Microplastics in brown trout (Salmo trutta Linnaeus, 1758) from an Irish riverine system

Factors affecting the accumulation of organotins by wild fish: A case study in the Three Gorges Reservoir, China

Organotin compounds (OTs) accumulate in fish easily, however, research on their influencing factors is still limited. This study collected 25 species of fish with different diets, habitats, and age from the Three Gorges Reservoir (TGR), the largest deep-water river channel-type reservoir in China, and analyzed the accumulation characteristics of OTs in these fish. The results showed that tributyltin (TBT) and triphenyltin (TPhT) were the dominant OTs in fish from the TGR. The correlation between OTs concentration and age, body length, and body weight varied with fish species. The concentrations of TBT and TPhT in carnivorous fish (mean, 25.78 and 11.69 ng Sn/g dw, respectively) were higher than those in other diet fish (P<0.01), but there was no significant difference in fish at different habitat water layers (P>0.05). In addition, the degradation rates of TBT and TPhT in different fish species were all below 50%. In summary, the accumulation of TBT and TPhT in fish is mainly influenced by diet, and both TBT and TPhT were difficult to degrade in fish. These results reveal the pollution characteristics of OTs in fish from the TGR, and can improve our understanding of the factors influencing TBT and TPhT accumulation in freshwater fish.

Improvement of biodegradation of PET microplastics with whole-cell biocatalyst by interface activation reinforcement

Polyethylene terephthalate (PET) is an important basic polymer, which was used widely in variety of fields. Due to its high crystallinity, compact structure and strong surface hydrophobicity, PET has prominent resistance to biodegradation. In recent years, microplastics, especially polyethylene terephthalate (PET) microplastics, was considered as serious threaten to ecosystems. In this study, alkali-resistant bacteria were used as whole-cell catalysts to try to improve the biodegradation of PET microplastics by increasing the bio-interfacial activity of the polymer substrate. Surfactants were applicated to enhance interfacial activation of enzyme and PET interactions. And an integrated strategy was constructed based on alkali resistant bacteria to catalysis the hydrolysis of PET. The results showed that Tween 20 had the most obvious promoting effect among the four interfacial biocatalysts on biological-chemical combined hydrolysis of PET microplastics with whole-cell biocatalysts in alkaline environment. Obvious etching and fracture were observed on the PET fibre surface after biodegradation in presence of surfactant. The weight loss rate of PET substrate can reach 11.04% after 5 days of biodegradation. Thus, this research provides a promising method for efficient degradation of PET microplastics.

Microplastics in the Surface Water and Gastrointestinal Tract of Salmo trutta from the Mahodand Lake, Kalam Swat in Pakistan

Microplastic pollution is becoming an increasingly severe environmental problem. As compared to the marine ecosystem, freshwater ecosystems at high-altitude, remote regions are less studied and lag far behind. Thus, the present study aims to highlight this issue and fill the gap in this regard. The presence of microplastics (MPs) in the surface water and the gastrointestinal tracts (GITs) of brown trout (Salmo trutta) from Lake Mahodand, Kalam Swat, Pakistan, at a high altitude of 2865 m above sea level was investigated. For microplastic extraction, samples were digested with H2O2, NaCl solution was added for density separation, and then samples were filtered with a cellulose nitrate filter (pore size 0.45 µ). After this, visual observation and polymer detection with Fourier transform infrared spectroscopy, microplastics were characterized by their shapes, sizes, colors, and polymer types. In the surface water sample, MP particles were found in the range of 0−5 MPs/L, where the mean concentration of MPs was 2.3 ± 1.52 MPs/L and 1.7 ± 1.05 MPs/gastrointestinal tract (GIT) isolated from the GIT of brown trout. Particles of relatively larger size (500−300 µm) were more abundant than other ranges of particles (300−150 and 150−50 µm) in the surface water and fish samples. The fiber was the most abundant shape of MP particles, followed by sheets and fragments in surface water and fish samples (fibers > sheets > fragments). Four types of polymer viz. low-density polyethylene (LDPE) (44.4%), polypropylene homopolymer (PPH) (19.4%), polyvinyl chloride (PVC) (30.5%), and high-density polyethylene (HDPE) (5.5%) were detected by FTIR spectroscopy. The findings of the present study showed that MPs reached into higher altitudes in remote areas due to tourism activities.

