Microplastics in Seafood and the Implications for Human Health — TEI-tagged view

Madeleine SmithpersName, David C. LovepersName, Chelsea M. RochmanpersName, Roni NeffpersName (2018date). “Microplastics in Seafood and the Implications for Human Health.” Current Environmental Health Reportstitle·venue.

Object of study — human exposure to microplasticsterm through seafood, and what is known about its health effects

Research question — whether microplasticsterm ingested with seafood harm human health, and what the evidence for that currently supports

Contribution — a reviewterm·mth that characterises current knowledge and names its gaps, written into a public-health tension: seafood consumption is being encouraged at the same time as this concern is being raised

Full text — tagged

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# Abstract Purpose of Reviewterm·mth We describe evidence regarding human exposure to microplasticsterm via seafood and discuss potential health effects.

Recent Findings Shellfish and other animals consumed whole pose particular concern for human exposure. If there is toxicity, it is likely dependent on doseterm·var, polymer typeterm·var, size, surface chemistry, and hydrophobicityterm.

Summary Human activity has led to microplasticterm contamination throughout the marine environment. As a result of widespread contamination, microplasticsterm are ingested by many species of wildlife including fish and shellfish. Because microplasticsterm are associated with chemicals from manufacturing and that sorb from the surrounding environment, there is concern regarding physical and chemical toxicity. Evidence regarding microplasticterm toxicity and epidemiology is emerging. We characterize current knowledge and highlight gaps. We also recommend mitigation and adaptation strategies targeting the life cycle of microplasticsterm and recommend future research to assess impacts of microplasticsterm on humans. Addressing these research gaps is a critical priority due to the nutritional importance of seafood consumption.

Keywords: Microplasticsterm, Toxicology, Ocean, Seafood, Fish, Human health impacts Introduction Since the 1960s, plastic production has increased by approximately 8.7% annually, evolving into a $600 billion global industry [1, 2]. Approximately eight million metric tons of plastics enter the oceans annually [2], and conservative estimates suggest 5.25 trillion plastic particles currently circulate in ocean surface waters [3•]. While some plastics enter oceans from maritime operations, 80% is suspected to originate from land-based sources [1]. Discarded plastic materials enter the marine environment as trash, industrial discharge, or litter through inland waterways, wastewater outflows, and transport by winds or tides [4]. Waste generation and waste leakage are inextricably linked and proportionally associated with economic development, local infrastructure, and legislation. Today, uncollected waste accounts for 75% of these land-based discharges, while the remaining 25% comes from within the waste management system [4].

When plastics enter the ocean, the rate of degradation and persistence of plastics varies by polymer, shape, density, and the purpose of the plastic itself [3•]. These characteristics also govern where in the water column plastics may be found. For example, more buoyant plastics are more likely to be carried by ocean currents and wind across the environment [3•]. Additionally, when plastics are exposed to natural forces like sunlight and wave action, plastics will degrade into microplasticsterm—defined as plastic particles under 5 mm in size. This definition commonly includes plastic pieces in the nano-scaleterm, < 1 μm in size. The extent of plastic degradation depends on factors including polymer typeterm·var, age, and environmental conditions like weathering, temperature, irradiation, and pH [5]. Over time, plastic particles contaminate the marine ecosystem and the food chain, including foodstuffs intended for human consumption [6]. In vivo studies have demonstrated that nanoplastics can translocate to all organs [6]. Evidence is evolving regarding relationships between micro- and nanoplastic exposure, toxicology, and human health.

Nutritional authorities advise Americans to double their seafood consumption; however, awareness or concerns about microplasticsterm in seafood could lead consumers to reduce their consumption. Research to understand and reduce human health risks is critical in order to simultaneously protect consumers and support their nutritional health.

This reviewterm·mth begins with a background on microplasticsterm, ocean dispersal, physical and chemical properties, and degradation. Where relevant, we provide information about nanoplastics. We then explore the life cycle of microplasticsterm including their toxicity and epidemiology in humans and animals, strategies for mitigation and adaptation, and research needs.

Approach We conducted an unstructured literature reviewterm·mth using PubMed, Google Scholar, Nature’s database, and Science Direct, focused on literature published after 2004 (the year the term, “microplasticterm,” was introduced). We employed the following keywords: microplasticsterm, microdebris, primary microplasticsterm, secondary microplasticsterm, nanoplastics, pellets, marine debris and plastics, microbeadsterm, marine biota, food web, harmful effects, environmental policies, and industry. These sites were searched until saturation occurred. Websites of organizations with interest in this topic were also explored: Food and Agriculture Organization (FAO) and The Group of Experts on Scientific Aspects of Marine Environmental Protection (GESAMP) of the United Nations, European Food Safety Authority (EFSA), United States Department of Agriculture (USDA), Food and Drug Administration (FDA), and National Oceanic and Atmospheric Administration (NOAA). The resultant articles were organized and synthesized into an overview describing the current state of the science. Insights from this reviewterm·mth were used to identify recommendations for future research and mitigation.

