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.