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PENCIL Publication of Biological Sciences Vol. 3(1):40-54 ISSN: 2408-5561 Available at: www.pencilacademicpress.org/ppbs (c)2016 PENCIL Academic Press OCEANOGRAPHY Review Plastic marine debris: Sources, distribution and impacts on coastal and ocean biodiversity Prabhakar R. Pawar*, Sanket S. Shirgaonkar and Rahul B. Patil Authors' Affiliations ABSTRACT Veer Wajekar Arts, Science and Commerce College, Mahalan Vibhag, Phunde, Tal. -Uran, Dist. - Raigad, Navi Mumbai - 400 702, Maharashtra, India. Marine debris is a globally recognized environmental issue of increasing concern. Marine ecosystems worldwide are affected by human-made refuse, much of which is plastic. Marine debris includes consumer items such as glass or plastic bottles, cans, bags, balloons, rubber, metal, fiberglass, cigarettes, and other manufactured materials that end up in the ocean and along the coast. It also includes fishing gear such as line, ropes, hooks, buoys and other materials lost on or near land, or intentionally or unintentionally discarded at sea. Debris in oceans and seas is an aesthetic problem, it incurs considerable costs and can have severe impacts on marine organisms and habitats. This review focuses on plastic marine debris with respect to: (1) definition and types; (2) sources and distribution; (3) environmental impacts on coastal and ocean biodiversity; and (4) effective solutions to tackle the plastic marine debris. *Corresponding author. E-mail: [email protected] Accepted: 18th January, 2016. Published: 27th January, 2016. Key words: Plastic marine debris, entanglement, ingestion, marine environment, pollution. INTRODUCTION The National Oceanic and Atmospheric Administration (NOAA) defines marine debris as “any persistent solid material that is manufactured or processed and directly or indirectly, intentionally or unintentionally disposed of or abandoned into the marine environment…” (http://marinedebris.noaa.gov/) (Brander et al., 2011). While this definition encompasses a very wide range of materials, most items fall into a relatively small number of material types such as plastic/polystyrene pieces, rope/cord/nets, cotton swabs, and light weight food packaging (GEF, 2012b). Marine debris is a problem along shorelines, and in coastal waters, estuaries, and oceans throughout the world. It is any man-made, solid material that gain entrance into waterways either directly or indirectly. In India, it gained entrance into oceans and coasts through a number of land- and ocean-based sources. Yearly, more people move near the coastal area of the country, and the production of trash and the potential for marine debris continues to increase. It is necessary to better control the disposal of trash and other wastes, or continue to find marine debris in our rivers, streams, and oceans (Factsheet: Marine Debris, 2012). The geographies of countries play an important part in their contribution to marine debris. Among the top 20 ocean polluters are Sri Lanka, Philippines, Indonesia and countries with long coastlines, such as China and Vietnam (Jambeck, 2015). Marine litter is found in all oceans of the world, from the poles to the equator, and from continental coastlines to small remote islands. It occurs not only close to densely populated coasts, but also in remote places far away from any obvious sources. It consists of slow degrading materials and however, the continuous input 41. PENCIL Pub. Biol. Sci. of large quantities of such items from many land- and sea-based sources results in a gradual build-up in the marine and coastal environment, which spoils beaches, floats on the surface, drifts in the water column, and is even found on the deep seabed. Over the past five or six decades, contamination and pollution of the world’s enclosed seas, coastal waters and the wider open oceans by plastics and other synthetic, non-biodegradable materials has been an ever-increasing phenomenon. The environmental and other problems that may arise from the indiscriminate disposal of marine debris into global oceans and seas are chronic in nature rather than acute, and are long-recognized international problems (Thompson et al., 2009; Gregory, 2009). Plastic and synthetic materials are the most common types of marine debris and are the major cause of problems for marine animals and birds. At least 267 different species are known to have suffered from the entanglement or ingestion of marine debris, including seabirds, turtles, seals, sea lions, whales and fish (Sheavly, 2005). Debris sizes can broadly be divided into the following generally accepted categories: macro-debris (>20 mm diameter), meso-debris (5–20 mm) and micro-debris (<5 mm). The term mega-debris (>100 mm) is also used and can be applied to large debris items such as derelict fishing nets (Barnes et al., 2009). TYPES OF MARINE DEBRIS Marine debris may consist of plastic, glass, metals, styrofoam, rubber, derelict fishing gear and derelict vessels. Plastics are the predominant type of marine debris in the Pacific Gyre; it represents between 60 and 80% of the total marine debris in the world’s oceans (Gregory and Ryan, 1997; EPA, 2011a). It also consists of rope and netting, fragments, packaging, other fishing debris, microplastics, paper, glass and metal (GEF, 2012). High quantities of marine debris may be found on the shoreline close to urban areas. UNEP/IOC has included the following items in the list of marine debris: -Plastic (moulded, soft, foam, nets, ropes, buoys, monofilament line) -Fisheries related equipment, -Smoking related items such as cigarette butts or lighters, -Metal (drink cans, bottle caps, pull tabs), -Glass (buoys, light globes, fluorescent globes, bottles) -Processed timber (including particle board), -Paper rubber and cloth. The highest percentage of item of marine debris consists Pawar et al. (2016) of cap, spoon, small sachets, syringe, paste tube, straw, pen assorted, plastic bits, bead, hair clips and the plastic and nylon ropes followed by thermocol