Abandoned cinnabar mine sites continue to be a major source of mercury (Hg) pollution in the San Francisco Bay Area. The atmosphere may be an important route of transport of mercury from the mines to sensitive receptor regions. However, traditional methods of monitoring atmospheric mercury are spatially limited, inconvenient, expensive, and time consuming. Lichen biomonitoring can be used as a low-cost, efficient, and effective pollution indicator. Our previous studies have only focused on a limited selected of lichen species, which poses challenges when investigating new areas where specific species are unavailable. In this study, we observed the effect of two former mercury mining districts, New Almaden Quicksilver Mining District and Knoxville Mining District, on the distribution of Hg across the landscape.

Mercury, a highly toxic heavy metal, remains of global concern due to its capacity to cause significant harm to human health and the environment. Mercury (Hg) can travel long distances within the atmosphere, bioaccumulate in living organisms, and act as a potent neurotoxin. Mercury contamination remains a prevalent issue due to historic mining practices, as it was once mined for various industrial applications and for its ability to form a gold amalgam. Large amounts of mine waste, also known as calcines, remain at historic mercury mines, representing significant sources of Hg emissions to the local environment through wet and dry atmospheric deposition. Even though the presence of mercury contamination at these abandoned mines has been documented, there is a notable gap in our understanding of how mercury emissions from mine waste can contaminate the environment through atmospheric transport. This study aims to investigate the spatial and temporal environmental impacts of Hg emissions and determine atmospheric pathways of contamination from mine waste at the New Almadén Mining District (NAMD) and the Sulphur Bank Mercury Mine (SBMM) in Northern California. However, traditional methods of monitoring atmospheric mercury present challenges due to the high cost of equipment and the temporal and spatial variability of air pollution. So, in this study, we employed lichen as a bioindicator of atmospheric mercury emissions due to its abundance in the study area, low cost, and past success in using lichen to record Hg. Measuring total mercury concentrations across various lichen species and locations at the NAMD and the SBMM allowed us to identify Hg emission hotspots and provide valuable insights into the spatial and temporal distribution of Hg in a contaminated environment. The concentration of total mercury in lichen samples reached 45 ppm at the Sulphur Bank Mercury Mine, indicating significant levels of contamination in historic calcine processing areas.

Monomethylmercury (MeHg, CH3Hg+) is a neurotoxin that bioaccumulates in the food web. Previous investigations have found eutrophication to be associated with both increases and decreases in MeHg accumulation. We embarked on a time series study at Younger Lagoon Reserve, adjacent to agricultural fields, to investigate the influence of anthropogenic nitrate on MeHg production in a local lagoon. Our work hints at why it is possible for dichotomous results to exist, and also again demonstrates that sulfur is an important control on MeHg production. MeHg production in soils has received less attention than wetland and marine environments, yet agricultural soils such as vineyards are of interest as they receive elemental sulfur applications. Our research reveals the results of a first inquiry into the fate of sulfur in vineyards and its implications for potential methylation.