Accumulation Of Microplastics Research Articles

Microplastic accumulation, morpho-polymer characterization, and dietary exposure in urban tap water of a developing nation

The recent detection of microplastics (MPs) in a large number of commercially important food items and beverages, including tap water, has drawn significant attention because of direct exposure and negative health effects on humans. Nevertheless, there is insufficient information on microplastic contamination in the tap water of developing countries. In the present study, we primarily analyzed supplied tap water samples from four major cities in Bangladesh to determine and characterize MPs using a stereomicroscope and Fourier transform infrared spectroscopy (FTIR). Several indices were employed to calculate human health exposures to microplastics. MPs were found in all of the water samples tested, with an overall mean of 35.33 ± 19.55 particles/L. The results of this study diverge from those of comparable research conducted globally, revealing that tap water in Bangladesh exhibited higher levels of contamination compared to other nations. MPs were found in three different shapes (fibers, fragments, and films), with fibers dominating the samples (96.2%), and 98.1% of the microplastics were less than 0.5 mm in size. Six different colors of MPs were observed, and transparent particles were dominant (63.9% of all observed MPs). FTIR infrared spectrum analysis revealed two major types of polymers: low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The projected daily consumption of microplastics was determined to be 2.65 particles per person per day, raising potential concerns for human health. The findings show that the treatment process of the water supply system is inadequate. Additionally, the sources of microplastics in tap water may come from where the water was collected for treatment and may be linked to a variety of anthropogenic activities, such as urbanization, sewage discharge, industrial waste disposal, and runoff from catchment areas.

Quantification and polymeric characterization of microplastics in composts and their accumulation in lettuce

Organic fertilizers have become a vector for the transport of microplastics (MPs), which pose human health concerns through the food chain. This study aimed to quantify and characterize MPs in eight different compost samples of various raw materials and their subsequent translocation to lettuce (Lacuta sativa) grown on contaminated composts. The results revealed that the MP abundance ranged from 3810 to 16530 MP/kg. Municipal solid waste compost (MSWC) had highest abundance (16082 ± 632 MP/kg), followed by leaf compost (LC) and organic compost (OC) (6299 ± 1011 and 3680 ± 419 MP/kg, respectively). MPs of <100 μm in size were most dominant in MSWC and LC. Fragments and fibers were the prevalent shape types, with white/transparent colored MPs being more abundant. Polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were the dominant polymers. MPs accumulation in the lettuce leaves was greatest in the lettuce plants grown on MSWC, followed by those grown on LC and OC, indicating that MSWC grown lettuce is not suitable for human consumption. The decrease in the growth (leaf length, number of leaves, leaf fresh and weights) and physiological (membrane stability index, relative water contents) parameters of lettuce was in line with the trend of MP accumulations. Hence, it is highly important to regulate the plastic contents in compost because it is a threat to ecosystems and human health.

Protists in science communication

Despite their high abundance and wide distribution in ecosystems, most protists remain unknown to the public. Although science communication approaches were developed in historical times to raise public awareness of these ‘enigmatic’ taxa, many aspects have not been considered in the spotlight of modern techniques. We present selected ideas and activities on how to attract the public to unicellular eukaryotes. We give examples of how protists can be included in educational work. We explain that trained non-experts can understand and teach others how to recognize protists, where they live, in which habitats they can be found, what they look like and why they are important. Consequently, members of the public can learn how environmental threats impact not only the lives of protists but also ours, e.g., by the accumulation of microplastics through an aquatic food web, up to fish used for human consumption. We suggest age-appropriate methods for application in workshops on protist recognition.

Microplastic Accumulation in Coral Reef Ecosystems at Peukan Bada District, Aceh Besar

Microplastic Accumulation in Coral Reef Ecosystems at Peukan Bada District, Aceh Besar

A bibliometric perspective on the occurrence and migration of microplastics in soils amended with sewage sludge.

