Impact of Fish Feeding Habitat and Diet on Microplastic Concentrations in Gastrointestinal Tracts of St. Lawrence River Fish

Approximately 370 million tons of plastic are being produced annually (Plastics Europe, 2020). Only a small portion is recycled due to poor waste management practices. An estimated eight million tons of plastic moves from the land to ocean every year (IUCN, 2018) while rivers transport between 1.15 and 2.41 million tons of debris into the oceans annually (Lebreton et al., 2017). The pervasiveness of microplastics (MP), plastic polymer debris less than 5mm in diameter, in aquatic environments, their ingestion by freshwater fish, and the accumulation of MP through trophic transfer in food webs raise concern for the sustainability of fisheries, food security, and public health (Campbell et al., 2017; Wagner et al., 2019). Fish are excellent indicators of aquatic ecosystem health since they integrate changes in their physical environment (Pinheiro et al., 2017). Assessing MP contamination in fish therefore provides valuable information about MP concentrations in freshwater systems and raises attention to potential risks. My research investigated how fish feeding habitats, trophic position, body size (weight and length), and species variation influence MP ingestion and accumulation in St Lawrence River freshwater fish by collecting samples of pelagic, bentho-pelagic, and benthic fish species. I hypothesized that MP particles would be present in the GI tracts of most fish samples regardless of feeding habitat since MP can be found throughout the water column in most aquatic environments, and that the GI tracts of benthic fish would contain higher concentrations of MP beads and fragments while the GI tracts of pelagic fish would contain higher concentrations of MP fibers. I expected a greater concentration of plastic particles would be found in benthic than pelagic fish because of the prevalence of MPs found in the St Lawrence River sediments (Crew et al., 2020; Castaneda et al., 2014), and the data modeling performed by Lebreton et al. (2018). To address these questions, I collected 73 fish (seven species) from the Lake Saint Louis region of the St Lawrence River using traditional fishing lines and tackle. The fish samples were weighed and measured, gastrointestinal (GI) tracts removed, and contents chemically digested to eliminate organic matter. Once separated, MP particles were observed under a microscope and categorized according to physical characteristics (color, size) and morphology (fragment, bead, fiber), counted, and verified using a hot needle test. All 73 fish contained MPs. MPs were higher in the GI tracts of these St. Lawrence fish (14.9 +/- 6.9; mean +/- SD) compared with other studies (0-10 MP/ fish; Gouin, 2020). I observed no significant relationship between body size, trophic level, or feeding habitat and MP load. Fibers were the most abundant MP morphology, consistent with other studies examining fish GI tracts (Jabeen et al., 2017; Horton et al., 2018; McNeish et al., 2018; Rochman et al., 2015). Feeding habitat may play a role in MP morphology abundance since a higher percentage of fibers were present in pelagic species, while fragments were more abundant in benthic species. The high mean abundance of MP/ fish demonstrated in this study suggest the pollution sources in the St Lawrence River are likely more numerous than those in other study areas. These findings highlight the need for greater understanding about the consequences and potential risks of plastic pollution in riverine environments and the need for more vigilant policy decisions regarding plastics production and waste management practices.