Background on Microplasticsterm Sources and Distribution In the marine environment, microplasticsterm are a heterogeneous group of particles (< 5 mm), varying in size, shape, and chemical composition. They are found in sediment, on the sea surface, in the water column, and in wildlife [7, 8]. Table 1 describes the most common plastic polymer typesterm·var in the marine environment. Of these, the most common plastic types manufactured are polyethylene and polypropylene [7].

Table 1.

Common application of plastic found in the marine environment and the frequency of polymer typeterm·var identified in 42 studies of microplasticterm debris sampled at sea or in marine sediment | Plastic resin type (acronym) | Application | Percent of studies ( n) that identified specific polymers | | --- | --- | --- | | Polyethylene, high-density (PE-HD) | Milk and juice jugs | 79 (33) | | Polyethylene, low-density (PE-LD) | Plastic bag, six pack rings, bottles, netting, and drinking straws | | Polypropylene (PP) | Rope, bottle caps, and netting | 64 (27) | | Polystyrene (PS) | Plastic utensils, food containers | 33 (17) | | Polyamide (PA) | Nylon fabric | 17 (7) | | Polyester (PES) | Polyester fabric | 10 (4) | | Polyvinylchloride (PVC) | Film, containers and pipes | 5 (2) | | Polyethylene terephthalate (PET) | Plastic beverage bottles | 2 (1) | Adapted from [9•, 10] Microplasticsterm are often categorized into primary and secondary types. Primary microplasticsterm were originally produced to be < 5 mm in size, while secondary microplasticsterm result from the breakdown of larger itemsterm. Microbeadsterm in personal care products are an example of primary microplasticsterm [9•]. While they are now being phased out globally, in 2015, an estimated eight billion microbeadsterm were released into aquatic habitats from the USA daily [10]. Other sources of primary microplasticsterm include industrial abrasivesterm and pre-production plastic pelletsterm used to make larger plastic items. Sources of secondary microplasticsterm include microfibersterm from textiles, tire dustterm, and larger plastic items that degrade and, consequently, fragment into microplasticterm particles, mostly due to weathering degradationterm [11]. Even if humans halted plastic production and prevented plastic waste dumping, marine microplasticsterm would continue to increase as larger plastic litter degrades into secondary microplasticsterm [9•].

Physical and Chemical Properties Microplasticsterm in the marine environment are typically found as pellets, fragments, or fibers and are composed of diverse polymers [12], some denser than seawater and expected to sink to the seafloor. These include polyamide, polyester, polymerizing vinyl chloride (PVC), and acrylic, among others. Others are lighter than seawater and are often found floating at the surface, including polyethylene, polypropylene, and polystyrene.

Plastic products are composed of monomers joined to make the polymer structure and additiveterm chemicals. During production, plastic is processed with additivesterm to provide specific properties [13]. Several thousand distinct additivesterm are used, including plasticizers, flame retardants, pigments, antimicrobial agents, heat stabilizers, UV stabilizers, fillers, and flame retardants such as polybrominated diphenyl ethers (PBDEs) [13, 14••, 15]. Additivesterm account for approximately 4% of the weight of microplasticsterm [14••]. Once created, plastic polymers are described as non-toxicterm·def because they are not reactive and generally cannot easily transport across biological membranes due to their size [16]. However, non-polymeric substances, like chemical additivesterm or residual monomers, can be hazardous to human health and the environment when they leach from the plastic polymer matrix [6]. As plastics progressively degrade, the surface area to volume ratio increases and additiveterm chemicals are expected to leach [17]. Leached chemicals may bioaccumulate in animals from seawater [17]. For organisms that have directly ingested microplasticsterm, the uptake rate of additiveterm chemicals by an organism’ gastrointestinal tract is primarily influenced by the chemical fugacity gradientterm between the organisms’ tissues and the plastic, the gut retention timeterm of the microplasticsterm, and the material-specific kinetic factorsterm [18].

