Vertical transfer of microplastics in nearshore water by cultured filter-feeding oysters.

Microplastics (MPs) are widely distributed in the sea, but the vertical transfer of MPs by marine organisms in coastal area is still poorly understood. In this study, we used laser direct infrared (LDIR) spectroscopy to determine the number and characteristics of MPs deposited by cultured oyster Crassostrea gigas and further compared the differences between MPs of natural deposit and biodeposit in field environments. The amounts of MPs found in the biodeposit of cultured oysters were 3.54 times greater than that in the natural deposition. The polymer types of biodeposit MPs also differed from those of natural deposition. It was estimated that a single oyster can deposit 15.88 MPs per day, which is a figure much higher than the initial results, and hotspots of MPs deposition may be formed within the oyster aquaculture area. We used generalized linear mixed model (GLMM) to further infer the sources of MPs in sediments and found that distance to shore, cultured zone and urban center were important predictors of MPs abundance in sediments of aquaculture area. The above results suggest that cultured bivalves have an important capacity for MPs biodeposition and will further change the vertical distribution pattern of MPs in coastal environments.

Potential threats of microplastics and pathogenic bacteria to the immune system of the mussels Mytilus galloprovincialis.

As one of the main components of marine pollution, microplastics (MPs) inevitably enter the mussel aquaculture environment. At the same time, pathogenic bacteria, especially pathogens such as Vibrio, can cause illness outbreaks, leading to large-scale death of mussels. The potential harm of MPs and pathogenic bacteria to bivalve remains unclear. This study designed two experiments (1) mussels (Mytilus galloprovincialis) were exposed to 100 particles/L or 1,000 particles/L polymethyl methacrylate (PMMA, 17.01 ± 6.74 µm) MPs and 1 × 107 CFU/mL Vibrio parahaemolyticus at the same time (14 days), and (2) mussels were exposed to 100 particles/L or 1,000 particles/L MPs for a long time (30 days) and then exposed to 1 × 107 CFU/mL V. parahaemolyticus to explore the effects of these two stresses on the mussel immune system. The results showed that after the combined exposure of V. parahaemolyticus and MPs, the lysosomal membrane stability of hemocytes decreased, lysozyme activity was inhibited, and hemocytes were induced to produce more lectins and defensins to fight pathogenic invasion. Long-term exposure to MPs caused a large amount of energy consumption in mussels, inhibited most of the functions of humoral immunity, increased the risk of mussel infection with pathogenic bacteria, and negatively affected mussel condition factor, the number of hemocytes, and the number of byssuses. Mussels may allocate more energy to deal with MPs and pathogenic bacterial infections rather than for growth. Above all, MPs exposure can affect mussel immune function or reduce its stress resistance, which in turn has an impact on mollusk farming.

The physiological response of the clam Ruditapes philippinarum and scallop Chlamys farreri to varied concentrations of microplastics exposure.

Microplastics (MPs) pollution's impact on the marine ecosystem is widely recognized. This study compared the effects of polyethylene (PE) and polyethylene terephthalate (PET) on two bivalve species, Ruditapes philippinarum (clam) and Chlamys farreri (scallop), at two particle concentrations (10 and 1000 µg/L). MPs were found in the digestive glands and gills of both species. Although clearance rates showed no significant changes, exposure to different MPs caused oxidative stress, energy disruption, and lipid metabolism disorders in both clam and scallop. Histopathological damage was observed in gills and digestive glands. IBR values indicated increasing toxicity with concentration, with PET being more toxic than PE. WOE model suggested increasing hazard with concentration, highlighting higher PET toxicity on clam digestive glands. In contrast, PE hazard increased in gills, showing different species responses. R. philippinarum exhibited higher sensitivity to MPs than C. farreri, providing insights for assessing ecological risk under realistic conditions and stress conditions.

Alteration of microbial mediated carbon cycle and antibiotic resistance genes during plastisphere formation in coastal area.

Microorganisms can attach on the surface of microplastics (MPs) through biological fouling process to form a diverse community called the "plastisphere", which has attracted extensive attention. Although the microbial structure and composition of biofilm have been studied, the knowledge of its microbial function and ecological risk is still limited. In this study, we investigated how the surface properties of MPs affect the biofilm communities and metabolic features under different environmental conditions, and explored the biofilm enrichment of antibiotic resistance genes (ARGs). The results showed that the incubation time, habitat and MPs aging state significantly influenced the structure and composition of biofilm microbial communities, and a small amount of pathogens have been found in the MPs-attached biofilm. The microbial carbon utilization capacity of the biofilm in different incubation habitats varies greatly with highest metabolism capacity appear in the river. The utilization efficiency of different carbon sources is polymer > carbohydrate > amino acid > carboxylic acids > amine/amide, which indicates that the biofilm communities have selectivity between different types of carbon sources. More importantly, ARGs were detected in all the MPs samples and showed a trend of estuary > river > marine. The aged MPs can accumulate more ARGs than the virgin items. In general, MPs in the aquatic environment may become a carrier for pathogens and ARGs to spread to other environment, which may enhance their potential risks to the ecosystem and human health.

