Spatiotemporal distribution of microplastics in surface water, biofilms, and sediments in the world's largest drinking water diversion project

Fatty-acid incorporation improves hydrophobicity of pea protein based films towards better oxygen/water barrier properties and fruit protecting ability

The current study was undertaken to synthesize pea protein based films containing fatty acids with various chain lengths. Films namely PFAF1, PFAF2, and PFAF3 were fabricated in the presence of pelargonic acid, margaric acid, and pentacosanoic acid, respectively. Also, negative (PF: film formulated using protein alone) and positive control (PCF: film formulated using mixture of protein and chitosan) control were prepared. Interactions occurring within films were clarified by FTIR. Moreover, morphology and thermal behavior of samples were evaluated by SEM and TGA. Variations in thickness (PF: 0.03 mm, PFAF1: 0.03 mm, PFAF2: 0.04 mm, PFAF3: 0.04 mm, PCF: 0.06 mm) and water content (PF: 28.85 %, PFAF1: 16.20 %, PFAF2: 14.51 %, PFAF3: 12.04 %, PCF: 13.83) were obvious. Superior opacity was identified in PCF, followed by PFAF3, PFAF2, PFAF1, and PF. PFAF3 together with PCF were more successful than others in reducing/protecting oxygen and water permeation. Adding fatty acid or chitosan to protein films led to the decline in tensile strength (TS) and increment in elongation at break (E). As for preservation performances, maximum limitations against shifts in weight and color of bananas during 7-day storage were provided by PFAF3. Also, except for PF, all coatings (especially PFAF3) postponed the rotting of fruits.

Water transfer projects and microplastics: Analyzing changes in lake environments with a focus on Wabu Lake, China

Microplastics are widespread in freshwaters, yet their interaction with navigational structures remains unclear. This study compared the distribution and characteristics of microplastics before and after navigation in Wabu Lake. Microplastic concentrations decreased significantly in both surface water and sediment due to navigation opened, from 13.7 ± 6.56 to 3.12 ± 1.8 p L-1 (p < 0.001) and from 568 ± 286 to 174 ± 60.2 p kg-1 (p < 0.001), respectively. Acrylates copolymer was frequently detected in surface water and sediment before navigation, whereas the dominant polymer after navigation was chlorinated polyisoprene in surface water and chlorinated polyethylene in sediment. The results showed that three-years dredging induced relatively severe microplastic pollution before navigation, however, these microplastics were apparently eliminated after navigation, as the distribution and characteristics of microplastics thoroughly varied. This study provides a valuable finding that microplastic transport process can be facilitated by water transfer project, which should be considered for preventing microplastic pollution.

Occurrence, distribution and sources of microplastics in typical marine recirculating aquaculture system (RAS) in China: The critical role of RAS operating time and microfilter

Industrial mariculture, a vital means of providing high quality protein to humans, is a potential source of microplastics (MPs) which have recently received increasing attention. This study investigated the occurrence and distribution of microplastics in feed, source water and recirculating aquaculture system (RAS) with long & short operating times as well as in fish from typical industrial mariculture farms in China. Results showed that microplastics occurred in all samples with the average concentration of 3.53 ± 1.39 particles/g, 0.70 ± 0.17 particles/L, 1.53 ± 0.21 particles/L and 2.21 ± 0.62 particles/individual for feed, source water, RAS and fish, respectively. Microplastics were mainly fiber in shape, blue in color and 20-500 μm in size. Compared with short operated RAS, long operating time led to higher microplastic concentration in RAS, especially that of microplastic in 20-500 μm, granular and blue. Regardless of short or long operating time, microplastics in RAS mainly gathered in culture tank, tank before microfilter and fixed-bed biological filter, and the microfilter removed efficiently the microplastic with the shape of film, granule, fragment as well as those with size > 1000 μm. As for the polymer types, polyamide (PA, 71.9 %) and polyethylene terephthalate (PET, 65.7 %) dominated in feed and source water, respectively, which may be the reason for the high proportion of PA (38.8 % and 26.4 %) and PET (31.8 % and 30.2 %) in RAS and fish. In addition, polypropylene (PP) was also detected in RAS (18.7 %) and fish (22.6 %), indicating that other plastic facilities such as PP brush carrier also made a contribution. Positive matrix factorization (PMF) model revealed three sources of MP in RAS, namely plastic facilities, industrial sewage and plastic packaging products. Our results provided a theoretical basis for the management of MP in RAS.

