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

Pollution characteristics and prospective risk of microplastics in the Zhengzhou section of Yellow River, China

The ubiquitous occurrence of microplastics (MPs) in the freshwater has attracted widespread attention. The Zhengzhou section of the Yellow River was the most prosperous region in ancient China, and the rapid urbanization, industrialization, and agricultural practices contributed to MPs pollution in aquatic systems recently, whereas the contamination status of MPs in the area is still not available. In this study, a total of fourteen sampling cross-sections were selected in the region to collect water samples systematically for the analysis of MPs pollution characteristics and potential risks. Results showed that abundance of MPs in the water were ranged from 2.33 to 15.50 n/L, with an average value of 6.40 ± 3.40 n/L, which was higher than it in other inland rivers from China. Moreover, the MPs of 0.5-2 mm were the dominant sizes in Yellow River of Zhengzhou region, and most of them were black fibres. The top three polymers were Polyethylene terephthalate (PET), Polyamide (PA) and Polypropylene (PP). High diversity indices of MPs observed at S3, S4, S5, S6, S7, and S8 for size, colour, polymer and shape indicated diverse and complex sources of MPs in those cross-sections. The MPs in water from Zhengzhou area of Yellow River probably degraded from textiles, fishing net, plastic bags, mulching film, packaging bags, and tire wear. The chemical risk assessment revealed a level III risk for study area, while S8 and S11 in which PVA or PAN with higher hazard score detected were categorised as class V risk. Coincidentally, probabilistic risk assessment showed a considerable ecological risk of MPs from Yellow River in Zhengzhou City, with possibility of 99.48 and 98.01 % adverse effect for food dilution and translocation-mediated mechanism, respectively. The results are expected to assistance for development of policies and ultimately combating MPs pollution.

Understanding microplastic presence in different wastewater treatment processes: Removal efficiency and source identification

Municipal effluents discharged from wastewater treatment plants (WWTPs) are a considerable source of microplastics in the environment. The dynamic profiles of microplastics in treatment units in WWTPs with different treatment processes remain unclear. This study quantitatively analyzed microplastics in wastewater samples collected from different treatment units in two tertiary treatment plants with distinct processes. The influents contained an average of 15.5 ± 3.5 particles/L and 38.5 ± 2.5 particles/L in the two WWTPs with in the oxidation ditch process and the integrated fixed-film activated sludge process, respectively. Interestingly, microplastic concentrations in the influent were more influenced by the population density in the served area than sewage volume or served population equivalent. Throughout the treatment process, concentrations were reduced to 1.5 ± 0.5 particles/L and 1.0 ± 1.0 particles/L in the final effluents, representing an overall decrease of 90% and 97%, in WWTPs with the oxidation ditch process and integrated fixed-film activated sludge process, respectively. A significant proportion of the microplastics were removed during the primary treatment stage in both WWTPs, with better performance for foam, film, line-shaped and large-sized microplastics. Most microplastics were accumulated in activated sludge, indicating its key role as the primary sink in WWTPs. The multiple correspondence analysis identified laundry washing and daily necessities such as packaging and containers as the major contributors to microplastics in WWTPs. The study proposed recommendations for upgrading WWTPs, modifying designs, and implementing strategies to reduce microplastic sources, aiming to minimize the release of microplastics into the environment. These findings can shed lights on the sources of microplastics in WWTPs, and advance our understanding of the mechanisms for more effective microplastic removals in wastewater treatment technologies in future applications.

Occurrence and fate of pharmaceuticals and personal care products in a wastewater treatment plant with Bacillus bio-reactor treatment