Combined effects of salinity and polystyrene microplastics exposure on the Pacific oysters Crassostrea gigas: Oxidative stress and energy metabolism.

Microplastics (MPs) pollution and salinity variation are two environmental stressors, but their combined effects on marine mollusks are rarely known. Oysters (Crassostrea gigas) were exposed to 1 × 104 particles L-1 spherical polystyrene MPs (PS-MPs) of different sizes (small polystyrene MPs (SPS-MPs): 6 µm, large polystyrene MPs (LPS-MPs): 50-60 µm) under three salinity levels (21, 26, and 31 psu) for 14 days. Results demonstrated that low salinity reduced PS-MPs uptake in oysters. Antagonistic interactions between PS-MPs and low salinity mainly occurred, and partial synergistic effects were mainly induced by SPS-MPs. SPS-MPs induced higher lipid peroxidation (LPO) levels than LPS-MPs. In digestive glands, low salinity decreased LPO levels and glycometabolism-related gene expression, which was related to salinity levels. Low salinity instead of MPs mainly affected metabolomics profiles of gills through energy metabolism and osmotic adjustment pathway. In conclusion, oysters can adapt to combined stressors through energy and antioxidative regulation.

The adverse impact of microplastics and their attached pathogen on hemocyte function and antioxidative response in the mussel Mytilus galloprovincialis.

Microplastics (MPs) are widely distributed in marine environments, and they are easily attached by various microorganisms, including pathogenic bacteria. When bivalves mistakenly eat MPs, pathogenic bacteria attached to MPs enter their bodies through the Trojan horse effect, causing adverse effects. In this study, the mussel Mytilus galloprovincialis was exposed to aged polymethylmethacrylate MPs (PMMA-MPs, 20 µm) and Vibrio parahaemolyticus attached to PMMA-MPs to explore the effect of synergistic exposure by measuring lysosomal membrane stability, ROS content, phagocytosis, apoptosis in hemocytes, antioxidative enzyme activities and apoptosis-related gene expression in gills and digestive glands. The results showed that MP exposure alone did not cause significant oxidative stress in mussels, but after long-term coexposure to MPs and V. parahaemolyticus, the activities of antioxidant enzymes were significantly inhibited in the gills of mussels. Both single MP exposure and coexposure will affect hemocyte function. Coexposure can induce hemocytes to produce higher ROS, improve phagocytosis, significantly reduce the stability of the lysosome membrane, and induce the expression of apoptosis-related genes, causing apoptosis of hemocytes compared with single MP exposure. Our results demonstrate that MPs attached to pathogenic bacteria have stronger toxic effects on mussels, which also suggests that MPs with pathogenic bacteria might have an influence on the immune system and cause disease in mollusks. Thus, MPs may mediate the transmission of pathogens in marine environments, posing a threat to marine animals and human health. This study provides a scientific basis for the ecological risk assessment of MP pollution in marine environments.

Impact of aged and virgin microplastics on sedimentary nitrogen cycling and microbial ecosystems in estuaries.

Microplastics (MPs) entering the environment undergo complex weathering (aging) processes, however, the impacts of aged MPs on estuarine nitrogen cycling and microbial ecosystems remain largely unknown. In this study, a 50 days microcosm experiment was conducted to investigate the response of sedimentary nitrogen (N) transformation processes, N2O emission and microbial communities to virgin and aged MPs (PE and PS) exposure. We found that aged MPs influenced sediment nitrogen turnover more rapidly and profoundly than virgin MPs and showed type and dose-response effect. During the first 10 days, higher concentration (3 % by weight of sediment) aged MPs (both PS and PE) treatments significantly promoted denitrification (ANOVA, P < 0.05), while virgin MPs treatments had weak effect on denitrification, compared with the control (P > 0.05). Moreover, higher concentration aged PS-MPs remarkably enhanced N2O emission on the 10th day, while N2O was consumed in the control. After 50 days incubation, there was an overall increase in nirK gene abundance exposed to MPs, and nosZ gene copies in aged PS treatments were around twice that in the control based on qPCR (P < 0.05). The function prediction also showed significant elevation of relative abundance of denitrification and DNRA relevant genes in bacterial community. In addition, aged PS treatment (3 %) recruited specific bacterial and archaeal assemblies, with Sedimenticolaceae, Lentimicrobiaceae, SCGC_AAA011-D5, SG8-5, Lokiarchaeia, and Odinarchaeia selectively enriched in the treatment. Our study highlighted that virgin and aged MPs had different impact on sediment nitrogen cycling, and the ecological risks of aged MPs should be concerned since all MPs eventually get weathered when they enter the environment.

