A meta-analysis of the effects of exposure to microplastics on fish and aquatic invertebrates

Spatial distribution of meso and microplastics in the sediments of river Ganga at eastern India

Small plastic debris is one of the most significant emerging pollutants, due to their extreme durability and synthetic nature, possessing a tremendous threat to the aquatic environment. In the present study, sediments of river Ganga at a lower stretch were analyzed for distribution of meso and microplastics at seven different locations viz. Buxar, Patna, Bhagalpur, Nabadwip, Barrackpore, Godakhali and Fraserganj. All the sediments were found to contain mesoplastics (>5 mm) and microplastics (<5 mm) particles with varying degree of the mass fraction (11.48 to 63.79 ng/g sediments), numerical abundance (99.27-409.86 items/kg) and morphotypes. Analysis of the mesoplastics with FT-IR revealed polyethylene terepthalate (39%) as the major contributing plastic debris in the sediments followed by polyethylene (30%). Statistical analysis revealed a strong correlation between microplastics abundance and the pollution traits, BOD and available phosphate, of water and sediment, respectively. This study exhibits the spatial distribution of meso and microplastics in the highly populated locations along the river Ganga emphasizing the attention to be given to this emerging pollutant in the inland river system underlining their role as a transporter of plastic fragments finally to the ocean.

Size-dependent elimination of ingested microplastics in the Mediterranean mussel Mytilus galloprovincialis

Filter feeding organisms have been reported to ingest microplastics (MP) in marine environments. However, information regarding how long the ingested MPs are retained in their digestive tracts remains limited. Here, we report the gut retention time (GRT₉₀) and the long-term egestion time of three different sized polystyrene microspheres (1, 10, and 90 μm) in the Mediterranean mussel Mytilus galloprovincialis. We found significant differences in GRT₉₀ with respect to MP size. With respect to the long-term egestion of MPs, most of the smaller MPs were excreted immediately, although some were detected intermittently until day 40. In comparison, larger MPs were slowly excreted in bulk, after which they were not detected. The results indicate that different sized MPs are retained differently in the digestive tract of mussels. The size-dependent effects of MPs should thus be considered when evaluating the effects of MPs in mussels.

Microplastic-induced damage in early embryonal development of sea urchin Sphaerechinus granularis

Two microplastic sets, polystyrene (PS) and polymethyl methacrylate (PMMA), were tested for adverse effects on early life stages of Sphaerechinus granularis sea urchins. Microparticulate PS (10, 80 and 230 μm diameter) and PMMA (10 and 50 μm diameter) were tested on developing S. granularis embryos from 10 min post-fertilisation (p-f) to the pluteus larval stage (72 h p-f), at concentrations ranging from 0.1 to 5 mg L^-1. Both PS and PMMA exposures resulted in significant concentration-related increase of developmental defects and of microplastic uptake in plutei. Moreover, embryo exposures to PS and PMMA (5 and 50 mg L^-1) from 10 min to 5 h p-f resulted in a significant increase of cytogenetic abnormalities, expressed as significantly increased mitotic aberrations, while mitotoxicity (as % embryos lacking active mitoses) was observed in embryos exposed to PS, though not to PMMA. When S. granularis sperm suspensions were exposed for 10 min to PS or to PMMA (0.1-5 mg L^-1), a significant decrease of fertilisation success was observed following sperm exposure to 0.1 mg L^-1 PS, though not to higher PS concentrations nor to PMMA. Sperm pretreatment, however, resulted in significant offspring damage, as excess developmental defects in plutei, both following sperm exposure to PS and PMMA, thus suggesting transmissible damage from sperm pronuclei to the offspring. The overall results point to relevant developmental, cytogenetic and genotoxic effects of PS and PMMA microplastics to S. granularis early life stages, warranting further investigations of other microplastics and other target biota.

Temperature and clone-dependent effects of microplastics on immunity and life history in Daphnia magna

Microplastic (MP) pollution is potentially a major threat to many aquatic organisms. Yet we currently know very little about the mechanisms responsible for the effects of small MPs on phenotypes, and the extent to which effects of MPs are modified by genetic and environmental factors. Using a multivariate approach, we studied the effects of 500 nm polystyrene microspheres on the life history and immunity of eight clones of the freshwater cladoceran Daphnia magna reared at two temperatures (18 °C/24 °C). MP exposure altered multivariate phenotypes in half of the clones we studied but had no effect on others. In the clones that were affected, individuals exposed to MPs had smaller offspring at both temperatures, and more offspring at high temperature. Differences in response to MP exposure were unrelated to differences in particle uptake, but were instead linked to an upregulation of haemocytes, particularly at high temperature. The clone-specific, context-dependent nature of our results demonstrates the importance of incorporating genetic variation and environmental context into assessments of the impact of plastic particle exposure. Our results identify immunity as an important mechanism underpinning genetically variable responses to MP pollution and may have major implications for predicting consequences of MP pollution.

Microplastics in ballast water as an emerging source and vector for harmful chemicals, antibiotics, metals, bacterial pathogens and HAB species: A potential risk to the marine environment and human health

Microplastic pollution in marine waters around the globe is increasing exponentially. This is the first comprehensive review which focuses on microplastics as a source and vector for metals, antibiotics, toxic chemicals, pathogenic bacteria (Vibrio cholerae), and Harmful Algal Bloom (HAB)-forming dinoflagellates across the continents through ballast water. Microplastics in ballast waters serve as 'hotspots' for the development and spread of multiple drug-resistant human pathogens through co-selection mechanisms. Microplastic inoculation at distant countries through ballast water may pose a serious threat to human health due to higher incidences of bacterial disease outbreaks and HABs. The 2017 ballast water management convention lacks a provision for on-board treatment of microplastic-contaminated ballast water. We conclude that there is a pressing need to include microplastics in the ballast water management convention as a hazardous material. Efficient on-board ballast water treatment strategies and effective limits for microplastics in ballast waters need to be developed.

