Legacy additives in a circular economy of plastics: Current dilemma, policy analysis, and emerging countermeasures

Plastics are widely used because of their diverse mechanical and physicochemical properties, however, many plastic products can only achieve their specific characteristics if mixed with additives, like flame retardants, stabilizers, and plasticizers. Some of the formerly used plastic additives, however, are in the meantime evaluated as substances of very high concern (SVHC) or even persistent organic pollutants (POP) and are referred to as legacy additives. Therefore, the improper disposal of legacy plastic waste as well as the recycling and reuse of such can lead to continuous circulation of harmful additives into the environment, threatening plant and animal life, and human health. The environmental threats posed by hazardous additives have been addressed by international regulations like the Registration, Evaluation, and Authorization of Chemicals (REACH) regulation and the Stockholm Convention. They set thresholds for hazardous chemicals including some legacy additives, which regulate trading and waste management, and aim at a fast phase out of hazardous compounds. At the same time, governmental, non-governmental and industrial players support a circular economy of goods including plastics, which resulted and will further result in increasing recycling quotas for waste plastics. When it comes to plastics containing legacy additives a conflict of objectives may arise, namely saving polymeric resources versus phase-out of hazardous compounds. This review paper discusses legacy additives in plastic waste streams, their end-of-life treatment options related to legislation covering these additives and links between regulation and waste management.