The impacts of plastics’ life cycle

Abstract

Plastics are commonly synthetic polymers used by many industries because they are inexpensive, durable, moldable, and have a wide range of applications. However, plastics production, use, and waste are associated with numerous challenges, including unsustainable resource use, greenhouse gas emissions, toxic chemicals, and unprecedented environmental pollution. Here, we provide an overview of plastic production, use, and end of life, highlighting how this has become such a ubiquitous problem. Interventions need to happen along the entire life cycle of plastics to reduce the burdens on communities where plastics are produced, provide more choices to consumers who want to avoid plastics, reduce quantities that leak out into our environment, and reduce harm to wildlife and humans currently being impacted by plastics use and leakage into the environment. Plastics are commonly synthetic polymers used by many industries because they are inexpensive, durable, moldable, and have a wide range of applications. However, plastics production, use, and waste are associated with numerous challenges, including unsustainable resource use, greenhouse gas emissions, toxic chemicals, and unprecedented environmental pollution. Here, we provide an overview of plastic production, use, and end of life, highlighting how this has become such a ubiquitous problem. Interventions need to happen along the entire life cycle of plastics to reduce the burdens on communities where plastics are produced, provide more choices to consumers who want to avoid plastics, reduce quantities that leak out into our environment, and reduce harm to wildlife and humans currently being impacted by plastics use and leakage into the environment. Plastics have changed nearly every aspect of our society, and although their use is relatively recent, it is difficult to imagine certain aspects of life without the material. But with the impacts of plastic pollution becoming more evident each day, the entire life cycle of the material must be examined to find ways to reduce pollution (Table 1). Over 400 Mt plastics, adhesives, and coatings are produced for use globally each year. Roughly 98% of the feedstocks used to make plastics are from fossil fuels, oil, and gas. Those same feedstocks can contribute to making plastic additives that have the potential to be toxic. Plastic pollution starts at production facilities where feedstocks are refined and petrochemicals generated. And once plastic has been used, plastic waste can leak into the environment and impact wildlife.Table 1Summary of potential plastics impactsEnvironmentcontaminationair (e.g., indoor dust, sea spray, etc.)water (e.g., surface water, groundwater, sea ice, glaciers, oceans)soil (e.g., agricultural lands, landfills)impact to plant growth/agriculture from plastics in soilschemical release and transformationpolymer-associated chemicalsadsorbed environmental contaminantsclimateextraction of fossil fuels for plastic productioncarbon cycling impeded by microplasticsBiodiversityentanglementlimited mobilitystrangulationdeathingestion and inhalationtoxicityphysical lacerationsdietary dilutiondecreased reproductive healthhabitat displacement or creationtransportinvasive speciesviruses and pathogensmicrobial growth and community dynamicsHuman health and societyexposure to chemicals near production facilitieseconomic losses from littered beachespsychological impacts from littered beachesobserved in drinking water (bottled and tap), beer, sea salt, seafood, honeycorrelation with irritable bowel syndrome (IBS)observed in the placenta, lung tissue, bloodingestion, inhalation, and dermal exposurephysical particle toxicity and accumulationchemical toxicity and accumulation Open table in a new tab Plastics have facilitated globalization and advances in medicine and electronics and have reduced immediate costs of some goods. But at what price? Once polymers are produced, they become the plastic items used every day as they get molded into products. Once these products come to their end of use, they either get discarded into the environment or enter the waste stream, where few of them get recycled and most end up in landfills. Besides use of fossil fuels as feedstocks, plastic pollution is connected to climate change through greenhouse gas emissions during production, by small amounts of emissions during their lifetime, and by impacting carbon cycling in the ocean due to trillions of microplastics that are both a new carbon source in the ocean and block sunlight for photosynthetic phytoplankton. Addressing the plastics crisis requires interventions throughout the plastics value chain. This primer provides an overview of the plastic life cycle and highlights the environmental and social costs throughout. We also discuss pathways of positive change where interventions are beginning to disrupt negative impacts. Plastics are made of polymers, a series