From the Arctic depths to the Pyrenees, plastic waste has pervaded every corner of Earth. Agricultural land, surface water, freshwater lakes, and river sediments have all been reportedly contaminated by discarded plastic and plastic particles. Particles under five millimetres in diameter form the most-recently identified microplastic pollution threat - these often include microfibers, or strands of synthetic textiles shed by clothing run through washing machines.
Plastics are a clear, visible, and established cause of pollution both on land and in water. More than 5 trillion plastic pieces weighing over 250,000 tones are estimated to be floating around the globe, and ocean currents have accumulated them in areas like the “Great Pacific garbage patch” now covering an area larger than Greenland.
Microplastic pollution is now globally pervasive; it has been found in every ecosystem on Earth, including the Arctic, deep ocean trenches, and on remote slopes of the French Pyrenees.
A typical, five-kilogram load of polyester fabrics is estimated to produce over six million microfibers in one wash. Deteriorating car tyres are also thought to be a top contributor to microplastic pollution, and are the subject of ongoing research.
Microplastics have also been detected in the digestive tracts of animals including coral and tiny creatures like plankton. This could cause serious harm due to bio-amplification along the food chain - some 90% of seabirds are estimated to have ingested plastic - and due to pollutants or toxins that accumulate on their surfaces.
Soluble plastic additives to shampoos, soaps, detergents, cleaning products, and fabric treatments also present threats as aquatic pollutants - and on a scale that while difficult to quantify is nonetheless likely significant.
New technologies for the clean-up of plastic pollution have been developed, but are still far from perfect - or are not applicable on a broad scale. For example, technology solutions focused on removing free-floating plastic from the ocean surface have faced challenges including relatively high costs and unintended negative effects on sea life.
Plastic Reduction and Replacement
There are several potentially negative consequences of banning plastic worth considering. The first priority of any “circular economy” (as opposed to the traditional, “take, make and dispose” model) approach to the issue should be to reduce the overall use of plastics. Just reducing annual growth in plastics demand from the current 4% to 2% would result in a 60% reduction in carbon emissions generated by the plastics sector by 2050. Total global plastic production rose to 348 million tonnes by 2017, compared with 335 million tonnes in the prior year, according to the pan-European plastics manufacturers association PlasticsEurope.
70 countries have now introduced bans on single-use plastic bags, and many countries are moving towards full bans on all single-use plastic products including straws, cups, bottles and utensils. However, there are potential unintended consequences of a move away from plastic.
These include a possible, related increase in demand for aluminium, paper, or wood - the use of which may deliver a heavy environmental impact. A UK government study found that a single cotton tote bag must be reused more than 130 times in order to have lower global warming impact than a conventional, single-use polyethylene plastic bag.
The issue of less-than-helpful alternatives is particularly relevant in countries such as India, which has instituted a ban on single-use plastics - but already has relatively low per-capita use of plastics (11 kilograms annually per capita, compared to 96 in the US), coupled with high economic growth expectations.
Plastics are ubiquitous in any modern economy, and could actually be a vital means to help us to achieve several Sustainable Development Goals - the 17 United Nations guideposts designed to help put the world on a more sustainable footing by 2030.
Building the infrastructure required to supply clean energy, for example, requires plastic for related electronics, while plastic packaging helps preserve and protect food necessary to feed an expanding global population, and sterile, lightweight plastics are essential for medical devices like catheters, syringes, and IV bags. However, the extensive and expanding use of single-use plastics is causing severe environmental damage.
Bans or taxes on items such as plastic bags or straws in several countries have already resulted in substantial reductions in use. In the United Kingdom, single-use plastic bag use has declined by 86% since the introduction of a 5p tax per bag in 2014.
PLASTICS AND THE ENVIRONMENT
New non-petrochemical feedstocks and materials, policies, and regulations are required in order to responsibly reduce plastic consumption and transition to a more circular plastics economy. Emerging technologies, such as chemical recycling, may accelerate this transformation.
About 350 million tons of plastics are produced annually, and more than half of that is dumped in either a landfill or the oceans every year. Plastics - whether soluble, disposable, or durable - cause pollution at almost every stage of their lifecycle, starting with the use of fossil fuels for their production.
