Mercury Levels in Vegetation Growing on Contaminated Soils in Southwestern Montana

Abstract

Contamination at former gold mine sites is common because mercury was used to extract gold by amalgamation of which some was lost to soils. Mobilization from soil to plants at these sites could result in high levels of mercury in plant tissues causing concern over spread of mercury through natural pathways such as grazing. We determined whether vegetation growing on three sites in southwestern Montana mobilized mercury from soil into roots or leaves. Two sites were known or suspected to have mercury contamination from past mining activity. The third site was an engineered repository for mining wastes. Soil mercury levels were highly elevated at the sites with past mining activity. Two grass species growing on the most contaminated site did not accumulate substantial amounts of mercury in either roots or leaves. Ponderosa pine (Pinus ponderosa) showed similar results (no accumulation) but we found Douglas-fir (Pseudotsuga menziesii) roots to have an accumulation of mercury. Repository soil had levels of mercury double the amount reported for U.S. topsoils, but levels in grass roots and leaves were not substantially elevated above soil levels. Hence, this repository is currently preventing movement of mercury from covered tailings into the vegetation on its surface. Species that were not accumulating mercury (thus not mobilizing mercury) could be utilized for vegetation rehabilitation on other mercury-contaminated sites.