Characterization of Leachable and Bioaccessible Polymer Additives in Microplastics

Abstract

The exponential growth of global plastic production has intensified concerns regarding environmental persistence and human exposure to microplastics and their associated chemical additives. This dissertation, Characterization of Leachable and Bioaccessible Polymer Additives in Microplastics, addresses critical gaps in our understanding of polymer-associated chemical (PAC) release and its subsequent bioaccessibility, thereby informing more accurate risk assessments. An extensive literature review and compilation of data revealed that current research disproportionately targets a narrow subset of known additives and polymer types, leaving significant gaps in exposure estimates, material properties, and real-world application data. In particular, the lack of up-to-date global production metrics and standardized reporting of crucial material and chemical properties are gross knowledge gaps in this field. The former is paramount to ensuring research is relevant to the ever-increasing and ever-changing production of plastics worldwide. The latter is imperative to the use of prolific microplastics research in necessary predictive modeling of additive leaching behavior and well-informed risk assessment of this complex class of pollutants.To address these deficiencies, long-term freshwater leaching experiments were conducted with 27 different plastics, demonstrating that additive release is a dynamic process with distinct temporal profiles. Initial rapid leaching accounts for only a fraction of the total additive content, while subsequent releases highlight the potential for long-range environmental transport and chemical transformation. Importantly, comparisons between reference polymers and commercially relevant materials underscored that uncolored pre-production pellets may underrepresent the complexity and quantity of additives present in everyday products. Complementing these findings, innovative three-phase leaching experiments, using engineered microplastic fibers (MPFs) and commercial fleece fibers, investigated azobenzene disperse dye (ADD) bioaccessibility in simulated epithelial lung fluid. Utilizing solid phase microextraction (SPME) as a passive sampling technique, the study quantified dissolved concentrations of ADDs in simulated lung fluid, revealing that even low but measurable levels of additives can be liberated under physiologically relevant conditions. Collectively, the integrated findings of this dissertation underscore the necessity for standardized experimental methodologies, comprehensive additive characterization, and investigating understudied additive classes. Advancing our understanding of both the leachable and bioaccessible fractions of polymer additives is essential for developing robust exposure models and mitigating the potential health risks posed by microplastic pollution.