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BIOLOGICAL SCIENCES / ENVIRONMENTAL SCIENCES
Whole-ecosystem study shows rapid fish-mercury response to changes in mercury deposition
aTetra Tech Inc., 180 Forestwood Drive, Oakville, ON, Canada L6J 4E6; cR&K Research Inc., 675 Mt. Belcher Heights, Salt Spring Island, BC, Canada V8K 2J3; dDépartement de Sciences Biologiques, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, QC, Canada H3C 3J7; eEnvironmental Chemistry and Technology Program, University of Wisconsin, 660 North Park Street, Madison, WI 53706; fFreshwater Institute, Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, MB, Canada R3T 2N6; gPenobscot River Mercury Study, 115 Oystercatcher Place, Salt Spring Island, BC, Canada V8K 2W5; hDepartment of Geography, University of Toronto, South Building, 3359 Mississauga Road, North Mississauga, ON, Canada L5L 1C6; iSmithsonian Environmental Research Center, P.O. Box 28, 647 Contees Wharf Road, Edgewater, MD 21037; jDepartment of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9; kChesapeake Biological Laboratory, University of Maryland Center for Environmental Science, University of Maryland, P.O. Box 38, Solomons, MD 20688-0038; lDepartment of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, ON, Canada K9J 7B8; mU.S. Geological Survey, 8505 Research Way, Middleton, WI 53562; nOak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, TN 37831-6036; oDepartment of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340; and pCanadian Forest Service, 1219 Queen Street East, Sault St. Marie, ON, Canada P6A 5M7
Edited by Deborah Swackhamer, University of Minnesota, St. Paul, MN, and accepted by the Editorial Board August 10, 2007 (received for review May 4, 2007)
Methylmercury contamination of fisheries from centuries of industrial atmospheric emissions negatively impacts humans and wildlife worldwide. The response of fish methylmercury concentrations to changes in mercury deposition has been difficult to establish because sediments/soils contain large pools of historical contamination, and many factors in addition to deposition affect fish mercury. To test directly the response of fish contamination to changing mercury deposition, we conducted a whole-ecosystem experiment, increasing the mercury load to a lake and its watershed by the addition of enriched stable mercury isotopes. The isotopes allowed us to distinguish between experimentally applied mercury and mercury already present in the ecosystem and to examine bioaccumulation of mercury deposited to different parts of the watershed. Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.
bioaccumulation | mercury methylation | stable isotopes | whole-ecosystem experimentation | methylmercury
Author contributions: R.C.H., J.W.M.R., M.A., K.G.B., P.J.B., B.A.B., C.C.G., J.A.G., A.H., H.H., J.P.H., C.A.K., D.P.K., S.E.L., M.J.P., C.L.P., A.R., and V.L.S.L. designed research; R.C.H., J.W.M.R., M.A., C.L.B., K.G.B., P.J.B., B.A.B., C.C.G., J.A.G., A.H., H.H., J.P.H., C.A.K., D.P.K., S.E.L., R.P.M., M.J.P., C.L.P., A.R., K.A.S., G.R.S., V.L.S.L., and M.T.T. performed research; M.A., K.G.B., P.J.B., B.A.B., C.C.G., J.A.G., A.H., H.H., J.P.H., C.A.K., D.P.K., S.E.L., R.P.M., M.J.P., C.L.P., A.R., G.R.S., V.L.S.L., and M.T.T. contributed new reagents/analytic tools; R.C.H., J.W.M.R., M.A., C.L.B., K.G.B., P.J.B., B.A.B., C.C.G., J.A.G., A.H., H.H., J.P.H., C.A.K., D.P.K., S.E.L., R.P.M., M.J.P., C.L.P., K.A.S., G.R.S., V.L.S.L., and M.T.T. analyzed data; and R.C.H., J.W.M.R., M.A., P.J.B., R.A.B., B.A.B., C.C.G., J.A.G., A.H., H.H., J.P.H., C.A.K., D.P.K., S.E.L., M.J.P., C.L.P., K.A.S., and V.L.S.L. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. D.S. is a guest editor invited by the Editorial Board.
See Commentary on page 16394.
bTo whom correspondence should be addressed: E-mail: john_rudd{at}gulfislandswireless.com
© 2007 by The National Academy of Sciences of the USA
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  D. R. Engstrom Fish respond when the mercury rises PNAS, October 16, 2007; 104(42): 16394 - 16395. [Full Text] [PDF]
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