of long-chain carbon-based molecules. Because of the properties of polymers, plastics can be molded into any shape, can have varying degrees of flexibility, are durable, and can be pigmented any color, making them useful for almost any imaginable application. Documenting all the plastic items one person touches or uses in a single day can feel like a herculean task. But it was not so long ago that plastics as we know today did not exist. While “plastics” made of naturally occurring materials, like cellulose and camphor, were on the scene in the 1800s, the first synthetic materials were invented in the early 1900s. The most used building blocks of plastics are the carbon molecules sourced from oil refining or extracted gas. For example, when raw crude oil is extracted, it is separated by distillation into various components, including fuel and naptha (a mix of hydrocarbons), for use in many applications (Figure 1). Gas extraction can also be a source of hydrocarbons (with single carbon–carbon bonds) like ethane, propane, and butane, among other components (Figure 1). The naphtha and/or hydrocarbons from gas are steam cracked at very high temperatures and then quenched, compressed, and fractionated to create olefins like ethylene and propylene (now with double carbon–carbon bonds). Ethylene, discovered in the late 1600s, is the most abundantly produced hydrocarbon in the world, at 214 Mt in 2021, and is the precursor to polyethylene (PE), polyethylene terephthalate (PET), polyesters, polyvinyl chloride (PVC), and polystyrene (PS). Initial ethylene applications were for chemical production, but there is limited application and demand for these chemicals compared with plastics. When the polymerization of ethylene was perfected to make plastics, a new, more expansive use of ethylene, polyethylene, provided and continues to provide significant applications. Petrochemical companies who may not otherwise have had use for the monomer could make plastics for use in millions of possible products. Currently, 50% of ethylene is polymerized into polyethylene, but that is not the only fraction that goes to create plastics. Ethylene is also used to make other polymers like polystyrene and polyester (Figure 1). The US produces approximately 40% of the global ethane-based petrochemicals worldwide. With fossil fuels as the primary feedstocks, plastics are inextricably tied to carbon emissions and, therefore, climate change. The steam-cracking process requires high energy and heat, which utilizes fuel and results in carbon emissions. Steam cracking of ethylene and propylene alone results in an estimated 543 Mt CO2 equivalent emissions. Plastics have been used in lightweight packaging to reduce carbon emissions for global transport. However, when the entire life cycle of all plastics is considered, along with their carbon footprint, plastic production and use comprise 3.4% of global greenhouse gas emissions. While the building blocks of plastic (monomers, like ethylene) were discovered in the 1700s, and then polymers in the 1800s, plastics as we mostly know them today did not become widely used until war times in the early 1900s, with the first annual record of production of thermoplastics, thermosets, and polyurethane (PUR). Thermoplastics have the advantage of being pliable at elevated temperatures but harden when cooled. In 1950, production of these plastics was 2 Mt; by 2021, production had increased to 390.7 Mt. However, these values do not account for plastics used in producing textiles, adhesives, sealants, coatings, paints, or varnishes or within the production of cosmetics, medicines, or chemical processes. Production of plastics became a global phenomenon, located near readily accessible supplies of oil and gas. Geographically in 2021, the majority of production takes place in China (32%), the EU (19%), North America (18%), and the rest of Asia (17%) (Figure 2). Plastic production facilities are often co-located with fossil fuel feedstocks (oil refining and gas extraction) for creating plastics. For example, in the US, the petrochemical corridor from New Orleans to Baton Rouge, LA, and the shale gas region of Appalachia and the Ohio River Valley host about 20% of the US refining capacity and 32% of the gas production, respectively, making up a significant portion of the petrochemical industry. In addition, refineries and processing facilities are often located along transportation corridors like major rivers to facilitate the transport of various production materials and products. These facilities have been placed in and near historically marginalized and underserved communities, burdening them with chemical and plastic pollution exposure at the production stage, creating environmental justice concerns for communities near industrial facilities or environmental spillage of plastic and plastic byproducts. In 2023, the Norfolk Southern railway derailed and released 100,000 gallons of vinyl chloride