The land application of sewage sludge from wastewater treatment plants has been recognized as a major source of microplastic contamination in soil. Nevertheless, the fate and behavior of microplastics in soil remain uncertain, particularly their distribution and transport, which are poorly understood. This study does a bibliometric analysis and visualization of relevant research publications using the CiteSpace software. It explores the limited research available on the topic, highlighting the potential for it to emerge as a research hotspot in the future. Chinese researchers and institutions are paying great attention to this field and are promoting close academic cooperation among international organizations. Current research hot topics mainly involve microplastic pollution caused by the land application of sewage sludge, as well as the detection, environmental fate, and removal of microplastics in soil. The presence of microplastics in sludge, typically ranging from tens of thousands to hundreds of thousands of particles (p)/kg, inevitably leads to their introduction into soil upon land application. In China, the estimated annual accumulation of microplastics in the soil due to sludge use is approximately 1.7 × 1013 p. In European countries, the accumulation ranges from 8.6 to 71 × 1013 p. Sludge application has significantly elevated soil microplastic concentrations, with higher application rates and frequencies resulting in up to several-fold increases. The primary forms of microplastics found in soils treated with sludge are fragments and fibers, primarily in white color. These microplastics consist primarily of components such as polyamide, polyethylene, and polypropylene. The vertical transport behavior of microplastics is influenced by factors such as tillage, wind, rainfall, bioturbation, microplastic characteristics (e.g., fraction, particle size, and shape), and soil physicochemical properties (e.g., organic matter, porosity, electrical conductivity, and pH). Research indicates that microplastics can penetrate up to 90 cm into the soil profile and persist for decades. Microplastics in sewage sludge-amended soils pose potential long-term threats to soil ecosystems and even human health. Future research should focus on expanding the theoretical understanding of microplastic behavior in these soils, enabling the development of comprehensive risk assessments and informed decision-making for sludge management practices. PRACTITIONER POINTS: Microplastics in sewage sludge range from tens to hundreds of thousands per kilogram. Sludge land application contributes significantly to soil microplastic pollution. The main forms of microplastics in sludge-amended soils are fragments and fibers. Microplastics are mainly composed of polyamide, polyethylene, and polypropylene. Microplastics can penetrate up to 90 cm into the soil profile and persist for decades.

Beneath the surface: Exploring microplastic intricacies in Anadara granosa

Anadara granosa or blood cockles have been reported to be a candidate for biomonitoring agents due to their sedimentary nature and their nutrient uptake mechanisms. Yet, this bivalve is still regarded as a delicacy in Asian cuisine. Malaysia is the largest exporter of this sea product that contaminated cockles may also be experienced by the importing countries. However, the bioaccumulation of microplastics in A. granosa cultivated in Malaysia has not been extensively studied. It is crucial to comprehend the risk posed to humans by consuming A. granosa in their diet. Therefore, the purpose of this research is to investigate the levels of microplastic accumulation in A. granosa from major exporters in Peninsular Malaysia, to evaluate the associated risk of microplastics on the species, and to estimate daily human consumption of microplastics through the consumption of A. granosa. The abundance of microplastics was quantified through the use of a stereo microscope, and the polymer type was determined using FTIR and micro-FTIR. Findings from this investigation revealed that all samples of A. granosa were contaminated with microplastics, with the highest levels of accumulation found in bivalves collected from the west coast (0.26 ± 0.15 particles/g) of Peninsular Malaysia. Fragment and fiber microplastics, measuring between 0.05 and 0.1 mm in size, were found to be the most prevalent in A. granosa, with blue being the dominant identified colour and rayon being the most common polymer type. Microplastic risk assessment due to the presence of polyacrylate, polycarbonate (PC), and polymethyl methacrylate (PMMA) resulted in a high risk of contamination for A. granosa. It was further determined that the current estimated dietary intake (EDI) suggests that consumers of A. granosa uptake approximately 21.8–93.5 particles/person/year of microplastics. This study highlights that A. granosa accumulates microplastics, which could potentially result in bioaccumulation and biomagnification in humans through consumption.

How do fish consume microplastics? An experimental study on accumulation pattern using Nile tilapia (Oreochromis niloticus).

