics distribution and plastisphere community: A field study in the Pearl River, China

Microplastic contamination is a global problem which has been threatening human health and the environment. There is still a knowledge gap about the effect of persistent rain on microplastics distribution and plastisphere community in fluvial environments. In this study, the abundance and composition of microplastics in the sediment and surface water from the Pearl River was investigated. Thirty polymers (10-500 μm) were identified from thirty-eight samples collected at ten sites using the newly developed laser direct infrared (LDIR) technique. The average concentrations of microplastics in the sediment and surface water were 1974 particles kg^-1 and 290 particles L^-1, respectively. Abnormally high concentrations of polyurethanes (PU) were possibly due to particulate pollution from ship antifouling. The persistent rain increased the abundance and diversity of microplastics in the surface water, whereas an opposite trend was observed in the sediment. Sediments could temporarily switch from microplastics sinks to potential sources under the effect of violent hydrodynamic disturbances. Additionally, plastisphere communities and predicted functional profiles indicated significant differences before and after the rain. Our study highlights the important impact of persistent rain on microplastic contamination in the environment.

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.

New insights into the distribution, potential source and risk of microplastics in Qinghai-Tibet Plateau

Microplastics (MPs) as emerging contaminants have become a major global concern, however, the distribution and origin of MPs in Qinghai-Tibet Plateau (QTP) and their impacts on ecosystem are poorly known. Hence, we systematically evaluated the profile of MPs on the representative metropolitan locations of Lhasa and Huangshui Rivers and the scenic sites of Namco and Qinghai Lake. The average abundance of MPs in the water samples was 7020 items/m³, which was 34 and 52 times higher than those for the sediment (206.7 items/m³) and soil samples (134.7 items/m³), respectively. Huangshui River had the highest levels, followed by Qinghai Lake, Lhasa River and Namco. Human activities rather than altitude and salinity impacted the distribution of MPs in those areas. Besides the consumption of plastic products by locals and tourists, laundry wastewater and exogenous tributary inputs, the unique prayer flag culture also contributed to the MPs emission in QTP. Notably, the stability and fragment of MPs were crucial for their fate. Multiple assessment models were employed to evaluate the risk of MPs. PERI model took MP concentration, background value and toxicity into account, comprehensively describing the risk differences of each site. The large PVC proportion in Qinghai Lake posed the highest risk. Furthermore, concerns should be raised about PVC, PE and PET in Lhasa and Huangshui Rivers, and PC in Namco Lake. Risk quotient suggested that aged MPs in sediments slowly released biotoxic DEHP and should be cleaned up promptly. The findings offer baseline data of MPs in QTP and ecological risks, providing important support for the prioritization of future control measures.

Microplastic occurrence and ecological risk assessment in the eight outlets of the Pearl River Estuary, a new insight into the riverine microplastic input to the northern South China Sea

Estuaries are unique transition zones connecting terrestrial and coastal environments and are recognized as primary conveyors for land-derived plastics to open oceans. Riverine microplastics (MPs) have been commonly investigated using sequential sampling which might not effectively reflect the actual load. In this study, sampling at eight outlets was performed during a complete tidal cycle to estimate the MP flux to the Pearl River Estuarine (PRE) using a concurrent sampling strategy. The MP abundances ranged from 2.90 ± 0.57-5.9 ± 2.27 particles/L. A remarkable difference between tides in MP abundances suggests tidal effect should not be overlooked in assessment. The MP load through the eight outlets was estimated at 304 trillion particles or 1102 tons into the PRE annually. Additionally, similar potential ecological risk assessment among eight rivers implied that environmental threats posed by less urbanized and populated rural areas on the western side have been under-evaluating for decades.

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.

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.

