Pharmaceutical residues in plastic tablet containers: Impacts on recycling and the environment.

High-density polyethylene tablet containers are potentially very suitable for recycling, but no data are publicly available on active pharmaceutical ingredients' (API) residues in empty containers and if they affect the recyclability of pharmaceutical packaging. Plastic tablet containers represented 15 % of pharmaceutical primary packages sold in Finland in 2020 and 2021, equalling 350 tons of plastic per year. We studied the residues of six APIs remaining or adsorbed inside plastic tablet containers. The effects of tablet coating and usage in dose-dispensing services versus households on the API residues, and rinsing water's ability to remove the residues were evaluated. Up to 940,000 µg/kg of carbamazepine was detected in a container of uncoated carbamazepine tablets. The residues from coated tablets containing the other five APIs were 2.4-6,100 µg/kg. Ten times higher paracetamol residues were obtained in containers from household use than from a dose-dispensing unit. Rinsing can remove most API residues, but it leads to environmental emissions. For example, rinsing water can double carbamazepine emissions from a Finnish wastewater treatment plant where plastic packaging waste effluents are processed. Considering the API concentrations, decreasing residues by rinsing and dilution with other plastic packaging waste, the residues of the studied APIs are not considered an obstacle to the recycling of plastic tablet containers. However, further research is needed on more toxic APIs and the fate of APIs in the plastics recycling process.