The aim of this study was to investigate microplastic (MP) exposure by Nile tilapia (Oreochromis niloticus) in laboratory conditions. A total of 150 tilapia fishes were equally distributed randomly in 15 different glass tanks with five experimental conditions. Observed results depicted that the presence of MPs in different organs was mainly accumulated from the fish feed rather than externally added MPs in the culture tanks. It was also revealed that the gastrointestinal tract (GIT) was found to be the most susceptible to MPs accumulation followed by gills and muscles in order. However, muscle contained the least size of MPs followed by GITs and gills. A statistical test showed significant correlations among the average length and weight of fish with MP exposure. A filamentous shape was found to be dominant in both GITs and gills while fragment shape was dominant in muscles. FTIR results revealed a total of 12 different polymers in the fish of which two polymers (polyvinyl alcohol and ethylene vinyl acetate) were not detected in the feed-only tanks. Polypropylene (PP) and polyethylene terephthalate (PET) were found to be dominant polymers in all the experimental GIT, gills, and muscle organs. FESEM results indicated the presence of different textures including cracks, edges, flakes, scratches, grooves, and adhering particles. EDX results exhibited the presence of Na, Si, K, Ni, Cu, Zn, As, and Cd in the analyzed samples that may pose additional health risks. Thus, this study could act as baseline data for laboratory-based studies of aquaculture species in future research.

Effects of food quantity on the ingestion and egestion of MPs with different colors by Daphnia magna

Aquatic organism uptake and accumulate microplastics (MPs) through various pathways, with ingestion alongside food being one of the primary routes. However, the impact of food concentration on the accumulation of different types of MPs, particularly across various colors, remains largely unexplored. To address this gap, we selected Daphnia magna as a model organism to study the ingestion/egestion kinetics and the preference for different MP colors under varying concentrations of Chlorella vulgaris. Our findings revealed that as the concentration of Chlorella increased, the ingestion of MPs by D. magna initially increased and then showed a decline. During the egestion phase within clean medium without further food supply, an increase in food concentration during the ingestion phase led to a slower rate of MP discharge; while when food was present during the egestion phase, the discharge rate accelerated for all treatments, indicating the importance of food ingestion/digestion process on the MPs bioaccumulation. Furthermore, in the presence of phytoplankton, D. magna demonstrated a preference for ingesting green-colored MPs, especially at low and medium level Chlorella supply, possibly due to the enhanced food searching activities. Beyond gut passage, we also examined the attachment of MPs to the organism's body surface, finding that the number of adhered MPs increased with increasing food concentration, likely due to the intensified filtering current during food ingestion. In summary, this study demonstrated that under aquatic environment with increasing phytoplankton concentrations, the ingestion and egestion rates, color preferences, as well as surface adherence of MPs to filter feeding zooplanktons will be significantly influenced, which may further pose ecological risks. Our results offer novel insights into the unintentional accumulation of MPs by zooplankton, highlighting the complex interactions between food availability and MPs accumulation dynamics.

Deciphering the pathogenic risks of microplastics as emerging particulate organic matter in aquatic ecosystem

Microplastics are accumulating rapidly in aquatic ecosystems, providing habitats for pathogens and vectors for antibiotic resistance genes (ARGs), potentially increasing pathogenic risks. However, few studies have considered microplastics as particulate organic matter (POM) to elucidate their pathogenic risks and underlying mechanisms. Here, we performed microcosm experiments with microplastics and natural POM (leaves, algae, soil), thoroughly investigating their distinct effects on the community compositions, functional profiles, opportunistic pathogens, and ARGs in Particle-Associated (PA) and Free-Living (FL) bacterial communities. We found that both microplastics and leaves have comparable impacts on microbial community structures and functions, enriching opportunistic pathogens and ARGs, which may pose potential environmental risks. These effects are likely driven by their influences on water properties, including dissolved organic carbon, nitrate, DO, and pH. However, microplastics uniquely promoted pathogens as keystone species and further amplified their capacity as hosts for ARGs, potentially posing a higher pathogenic risk than natural POM. Our research also emphasized the importance of considering both PA and FL bacteria when assessing microplastic impacts, as they exhibited different responses. Overall, our study elucidates the role and underlying mechanism of microplastics as an emerging POM in intensifying pathogenic risks of aquatic ecosystems in comparison with conventional natural POM.

