LABORATORY CONCLUSIONS TURNED FIELD HYPOTHESES: POTENTIAL CONTROL OF MERCURY REACTIVITY BY IRON- AND SULFUR-BEARING NANOPARTICLES

Mercury (Hg) used to amalgamate gold and silver at the historic Bodie and Aurora mining districts (California and Nevada) has resulted in the release of inorganic Hg to the Walker River basin. Trophic transfer of mercury from tui chub to Common loons residing in Walker Lake, far downstream of stamp mill sites, suggests that inorganic Hg emitted from mine-contaminated and/or naturally enriched soil and sediment is transported over long distances from the Bodie and Aurora mine sites, methylated, taken up by lower trophic-level biota, and transferred to higher trophic-level organisms. Some sulfate- and iron-reducing bacteria methylate Hg. Although laboratory experiments suggest that a variety of reduced sulfur species should affect the availability of mercury to such microorganisms, the effect of a multitude of abiotic and biotic reactions involving iron and sulfur under fluctuating redox conditions on the reactivity of mercury has yet to be identified in field systems. By presenting a progress report of an ongoing field investigation of the Bodie mining region, I will discuss how the scale of observation affects the ability to interpret and compare field-based measurements presumably indicative of the activity of sulfate-reducing bacteria, sulfide oxidation via iron reduction, and the reactivity of mercury in mine-impacted stream sediments with reaction mechanisms deciphered from model laboratory experiments.