The factors influencing the vertical transport of microplastics in marine environment: A review.

There have been numerous studies that have identified the presence of low-density microplastics (MPs) in the water column and sediments. The focus of current MPs research has shifted towards the interaction of MPs with marine organisms and their potential hazards, including the uptake characteristics, biological transport and toxicological effects of MPs, but the processes involved in the deposition behavior of MPs are still poorly understood. In this review, we summarize the current state of knowledge on the vertical transport of MPs influenced by their physicochemical properties and marine organisms, and discuss their potential impact on MPs deposition. The physicochemical properties of MPs determine their initial distribution. The density, shape, and size of MPs influence their settling state in the marine environment. Marine biota play a key role in the transport of MPs to deep marine environment, mainly by changing the density and adsorption of MPs. Biofouling can alter the surface properties of MPs and increase the overall density, thus affecting the vertical flux of the plastic. Macroalgae may trap MPs particles by producing chemicals or by using electrostatic interactions. Marine swimming organisms ingest MPs and excrete them encapsulated in fecal particles, while the activity of marine benthic organisms may contribute to the transfer of MPs from surface sediments to deeper layers. In addition, MPs may be incorporated into organic particles produced by marine organisms such as marine snow or marine aggregates, increasing the vertical flux of MPs. However, due to the complexity of different sea areas and MPs properties, the deposition behavior of MPs may be the result of the interaction of multiple factors. Thus, the effects of MPs properties, marine organisms and the natural environment on MPs deposition in marine environment needs further research to fill this gap.

First record of microplastics in the Gigantidas platifrons (Mytilidae: Bathymodiolus) and Shinkaia crosnieri (Munidopsidae: Shinkaia) from cold-seep in the South China Sea.

The deep sea is considered the final sink for microplastics (MPs) pollution in marine environments. Despite MPs being consumed by many organisms, their presence in cold-seep organisms remains unclear. At cold seep site F in the South China Sea, which lies 1155 m deep, MPs were investigated in Gigantidas platifrons and Shinkaia crosnieri, both ecologically important species. Microplastics ingestion rates were 80.98 % and 81.25 % in G. platifrons and S. crosnieri, respectively. The average MPs abundance for G. platifrons and S. crosnieri was 2.80 ± 0.69 MPs/ind (2.20 ± 2.75 MPs/g) and 2.30 ± 0.27 MPs/ind (4.74 ± 3.08 MPs/g), with no significant difference between species. There were predominantly fibrous MPs ingested by cold-seep organisms, sized 500-1000 µm, blue in color, and polyethylene terephthalate and cellophane in composition. The results confirm the presence of MPs in cold-seep organisms in the South China Sea, providing further evidence that MP pollution exists in the deep sea.

Toxicokinetics and toxicodynamics of plastic and metallic nanoparticles: A comparative study in shrimp.

Nanoplastic is recognized as an emerging environmental pollutant due to the anticipated ubiquitous distribution, increasing concentration in the ocean, and potential adverse health effects. While our understanding of the ecological impacts of nanoplastics is still limited, we benefit from relatively rich toxicological studies on other nanoparticles such as nano metal oxides. However, the similarity and difference in the toxicokinetic and toxicodynamic aspects of plastic and metallic nanoparticles remain largely unknown. In this study, juvenile Pacific white shrimp Litopenaeus vannamei was exposed to two types of nanoparticles at environmentally relative low and high concentrations, i.e., 100 nm polystyrene nanoplastics (nano-PS) and titanium dioxide nanoparticles (nano-TiO2) via dietary exposure for 28 days. The systematic toxicological evaluation aimed to quantitatively compare the accumulation, excretion, and toxic effects of nano-PS and nano-TiO2. Our results demonstrated that both nanoparticles were ingested by L. vannamei with lower egestion of nano-TiO2 than nano-PS. Both nanoparticles inhibited the growth of shrimps, damaged tissue structures of the intestine and hepatopancreas, disrupted expression of immune-related genes, and induced intestinal microbiota dysbiosis. Nano-PS exposure caused proliferative cells in the intestinal tissue, and the disturbance to the intestinal microbes was also more serious than that of nano-TiO2. The results indicated that the effect of nano-PS on the intestinal tissue of L. vannamei was more severe than that of nano-TiO2 with the same particle size. The study provides new theoretical basis of the similarity and differences of their toxicity, and highlights the current lack of knowledge on various aspects of absorption, distribution, metabolism, and excretion (ADME) pathways of nanoplastics.