and sponge (Sulochanan et al., 2013). SOURCES OF MARINE DEBRIS The United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) estimated that land-based sources are responsible for up to 80% of marine debris and the remainder was due to sea-based activities (Sheavly, 2005). The main land and sea-based sources of marine debris are thus listed and explained Land-based sources Marine debris from land-based sources is blown into the sea, washes into the sea or is discharged into the sea (Sheavly, 2005). Land-based sources include the following: -Storm water discharges: Storm drains collect runoff water generated during heavy rain events. The drains directly discharge this wastewater into nearby streams, rivers or the ocean. Rubbish from streets can be washed into storm drains and is then discharged straight into the ocean or to streams/rivers which, in turn, may carry the rubbish to the ocean. -Combined sewer overflows: Combined sewers carry sewage, as well as storm water. During heavy rains, the handling capacity of the wastewater treatment system may be exceeded and the sewage plus storm water is directly discharged into nearby rivers or oceans. This waste can include rubbish such as condoms, tampon applicators, syringes and street litter (Sheavly, 2005). -Littering: Beachgoers may carelessly leave litter at the coast and this will become marine debris, thus the debris includes food packaging and beverage containers, cigarette butts and plastic beach toys. Fishermen may leave behind fishing gear. Litter from inland areas can become marine debris if it gets into streams or rivers. In this way marine debris may result from rubbish left by workers in forestry, agriculture, construction and mining operations. (Sheavly, 2005). -Solid waste disposal and landfills: Run-off from landfills located in coastal areas or near to rivers may find its way into the marine environment. In addition to loss from landfills, garbage may be lost to the marine 42. PENCIL Pub. Biol. Sci. environment during its collection or transportation. Illegal dumping of domestic or industrial wastes into coastal and marine waters is another source of marine debris (Sheavly, 2005). -Industrial activities: Industrial products may become marine debris if they are improperly disposed of on land or if they are lost during transport or loading/unloading at port facilities (US EPA, 2002). Small plastic resin pellets, about 2-6 mm in diameter, are the raw material for the manufacture of plastic products (Derraik, 2002). These pellets have been released into the marine environment from accidental spillage during production and processing, transport and handling. Plastic pellets have become ubiquitous in ocean waters, sediments and on beaches and are ingested by marine wildlife (Redford et al., 1997). Ocean-based sources All types of boats, ships and offshore industrial platforms are potential sources of marine debris. The debris may originate from accidental loss, indiscriminate littering or illegal disposal. It may also due to the waste management disposal practices carried out in the past (Sheavly, 2005). Ocean-based sources of marine debris include: -Commercial fishing: Commercial fishermen generate marine debris when they fail to retrieve fishing gear or when they discard fishing gear or other rubbish overboard. Debris resulting from commercial fishing includes nets, lines and ropes, strapping bands, bait boxes, bags, gillnet or trawl floats plus galley wastes and household trash (Sheavly, 2007, Morishige e al., 2007; Pichel et al., 2007). -Recreational boaters: Boaters may deposit garbage overboard such as bags, food packaging and fishing gear (Sheavly, 2005). -Merchant, military and research vessels: Rubbish from vessels may be accidentally released or blown into the water or may be deliberately thrown overboard. Large vessels with many crew members, generate solid wastes daily which may end up as marine debris if it is not secured and stored properly (US EPA, 1992a; Sheavly, 2005). -Offshore oil and gas platforms and exploration: Activities on oil and gas platforms may generate items, which are deliberately or accidentally released into the Pawar et al. (2016) marine environment including hard hats, gloves, 55gallon storage drums, survey materials and personal waste. Undersea exploration and resource extraction also contribute to marine debris (US EPA, 1992a; Sheavly, 2005). PLASTIC MARINE DEBRIS Introduction and definition Plastic is a synthetic material that is made by polymerizing molecules of monomer, materials that are derived from coal, petroleum or natural gas (Selukar et al., 2014). At present, plastic has achieved a pivotal status, with extensive commercial, industrial, medicinal and municipal applications. Demand is considerable; annual plastic production has increased dramatically from 1.5 million tonnes in the 1950s to approximately 280 million tonnes in 2011 (Plastics Europe, 2012). Plastic has become the most common form of marine debris since it entered the consumer arena less than 60 years ago, and presents a major and growing global pollution problem (Andrady, 2011). The current global annual production, estimated at 245 million tonnes represents 35 kg of plastic produced annually for each of the 7 billion humans on the planet, approximating the total human biomass (Zettler et al., 2013). Plastic debris at the micro and potentially at the nanoscale, are widespread in the environment. Microplastics have accumulated in oceans and sediments worldwide in recent years, with maximum concentrations reaching 100 000 particles m3. Due to their small size, microplastics may be ingested by low trophic fauna, with uncertain consequences for the health of the organism (Wright et al., 2013). Sediment from densely populated coastal areas can be heavily contaminated with microplastics. Industrial coastal areas have also been identified as microplastic hotspots; concentrations of approximately 100 000 plastic particles m3 of seawater have been reported in a Swedish harbour area adjacent