Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat.[1][2] Plastics that act as pollutants are categorized by size into micro-, meso-, or macro debris.[3] Plastics are inexpensive and durable, making them very adaptable for different uses; as a result, manufacturers choose to use plastic over other materials.[4] However, the chemical structure of most plastics renders them resistant to many natural processes of degradation and as a result they are slow to degrade.[5] Together, these two factors allow large volumes of plastic to enter the environment as mismanaged waste which persists in the ecosystem and travels throughout food webs.[6][7]
Plastic pollution can afflict land, waterways and oceans. It is estimated that 1.1 to 8.8 million tonnes of plastic waste enters the ocean from coastal communities each year.[8] It is estimated that there is a stock of 86 million tons of plastic marine debris in the worldwide ocean as of the end of 2013, with an assumption that 1.4% of global plastics produced from 1950 to 2013 has entered the ocean and has accumulated there.[9] Global plastic production has surged from 1.5 million tons in the 1950s to 335 million tons in 2016, resulting in environmental concerns. A significant issue arises from the inefficient treatment of 79% of plastic products, leading to their release into landfills or natural environments.[10]
Some researchers suggest that by 2050 there could be more plastic than fish in the oceans by weight.[11] Living organisms, particularly marine animals, can be harmed either by mechanical effects such as entanglement in plastic objects, problems related to ingestion of plastic waste, or through exposure to chemicals within plastics that interfere with their physiology. Degraded plastic waste can directly affect humans through direct consumption (i.e. in tap water), indirect consumption (by eating plants and animals), and disruption of various hormonal mechanisms.[12]
As of 2019, 368 million tonnes of plastic is produced each year; 51% in Asia, where China is the world's largest producer.[13] From the 1950s up to 2018, an estimated 6.3 billion tonnes of plastic has been produced worldwide, of which an estimated 9% has been recycled and another 12% has been incinerated.[14] This large amount of plastic waste enters the environment and causes problems throughout the ecosystem; for example, studies suggest that the bodies of 90% of seabirds contain plastic debris.[15][16] In some areas there have been significant efforts to reduce the prominence of free range plastic pollution, through reducing plastic consumption, litter cleanup, and promoting plastic recycling.[17][18]
As of 2020, the global mass of produced plastic exceeds the biomass of all land and marine animals combined.[19] A May 2019 amendment to the Basel Convention regulates the exportation/importation of plastic waste, largely intended to prevent the shipping of plastic waste from developed countries to developing countries. Nearly all countries have joined this agreement.[20][21][22][23] On 2 March 2022, in Nairobi, 175 countries pledged to create a legally binding agreement by the end of the year 2024 with a goal to end plastic pollution.[24]
The amount of plastic waste produced increased during the COVID-19 pandemic due to increased demand for protective equipment and packaging materials.[25] Higher amounts of plastic ended up in the ocean, especially plastic from medical waste and masks.[26][27] Several news reports point to a plastic industry trying to take advantage of the health concerns and desire for disposable masks and packaging to increase production of single use plastic.[28][29][30][31]
Causes
There are differing estimates of how much plastic waste has been produced in the last century. By one estimate, one billion tons of plastic waste have been discarded since the 1950s.[32] Others estimate a cumulative human production of 8.3 billion tons of plastic, of which 6.3 billion tons is waste, with only 9% getting recycled.[33][34][35]
It is estimated that this waste is made up of 81% polymer resin, 13% polymer fibres and 32% polymer additives. In 2018 more than 343 million tonnes of plastic waste were generated, 90% of which was composed of post-consumer plastic waste (industrial, agricultural, commercial and municipal plastic waste). The rest was pre-consumer waste from resin production and manufacturing of plastic products (e.g. materials rejected due to unsuitable colour, hardness, or processing characteristics).[35]
A large proportion of post-consumer plastic waste consists of plastic packaging. In the United States plastic packaging has been estimated to make up 5% of MSW. This packaging includes plastic bottles, pots, tubs and trays, plastic films shopping bags, rubbish bags, bubble wrap, and plastic or stretch wrap and plastic foams e.g. expanded polystyrene (EPS). Plastic waste is generated in sectors including agriculture (e.g. irrigation pipes, greenhouse covers, fencing, pellets, mulch; construction (e.g. pipes, paints, flooring and roofing, insulants and sealants); transport (e.g. abraded tyres, road surfaces and road markings); electronic and electric equipment (e-waste); and pharmaceuticals and healthcare. The total amounts of plastic waste generated by these sectors is uncertain.[35]
Several studies have attempted to quantify plastic leakage into the environment at both national and global levels which have highlight the difficulty of determining the sources and amounts of all plastic leakage. One global study has estimated that between 60 and 99 million tonnes of mismanaged plastic waste were produced in 2015. Borrelle et al. 2020 has estimated that 19–23 million tonnes of plastic waste entered aquatic ecosystems in 2016. while the Pew Charitable Trusts and SYSTEMIQ (2020) have estimated that 9–14 million tonnes of plastic waste ended up in the oceans the same year.
