Release of additives and non-intentionally added substances from microplastics under environmentally relevant conditions

Microplastics and their associated plastic additives are contaminants of emerging environmental concern. The extent and rate of additive leaching affects the behaviour and fate of these contaminants, and therefore the risk they present to organisms. However, most studies examining the leaching of additives from microplastics use methods that are not environmentally relevant. We evaluated additive leaching from a range of common plastics using an environmentally relevant dynamic leaching method with additives and non-intentionally added substances quantified by liquid chromatography-mass spectrometry. The leaching method was validated to ensure sink conditions were maintained over the duration of the test. Release was not solubility limited indicating that the test conditions were representative of those occurring in the environment. Leaching profiles showed significantly different kinetics across the different types of plastic, with cumulative additive release over 64 days spanning more than five orders of magnitude. This study highlights the wide variation in additive leaching behaviour between different plastics and the importance of understanding leaching kinetics to assess the chemical impacts of microplastic pollution. Furthermore, we identify the need for environmentally relevant leaching methods and suggest the creation of standardised methods to enable robust risk assessments and regulation.