Adsorption behavior of three triazole fungicides on polystyrene microplastics

Environmental pollution caused by microplastics (MPs) and pesticides has become a global challenge, and increasing evidence shows that MPs can adsorb organic pollutants which may affect their distribution and bioavailability. As widely used pesticides, triazole fungicides with potential environmental and human safety risks often coexist with MPs in the environment. Understanding the adsorption behavior is the basis of risk assessment of co-exposure of MPs and triazole fungicides. In this study, the adsorption behavior of three commonly used triazole fungicides on polystyrene (PS) was studied using adsorption test. The influences of PS particle size and environmental factors on adsorption capacity were evaluated, and the adsorption mechanisms were discussed. Results suggested that the adsorption kinetics and isotherm conformed to the Pseudo-second-order and Freundlich model, respectively. The order of adsorption and desorption capacity was hexaconazole (HEX) > myclobutanil (MYC) > triadimenol (TRI), which was positively correlated with LogKow of pesticides. To a certain extent, the decrease in PS particle size and change in solution pH value and increase in salt ion strength all contribute to increasing adsorption capacity. The main mechanisms of adsorption were hydrophobic and electrostatic interactions. MPs can adsorb and may become the source and sink of triazole fungicides in aqueous environments. Our results demonstrate that more attention should be given to the combined water pollution risk of MPs and triazoles fungicides.

Toward the Development and Application of an Environmental Risk Assessment Framework for Microplastic

Emissions of plastic waste to the environment and the subsequent degradation into microplastic particles that have the potential to interact with biological organisms represent a concern for global society. Current understanding of the potential impacts on aquatic and terrestrial population stability and ecosystem structure and function associated with emissions of microplastic particles is limited and insufficient to fully assess environmental risks. Multistakeholder discussions can provide an important element in helping to identify and prioritize key knowledge gaps in assessing potential risks. In the present review, we summarize multistakeholder discussions from a 1-d International Council of Chemical Associations-sponsored symposium, which involved 39 scientists from 8 countries with representatives from academia, industry, and government. Participants were asked to consider the following: discuss the scientific merits and limitations of applying a proposed conceptual environmental risk assessment (ERA) framework for microplastic particles and identify and prioritize major research needs in applying ERA tools for microplastic particles. Multistakeholder consensus was obtained with respect to the interpretation of the current state of the science related to effects and exposure to microplastic particles, which implies that it is unlikely that the presence of microplastic in the environment currently represents a risk. However, the quality and quantity of existing data require substantial improvement before conclusions regarding the potential risks and impacts of microplastic particles can be fully assessed. Research that directly addresses the development and application of methods that strengthen the quality of data should thus be given the highest priority. Activities aimed at supporting the development of and access to standardized reference material were identified as a key research need. Environ Toxicol Chem 2019;38:2087-2100. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Marine debris: A review of impacts and global initiatives

Marine debris, defined as any persistent manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment, has been highlighted as a contaminant of global environmental and economic concern. The five main categories of marine debris comprise of plastic, paper, metal, textile, glass and rubber. Plastics is recognised as the major constituent of marine debris, representing between 50% and 90% of the total marine debris found globally. Between 4.8 and 12.7 million metric tonnes of consumer plastics end up in the world oceans annually, resulting in the presence of more than 100 million particles of macroplastics in only 12 regional seas worldwide, and with 51 trillion particles of microplastic floating on the ocean surface globally. The impacts of marine debris can be branched out into three categories; injury to or death of marine organisms, harm to marine environment and effects on human health and economy. Marine mammals often accidentally ingest marine debris because of its appearance that can easily be mistaken as food. Moreover, floating plastics may act as vehicles for chemicals and/or environmental contaminants, which may be absorbed on to their surface during their use and permanence into the environment. Additionally, floating plastics is a potential vector for the introduction of invasive species that get attached to it, into the marine environment. In addition, human beings are not excluded from the impact of marine debris as they become exposed to microplastics through seafood consumption. Moreover, landscape degradation owing to debris accumulation is an eyesore and aesthetically unpleasant, thus resulting in decreased tourism and subsequent income loss. There are a wide range of initiatives that have been taken to tackle the issue of marine debris. They may involve manual removal of marine debris from coastal and aquatic environment in form of programmes and projects organised, such as beach clean-ups by scientific communities, non-governmental organizations and the removal of marine litter from Europe's four regional seas, respectively. Other initiatives focus on assessment, reduction, prevention and management of marine debris under the umbrella of international (the United Nations Environment Programme/Mediterranean Action Plan, the Oslo/Paris Convention) and regional organisations - that is, the Helsinki Commission. There are also a number of international conventions and national regulations that encourage mitigation and management of marine debris. However, it is argued that these initiatives are short-term unsustainable solutions and the long-term sustainable solution would be adoption of circular economy. Similarly, four of the sustainable developmental goals have targets that promote mitigation of marine debris by efficient waste management and practice of 3R. As evident by the Ad Hoc Expert Group on Marine Litter and Microplastics meeting, tackling the marine debris crisis is not a straightforward, one-size-fits-all solution, but rather an integrated and continuous effort required at local, regional and global level.