In addition to additiveterm chemicals being associated with plastic debris, microplasticsterm in the ocean accumulate persistent organic pollutantsterm (POPs) such as polychlorinated biphenylsterm (PCBs), polycyclic aromatic hydrocarbonsterm (PAHs), and organochlorine pesticidesterm like dichlorodiphynyltrichloroethane (DDT) or hexachlorobenzene (HCB) from the water [18, 19]. These have a greater affinity for plastic than water, and concentrations on microplasticsterm are orders of magnitude greater than in surrounding water [19, 20]. PBDEs are human-made flame-retardant chemicals. PBDEs enter the marine environment mainly via discarded or leaked consumer goods or municipal waste. Plastic deposited on beaches from the marine environment have been found to contain from 0.03 to 50 ng/g PBDE [17].

The global distribution of chemicals in the marine environment may affect environmental and human health, but microplasticsterm do not represent the only exposure pathway. In fact, microplasticsterm may represent a relatively small contributor to the total risk as there are many other sources for chemical exposure [18]. For example, the total dietary intake of PCBs from microplasticsterm is likely minimal compared to that from other sources, as identified in Table 2 [6]. For other chemicals, such as bisphenol A (BPA) or PBDEs, sources of exposure may be limited to or originate from microplasticterm degradation.

Table 2.

Comparing the estimated total dietary exposure to contaminants and additivesterm directly from microplasticsterm in seafood | Compound | Highest concentration in microplasticsterm | Calculated intake from microplasticsterm (pg/kg bw/day) | Total intake from the diet (pg/kg bw/day) | Ratio intake microplasticterm/total dietary intake (pg/kg bw/day) (%) | | --- | --- | --- | --- | --- | | Contaminants | | Non-dioxin like PCBs | 2970 | 0.3 | – | – | | EFSA, 2012 | – | – | 4300a | 0.007 | | JECFA, 2016 | – | – | 1000a | 0.03 | | PAHs | 44,800 | 4.5 | – | – | | EFSA, 2008 | – | – | 28,800b | 0.02 | | JECFA, 2006 | – | – | 4000c | 0.1 | | DDT | 2100 | 0.2 | – | – | | EFSA, 2006 | – | – | 5000d | 0.004 | | JECFA, 1960 | – | – | 100,000,000j | 0.0000002 | | Additivesterm/monomers | | Bisphenol A | 200 | 0.02 | | | | EFSA, 2015a | – | – | 130,000e | 0.00002 | | FAO/WHO, 2011 | – | – | 400,000f | 0.000005 | | PBDEs | 50 | 0.005 | – | – | | EFSA, 2011 | – | – | 700g | 0.0007 | | JECFA, 2006 | – | – | 185h | 0.003 | | NP | 2500 | 0.3 | NAi | – | | OP | 50 | 0.005 | NAi | – | Reproduced with permission from the Food and Agriculture Organization of the United Nations (2017) and Lusher et al. [6] PCBs polychlorinated biphenylsterm, PAHs polycyclic aromatic hydrocarbonsterm, DDT dichlorodiphenyltrichloroethane, PBDEs polybrominated diphenyl ethers, NP nonylphenol, OP octylphenol aLowest intake of six indicators of non-dioxin like PCBs, representing about 50% of all non-dioxin like PCBs bMedian intake (EFSA, 2008) cMean intake of benzo[ a]pyrene (JECFA) dLowest intake, DDT, and related compounds (EFSA, 2006) eAverage intake adults (EFSA, 2015a) fLowest intake FAO/WHO gLowest intake, sum of BDE-47, BDE-209, BDE-153, and BDE-154 (EFSA, 2011) hLowest intake JECFA iNA: dietary intake not available from EFSA or JECFA jProvisional tolerable daily intake (JECFA) Degradation of Marine Plastics Plastic is persistent in the marine environment because it is manufactured to be durable. Still, plastic polymers can be degraded slowly by microorganisms (e.g., Bacillus cereus, Micrococcus sp., or Corynebacterium), heat, oxidation, light, or hydrolysis, as identified in Table 3. The rate and extent of plastic degradation are determined by the environmental variables present.

Table 3.

Explanation of degradation processes [10] | Degradation process | Explanation | | --- | --- | | Biodegradation | Decomposition of organic materials by microorganisms | | Photo degradation | Action of light or photons, usually sunlight (UVA or greater, > 320 nm) | | Thermooxidative degradation | Slow oxidative, molecular deterioration at moderate temperatures | | Thermal degradation | High temperature cause molecular deterioration (not an environmental mechanism) | | Hydrolysis | Reaction with water | Microplasticsterm in the Food Chain Exposure to Microplasticsterm by Marine Animals A 2016 UN report documented over 800 animal species contaminated with plastic via ingestion or entanglement—a figure 69% greater than that reported in a 1977 reviewterm·mth, which estimated only 247 contaminated species [21, 22]. Of these 800 species, 220 have been found to ingest microplasticterm debris in natura [6].