Pharmaceuticals and personal care products (PPCPs) have attracted wide attention due to their environmental impacts and health risks. PPCPs released through wastewater treatment plants (WWTPs) are estimated to be 80 %. Nevertheless, the occurrence of PPCPs in the WWTPs equipped with Bacillus spec.-based bioreactors (BBR) treatment system remains unclear. In this study, sludge and waste water samples were collected during separate winter and summer sampling campaigns from a typical BBR treatment system. The results indicate that out of 58 target PPCPs, 27 compounds were detected in the waste water (0.06-1900 ng/L), and 23 were found in the sludge (0.6-7755 ng/g dw). Paraxanthine was the chemical of the highest abundance in the influent due to the high consumption of the parent compounds caffeine and theobromine. The profile for PPCPs in the wastewater and sludge exhibited no seasonal variation. Overall, the removal of target PPCPs in summer is more effective than the winter. In the BBR bio-reactor, it was found that selected PPCPs (at ng/L level) can be completely removed. The efficiency for individual PPCP removal was increased from 1.0 % to 50 % in this unit, after target specific adjustments of the process. The effective removal of selected PPCPs by the BBR treatment system is explained by combined sorption and biodegradation processing. The re-occurrence of PPCPs in the wastewater was monitored. Negative removal efficiency was explained by the cleavage of Phase II metabolites after the biotransformation process, and the lack of equilibrium for PPCPs in the sludge of the second clarifier. A compound specific risk quotient (RQ) was calculated and applied for studying the potential environmental risks. Diphenhydramine is found with the highest environmental risk in wastewater, and 15 other PPCPs show negligible risks in sewage sludge.

The distribution of sediment microplastics assemblages is driven by location and hydrodynamics, not sediment characteristics, in the Gulf of Maine, USA

Microplastics (MP) are found in marine sediments across the globe, but we are just beginning to understand their spatial distribution and assemblages. In this study, we quantified MP in Gulf of Maine, USA sediments. MP were extracted from 20 sediment samples, followed by polymer identification using Raman spectroscopy. We detected 27 polymer types and 1929 MP kg-1 wet sediment, on average. Statistical analyses showed that habitat, hydrodynamics, and station proximity were more important drivers of MP assemblages than land use or sediment characteristics. Stations closer to one another were more similar in their MP assemblages, tidal rivers had higher numbers of unique plastic polymers than open water or embayment stations, and stations closer to shore had higher numbers of MP. There was little evidence of relationships between MP assemblages and land use, sediment texture, total organic carbon, or contaminants.

Diverse and high pollution of microplastics in seasonal snow across Northeastern China

Snow scavenging is recognized as one of the major sinks for atmospheric microplastics (MPs). However, little is known about the properties of MPs in large-scale surface snow. Using Nile Red staining and micro-Fourier transform infrared spectroscopy, we identified the shapes, sizes, and polymer components of MPs in seasonal snow across northeastern (NE) China, a major industrial area. The average concentration of MPs was (4.52 ± 3.05) × 104 MPs L-1, and the highest contamination (6.65 ± 3.89) × 104 MPs L-1 was observed in Changbai Mountains, which was the highest concentration observed in surface snow to the extent of literature. The majority of snow MPs were smaller than 50 μm and composed primarily of fragments. Ethylene vinyl acetate and polyethylene were the dominant contributors to their chemical components. Investigation with positive matrix factorization revealed that the MPs were primarily generated by debris from packaging materials, followed by industrial and construction activities. In addition, the winter atmospheric circulation over the northwestern Siberian and Mongolian plateaus likely dominated the wide-range dispersion and deposition of the MPs across NE China. These results provide a first comprehensive perspective of MPs from sources to removal associated with snow in a large geographic region.

Research progress on occurrence characteristics and source analysis of microfibers in the marine environment

Synthetic microfiber pollution is a growing concern in the marine environment. However, critical issues associated with microfiber origins in marine environments have not been resolved. Herein, the potential sources of marine microfibers are systematically reviewed. The obtained results indicate that surface runoffs are primary contributors that transport land-based microfibers to oceans, and the breakdown of larger fiber plastic waste due to weathering processes is also a notable secondary source of marine microfibers. Additionally, there are three main approaches for marine microplastic source apportionment, namely, anthropogenic source classification, statistical analysis, and numerical simulations based on the Lagrangian particle tracking method. These methods establish the connections between characteristics, transport pathways and sources of microplastics, which provides new insights to further conduct microfiber source apportionment. This study helps to better understand sources analysis and transport pathways of microfibers into oceans and presents a scientific basis to further control microfiber pollution in marine environments.