to a PE production plant (Noren and Naustvoll, 2010). Worldwide, about 280 million t of plastic are produced annually for the manufacturing of products such as storage containers, packaging material, or even automobiles. Plastic has become an optimal medium used in vast amounts of consumer products because it is lightweight, durable, inexpensive, and a good insulator (Shaw and Sahni, 2014). It is difficult to eliminate plastic waste due to the fact that it does not biodegrade in nature, but only photo degrades into smaller pieces. The percentage of plastics that make up the total municipal solid waste has 43. PENCIL Pub. Biol. Sci. increased by 12% over the last four decades (EPA, 2014). Almost one third of the plastic produced is used to manufacture single-use plastics (DiGregorio, 2012) such as coffee cup lids, stirrers, or straws. Plastics are synthetic organic polymers, although they have only existed for just over a century (Gorman, 1993). The versatility of these materials has lead to a great increase in their use over the past three decades, and they have rapidly moved into all aspects of everyday life (Hansen, 1990). Plastics are lightweight, strong, durable and cheap, characteristics that make them suitable for the manufacture of a very wide range of products. These same properties happen to be the reasons why plastics are a serious hazard to the environment (Laist, 1987). Plastics do not disappear and will remain in our environments indefinitely affecting wildlife, until the pollution is reduced (Sigler, 2014). Plastic marine debris has become a pervasive pollution problem affecting all the world’s oceans, and it is the direct cause of injuries and death to marine animals and birds, either because they become entangled in it or mistake plastic for food (Allsopp et al., 2006). Fauna in case study beaches are affected by marine debris, especially microplastics (Vlieststra and Parga, 2002; Endo et al., 2005). The environmental and other problems that arise from the indiscriminate disposal of plastics and other persistent synthetic materials (marine debris) into the global oceans and seas are chronic in nature rather than acute, and are long-recognized international problems (Thompson et al., 2009). It has recently been estimated that the 1982 report of 8 million marine debris items entering the world’s oceans and seas each day now needs to be updated by being multiplied several fold (Barnes, 2005). Types of plastic marine debris Plastics are synthetic organic polymers, and though they have only existed for just over a century (Derraik, 2002). Since plastics are buoyant, an increasing load of plastic debris is being dispersed over long distances, and when they finally settle in sediments, they may persist for centuries (Goldberg, 1997). Some common types of plastic wastes are shown in Table 1. Sources and distribution of plastic marine debris The ever-growing problem of marine debris begins on land, where streams and rivers carry debris to the coast. Ocean currents then transport the debris to remote Pawar et al. (2016) areas, where it may take centuries to break down (Goldberg, 1997). The Eastern Pacific Garbage Patch (EPGP), an area between California and Hawaii, contains a large quantity of small “microplastic” pieces derived from the breakdown of larger plastic items (Marks and Howden, 2008). The sources of marine debris are both land- and marine-based, their origins may be local or distant, and the environmental consequences are many and varied (Gregory, 2009). Some fraction of the increasing amount of postconsumer plastic trash inevitably escapes the recycling and waste streams and makes its way to the global oceans (Zettler et al., 2013). Additionally, tsunamis and storms can result in large pulses of plastic entering the ocean from coastal areas. Plastic accumulates not only on beaches worldwide, but also in “remote” open ocean ecosystems (Andrady, 2011). Through accidental release and indiscriminate discards, plastic waste has accumulated in the environment at an uncontrollable rate, where it is subjected to wind and river-driven transport, ultimately reaching the coast (Wright et al., 2013). Annually, more than 35 million plastic bottles and 500 billion plastic bags are used by consumers, many of which end up in oceans and along beaches (What a Waste, 2010). The accumulation of plastics in the environments is a result of improper disposal or shipping spills. Since they are lightweight and durable, plastics are capable of travelling long distances; ending up in terrestrial environments, along shorelines, or floating in the open ocean (Zbyszewski and Corcoran, 2011). Plastic materials also end up in the marine environment when accidentally lost, carelessly handled or left behind by beachgoers. They also reach the sea as litter carried by rivers and municipal drainage systems. There are major inputs of plastic litter from land-based sources in densely populated or industrialized areas, most in the form of packaging (Gregory, 1999). Drifter buoys and physical oceanographic models have shown that surface particles such as PMD can passively migrate from Eastern Seaboard locations all the way to the interior of the North Atlantic Subtropical Gyre in less than 60 days, illustrating how quickly human-generated debris can impact the gyre interior that is more than 1000 km from land (Zettler et al., 2013). -Lost and discarded nets and lines from fishing vessels are important contributors to marine debris, especially in heavily fished areas. These vessels also lose plastic floats, traps, pots, and other gear (UNEP and NOAA). -Other sea-based sources of plastic pollution include oil and gas platforms, aqua culture facilities, and cargo ships 44. PENCIL Pub. Biol. Sci. Pawar et al. (2016) Table 1. Some common types of plastic wastes. Plastic code 1 2 Acronym PETE/PET HDPE Full Name Polyethylene terephthalate Common Examples Soda bottles, Films, High density polyethylene Milk jugs, Packaging, Shampoo bottles, Yogurt containers, Detergent bottles, Shopping