Potential of microplastics participate in selective bioaccumulation of low-ring polycyclic aromatic hydrocarbons depending on the biological habits of fishes

Currently, although the cumulative effects of microplastics (MPs) and organic pollutants (OPs) in the environment and within organisms are being investigated, whether and how MPs participate in bioaccumulation of OPs based on a carrier effect is still unclear. In the present study, water and aquatic organisms were collected from the Pearl River. Polycyclic aromatic hydrocarbons (PAHs) and MPs were separated by solid phase extraction and were measured by gas chromatography mass spectrometry and Fourier transform infrared spectroscopy, respectively. Higher PAH concentrations at the river outlet and higher MPs abundance in the inner river were observed, indicating a mismatched distribution between PAHs and MPs. No correlation between MP abundance and PAH concentration in fishes was detected, implying that MPs exerted limited influence on PAH concentrations. Interestingly, bioconcentration factors of one major low-ring PAH (phenanthrene) in fishes showed a significant correlation with MPs abundance, implying that although MPs did not affect the variation in PAH concentrations, they potentially participated in selective bioaccumulation of PAHs. Moreover, significant correlations between MPs abundance and PAHs in fishes with different feeding and living habits were found, indicating that MPs' participation in PAH bioaccumulation was dependent on fish biology and life history. Furthermore, the health risk posed by PAHs in fishes at the river outlet surpassed the line of potential high risk, while the ecological risk posed by MPs at the inner river was in the danger category, indicating the ecological risks posed by PAHs and MPs are uneven along the Pearl River. These findings deepen our understanding of the underlying mechanism of MPs participating in selective bioaccumulation of low-ring PAHs in fishes based on fish biology and point out the present risks posed by these two pollutants in the Pearl River and its estuary, which contribute to aquatic environmental protection and fishery production in this region.

Seasonal variation of temperature affects HMW-PAH accumulation in fishery species by bacterially mediated LMW-PAH degradation

Currently, the specific mechanism generating seasonal variation in polycyclic aromatic hydrocarbons (PAHs) via bacterial biodegradation remains unclear, and whether this alteration affects PAH bioaccumulation is unknown. Therefore, we performed a study between 2015 and 2020 to investigate the effects of seasonal variation on bacterial communities and PAH bioaccumulation in the Pearl River Estuary. Significantly high PAH concentrations in both aquatic and fishery species were determined in dry seasons (the mean ∑₁₆PAH concentration: water, 37.24 ng/L (2015), 30.83 ng/L (2020); fish, 51.01 ng/L (2015) and 72.60 ng/L (2020)) compared to wet seasons (the mean ∑₁₆PAH concentration: water, 22.38 ng/L (2015), 19.40 ng/L(2020); fish, 25.28 ng/L (2015) and 32.59 ng/L (2020)). Distinct differences in taxonomic and functional composition of bacterial communities related to biodegradation of low molecular weight PAHs (LMW-PAHs) were observed between seasons, and the concentrations of PAHs were negatively correlated with seasonal variation in temperature. Temperature-related specific bacterial taxa (e.g., Stenotrophomonas) directly or indirectly participated in LMW-PAH degradation via encoding PAH degradation enzymes (e.g., protocatechuate 4,5-dioxygenase) that subsequently led to bioaccumulation of high molecular weight PAHs (HMW-PAHs) in wild and fishery species due to LMW-PAHs in the water. Based on this alteration, the ecological risk posed by PAHs decreased in wet seasons, and an unbalanced spatio-temporal distribution of PAHs was observed in this estuary. These results suggest that seasonal variation of temperature affects HMW-PAH accumulation in fishery species via bacterially mediated LMW-PAH biodegradation.

A review of sources, status, and risks of microplastics in the largest semi-enclosed sea of China, the Bohai Sea

The largest semi-enclosed sea of China, the Bohai Sea, serves as an important sink of microplastics (MPs) originated from terrestrial and marine sources. This study summarized potential sources and migration pathways of MPs in the Bohai Sea and reviewed the abundance and characteristics of MPs in water, sediments, and organisms. Coastal anthropogenic activities (i.e., plastic production, agricultural activities, and industrial and domestic sewage discharge) and marine origins (i.e., aquaculture, marine litters, and transportation) might accelerate the MPs enrichment in the Bohai Sea. The abundance of MPs ranged from 0.07 to 5200 items/m³ in the seawater, mainly influenced by the application of different trawl nets/sieves with different sizes (0.005-0.33 mm). Sediments of coastal rivers contained the MPs ranging from 56.7 to 1795 items/kg, significantly higher than that of the Bohai Sea (6.24-461.6 items/kg). Among organisms, the average abundance of MPs was the lowest in zooplanktons (0.03 items/animal), significantly lower than that in invertebrates (1.39 items/animal) and fish (2.12 items/animal), but no biomagnification of MPs was observed. The preliminary risk assessment indicated that seawater in the Liaodong Bay had medium ecological risk of MPs while other bays of the Bohai Sea had minor risks. To make the ecological risk of MPs quantifiable and comparable, future research priorities are recommended to focus on more frequent field surveys, standardization of sampling methods, and establishment of toxicity database of common polymer types of MPs in the Bohai Sea.