However, they are also essential for a cleaner and more sustainable future, thanks to practical applications ranging from water-purification to medical devices.
It is time to take action! Join our Tribe of Changemakers. Sign up for Virtual Conversations!
Plastic Waste Management
The scale of the plastic waste problem unfortunately hampers international regulation, which requires action at a local, national and global level. Developing countries have complained about a deluge of plastic waste from the developed world.
Despite decades of progressively stricter environmental regulation in many countries and multiple voluntary international pledges to limit marine litter generally and plastic pollution specifically, land-based pollution remains a significant source of harm to the oceans.
Many waste flows have been diverted to other countries such as Indonesia, the Philippines, Thailand, Malaysia, and Viet Nam, despite the fact that the United Nations Development Programme has been arguing since 1989 that the export of waste from developed to developing countries perpetuates inequality.
Some countries, following China, have begun questioning their expanded role as repositories for the world’s plastic waste; Cambodia announced in mid-2019 it would return thousands of tonnes of plastic waste found in containers shipped from the US and Canada, while Indonesia and Malaysia have also announced plans to return loads of waste to countries including Australia and France.
Infrastructure for the waste management of plastics that have reached the end of their useful existence can sometimes be non-existent - particularly in developing countries. This can lead to plastics being dumped straight into the environment (a study published in 2019 found that plastic recycling rates in developing economies with a minimal industrial base were close to 0%, compared with about 30% in developed economies with regulations encouraging the practice).
Where the infrastructure does exist for plastic waste management, it can often be unfit for purpose and a major barrier to both innovation and responsible regulation. Landfills, for example, are unsustainable in the long-term, particularly in countries with high-density populations. They can also be a source of pollution and negative health impacts due to seepage or waste burned on open fires.
Recycling infrastructure in general can be problematic if it is poorly used domestically or relies on overseas processing. According to a study published in 2018, China had imported 42% of the world’s plastic waste accumulated since 1992 - making China’s ban on imported waste in 2018 enormously disruptive for the global plastic waste trade.
Chemical recycling and promising new technologies need to be more fully explored. Further innovation is therefore essential, ideally with a focus on both mixed mechanical recycling and chemical recycling. The latter uses thermolysis (applying heat) or catalysts to break down plastics into their component parts, which can then be re-built into new plastics.
In order to make recycled plastic products, old PET or polyethylene is blended with virgin plastics in an expensive, energy-intensive process that ultimately results in lower-quality finished material.
Complete depolymerisation involves breaking a plastic down to monomers (molecules), which can enable multiple recycling loops with lower energy requirements - all while maintaining the material properties of the finished product.
Mechanical recycling is the only method now commonly used for the large-scale treatment of solid plastic waste. Because every type of plastic differs in terms of chemical composition, mechanical behaviours, and thermal properties, however, conventional mechanical recycling requires pre-sorting to separate non-plastic items and different varieties - which can be costly and time-intensive. In addition, the two types of plastic that can currently be mechanically recycled, polyethylene terephthalate, or “PET,” and some grades of polyethylene, together make up less than half (46%) of all annual plastic production.
Plastics additives and impurities can interfere with recycling, and policies that make plastic producers responsible for the impact of the entire product lifecycle may help commit more manufacturers to better design, while improving the economics of current end-use options.
In general, chemical recycling is under-explored - though it is also the most feasible approach for dealing with PET (it is also expected to become possible for biodegradable and compostable polyesters). Innovative recycling technologies that enable the direct processing of mixed plastic waste without pre-sorting may offer other potential solutions. This would require a means to stabilize the behaviour of mixed plastic waste during the recycling process - and would have to be facilitated by better design of the ways that plastic products reach their “end-of-life.”
Some positive related signs include Unilever’s pledge that by 2025 all of its plastic packaging will be fully reusable, recyclable, or compostable. Moves like this are more necessary than ever before, as new plastics can create problems for mixed waste recycling; for example, PET and the bio-polymer PLA (polylactic acid) can each compromise the recycling of the other if they are mixed.
