Methods for the analysis of sulfide in surface waters and results from two Ontario lakes

Sulfide is an important controlling factor in the cycling of heavy metals in the environment and mercury in particular. The aim of this study was to develop a method for the determination of sulfide over the concentration range found in natural surface waters. Furthermore, profiles for inorganic and methylmercury were also generated to assess whether or not sulfide is influencing mercury cycling. An HPLC method was developed for the analysis of sulfide by methylene blue, using a purge and trap concentration step, which resulted in a detection limit of approximately 7.5 ng/L. Sampling was conducted in two Ontario Lakes: Plastic Lake in Central Ontario and Lake 658 in Northwestern Ontario. Sulfide profiles in each lake were a mirror image of the dissolved oxygen profile. There was a strong correlation between sulfide and inorganic mercury (r = 0.88, p = 0.00078) as well as methyl mercury (r = 0.96, p = 1.2x10 -5) in Lake 658. Plastic Lake showed no significant correlation between methyl mercury and sulfide.