Bags 3 PVC Polyvinyl chloride Clear food packaging, Candy wrappers, Some bottles, Water pipes, Curtains, Credit card, Packaging films, Water films 4 LDPE Low density polyethylene Plastic bags, Wire cloth, Squeezable bottles, Shopping bags, 5 PP Polypropylene Caps, straws, Some bottles, Plastic bag and toy, Drinking straws, 6 PS Polystyrene Takeout food containers, Disposable cups & plates, Fast food boxes, CD cases, 7 PC PA Other Polycarbonate Polyamide/Nylon Acrylonitrile butadiene styrene that lose containers to the sea. -Plastic debris from land comes primarily from two sources: first, ordinary litter; and, second, material disposed in open dumps or landfills that blows or washes away, entering the ocean from inland waterways, wastewater outflows, and the wind (Ambeck et al., 2015; Lechner et al., 2014). Environmental impacts of plastic marine debris Countless marine animals have been killed or harmed by marine debris primarily because they either become entangled in it, or mistake plastic debris for food and ingest it. Marine debris emanates from both land and sea-based sources and can travel immense distances. It can pose a navigation hazard, smother coral reefs, transport invasive species and negatively affect tourism. It also injures and kills wildlife, has the potential to transport chemical contaminants, and may pose a threat to human health. Marine litter is a complex and multi-dimensional problem, with significant implications for the marine and Water jugs, DVDs, Sunglasses, Toothbrushes coastal environment and human activities all around the world. Plastic poses a major threat to marine mammals, birds, turtles and fish due to entanglement and ingestion. Plastics and polystyrene account for approximately 75 per cent of marine litter. Another emerging threat is the ingestion by marine organisms of microscopic plastic particles accumulating in the pelagic zone and sedimentary habitats at concentrations of 150-2,400 particles per m3. Marine litter causes further ecological damage by dispersing invasive alien species, which ‘hitch-hike’ on floating debris. The benthos is likely to be a sink for high density microplastics. Benthic suspension- and deposit- feeders are therefore likely to ingest sinking and sedimentary microplastics. Fibres are the most commonly encountered form of microplastics in the marine environment. Benthic holothurians were found to selectively ingest microplastics, showing a preference for fibrous shapes. Microplastics may not only affect species at the organism-level; they also have the capacity to modify population structure (Wright et al., 2013). Not only the aesthetically distasteful plastic litter, but also less conspicuous small plastic pellets and granules 45. PENCIL Pub. Biol. Sci. are a threat to marine biota. The latter are found in large quantities on beaches (Redford et al., 1997), and are the raw material for the manufacture of plastic products that end up in the marine environment through accidental spillage during transport and handling, not as litter or waste, but as other forms of plastics. Their sizes usually vary from 2–6 mm, though occasionally much larger ones can be found. Durability of Plastic pellets in the marine environment is still uncertain but they seem to last from 3 to 10 years, and additives can probably extend this period to 30–50 years (Gregory, 1978). Countless marine animals have been killed or harmed by marine debris primarily because they either become entangled in it, or, they mistake plastic debris for food and ingest it (Gregory, 2009). Entanglement and ingestion of seabirds, marine mammals and fish may lead to death from starvation and debilitation, with a reduced quality of life and lowered reproductive performance (Laist, 1987). Other impacts to receive limited attention are of no less importance, e.g. damage to subsistence fisheries; hazards to recreational boating and larger commercial vessels; impact of plastic sheeting that blankets the biota of soft sediment, reef and rocky substrata, as well as anoxia and hypoxia induced by inhibition of gas exchange between pore waters and overlying sea water (Gregory and Andrady, 2003). Marine debris travels throughout the world’s oceans, accumulating on beaches and within gyres, and this debris can degrade physical habitats, transport chemical pollutants, threaten marine life, and interfere with human uses of marine and coastal environments. Plastic marine debris is considered to have the greatest potential to alter the environment and impact biota and humans, since it floats at the surface, is widely transported by ocean currents, persists in the environment for years, and is not readily digestible when consumed. Therefore, the impact of plastic marine debris is much more than a mere aesthetic problem (EPA, 2011b). Physical habitat impacts of plastic marine debris Physical habitat alteration is caused by the following: 1. Accumulation of debris: As debris accumulates in oceanic convergence zones, on beaches, and submerged benthic habitats, habitat structure may be modified, light levels may be reduced in underlying waters, and oxygen levels may be depleted. These changes can undermine the ability of open water and benthic habitats to support marine life (EPA, 2011b). 2. Habitat degradation: Degradation of habitat occurs Pawar et al. (2016) due to smothering, abrasion, and fragmentation of sensitive habitats and habitat forming species, such as macro algal beds and coral reefs (Asoh et al., 2004). 3. Damage and degradation of coral reef and soft sediment: Derelict fishing gear, including nets and lines, can settle on coral reefs as currents and waves transport them to shallow habitats. It can entangle branching species of corals resulting in fragmentation and abrasion, potentially reducing habitat heterogeneity and providing open substrate for macroalgal colonization (Chiappone et al., 2005). 4. Smothering: Plastic marine debris can smother the benthos, reducing light penetration and oxygen exchange (Uneputty and Evans, 1997). 