Speciation and bioavailability of mercury in well-mixed estuarine sediments Elsie M. Sunderland a,b, * ,1 , Frank A.P.C. Gobas a , Andrew Heyes c , Brian A. Branfireun d , Angelika K. Bayer d , Raymond E. Cranston e , Michael B. Parsons e a School of Resource and Environmental Management, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6 b Office of Science Policy (8104S), Office of Research and Development, United States Environmental Protection Agency, 1200 Pennsylvania Ave. N.W., Washington, DC 20007, USA c Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, University System of Maryland, P.O. Box 38, Solomons, MD 20688-0038, USA d Department of Geography, University of Toronto at Mississauga, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6 e Natural Resources Canada, Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2 Received 12 June 2003; received in revised form 19 November 2003; accepted 16 February 2004 Available online 7 June 2004 Abstract Despite regulations controlling anthropogenic mercury sources in North America, high levels of mercury in coastal fish and shellfish are an ongoing problem in Maritime Canada and the Northeastern United States. This study presents sediment core data from a macrotidal estuary located at the mouth of the Bay of Fundy showing stratigraphic profiles of total and methylmercury concentrations and potential methylation rates measured using stable mercury isotopes. The results show that in contrast to the expected methylmercury profile typically observed in unmixed sediments, methylmercury production occurs throughout the estimated 15-cm-thick active surface layer of these well-mixed sediments. The resulting large reservoir of methylmercury in these sediments helps to explain why mercury concentrations in organisms in this system remain high despite emissions reductions. Current management policies should take into account the expected delay in the response time of well- mixed estuarine systems to declines in mercury loading, considering the greater reservoir of historic mercury available in these sediments that can potentially be converted to methylmercury and biomagnify in coastal food chains. D 2004 Elsevier B.V. All rights reserved. Keywords: Methylmercury; Estuaries; Enrichment factor; Sediment burial; Bay of Fundy 1. Introduction Mercury emissions from anthropogenic sources in Maritime Canada and the Northeastern United States have declined by more than 50% from peak levels in the 1970s as a result of pollution control measures (Sunderland and Chmura, 2000). However, there is no 0304-4203/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.marchem.2004.02.021 * Corresponding author. Office of Science Policy (8104R), Office of Research and Development, United States Environmental Protection Agency, 1200 Pennsylvania Ave. N.W., Washington, DC 20007, USA. Tel.: +1-202-564-6754; fax: +1-202-565-2925. E-mail address: sunderland.elsie@epa.gov (E.M. Sunderland). 1 This research was conducted while Dr. Sunderland was a graduate student at Simon Fraser University and reflects the author’s personal views. This study is not intended to portray policies or views of the U.S. EPA. www.elsevier.com/locate/marchem Marine Chemistry 90 (2004) 91 – 105