Plastic ingestion occurs across taxa within different trophic levels, including marine mammals, fish, invertebrates, and fish-eating birds [8, 9•]. Plastic particles are often found concentrated in an organism’s digestive tract during carcass dissection and laboratory research. With preference to smaller particles, micro- and nanoplastics can persist in the animal’s body [6, 9•, 11, 22, 23] and translocate from the intestinal tract to the circulatory system or surrounding tissue [6].

Human Exposure Pathways Seafood consumption represents one pathway for human microplasticterm exposure. As of 2015, global seafood intake represented 6.7% of all protein consumed and approximately 17% of animal protein consumption [24]. Global per capita seafood consumption is over 20 kg/year; in the USA, it is 7 kg annually [25]. Global seafood trade in 2016 was $132.6 billion, and over 90% of US seafood was imported from geographic regions with significant waste leakage and pelagic plastic pollution [6]. Roughly half of seafood is farmed (e.g., aquaculture) and half is wild-caught. It is possible to control environmental conditions in aquaculture—by raising animals in ponds, tanks, or selected water bodies—and animals generally have shorter lifespans in aquaculture than in the wild, which could provide less opportunities and time for microplasticterm exposure and uptake. Due to few studies, there is uncertainty about the differences in microplasticsterm for farmed and wild fish and shellfish.

Because of their small size, microplasticsterm can be ingested by a wide variety of marine organisms. Ingestion may be direct or indirect via trophic transferterm (e.g., up the food web). Microplasticterm ingestion has been documented in planktonic organisms and larvae at the bottom of the food chain [25– 28], in small and large invertebrates [6, 7, 11, 29, 22] and in fish [6]. Trophic transferterm of microplasticsterm was observed in the predatory Crucian carps [30].

Microplasticsterm are found in many species intended for human consumption including invertebrates, crustaceans, and fish [23, 31•]. Plastic particles are often found concentrated in an organisms’ digestive tracts such that bivalves and small fish consumed whole are more likely to expose microplasticsterm to the human diet [9•]. For example, Fig. 1 illustrates movement of plastic from bivalve mollusks to the human diet. Van Cauwenberghe and Janssen [23] found farmed mussels had significantly higher microplasticterm concentrations (178 microfibersterm) than wild-caught mussels (126 microfibersterm) [23]. Additionally, RochmanpersName et al. identified the presence of microplasticsterm (> 500 μm) in commercially sold, wild-caught fish from markets in Makassar, Indonesia (28% of fish processed contained microplasticsterm), and California, USA (25% of commercial fish processed contained microplasticsterm) [31•]. Karami et al. investigated the potential presence of microplasticsterm in dried fish tissue: excised organs (viscera and gills) and eviscerated flesh (whole fish, excluding the viscera and gills) [32]. In four of 30 commonly consumed dried fish species, 36 of 61 isolated foreign particles were identified as plastic polymers [32]. In young and adult fish, Yifeng et al. demonstrated microplasticterm particle translocation from digestive tracts to the gills and liver of zebra fish ( Danio rerio), a common prey fish [33]. Microplasticterm particle translocation is also documented in European seabass and the common goby ( Pomatoschistus microps) [34]. Together, these studies demonstrate the presence of microplasticsterm, not the chemical constituents, in some seafood and indicate that the challenge could be widespread due to ubiquity in the environment and translocation potentially moving particles to animal parts typically eaten by humans.

Fig. 1.

 An example of how microplasticsterm could end up on a consumer’s plate (Reproduced with permission from Maphoto/Riccardo Pravettoni; originally published by Marine Litter GRID-ADRENAL, available at www.grida.no/resources/6915 Because water and salt are often extracted from the natural world, researchers investigated whether products made with these ingredients were also contaminated with nano- and microplasticsterm. They investigated and found microplasticsterm in beer [35], honey [36], and sea salt [37]. While the origin of these contaminants is uncertain, potential sources include atmospheric emission and uptake of microplasticsterm by the basic components of the food products, impurities introduced by processing materials, and the contaminants present in packaging [35]. Increasingly, scientific evidence outlines multiple pathways of microplasticterm exposure via food including evidence that microplasticsterm are present in species which contribute to global marine fisheries [6]. Accordingly, microplasticsterm pose an emerging food safety concern [6]. International scientific committees such as the Joint FAO/WHO Expert Committee on Food Additivesterm (JECFA) has not evaluated the food safety concern posed by microplasticsterm [6]; however, state-level environmental protection agencies have begun assessing the public health implications of microplasticsterm and nanoplastics [38].