5. Decline in species: Decline of benthic habitatforming species and modification of the physical structure of the habitats, indirect impacts of marine debris may cause declines in species that are dependent on the habitats for foraging and shelter (EPA, 2011a). 6. Alien species invasions: Marine litter items can assist in alien species invasions as they drift on litter across great distances (Factsheet 1, 2013). The introduction of alien species can have major consequences for marine ecosystems (Grassle et al., 1991). This biotic mixing is becoming a widespread problem due to human activities, and it is a potential threat to native marine biodiversity (McKinney, 1998). Drift plastics can increase the range of certain marine organisms or introduce species into an environment where they were previously absent (Winston, 1982). The arrival of unwanted and aggressive alien taxa could be detrimental to littoral, intertidal and shoreline ecosystems (Gregory, 1999). Rapid and heavy fouling of floating plastic (and other objects) may increase the density of plastic object causing them to sink to the sea floor (Ye and Andrady, 1991). Blanketing effects of plastic sheeting on the sea floor could lead to anoxia and hypoxia induced by the inhibition of gas exchange between pore water and sea water (Goldberg, 1997). Chemical impacts of plastic marine debris -Accumulation and transport of persistent organic pollutants (POPs): Accumulation and transport of POPs, such as polychlorinated biphenyls (PCBs) and pesticides, have been found at concentrations that are in orders of magnitude greater than the surrounding environment (Rios et al., 2007). Teuten et al. (2009) reported that the 46. PENCIL Pub. Biol. Sci. highest PCB concentrations in plastics occurred in areas with the highest production and use patterns, as well as concentrations in the environment. Plastic debris accumulates pollutants such as PCBs (polychlorinated biphenyls) up to 100,000 to 1,000,000 times the levels found in seawater (NOAA, 2010). It is apparent that plastics have the potential to adsorb chemicals of concern from the environment, and serve as a potential global transport mechanism for contaminants of concern (EPA, 2011b). -Leaching of constituent contaminants from plastics: Contaminants can be released from plastics to the environment and biota by the breakdown of plastics through ultraviolet (UV) radiation, mechanical forces, and weathering, as well as by ingestion by biota (EPA, 2011b). For example, the accumulation of POPs from plastics has been documented in seabirds (Ryan et al., 1988), and benthic organisms (Teuten et al., 2009). Two broad classes of plastic-related chemicals are of critical concern for human health, that is, Biphenyl-A (BPA) and additives used in the synthesis of plastics, which are known as phthalates.: A. BPA: It is a common synthetic chemical found in plastics, foods can linings, beverage can linings, and other consumer products, which interferes with human hormones (Sarkar et al., 2012). B. Phthalates: They are chemicals used to soften plastics, to carry fragrance and scent, and are used in other everyday products. They linked to birth defects and are harmful to reproductive system (Selukar et al., 2014). These aforementioned chemicals have a detrimental effect on marine organisms even at very low levels and plastic pellets could be a route for PCBs into marine food chains. PCBs lead to reproductive disorders or death; they increase risk of diseases and alter the hormone levels (Ryan et al., 1988; Lee et al., 2001). The toxic chemicals added to make plastics more flexible, known as plasticizers, can leach out into the environment and in turn into organisms that ingest plastic (Rahman ant Brazel, 2004). Other dangerous chemicals can concentrate on plastic surfaces (Mato et al., 2001), increasing the toxicity of plastics. The toxic compounds in or associated with plastics, their uses and effects are shown in Table 2 (Brander et al., 2011). Biological impacts of plastic marine debris Plastic marine debris has deleterious effects on marine Pawar et al. (2016) biota (Derraik, 2002). It has been estimated that plastic marine debris adversely affects 267 species globally, including 86% of sea turtles, 44% of seabirds, and 43% of marine mammals (Laist, 1997). The most common threats to biota include ingestion and entanglement (Laist, 1997; Quayle 1992). Microplastics resemble phytoplanktons, which are eaten by fish and cetaceans (Boerger et al., 2010). Ingested plastic debris has been found to reduce stomach capacity, hinder growth, cause internal injuries, and create intestinal blockage (Plot and Georges, 2010). Plastic entanglement with fishing nets or other ring shaped materials can result in strangulation, reduction of feeding efficiency, and in some cases drowning (Allen et al., 2012). Globally, at least 23% of marine mammal species, 36 % of seabird species, and 86 % of sea turtle species are known to be affected by plastic debris (Stamper et al., 2009). The consumption of plastic by marine organisms adds persistent, bioaccumulative, and toxic substances to the aquatic food chain (Pascall et al., 2005). The entanglement in and ingestion of macroplastic items is widely recognised in vertebrates. Over 250 marine species are believed to be impacted by plastic ingestion (Laist, 1997). Over 80% of reported incidents between organisms and marine debris were associated with plastic whilst 11% of all reported encounters are with microplastics (GEF, 2012a). Microplastics can be ingested by low trophic suspension, filter and deposit feeders, detritivores and planktivores (Murray and Cowie, 2011). Toxicity could also arise from leaching constituent contaminants such as monomers and plastic additives, capable of causing carcinogenesis and endocrine disruption (Talsness et al., 2009). A major concern about the toxic compounds associated with plastics is that they can disrupt hormone regulation in the cells of organisms (Oberdörster & Cheek, 2001). Hormone disruption occurs when a chemical acts as a natural hormone in a cell; it can change reproductive ability and mating behaviour, contribute to tumour development, and negatively affect offspring (Wuttke et al., 2010). Ingestion: The threats to marine life are primarily mechanical due to ingestion of plastic debris (Quayle, 1992). The potential for plastic ingestion is largely associated with foraging strategies and prey types (EPA, 2011b). Marine turtles: Globally, approximately one third of marine turtles have likely ingested debris. Most items eaten by turtles are plastic and positively buoyant. 