Natural emissions of mercury to the atmosphere in Canada

Abstract

The only Canadian inventory of natural source emissions of mercury (Hg) was prepared in 1981, but is now considered unreliable. As a result, the primary reference relied upon by Canadian regulators concerning the relative contribution of natural sources to environmental Hg contamination is a global inventory that was published in 1989. The relevance to Canada of a global inventory that included volcanic emissions is questionable. Therefore, a new inventory of natural Hg emissions in Canada was undertaken. Consistent with earlier inventories, natural Hg emission sources included wind erosion of soil, sea salt spray, forest and brush fires, biogenic Hg vapour emissions from terrestrial vegetation, and evasion of vapour from soil, ocean surfaces (within territorial limits) and lakes and rivers. Meteoritic dust was also considered. Recognizing the variability and uncertainty in available data, probabilistic methods were employed to derive mean estimates with 90% confidence limits. Estimated total annual natural source emissions of Hg in Canada averaged 1.1 × 106 kg with lower and upper 90% confidence limits of 0.54 × 106and 2.3 × 106 kg. Evasion of Hg vapour from terrestrial vegetation and evasion from soil predominated as natural sources of Hg in Canada; other sources were minor or insignificant. The estimated mean annual emission was approximately one third of that estimated in 1981. It was impossible with currently-available data to quantitatively differentiate natural emissions of Hg from those that are re-emitted following previous anthropogenic release and deposition. Therefore, the estimates provided herein include an unquantifiable contribution by re-emitted anthropogenic Hg.Key words: natural, mercury, emissions, atmosphere, Canada.