How plastic waste management affects the accumulation of microplastics in waters: a review for transport mechanisms and routes of microplastics in aquatic environments and a timeline for their fate and occurrence (past, present, and future)

An increasing global problem is the buildup of improperly handled plastic garbage in the environment. One of the biggest environmental issues facing aquatic ecosystems today is contamination from bulk plastics and plastic detritus. Specifically, microplastics (MPs) and nanoplastics, which are small-scale plastic waste, are now the main causes of pollution in freshwater and marine environments. On the other hand, contamination of aquatic systems is now acknowledged as one of the major environmental hazards facing our world. Currently, concerns have been raised regarding the breakdown of plastic products into micro and nanosized particles, because of the ineffective plastic waste management. To prioritize regions for mitigation policy implementation, it is critical to pinpoint the precise MPs’ transport mechanisms and the locations where trash is created. In order to show the historical and contemporary circumstances as well as forecasts and scenarios of global plastic waste management from now until 2060, we used continent-level data on trash management. This study, finally, presents a potential future scenario of estimates on the destiny, transport, and occurrence of plastic waste in aquatic habitats, highlighting the different factors that trigger the transport of MPs into water and the necessity of rational management of plastic waste.

Microplastic accumulation in groundwater: Data-scaled insights and future research

Given that microplastics (MPs) in groundwater have been concerned for risks to humans and ecosystems with increased publications, a Contrasting Analysis of Scales (CAS) approach is developed by this study to synthesize all existing data into a hierarchical understanding of MP accumulation in groundwater. Within the full data of 386 compiled samples, the median abundance of MPs in Open Groundwater (OG) and Closed Groundwater (CG) were 4.4 and 2.5 items/L respectively, with OG exhibiting a greater diversity of MP colors and larger particle sizes. The different pathways of MP entry (i.e., surface runoff and rock interstices) into OG and CG led to this difference. At the regional scale, median MP abundance in nature reserves and landfills were 17.5 and 13.4 items/L, respectively, all the sampling points showed high pollution load risk. MPs in agricultural areas exhibited a high coefficient of variation (716.7%), and a median abundance of 1.0 items/L. Anthropogenic activities at the regional scale are the drivers behind the differentiation in the morphological characteristics of MPs, where groundwater in residential areas with highly toxic polymers (e.g., polyvinylchloride) deserves prolonged attention. At the local scale, the transport of MPs is controlled by groundwater flow paths, with a higher abundance of MP particles downstream than upstream, and MPs with regular surfaces and lower resistance (e.g., pellets) are more likely to be transported over long distances. From the data-scaled insight this study provides on the accumulation of MPs, future research should be directed towards network-based observation for groundwater-rich regions covered with landfills, residences, and agricultural land.

Terrestrial wildlife as indicators of microplastic pollution in western Thailand.

