Estimating the mass of chemicals associated with ocean plastic pollution to inform mitigation efforts

Plastic pollution in the marine environment is well documented. What remains less recognized and understood are the chemicals associated with it. Plastics enter the ocean with unreacted monomers, oligomers and additives, which can leach over time. Moreover, plastics sorb organic and inorganic chemicals from surrounding seawater, e.g., polychlorinated biphenyls (PCBs) and metals. Thus, interception and clean-up of plastics reduces the amount of chemical contaminants entering or re-entering the oceans, and removes those already present. Here, we estimate: 1) the mass of selected chemical additives entering the global oceans with common plastic debris items, and 2) the mass of sorbed chemicals (using PCBs as a case study) associated with microplastics in select locations. We estimate the mass of additives that entered the oceans in 2015 as constituents of seven common plastic debris items (bottles, bottle caps, expanded polystyrene containers, cutlery, grocery bags, food wrappers and straws/stirrers). We calculate that approximately 190 Tonnes of 20 chemical additives entered the oceans with these items in 2015. We also estimate the mass of PCBs associated with microplastics in two coastal (Hong Kong and Hawaii) and two open ocean (N. Pacific and S. Atlantic gyres) locations, as comparative case studies. We find that the mass of chemicals is related to the mass of plastics in a location, with greater mass of PCBs closer to the source (i.e., land), where there is more plastic per unit area compared to the open ocean. We estimate approximately 85,000 times more PCBs associated with plastics in an average 4.5 km stretch of beach in Hong Kong than from the same size transect in the N. Pacific gyre. In conclusion, continuing efforts for plastic interception and clean-up on shorelines effectively reduces the amount of plastic related chemicals entering and/or re-entering the marine environment. This article is protected by copyright. All rights reserved.