47. PENCIL Pub. Biol. Sci. Pawar et al. (2016) Table 2. Toxic compounds in or associated with plastics: their uses and effects. Toxic compound Bisphenol A (BPA) Phthalates Use Plasticizer, can liner Plasticizer, artificial Fragrances Effects Mimics estrogen Interferes with testosterone, sperm motility Plastic Types PVC, PC PS, PVC Persistent organic pollutants (POPs) Pesticides, flame retardants, etc. Possible neurological and reproductive damage All plastics Dioxins Produced in manufacture of PVC, during waste incineration Carcinogen, interferes with testosterone All plastics Nonylphenol Antistatic, antifog, Surfactant (in detergents) Mimics estrogen PVC Polyaromatic Hydrocarbons (PAHs) Produced when fossil fuels are burned Developmental and reproductive toxicity All plastics Polychlorinated biphenyls (PCBs) Electronics manufacture Interferes with thyroid function All plastics Styrene monomer Structure of polystyrene Forms DNA adducts PS Smaller oceanic turtles are more likely to ingest debris than coastal foragers; herbivores are more likely to ingest debris than carnivorous species; oceanic leatherback turtles and green turtles are at the greatest risk of ingested marine debris effects. Sea turtles readily consume plastic bags and other floating debris that appear similar to their gelatinous prey (Bugoni et al., 2001; Tomas et al., 2002). Debris including fishing line, ropes, nets, six pack rings, Styrofoam, and plastic bags have been extracted from turtle digestive tracts. Plastic bags floating in the water strongly resemble the shape of jellyfish, a primary food source for sea turtles, thus resulting in the ingestion of the bags (Mascarenhas et al., 2004). For the past 40 years, of the 371 autopsies conducted on leatherback turtles, it was shown that 37.2% of the turtle had plastic in their gastrointestinal tracts (Mrosovsky et al., 2009). Plastic has also been found to block the passage of female eggs and cause internal damage (Plot and Georges, 2010). Green turtles (Chelonia mydas) and loggerheads (Caretta caretta) have been found in similar predicaments and of the acquired 52 loggerheads through by-catch in the Atlantic Ocean, 35% were found to have plastics in their digestive tracts (Parker et al., 2005). Ingestion of plastics is of great concern because it can impact on turtle populations and the green turtle, leatherback turtle, hawksbill turtle, Kemp’s ridley and olive ridley are listed as endangered species whilst the loggerhead turtle is listed as threatened (NOAA, 2005). According to research, high numbers of sea turtles ingest marine debris and plastic is the most common sort of debris ingested (Tomás et al., 2002). The problems associated with ingestion of plastics and microplastics in marine turtles are: -Suppurating skin lesions and ulcerating sores; -Reduction in quality of life and reproductive capacity; -Drowning and limited predator avoidance; -Development of internal and external wounds. -Impairment of feeding capacity due to the buildup of the digestive system. -Decreased mobility and predatory avoidance, and toxicity. -Gastrointestinal blockages by plastics (Derraik, 2002). -Block the passage of female eggs and cause internal damage (Plot and Georges, 2010). -Starvation due to accrue of plastics in the stomach cavities. -Satiation, starvation and general debilitation often leading to death. -Plastic resin pellets may adsorb and concentrate potentially damaging water quality. -Blockage of enzyme production; -Diminished feeding stimulus; nutrient dilution; -Reduced growth rates; 48. PENCIL Pub. Biol. Sci. -Lowered steroid hormone levels; -Delayed ovulation and reproductive failure and absorption of toxins. -To clog and block the feeding appendages of marine invertebrates or even to become embedded in tissues. Pelagic seabirds: The amount of plastic ingested by different species of birds may be an indicator of the accumulation of plastics in an area (Sigler, 2014). Around the world, nearly half of all seabird species are likely to ingest debris. Birds eat everything from balloons to glow sticks, industrial plastic pellets, hard bits of plastic, foam, metal hooks and fishing line. Small plastics such as bottle caps are often mistaken by seabirds for food. It was found that diving birds that fed on fish in the water column had less plastic in their stomachs as compared with those of surface eaters (Provencher et al., 2010). Birds such as the albatross and shearwater had more plastic in the first region of their stomachs and gizzards (Moser and Lee, 1992). Juvenile albatross and shearwaters were found to ingest more plastics than adults (Avery-Gomm et al., 2013). Blight and Burger (1997) reported in the eastern North Pacific that, of the 353 ingested items recovered from 11 species of seabirds, 29.2% were industrial pellets and 70.5% were broken pieces of everyday use plastics. Among sea birds, the ingestion of plastics is directly correlated to foraging strategies and technique, and diet. Some seabirds select specific plastic shapes and colors, mistaking them for potential prey items (Moser and Lee, 1992). Seabirds with large plastic loads have reduced food consumption, which limits their ability to lay down fat deposits, thus reducing fitness (Ryan et al., 1988). Plastic materials of varying kinds had spread to all oceans and adjacent seas and wide concern was being expressed over the amounts of cylindrical, virgin plastic pellets together with fragmented plastic