The expansion of global plastics reprocessing, driven by circular economy initiatives and efforts to reduce pollution, presents complex challenges for occupational and public health. A systematic scoping review, conducted under PRISMA-ScR methodology, examined two critical aspects: legacy contamination in secondary plastics and exposure risks during extrusion in mechanical reprocessing. These factors, while often overlooked in public discourse, hold significant implications for material safety and environmental integrity.
Legacy contamination refers to chemical substances retained from the original use phase of plastics, which can persist through recycling and reappear in new products. These substances, including brominated flame retardants (BFRs), phthalates such as di(ethylhexyl) phthalate (DEHP), and persistent organic pollutants (POPs), may survive established regulatory safeguards. Even when present at concentrations below immediate hazard thresholds, their persistence suggests a potential for broader pollution dispersion over time. The review noted that “small amounts of potentially hazardous substances contained in waste plastics are able to pass through established safeguards and re-enter the next use phase,” underscoring a systemic vulnerability in feedstock control.
Extrusion, the final stage of conventional mechanical reprocessing, was identified as the highest-risk scenario in the semi-quantitative assessment of nine potential exposure pathways. This process, particularly in contexts relying solely on passive ventilation, dilution, and dispersion, can release volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and potentially toxic elements (PTEs) into the working environment. Without robust engineering controls or respiratory protective equipment (RPE), workers may face elevated risks of inhalation exposure, with potential long-term health consequences.
The review’s findings carry particular weight in low-income and middle-income countries (LIMICs), where informal or small-scale recycling operations often lack safe systems of work. In these settings, poor control over feedstock composition and minimal investment in emission mitigation can amplify risks to both workers and surrounding communities. The authors emphasized that “lack of safe systems of work in parts of Global South risk health of poorest,” highlighting the intersection of environmental justice and industrial safety.
Material types implicated in contamination risks span common polymers such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), and acrylonitrile butadiene styrene (ABS). When sourced from waste electrical and electronic equipment (WEEE) or non-specified packaging (NSP), these feedstocks may carry polycyclic aromatic hydrocarbons (PAHs), polybrominated biphenyls (PBBs), and tetrabromobisphenol A (TBBPA), among other hazardous compounds. The mechanical reprocessing of such materials without rigorous screening can inadvertently reintroduce restricted substances into consumer products, challenging compliance with directives like RoHS (Restrictions on Hazardous Substances).
From an engineering perspective, the extrusion stage demands particular attention due to its thermal and mechanical conditions. Elevated temperatures can volatilize embedded contaminants, while shear forces may facilitate the release of micro-scale particulates. Inadequate ventilation systems—especially those relying on natural airflow rather than controlled extraction—allow airborne pollutants to disperse into adjacent work areas, increasing exposure potential.
The semi-quantitative risk ranking applied in the review integrated uncertainty, strength of knowledge, and methodological robustness (USMR) to prioritize intervention points. Scenarios involving uncontrolled extrusion in poorly ventilated facilities consistently scored highest, suggesting that targeted improvements in process engineering could yield significant health benefits. Enhanced feedstock screening, adoption of closed-loop ventilation systems, and mandatory use of RPE are among the measures that could mitigate these risks.
For sectors engaged in advanced materials, including aerospace and automotive manufacturing, the integrity of recycled polymers is critical. Contaminants not only pose health hazards but can also compromise material performance, affecting mechanical properties, thermal stability, and long-term durability. As recycled content becomes a larger fraction of supply chains, understanding and controlling legacy substances will be essential to maintain both safety and quality standards.
The review’s emphasis on proactive risk management aligns with broader sustainability goals. By addressing feedstock control and extrusion emissions, the plastics reprocessing industry can move toward a genuinely non-polluting circular economy, ensuring that the benefits of resource recovery do not come at the expense of human health.