Microplastics contamination in two species of gobies and their estuarine habitat of Indian Sundarbans

Sundarbans, a Ramsar site of India is contaminated with heterogeneous microplastic wastes. Boddart's goggle eye mudskipper and Rubicundus eelgoby, were common gobies of Sundarbans estuary which accumulated microplastics during their normal biological activities. We estimated the abundance of microplastics in water, sediment; skin, gills, bucco-opercular cavity and gastrointestinal tract of these two goby fishes. Microplastic load estimated in gobies were 0.84 and 2.62 particles per fish species with a dominance of transparent, fibrous microplastics with 100-300 μm in length. ATR-FTIR and Raman spectroscopy revealed polyethylene as prevalent polymer. Surface degradations and adsorption of contaminants on microplastic surface were investigated by SEM-EDX analysis. Presence of hazardous polymers influenced high polymer hazard index and potential ecological risk index which indicated acute environmental threat to Sundarbans estuary and its resident organisms. Current study will provide a new information base on the abundance of microplastics and its ecological hazard in this biosphere reserve.

Spatial distribution, source apportionment and potential ecological risk assessment of suspended atmosphere microplastics in different underlying surfaces in Harbin

Although suspended atmospheric microplastics (SAMPs) have been found to be ubiquitous and have potential impacts on human health, whereas studies related to source apportionment and potential ecological risk assessment in the atmospheric environment are still limited. This study investigated spatial distribution, source apportionment and potential ecological risk of SAMPs in six underlying surfaces of Harbin, China. The results show that all six underlying surfaces existed SAMPs, including polypropylene (PP), polyethylene terephthalate (PET) polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC), with approximate 26.13 %, 24.10 %, 23.87 %, 13.51 %, and 12.39 %, respectively. SAMPs abundances from filtered air were relatively high and averaged 1.76 n/m3. The SAMPs mainly contained fibrous (59.01 %), fragmented (30.18 %), and granular (10.81 %) with transparent (62.39 %), black 13.74 %), red (7.43 %), white (6.53 %), blue, and yellow (3.60 %), and particle size ranged from 1.3 to 518 μm. In addition, source apportionment of SAMPs shows that SAMPs were originated from five emission sources including living source (19.53 %), construction source (12.08 %), transportation source (47.25 %), industrial source (5.11 %), and agricultural source (16.13 %) in Harbin. A significant correction was observed between SAMPs abundances and human activity (R = 0.68, P = 0.66), atmospheric humidity (R = -0.40, P = 0.02), and wind direction (R = 0.22, P = 0.04) in different underlying surface. Furthermore, potential ecological hazardous single index (EI) of PVC and PS were higher than PP, PET, and PS in the construction land, cultivated land, forest land, grassland, water area, and unused land. An estimation of the potential ecological risk index (RI) from SAMPs using Positive Matrix Factorization (PMF) model indicated that Harbin presented a minor ecological risk with average 16.59 of RI index of microplastics in environments. In conclusion, data in this study indicate that SAMPs are existed in atmospheric environments, which have possible risks for human health via inhalation.

Seasonal distribution characteristics and ecological risk assessment of phthalate esters in surface sediment of Songhua River basin

Phthalic acid esters (PAEs) are typical industrial chemicals used in China. PAEs have received considerable attention because of their ubiquity and potential hazard to humans and the ecology. The spatiotemporal distributions of six PAEs in the surface sediments of the Songhua River in the spring (March), summer (July), and autumn (September) are investigated in this study. The total concentration of phthalic acid esters (∑6PAEs) ranges from 1.62 × 102 ng g-1 dry weight (dw) to 3.63 × 104 ng g-1·dw, where the amount in the spring is substantially higher (p < 0.01) than those in the autumn and summer. Seasonal variations in PAEs may be due to rainfall and temperature. The ∑6PAEs in the Songhua River's upper reaches are significantly higher than those in the middle and lower reaches (p < 0.05). Dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) are the two most abundant PAEs. The ecological hazard of five PAEs is assessed using the hazard quotient method. DBP and DEHP pose moderate or high ecological risks to aquatic organisms at various trophic levels. PAEs originate primarily from industrial, agricultural, and domestic sources. Absolute principal components-multiple linear regression results indicate that agricultural sources are the most dominant contributor to the ∑6PAEs (53.7%). Guidelines for controlling PAEs pollution in the Songhua River are proposed.