What makes plastics so effective can make them catastrophic for the environment. In general, there are fears that labelling products as biodegradable or compostable triggers negative behaviour including littering, and that a lack of effective recycling systems means these plastics will end up as landfill or be incinerated. Biodegradability depends on conditions and timing; “PLA” (polyactic acid), for example, degrades in about 12 months if placed in composting plants at specific temperatures and with specific micro-organisms.
The durability of plastics is one of the reasons they are so successful and widely used. About 60% of the plastics market is made up of long-life polymers used in the automotive and construction sectors, where products need to be built to last. However, many plastics - especially the single-use variety - last far longer than they are useful. Improving degradability is therefore one way to reduce the risk of plastic pollution.
There are two main types of plastic that can break down relatively quickly: biodegradable, and oxo-biodegradable. The biodegradable variety degrades with the assistance of a biological agent, though there are many different chemical formulations that break down in different ways, in different circumstances, and over different time periods. Biodegradable plastics that feature ester (a compound derived from an acid) or glycoside (a sugar molecule) linkages fully break down naturally, whereas others contain carbon-carbon bonds that cannot be naturally broken.
Biomass-based plastics are often but not always biodegradable, and one step removed from compostable plastics that can be identifiable thanks to labeling standards.
These materials can fully biodegrade at temperatures over 60°C in less than 12 weeks, and some can degrade in domestic compost.
Oxo-biodegradable plastics are conventional plastics with additives that help them react with oxygen to speed up degradation. There are concerns that these could lead to an accumulation of microplastics, because once they fragment there is not always further degradation (the European Union, for example, has restricted their use).
One recent study found that plastic bags labelled as biodegradable or oxo-biodegradable were found to be intact and able to hold weight after three years in seawater or buried underground, while compostable plastic bags were intact after being buried for three years. While compostable plastics can degrade in a natural environment, this may take a long time barring ideal conditions.
A UN Environment Programme report published in 2015 concluded that complete biodegradation of plastics occurs in conditions “rarely, if ever, met in marine environments.”
Plastics and Net Zero Emissions
More sustainable alternatives have yet to gain significant market share.
The plastics industry can act to reduce related carbon emissions to net-zero; there are several innovative, low-carbon feedstocks that are potential alternatives to virgin petrochemicals. Some examples include wood, corn starch, agricultural by-products, recycled plastics, and even direct production using existing carbon dioxide emissions.
The scale and cost of the existing plastics infrastructure is a significant barrier to large-scale introduction of these alternatives. In order to be more competitive, alternative plastics will need to be capable of being integrated into the existing infrastructure - and to deliver the same material properties and economics of existing plastics.
The vast majority of plastics are manufactured using petrochemicals. About 10% of all the oil and gas produced in the world goes towards making plastics, which ultimately accounts for 3.5% of all greenhouse gas emissions. While most of these emissions are generated by the production and manufacturing of plastic products, some come from their disposal.
Polycarbonate polymers, for example, can be made up of as much as 50% carbon dioxide, and can replace conventional polyurethanes used for housing insulation, foams and fillers, locking up substantial amounts of CO2 for decades.
About a quarter of all plastic waste is incinerated, causing direct emissions, and 55% is discarded either into a landfill or straight into the environment. Landfills are not sustainable, and up to 40% of landfill waste is potentially burned in open fires in a way that releases carbon dioxide and other pollutants.
Using agricultural waste material to create new plastics is a particularly attractive proposal, not least because it could reduce the risk of land competition for food crops. Corn, cassava and sugarcane crops are already being used to create one alternative biodegradable bio-polymer, “PLA” (polyactic acid), which generates relatively less greenhouse gas over its lifecycle than conventional plastics. PLA has already been commercialized for use in packaging, though its share of the overall market remains small.
To reach net-zero emissions, the industry will also need to transition to renewable energy sources to power its operations; this alone could reduce overall emissions from plastics by about half. Ultimately, alternative plastics are unlikely to become genuinely sustainable without having a proper infrastructure in place for collection and recycling.