Human health effects depend on exposure concentrations. Due to data gaps in microplasticterm research, there is insufficient information to assess the true amount of microplasticsterm humans may be exposed to via food. Researchers have predicted that the total microplasticterm intake from salts is at most 37 particles per individual annually [37]. Researchers have also estimated that a top European shellfish consumer eats approximately 11,000 plastic particles annually [23, 32, 37]. The implications are unknown.

Microplasticterm exposure also can confer exposure to associated chemicals. Few studies have assessed the relative contribution of microplasticterm exposure to additivesterm or chemicals found in organisms, versus alternative exposure pathways [39]. The EFSA monitors six indicators for non-dioxin-like PCBs in food to assess average total dietary exposure to PCBs. While the portion of exposure from microplasticsterm is unknown, fish, meat, and dairy contribute the greatest dietary exposure to PCBs, demonstrating a route of persistent exposure to animal tissue and trophic level transfer [40]. It was determined that total dietary PCB intake ranged from 1 to 83 ng PCB/kg bodyweight (bw) per day [41]. The average dietary intake of PAHs, using benzo[ a]pyrene as the reference marker, ranged from 4 to 10 ng/kg b.w. per day [41].

The US FDA residue limit for PCBs in fish and shellfish is 0.2 ppm for infants and juniors and 2 ppm for adults, corresponding to developmental effects, hormonal disruption, immune system, thyroid effects, and cancer [40]. The FDA has not established a limit governing the concentration of PAH content in foodstuffs [42]. In animals, the US Environmental Protection Agency has identified a reference doseterm·var for oral benzo( a)pyrene exposure, the most studied PAH, at 0.0003 mg/kg/day [42]. The oral reference doseterm·var applies to food and water and estimates the concentration at which adverse effects on human health are known to occur. Additional studies are needed to understand the biological processes influencing the release of chemicals associated with microplasticterm ingestion, and all routes of chemical exposure [43].

Today, evidence is mounting suggesting that microplasticterm ingestion or its associated chemicals pose a threat to marine animals [9•, 14••, 31•]. Understanding whether microplasticterm exposures impact human health requires standardized and reproducible methods for sampling, exposure characterization, ecological assessment, and human health assessment. There is no standard operating procedure for sampling occurring on beaches, in subtidal sediments, in biota, or within the water column.

Toxicity to Humans Microplasticsterm may cause harm to humans via both physical and chemical pathways. While it is not possible to completely disentangle these, we separate them for the purpose of this discussion.

Potential Physical Effects of Microplasticsterm Microplasticsterm are ubiquitous in the marine environment and are increasingly contaminating species in the marine environment. Given levels of seafood consumption worldwide, it is inevitable that humans are exposed to microplasticsterm at some level. The human body’s excretory system eliminates microplasticsterm, likely disposing of > 90% of ingested micro- and nanoplastic via feces [14••, 44•]. Factors affecting retention and clearance rates are the size, shape, polymer typeterm·var, and additiveterm chemicals of microplasticsterm ingested by humans [6]. The severity of adverse effects resulting from exposures depends on the nature of the toxic chemical, exposure characteristics, individual susceptibility, and hazard controls. The physical effects of accumulated microplasticsterm are less understood than the distribution and storage of toxicants in the human body, but preliminary research has demonstrated several potentially concerning impacts, including enhanced inflammatory response, size-related toxicity of plastic particles, chemical transfer of adsorbed chemical pollutants, and disruption of the gut microbiome [44•].

Surface functional groups, size, shape, surface charge, buoyancy, and hydrophobicityterm predict microplasticterm uptake [45]. Mammalian systems modeling suggests that microplasticsterm with certain characteristics can translocate across living cells, such as M cells or dendritic cells, to the lymphatic and/or circulatory system, accumulate in secondary organs, and impact the immune system and cell health [14••, 43, 45– 51]. Microplasticsterm may contact the airway or gastrointestinal epithelium demonstrating several routes of uptake and translocation, such as endocytic pathwaysterm and persorptionterm [44•]. Medical literature related to the impact of micro- and nanoplastics originating from surgical procedures and inhalation provides insight into the kinetic movement of plastics in humans [6]. For example, micro- and nanoplastics released from surgical materials mimic the effects of absorbed particles in the bloodstream and tissue [6], while inhaled particles interact with the same type of epithelial tissue as that involved during ingestion. For example, microbes colonized on the surface of ingested microplasticsterm may serve as a vector of harmful bacteria when ingested, potentially resulting in direct physiological effects (nutritional, toxicological, immunological, or developmental) on marine animals. Wright and Kelly predict that ingested microplasticsterm may cause inflammation in tissue, cellular proliferation, and necrosis and may compromise immune cells [44•]. While laboratory research has demonstrated that plastic microspheres ingested by blue crabs ( Callinectes sapidus) stimulate hemocyte aggregation and reduce their respiratory function [52]. Moreover, after ingesting microspheres, blue mussels experienced an immune response and the formation of granulomas [53]. The Japanese medaka ( Oryzias latipes) experienced hepatic stress after ingesting virgin polyethylene fragments [54]. Factors influencing the biological and ecological impact of microplasticsterm include presence, sizes, and frequency of engagement between biota-microplastics. More research is needed to further inform a risk assessment of the impact of microplasticsterm on seafood and consequently human health. It would be valuable to conduct a risk analysis monitoring microplasticsterm and the related chemical concentrations in seafood, particularly shellfish to identify the potential biological consequences of microplasticterm exposure. Additionally, in this stage, it is important to monitor consumer consumption rates of seafood, particularly bivalves. This information will inform a risk evaluation and management or mitigation strategies connecting sources and drivers of microplasticterm pollution. This approach integrates a systems perspective that employs precautionary measures to reduce the threat of harm posed by microplasticsterm to the environment and to humans given present uncertainty.