Observational and model studies on transport and inventory of microplastics from a leak accident on the beaches of Yantai.

We investigated an unexpected microplastic (MP) leakage event that occurred along the coastline of Yantai in January 2021. Sediment samples were collected from three zones on 9 beaches. MPs were identified with an average abundance of 247.6 ±â€¯125.6 items/m2 on 7 beaches. The total amount of MPs from the leak accident was estimated to be 1.50 × 107 items (514.67 kg). The MPs were identified as polyethylene (PE), polypropylene (PP), and PP/PE blends using µ-FT-IR analysis. By utilizing a numerical model, the transmission process and potential source of MPs were demonstrated. The modeling results showed that the MPs might originate from the central and western part of the Bohai Sea and be driven to the beaches of Yantai by northwest wind and wind-induced surface current. However, due to the absence of direct evidence, the simulation results might only indicate the range of the leaking source, which was the movement trajectory of MPs.

Incubation habitats and aging treatments affect the formation of biofilms on polypropylene microplastics.

Microbial colonization and biofilm formation associated with microplastics (MPs) have recently attracted wide attention. However, little is known about the effect of MP aging and different exposed habitats on biofilm formation and associated microbial community characteristics. To obtain a comprehensive understanding, virgin and aged polypropylene MPs were selected as attachment substrates and exposed to different aquatic habitats (marine, estuary, and river). The results showed that the aging process could destroy surface structure and increase oxygen-containing groups of MPs. The total biomass of the biofilms, attached-bacterial OTU numbers, and α diversities increased with exposure time. The biofilms biomass and α diversity of MPs in the river were significantly higher than those in the marine and estuary habitats, and temperature and salinity were primary factors affecting microbial colonization. Bacterial communities in MP-attached biofilms were significantly different from those in surrounding water. Microorganisms tend to adhere to aged MPs, and especially, genes related to human pathogens were significantly expressed on aged MPs, suggesting a potential ecological and health risk of aged MPs in aquatic ecosystems. Our results showed that aged MPs and different habitats have an important influence on microbial colonization, and the weathering process can accelerate biofilm formation on MPs.

Microplastics in fish meals: An exposure route for aquaculture animals.

Microplastics (MPs) are widely detected in many marine fishes. Fish meal contaminated by MP may constitute a potential threat to aquaculture animals. This study analyzed the characteristics of MP in fish meals from ten major fish meal-producing countries around the world. Microplastics were isolated from fish meal, examined under a microscope and identified using Fourier transform infrared microspectroscopy (µ-FT-IR). The results showed that MP pollution was widely detected in fish meal samples from ten countries. The average MP abundance of fish meals was 5.5 ± 1.6 items/g, with higher levels in China, Peru and Myanmar, which might be related to the high pollution level in fish and their habitats. In isolated MPs, fibers were the main shape type, and the most common size was 500-1000 µm. A total of 6 polymers were identified, with cellophane (CP), polypropylene (PP) and polyethylene teraphalate (PET) being the most common types. The total amount of MP ingestion from fish meals by different cultured animals was also estimated, with Atlantic salmon Salmon salar ingesting the largest number of MPs (9361 items), and red swamp crayfish Procambarus clarkii ingesting the smallest number of MPs (19 items). Thus, fish meal constitutes an important exposure route of MPs for aquaculture animals. The results of this study will provide a basis to assess the potential health risks of MPs in fish meals around the world.

Pollution Characteristics of Microplastics in Mollusks from the Coastal Area of Yantai, China.

Microplastic pollution to the marine environment is a global issue. This study investigated microplastic pollution in ten species of different mollusks. Microplastic shape and size were determined under a microscope. Additionally, the polymer types were identified using Fourier transform infrared microspectroscopy (µ-FT-IR). The results showed that the microplastic abundance varied from 0.19 to 1.76 items/g (wet weight) and 4.3 to 36.6 items/individual. Four types of microplastics were observed, including fibers, fragments, films, and pellets. Fibers smaller than 500 µm were the most common. Cellophane (CP) and polyethylene terephthalate (PET) were the main polymer types. The microplastic abundance in the buried bivalve Ruditapes philippinarum demonstrated the highest level of microplastic contamination assessed by wet weight (1.76 ± 0.95 items/g). Furthermore, the Spearman correlation test showed that there was a significant negative correlation between the microplastic abundance calculated by weight and the biometric parameters (shell length, shell height and soft tissue wet weight). Our results will provide valuable information for assessment of the potential health risks of microplastics in China's seafood.

