ENVIRONMENTAL LEGACY OF THE CALIFORNIA GOLD RUSH: 1. MERCURY CONTAMINATION AND BIOACCUMULATION ASSOCIATED WITH ABANDONED PLACER-GOLD MINES
The most elevated Hg-T concentrations in water and sediment were found in ground and tunnel sluicesthe sites of historical placer gold ore processing. Elevated MeHg concentrations were detected in water from some tunnel sluices and pit lakes formed by partially blocked drain tunnels. Isotopic rate measurements of mercury methylation potential [using 203Hg(II)] and mercury demethylation potential (using 14C) are consistent with relatively high levels of mercury bioaccumulation in organic-rich, near-neutral pit lakes. Predatory insects, such as water striders (family Gerridae) and dragonflies (order Odonata, suborder Anisoptera), were shown to be reliable indicators of bioavailable mercury, making them useful for comparing mercury contamination among sites. Elevated Hg-T concentrations in sport fish, especially black bass (Micropterus spp.) in reservoirs and brown trout (Salmo trutta) in streams prompted local officials to issue consumption advisories. A long-term monitoring program is needed to evaluate the local and regional benefits of recent and future mine-site remediation projects.