Buy-now-pay-later: Hazards to human and planetary health from plastics production, use and waste

Global plastic waste management has lagged behind waste production with only approximately 9% being recycled. 1 Traditional mechanical recycling methods largely yield down‐cycled plastic of inferior quality, more limited application and reduced recycling options. 64 Emerging chemical recycling technologies provide potential recycling of the same plastic, 65 , 66 but need further development to address high cost and energy requirements. A greater proportion (12%) is incinerated in purpose‐built facilities. This provides an option for lower grade non‐recyclable plastic, but releases the embedded carbon as carbon dioxide. In the absence of controlled incineration, open burns are common, releasing toxic airborne pollutants alongside embedded carbon. 67 The vast majority (79%) of plastic waste is discarded. 1 Even in the best‐case scenario, processing and landfill results in accumulation because anaerobic conditions limit degradation. 68 Of all plastics produced annually, nearly half is mismanaged, 69 with littering or leaking from landfills resulting in pollution of land, freshwater waterways and the ocean. 70 The visible components of plastic waste are macroplastics including plastic products that retain sufficient integrity to be recognisable and initial fragmentation products. Progressive weathering and fragmentation lead to ever smaller fragments, namely microplastics (<5 mm) 71 and nanoplastics (typically defined either as <1 μm or <100 nm). 5 , 71 Macroplastics present certain physical hazards to humans such as injury and substantive hazards to marine life. 72 There is strong public awareness of these environmental hazards, especially for marine life, but less so of micro‐ and nanoplastics. 6 , 7 Micro‐ and nanoplastics present very different hazards, with four key areas of concern being: leaching of additives; plastic particles as vectors for environmental contaminants and micro‐organisms; indirect effects through actions at the lining of our guts or lungs; and, for particles small enough to pass through biological barriers, direct effects within tissues. In addition to degradation of waste macroplastics, micro‐ and nanoplastics are also intentionally added, for example as abrasives in personal care products, 73 , 74 , 75 , 76 or released from plastic products during daily use, including synthetic clothing, 73 , 75 , 77 plastic food containers and even baby bottles. 78 Most research has focused on larger microplastics >10 μm that are visible with microscopy techniques. There are concerning knowledge gaps regarding nanoplastics which, because of their smaller size, are anticipated to pose greater hazards for human toxicity. 5 The smallest microplastics (<10 μm) and nanoplastics are too small to detect with microscopy techniques used for larger microplastics, and their small size poses additional analytical challenges, 5 with techniques only beginning to emerge. Microplastics have been detected in almost every part of the environment, 75 , 76 , 79 including freshwater and air, 73 , 75 , 76 in drinking water and a diverse range of foods and beverages including honey, milk, seafood, table salt and beer. 73 , 74 , 75 Estimates of microplastic ingested are imprecise, but could be as high as approximately 200 000 microplastic particles/day or 0.1–5 g/week. 80 Microplastics are present in stools of humans and also many animals. 81 Animal studies have reported multiple local effects of engineered nano‐ and microplastics in the gut, including inflammation, barrier function deterioration and gut microbiota changes. 76 Airborne microplastics are prevalent even in very remote planetary regions. 82 Inhalation of airborne microplastics is modelled to be a major route of human exposure, 73 , 83 with evidence for plastic fibres in human lung tissue. 82 , 84 There are multiple sources of airborne microplastics including microplastic fibres from synthetic textiles and the synthetic textile industry 82 , 83 and microplastic degradation products from vehicle tyres. 82 ‘Tyre crumb’ alone is a substantive component of overall PM 2.5 and PM 10 particulate air pollution, 82 although the overall contribution of microplastics is unknown. 82 Occupationally exposed textile workers may experience a range of interstitial lung disease 82 , 83 : lung biopsies reveal inflammation, fibrosis and granuloma formation. 82 , 83 In vitro studies in human lung cell lines have separately reported pro‐inflammatory, cytotoxic or pro‐apoptotic effects of engineered nano‐ and microplastics. 82 The likelihood of uptake of micro‐ and nanoplastics through gastrointestinal and alveolar epithelium differs by size. 5 , 73 Animal and in vitro models of human biological barriers show translocation of microplastics below 5–10 μm from the gut into the circulatory and/or lymphatic systems. 