Hudson River juvenile Blueback herring avoid ingesting microplastics

Microplastics in aquatic environments, and specifically their effects on the health of organisms, are of growing concern worldwide. Of particular concern are microplastics in a similar size range to zooplankton, as they have been found in the digestive tracks of organisms, such as fish, who typically seek zooplankton as a food source. It is unclear, however, to what degree, if any, fish select for or against microplastic particles when feeding. It is also unclear whether ingestion of microplastics affects fish condition. To answer these questions, the estimated physical condition and degree of selective feeding on microplastics were determined for juvenile fish collected from the Hudson River. Considering only particles 0.335-5.0 mm, microplastics made up 12% of fish diets but 21% of particles found in the surrounding water column. Relying on Jacob's Modified Electivity (JME) to quantify selectivity in feeding, our results reveal selective feeding on zooplankton and avoidance of microplastics. There was no correlation between condition and degree of selectivity toward any particular food types, including microplastics. Future work needs to consider fish with different feeding strategies and potential bioaccumulation of microplastics in the food web. Fish selectivity of ingestion in regards to microplastics should additionally be tested on wider spatial and temporal scales.

Adverse outcome pathways potentially related to hazard identification of microplastics based on toxicity mechanisms

Increasing concern over microplastics has recently brought increased attention to studies on microplastic toxicity. Here, we conduct a systematic review on toxicity of microplastics that focuses on identifying data gaps in the mechanisms of microplastic toxicity. We observe that microplastic toxicology research thus far has focused on ecotoxicity using apical endpoints and only a few studies deal with toxicity mechanisms. Based on this review, we propose putative Adverse Outcome Pathways (AOPs) applicable to microplastic management to understand microplastic toxicity. We matched toxicity mechanisms and apical endpoints to a key event (KE) and adverse outcome (AO) information from the AOP Wiki. Overall, our results suggest that the molecular initiating event (MIE) was reactive oxygen species (ROS) formation and the AO was increased mortality, decreased growth and feeding, and reproduction failure. However, there are a limited number of studies on toxicity mechanisms of microplastics and, therefore, evidence concerning the relationship between KEs is not sufficient. Clearly, more studies on toxicity mechanisms are required to fill these gaps in data. This study also suggests that the AOP framework is a suitable tool to integrate existing data from various literature sources and can identify data gaps in microplastic toxicity mechanisms.

Neurotoxicity, Behavior, and Lethal Effects of Cadmium, Microplastics, and Their Mixtures on Pomatoschistus microps Juveniles from Two Wild Populations Exposed under Laboratory Conditions-Implications to Environmental and Human Risk Assessment

Microplastics (MPs) were found to modulate the toxicity of other pollutants but the knowledge on the topic is still limited. The goals of this study were to investigate the short-term toxicity of cadmium (Cd) to wild Pomatochistus microps juveniles, the potential modulation of acute Cd toxicity by 1-5 µm polyethylene MPs in this species, and possible differences of sensitivity to Cd and MPs-Cd mixtures between juveniles from two distinct wild populations. Juveniles were collected in the estuaries of Minho (M-est) and Lima (L-est) Rivers (NW Portugal). One 96 h bioassay with M-est juveniles and another one with L-est juveniles were carried out in laboratory conditions. Each bioassay had 12 treatments: control, 5 Cd concentrations, 1 MPs concentration, and 5 MPs-Cd mixtures. No significant differences in Cd-induced mortality between juveniles from distinct estuaries or between juveniles exposed to Cd alone and those exposed to MPs-Cd mixtures were found. The total 96h LC10 and LC50 of Cd alone were 2 mg/L (95% CI: 0-4 mg/L) and 8 mg/L (95% CI: 2-17 mg/L), respectively. Cd alone significantly decreased the post-exposure predatory performance (PEPP) of M-est (≥6 mg/L) and L-est juveniles (≥3 mg/L), and acetylcholinesterase (AChE) activity of M-est juveniles (13 mg/L). MPs alone (0.14 mg/L) significantly reduced the PEPP and AChE activity of L-est juveniles but not of M-est juveniles. MPs-Cd mixtures (3-13 mg/L of Cd + 0.14 mg/L of MPs) significantly inhibited the PEPP of juveniles from both estuaries and AChE of L-est estuary juveniles but not of M-est juveniles. Evidences of toxicological interactions, namely antagonism, between MPs and Cd were found. Overall, the results indicate that MPs modulated the sub-lethal toxic effects of Cd in wild P. microps juveniles, especially neurotoxicity. Moreover, the environmental conditions of the natural habitats to which juveniles were exposed during pre-developmental phases influence the sub-lethal toxicity of Cd, MPs, and their mixtures. The implications to environmental and human risk assessment are discussed and further research is needed.

Selective Ingestion and Egestion of Plastic Particles by the Blue Mussel (Mytilus edulis) and Eastern Oyster (Crassostrea virginica): Implications for Using Bivalves as Bioindicators of Microplastic Pollution

Microplastics (MP; 1 μm to 1 mm) of various shapes and compositions are ingested by numerous marine animals. Recently, proposals have been made to adopt bivalve molluscs as bioindicators of MP pollution. To serve as indicators of MP pollution, however, the proposed organisms should ingest, without bias, the majority of plastic particles to which they are exposed. To test this premise, eastern oysters, Crassostrea virginica, and blue mussels, Mytilus edulis, were offered variously sized polystyrene microspheres (diameters 19-1000 μm) and nylon microfibers (lengths 75-1075 × diameter 30 μm), and the proportion of each rejected in pseudofeces and egested in feces was determined. For both species, the proportion of microspheres rejected increased from ca. 10-30% for the smallest spheres to 98% for the largest spheres. A higher proportion of the largest microsphere was rejected compared with the longest microfiber, but similar proportions of microfibers were ingested regardless of length. Differential egestion of MP also occurred. As a result of particle selection, the number and types of MP found in the bivalve gut will depend upon the physical characteristics of the particles. Thus, bivalves will be poor bioindicators of MP pollution in the environment, and it is advised that other marine species be explored.