Factors affecting microplastic accumulation by wild fish: A case study in the Nandu River, South China

Quantifying microplastic accumulation in aquatic organisms is important for risk assessments in natural habitats. However, studies on the factors influencing microplastic accumulation by fish, particularly in natural water bodies, remain limited. In this study, we monitored the microplastic pollution characteristics in the fish digestive tract and surface water of the Nandu River, the largest river in Hainan, China. Among the 179 fish examined, microplastics were detected in 90.5 %, covering 27 fish species. Moreover, low abundance of microplastics occurred among the different fish, with an average of 3.20 ± 2.60 particles per fish. Fibrous microplastics with a large size (>500 μm) were dominant in both the water column and fish. In this study, fish size, feeding habits, and living habitats did not affect microplastic abundance in fish. Based on the analysis of differences in the abundance and morphological characteristics of microplastics in water column and fish, we suggested that the random intake and differential excretion of microplastics with different characteristics by fish might lead to the homogeneity of microplastic accumulation in different fish. Our study suggest that more attention should be given to the negative effects of microplastics on small fish owing to the higher microplastic exposure per gram weight, and further improvement in microplastic risk assessment methods is required.

Effect of land use on microplastic pollution in a major boundary waterway: The Arvand River

The occurrence of microplastics (MPs) was investigated in the Arvand River (Iran). The Arvand River (200 Km) is a major water body that flows through land with diverse use and it meets the Persian Gulf. This study constitutes the first assessment of MP pollution (prevalence and physico-chemical characteristics) in the Arvand river, both in the sediment and in the water. MP monitoring has been carried out in 24 stations located along the river. The MP pollution found ranged between 1 and 291 items·L^-1 and 70 to 15,620 items·kg^-1 (dw), in water and sediment, respectively. The majority of MPs were fibres, black/grey and yellow/orange in colour, and mainly 250-500 μm and >1000 μm in size. Polyethylene terephthalate (PET), polypropylene (PP), nylon (NYL), high-density polyethylene (HDPE), and polystyrene (PS) were found in sediment samples. All these polymers, except HDPE, were also identified in the water samples. PET and PP were dominant in the water samples; whereas PET and PS were the most abundant in the sediments. The vicinity of urban wastewater effluents could be behind MP pollution in both water and sediments. Significant differences (p < 0.05) of MP concentrations were affected by different land uses when comparing MP levels in undisturbed natural area with urban areas. A strong correlation between MP fibres and fragments found with PCA biplots revealed their similar distribution in water. In the sediment samples, fibre and fragment MP particles were significantly correlated with colloidal particles (e.g., clay and organic matter) suggesting a relevant role of colloidal particles in the aquatic ecosystem of the Arvand River in transporting MPs. This study contributes to the better understanding of the presence of MP in major rivers, which are systems that have been scarcely investigated for this type of pollution, and it can inform interventions to reduce MP inputs to the river and sea.

The distribution and risk of microplastics discharged from sewage treatment plants in terrestrial and aquatic compartment

Many microplastics (MPs) were produced in daily life, which would enter sewage treatment plants (STPs) with the wastewater. Although the STPs has a good interception effect on these MPs, there will still be a part of MPs entering the environment with the effluent and sludge treatment, causing a certain ecological risk. This study investigated the abundance, characteristics and retention of MPs in different STPs, as well as the ecological risks caused by MPs entering the environment. The abundance of MPs in influent and effluent was ranged from 2.02 to 2.50 items L^-1 and 0.27-0.48 items L^-1, respectively. The abundance of MPs in dewatered sludge and sediment of Lake Dianchi was ranged from 3.719-6.949 × 10³ items (kg Ds)^-1 and 1.84-5.23 × 10³ items (kg Ds)^-1, respectively. So roughly 80% of the MPs were trapped and transferred into the dewatered sludge. The observed colors of MPs were transparent, black, blue, red, pale brown, green and gray, and their main species were polypropylene (PP) and polyethylene (PE). To further evaluate the ecological risks of MPs, the oyster mushroom was cultivated in a medium supplemented with MPs. It was found that MPs could be absorbed by oyster mushrooms with a 7-11% of absorption rate, the fibers were widely distributed in the stipes and the pileus. This study had theoretical significance for exploring the distribution of MPs in STPs and clarifying the ecological risk posed by MPs in the environment.