Plastic pollution in terrestrial wildlife represents a new conservation challenge, with research in this area, especially within protected areas (PAs), being scant. This study documents the accumulation of microplastics (MPs) in terrestrial wildlife both inside and outside PAs in western Thailand. Carcasses of road-killed vertebrates in good condition, as well as live tadpoles, were collected to examine their exposure to plastic pollution. The digestive tracts of the vertebrate carcasses and the entire bodies of tadpoles were analyzed for MPs, which were identified if they measured over 50 µm. A total of 136 individuals from 48 vertebrate species were examined. The sample comprised snakes (44.12%), birds (11.03%), lizards (5.15%), tadpoles (32.25%), amphibians (5.88%), and mammals (1.47%). In total, 387 MPs were found in 44 species (91.67%), with an average occurrence of 3.25 ± 3.63 MPs per individual or 0.05 ± 0.08 MPs per gram of body weight. The quantities of MPs significantly varied among the animal groups, both in terms of number per individual (p < 0.05) and number per gram of body weight (p < 0.01). Furthermore, a significant difference in MP quantities was observed between specimens collected inside and outside PAs on an individual basis (p < 0.05), but not on a body weight basis (p = 0.07). Most MPs were fibers (77%), followed by fragments (22.22%), with only a minimal presence of film (0.52%) and foam (0.26%). Of all the MPs identified, 36.84% were confirmed as plastics or fibers made from natural materials, and 31.58% were plastics, including Polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), Polyvinylidene chloride (PVDC), and polyester (PES). Additionally, fibers made of cotton, and those containing polyurethane (PU), rayon, PES, and combinations of rayon and PU, were identified. The quantities of MPs were significantly influenced by animal body weight, factors associated with human settlement/activity, and land use types. Our findings highlight the prevalence of plastic pollution in terrestrial vertebrates within Thai PAs. Further toxicological studies are required to establish plastic pollution standards. It is proposed that snakes, obtained from road kills, could serve as a non-invasive method for monitoring plastic pollution, thus acting as an indicator of the pollution threat to species within terrestrial ecosystems. There is an urgent need for the standardization of solid waste management at garbage dump sites in remote areas, especially within PAs. Conservation education focusing on MP occurrence, potential sources, and impacts could enhance awareness, thereby influencing changes in behaviors and attitudes toward plastic waste management at the household level.

A Microplastic Pollution Hotspot: Elevated Levels in Sediments from the San Francisco Bay Area

San Francisco Bay’s sediment is currently monitored for a variety of contaminants; however, data regarding the microplastics (MPs) in the area are still scarce. MPs’ occurrence in sediment samples has gained recognition as a reservoir for MP accumulation. Moreover, Bay sediment is also an important matrix for monitoring because sediment tends to accumulate certain contaminants and act as a source of contaminants in the Bay food web. This study analyzed MPs ranging from 25 µm to 5 mm in surface sediment grab samples (n = 8) and two sediment core samples (n = 2 cores analyzed with 11 samples from different depths). Our findings provide an evaluation of MP levels in different regions of the bay. The MP levels detected in Bay surface grab samples ranged from 2.1 to 11.9 MPs/g dry weight (n = 8), with a mean value of 6.2 MPs/g. The most abundant morphology was fibers, followed by fragments and films.

Trophic transfer, bioaccumulation and translocation of microplastics in an international listed wetland on the Montreux record

Microplastics (MPs) are concerning emerging pollutants. Here, MPs in four edible aquatic species of different trophic levels (between ∼2 and 4), including fish species Esox lucius (Esocidae: Esocinae); Cyprinus carpio (Cyprinidae: Cyprininae); and Luciobarbus caspius (Cyprinidae: Barbinae); and the swan mussel Anodonta cygnea (Unionidae), were assessed in the Anzali freshwater ecosystem. It is a listed wetland in the Montreux record. MPs were extracted from gastrointestinal tracts (GI), gills, muscles, and skin. All the studied fish and mussels (n = 33) had MPs. MP fibres, fragments and sheets were detected in every GI examined, however, fibres were the only type of MPs in skins, muscles and gills and were the most abundant MP. The MPs found in the fish and mussels were mainly made of nylon (35% of the total MPs), polypropylene-low density polyethylene (30%), and polycarbonate (25%). The average numbers of MPs found in every fish specimen, expressed per wet body mass, had a moderate negative correlation with the condition factor (K) (MP/g - K: Pearson correlation r = −0.413, p = 0.049), and there was no significant relation with the growth factor (b) (r = −0.376; p = 0.068). Importantly, Luciobarbus caspius (with trophic level 2.7–2.8) bioaccumulated MPs and presented a strong correlation between their MP contamination and age (r = 0.916 p < 0.05). Greater gill mass (or related factors) played an important role in the accumulation of MPs, and there was a strong correlation between these factors for Esox lucius and Cyprinus carpio (r = 0.876; r = 0.846; p < 0.05 respectively). The highest MP/g gills (1.91 ± 2.65) were in the filter feeder Anodonta cygnea inhabiting the benthic zone. Esox lucius (piscivorous, trophic level 4.1) was the most contaminated species overall (a total of 83 MPs in 8 individuals, with 0.92 MP/g fish), and their gills where MPs mainly accumulated. Cyprinus carpio was the most contaminated specimen (MPs in specimens), while the number of MPs per mass unit increased with the trophic level. Their feeding and ecological behavior in the aquatic habitat affected the level of accumulation. This work includes evidence of translocation of MPs within the aquatic organisms.

