Tracking Mercury and Mercury Stable Isotopes Throughout the Wabigoon/English River System: A Preliminary Assessment

In the Wabigoon/English River system, mercury concentrations downstream from Dryden, ON, where there was a former chlor-alkali plant, remain elevated in sediments and biota. Understanding the current extent and severity of mercury contamination downstream from the former chlor-alkali plant is of great interest in furthering the clean-up of mercury within the traditional territory of Asubpeeschoseewagong Netum (Grassy Narrows) First Nation. The objective of this study was to evaluate the current level and extent of mercury contamination within sediments, crayfish, Hexagenia mayflies, yellow perch, spottail shiner and walleye in the Wabigoon/English River system. An additional objective was to use mercury stable isotope analysis to distinguish between legacy mercury from the former chlor-alkali plant and mercury from geogenic sources. Mercury contamination within surface sediments and biota at locations as far as 178 kms downstream of the historical source of mercury contamination are elevated relative to the reference lake, Wabigoon Lake. Isotope ratios in young of the year fish and sediments collected from within the system were distinct from fish from the reference lake, Wabigoon Lake, indicating that anthropogenic mercury contamination is distinguishable from geogenic mercury.