Plastic waste reprocessing for circular economy: A systematic review of risks to occupational and public health from legacy substances and extrusion

Abstract

Increasing aspirations to develop a circular economy for waste plastics will result in an expansion of the global plastics reprocessing sector over the coming decades. Here we focus on two critical challenges within the value chain that as a result of such increased circularity may exacerbate existing issues for occupational and public health (1): Legacy contamination in secondary plastics, addressing the risk of materials and substances being inherited from the previous use and carried through into new products when the material enters its subsequent use phase; and challenge (2): Extrusion of secondary plastics in reprocessing, an end process of conventional mechanical recycling of plastics, involving heating secondary plastics under pressure until they melt and can be formed into new products. Via a systematic review (PRISMA guidelines, adapted), we considered over 4,000 sources of information, refined and consolidated into 20 relevant sources, which were critically assessed. We also derive prevalent risk scenarios of hazard-pathway-receptor combinations, subsequently being ranked. Our critical analysis highlights that despite stringent regulation, industrial diligence and enforcement, occasionally small amounts of potentially hazardous substances are able to pass through these safeguards and re-enter in the new product cycle. Although many are present at concentrations unlikely to pose a serious and imminent threat, their existence may be an indication of a wider or possibly increasing challenge of pollution dispersion, as the plastics reprocessing sector proliferates. But, in the Global South context, such controls may not be in place. Several studies showed emission control by passive ventilation, through open doors and windows followed by dilution and dispersion in the atmosphere, resulting in increased occupational exposure. It is recommended that further investigations are undertaken to establish the scale and magnitude of such phenomena, especially given the limited evidence base, with results informing improved future risk management protocols of a circular economy for plastics.

Mismanagement of Plastic Waste through Open Burning with Emphasis on the Global South: A Systematic Review of Risks to Occupational and Public Health

“…The present review is part of a wider piece of research that investigated the risks to human health and safety from the mismanagement of plastic waste. While this paper presents findings on the risks to human health from the open, uncontrolled burning, another paper by Cook et al presents on plastics extrusion and legacy substance contamination in secondary plastics. The same initial pool of literature was used in the preparation of the two reviews as detailed in Section S.1.4, obtained by the same PRISMA adapted method, presented in Cook et al…”

Safely recovering value from plastic waste in the Global South: Opportunities and challenges for circular economy and plastic pollution mitigation

“…Emissions from extrusion of the main conventional plastics used in packaging, such as polypropylene (PP), PE, PET, high density polyethylene and low density polyethylene (LDPE) are not thought to result in harm to human health if carried out at controlled temperatures and using relatively pure In the Global South, ventilation may not always be provided in plastics extrusion facilities. For example, a review by Cook et al (2020b) found examples of facilities investigated in China where only passive ventilation was provided as a control measure. Other examples were identified in the multimedia evidence presented in Table 4, where workers were in close proximity to extruders without any observable mechanical ventilation or personal protective equipment.…”

“…Although the most common polyolefins and PET do not usually result in harmful emissions if ventilation is sufficiently controlled, there some is evidence that if materials are not sourced or sorted carefully then they may be inadvertently mixed with plastics such as polystyrene and PVC, both of which result in harmful emissions when extruded (Cook et al, 2020b;He et al, 2015). Moreover, if the polyolefins and PET have originated form a source that involves some potentially hazardous substances being added, for example electrical casings, then these substances may volatilise when heated, exposing workers.…”

“…Some plastics contain potentially hazardous substances that have been added intentionally or which have been unintentionally incorporated through adsorption, absorption, during production or conversion (Cook et al, 2020b). These substances are not usually bonded to the polymers themselves, but exist between the polymer chains as part of a mixture (Hahladakis et al, 2018;Wiesinger et al, 2021).…”

“…In much of the Global North and South, the use of hazardous substances in food contact packaging is tightly controlled by legislatory frameworks designed to limit exposure to human health and the environment depending on the application (Cook et al, 2020b). Thus, the use of recycled (secondary) plastics in food contact materials presents additional challenges because of the potential uncertainty around the origin of the material (primary production and manufacturing phase), its previous use (usephase) and the way that it may have been handled, stored and treated after it has been used (end-oflife-phase).…”