particles of varying size and shape that were being ingested by pelagic seabirds (Shomura and Yoshida, 1985). The problems associated with ingestion of plastics and microplastics in pelagic seabirds are: -Reduced body weight (Spear et al., 1995), -Inhibit fat deposition (Connors and Smith, 1982), -Reduce reproductive capacity (Azzarello and Van Vleet, 1987). -Swallowed plastic can obstruct and damage a bird’s digestive system, reducing its foraging capabilities. -Reduced food consumption, thus reducing fitness (Ryan et al., 1988). Cetaceans: Predatory organisms, such as fur seals, may indirectly consume plastics through consumption of Pawar et al. (2016) pelagic fish and other prey (Eriksson and Burton, 2003). Microplastics resemble phytoplanktons, which are eaten by fish and cetaceans (Boerger et al., 2010). Most cetaceans live far from the shoreline, which limits the amount of research on the ingestion of marine debris (Sigler, 2014). If plastic causes unnatural death, cetaceans will most likely sink to the bottom of the ocean. At least 26 species of cetaceans have been documented to ingest plastic debris (Baird and Hooker, 2000). Ingestion is most likely because the debris was mixed with the desired food. Jacobsen et al. (2010) reported that two sperm whales (Physeter macrocephalus) were found off the coast of northern California in 2008 with a large amount of fishing gear in their gastrointestinal tracts. Currently, there have not been enough trends found in collected data that prove ingested plastics are the primary cause of death contributing to the decline of cetaceans (Baulch and Perry, 2014). Plastic marine debris can cause direct mortality of cetaceans or even create debilitating scenarios that make the mammals more prone to predation or disease (Sigler, 2014). Baird and Hooker (2000) cited other cetaceans that have been reported with ingested plastics, such as the killer whale (Orcinus orca). The deaths of whales, manatees, and dolphins have been attributed to gastrointestinal blockages by plastics (Derraik, 2002). Fish: Ingestion of plastic debris by fishes has been widely documented and incidences of ingestion have been reported for fishes by Carpenter et al. (1972). There is plenty of evidence supporting that fish are consuming plastics (Sigler, 2014). Of the 7 species studied in the North Sea, only 2.6% of the 1203 collected fish contained plastic pieces in the digestive tracts (Foekema et al., 2013). When the gastrointestinal tracts of 504 fish were studied in the English Channel, 36.5 % contained plastics (Lusher et al., 2013). The inconsistent results found among studies could possibly indicate important variables such as location, accumulation of plastics, and fish species (Sigler, 2014). Most of the plastic pieces ingested by fishes were blue, white or clear, which are of the same colors as plankton, the primary food source of fish (Boerger et al., 2010). Davison and Asch (2011) speculate that plastic between 12,000 and 24,000 t are consumed by fish each year. Small fragments of plastic may facilitate the transport of absorbed pollutants to predators within the food chain (Dau, 2012). Entanglement: Over 250 species of marine animals impacted by entanglement includes turtles; penguins; albatrosses, 49. PENCIL Pub. Biol. Sci. petrels and shearwaters; shorebirds, skuas, gulls and auks; coastal birds other than seabirds; baleen whales, toothed whales and dolphins; earless or true seals, sea lions and fur seals; manatees and dugong; sea otters; fish and crustaceans (Laist, 1997; Gregory, 2009). One of the greatest threats of entanglement to marine life and seabirds is derelict fishing gear, including monofilament line; trawl nets, and gill nets. Lost and free floating fishing gear can continue to ―ghost fish for months and even years, ensnaring a wide range of species, particularly in areas adjacent to fishing grounds, along current convergence zones, and along shorelines where debris is deposited by currents and waves. Seabirds, turtles, whales, dolphins, dugongs, fish, crabs and crocodiles and numerous other species are killed and maimed through entanglement (EPA, 2011b). Entanglement in plastic debris, especially in discarded fishing gear, is a very serious threat to marine animals (Derraik, 2002). According to Vauk and Schrey (1987), entanglement accounts for 13–29% of the observed mortality of gannets (Sula bassana) at Helgoland, German Bight. Entanglement is a particular problem for marine mammals, such as fur seals, which are both curious and playful (Mattlin and Cawthorn, 1986). Once an animal is entangled, it may drown, and its ability to catch food or avoid predators is impaired, or incur wounds from abrasive or cutting action of attached debris. Lost or abandoned fishing nets pose a particular great risk (Jones, 1995). These ‘‘ghost nets’’ continue to catch animals even if they sink or are lost on the seabed (Laist, 1987). Whales are also caught in their mouths or wrapped around their heads and tails’’ (Weisskopf, 1988). Accumulation: There is a potential danger to marine ecosystems from the accumulation of plastic debris on the sea floor (Derraik, 2002). Kanehiro et al. (1995) documented that plastics are made up 80–85% of the seabed debris in Tokyo Bay and accumulation of such debris can inhibit the gas exchange. The accumulation of POPs from plastics has been documented in seabirds (Ryan et al., 1988),and benthic organisms (Teuten et al., 2009). Accumulation of microplastic particles in marine invertebrates could potentially cause blockages throughout the digestive system, suppressing feeding due to satiation. Alternatively, predation of microplasticcontaminated marine invertebrates may present a pathway for plastic transfer along the food chain. The capacity for microplastics to accumulate within an organism is likely to affect the associated physical impact of microplastic ingestion (Wright et al., 2013). Pawar et al. (2016) Between the overlying waters and the pore waters of the sediments, the resulting hypoxia or anoxia in the benthos can interfere with the normal ecosystem functioning and alter the make-up of life on the sea floor (Goldberg, 1997). Accumulation of plastic debris within the waters and on the shorelines has impacts on 13 marine species that are listed as threatened or endangered under the Endangered Species Act (ESA) as shown in Table 3 (EPA, 2011b; Laist 1997). Impacts of plastic marine debris on human Plastic marine litter can also impact human health and safety as follows: 1. Degradation of the habitats and ecosystem services: -Ghost fishing by lost nets and pots can remove fish and invertebrates that are targeted by local commercial and recreational fisheries (EPA, 2011b). 