Role of Environmental Weathering and Gastrointestinal Digestion on the Bioavailability and Toxicity of Microplastic and Cadmium Mixtures - A Platform for Undergraduate Interdisciplinary Training

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Project Summary Microplastics (MPs) represent an emerging human health hazard as either a direct environmental contaminant or as a component of other mixed pollutants. Microplastics in the environment are exposed to ultraviolet radiation (UV) that change their chemical, morphological composition, and reactivity. Microplastics frequently interact with other heavy metals (e.g., cadmium (Cd)) in contaminated aquatic systems. Fish are continuously exposed to UV-degraded MPs directly by accidental ingestion or indirectly by ingesting pray contaminated with MPs. Humans are mainly exposed to MPs via ingestion of contaminated food and water. The fate of MPs during digestion is largely unknown. The key barrier to advancing our understanding of the health risk of MPs is a lack of information linking MPs’ environmental chemical transformations with bioaccumulation of MPs, and specific health impacts. Our overall goal is to involve undergraduate researchers in an interdisciplinary environmental engineering and toxicology project that targets key knowledge gaps of MP transformation, reactivity, bioavailability, and toxicity to develop a strong set of skills in undergraduate students that encourages to pursue a graduate degree and career in STEM. The overarching objective is to use quantifiable approaches and innovative tools to better understand the role of environmental weathering and gastrointestinal digestion on the bioavailability and toxicity of MPs and MPs and cadmium mixtures. We hypothesize that ultraviolet weathering of MPs increases sorption of legacy pollutants (i.e., Cd) and gastrointestinal processes affect their bioavailability and toxicity at the intestinal epithelium. Moreover, considering that MPs are taken up via endocytosis we propose that MPs can interfere with endosome and lysosome function, specifically affecting essential trace metal metabolism. To test this hypothesis, we propose the following interconnected aims: Specific Aim 1: Evaluate the transformation and reactivity of ultraviolet-aged micro- and nanoplastics in freshwater, commercial mineral water, and gastrointestinal (GI) fluids (i.e., during digestion); Specific Aim 2: Evaluate the bioavailability and acute toxicity of MPs and MPs/Cd mixtures in intestinal cells form fish RTgutGC cells, and human Caco-2 cells. The goal of aim 2 is to investigate the link between MPs type (size and composition) and chemical modifications (aim 1) to bioavailability and acute toxicity of MPs alone or in combination with Cd. Specific Aim 3: Evaluate the physiological impact of MPs on intestinal cells: using data from aim 1 we will select MPs with higher reactivity and sorption capability and using data from aim 2 we will select subtoxic but detectable doses of MPs and MPs/Cd mixtures and evaluate their impact on essential trace metal homeostasis and metabolism. Our results will contribute to bridge the knowledge gap between chemical transformations of MPs in the environment and implications on fish and human health. Our project will serve as a platform for integrating undergraduate students into multidisciplinary research and will allow them to acquire multiple skills spanning from environmental chemistry to cell biology and toxicology.