Accumulation of polyethylene microplastics in river biofilms and effect on the uptake, biotransformation and toxicity of the antimicrobial triclosan

The interaction of multiple stressors in freshwater ecosystems may lead to adverse effects on aquatic communities and their ecological functions. Microplastics (MPs) are a class of contaminants of emerging concern that can exert both direct and indirect ecotoxicological effects. A growing number of studies have investigated MPs-attached microbial communities, but the interaction between MPs and substrate-associated biofilm (i.e., on natural river substrates, such as stones and sediments) remains poorly studied. In this work, the combined effects of polyethylene MPs (PE-MPs) with a particle size of 10-45 μm (2 mg/L) and the antimicrobial triclosan (TCS) (20 μg/L) were investigated on river biofilms through a short-term exposure experiment (72 h). To the best of authors' knowledge, this is the first time that the combined effects of MPs and chemical contaminants in substrate-associated river biofilms were assessed. Different response parameters were evaluated, including (i) exposure assessment and ii) contaminants effects at different levels: bacterial community composition, antibiotic resistance, extracellular polymeric substances (EPS), photosynthetic efficiency (Yeff), and leucine aminopeptidase activity (LAPA). Triclosan was accumulated in river biofilms (1189-1513 ng/g dw) alongside its biotransformation product methyl-triclosan (20-29 ng/g dw). Also, PE-MPs were detected on biofilms (168-292 MP/cm2), but they had no significant influence on the bioaccumulation and biotransformation of TCS. A moderate shift in bacterial community composition was driven by TCS, regardless of PE-MPs co-exposure (e.g., increased relative abundance of Sphingomonadaceae family). Additionally, Yeff and EPS content were significantly disrupted in TCS-exposed biofilms. Therefore, the most remarkable effects on river biofilms were related to the antimicrobial TCS, whereas single PE-MPs exposure did not alter any of the evaluated parameters. These results demonstrate that biofilms might act as environmental sink of MPs. Although no interaction between PE-MPs and TCS was observed, the possible indirect impact of other MPs-adsorbed contaminants on biofilms should be further assessed.

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.

The threat of micro/nanoplastic to aquatic plants: current knowledge, gaps, and future perspectives

Plastics have been recognized as an emerging pollutant and have raised global concerns due to their widespread distribution in the environment and potential harm to living systems. However, research on the threat of micro/nanoplastics (MPs/NPs) to the unique group of aquatic plants is far behind, necessitating a comprehensive review to summarize current research progress and identify future research needs. This review explores the sources and distribution patterns of MPs/NPs in aquatic environments, highlighting their uptake by aquatic plants through roots and leaves, and subsequent translocation via the vascular system facilitated by the transpiration stream. Exposure to MPs/NPs elicits diverse effects on the growth, physiology, and ecological interactions of aquatic plants, with variations influenced by plastic properties, plant species, and experimental conditions. Furthermore, the presence of MPs/NPs can impact the toxicity and bioavailability of other associated toxicants to aquatic plants. This review shows critical knowledge gaps and emphasizes the need for future research to bridge the current understanding of the limitations and challenges posed by MPs/NPs in aquatic 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.

Hydro-geomorphic perspectives on microplastic distribution in freshwater river systems: A critical review

