Microplastic in riverine fish is connected to species traits

Abstract

Microplastic is a contaminant of concern worldwide. Rivers are implicated as major pathways of microplastic transport to marine and lake ecosystems, and microplastic ingestion by freshwater biota is a risk associated with microplastic contamination, but there is little research on microplastic ecology within freshwater ecosystems. Microplastic uptake by fish is likely affected by environmental microplastic abundance and aspects of fish ecology, but these relationships have rarely been addressed. We measured the abundance and composition of microplastic in fish and surface waters from 3 major tributaries of Lake Michigan, USA. Microplastic was detected in fish and surface waters from all 3 sites, but there was no correlation between microplastic concentrations in fish and surface waters. Rather, there was a significant effect of functional feeding group on microplastic concentration in fish. Neogobius melanostomus (round goby, a zoobenthivore) had the highest concentration of gut microplastic (19 particles fish^-1) compared to 10 other fish taxa measured, and had a positive linear relationship between body size and number of microplastic particles. Surface water microplastic concentrations were lowest in the most northern, forested watershed, and highest in the most southern, agriculturally dominated watershed. Results suggest microplastic pollution is common in river food webs and is connected to species feeding characteristics. Future research should focus on understanding the movement of microplastic from point-source and diffuse sources and into aquatic ecosystems, which will support pollution management efforts on inland waters.

Figure 1

Muskegon River, Milwaukee River, and St. Joseph River watersheds and site locations around Lake Michigan, USA.

Figure 2

Mean microplastic concentration in fish (a) and mean microplastic surface water concentration (b) between Muskegon, Milwaukee, and St. Joseph Rivers during summer 2016. Letters indicate significant difference between sites at P < 0.05.

Figure 3

Mean microplastic between fish taxa categorized as either zoobenthivore, omnivore, or detritivore. Zero indicates there was no microplastic present in the indicated taxa.

Figure 4

Linear regression analysis for number of microplastic within pooled fish and fish body size (a) round goby size and number of microplastic (b), and fish trophic fraction and number of microplastic (c).

Figure 5

Relative abundance of fiber size in surface water (a) and fish (b) collected from the Muskegon, Milwaukee, and St. Joseph Rivers. Maine coast refers to surface water fiber size from Barrows et al. collected off the coast of Maine USA.

Figure 6

Surface water and fish samples compared to their corresponding lab controls for microplastic concentration (a), category (b), fiber size (c), and fiber color (d). An asterisk indicates significant difference at ^***P < 0.01 and ^****P < 0.001.