Mangrove mud clam as an effective sentinel species for monitoring changes in coastal microplastic pollution

The worldwide mangrove shorelines are experiencing considerable contamination from microplastics (MPs). Finding an effective sentinel species in the mangrove ecosystem is crucial for early warning of ecological and human health risks posed by coastal microplastic pollution. This study collected 186 specimens of the widely distributed mangrove clam (Geloina expansa, Solander, 1786) from 18 stations along the Leizhou Peninsula, the largest mangrove coast in Southern China. This study discovered that mangrove mud clams accumulated a relatively high abundance of MPs (2.96 [1.61 – 6.03] items·g-1) in their soft tissue, wet weight, as compared to previously reported levels in bivalves. MPs abundance is significantly (p < 0.05 or 0.0001) influenced by coastal urban development, aquaculture, and shell size. Furthermore, the aggregated MPs exhibit a significantly high polymer risk index (Level III, H = 353.83). The estimated annual intake risk (EAI) from resident consumption, as calculated via a specific questionnaire survey, was at a moderate level (990 – 2475, items·g -1·Capita -1). However, the EAI based on suggested nutritional standards is very high, reaching 113,990 (79,298 − 148,681), items·g -1·Capita -1. We recommend utilizing the mangrove mud clam as sentinel species for the monitoring of MPs pollution changing across global coastlines.

Characteristics of microplastics and their effects on phthalates and microbial activity in greenhouse soil after long-term planting

As an exogenous pollutant, the microplastics accumulated in soil could alter microbial activity. The use of plastic mulch in greenhouse vegetable planting not only enhances vegetable yield and quality, but also leads to the formation and accumulation of microplastics in the soil over time. It is essential to determine the characteristics of microplastics and microorganisms in soils with varying years of planting is crucial for ensuring vegetable quality and quantity. Therefore, this study investigated the abundance and particle size of microplastics, the concentration of phthalates (PAEs), and the dynamics of soil microbial activity in greenhouse soils with different planting years (5, 10, 15, 20, 25, and 30 years). Results showed that microplastics increased in abundance, particle size, and PAEs concentration as planting years progressed. Specifically, the abundance of microplastics rose from 70.0 ± 8.7 to 224.0 ± 10.4 items/kg, with the proportion of microplastics sized 0–2 mm increasing from 14.02 to 69.11 %, and the total PAEs concentration in the soil escalating from 0.31 to 1.89 mg/kg. Additionally, Bacteroidetes and Actinobacteria levels increased, correlating with organic matter degradation. Metabolic pathway linked to degradation were enriched according to KEGG analysis. Correlation analysis revealed that microplastics notably decreased soil pH, creating an acidic environment that boosted urease activity and the relative abundance of Nitrospirae. This study sheds light on the accumulation characteristics of microplastics and their impact on soil microbial activity following prolonged planting.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12–13% and 13–14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55–0.69 mg/kg), nitrate nitrogen (NO3−-N) (7.02–8.65 mg/kg) contents, and N cycle related enzyme activities (33.47–42.39 μg/h/g) by 37.7–50.9%, 22.6–37.2%, and 34.2–48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Assessment and accumulation of microplastics in the Indian riverine systems: Risk assessment and implications of translocation across the water-to-fish continuum