On Some Possible Ramifications of the "Microplastics in Fish" Case

Cases of research misconduct in the ecological and environmental sciences appear to be relatively rare. A controversial paper published in Science in 2016 documenting the effects of microplastics on the feeding and innate behaviours of fish larvae has recently been retracted, with the authors found guilty of scientific misconduct. In addition to the expected fallout, such as individual and institutional reputational damage from a research misconduct finding, this case has two possibly wider-ranging ramifications. Firstly, there may be a presumptive notion that a strong negative effect could be more successfully published than a neutral effect. This presumption would belie the true stringency and rigor of research adopted by workers in the field. Secondly, the case may have a negative impact on the public's perception of and trust in legitimate and good science that addresses critical environmental issues, such as anthropogenic climate change.

Can the Atlantic ghost crab be a potential biomonitor of microplastic pollution of sandy beaches sediment?

The objective of the present study was to test whether the Atlantic ghost crab Ocypode quadrata is a reliable biomonitor of microplastic (MP) pollution of beach sediments. To test the hypothesis (H1) that the sediment is the main source of MP ingestion, the proportion of MP types (hard plastic, microfibers, pellet, soft plastic, and extruded polystyrene foam) in the gut content was compared with that on the strandline. The types of MPs in the gut content and sediment had similar proportions; black (~49%) and blue (~45%) microfibers were responsible for this similarity (55%), hence confirming H1. However, the second hypothesis (H2) that prevalence of MP in the gut content is related to its density on beach with distinct urbanization degree was not accepted. These results indicate that high trophic plasticity of the ghost crab and, consequently, multiple-sources of contamination may interfere with its use as a biomonitor of MP pollution.

Ingestion, egestion and post-exposure effects of polystyrene microspheres on marine medaka (Oryzias melastigma)

Microplastics (MPs) are of environmental concern due to their bioavailability and potential impacts on a wide range of marine biota. In this study, we investigated the ingestion, bioaccumulation and egestion of fluorescent polystyrene (PS) micospheres (10 μm) in both larvae and adults of marine medaka (Oryzias melastigma), with or without food supply. The post-exposure effects of non-fluorescent PS (10 μm) on the survival, growth and reproduction of medaka larvae were also explored. Results showed that the PS microspheres could be ingested by both larvae and adults during the 48 h-exposure. Notably, feeding status was found to significantly affect the ingestion in medaka adults, which was not observed in the larvae. The egestion process of PS was rapid during the first recovery day but there was still certain percent of particles retained in digestive tracts at the end of 7 d recovery for either larvae or adults. After a 14 d pre-exposure with the non-fluorescent PS microspheres, the subsequent survival, growth and reproduction of medaka larvae were all significantly affected at the end of 120 d of experiment without PS. Overall, these results indicate that fishes might ingest or retain more MPs if the environmental abundance of MPs continues to increase while the available food decreases. Medaka fishes in larval stage have no capacity to select natural food sources like the adults. The chronic and "legacy effect" of MPs might also be a problem worthy paid more attention in future research instead of acute and immediate effect studies.

The influence of microplastics pollution on the feeding behavior of a prominent sandy beach amphipod, Orchestoidea tuberculata (Nicolet, 1849)

Pollution by microplastics has become a global threat affecting coastal habitats such as sandy beaches and their resident macrofauna. The goal of this study was to assess the influence of microplastics on the feeding behavior and growth rate of a widespread sandy beach amphipod, Orchestoidea tuberculata. These organisms were exposed to artificial food prepared with Poly(styrene-co-divinylbenzene) microspheres (8 μm particle size) at 3 different concentrations (0%, 5% and 10%). The amphipods consumed significantly more food when the concentration of microplastics was 0% and significantly less when the concentration was 10%, both in trials in which they had a choice (preference experiments) and those in which they did not have a food choice. In contrast to this, the amphipod's absorption efficiency and estimated growth rates were not significantly affected by the concentration of microplastics. Combined, these results indicate that high microplastics concentrations (e.g. 10%) cause a reduction in the amphipod's consumption rates and, indirectly, may affect the role of this species as a main consumer of stranded seaweeds in sandy beaches ecosystems.

Uptake and effects of different concentrations of spherical polymer microparticles on Artemia franciscana

Artemia cysts have a huge economic importance for the aquaculture sector due to the fact that they are used as live feed for larviculture. Microplastics (MPs) are common and emergent pollutants in the aquatic environments, with unknown and potential long-term effects on planktonic species such as Artemia spp. When used as live feed, Artemia could transfer contaminants to fish along the food chain, with possible adverse effects on human health through their consumption. This study aims to assess the uptake of different concentrations of spherical polymer microparticles (FRM) (1-5 μm diameter) and their associated chronic effects on feeding, growth, mortality, and reproductive success from juvenile to adult stage of brine shrimp Artemia franciscana. Individuals were exposed for 44 days to 0.4, 0.8 and 1.6 mg.L^-1 of FRM. No significant detrimental effects on growth, ingestion and mortality rates of A. franciscana were observed in all tested conditions. However, reproductive success was strongly affected by the increase of MP concentrations. The results of the present study showed that A. franciscana juveniles and adults were able to survive different experimental MP concentrations, but their reproductive success and progeny were significantly impacted by exposure to FRM particles.

