88 - The Coupled Trophic Transfer of Selenium and Mercury in a Large River

Mercury (Hg) is a naturally occurring contaminant that bioaccumulates and biomagnifies in aquatic food webs. Potential consequences of excess Hg exposure include neurotoxicity, teratogenesis, and mortality, especially in high trophic level consumers. Some studies suggest that selenium (Se) can mediate Hg methylation, bioaccumulation, and toxicity, yet uncertainties remain in the consistency of this phenomenon across taxa and ecosystems. One emerging hypothesis from this literature is that the availability of Se may interfere with Hg trophic transfer by reducing Hg bioavailability or enhancing Hg detoxification and elimination. To address the related question of whether Se limits Hg trophic transfer from prey to predator, we draw on the results of an intensive sampling effort that spanned 60 river miles of the Se-impaired Lower Gunnison River Basin (Colorado) in 2016. Concentrations of Se and Hg in green algae (n=12), macroinvertebrates (n=39), and Speckled Dace (n=78) ranged from 1.59 – 12.9 and 0.009 – 0.168 ppm dw, respectively, and increased with trophic level. Mean Se:Hg molar ratios in macroinvertebrates were 286 ± 56 and 220 ± 85 in Speckled Dace. Initial results provide associative evidence that Hg concentrations in consumers are positively related to Se concentrations in their diet. Mechanisms and implications of potential Se-Hg interactions for Hg bioaccumulation and biomagnification will be discussed.

Authors: Jessica Brandt, Raul Flamenco, Travis Schmidt, Collin Eagles-Smith, James Roberts, Craig Stricker