Microplastics across biomes in diadromous species. Insights from the critically endangered Anguilla anguilla

Microplastic pollution affects freshwater and marine biota worldwide, microplastics occurring even inside the organisms. With highly variable effects, from physical damage to toxicity of plastic compounds, microplastics are a potential threat to the biodiversity, community composition and organisms' health. This emerging pollutant could overstress diadromous species, which are exposed to both sea and river water in their life cycle. Here we have quantified microplastics in young European eel Anguilla anguilla, a critically endangered catadromous fish, entering three rivers in southwestern Bay of Biscay. River water, sediments and seawater were also analysed for microplastics. The microplastic type was identified using Fournier-Transform Infrared spectroscopy and then searched for their hazard potential at the European Chemical Agency site. Both riverine and sea microplastic pollution were predictors of eels' microplastic profile (types of microplastics by shape and colour): A. anguilla juveniles entering European rivers already carry some marine microplastics and acquire more from river water. Potentially hazardous plastic materials were found from eels, some of them dangerous for aquatic life following the European Chemical Agency. This confirms microplastics as a potential threat for the species. Between-rivers differences for microplastics profiles persistent over years highlight the convenience of analysing and preventing microplastics at a local spatial scale, to save diadromous species from this stressor. Since the origin of microplastics present in glass eels seems to be dual (continental + seawater), new policies should be promoted to limit the entry of microplastics in sea and river waters.

Assessment of microplastics in Irish river sediment

Microplastics (MPs) are environmental pollutants of growing concern, and awareness of MPs pollution in marine and freshwater environments has increased in recent years. However, knowledge of MPs contamination in riverine sediments in Ireland is limited. To address this, we collected and analysed sediment samples from 16 selected sites along the River Barrow. Microplastics were extracted through a density separation method, after which their size, colour, and shape were analysed under a stereo microscope (Optica SZM-2). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to identify polymer types. A total of 690 MPs were recovered from the 16 sites, with fibres as the dominant MP type. The highest concentration of MPs was 155 MP fibres kg-1 wet sediment found in samples collected from Graiguenamanagh, Co. Kilkenny (GK). The majority of the recovered MPs were polyethylene (PE), polypropylene (PP), nylon, and cellulose acetate (CA) fibres. Overall, this study highlighted the presence of MPs in Irish river sediments and provided a baseline for future studies on MPs pollution. Further research is needed to better understand sources, distribution, and effects of MPs in freshwater ecosystems.

Microplastics Risk into a Three-Link Food Chain Inside European Hake

Microplastics (MPs) are increasing in the marine environment as well as inside marine organisms, having an important effect on biological diversity. The trophic transfer of MPs was demonstrated under laboratory conditions, but this study is based on the analysis of preys found in stomach contents. MPs from Merluccius merluccius individuals caught in the Cantabrian Sea and preys inside their guts (blue whiting, and northern krill inside blue whiting) were analyzed. MPs with different chemical composition occurred inside every hake and their preys, with different damages, from aquatic life hazards with long lasting effects, to allergic skin reactions and respiratory irritation, not only for aquatic species and fishing resources, but also for humans through hake consumption. The similarity of MPs profiles from gills and seawater samples would support seawater as the main source of gill microplastics. The MPs profile of hake GIT was similar to that of hake preys inside. Despite the small sample size, the presence of MPs in all the tissues analyzed of hakes and their preys, together with the evidence of hazard compositions of some of them, highlights the need for policies and actions to reduce plastic and microplastic production and consumption.

A Meta-Analysis of the Characterisations of Plastic Ingested by Fish Globally

Plastic contamination in the environment is common but the characterisation of plastic ingested by fish in different environments is lacking. Hence, a meta-analysis was conducted to identify the prevalence of plastic ingested by fish globally. Based on a qualitative analysis of plastic size, it was determined that small microplastics (<1 mm) are predominantly ingested by fish globally. Furthermore, our meta-analysis revealed that plastic fibres (70.6%) and fragments (19.3%) were the most prevalent plastic components ingested by fish, while blue (24.2%) and black (18.0%) coloured plastic were the most abundant. Polyethylene (15.7%) and polyester (11.6%) were the most abundant polymers. Mixed-effect models were employed to identify the effects of the moderators (sampling environment, plastic size, digestive organs examined, and sampling continents) on the prevalence of plastic shape, colour, and polymer type. Among the moderators, only the sampling environment and continent contributed to a significant difference between subgroups in plastic shape and polymer type.

Genomic Hatchery Introgression in Brown Trout (Salmo trutta L.): Development of a Diagnostic SNP Panel for Monitoring the Impacted Mediterranean Rivers