A case study investigating temporal factors that influence microplastic concentration in streams under different treatment regimes

Microplastics, particles less than 5 mm in size, are an emerging contaminant in waterways worldwide. Most microplastic studies focus on spatial trends in concentration, but in systems as dynamic as rivers, to draw conclusions from existing spatial studies, we must first examine how microplastic concentrations may change with time and flow conditions. In this study, we investigate how microplastic concentrations change over a 24-h period and between seasonally high and low flows. We do this in two streams, controlling for wastewater treatment strategy: one stream in a watershed where waste is treated with septic systems and the other receiving wastewater treatment plant effluent. We hypothesized that a stream with wastewater treatment plant effluent would exhibit higher and more variable microplastic concentrations than a stream in a watershed with septic systems. Results indicate, however, that there is no significant difference between the two streams despite their differing treatment strategies. Additionally, no significant variation in concentrations was measured over two 24-h sampling campaigns. There was, however, significantly higher concentrations measured in summer low flow conditions relative to spring high flow conditions across both sampled streams (p value <0.001), indicating that increases in stream discharge unrelated to storm events dilute and decrease measured microplastic concentrations. From this, we learn that pairing measured concentrations with a description of flow conditions at sampling time is a requisite for a robust microplastic literature that allows for comparisons between existing spatial studies and extrapolations to global loads.

Integrating physiological data with the conservation and management of fishes: a meta-analytical review using the threatened green sturgeon (Acipenser medirostris)

Reversing global declines in the abundance and diversity of fishes is dependent on science-based conservation solutions. A wealth of data exist on the ecophysiological constraints of many fishes, but much of this information is underutilized in recovery plans due to a lack of synthesis. Here, we used the imperiled green sturgeon (Acipenser medirostris) as an example of how a quantitative synthesis of physiological data can inform conservation plans, identify knowledge gaps and direct future research actions. We reviewed and extracted metadata from peer-reviewed papers on green sturgeon. A total of 105 publications were identified, spanning multiple disciplines, with the primary focus being conservation physiology (23.8%). A meta-analytical approach was chosen to summarize the mean effects of prominent stressors (elevated temperatures, salinity, low food availability and contaminants) on several physiological traits (growth, thermal tolerance, swimming performance and heat shock protein expression). All examined stressors significantly impaired green sturgeon growth, and additional stressor-specific costs were documented. These findings were then used to suggest several management actions, such as mitigating salt intrusion in nursery habitats and maintaining water temperatures within optimal ranges during peak spawning periods. Key data gaps were also identified; research efforts have been biased towards juvenile (38.1%) and adult (35.2%) life-history stages, and less data are available for early life-history stages (embryonic, 11.4%; yolk-sac larvae, 12.4%; and post yolk-sac larvae, 16.2%). Similarly, most data were collected from single-stressor studies (91.4%) and there is an urgent need to understand interactions among stressors as anthropogenic change is multi-variate and dynamic. Collectively, these findings provide an example of how meta-analytic reviews are a powerful tool to inform management actions, with the end goal of maximizing conservation gains from research efforts.

Size and shape matter: A preliminary analysis of microplastic sampling technique in seawater studies with implications for ecological risk assessment

Microplastic particles (MPs) are widely distributed in seawater. Fibrous MPs (microfibres) are often reported as the most commonly encountered shape of particle. To estimate MP concentrations in seawater, samples are often collected using towed nets (generally 300-350-μm mesh) and may underestimate the amount of microfibres present, which may pass through the mesh due to their narrow width. We compared the potential microplastic particle (PMP) concentration estimates provided by two different seawater sampling methods conducted at three commercial shellfish farms and three unfarmed sites in Baynes Sound, British Columbia, Canada. The methods were: 10-L bucket samples sieved through 63-μm mesh in situ and subsequently filtered through an 8-μm polycarbonate membrane; and 1-L bulk samples collected in jars and subsequently filtered to 8 μm. The jar samples yielded PMP concentrations averaging approximately 8.5 times higher than the bucket samples per L of water (at the site level), largely driven by differences in the number of microfibres. There was no significant difference in PNP concentration between shellfish farms and unfarmed sites. An analysis of MP concentrations and mesh sizes reported in the literature suggests that using a 300-350-μm mesh may underestimate total MP concentrations by one to four orders of magnitude compared with samples that are filtered through much smaller mesh sizes (e.g. <100 μm), despite the effect of sample volume. Particles <300 μm in diameter make up a large component of MPs commonly found in fish and invertebrates. As such, common sampling practices fail to adequately measure a biologically relevant class of MPs, thereby undermining the ability to quantify ecological risk. We suggest that seawater sampling methods be designed to filter to <10 μm (the approximate width of many microfibres), either using pressurized pumps for large-volume samples, or by using sufficient replication of small-volume discrete samples.