Abundance, characteristics, and ecological risks of microplastics in the riverbed sediments around Dhaka city

Microplastic (MP) pollution has become an escalating problem in Bangladesh due to its rapid urbanization, economic growth, and excessive use of plastics; however, data on MP pollution from fresh water resources in this country are limited. This study investigated microplastics pollution in riverbed sediments in the peripheral rivers of Dhaka, the capital of Bangladesh. Twenty-eight sediment samples were collected from the selected stations of the Buriganga, Turag, and Balu Rivers. Density separation and wet-peroxidation methods were employed to extract MP particles. Attenuated total reflectance-Fourier transform infrared spectroscopy was used to identify the polymers. The results indicated a medium-level abundance of MPs in riverbed sediment in comparison with the findings of other studies in freshwater sediments worldwide. Film shape, white and transparent color, and large-size (1-5 mm) MPs were dominant in the riverbed sediment. The most abundant polymers were polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). Pollution load index (PLI) values greater than 1 were observed, indicating that all sampling sites were polluted with MPs. An assessment of ecological risks, using the abundance, polymer types, and toxicity of MPs in the sediment samples, suggested a medium to very high ecological risk of MP pollution of the rivers. The increased abundance of MPs and the presence of highly hazardous polymers, namely; polyurethane, acrylonitrile butadiene styrene, polyvinyl chloride, epoxy resin, and polyphenylene sulfide, were associated with higher ecological risks. Scanning electron microscopy (SEM) analysis indicated that the MPs were subjected to weathering actions, reducing the size of MPs, which caused additional potential ecological hazards in these river ecosystems. This investigation provides baseline information on MP pollution in riverine freshwater ecosystems for further in-depth studies of risk assessment and developing strategies for controlling MP pollution in Bangladesh.

Adsorption of 2-hydroxynaphthalene, naphthalene, phenanthrene, and pyrene by polyvinyl chloride microplastics in water and their bioaccessibility under in vitro human gastrointestinal system

The interaction of microplastics (MPs) and organic pollutants has recently become a focus of investigation. To understand how microplastic residues affect the migration of organic pollutants, it is necessary to examine the adsorption and desorption behavior of organic pollutants on MPs. In this study, integrated adsorption/desorption experiments and theoretical calculations were used to clarify the adsorption mechanism of 2-hydroxynaphthalene (2-OHN), naphthalene (NAP), phenanthrene (PHE), and pyrene (PYR) by polyvinyl chloride microplastics (PVC-MPs). Based on the phenomenological mathematical models, the rate-limiting step for analyte adsorption onto PVC-MPs was adsorption onto active sites (R² = 0.865-0.995). Except for PHE, analyte adsorption isotherms were well described by the Freundlich model (R² = 0.992-0.998), and adsorption thermodynamics showed that analyte adsorption on PVC-MPs was a spontaneous exothermic process (ΔH⁰ < 0; ΔG⁰ < 0). Based on the order of adsorption efficiency of 2-OHN < NAP < PHE < PYR, which is identical to the competitive adsorption experiment, polycyclic aromatic hydrocarbon (PAH) adsorption on PVC-MPs increased as the aromatic ring number increased and the hydroxyl content decreased. The release of 2-OHN (49 %-52 %) from PVC-MPs into the simulated gastrointestinal environment was greater than that of NAP (5.5 %-5.7 %). Theoretical calculations and adsorption tests indicated that hydrophobic interaction was the primary influence on the adsorption of PAHs and their hydroxylated derivatives by PVC-MPs. These findings improve our understanding of MPs' behavior and dangers as pollutant carriers in the aquatic environment and help us develop recommendations for the pollution control of MPs.

