Effects of Body Size, Trophic Position and Ecosystem Type On Mercury in Fishes of the Upper Paraná River Basin, Brazil

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 through food webs. MeHg contamination has been shown to affect fish survival, reproduction, and behavior as well as pose risks to human health. This study focuses on understanding how MeHg is distributed in food webs of the Upper Paraná River Basin, Brazil, and examines relationships between MeHg and ecological parameters that may mediate MeHg bioaccumulation in these highly-connected and species-rich tropical food webs. Samples were collected from multiple locations for different ecosystem types (e.g. low-gradient rivers, high-gradient rivers, reservoirs) along an approximately 500 km stretch of the river basin.  Several fish species had mean Hg concentrations above 300 μg/kg (wet weight), exceeding the level at which the US EPA recommends limiting consumption to avoid adverse human health effects. Results also demonstrate a positive correlation between standard length, trophic position, and Hg concentration indicating biomagnification in these ecosystems. 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.