Brown trout (Salmo trutta L.) populations have been restocked during recent decades to satisfy angling demand and counterbalance the decline of wild populations. Millions of fertile brown trout individuals were released into Mediterranean and Atlantic rivers from hatcheries with homogeneous central European stocks. Consequently, many native gene pools have become endangered by introgressive hybridization with those hatchery stocks. Different genetic tools have been used to identify and evaluate the degree of introgression starting from pure native and restocking reference populations (e.g., LDH-C* locus, microsatellites). However, due to the high genetic structuring of brown trout, the definition of the "native pool" is hard to achieve. Additionally, although the LDH-C* locus is useful for determining the introgression degree at the population level, its consistency at individual level is far from being accurate, especially after several generations were since releases. Accordingly, the development of a more powerful and cost-effective tool is essential for an appropriate monitoring to recover brown-trout-native gene pools. Here, we used the 2b restriction site-associated DNA sequencing (2b-RADseq) and Stacks 2 with a reference genome to identify single-nucleotide polymorphisms (SNPs) diagnostic for hatchery-native fish discrimination in the Atlantic and Mediterranean drainages of the Iberian Peninsula. A final set of 20 SNPs was validated in a MassARRAY® System genotyping by contrasting data with the whole SNP dataset using samples with different degree of introgression from those previously recorded. Heterogeneous introgression impact was confirmed among and within river basins, and was the highest in the Mediterranean Slope. The SNP tool reported here should be assessed in a broader sample scenario in Southern Europe considering its potential for monitoring recovery plans.

Microplastics as Emerging Food Contaminants: A Challenge for Food Safety

Microplastics (MPs) have been identified as emerging environmental pollutants classified as primary or secondary based on their source. Composition, shape, size, and colour, among other characteristics, are associated with their capacity to access the food chain and their risks. While the environmental impact of MPs has received much attention, the risks for humans derived from their dietary exposure have not been yet assessed. Several institutions and researchers support that the current knowledge does not supply solid data to complete a solid risk characterization of dietary MPs. The aim of this paper is to review the current knowledge about MPs in foods and to discuss the challenges and gaps for a risk analysis. The presence of MPs in food and beverages has been worldwide observed, but most authors considered the current data to be not only insufficient but of questionable quality mainly because of the outstanding lack of consensus about a standardized quantifying method and a unified nomenclature. Drinking water, crustaceans/molluscs, fish, and salt have been identified as relevant dietary sources of MPs for humans by most published studies. The hazard characterization presents several gaps concerning the knowledge of the toxicokinetic, toxicodynamic, and toxicity of MPs in humans that impede the estimation of food safety standards based on risk. This review provides a tentative exposure assessment based on the levels of MPs published for drinking water, crustaceans and molluscs, fish, and salt and using the mean European dietary consumption estimates. The intake of 2 L/day of water, 70.68 g/day of crustaceans/molluscs, 70.68 g/day of fish, and 9.4 g/day of salt would generate a maximum exposure to 33,626, 212.04, 409.94 and 6.40 particles of MPs/day, respectively. The inexistence of reference values to evaluate the MPs dietary intake prevents the dietary MPs risk characterization and therefore the management of this risk. Scientists and Food Safety Authorities face several challenges but also opportunities associated to the occurrence of MPs in foods. More research on the MPs characterization and exposure is needed bearing in mind that any future risk assessment report should involve a total diet perspective.

Towards more ecologically relevant investigations of the impacts of microplastic pollution in freshwater ecosystems

Microplastic pollution is a major environmental concern and the subject of a rapidly growing body of research. Much of this research has focused on the direct effects of microplastics on single species and there is limited information on how microplastics affect different functional groups of organisms, multi-species interactions, and ecosystem processes. We focused on freshwater systems and reviewed 146 studies of microplastic effects on freshwater biota and recorded features including particle characteristics, study designs, functional types of species tested and ecotoxicological endpoints measured. Study species were categorized based on their ecosystem role/functional feeding group rather than taxonomy. We found that most studies were conducted on single species (95%) and focused on a narrow range of functional groups of organisms (mostly filter feeders, 37% of studies). Very few studies have investigated multi-species interactions and ecosystem processes. In many studies, certain characteristics of microplastics, such as polymer type were not well matched with the feeding and habitat ecology of test species, potentially reducing their ecological relevance. Median laboratory study test concentrations were 5-6 orders of magnitude higher than those reported in the field and few studies considered the effects of chemical additives in plastics (6%). We recommend that studies addressing the ecological effects of microplastics need to address neglected functional groups of organisms, design experiments to better match the ecology of test species, and increase in experimental scale and complexity to identify any indirect effects on species interactions and ecosystem processes. We suggest that examining microplastics through an ecological lens that better integrates the feeding and habitat ecology of test organisms will advance our understanding of the effects microplastics have in the environment.