Microplastic uptake in commercial fishes from the Bohai Sea, China.

Microplastic (MP) pollution has become an emerging global concern in marine environments, but research on the uptake of MPs by commercial marine fish is relatively sparse. In this study, 29 commercial fish species (n = 584) with different feeding habits and trophic levels were collected from 8 sites along the Bohai Sea for MP uptake analysis. Approximately 85.4% of the total fish among all species ingested MPs, and there was an average abundance of 2.14 items/individual or 0.043 items/g of wet weight. Compared with other studies, MP pollution in fishes from the Bohai Sea was relatively moderate. The MPs were predominantly fibrous in shape and were cellophane, polyethylene terephthalate (PET) and polypropylene (PP) in polymer composition. The highest abundance and polymer composition of MPs was observed in benthivores, suggesting that they might ingest these MPs from their food. The small fish Konosirus punctatus, which had a high level of MPs, may increase the risk of human exposure to the MPs when it is dried and consumed. Moreover, the spatial variation of MPs was determined in terms of abundance, shape composition, and major polymer types, but there was no marked relationship between MP abundance and the trophic levels of fish. Overall, this study provides a basis for the ecological risk assessment of MPs in fish and for a health risk assessment for human beings.

Toxic effects of exposure to microplastics with environmentally relevant shapes and concentrations: Accumulation, energy metabolism and tissue damage in oyster Crassostrea gigas.

Microplastics (MPs) are widely found in coastal areas and oceans worldwide. The MPs are environmentally concerning due to their bioavailability and potential impacts on a wide range of marine biota, so assessing their impact on the biota has become an urgent research priority. In the present study, we exposed Crassostrea gigas oysters to irregular MPs of two polymer types (polyethylene (PE) and polyethylene terephthalate (PET)) at concentrations of 10 and 1000 µg L-1 for 21 days. Accumulation of MPs, changes in metabolic enzyme activity, and histological damage were evaluated, and metabolomics analysis was conducted. Results demonstrated that PE and PET MPs were detected in the gills and digestive gland following exposure to both tested concentrations, confirming ingestion of MPs by the organisms. Moreover, both PE and PET MPs inhibited lipid metabolism, while energy metabolism enzyme activities were activated in the oysters. Histopathological damage of exposed oysters was also observed in this study. Integrated biomarker response (IBR) results showed that MPs toxicity increased with increasing MPs concentration, and the toxic effects of PET MPs on oysters was greater than PE MPs. In addition, metabolomics analysis suggested that MPs exposure induced alterations in metabolic profiles in oysters, with changes in energy metabolism and inflammatory responses. This study reports new insights into the consequences of MPs exposure in marine bivalves at environmentally relevant concentrations, providing valuable information for ecological risk assessment of MPs in a realistic conditions.

Microplastic pollution in intertidal sediments along the coastline of China.

Research on microplastic (MP) pollution in the marine environment has received widespread attention in recent years. To assess the degree of MP contamination in the intertidal zone of China, the abundance, shape, particle size and composition of MPs in sediment were investigated in this study. Sediment samples were collected from 13 stations along the coast of China. The density separation method was employed to isolate MPs from sediment and the polymer types of the MPs were determined by Fourier transform infrared microspectroscopy. Our study demonstrated that MP pollution was widespread in the 13 intertidal stations. The average abundance of MPs was 309 ± 81 items/kg dry weight. Fiber accounted for 71.5% of the isolated MPs, and the particles of less than 500 µm accounted for the highest proportion (35.0%). A total of 12 polymers were identified; the main types were rayon (RY), polypropylene (PP), polyethylene terephthalate (PET) and polyethylene (PE). The shape and chemical composition of the MPs from the intertidal sediments of South and North China were different. In South China, MP fragments were more extensive, and PP was a more important component. In contrast, the intertidal sediments of North China contained more MP fibers with the majority being RY, indicating that the major source of MPs in the intertidal zone of North China may be domestic sewage. Additionally, the abundance of MPs in the intertidal sediments of the Pearl River and Jiulong River estuaries was higher than at other sites. A Spearman's correlation analysis showed that there was no correlation between MP abundance and sediment grain size or organic matter content. Our study highlights the ubiquitous distribution of MPs in the sediment along the coast of China and provides valuable information for risk assessment and source control of MP pollution in China's intertidal zone.