MP9 Metals and Bioaccumulation
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(FOW-1117-754252) What are the sources of elevated mercury concentrations in fish from the St. Lawrence River at Cornwall?

Fowlie, A¹, Hodson, P¹, Hickey, M², ¹ Queen's University, Kinston, Ontario, Canada² St. Lawrence River Institute of Environmental Sciences, Cornwall, Ontario, Canada

ABSTRACT- The Cornwall river waterfront (St. Lawrence River, Ontario, Canada) has received inputs of mercury from decades of industrial pollution. Identified as an "Area of Concern" by the International Joint Commission, the sediments from depositional zones along the waterfront are contaminated with mercury. Methyl mercury concentrations in fish downstream from these sources are also elevated, but it is not clear whether sediment contamination is the primary source. We are investigating methyl mercury transfer through aquatic food chains at reference and contaminated sites. Preliminary evidence indicates that methyl mercury bioaccumulates in yellow perch (Perca flavescens) as small as 11.2 cm to levels exceeding Canadian human consumption guidelines (0.2 ppm). Surprisingly, fish from a contaminated upstream zone contained more mercury than fish from a contaminated zone only 2 km downstream. This trend was also confirmed with other fish species such as rock bass (Ambloplites rupestris) and brown bullhead (Ictalurus nebulosus). Possible reasons could include differences among sites in food web complexity (more trophic transfers and biomagnification), differences in the fish growth rate and population structure, or a local source at the upstream site, including conditions that would favour mercury methylation (such as pockets of organic enrichment). To test these hypotheses we are using multiple lines of evidence that include a description of the aquatic food web as indicated by fish stomach contents, and benthos and fish sampled from each site. Trophic level will be assigned by stable nitrogen and carbon isotope analyses, and components of the food web (fish and invertebrates) will be analyzed for methyl mercury.

Key words: bioaccumulation, mercury, nitrogen and carbon stable isotopes, aquatic food chain