Nanoplastic movement provides insight into the movement and potential effects of non-degradable particles in the human body. The potential health risks of micro- and nanoplastics could be evaluated similar to those of engineered nanoparticles [14••]. Following oral exposure, nanoplastics are transported by M cells, specialized epithelial cells of the mucosa, from the gut into the blood where they are carried through the lymphatic system and into the liver and gall bladder [55]. Their size and hydrophobicityterm enable their passage through the placenta and blood-brain barrier and into the gastrointestinal tract and lungs, potential sites for harm to occur [56]. Their large surface area to volume ratio makes them potentially very chemically reactive, more so than some microplasticsterm. Research studies have demonstrated toxicity in vitro to lung cells, liver, and brain cells [9•]. The systemic distribution from oral exposure to nanoparticles has been shown to have numerous effects: cardiopulmonary responses, alterations of endogenous metabolites, genotoxicity, inflammatory responses, oxidative stress, effects on nutrient absorption, gut microflora, and reproduction [14••, 36, 46]. Parallel research into nanoparticle movement and toxicity provides insight into threats posed by microplasticsterm and nanoplastics.

Potential Effects of Chemical Additivesterm Chemical additivesterm in plastic may cause toxic effects. Moreover, the ability for microplasticsterm to accumulate POPs raises concern that microplasticsterm could transfer hazardous POPs to marine animals and subsequently humans [6]. Chemical partitioningterm between microplasticsterm and animal tissue is a dynamic process; there are few studies that model variables and mechanisms like bioaccumulationterm, kinetics, and the physicochemical properties of marine microplasticsterm [57].

Direct exposures to POPs and other chemicals associated with microplasticsterm may affect biological systems and pose specific threats to juvenile humans and animals, including at low dosesterm·var [9•, 40]. Current guidelines for toxicity testing of chemical components use high contaminant concentrations from a single substance to estimate risk at lower exposure levels or to make low-dose extrapolations. This method fails to capture concerns related to low-dose contaminants or mixed groups of contaminants. Additionally, this method makes it challenging to account for non-linear doseterm·var relationships. As a result, these methods fail to generate data that captures the potential threat posed by chemicals associated with microplasticsterm.

Ingestion is a common interaction between biota and microplasticsterm. The fate and impact of microplasticsterm and their associated chemicals vary across species and environments [6]. Laboratory studies demonstrate increased toxicity from the combination of microplasticsterm and associated chemicals [51, 58]. It is difficult to evaluate whether toxicological impacts translate to humans, however [59]. In animals, the quantity of chemicals from microplasticsterm is suspected to be minimal compared to that from other components of the diet [6]. Microplasticsterm and their constituents may exert localized particle toxicityterm, but chronic exposureterm producing a cumulative effect is of greater concern. In summary, further work is required to estimate the doseterm·var of chemicals to humans from microplasticsterm in seafood and the related effects, including studies of seafood intake, chemical characterization in seafood, and kinetic studies.

Epidemiology In human medicine, microplasticsterm are used as carriers of medications into body tissues [60]. A report commissioned by the House of Commons Environmental Audit Committee of the UK Parliament speculates that the additivesterm and contaminants of concern, when adsorbed to marine microplasticsterm, would act similarly to microplasticsterm used in medical procedures, which transfer to human tissues [60], though there is insufficient data demonstrating this [61].

We do not fully understand how microplasticsterm interact with human biological tissue. For example, if there is an adverse interaction, the effects may be apparent and significant to the individual, but without sufficient and extensive epidemiological studies, impacts may be difficult to detect at a population level. There is a significant correlation between urine BPA levels and both cardiovascular disease and type 2 diabetes [62]. BPA exposures in humans occur both from low-dose exposures to microplasticsterm and both low- and high-dose exposures from non-microplastic sources via inhalation of air and dust or ingestion of foodstuffs. Research is needed to thoroughly assess the risk of microplasticsterm and nanoplastic dietary exposure.

