Mercury fallout in Hawaii

Abstract

Mercury fallout was measured 10 m from the selected emission site, the Sulfur Banks fumarole area, Hawaii Volcanoes National Park; at stations on Maui and Oahu, respectively 200 km and 380 km distant from the Sulfur Banks; and at the Hawaii Geothermal Project drill site, only 40 km from source. Sulfur Banks and Oahu measurements were carried out on six occasions between 1972 and 1976, each time within the same 24 h period.

Gold foil was used for collection of elemental mercury (Hg°) and copper foil for both oxidized (Hg_ox) and elemental forms.

The rate of deposition at the Sulfur Banks was high − 800 μm m⁻² day⁻¹, or 300 kgkm⁻² annually. The same figure applied to the relatively nearby geothermal project site. At both remote stations the fallout rate was approximately 10 fold lower.

At four measurement times out of six the ratio Hg^O/Hg_ox ranged from 0.195 to 0.463 at the Sulfur Banks source and from 1.80 to 5.15 at the remote stations. On two occasions, heavy rains selectively reduced Hg_ox at the emission site.

Model calculations compared Sulfur Banks fallout with rates of re-emission of Hg by vegetation, and the importance of the biotic factor in determination of mass balances and fluxes was emphasized. Aspects of the geochemistry and toxicology of Hg were considered briefly in relation to emission and deposition, and to the occurrence of Hg°.