into the environment, including waterways. Vinyl chloride is a known carcinogen used in making plastic products like PVC for pipes, flooring, and siding. This rapid release of polymer-associated contaminants into the environment resulted in an estimated death toll of 43,000 aquatic animals, and some cities and households were shut off from drinkable municipal and well water. Even when plastic feedstock and products make it to their destination, the production of plastic can lead to the release of hazardous chemicals into the air and water of neighboring fenceline communities. Globally in 2021, the primary polymers produced, along with their resin codes (which do not necessarily indicate recyclability), are polypropylene (PP) (#5), low-density and linear low-density polyethylene LD/LLDPE (#4), PVC (#3), high- and medium-density polyethylene H/MDPE (#2), PET (#1), PUR (#7), polystyrene/expanded polystyrene (PS/EPS) (#6), and others (#7). When combined, PE plastics (HD/MD/LD/LLDPE) comprise most polymers produced, at 27%. When all plastics that use ethylene in their production are combined (all PE, PET, PVC, and PS), it is equal to just over half of all plastics produced (51%), and this does not include textiles, which are often polyesters similar to PET. Biobased plastics, currently only 2% of global production, can be made from alternative feedstocks. Initial formulations of plastics were imperfect in that they could be brittle or too tough, sometimes flammable, or just dull in appearance. Polymer-associated chemicals were produced to aid in the processing and manufacturing of a polymer or be the monomeric building block of the polymer. Over 10,000 of these chemicals serve different functionalities or aid in the longevity of the polymer, including antioxidants, plasticizers, flame retardants, UV inhibitors, antistatic agents, catalysts, lubricants, processing aids, biocides, and dyes. However, the process of manufacturing plastics also leads to non-intentionally added substances (NIASs). NIASs include chemical residue from incomplete reactions from catalysts or thermal breakdown products. NIASs also include chemicals that the manufacturer was unaware of, like additional trace chemical impurities used in the feedstocks for the polymer. Polymer-associated chemicals and their environmental transformation products or metabolites can be toxic. Roughly 92 of 906 chemicals likely associated with plastic packaging are environmental or human health hazards. One example is bisphenol A (BPA), which can function as an antioxidant in one polymer type but as a monomer for other polymers like epoxy and polycarbonate. BPA is a known endocrine disruptor linked to impacts to male and female fertility, increased risk of cancer, and metabolic disorders. Per- and poly-fluorinated compounds (PFASs) are used as lubrication, fire resistance, and stain resistance for plastic products like furniture, firefighting protective gear, or fast food wrapped products. PFASs are persistent in the environment and body and can cause harm to fetal development, increase cancer risks, and reduce vaccine effectiveness. N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) is an antioxidant used in tires that has been found to environmentally transform into 6PPD-quinone. This transformation product is linked to the mortality events of coho salmon after rain events that wash in tire rubble from roadsides into Northwestern Pacific freshwater streams. Mixtures of these released polymer-associated chemicals can have additive, synergistic, or antagonistic impacts that are not fully understood. These chemicals are not bound to the polymer and can be released into a variety of matrices at different rates that are dependent on the physical-chemical properties of both the chemical, plastic, and environmental conditions. For example, small hydrophilic polymer-associated chemicals in plastics will be released much faster into water compared with larger hydrophobic additives. Once released from the polymer, these chemicals may not remain in their original structure but can be environmentally transformed or biologically metabolized. Every plastic has a unique formulation of polymer-associated chemicals that differs by plastic type and the plastic product made. You can see this even in the labeling of a product. The recycling label on the bottom of multiple containers may say plastic type #1, but they can be different colors, which visually indicates that different chemical dyes were used in making the plastic. There is no standardization in how plastic is produced or what chemicals are utilized for each plastic type because plastic formulations are considered confidential business information or trade secrets. This makes mixing the plastic waste stream a difficult venture because the process can lead to an increase in NIASs like the original polymer additives in the previous versions of the product or environmental contaminants that are