ICMGP - Conference Presentation

Abstract Information :

Gaseous mercury (Hg) emissions continue to be released from Hg mines that were shut down more than 50 years ago in central California. Many reservoirs are in the watersheds that are impacted by these former Hg mines and thus there is a potential for atmospheric deposition of Hg to be an important source of methylmercury (MeHg) to these aquatic systems. To assess this potential and map out emission hot-spots, we collected 4 genera of native tree lichens from the New Almaden Mining District (NAMD) near San Jose, California and analyzed these for total Hg, and a subset of samples was analyzed for speciated Hg (Hg0, MeHg, HgII). We found there was no statistical difference in THg concentrations between lichen genera and that there was also no difference between DI-water rinsed and unrinsed samples. This suggest that lichens are taking up primarily Hg0 (as opposed to surface debris) with similar rates across genera. We also found that about 86% of the THg in a subset of samples (N=48) was in the HgII form indicating that Hg is oxidized within the lichen and is not easily lost back to the atmosphere. The THg concentrations of lichens in the NAMD revealed that samples collected close to former furnaces were the highest (up to 14,000 ng/g). Fitting all the THg data vs. distance from the nearest furnace or retort site at NAMD resulted in a result of 9.4 km, which is the distance away from the point source with background concentrations of THg in lichen. This puts several reservoirs in the cone of elevated Hg deposition from the point sources and suggests the atmospheric inputs should be reduced through soil remediation techniques.