Freshwater river systems are commonly defined as the main transport paths of microplastics (MP) from land into the seas. A shift in research interest from oceans to rivers can be observed, as a large number of i) case studies, ii) review papers and iii) experimental studies in this field have been published recently. Still, studies often lack an in-depth consideration of quantification, as units are mostly based on item numbers. Spatiotemporal aspects are often neglected. Transport paths linking MP sources and sinks in the environment are insufficiently understood and only recently the awareness increased that sustainable management of the MP pollution cannot be addressed without a sound knowledge of water- and sediment-driven MP transport. Within this review paper, we therefore i) reviewed 92 MP case-studies, with a special focus on spatiotemporal aspects and ii) gathered and compared global load-estimation data from these studies. We then outlined the key processes determining MP movement in rivers on the basis of existing laboratory experiments and theoretical approaches. A procedure to effectively compare units of MP in the water column and in riverine sediments was developed on the basis of i) an extensive MP-dataset in German waterways and ii) suspended sediment concentrations (SSC) of nearest monitoring stations of the German water and shipping authority. Our analysis indicates that relating MP in water samples to SSC reduces the often stated large difference between MP concentrations in the water column and bed sediments and therefore relativizes the importance of river beds as a major "MP sink". As for a quantification of MP fluxes, the use of MP masses as unit is crucial, we applied an approach to convert MP items to masses with the help of i) a power-law distribution of MP-particle size, triangular distributions of ii) form-ratios and iii) polymer densities. An evaluation with an own, extensive dataset of MP-particles showed reasonable results. Therefore, we translated global load data from item numbers to mass values for further analysis. Values were within a reasonable range, especially when considering the respective catchment size of each river at the sampling site.

New insight into the effect of microplastics on antibiotic resistance and bacterial community of biofilm

Microplastics (MPs) could serve as substrates for microbial colonization and biofilm formation. However, research on the effects of different types of microplastics and natural substrates on biofilm formation and community structure in the presence of antibiotic-resistant bacteria (ARB) is limited. In this study, we employed by means of microcosm experiments to analyze the situation of biofilms conditions, bacterial resistance patterns, antibiotic resistance genes (ARGs) distribution, and bacterial community on different substrates using microbial cultivation, high throughtput sequencing and PCR. The result showed that biofilms on different substrates markedly increased with time, with MPs surfaces formed more biofilm than stone. Analyses of antibiotic resistant showed negligible differences in the resistance rate to the same antibiotic at 30 d, but tetB would be selectively enriched on PP and PET. The microbial communities associated with biofilms on MPs and stones exhibited variations during different stages of formation. Notably, phylum WPS-2 and Epsilonbacteraeota were identified as the dominant microbiomes of biofilms on MPs and stones at 30 d, respectively. Correlation analysis suggested that WPS-2 could potentially be a tetracycline-resistant bacterium, while Epsilonbacteraeota did not correlate with any detected ARB. Our results emphasized the potential threat posed by MPs as attachment carriers for bacteria, particularly ARB, in aquatic environments.

Beyond ingestion: Adhesion of microplastics to aquatic organisms

The interactions of microplastics with aquatic organisms have been studied primarily using animal species, with dietary ingestion being the most important uptake route. However, recent research indicated that microplastics also interact with biota via bioadhesion. This process has been studied in aquatic macrophytes under laboratory conditions where microplastics adhered to their biomass, but monitoring studies also confirmed that microplastic bioadhesion occurs in other species and in the natural environment. Similarly, microplastics adhere to microorganisms, and in the aquatic environment they can be retained by ubiquitous biofilms. This can occur on a natural substrate such as sediment or rocks, but biofilms are also responsible for enhanced bioadhesion of microplastics to other biotic surfaces such as plant surfaces. Adhesion to these large biotic surfaces could influence the abundance and bioavailability of microplastics in the environment. Only few studies have been conducted on the bioadhesion of microplastics to animals, but their results confirmed that bioadhesion may be even greater than particle ingestion by some animals, such as corals or bivalves. However, the ecotoxicological effects are not yet fully understood and the possible transport of microplastics, e.g. adhered to fish or aquatic insects, also needs to be considered. In summary, bioadhesion seems to be an important process for the interactions of microplastics and biota. Neglecting bioadhesion in an environmental context may limit our understanding of the behavior, fate, and effects of microplastics in the aquatic environment.

To the north: eDNA tracing of the seasonal and spatial dynamics of fish assemblages along the world's largest water diversion project

Extensive water diversion projects that have been increasingly installed worldwide transport essential water resources as well as a large number of biota. However, studies of the dynamic processes of such transport have been limited. The South-to-North Water Diversion Project of China is the largest manmade water diversion system ever constructed. Here, in a year-long project, we used environmental DNA (eDNA) metabarcoding to assess fish biodiversity and assemblage composition along the Project's 1277-km main canal, while also investigating the temporal, spatial, and functional trait drivers of changes in the fish assemblages. Together, 45 fish taxa were detected, with substantial compositional variations between seasons. The number of detected species typically dropped upon entering the canal but remained relatively constant along the canal's length. Spatial variations in fish assemblages were generally dominated by the turnover component over nestedness, and a positive spatial autocorrelation of qualitative assemblage composition was detected within 80 km in all seasons. Furthermore, several functional traits, such as smaller body size, invertivorous diet, rheophilic living, and lithophilic and demersal spawning, were positive predictors of fish presence along the length of the canal and they may boost species chances of introduction to the recipient areas. Our results provide crucial information for ecological management of diversion projects and have key implications for modelling and predicting foreign species invasion through water transfers.