Effects of microplastics on microalgae populations: A critical review

Microplastics are persistent contaminants accumulating in the environment. Aquatic ecosystems have been studied worldwide, revealing ubiquitous contamination with microplastics. Microalgae, one of the most important primary producers in aquatic ecosystems, could suffer from microplastic contamination, leading to larger impacts on aquatic food webs. Nonetheless, little is known about the toxic effects of microplastics on microalgae populations. Thus, the objective of this review was to identify these effects and the impacts of microplastics on microalgae populations based on currently available literature, also identifying knowledge gaps. Even though microplastics seem to have limited effects on parameters such as growth, chlorophyll content, photosynthesis activity and reactive oxygen species (ROS), current environmental concentrations are not expected to induce toxicity. Even so, microplastics could disrupt population regulation mechanisms, by reducing the availability or absorption of nutrients (bottom-up) or reducing the population of predator species (top-down). Microplastics' properties can also influence the effects on microalgae, with smaller sizes and positive surface charges having higher toxicity. Therefore, more research is needed to better understand the effects of microplastics on microalgae, such as adaptation strategies, effects on population dynamics and microplastics properties influencing toxicity.

Microplastic exposure and effects in aquatic organisms: A physiological perspective

The impact of microplastics (MPs) on aquatic life, given their ubiquitous presence in the water compartment, represents a growing concern. Consistently, scientific knowledge is advancing rapidly, although evidence on actual adverse effects is still highly fragmented. This paper summarizes the recent literature on MP impacts on aquatic organisms in an attempt to link routes of uptake, possible alterations of physiological processes, and outcomes at different levels of biological organization. Animal feeding strategies and MP biodistribution is discussed, alongside with relevant effects at molecular, cellular, and systemic level. Pathways from animal exposure to apical physiological responses are examined to define the relevance of MPs for animal health, and to point out open questions and research gaps. Emphasis is given to emerging threats posed by leaching of plastic additives, many of which have endocrine disruption potential. The potential role of MPs as substrates for microorganism growth and vehicle for pathogen spreading is also addressed.

The Multixenobiotic resistance system as a possible protective response triggered by microplastic ingestion in Mediterranean mussels (Mytilus galloprovincialis): Larvae and adult stages

The emerging paradigm on plastic pollution in marine environments is that microsize particles (MPs) have far more subtle effects than bigger fragments, given their size range overlapping with that of particles ingested by filter-feeders. The impacts include gut blockage, altered feeding and energy allocation, with knock-on effects on widespread physiological processes. This study investigated whether ingestion of polystyrene MPs (PS-MPs) triggers protective processes in marine mussels. The Multixenobiotic resistance (MXR) system is a cytoprotective mechanism acting as an active barrier against harmful xenobiotics and a route of metabolite detoxification. Both larvae and adults were employed in laboratory experiments with different concentrations of 3-μm PS-MPs (larvae), and 3-μm and 45-μm PS-MPs (adults) matching size range of planktonic food through the mussel lifecycle. Embryos grown in the presence of 3-μm PS-MPs showed significant reduction of MXR activity and down-regulation of ABCB and ABCC transcripts encoding the two main MXR-related transporters P-glycoprotein and the Multidrug resistance-related protein, respectively. In adults, effects of PS-MPs were assessed in haemocytes and gills, which showed different modulation of MXR activity and ABCB/ABCC expression according to MP size (haemocyte and gills) or particle concentration (haemocyte). These data showed that modulation of MXR activity is part of a generalized response triggered by particle ingestion.

Research and management of plastic pollution in coastal environments of China

Marine plastic waste has become an ever-increasing environmental threat in the world's ocean largely due to their unique properties and ubiquitous occurrence. They include diverse forms of land- and ocean-based sources of plastics and are estimated to account for up to 85% of marine debris worldwide. As secondary pollutants, marine microplastic particles (<5 mm) are derived from pellet loss and degradation of macroplastics. Up to now, several reports have proposed negative impacts of both macro-sized and micro-sized plastics on marine biota. As one of the rapidly growing economies, China is the topmost contributor of plastic waste in the world. China's massive impact on the plastic levels of the ocean are a definite cause of concern and is developing multiple economic, environmental and biological complications. The research of plastics impact on coastal environments in China is only incipient. Here we review the available information on plastic waste, their impacts on marine biota and human health, and Chinese government policies and management initiatives. Although Chinese coastal environments (surface water, coastal sediments, water column) are affected by microplastics pollution, both from land-based and sea-based activities, their impacts on marine biota remain to be elucidated. Though national-level policies are modern and well suited for minimizing the impacts of plastic pollution, there is hardly any legislation for containment of microplastic pollution. Our objective is to review and summarize the information about the occurrence, impacts, and management of plastic pollution in the Chinese coastal environments in order to comprehend their widespread repercussions. MAIN FINDING: Microplastics are increasingly being detected and quantified in Chinese coastal environments and legislation for containment of such pollution is highly recommended.

A catchment-scale perspective of plastic pollution

Plastic pollution is distributed across the globe, but compared with marine environments, there is only rudimentary understanding of the distribution and effects of plastics in other ecosystems. Here, we review the transport and effects of plastics across terrestrial, freshwater and marine environments. We focus on hydrological catchments as well-defined landscape units that provide an integrating scale at which plastic pollution can be investigated and managed. Diverse processes are responsible for the observed ubiquity of plastic pollution, but sources, fluxes and sinks in river catchments are poorly quantified. Early indications are that rivers are hotspots of plastic pollution, supporting some of the highest recorded concentrations. River systems are also likely pivotal conduits for plastic transport among the terrestrial, floodplain, riparian, benthic and transitional ecosystems with which they connect. Although ecological effects of micro- and nanoplastics might arise through a variety of physical and chemical mechanisms, consensus and understanding of their nature, severity and scale are restricted. Furthermore, while individual-level effects are often graphically represented in public media, knowledge of the extent and severity of the impacts of plastic at population, community and ecosystem levels is limited. Given the potential social, ecological and economic consequences, we call for more comprehensive investigations of plastic pollution in ecosystems to guide effective management action and risk assessment. This is reliant on (a) expanding research to quantify sources, sinks, fluxes and fates of plastics in catchments and transitional waters both independently as a major transport routes to marine ecosystems, (b) improving environmentally relevant dose-response relationships for different organisms and effect pathways, (c) scaling up from studies on individual organisms to populations and ecosystems, where individual effects are shown to cause harm and; (d) improving biomonitoring through developing ecologically relevant metrics based on contemporary plastic research.