on the polymer surface. NIASs will need to be a class of chemicals commonly monitored to determine their risk to human health and the environment. In 2021, the largest sector of use for plastics was packaging (44%), followed by building and construction (18%), and then about equal percentages of automotive, electrical and electronics, and household, leisure, and sports sectors (Figure 2). Single-use packaging is used only for holding and transporting products and immediately becomes a material that must be recycled or disposed of. Therefore, the majority of plastics in use enter the waste stream relatively quickly (e.g., in less than a year). The building and construction sectors more often use durable goods that are in use for extended periods. While electronic and household goods might be used for longer periods, the inexpensive nature of some of these goods means they may create waste sooner than intended. Agricultural plastics are often used on cropland and can have a relatively higher risk of plastics or plastic fragments getting directly into the environment. Socioeconomic studies have shown that the use of plastics, especially single-use plastics, is driven by cost and convenience. Many people have been provided no affordable and accessible alternative when trying to meet their needs without single-use plastics. Global estimates are that humans generate about 2 billion metric tons of waste annually. With the primary use for plastics in packaging and items that end up in the waste stream relatively quickly, about 12% of this quantity (by mass) is plastic, which equals an estimated 240 Mt plastic waste generated annually. Since plastic is a relatively new material used with food packaging and other applications, people have had to adjust how waste is managed. Management systems have had to be redesigned to handle the rapid influx of millions of tons of plastics entering our waste stream. Of the cumulative plastic produced (8.3 billion metric tons), 77% had become waste (6.4 billion metric tons) as of 2015. 12% of this waste had been incinerated, with combustion quickly converting the carbon in plastics to carbon dioxide released into the air. On average, only 9% of plastic waste generated was mechanically recycled globally, while the majority of plastics were landfilled, with smaller fractions leaking into the environment. Plastic packaging and products are not typically designed with their end of cycle in mind. Therefore, collection, separation, and mechanical processing of a wide variety of plastics have been challenging since plastics began to enter the municipal solid waste stream in the 1950s. Today, plastics’ sheer quantity and variety continue to cause issues in the solid waste stream. For example, light, filmy plastic bags easily blow out of trash cans, trucks, and away from landfills. Plastic films also cause mechanical issues at material recovery facilities (MRFs) if they are accidentally put into curbside recycle bins. To recycle plastic bags and film in the US, people must drop them off at separate collection centers, typically grocery stores, where they may eventually become patio deck boards. Some plastics, especially those from biofeedstocks, can be made biodegradable or compostable. Polymers like polylactic acid (PLA) must reach high temperatures in industrial composting systems to biodegrade. Polymers like polyhydroxyalkanoates (PHA) do not need higher temperatures than normal when in contact with microbes to biodegrade; however, the speed of biodegradation will depend on the temperature and microbial consortia. Oxo-degradable additives to any non-biodegradable polymer only make that polymer fragment into smaller pieces faster but do not change biodegradation. One of the critical components of an efficient and effective waste management system is to match the waste components with the management infrastructure. If food waste is a significant component of the waste stream, composting can help avoid methane emissions. And if compostable or biodegradable packaging is a new component of the waste stream, it should be matched with industrial composting infrastructure; otherwise, it too can create methane emissions at landfills. The wide variety of plastic products does not always match the infrastructure and recycling markets for mechanical recycling to become a significant part of any plastic waste management system. Chemical and thermal recycling of municipal waste plastics remain unproven. Even with formal waste management, plastic waste has been shown to leak into the environment. Globally, millions of informal waste workers collect waste as their livelihood. Unfortunately, many informal workers are not provided proper health and safety protection and are often disrespected and unrecognized. Typically working under harsh conditions, they still help to keep valuable plastics out of the environment and in a recycling system, but it is often at a cost to their health. 