Microplastic abundance, distribution, and characterization in freshwater sediments in Iran: a case study in Kermanshah city

This paper focuses on abundance, distribution, and characteristics of microplastics (MPs) in freshwater sediments of Sarab Niloofar Lake, Kermanshah, Iran. After selecting an appropriate method for extraction of MPs, the characterization such as polymer types, surface morphology, and trace elements has been determined using Fourier transform infrared spectroscopy, scanning electron microscopic, and energy-dispersive X-ray spectroscopic analysis, respectively. The results highlighted that all sampling locations were contaminated by MP abundance ranged from 1733.33 to 4400 items kg^-1 d.w with an average of 2483.59 ± 805.30 items kg^-1 d.w. MPs with a size range of 0.025 to 1 mm (25-1000 μm) were the most frequently detected MPs in size (62%). Furthermore, the MPs found in this area mainly contain fiber (61%), fragment (19%), film (9%), foam (6%), and pallet (5%). The main color for detected MPs in sampling stations was black (51%) and followed by white/transparent (27%), red (11%), blue (7%), and yellow (4%). The results of polymer identification revealed that the polyethylene, polystyrene, polyurethane, and polypropylene were the principal polymers. This research work emphasized that various types of MPs have been distributed in freshwater sediments of Sarab Niloofar Lake, which is a first useful data for MPs in one the most important Kermanshah's tourist area.

The Response of Duckweed Lemna minor to Microplastics and Its Potential Use as a Bioindicator of Microplastic Pollution

Biomonitoring has become an indispensable tool for detecting various environmental pollutants, but microplastics have been greatly neglected in this context. They are currently monitored using multistep physico-chemical methods that are time-consuming and expensive, making the search for new monitoring options of great interest. In this context, the aim of this study was to investigate the possibility of using an aquatic macrophyte as a bioindicator of microplastic pollution in freshwaters. Therefore, the effects and adhesion of three types of microplastics (polyethylene microbeads, tire wear particles, and polyethylene terephthalate fibers) and two types of natural particles (wood dust and cellulose particles) to duckweed Lemna minor were investigated. The results showed that fibers and natural particles had no effect on the specific growth rate, chlorophyll a content, and root length of duckweed, while a significant reduction in the latter was observed when duckweed was exposed to microbeads and tire wear particles. The percentage of adhered particles was ten times higher for polyethylene microbeads than for other microplastics and natural particles, suggesting that the adhesion of polyethylene microbeads to duckweed is specific. Because the majority of microplastics in freshwaters are made of polyethylene, the use of duckweed for their biomonitoring could provide important information on microplastic pollution in freshwaters.

Ecotoxicological and health implications of microplastic-associated biofilms: a recent review and prospect for turning the hazards into benefits

Microplastics (MPs), over the years, have been regarded as a severe environmental nuisance with adverse effects on our ecosystem as well as human health globally. In recent times, microplastics have been reported to support biofouling by genetically diverse organisms resulting in the formation of biofilms. Biofilms, however, could result in changes in the physicochemical properties of microplastics, such as their buoyancy and roughness. Many scholars perceived the microplastic-biofilm association as having more severe consequences, providing evidence of its effects on the environment, aquatic life, and nutrient cycles. Furthermore, other researchers have shown that microplastic-associated biofilms have severe consequences on human health as they serve as vectors of heavy metals, toxic chemicals, and antibiotic resistance genes. Despite what is already known about their adverse effects, other interesting avenues are yet to be fully explored or developed to turn the perceived negative microplastic-biofilm association to our advantage. The major inclusion criteria for relevant literature were that it must focus on microplastic association biofilms, while we excluded papers solely on biofilms or microplastics. A total of 242 scientific records were obtained. More than 90% focused on explaining the environmental and health impacts of microplastic-biofilm association, whereas only very few studies have reported the possibilities and opportunities in turning the microplastic biofilms association into benefits. In summary, this paper concisely reviews the current knowledge of microplastic-associated biofilms and their adverse consequences and further proposes some approaches that can be developed to turn the negative association into positive.