Microplastics in rivers along an urban-rural gradient in an urban agglomeration: Correlation with land use, potential sources and pathways

Microplastics are ubiquitous and affect all environments, including rivers. In recent years the number of studies about microplastics in rivers has strongly increased. But still many questions exist regarding sources, pathways, and the role of land use patterns. In this study the relationship between microplastics abundance and anthropogenic factors (population density, urbanization, land use types), as well as the potential role of storm sewers as pathways in tributaries of the Wu River in Taichung, central Taiwan, were studied. Two river catchments of the Dali River were studied in greater detail to investigate the influence of land use on microplastics abundance along an urban-rural gradient, and to observe the change of microplastics abundance in the transition from rural to urban areas. Samples were taken from 41 different locations in urban and rural areas using a manta net with a mesh size of 0.3 mm. Results show abundances ranging from 0 pcs/m³ in unpopulated rural areas up to 230 pcs/m³ in densely populated urban centers, and are positively correlated with population density. Remarkably, a sharp increase in microplastics abundance was observed at the transition from rural to urban areas, which coincides with the appearance of storm sewers. Land use analysis revealed that microplastics abundance positively correlates with the size of industrial, residential and traffic areas in the catchment areas, and negatively correlates with the size of forest areas. Source areas for microplastics in the studied rivers are likely residential and commercial areas. Furthermore, the results of this study show that correlations between microplastics abundances and population density or land use patterns along urban-rural gradients are not trivial. Strength of correlations can depend on local factors or how well urban-rural gradients are developed. Absence of correlations need to be considered carefully, as existing correlations might be masked by the above-mentioned factors.

Microplastics in the foreshore coastal waters, sediment, and coastal fauna of a highly populated megacity - A study on the effect of anthropogenic discharge on clams

In this study, the microplastics (MPs) abundance, characteristics and their variations across three popular beaches of highly populated and largest megacity of India were documented using clams as an indicator species. The abundance of MPs in clams was 77.39 MPs items/g in soft tissue parts and 198.82 items/individual, while in coastal waters and sediments the abundance was 537.5 ± 95 items/L and 10,568.3 ± 3053.3 items/kg respectively. The observed higher microplastic diversity integrated (MDII) indicates numerous sources contributing to microplastics pollution and higher microplastic index (MPI) indicates greater bioavailability of MPs to clams. The bulk of the microplastics recovered from clams (55.78 %), coastal sediments (52.27 %) and coastal sea waters (54 %) belong to the <100 μm size range, and were identified as LDPE and polypropylene, polyamide and polystyrene. This investigation tried to validate the potential trophic transfer concerns associated with clam intake to both human health and marine ecology.

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.

Risk on assessment of 15 REEs and mixtures by DGT in Songhua River system sediments of China's largest old industrial base

Rare earth elements (REEs) are increasingly used in the high-tech sectors in the world and are therefore called burgeoning contaminants. As diffusive gradients in thin films (DGT) can be used to assess the bioavailability of inorganic matters, in this paper, we evaluated, for the first time, the ecotoxicology risks of REEs and their mixtures in river sediments of China's old industrial base by DGT. During our research, taking the Songhua River system (SRS) as an example, we detected its surficial sediments, of which the DGT-labile concentration of REEs (∑REEs) was 2.07-8.76 μg/L. As for the single toxicity, the risk quotient (RQ) values of Y at all sites were significantly greater than 1; while the values of Nd and Pr in some upstream reaches were all significantly greater than the threshold (1), indicating that these adverse effects of single REEs were not neglected. In terms of the combined toxicity of REEs mixtures, we carried out an assessment of the risks of probabilistic ecotoxicology, which showed that the SRS superficial sediments had a low probability of toxicity to aquatic organisms (0.54%).

Identification and Evaluation of the Polycentric Urban Structure: An Empirical Analysis Based on Multi-Source Big Data Fusion

Identifying and evaluating polycentric urban spatial structure is essential for understanding and optimizing current urban development. In order to accurately identify the urban centers of the Guangdong–Hong Kong–Macao Greater Bay Area (GBA), this study firstly fused nighttime light data, POI data, and population migration data based on wavelet transform, then identified the polycentric spatial structure of the GBA by carrying out cluster and outlier analysis, and evaluated the level of different urban centers byconducting geographical weighted regression analysis. Using data fusion, we identified 4579.81 km² of the urban poly-center area in the GBA, with an identification accuracy of 93.22%. Although the number and spatial extent of the identified urban poly-centers are consistent with the GBA development plan outline, the poly-center level evaluation results are inconsistent with the development plan, which shows there are great differences in actual development levels among different cities in the GBA. By identifying and grading the polycentric spatial structure of the GBA, this study accurately analyzed the current spatial distribution and could provide policy implications for the GBA’s future development and planning.