Spatial and temporal variations of microplastic concentrations in Portland's freshwater ecosystems

While microplastics are a pollutant of growing concern in various environmental compartments, less is known regarding the sources and delivery pathways of microplastics in urban rivers. We investigated the relationship between microplastic concentrations and various spatiotemporal factors (e.g., land use, arterial road length, water velocity, precipitation) in two watersheds along an urban-rural gradient in the Portland metropolitan area. Samples were collected in August, September, and February and were analyzed for total microplastic count and type. Nonparametric statistics were used to evaluate potential relationships with the explanatory variables, derived at both the subwatershed and near stream scales. In August, microplastic concentrations were significantly higher than in February. August concentrations also negatively correlated with flow rate, suggesting that lower flow rates may have facilitated the accumulation of microplastics. Smaller size microplastic particles (< 100 μm) were found more in August than September and February, while larger size particles were more dominant in February than the other months. Microplastic concentrations were positively related to 24-h antecedent precipitation in February. Negative correlations existed between wet season microplastic concentrations and agricultural lands at the near stream level. The results indicate that near stream variables may more strongly influence the presence and abundance of microplastics in Portland's waterways than subwatershed-scale variables. Fragments were the most commonly observed microplastic morphology, with a dominance of gray particles and the polymer polyethylene. The findings of this study can inform management decisions regarding microplastic waste and identify hotspots of microplastic pollution that may benefit from remediation.

Distribution and environmental risk assessment of microplastics in continental shelf sediments in the southern East China Sea: A high-spatial-resolution survey

We report a high-spatial-resolution study on the distributions, characteristics, and environmental risks of microplastics in surface sediments of the southern East China Sea. Microplastics were omnipresent in the sediments (concentration range: 53.3-246.7; mean: 138.4 particles/kg dry-weight sediment) and enriched in nearshore areas close to urban centers relative to lower offshore concentrations. The microplastics identified were dominated by polyethylene (41.2%) and polyethylene terephthalate (19.9%) in polymer type, fibers (45.8%) and fragments (40.3%) in shape, 0.1-0.5 mm (61.0%) in size, and black (52.0%) in color. The benthic environment experienced low to moderate microplastic pollution, with polyvinylchloride exhibiting the highest ecological risk index. The high-resolution sampling revealed highly diverse polymer types and strongly patchy distributions of microplastic abundance and pollution indices in sediments. Results from this study imply that complex physical, biological, and topographic interactions control the distribution of microplastics and the associated environmental risks in coastal sediments.

Microplastics in freshwater: A global review of factors affecting spatial and temporal variations

Microplastics are a pollutant of growing concern, capable of harming aquatic organisms and entering the food web. While freshwater microplastic research has expanded in recent years, much remains unknown regarding the sources and delivery pathways of microplastics in these environments. This review aims to address the scientific literature regarding the spatial and temporal factors affecting global freshwater microplastic distributions and abundances. A total of 75 papers, published through June 2021 and containing an earliest publication date of October 2014, was identified by a Web of Science database search. Microplastic spatial distributions are heavily influenced by anthropogenic factors, with higher concentrations reported in regions characterized by urban land cover, high population density, and wastewater treatment plant effluent. Spatial distributions may also be affected by physical watershed characteristics such as slope and elevation (positive and negative correlations with microplastic concentrations, respectively), although few studies address these factors. Temporal variables of influence include precipitation and stormwater runoff (positive correlations) and water flow/discharge (negative correlations). Despite these overarching trends, variations in study results may be due to differing scales or contributing area delineations. Thus, more rigorous and standardized spatial analytical methods are needed. Future research could simultaneously evaluate both spatial and temporal factors and incorporate finer temporal resolutions into sampling campaigns.