Assessing microplastic distribution within infaunal benthic communities in a coastal embayment

Marine anthropogenic litter is increasing in prevalence in both the marine environment and its inhabitants. This study assesses the levels of anthropogenic microplastics in benthic infauna from 20 subtidal stations in Galway Bay, Ireland. Microplastics were removed from the organisms using an alkaline digestion (KOH) and their synthetic origin was confirmed by μFTIR spectroscopic analysis. The average number of microplastics recorded for all organisms was 0.79 ± 1.14 particles individual^-1, similar to previously published results on subtidal fauna of the North Sea. Fibres were the dominant particle type (98%) and the majority were identified as natural (cellulose, cotton). Synthetic polymers identified included PVA (polyvinyl acetate), EPDM (synthetic rubber), PE (polyethylene) and PVC (polyvinyl chloride). Fibres less than 1 mm made up 55% of the recovered lengths. Colours recorded in the organisms were mainly blue and were reflective of the surrounding habitats. Of the five phyla collected, the highest incidence and uptake was associated with the Annelida. A significant difference in ingested MPs was only evident when depth (greater and less than 30 m) was considered as a factor. In addition, no significant differences were found between either the numbers of ingested MPs and phyla or feeding strategies. The results indicate that future studies should follow an ecosystem-based approach to monitor MPs levels in an area where specific bioindicator(s) have not been identified or are unsuitable.

Chemical Analysis of Microplastics and Nanoplastics: Challenges, Advanced Methods, and Perspectives

Microplastics and nanoplastics have become emerging particulate anthropogenic pollutants and rapidly turned into a field of growing scientific and public interest. These tiny plastic particles are found in the environment all around the globe as well as in drinking water and food, raising concerns about their impacts on the environment and human health. To adequately address these issues, reliable information on the ambient concentrations of microplastics and nanoplastics is needed. However, micro- and nanoplastic particles are extremely complex and diverse in terms of their size, shape, density, polymer type, surface properties, etc. While the particle concentrations in different media can vary by up to 10 orders of magnitude, analysis of such complex samples may resemble searching for a needle in a haystack. This highlights the critical importance of appropriate methods for the chemical identification, quantification, and characterization of microplastics and nanoplastics. The present article reviews advanced methods for the representative mass-based and particle-based analysis of microplastics, with a focus on the sensitivity and lower-size limit for detection. The advantages and limitations of the methods, and their complementarity for the comprehensive characterization of microplastics are discussed. A special attention is paid to the approaches for reliable analysis of nanoplastics. Finally, an outlook for establishing harmonized and standardized methods to analyze these challenging contaminants is presented, and perspectives within and beyond this research field are discussed.

Impacts of baseflow and flooding on microplastic pollution in an effluent-dependent arid land river in the USA

Effluent discharge from wastewater treatment plants can be a substantial source of microplastics in receiving water bodies including rivers. Despite growing concern about microplastic pollution in freshwater habitats, the literature has not yet addressed effluent-dependent rivers, which derive 100% of their baseflow from effluent. The objective of this study was to document and explore trends in microplastic pollution within the effluent-dependent lower Santa Cruz River near Tucson, Arizona (USA). We examined microplastic concentrations in the water column and benthic sediment and microplastic consumption by mosquitofish (Gambusia affinis) at 10 sites along a ~40 km stretch of the lower Santa Cruz River across two time periods: baseflow (effluent only) and post-flood (effluent immediately following urban runoff). In total, across both sampling periods, we detected microplastics in 95% of water column samples, 99% of sediment samples, and 6% of mosquitofish stomachs. Flow status (baseflow vs post-flood) was the only significant predictor of microplastic presence and concentrations in our models. Microplastic fragment concentrations in the water column were higher post-flood, microplastic fiber concentrations in benthic sediment were lower post-flood, and mosquitofish were more likely to have consumed microplastics post-flood than during baseflow. The additional microplastics detected after flooding was likely due to a combination of allochthonous material entering the channel via runoff and bed scour that exhumed microplastics previously buried in the riverbed. Effluent-dependent urban streams are becoming increasingly common; more work is needed to identify microplastic pollution baselines and trends in effluent rivers worldwide.

Plastic pollution: A focus on freshwater biodiversity

Plastics are dominant pollutants in freshwater ecosystems worldwide. Scientific studies that investigated the interaction between plastics and freshwater biodiversity are incipient, especially if compared to the marine realm. In this review, we provide a brief overview of plastic pollution in freshwater ecosystems around the world. We found evidence of plastic ingestion by 206 freshwater species, from invertebrates to mammals, in natural or semi-natural ecosystems. In addition, we reported other consequences of synthetic polymers in freshwater ecosystems-including, for instance, the entanglement of animals of different groups (e.g., birds). The problem of plastic pollution is complex and will need coordinated actions, such as recycling programs, correct disposal, stringent legislation, regular inspection, replacement of synthetic polymers with other materials, and ecological restoration. Current information indicates that the situation in freshwater ecosystems may be as detrimental as the pollution found in the ocean, although highly underappreciated.