Ten years after major releases of inorganic mercury from a chloralkalai plant were sharply reduced, methylmercury (MeHg) levels remain markedly elevated in waters in most of the Wabigoon River system downstream of Dryden, Ontario, Canada. The water column appears to be a very important site for methylation and demethylation. In water, MeHg and inorganic Hg appear to be in quasi equilibrium, as the MeHg: total mercury ratio is independent of contact time with sediments, the atmosphere, and the theoretical residence time of waters. The MeHg: total Hg ratio increased with distance downstream of Dryden, but MeHg always averaged less than 10% of the total Hg concentration. MeHg was mostly soluble, as defined by field centrifugation. Net production of MeHg appeared to be directly related to the amount of MeHg required to establish and maintain equilibrium conditions with inorganic Hg. A model is developed which adequately describes water column MeHg concentrations. Considerations of the model suggests different restoration strategies for different parts of the Wabigoon/English River–Lake system.

Young-of-the-year and yearling northern pike (Esox lucius), yearling yellow perch (Perca flavescens) and adult crayfish (Orconectes virilis) were collected in the mercury-contaminated Wabigoon/English/Winnipeg River System, Ontario, and analyzed for total mercury. Analysis of mercury concentrations in these organisms produced consistent geographical trends; i.e. mercury concentrations in biota downstream of Dryden > English River system > Winnipeg River system > control sites. In the Wabigoon River system the bioavailability of mercury increases with distance downstream of the historical point source. Mercury concentrations in the biota studied were highly correlated with mercury concentrations in fish species which are of sport and commercial interest. The locations where young fish obtain their bodyburdens are known typically within 100 m. The biota studied compare favourably with the criteria proposed by Phillips (1980) as prerequisites for biological indicators. The wide distribution of young pike, perch and crayfish in North America, Europe and Asia may enhance their appeal as biomonitors.

Ten years after major mercury loadings from a chlor-alkalai plant were sharply reduced, mercury levels in the surface sediments, water, and suspended sediments of the Wabigoon River downstream of Dryden, Ontario, remain markedly elevated. During 1979, a typical water year, average mercury concentrations in water throughout an 80-km reach were nearly five times the mean value at the control site. Elevated mercury levels in the Wabigoon River are primarily due to the chemical and biological remobilization of mercury from sediments. Lesser amounts are due to the erosion of mercury-enriched sediments during high flows and to current releases from the mill site at Dryden. In the absence of resuspended sediment during high flows, mercury levels in contaminated waters can be best described by a sediment – water – suspended solids partition. This condition was established within half a day in the most contaminated portion of the system. Mercury concentrations in water can fluctuate seasonally by an order of magnitude. Highest concentrations were associated with elevated summer temperatures.

No abstract

No abstract