Microplastic ingestion by freshwater and marine fish from the Brazos River basin and Texas nearshore marine waters.

This dissertation serves as one of the first comprehensive system investigations of microplastic ingestion by freshwater and marine fish from the Brazos River basin and Texas nearshore marine waters. In total, 436 freshwater sunfish were sampled and 45% contained ingested anthropogenic materials, consisting of -macro (4%) and -micro (96%) sized contaminants. Microplastic ingestion was greater within fish collected from urban areas, in comparison to upstream and downstream sites, suggesting that human development (i.e. paved roadways) and local urbanization are two possible factors impacting microplastic ingestion by sunfish. The marine portion of this research (Chapter Four) examined a total of 1,381 fish, inclusive of six species of a shared ecological guild, and 42.2% of stomachs contained microplastic fibers (86.4%), beads (12.9%) and fragments (<1%). Despite a substantial overlap in diet, ordination of ingested prey items clustered samples into distinctive species groupings, reflective of the foraging gradient among species. Grunt displayed the lowest overall frequency of microplastic ingestion and the most distinctive ordination grouping, indicating their selective invertebrate foraging preferences. While all six species had ingested microplastic, the results suggest that grunt, as selective invertebrate foragers, are less likely to ingest microplastic than species which exhibit generalist foraging preferences and methods of prey capture. When comparing microplastic ingestion between freshwater sunfish and marine pinfish, species which serve as ecological analogs between the systems, there was no significant difference in the overall frequency or mean number of microplastics ingested. However, the pinfish stomach content contained microplastic fiber, bead, and fragment morphologies, while the sunfish stomach content only contained microplastic fibers. Pyr-GC/MS analysis classified forty-three of the marine microplastic samples as polyvinyl chloride (34.8%), polyethylene terephthalate (9.3%), nylon (9.3%), silicone (2.3%), and epoxy resin (2.3%). Approximately 42% of samples could not be classified into a specific polymer class, due to a limited formation of pyrolytic products, low product abundance, or a lack of comparative standards. Overall, this dissertation demonstrates that microplastic ingestion is ubiquitous throughout Texas aquatic environments, influenced by species diet and foraging methods, and reflective of local land use patterns and major sources of pollution.