73 , 75 , 85 In animal models, in vitro and in a human placental perfusion study, engineered nanoplastics cross cell membranes as well as specialist biological barriers such as the mammalian placental barrier and blood–brain barrier. 73 , 75 To date, microplastics have been detected in human faeces, 86 lung 82 , 84 and colectomy samples 87 as well as placenta 88 , 89 although the latter requires further confirmation. Techniques to directly detect nanoplastics in human tissue are yet to be established. It is not known what the direct biological effects of micro‐ and nanoplastic fragments may be in the diverse tissues and organs but there is the potential, as shown in animal models and human in vitro studies, to disrupt fundamental processes across multiple cell types and trigger, for example, inflammation and oxidative stress. 75 , 85 , 90 Not only do micro‐ and nanoplastics contain complex mixtures of additives and other chemicals from their initial manufacture, but there is growing evidence that once in contaminated environments, like our ocean, toxic chemicals including POPs 75 , 77 and heavy metals 77 accumulate through adsorption. Decreasing particle size results in increasing surface‐area‐to‐volume ratio, providing greater opportunity for diffusion of additives from the plastic, or adsorption and subsequent release of chemicals from the environment. 5 Nanoplastics are of particular concern because the combination of available surface‐area for exchange and tissue penetration due to their small size could deliver locally high doses of leached compounds. 5 Environmental microplastics may also be coated with a biofilm or ‘eco‐corona’, 5 of particular concern due to mixing between microplastics and human effluent in sewerage. 77 There is evidence that biofilms carry pathogenic bacteria, some with microbial resistance. 72 , 75 , 77

We need to fundamentally re‐think plastics. Consumers perceive plastics to be cheap, convenient and recyclable. 7 But plastics are complex mixtures of industrial chemicals, and our review uncovers an intricate set of hazards that we poorly understand and are currently failing to manage. Not only are plastics rarely recycled to keep them out of waste streams and turn the virgin plastic production tap off, but they are also largely not recyclable with existing technology. As with other fossil fuel commodities, market forces are not factoring in the cost of managing hazards to human and planetary health, and current generations are effectively passing responsibility for the problem onto future generations who do not have a voice. As consumers, we can value the full cost of the plastic we use each day, ‘choose to refuse’ and reduce use. We can be curious and ask questions about where the plastic comes from, what is in it and where it goes. As medical professionals, we have expertise to share the science and the respected voice to advocate for the health of future generations and the planet that they depend on. We can use that voice to advocate with regulators so that industry takes responsibility for the hazards of their products, and to empower consumers to demand this of industry, regulators and brands. Change is possible. Plastics can be simpler, safer and recyclable. This will require improved recycling technology to turn off the tap on virgin plastic, 91 redesign of the plastics themselves and redesign plastic chemical regulation. Working with industry to introduce extended producer responsibility for plastic use and waste management will require intervention by policy‐makers to reduce demand for plastics, for example by banning unnecessary plastic applications, and to level the economic playfield for sustainable circular plastic, for example by taxing virgin fossil fuel‐based feedstocks and introducing minimum recycled content standards. A mechanism for post‐marketing surveillance, just as with pharmaceuticals or pesticides, is also critical. We should not be producing vast quantities of chemicals of unknown human toxicity if we cannot detect human exposure nor monitor health effects. Transparency around additives and non‐intentionally added substances in plastics is therefore essential, as are methods for detecting plastic chemicals in ongoing biomonitoring programmes. Investment in techniques to measure nanoplastics and study their health effects is also critical. Change is starting. Global bodies such as the Organisation for Economic Co‐operation and Development are reviewing our relationship with plastics, 92 as are influential regional regulatory bodies such as the European Union. 93 , 94 Canada has defined plastics as toxic, 95 acknowledging the environmental impact of plastic and its harm to human health. Adding the authoritative voice of medical professions to advocate for the health of future generations is a critical element that adds weight to the urgent need to regulate and redesign plastic.