Microplastic (MP) pollution has engulfed global aquatic systems, and the concerns about microplastic translocation and bioaccumulation in fish and other aquatic organisms are now an unpleasant truth. In the past few years, MP pollution in freshwater systems, particularly rivers and subsequently in freshwater organisms, especially in fish, has caught the attention of researchers. Rivers provide livelihood to approximately 40 % of the global population through food and potable water. Hence, assessment of emerging contaminants like microplastics in rivers and the associated fauna is crucial. This study assessed microplastics (MPs) in fish, sediment and freshwater samples across the third largest riverine system of peninsular India, the Mahanadi River. The number concentrations of MPs measured in water, sediment and fish ranged from 337.5 ± 54.4–1333.3 ± 557.2 MPs/m3, 14.7 ± 3.7–69.3 ± 10.1 MPs/kg. Dry weight and 0.4–3.2 MPs/Fish, respectively. Surprisingly, MPs were found in every second fish sample, with a higher MP number in the gut than in the gills. Black and blue coloured filaments with <0.5 mm size were the dominant MPs with polypropylene and polyethylene polymers in abundance. The Polymer Hazard Index (PHI) and the Potential Ecological Risk Index (PERI) studies revealed that the majority of the sampling sites fell in Risk category V (dangerous category). An irregular trend in the MP concentration was observed downstream of the river, though relatively elevated MP concentrations in water and fish samples were observed downstream of the river. t-Distributed Stochastic Neighbour Embedding (t-SNE) unveiled distinct patterns in MP distribution with a higher similarity exhibited in the MPs found in fish gill and gut samples, unlike water and sediment, which shared certain characteristics. The findings in the current study contribute to filling the knowledge gap of MP assessment and accumulation in global freshwater systems and highlight the microplastic contamination and accumulation in fish with its potential implications on human health.

Assessment of microplastic-contaminated liver through gene expression profiling of four commercial fish species in the Lagos Lagoon, Nigeria

Microplastic (MP) occurrence in the Lagos Lagoon has been on a progressive increase in recent years. The potential impacts and hazards of MPs on commercially available fish species from the Lagoon have been understudied. This study aims to assess molecular damage due to microplastic accumulation in the liver of four commercial fish species (Oreochromis niloticus, Chrysichthys nigrodigitatus, Clarias gariepinus, and Gymnarchus niloticus) sourced directly from the Lagoon. The results revealed that MP load in the liver of the fish species ranged between 7.2 ± 1.9 and 9.5 ± 4.4 particles/individual, with G. niloticus recording the maximum concentration. The observed extracted MPs are predominantly black and blue fibres while the Fourier Transform Infrared spectroscopy revealed polyethylene dominance in the plastic polymers. Relative gene expression results revealed statistically significant downregulation of the CYP 1a gene and upregulation of the HSP 70 gene in all the microplastic-laden liver samples except in G. niloticus. The findings from this study suggest that microplastic contamination in fish tissues may exacerbate cellular toxicity in commercially available biota in the Lagos Lagoon, thereby calling for urgent measures to curb microplastic and ultimately plastic pollution. However, there's a need for in-depth research on the effects of environmentally relevant microplastics on edible fish tissues to further elucidate their molecular impact.

Transport and retention of sinking microplastics in a well-mixed estuary

Estuaries have been shown to be potential hotspots of microplastic accumulation, but the hydrodynamic conditions and particle properties that control this process need further investigation. We have designed a series of numerical particle-tracking experiments to examine the sensitivity of retention in estuaries to particle size, particle density and varying tides and freshwater flow. At the end of the simulation, over 90 % of sinking particles are retained in the estuary, and the retention rate is further increased by high river runoff. In contrast, increased river discharge increases the number of marginally-buoyant (i.e. density close to estuarine water) particles that escape the estuary. Larger particle size tends to limit the downstream transport of sinking particles but can facilitate the transport of marginally-buoyant particles. Tidal asymmetry, vertical turbulent mixing and the vertical structure of the subtidal circulation are proposed as the underlying mechanisms controlling the fate of particles.