Microplasticsterm and their constituents may exert localized particle toxicityterm, but chronic exposureterm producing a cumulative effect is of greater concern. To address research gaps, it is recommended that scientists evaluate the relative impact of microplasticsterm as an exposure pathway. Further, it would be valuable to identify sorbed contaminant bioavailabilityterm and use biomonitoring methodsterm to contextualize safe toxicological exposure parameters for chronic exposureterm to microplasticsterm and their constituents [7].

Mitigation of and Adaptation to Risks The above sections have described the state of evidence linking microplasticsterm to potential human and animal health risk. Microplasticsterm, chemical toxicity, and chronic exposureterm to microplasticsterm may pose risk to human health, especially with increasing direct exposure to plastic and localized chemicals. And, while significant gaps remain, complimentary bodies of evidence indicate likely exposures and potential hazards from both particles and associated chemicals. The impact of microplasticsterm on human health is uncertain, but cannot be ignored, and presents one justification to mitigate the increasing influx of plastic into the environment. Governments, industry, and civil society all have important roles to play.

Multiple global agreements and domestic policies govern protection of the marine environment; Table 4 identifies several notable policies. Since the enactment of The United Nations Law of the Sea in 1982, a coastal country has sovereign rights extending 200 nautical miles from its shoreline. It is, therefore, the responsibility of governments in those locations to determine who may use this area and how. With diverse cultures, priorities, and opinions present in each coastal country, levels of protection differ considerably.

Table 4.

Global agreements and domestic legislation governing protection of the marine environment | Title | Description | | --- | --- | | A. Global agreements to protect the marine environment from dumping | | Convention of the Prevention of Marine Pollution by Dumping of Wastes and other Matter (London Convention 1972) | Limits the quantities of land-based waste permissible for dumping in the ocean | | International Convention for the Prevention of Pollution from Ships, 1973, as modified by the protocol of 1978 (MARPOL 73/78) | Provides measures to prevent pollution from ships and nation states, Annex V: garbage [63] | | 1982 UN Convention of the Law of the Sea (UNCLOS 1982) | Provides a maritime framework addressing the rights and obligations of states. XII: protection and preservation of the marine environment [64] | | Honolulu Strategy | A global framework to reduce marine plastic and its ecological, human health, and economic impacts [65] | | The United Nations Sustainable Development Goal 14.1, 2015 | By 2025, prevent and significantly reduce pollution marine debris, particularly from land-based activities [66] | | Clean Seas Campaign | Engaging individuals, industries, and member states of UNEP to voluntarily commit to reducing plastic pollution [67] | | B. Key US Federal legislation to protect the marine and coastal environment | | Marine Protection, Research, and Sanctuaries Act (MPRSA), 1972 (also known as the Ocean Dumping Act) | Regulates and restricts dumping materials of any kind into the oceans which would adversely affect human health, welfare, or amenities, or the marine environment, ecological systems, or economic potentialities [63] | | Federal Water Pollution Control Act Amendments of 1972 | Intended to protect and maintain the chemical, physical, and biological integrity of the nation’s waters [63] | | Resource Conservation and Recovery Act, 1976 (RCRA) | Principal federal law governing the disposal of solid and hazardous waste [63] | | Shore Protection Act 1988 (SPA) | Requires a vessel have a permit, number, or other marking visible if transporting municipal or commercial waste within coastal waters [63] | | Marine Debris Research, Prevention, and Reduction Act, 2006 (MDR PRA) (5. 362, 2006) | Identifies, determines sources of, assess, prevents, reduces, and removes marine debris in addition to addressing the adverse impacts of marine debris on the economy of the USA, marine environment, and navigation safety | | Microbead-Free Waters Act (H.R. 1321, 2015) | Prohibits the manufacture of personal care products containing microbeadsterm, including those made of biodegradable polymers, as of July 1, 2017 | | Save Our Seas Act (S.756, 2017) | Providing funding for marine debris cleanup in coastal states and educational outreach addressing the topic of marine debris as well as promoting international action to reduce the incidence of marine debris | Industry also plays a critical role in reducing microplasticterm prevalence throughout the supply chain, in the form of primary microplasticsterm used in industrial processes and secondary microplasticsterm. Extended producer responsibilityterm (EPR), a stewardship policyterm targeting corporations marketing consumer goods, holds manufacturers responsible for the post-consumer phase of plastic packaging [68]. IKEA, for example, has integrated EPR policies into its business model by promoting material reuse and recycling throughout its supply chain and consumer experience. The company indicates in their Sustainability Summary Report F17 that 590,258 t of waste was produced in 2017 across their supply chain of which 83% was recycled or incinerated for energy recovery [69].Other companies are utilizing focused upcycling strategiesterm in their supply chain by directly removing, recycling, and reclaiming plastic from the marine environment to create textile fibers which are then processed and manufactured into yarn for consumer goods. Adidas, for example, partnered with Parley for the Oceans in 2015, to manufacture sneakers and clothing from plastic pollution in the Maldives using a zero-waste 3D printing technique. In 2017, Adidas sold one million pairs of Parley collaborated shoes, equivalent to 16.5 million plastic bottles and 14.3 t of nylon gill nets [70, 71]. Unifi, Bureo, CityPlace, Method, and G-Star RAW clothing have also taken steps to reduce ocean plastic pollution through Ocean Plastic Programs [A.I.R., Avoid, Intercept, and Redesign] [72]. While these are not EPR stewardship policies, A.I.R. is a step in the right direction.