2. Impede commercial and recreational fishing: -Fishing gear that is lost or discarded at sea may have the greatest impact on humans due to impediments to commercial and recreational fishing. -Marine debris can block ship propellers or steering systems and do direct damage to vessels. 3. Threaten health and safety: -Entangling in nets and lines while swimming or being injured by sharp debris that accumulates on beaches. -Medical wastes, syringes, glass and other sharp dangerous items that are washed up on beaches result in direct risks to beachgoers. -Swimmers, divers and snorkelers may become entangled in submerged or floating debris. -Solid waste associated with sewage such as sanitary towels, condoms and cotton buds degrades the quality of the bathing water and may present a health risk. -Transfer of infections and disease due to medical waste, such as punctures by hypodermic needles. -Fish and shellfish meant for human consumption may contain (micro) plastics and poses a human health risk. -Marine litter poses a safety risk for sea vessels and their crews. -Burning of polystyrene polymers releases styrene gas, which can readily be absorbed through the skin and lungs and damage the eyes and mucous membranes. It can increase the risk of heart disease; aggravate 50. PENCIL Pub. Biol. Sci. Pawar et al. (2016) Table 3. List of threatened or endangered marine species listed under the Endangered Species Act (ESA). S/N 1 2 3 4 5 6 7 Animals Marine Mammals Common Name Hawaiian monk seal Humpback whale Sperm whale Blue whale Fin whale Sei whale North Pacific right whale Species Monachus schauinslandi Megaptera novaengliae Physeter macrocephalus Balaenoptera musculus Balaenoptera physalus Balaenoptera borealis Eubalena japonica 8 9 10 11 12 Marine Turtles Olive Ridley turtle Leatherback turtle Loggerhead turtle Hawksbill turtle Green turtle Lepidochelys olivacea Dermochelys coriacea Caretta caretta Eretmochelys imbricate Chelonia mydas 13 Seabirds Short-tailed albatross Phoebastria albatrus respiratory ailments, such as asthma and emphysema, and cause rashes, nausea or headaches, damages in the nervous system, kidney or liver, in the development system (Selukar et al., 2014). 4. Reduce tourism: -Reduces the aesthetic and recreational values of beaches and marine resources. 5. Interfere with navigation: Marine debris can block ship propellers or steering systems and do direct damage to vessels. A substantial number of marine rescues have resulted. Impacts of plastic marine debris on aesthetic values -Plastic Marine Debris reduces the aesthetic and recreational values of beaches and marine resources. -Marine debris attracts considerable media and public attention. -Visual affront of unsightly, discarded and/or accidentally lost plastic and other manufactured materials that tend to strand and concentrate along shorelines and sandy beaches - ones often of considerable recreational importance. -Concerns are commonly expressed about economic losses, health issues and harm to local biota, and otherwise general impressions of longer term deterioration in beach aesthetic values (e.g. Gabrielides, 1995). Effective solutions to tackle marine debris -Plastic is now an integral part of the everyday activity of human life and one cannot rule out the disadvantages of plastic, but its disadvantages can be reduced to some extent. -The most effective way to reduce and mitigate the harmful effects of marine debris is to prevent it from entering the marine environment in the first place. This requires incorporating an improved understanding of debris at the local, regional and national levels; improved waste management efforts; education and outreach activities; development of technology solutions; anti-dumping campaigns; reducing losses of fishing gear at sea; and incentives to reduce debris. -Marine litter is entirely due to human activity and therefore, has to be controlled by human management. -Recycling is one of the most identified practices available to reduce the impact of waste in landfills and in the environment through the reuse of materials. -Conversion of marine debris to adhesive is an economical, eco-friendly and efficient technique. -Other measures to address marine debris include manual clean-up operations of shorelines and the sea floor, as well as school and public education programmes. Conclusion Recycling is the current solution to the overuse of plastics. Thermal degradation may be the new solution to recycling and repurposing plastics such as high- 51. PENCIL Pub. Biol. Sci. density and low density polyethylene, polypropylene, and polystyrene, without causing further environmental degradation. ‘Thinking globally and acting locally’ is a fundamental attitude to reduce such an environmental threat. A combination of legislation and the enhancement of ecological consciousness through education are likely to be the best way to solve such environmental problems. It is possible that biodegradable plastics could be used where plastic is deemed necessary, but should not be seen as an environmentally sound alternative unless they are known to break down rapidly to nonhazardous substances in natural environments. The ultimate solution to waste prevention is to implement a responsible waste strategy, namely the concept of “Zero Waste”. 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