Despite global efforts to reduce the generation of plastic waste, losses to the environment are predicted to increase. Modelling indicates that, without major interventions, between 23 and 37 million tonnes per year of plastic waste could enter the oceans by 2040 and between 155 and 265 million tonnes per year could be discharged into the environment by 2060. Under a business as usual scenario, such increases would likely be attributable to a continuing rise in production of plastic products, driven by consumer demand, accompanied by insufficient improvements in waste management. As the plastic waste released into the environment already has a significant impact on ecosystems, an increase of this magnitude could have dramatic consequences.[35]
The trade in plastic waste has been identified as "a main culprit" of marine litter.[a] Countries importing the waste plastics often lack the capacity to process all the material. As a result, the United Nations has imposed a ban on waste plastic trade unless it meets certain criteria.[b]
Types of plastic debris
There are three major forms of plastic that contribute to plastic pollution: micro-, macro-, and mega-plastics. Mega- and micro plastics have accumulated in highest densities in the Northern Hemisphere, concentrated around urban centers and water fronts. Plastic can be found off the coast of some islands because of currents carrying the debris. Both mega- and macro-plastics are found in packaging, footwear, and other domestic items that have been washed off of ships or discarded in landfills. Fishing-related items are more likely to be found around remote islands.[37][38] These may also be referred to as micro-, meso-, and macro debris.
Plastic debris is categorized as either primary or secondary. Primary plastics are in their original form when collected. Examples of these would be bottle caps, cigarette butts, and microbeads.[39] Secondary plastics, on the other hand, account for smaller plastics that have resulted from the degradation of primary plastics.[40]
Microdebris
Microdebris are plastic pieces between 2 mm and 5 mm in size.[38] Plastic debris that starts off as meso- or macrodebris can become microdebris through degradation and collisions that break it down into smaller pieces.[3] Microdebris is more commonly referred to as nurdles.[3] Nurdles are recycled to make new plastic items, but they easily end up released into the environment during production because of their small size. They often end up in ocean waters through rivers and streams.[3] Microdebris that come from cleaning and cosmetic products are also referred to as scrubbers. Because microdebris and scrubbers are so small in size, filter-feeding organisms often consume them.[3]
Nurdles enter the ocean by means of spills during transportation or from land based sources. The Ocean Conservancy reported that China, Indonesia, Philippines, Thailand, and Vietnam dump more plastic in the sea than all other countries combined.[41] It is estimated that 10% of the plastics in the ocean are nurdles, making them one of the most common types of plastic pollution, along with plastic bags and food containers.[42][43] These micro-plastics can accumulate in the oceans and allow for the accumulation of Persistent Bio-accumulating Toxins such as bisphenol A, polystyrene, DDT, and PCB's which are hydrophobic in nature and can cause adverse health affects.[44][45]
Amounts, locations, tracking, and correlations of the microdebris
A 2004 study by Richard Thompson from the University of Plymouth, UK, found a great amount of microdebris on beaches and in waters in Europe, the Americas, Australia, Africa, and Antarctica.[5] Thompson and his associates found that plastic pellets from both domestic and industrial sources were being broken down into much smaller plastic pieces, some having a diameter smaller than human hair.[5] If not ingested, this microdebris floats instead of being absorbed into the marine environment. Thompson predicts there may be 300,000 plastic items per square kilometre of sea surface and 100,000 plastic particles per square kilometre of seabed.[5] International Pellet Watch collected samples of polythene pellets from 30 beaches in 17 countries which were analysed for organic micro-pollutants. It was found that pellets found on beaches in the US, Vietnam and southern Africa contained compounds from pesticides suggesting a high use of pesticides in the areas.[46] In 2020 scientists created what may be the first scientific estimate of how much microplastic currently resides in Earth's seafloor, after investigating six areas of around 3 km (1.9 mi) depth about 300 km (190 mi) off the Australian coast. They found the highly variable microplastic counts to be proportionate to plastic on the surface and the angle of the seafloor slope. By averaging the microplastic mass per cm3, they estimated that Earth's seafloor contains about 14 million tons of microplastic – about double the amount they estimated based on data from earlier studies – despite calling both estimates "conservative" as coastal areas are known to contain much more microplastic. These estimates are about one to two times the amount of plastic thought – per Jambeck et al., 2015 – to currently enter the oceans annually.[47][48][49]
Macrodebris
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Plastic debris is categorized as macrodebris when it is larger than 20 mm. These include items such as plastic grocery bags.[3] Macrodebris are often found in ocean waters, and can have a serious impact on the native organisms. Fishing nets have been prime pollutants. Even after they have been abandoned, they continue to trap marine organisms and other plastic debris. Eventually, these abandoned nets become too difficult to remove from the water because they become too heavy, having grown in weight up to 6 tonnes.[3]
Plastic production
9.2 billion tonnes of plastic are estimated to have been made between 1950 and 2017. More than half this plastic has been produced since 2004. Of all the plastic discarded so far, 14% has been incinerated and less than 10% has been recycled.[35]
Decomposition of plastics
Plastics themselves contribute to approximately 10% of discarded waste. Many kinds of plastics exist depending on their precursors and the method for their polymerization. Depending on their chemical composition, plastics and resins have varying properties related to contaminant absorption and adsorption. Polymer degradation takes much longer as a result of saline environments and the cooling effect of the sea. These factors contribute to the persistence of plastic debris in certain environments.[38] Recent studies have shown that plastics in the ocean decompose faster than was once thought, due to exposure to sun, rain, and other environmental conditions, resulting in the release of toxic chemicals such as bisphenol A. However, due to the increased volume of plastics in the ocean, decomposition has slowed down.[50] The Ocean Conservancy has predicted the decomposition rates of several plastic products. It is estimated that a foam plastic cup will take 50 years, a plastic beverage holder will take 400 years, a disposable nappy will take 450 years, and fishing line will take 600 years to degrade.[5]
Persistent organic pollutants
It was estimated that global production of plastics is approximately 250 Mt per year. Their abundance has been found to transport persistent organic pollutants, also known as POPs. These pollutants have been linked to an increased distribution of algae associated with red tides.
