ToxPoint: Waste incineration management of plastic materials—an issue of increasing global public health importance

Plastics, synthetic or semi-synthetic polymeric materials, were first synthesized in the late 19th century and mass-produced throughout the 20th and 21st centuries. They are essential materials in everyday life. Their plasticity, low density, toughness, and low electrical conductivity make them vital for numerous industries, including construction, medicine, consumer products, transportation, and food packaging. Plastics are typically derived from crude oil or gas processed into monomers and polymerized with various chemical additives to enhance properties like ultraviolet light (UV) stability, heat resistance, and flexibility, enabling their widespread and economical production. Because of their broad use, plastic production and waste generation have become critical environmental health issues, with up to 50% of plastics designated for single-use, resulting in significant waste (Chen et al. 2021). Global plastic production has doubled because the 21st century began, exceeding 380 million tons annually (Geyer et al. 2017; Pathak et al. 2023; Nayanathara Thathsarani Pilapitiya and Ratnayake 2024). Plastics, which can take centuries to decompose, add to the nearly 8 billion tons of existing waste, leaching harmful chemicals like bisphenol A (BPA), phthalates, and per- and polyfluoroalkyl substances (PFAS) into the environment. These compounds contaminate soil and water and bioaccumulate in organisms. Microplastics and the more damaging nanoplastics, which originate from larger debris and personal care products, are widespread in oceans, soil, air, and human food and water. With over 358 trillion microplastic pieces on the ocean’s surface alone (Prata 2018; Qiao et al. 2019; Lu et al. 2022; Walker and Fequet 2023), their pervasive presence is concerning. Plastic waste management is challenging, with 49% of waste going to landfills, 22% mismanaged, only 9% recycled, and 19% incinerated, which releases harmful chemicals into the air (Hu and Shy 2001; Simoneit et al. 2005; Verma et al. 2016; Geyer et al. 2017; de Titto and Savino 2019; Pathak et al. 2023). Hence, the increasing production and use of plastics necessitate improved waste management strategies to mitigate environmental contamination. Whereas accumulation and oral exposure to microplastics have gained significant attention, potential inhalational exposures as a consequence of incineration of plastics need to be considered.

Incineration of complex polymeric materials, such as plastics in municipal solid waste (MSW), introduces a variety of physical and chemical threats to the respiratory system. The United Nations Environment Program reports over 13,000 chemicals associated with plastics and highlights ten groups of high-toxicity chemicals, including flame retardants, UV stabilizers, and phthalates (Petrlik et al. 2024). Additional threats derived from plastic incineration include persistent organic pollutants (POPs) such as dioxins, PFAS, and polycyclic aromatic hydrocarbons (PAHs), as well as volatile organic compounds (VOCs), metalloids, carbon monoxide, and other chemicals known to contribute to respiratory, cardiovascular, endocrine, and neurological dysfunction and disease. In addition, smoke from plastic incineration contains large amounts of particulate matter (PM), a major contributor to premature global mortality and associated with respiratory, cardiovascular, and nervous system dysfunction. Consequently, incineration of mixed plastics produces overwhelmingly diverse physical and chemical emissions, making it challenging to identify and test all emission products. Due to its complex nature, further research is critical to fully understand the health risks associated with emission mixtures from plastic incineration.

In addition to the diversity of plastics themselves, the temperature of incineration significantly affects the chemical composition and physical characteristics of the emission mixtures. Higher incineration temperatures (500–600°C) result in peak concentrations of carbon monoxide and hydrogen cyanide, which correlate with severe respiratory issues and increased mortality in studies. Additionally, smoldering temperatures (500°C) produce more PM and VOCs than flaming temperatures (640°C) of plastic incineration, whereas flaming temperatures result in much greater PAH/g PM (Kim et al. 2018), highlighting how incineration temperatures affect particulate chemistry and the need for temperature control in incineration processes. Very high temperatures used in municipal thermal incinerators (980–1200°C) can achieve near-complete combustion, significantly reducing VOCs, PM, and PAHs, but residual pollutants may still remain in the ash.

As indicated above, approximately 19% of all plastic waste, translating to over 72 million tons is incinerated annually, resulting in the release of toxic chemicals and PM. In many low- and middle-income countries and rural areas of developed countries, lack of access to solid waste management services leads to household disposal of plastic waste, resulting in environmental contamination through open dumping, burning, or burial of waste (Bardales Cruz et al. 2023). The open burning of plastic is common in these regions, also often used as a fuel source for cooking and heating, exposing inhabitants to high levels of pollutants. For instance, in Guatemala, 43% of households burn their waste, contributing significantly to air pollution and health issues (Bardales Cruz et al. 2023). Unfortunately, developed countries further contribute to global plastic incineration emissions by exporting plastic waste to underdeveloped countries with insufficient waste management infrastructure. Backyard burning of plastics releases unfiltered toxic smoke into the atmosphere, directly introducing toxic and carcinogenic compounds into the environment. This highlights the need for improved waste management strategies and environmental justice, as waste facilities often disproportionately affect racial minorities and high-poverty communities.

Moving forward, understanding the public health effects of plastic incineration emissions is critical due to the increasing demand for plastic waste removal and the levels of respiratory toxins plastic incineration releases. However, exposure to plastic waste emissions is often part of a mix of various waste incineration emissions, making it difficult to isolate the effects of plastic alone. Studies are scarce but suggest significant systemic and respiratory health impacts, and increased risk for heart disease and neurological disorders (Nayanathara Thathsarani Pilapitiya and Ratnayake 2024); for instance, residents near a plastic reprocessing factory reported higher respiratory and mucocutaneous symptoms, whereas workers in the fiberglass and plastic industries experienced increased respiratory issues and impaired lung functions due to VOC and microplastic exposure (Sati et al. 2011; Helal and Elshafy 2013; Turcotte et al. 2013; Loomis et al. 2019; Zulu and Naidoo 2022). Evidence from general waste incineration emissions further indicates respiratory health risks, including reduced lung function and increased cancer risk for workers and nearby residents, linked to toxins like PAHs and dioxins present in plastic emissions (Li et al. 2001; Williams 2005; de Titto and Savino 2019; Conesa et al. 2020; Pathak et al. 2023). Additionally, exposure to open incineration in military burn pits often involving plastic waste, has shown severe respiratory consequences for military personnel. Together these studies highlight the need for further research on specific health outcomes related to plastic waste incineration. For example, characterizing biomarkers of plastic incineration emissions exposure, preclinical studies uncovering effect signatures, or remediation removing sources of exposure linked with population health data would help fill some of these knowledge gaps. As such, innovative solutions for plastic waste removal are needed. Interestingly, countries like Singapore are developing innovative mechanisms harnessing the energy generated through waste incineration to power thousands of households with electricity. As the toxicological consequences of plastic waste creation and management become further understood, new and innovative techniques to manage plastic waste and the toxic chemicals that can be released by incineration of such wastes as well as clear and strong regulations on emission and emission control measures are desperately needed.

Funding

This manuscript was supported by the U.S. Army Medical Research Acquisition Activity, through the Department of Defense Peer-Reviewed Medical Research Program under Award No. WI1XWH-18-1-0731 of the United States Department of Defense (I.J.) and grants (T32 ES007126) from National Institute of Environmental Health Sciences (K.R.). Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the Department of Defense.

Conflicts of interest. None.