Chemical Biological Pathway

Environmental Toxicology and Chemistry, Vol. 34, No. 10, pp. 2385–2394, 2015

# 2015 SETAC

Printed in the USA

MERCURY AND SELENIUM ACCUMULATION IN THE COLORADO RIVER FOOD WEB,

GRAND CANYON, USA

DAVID M. WALTERS,*y EMMA ROSI-MARSHALL,z THEODORE A. KENNEDY,x WYATT F. CROSS,k

and COLDEN V. BAXTER#

yUS Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, USA

zCary Institute of Ecosystem Studies, Millbrook, New York, USA

xUS Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, Arizona, USA

kDepartment of Ecology, Montana State University, Bozeman, Montana, USA

#Department of Biological Sciences, Idaho State University, Pocatello, Idaho, USA

(Submitted 23 December 2014; Returned for Revision 5 March 2015; Accepted 20 May 2015)

Abstract: Mercury (Hg) and selenium (Se) biomagnify in aquatic food webs and are toxic to fish and wildlife. The authors measured Hg

and Se in organic matter, invertebrates, and fishes in the Colorado River food web at sites spanning 387 river km downstream of Glen

Canyon Dam (AZ, USA). Concentrations were relatively high among sites compared with other large rivers (mean wet wt for 6 fishes was

0.17–1.59 mg g–1 Hg and 1.35–2.65 mg g–1 Se), but consistent longitudinal patterns in Hg or Se concentrations relative to the dam were

lacking. Mercury increased (slope ¼ 0.147) with d15N, a metric of trophic position, indicating biomagnification similar to that observed

in other freshwater systems. Organisms regularly exceeded exposure risk thresholds for wildlife and humans (6–100% and 56–100% of

samples for Hg and Se, respectfully, among risk thresholds). In the Colorado River, Grand Canyon, Hg and Se concentrations pose

exposure risks for fish, wildlife, and humans, and the findings of the present study add to a growing body of evidence showing that remote

ecosystems are vulnerable to long-range transport and subsequent bioaccumulation of contaminants....