Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Neff, Bryan

2nd Supervisor

Corcoran, Patricia



Microplastics (plastic particles < 5 mm) are abundant in aquatic environments, particularly near urban areas. Little is known, however, about how variation in microplastic abundances within watersheds affects fishes. Microplastics were examined in demersal fishes—white sucker (Catostomus commersonii) and common carp (Cyprinus carpio)—across 11 sites in the Thames River, Ontario. Microplastics were found in 44% of white sucker, ranging from 0-14 particles per fish, and 31% of common carp, ranging from 0-128 particles per fish. Across both species, the number of microplastics in fish was higher in urban sites than rural sites, and there was a positive relationship between the number of microplastics in the fish and the abundance of microplastics in the sediment. Body mass was also positively related to number of microplastics in fish. Together these results provide insight into environmental and biological factors that may be influencing the variation of microplastic ingestion in demersal river fishes.

Summary for Lay Audience

Microplastics (plastic particles < 5 mm) are a widespread form of pollution in the aquatic environment, and are of concern as they have been reported to be ingested by a number of organisms. Rivers often have high levels of microplastics, however few studies have been conducted in tributaries of the Great Lakes. In addition, limited information is available regarding factors that influence microplastic ingestion in bottom-dwelling fishes in rivers. Therefore, this study investigates a potential connection between sediment microplastic levels and ingestion by bottom feeding river fishes. This study also examines other factors that may influence ingestion of microplastics, such as differences among species, urban versus rural land use, and body size. Building on a previous study of microplastics in bottom sediment from the Thames River, Ontario, white sucker and common carp were collected from the upper Thames River. Overall, 44% of white sucker and 31% of common carp were found to contain at least one microplastic particle. Microplastics found in fish consisted of fragments, fibres and suspected tire wear particles, with the latter found in the greatest abundance. The number of microplastics in fish was found to be related to the body mass of individuals, with larger fish containing more microplastics. However, the number of microplastics did not differ between species, and this may be attributed to the similar way in which they feed. Land usage was related to number of suspected tire wear particles and fragments in fishes, but not fibres. Similarly, the number of fragments in fish were found to be related to abundance of fragments in sediment, but fibres lacked a relationship. Findings from this study show that individual factor of body size, as well as environmental factors such as land use and abundance of microplastics in sediment influence the number of microplastics that may be ingested by fishes. Overall, this study found evidence of microplastics in bottom-dwelling river fish in the Great Lakes system, and is the first study on biota of a proposed long-term investigation of microplastics in the Thames River.