Molybdenum, Silver, Thallium and Vanadium

Status and understanding of groundwater quality in the South Coast Interior groundwater basins, 2008: California GAMA Priority Basin Project

“…Molybdenum is a trace element that is found in the major ore mineral molybdenite, and to a lesser extent, in the mineral wulfenite (Evans and Barabash, 2010). High concentrations of molybdenum also are found in shales and phosphate deposits formed in strongly reducing marine environments (for example, Krauskopf, 1955).…”

Groundwater quality in the Western San Joaquin Valley study unit, 2010: California GAMA Priority Basin Project

“…At pH values greater than about 4.5, dissolved molybdenum is present primarily as the molybdate oxyanion, MnO 4 -2 over a wide range of redox conditions (Evans and Barabash, 2010). Concentrations of molybdenum in groundwater are limited at acidic and neutral pH values by sorbtion of the molybdate oxyanion to oxides, organic matter, and clays (Evans and Barabash, 2010). Alkaline conditions inhibit sorbtion of molybdate to mineral surfaces, thus resulting in higher concentrations of molybdenum in groundwater at higher pH values.…”

“…However, high concentrations of molybdenum also are found in organic-rich sediments and sedimentary rocks deposited in sulfidic environments (Crusius and others, 1996). Potential anthropogenic sources to groundwater include industrial sources and surface application of biosolids (Evans and Barabash, 2010). Molybdenum has an EPA HAL of 40 µg/L in drinking water and is on the EPA's Contaminant Candidate List 3 (U.S. Environmental Protection Agency, 2009).…”

“…High levels of molybdenum in animals (including humans) can interfere with uptake of copper. Molybdenum is an essential trace nutrient for some plants for nitrogen fixation and can even be a limiting nutrient in molybdenum-poor environments (Goldman, 1960;Evans and Barabash, 2010).…”

A method to determine silver partitioning and lability in soils

“…[18] In addition, the composition of soil organic matter (SOM) is important because ionic Ag (Ag þ ), being a soft metal cation, can form strong complexes with reduced sulfur and thiol groups in SOM. [20] The total concentration of metals in soils is known to be a poor indicator of the potential bioavailable fraction. [21] Methods that measure the total labile metal fraction (in solution and on solid phases in rapid exchange) such as chemical extractants, resin techniques and isotope dilution (ID) methods have been shown to be better indicators of the bioavailable fraction of metals in soils.…”