Extremely acidic mine waters with pH values as low as -3.6, total dissolved metal concentrations as high as 200 g/L, and sulfate concentrations as high as 760 g/L, have been encountered underground in the Richmond Mine at Iron Mountain, CA. These are the most acidic waters known. The pH measurements were obtained by using the Pitzer method to define pH for calibration of glass membrane electrodes. The calibration of pH below 0.5 with glass membrane electrodes becomes strongly nonlinear but is reproducible to a pH as low as -4. Numerous efflorescent minerals were found forming from these acid waters. These extreme acid waters were formed primarily by pyrite oxidation and concentration by evaporation with minor effects from aqueous ferrous iron oxidation and efflorescent mineral formation.

The Richmond Mine of the Iron Mountain copper deposit contains some of the most acid mine waters ever reported. Values of pH have been measured as low as ؊3.6, combined metal concentrations as high as 200 g͞liter, and sulfate concentrations as high as 760 g͞liter. Copious quantities of soluble metal sulfate salts such as melanterite, chalcanthite, coquimbite, rhomboclase, voltaite, copiapite, and halotrichite have been identified, and some of these are forming from negative-pH mine waters. Geochemical calculations show that, under a mine-plugging remediation scenario, these salts would dissolve and the resultant 600,000-m 3 mine pool would have a pH of 1 or less and contain several grams of dissolved metals per liter, much like the current portal eff luent water. In the absence of plugging or other at-source control, current weathering rates indicate that the portal eff luent will continue for approximately 3,000 years. Other remedial actions have greatly reduced metal loads into downstream drainages and the Sacramento River, primarily by capturing the major acidic discharges and routing them to a lime neutralization plant. Incorporation of geochemical modeling and mineralogical expertise into the decisionmaking process for remediation can save time, save money, and reduce the likelihood of deleterious consequences. Mining and Water QualityMining of metallic sulfide ore deposits (primarily for Ag, Au, Cu, Pb, and Zn) produces acid mine waters with high concentrations of metals that have harmful consequences for aquatic life and the environment. Deaths of fish, rodents, livestock, and crops have resulted from mining activities and have been noted since the days of the Greek and Roman civilizations. Mining and mineral processing have always created health risks for miners and other workers. In addition, mining wastes have often threatened the health of nearby residents by exposure to emissions of sulfur dioxide and oxides of As, Cd, Pb, and Zn from smelter stacks and flues, metal-contaminated soils, and waters and aquatic life with high concentrations of metals. As with most forms of resource extraction, human health risks accompany mineral exploitation.

Physical and biogeochemical characteristics of the aquatic environment that affect growth dynamics of phytoplankton and the zooplankton communities that depend on them may also affect uptake of methylmercury (MeHg) into the pelagic food web of oligotrophic reservoirs. We evaluated changes in the quality and quantity of suspended particulate material, zooplankton taxonomy, and MeHg concentrations coincident with seasonal changes in water storage of a mining-impacted reservoir in northern California, USA. MeHg concentrations in bulk zooplankton increased from 4 ngÁg -1 at low water to 77 ± 6.1 ngÁg -1 at high water and were positively correlated with cladoceran biomass (r = 0.66) and negatively correlated with rotifer biomass (r = -0.65). Stable isotope analysis revealed overall higher MeHg concentrations in the pelagic-based food web relative to the benthic-based food web. Statistically similar patterns of trophic enrichment of MeHg (slopes) for the pelagic and benthic food webs and slightly higher MeHg concentrations in zooplankton than in benthic invertebrates suggest that the difference in MeHg bioaccumulation among trophic pathways is set at the base of the food webs. These results suggest an important role for plankton dynamics in driving the MeHg content of zooplankton and ultimately MeHg bioaccumulation in top predators in pelagic-based food webs.Résumé : Les caractéristiques physiques et biogéochimiques du milieu aquatique qui affectent la dynamique de la croissance du phytoplancton et les communautés zooplanctoniques qui en dépendent peuvent aussi influencer l'introduction de méthylmercure (MeHg) dans le réseau alimentaire pélagique des réservoirs oligotrophes. Nous déterminons les changements dans la qualité et la quantité des matières particulaires en suspension, dans la taxonomie du zooplancton et dans les concentrations de MeHg qui coïncident avec les changements saisonniers d'emmagasinement d'eau dans un réservoir affecté par des activités minières dans le nord de la Californie, É .-U. Les concentrations de MeHg dans le zooplancton global augmentent de 4 ngÁg -1 aux basses eaux à 77 ± 6,1 ngÁg -1 aux hautes eaux et elles sont en corrélation positive avec la biomasse des cladocères (r = 0,66) et en corrélation négative avec la biomasse des rotifères (r = -0,65). Une analyse des isotopes stables indique des concentrations globalement plus élevées de MeHg dans le réseau alimentaire pélagique que dans le réseau alimentaire benthique. Les patrons statistiquement semblables d'enrichissement trophique de MeHg (pentes) dans les réseaux alimentaires pélagiques et benthiques et des concentrations légèrement supérieures de MeHg dans le zooplancton par rapport aux invertébrés benthiques font penser que la différence de bioconcentration de MeHg entre les voies trophiques s'établit dès la base des réseaux alimentaires. Ces résultats indiquent un rôle important joué par la dynamique du plancton dans le contenu en MeHg du zooplanction et, en fin de compte, dans la bioconcentration de MeHg chez les prédate...