The Hg/210Pb Hypothesis: Apportioning Regional and Global Components of Current and Historical Hg Deposition

摘要

In a paper published in 2001, Lamborg et al. reported good correlations between total Hg and the naturally occurring, particle-reactive radionuclide ~(210)Pb in rainwater from northern Wisconsin and the equatorial Atlantic Ocean. The precise cause of this correlation is not known, but suggests an analogy between the ~(210)Pb system (solid ~(226)Rafgaseous ~(222)Rnrparticulate ~(210)Pbrprecipitation ~(210)Pb) and Hg chemistry in the atmosphere (gaseous Hgsrgaseous Hg(II)rparticulate Hg(II)rprecipitation Hg(II)). The precipitation correlation of Hg and ~(210)Pb offers a hypothetical tool for discerning regional and global influences on local Hg depositional fluxes. This tool would take the form of Hg:~(210)Pb ratios in precipitation from a variety of locations. Sites which receive little local/regional Hg should show Hg:~(210)Pb ratio values similar to those observed at remote locations while sites that receive Hg deposition of a more localized nature should show greater ratio values. In effect, the application of ~(210)Pb as a normalizing tracer of particulate scavenging should remove the issue of site-to-site variation in climatology (rain depth, frequency, temperature, etc.) and permit direct comparison of sites from widely differing locations. We are currently engaged in a test of this hypothesis. ~(210)Pb and Hg determinations in precipitation are being made at 8 locations in North America, many at Mercury Deposition Network sites. These collections will continue for about 2 years and yield an unprecedented set of Hg and ~(210)Pb comparisons. Concurrently, we are collecting and analyzing sediment cores from undisturbed lakes from continental upwind (southeast Alaska) and downwind (Newfoundland) locations to assess the impact of continental/regional-scale sources on the anthropogenic enhancement of Hg deposition in the last few centuries.