Depuration reduces microplastic content in wild and farmed mussels

Plastic pollution is a pervasive problem to marine life. This study aimed (1) to investigate levels of microplastic in wild and farmed mussels (Perna perna), and (2) to assess the effectiveness of depuration in reducing microplastics. Wild and farmed mussels were sampled from Guanabara Bay (Southwestern Atlantic). Four treatments were compared (N = 10 mussels/treatment): wild non-depurated mussels, wild depurated mussels, farmed non-depurated mussels, and farmed depurated mussels. Up to 31.2 ± 17.8 microplastics/mussel (≥0.45 μm) were detected (means ± SD), and microplastics were present in all 40 individuals analyzed. Nylon fibers were more abundant than polymethyl methacrylate (PMMA) fragments. Blue, transparent, and red nylon fibers were more abundant in both wild and farmed mussels. Although 93 h-depuration significantly reduced microplastics (ANOVA, p = 0.02) in both wild (46.79%) and farmed mussels (28.95%), differences between farmed and wild mussels were not significant (p > 0.05). Depuration was more effective in removing blue fibers. Our results highlight the importance of depuration in reducing microplastic pollution in seafood.

Microfibres from apparel and home textiles: Prospects for including microplastics in environmental sustainability assessment

Textiles release fibres to the environment during production, use, and at end-of-life disposal. Approximately two-thirds of all textile items are now synthetic, dominated by petroleum-based organic polymers such as polyester, polyamide and acrylic. Plastic microfibres (<5 mm) and nanofibres (<100 nm) have been identified in ecosystems in all regions of the globe and have been estimated to comprise up to 35% of primary microplastics in marine environments, a major proportion of microplastics on coastal shorelines and to persist for decades in soils treated with sludge from waste water treatment plants. In this paper we present a critical review of factors affecting the release from fabrics of microfibres, and of the risks for impacts on ecological systems and potentially on human health. This review is used as a basis for exploring the potential to include a metric for microplastic pollution in tools that have been developed to quantify the environmental performance of apparel and home textiles. We conclude that the simple metric of mass or number of microfibres released combined with data on their persistence in the environment, could provide a useful interim mid-point indicator in sustainability assessment tools to support monitoring and mitigation strategies for microplastic pollution. Identified priority research areas include: (1) Standardised analytical methods for textile microfibres and nanofibres; (2) Ecotoxicological studies using environmentally realistic concentrations; (3) Studies tracking the fate of microplastics in complex food webs; and (4) Refined indicators for microfibre impacts in apparel and home textile sustainability assessment tools.

Microplastic ingestion ubiquitous in marine turtles

Despite concerns regarding the environmental impacts of microplastics, knowledge of the incidence and levels of synthetic particles in large marine vertebrates is lacking. Here, we utilize an optimized enzymatic digestion methodology, previously developed for zooplankton, to explore whether synthetic particles could be isolated from marine turtle ingesta. We report the presence of synthetic particles in every turtle subjected to investigation (n = 102) which included individuals from all seven species of marine turtle, sampled from three ocean basins (Atlantic [ATL]: n = 30, four species; Mediterranean (MED): n = 56, two species; Pacific (PAC): n = 16, five species). Most particles (n = 811) were fibres (ATL: 77.1% MED: 85.3% PAC: 64.8%) with blue and black being the dominant colours. In lesser quantities were fragments (ATL: 22.9%: MED: 14.7% PAC: 20.2%) and microbeads (4.8%; PAC only; to our knowledge the first isolation of microbeads from marine megavertebrates). Fourier transform infrared spectroscopy (FT-IR) of a subsample of particles (n = 169) showed a range of synthetic materials such as elastomers (MED: 61.2%; PAC: 3.4%), thermoplastics (ATL: 36.8%: MED: 20.7% PAC: 27.7%) and synthetic regenerated cellulosic fibres (SRCF; ATL: 63.2%: MED: 5.8% PAC: 68.9%). Synthetic particles being isolated from species occupying different trophic levels suggest the possibility of multiple ingestion pathways. These include exposure from polluted seawater and sediments and/or additional trophic transfer from contaminated prey/forage items. We assess the likelihood that microplastic ingestion presents a significant conservation problem at current levels compared to other anthropogenic threats.

Microplastic ingestion by riverine macroinvertebrates

Although microplastics are a recognised pollutant in marine environments, less attention has been directed towards freshwater ecosystems despite their greater proximity to possible plastic sources. Here, we quantify the presence of microplastic particles (MPs) in river organisms upstream and downstream of five UK Wastewater Treatment Works (WwTWs). MPs were identified in approximately 50% of macroinvertebrate samples collected (Baetidae, Heptageniidae and Hydropsychidae) at concentrations up to 0.14 MP mg tissue^-1 and they occurred at all sites. MP abundance was associated with macroinvertebrate biomass and taxonomic family, but MPs occurred independently of feeding guild and biological traits such as habitat affinity and ecological niche. There was no increase in plastic ingestion downstream of WwTW discharges averaged across sites, but MP abundance in macroinvertebrates marginally increased where effluent discharges contributed more to total runoff and declined with increasing river discharge. The ubiquity of microplastics within macroinvertebrates in this case study reveals a potential risk from MPs entering riverine food webs through at least two pathways, involving detritivory and filter-feeding, and we recommend closer attention to freshwater ecosystems in future research.

