Priority Plastic Additives of Environmental Concern in Marine-Leaked Micro- and Macroplastics: Occurrence, Distribution, and Management Implications

Additive-derived chemicals were measured in microplastics and macroplastics collected from coastal and offshore areas around Japan. A wide range of additives, including antioxidants, phthalate esters, and brominated flame retardants were detected in both microplastics and macroplastics. The size- and polymer-dependent distribution of Irgafos 168 and its oxidation product (collectively referred to as Irgafos 168-related compounds) suggested that leaching from the plastic matrix was a dominant process governing its occurrence in microplastics and highlighted its potential as indicators of plastic fragmentation and oxidative degradation. Di-(2-ethylhexyl) phthalate (DEHP), a substance restricted under the EU REACH Regulation and listed as a priority monitoring substance under Japan's Chemical Substances Control Law, was frequently detected. Higher concentrations of contaminants in microplastics than macroplastics, together with weak polymer dependence, were consistent with a stronger influence of external sorptive uptake from surrounding waters and particulate matter on microplastic DEHP levels. The results indicated that hexabromocyclododecane (HBCD), a persistent organic pollutant (POP), contained in microplastics can persist during marine transport and act as mobile secondary sources; they demonstrated that plastics containing additives at regulated or management-level concentrations are widely distributed in the marine environment; and they showed that fragmentation from macroplastics to microplastics does not necessarily reduce chemical hazards. There is hence a need to integrate additive content, chemical persistence, and size-dependent transport behavior into marine plastic risk assessment frameworks.