79% of plastic waste has gone into landfills or the environment, and on an annual basis, an estimated 11 Mt plastics reach our oceans. Terrestrial lands are the most common sink and source of plastic debris in the environment. However, plastic can be blown into the air or washed away into freshwater streams and rivers (Figure 2). Low-density plastics can float on the surface of freshwater and be transported into the ocean, where they can travel globally on currents. Litter studies find that about 60%–85% of litter (by abundance) is plastic. And of these items, the most common items from the 2022 International Coastal Cleanup are food wrappers, cigarette butts, plastic beverage bottles, bottle caps, plastic grocery bags, glass bottles, aluminum cans, straws, plastic cups, and plates. It was in the 1960s that plastics were first found in the environment, as US Fish and Wildlife scientists were finding birds interacting with and being impacted by plastics ending up in the environment. Some of these interactions include plastic ingestion or entanglement. Plastic in the environment has been observed to be ingested by 1,288 marine species and 277 terrestrial and freshwater species. Impacts on wildlife from interaction with plastic include nutritional dilutions, limited mobility, strangulation, habitat displacement, and toxicity to the organism. Some of these issues can lead to a decrease in the reproduction of species or even mortality events in a population, which can cascade into impacting the entire food web and biodiversity. Those losses in available seafood can impact more than 10% of the world’s population that depends on fishing for income. Plastics during use and disposal will eventually be weathered by the environment over time (e.g., oxidation exposure to air and sun, causing plastics to become brittle, crack, and fragment). Polymer degradation can range from days to thousands of years, depending on the exposure conditions (Table 2). This time range is determined by various factors: physical-chemical properties of the polymer, physical wear and tear, sunlight exposure, heat, water, biological consumption, etc. The process of polymer weathering leads to the release of fragments, microplastics, nanoplastics, and polymer-associated chemicals. Microplastics are smaller than 5 mm in size and are intentionally manufactured at those sizes (pre-production plastic pellets, glitter, etc.) or are fragments of larger pieces of macroplastics. Microplastics have gained widespread attention within research and the media due to their ability to easily travel globally through the environment to locally within organisms, animals, and the human body. Nanoplastics are similar to microplastics but are smaller than 1 μm, which allows these particles to travel further in the environment and into biological tissues. Trillions of microplastics are estimated to be on the ocean’s surface, and over a thousand tons of microplastics are deposited annually onto the western US national parks from the air. The majority of microplastics detected in the environment are microfibers originating from textiles like clothing, furniture, and carpets. Microplastics and nanoplastics have large surface areas, which can allow for increased release rates of polymer-associated chemicals.Table 2Summary of sources, pathways, transition, and sink areas for plastics in the environmentPlasticsSourcesPathwaysTransition and sink areasMicroplastics (e.g., plastic resin pellets, microfibers in water from washing, microfibers from dryers and abrasion of textiles into air, etc.)industrial pellet and material lossblown or washed by stormwater runoffterrestrial environment (e.g., urban/rural areas, biosolids on agricultural lands, landfills); remote beaches and ocean deposition sitesRivers (catchment areas); lake, river, ocean sedimentsFloat on the ocean surface to be carried globally, ingested by animalswastewater treatment facilitiesdischargetextiles, furniture, carpetsatmospheric transport and depositionMicroplastics (e.g, tire and paint particles, fragmentation of larger items, etc.)Macroplastics (e.g., general trash and items like plastic bags, etc.)stormwater runoff and combined sewer overflowwashed directly to waterways by drainage systemsroadside waste (e.g., litter) and dumpsitesblown or washed by stormwater runoffwaste management systemsblown away during collection, transport, and recycling/disposalMicroplastics (e.g, fragmentation of larger items)Macroplastics (e.g., general trash and items like plastic bags)Lost fishing gearfreshwater and marine recreation, boating, and fishingdirect into waterways, rivers, the oceancommercial fishingdirect into waterways, the ocean Open table in a new tab Plastics and polymer-associated chemicals may directly impact humans via inhalation, ingestion, and dermal exposure to plastic particles. Microplastics have been detected in the human digestive tract, lung tissues, blood, and placenta. These