Biodegradation of Microplastic Derived from Poly(ethylene terephthalate) with Bacterial Whole-Cell Biocatalysts

At present, the pollution of microplastic directly threatens ecology, food safety and even human health. Polyethylene terephthalate (PET) is one of the most common of microplastics. In this study, the micro-size PET particles were employed as analog of microplastic. The engineered strain, which can growth with PET as sole carbon source, was used as biocatalyst for biodegradation of PET particles. A combinatorial processing based on whole-cell biocatalysts was constructed for biodegradation of PET. Compared with enzymes, the products can be used by strain growth and do not accumulated in culture solution. Thus, feedback inhibition of products can be avoided. When PET was treated with the alkaline strain under high pH conditions, the product concentration was higher and the size of PET particles decreased dramatically than that of the biocatalyst under neutral conditions. This shows that the method of combined processing of alkali and organisms is more efficient for biodegradation of PET. The novel approach of combinatorial processing of PET based on whole-cell biocatalysis provides an attractive avenue for the biodegradation of micplastics.

Toxicities of polystyrene nano- and microplastics toward marine bacterium Halomonas alkaliphila

Nano- and microplastics have been shown to cause negative effects on marine organisms. However, the toxicities of nano- and microplastics toward marine bacteria are poorly understood. In this study, we investigated the toxic effects of polystyrene nano- and microplastics on the marine bacterium Halomonas alkaliphila by determining growth inhibition, chemical composition, inorganic nitrogen conversion efficiencies and reactive oxygen species (ROS) generation. The results showed that both nano- and microplastics inhibited the growth of H. alkaliphila in high concentrations, while nanoplastics rather than microplastics influenced the growth inhibition, chemical composition and ammonia conversion efficiencies of H. alkaliphila at concentration of 80 mg/L. The ROS generation indicated oxidative stress induced by nano- but not microplastics, and the oxidative stress induced by nanoplastics may provide a significant effect on bacteria. Furthermore, the positively charged nanoplastics (amine-modified 50 nm) induced higher oxidative stress toward bacteria than that induced by negatively charged nanoplastics (non-modified 55 nm). The increased extracellular polymeric substances as evidenced by transmission electron microscope (TEM) observation suggested the possible bacterial protective mechanisms. The present study illustrates for the first time the impact of plastics debris on the inorganic nitrogen conversion efficiencies of marine bacteria. Our findings highlight the effects of microplastics on the ecological function of marine organisms.

No evidence of microplastic impacts on consumption or growth of larval Pimephales promelas

Microplastics are an abundant pollutant in aquatic systems, but little is known regarding their effects on larval fish. We conducted foraging and growth experiments to observe how increasing densities of microplastics (polyethylene microspheres) impact the foraging and growth of Pimephales promelas larvae. We found minimal impacts on larval consumption of Artemia nauplii in the consumption study, as well as little impact on total length after 30 d of the growth experiment. Environ Toxicol Chem 2018;37:2912-2918. © 2018 SETAC.

Effect of Microplastic Amendment to Food on Diet Assimilation Efficiencies of PCBs by Fish

Diet assimilation efficiencies (AEs) of polychlorinated biphenyls (PCBs) absorbed to microplastics and food were determined in goldfish ( Carassius auratus). Microplastics were spiked with 14 environmentally rare PCBs and incorporated into fish pellets previously spiked with a technical PCB mixture (Aroclor 1254). Five diet treatments were created having microplastic contents of 0, 5, 10, 15, 20, and 25% and fed to fish within 24 h of the diet creation. Fish from each treatment were fed a microplastic amended food pellet and PCB AEs were determined by mass balance. Microplastic-associated PCBs had lower AEs (geomean 13.36%) compared to food matrix-associated PCBs (geomean 51.64%). There were interactions between PCB AEs and the microplastic content of the diet. PCBs affiliated with microplastics became more bioavailable with increasing microplastic content of food while food matrix-associated PCB bioavailability declined when microplastic contents exceeded 5%. Despite controlling for microplastic-food contact time, there was some evidence for redistribution of lower K_OW food matrix-associated PCBs onto microplastics causing a decrease in their AE relative to nonplastic and low plastic containing diets. The low bioavailability of microplastic-associated PCBs observed in the present study provides further support to indicate that microplastics are unlikely to increase POPs bioaccumulation by fish in aquatic systems.

Marine microplastic debris: An emerging issue for food security, food safety and human health

Recent studies have demonstrated the negative impacts of microplastics on wildlife. Therefore, the presence of microplastics in marine species for human consumption and the high intake of seafood (fish and shellfish) in some countries cause concern about the potential effects of microplastics on human health. In this brief review, the evidence of seafood contamination by microplastics is reviewed, and the potential consequences of the presence of microplastics in the marine environment for human food security, food safety and health are discussed. Furthermore, challenges and gaps in knowledge are identified. The knowledge on the adverse effects on human health due to the consumption of marine organisms containing microplastics is very limited, difficult to assess and still controversial. Thus, assessment of the risk posed to humans is challenging. Research is urgently needed, especially regarding the potential exposure and associated health risk to micro- and nano-sized plastics.