Interactive impacts of microplastics and chlorine on biological stability and microbial community formation in stagnant water

Possibility of human exposure to microplastics (MPs) in water environment has been escalating, and subsequent challenges of MPs to biostability and biosafety in drinking water deserve more attention, especially in stagnant water. The present study explored the integrated impacts of MPs and chlorine on disinfection kinetics, microbial growth, and microbial community formation in drinking water, by setting MPs or microplastic-biofilm (MP-BM) under different disinfection conditions. The following were the primary conclusions: (1) The presence of MP and MP-BM led to the deterioration of water indices (especially turbidity) when chlorine was less than 1 mg/L. (2) MP/MP-BM accelerated the decay of disinfectants and MP-BM consumed more rapidly. Meanwhile, chlorine contributed to the level of BRP, ranging from 4.78 × 10⁵ CFU/mL to 1.42 × 10⁷ CFU/mL. (3) MP/MP-BM and chlorine integrally shaped microbial communities in water samples and biofilm samples. Microbial dissimilarity between isolated and hybrid MP-BM indicated manners of microbial field or non-contact communication. Microbial abundance and OPs were effectively controlled when chlorine was over 1 mg/L. (4) According to time-lag differential equations simulation, impulsive chlorination contributed to controlling microbial risks and DBPs induced by MP/MP-BM and water stagnation.

Aquatic Biofilms-Sink or Source of Microplastics? A Critical Reflection on Current Knowledge

The scientific understanding regarding sources, occurrence, and effects of microplastics in the aquatic environment has advanced rapidly, leaving some meaningful knowledge gaps virtually untouched. One of them is the interactions of microplastics and biofilms, microbial communities ubiquitous in aquatic ecosystems and fundamental for a range of ecosystem-level processes. It is evident that biofilms can quickly develop on the microplastic surface and consequently change particle properties and, as such, its fate and ecotoxicity. Moreover, microplastics interact with ubiquitous biofilms that are developed on any surfaces in aquatic ecosystems. Although the knowledge about these interactions is at best limited, it is expected that microplastics attach to the water-biofilm interface or penetrate the biofilm matrix. Microplastics can accumulate and ab- or adsorb to those biofilms where they are subjected to transformation processes such as fragmentation. Thus, biofilms may function as a sink. Changes in environmental conditions may, however, stress biofilms initiating their dieback and microplastic release, which could turn biofilms into a source of microplastics. We argue that the accumulation and release dynamics are a largely overlooked but potentially important piece to the puzzle that is a comprehensive understanding of microplastic fate in the environment and thus under the influence of multiple interacting factors. Environ Toxicol Chem 2022;41:838-843. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Microplastics and Nanoplastics: Emerging Contaminants in Food

As current concerns about food safety issues around the world are still relatively serious, more and more food safety issues have become the focus of people's attention. What's more serious is that environmental pollution and changes in human lifestyles have also led to the emergence of contaminants in food, microplastics (MPs) and nanoplastics (NPs) being typical representatives. MPs and NPs (M/NPs) in food are gradually becoming recognized by regulatory authorities and the public. Most published reviews on M/NPs have been focused on the environmental ecosystems. In those papers, it is only sporadically mentioned that M/NPs can also appear in food. As far as we know, there has not been a systematic review of the pollution and existing status of M/NPs in food. This Review focuses on the harmfulness of M/NPs, the ways in which M/NPs contaminate food, the residual amount of M/NPs in food, and the current analysis and detection methods for M/NPs in food. Current analysis and detection methods have problems such as being time-consuming, involving cumbersome operation, and giving poor accuracy. In the future, it will be necessary to increase the research on methods for efficient and sensitive separation and detection of M/NPs in food. Finally, it is hoped that this Review will arouse more people's awareness of and attention to the seriousness of M/NPs in food.