Distributions of mercury in fish of the Paraná River, Brazil

Background/Question/Methods

Methylmercury (MeHg) is a chemical contaminant found at measurable concentrations throughout the earth’s waterways.  MeHg is known to bioaccumulate within the tissues of aquatic organisms and biomagnify as it moves into higher trophic levels.  MeHg contamination has been shown to affect fish survival, reproduction, and behavior as well as pose risks to human health.  Biological characteristics such as fish age, size, and growth rate all have varying effects on MeHg bioaccumulation.  This study focuses on understanding how MeHg is distributed in the complex food web of the Upper Paraná River, Brazil, and will examine relationships between MeHg and several ecological parameters that may mediate MeHg bioaccumulation in this highly-connected and species-rich tropical food web.  Furthermore, mercury is not evenly distributed across the landscape, and we examine MeHg in food webs across scales linked by long-distance migratory fish species.  Samples were collected from several locations (e.g. reservoir, floodplain, rivers below reservoirs) along an approximately 500 km stretch of the river basin, and at each site species were selected that are important to the artisanal fisheries and that occur at different positions in the food web.  Species trophic positions and relative importance of different carbon pathways were determined using C and N stable isotope analyses and multiple end-member mixing models. We have collected 220 fish representing 39 species (n > 5 individuals per species) including many individuals acquired from local artisanal fisherman and markets.

Results/Conclusions

Twenty eight percent of the fish examined (n=25) had concentrations of mercury above 300 μg/kg (wet weight), the level at which the US EPA recommends limiting consumption to avoid adverse human health effects.  This study has direct applications to the quality of artisanal fisheries as a key ecosystem service utilized by local communities, and may identify species or ecological traits that correlate with low risk for MeHg in fisheries species.