Another approach to mitigation is beach cleanup programs. These are generally organized by non-governmental organizations (NGOs) globally and aim both to raise awareness about marine debris and to remove materials that could cause harm and gradually degrade into microplasticsterm. The International Coastal Cleanup (ICC) coordinated by the Ocean Conservancy, a US NGO, is one of the largest operational organizers of these programs, providing significant financial and social input [64]. The ICC engages 70 countries globally in an annual September weekend litter survey and beach cleanup activity [64]. From the 2016 event, 790,000 volunteers participated in collecting 18 million pounds of trash across over 25,000 miles of shoreline [64].

The extent to which these efforts influence marine plastic pollution or protect the environment is unknown. It is also unclear how measures aimed at preventing plastic pollution leakage compare with reactive measures such as beach cleanups, in terms of cost-effectiveness.

Conclusions We know that humans ingest microplasticsterm. Considering the totality of research findings on microplasticsterm to date, we know that shellfish and other marine organisms consumed with intact GI tracts pose particular concern because they accumulate and retain microplasticsterm. The toxicity associated with consuming microplasticsterm is likely dependent on size, associated chemicals, and doseterm·var. Our collective understanding is limited regarding the sources, fate, exposure, bioavailability, and toxicity of microplasticsterm and their associated chemicals in the marine environment. Current knowledge is mostly based on research conducted within the last decade; however, interest in studying microplasticsterm is growing. The following are key research needs for microplasticsterm and their effects on human health: - Assess microplasticsterm’ impact on ecological systems and food safety and improve understanding of potential toxicological mechanisms and public health effects.

- Identify, if possible, lower risk species, production methods, or regions, and interactions of microplasticsterm with nutrients and various seafood processing and cooking methods, in order to promote adjustments rather than consumer avoidance of seafood.

- Standardize data collection methods for microplasticterm occurrence in the environment and food stuffs, followed by exposure assessment for dietary intake.

- Standardize data collection assessing major seafood production types and seafood producing countries.

- Collect data on presence, identity and quantity of degraded plastic in food, and data on the translocation of microplasticsterm through the aquatic food web and human food system.

- Develop methods to assess physical and chemical changes of micro- and nanoplastics when interacting with biological systems.

- Collect toxicity exposure data evaluating mixtures of various additivesterm/monomers.

- Collect toxicological data on the most common polymers and their relative contributions to microplasticterm contamination.

- Develop specific biomonitoring processes and body burden measurements for additivesterm and monomers.

- Research the toxicokinetics and toxicity of micro- and nanoplastics and their associated chemical compounds, to determine local gastrointestinal (GI) tract effects in animals and humans.

While much remains to be learned, filling these gaps is essential for advancing the dual goals of promoting seafood consumption and protecting consumers from negative health effects from microplasticsterm in the marine environment.

Acknowledgments Support for D.C.L. and R.A.N. was provided by the Johns Hopkins Center for a Livable Future (CLF) with a gift from the GRACE Communications Foundation, which had no role in study design, analysis, findings, or development of recommendations. The authors thank Jillian Fry, Shawn McKenzie, Jim Yager, Keeve Nachman, Mardi Shoer, and Marc Weisskopf for their insightful feedback.

Conflict of Interest Madeleine SmithpersName, David C. LovepersName, Chelsea M. RochmanpersName, and Roni A. NeffpersName declare that they have no conflict of interest.

Human and Animal Rights and Informed Consent This article does not contain any studies with human or animal subjects performed by any of the authors.

Footnotes This article is part of the Topical Collection on Food, Health, and the Environment