Leaching behavior and toxic effect of plastic additives as influenced by aging process of microplastics

Microplastics (MPs) may experience different levels of aging in the actual environments, altering their physicochemical characteristics and affecting their biogeochemical behavior. However, it still remains unclear how aging process affects the leaching behaviors and toxic effects of plastic additive. Here, we intend to take aging reactions of MPs as the starting point, systematically analyze the impact of aging on the leaching and toxicity of MP additive. Current progress and limitations related to this topic have been discussed in detail, and scientific problems to be solved have been proposed. This study critically integrates aging-induced structural transitions of MPs with additive leaching kinetics and resulting toxicological profiles. A conceptual framework is proposed to unravel the coupled physicochemical and biological processes controlling MPs-associated risk in natural environments. Future work should elaborate the influence of aging conditions on physicochemical characteristics of MPs and leaching mechanisms of additives in MPs during aging. Modeling the leaching process of plastic additives is also required. Toxic effect of aged MPs on different trophic organisms and contribution of additives released to MPs toxicity need to be investigated. On this basis, the leaching behavior of additives and their toxic effects on organisms may be regulated aiming to alleviate the harm of additives during aging. This study will be useful to accurately assess the impact of aging processes on the environmental fate of plastic additives, and provide theoretical basis and technical guidance to reduce the ecological risks caused by MPs in the actual environments. • Release characteristics and toxic effects of plastic additives in MPs are discussed. • Leaching rules of additives within MPs under aging conditions should be revealed. • Correlations between MP surface properties and additives leaching are elucidated. • Toxicity prediction models and leaching models of plastic additives are studied.