substances may cause harm to the body as they are foreign objects that can release potentially hazardous polymer-associated chemicals. In addition to the chemical exposure, there is the physical toxicity of the nanoplastics and microplastics because they can have jagged edges, host microbial communities, and viruses, have adsorbed environmental contaminants, and contain charged surfaces. Many of the impacts of plastic contamination in the human body are not fully understood and will require further study. Waste generation reduction, especially in high-income countries where plastic waste generation rates are highest, is a critical component of addressing plastic waste management. In addition, the impossible task of connecting an estimated 500,000 people to solid waste collection services each day until 2040 is what would be needed to collect all waste to keep plastics out of the environment and the ocean. While evolved waste management is necessary to reduce plastic pollution, it cannot be the only component. As a result of the massive volume of plastic and microplastic pollution that is not readily recoverable and the release of these polymer-associated chemicals, plastic pollution is now being considered a planetary boundary threat. The use of petrochemicals, plastics, and plastic pollution is a wicked problem in a complex system that can benefit from the use of systems thinking, interdisciplinary, and mixed-method approaches. Plastics touch all aspects of our lives, so many disciplines can contribute to the body of science and interventions to reduce plastic pollution, from physical, natural, and health sciences to social sciences and humanities, business and marketing, engineering and material science, journalism and communications, education, and the arts. Creativity can expand the horizons for interdisciplinary and holistic approaches to this issue. Interventions need to happen along the entire life cycle of plastics to reduce the burdens on communities where plastics are produced, provide more choices to consumers who want plastic alternatives, reduce plastic quantities that leak out into our environment, and reduce harm to animals, including humans, currently being impacted by plastic use and leakage into the environment. Source separation of organic materials, materials for recycling, and residuals can help reduce landfilling, even reaching a goal of 90% landfill diversion or “zero waste.” Interventions to reduce use include looking at unnecessary, avoidable, and problematic (UAP) plastics. While these terms are context dependent (some plastic items may be necessary in certain locations where, in other cases, they are not, e.g., water bottles). Problematic plastics are items that contain compounds or additives that we know are toxic (e.g., BPA, 6PPD, PFAS) or make them harder to manage at the end of life (e.g., black in color). Chemical simplification of plastics and plastic-associated chemicals that is listed in publicly accessible databases will allow recycling to be better streamlined and reduce the opportunity for potentially hazardous chemicals to be mixed into a recycled product. But where there are alternatives, petroleum-based plastics can be replaced in various applications to avoid fossil feedstock use and reduce plastics’ contributions to climate change. Further upstream from where plastic is used and waste is generated, there are options like reuse schemes, which can be centralized (e.g., return shipping for wash and refill) or decentralized (e.g., local refineries, bulk good stores, and food container wash/reuse schemes). Companies in the plastic space are making commitments to change, especially when consumers express a preference for alternatives to plastics. The cost of plastic and the convenience of fast-paced lifestyles continue to be drivers for plastic use. Policies are, and will be, an essential part of life cycle interventions. Bans, taxes, recycling and procurement requirements, and extended producer responsibility (EPR) are policies enacted to reduce plastic pollution. Cities worldwide, which often bear the brunt of waste management and pollution, are collecting data on their circularity, making zero waste goals, and deciding what will work best for them in their context. However, cities and community members are still limited by the larger system. The commitment made at the United Nations Environment Assembly (UNEA) 5 in 2022 to create a legally binding global treaty is one path to bring all stakeholders together to address plastic pollution along the entire life cycle of plastic. While the treaty is under negotiation (set to be complete by 2024), there are still opportunities for national, state, and local governments, companies, and non-governmental and grassroots organizations to move forward with their own initiatives with the knowledge at hand. J.R.J. is a co-founder of Can I Recycle This (CIRT) and a board member of the Marine Debris Foundation.