Background
The following are some sources for background data for the USA.
Abstract - In 2007, the U.S. Geological Survey initiated a low-density (1 site per 1,600 square kilometers, 4,857 sites) geochemical and mineralogical survey of soils of the conterminous United States as part of the North American Soil Geochemical Landscapes Project. Sampling and analytical protocols were developed at a workshop in 2003, and pilot studies were conducted from 2004 to 2007 to test and refine these recommended protocols. The final sampling protocol for the national-scale survey included, at each site, a sample from a depth of 0 to 5 centimeters, a composite of the soil A horizon, and a deeper sample from the soil C horizon or, if the top of the C horizon was at a depth greater than 1 meter, from a depth of approximately 80–100 centimeters. The <2-millimeter fraction of each sample was analyzed for a suite of 45 major and trace elements by methods that yield the total or near-total elemental content. The major mineralogical components in the samples from the soil A and C horizons were determined by a quantitative X-ray diffraction method using Rietveld refinement. Sampling in the conterminous United States was completed in 2010, with chemical and mineralogical analyses completed in May 2013. The resulting dataset provides an estimate of the abundance and spatial distribution of chemical elements and minerals in soils of the conterminous United States and represents a baseline for soil geochemistry and mineralogy against which future changes may be recognized and quantified. This report (1) describes the sampling, sample preparation, and analytical methods used; (2) gives details of the quality control protocols used to monitor the quality of chemical and mineralogical analyses over approximately six years; and (3) makes available the soil geochemical and mineralogical data in downloadable tables.
Element Concentrations in Soils and Other Surficial Materials of the Conterminous United State
Abstract - Samples of soils or other regoliths, taken at a depth of approximately 20 cm from locations about 80 km apart throughout the conterminous United States, were analyzed for their content of elements. In this manner, 1,318 sampling sites were chosen, and the results of the sample analyses for 50 elements were plotted on maps. The arithmetic and geometric mean, the geometric deviation, and a histogram showing frequencies of analytical values are given for 47 elements.
The lower concentrations of some elements (notably, aluminum, barium, calcium, magnesium, potassium, sodium, and strontium) in most samples of surficial materials from the Eastern United States, and the greater abundance of heavy metals in the same materials of the Western United States, indicates a regional geochemical pattern of the largest scale. The low concentrations of many elements in soils characterize the Atlantic Coastal Plain. Soils of the Pacific Northwest generally have high concentrations of aluminum, cobalt, iron, scandium, and vanadium, but are low in boron. Soils of the Rocky Mountain region tend to have high concentrations of copper, lead, and zinc. High mercury concentrations in surficial materials are characteristic of Gulf Coast sampling sites and the Atlantic coast sites of Connecticut, Massachuetts, and Maine. At the State level, Florida has the most striking geochemical pattern by having soils that are low in the concentrations of most elements considered in this study. Some smaller patterns of element abundance can be noted, but the degree of confidence in the validity of these patterns decreases as the patterns become less extensive.
Trace Elements and Radon in Groundwater Across the United States, 1992-2003
Abstract - Trace-element concentrations in groundwater were evaluated for samples collected between 1992 and 2003 from aquifers across the United States as part of the U.S. Geological Survey National Water-Quality Assessment Program. This study describes the first comprehensive analysis of those data by assessing occurrence (concentrations above analytical reporting levels) and by comparing concentrations to human-health benchmarks (HHBs). Data from 5,183 monitoring and drinking-water wells representing more than 40 principal and other aquifers in humid and dry regions and in various land-use settings were used in the analysis. Trace elements measured include aluminum (Al), antimony (Sb), arsenic (As), barium (Ba), beryllium (Be), boron (B), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), manganese (Mn), molybdenum (Mo), nickel (Ni), selenium (Se), silver (Ag), strontium (Sr), thallium (Tl), uranium (U), vanadium (V), and zinc (Zn). Radon (Rn) gas also was measured and is included in the data analysis.
Climate influenced the occurrence and distribution of trace elements in groundwater whereby more trace elements occurred and were found at greater concentrations in wells in drier regions of the United States than in humid regions. In particular, the concentrations of As, Ba, B, Cr, Cu, Mo, Ni, Se, Sr, U, V, and Zn were greater in the drier regions, where processes such as chemical evolution, ion complexation, evaporative concentration, and redox (oxidation-reduction) controls act to varying degrees to mobilize these elements. Al, Co, Fe, Pb, and Mn concentrations in groundwater were greater in humid regions of the United States than in dry regions, partly in response to lower groundwater pH and (or) more frequent anoxic conditions. In groundwater from humid regions, concentrations of Cu, Pb, Rn, and Zn were significantly greater in drinking-water wells than in monitoring wells.
Samples from drinking-water wells in dry regions had greater concentrations of As, Ba, Pb, Li, Sr, V, and Zn, than samples from monitoring wells. In humid regions, however, concentrations of most trace elements were greater in monitoring wells than in drinking-water wells; the exceptions were Cu, Pb, Zn, and Rn. Cu, Pb, and Zn are common trace elements in pumps and pipes used in the construction of drinking-water wells, and contamination from these sources may have contributed to their concentrations. Al, Sb, Ba, B, Cr, Co, Fe, Mn, Mo, Ni, Se, Sr, and U concentrations were all greater in monitoring wells than in drinking-water wells in humid regions.
Groundwater from wells in agricultural settings had greater concentrations of As, Mo, and U than groundwater from wells in urban settings, probably owing to greater pH in the agricultural wells. Significantly greater concentrations of B, Cr, Se, Ag, Sr, and V also were found in agricultural wells in dry regions. Groundwater from dry-region urban wells had greater concentrations of Co, Fe, Pb, Li, Mn, and specific conductance than groundwater from agricultural wells.
The geologic composition of aquifers and aquifer geochemistry are among the major factors affecting trace-element occurrence. Trace-element concentrations in groundwater were characterized in aquifers from eight major groups based on geologic material, including (1) unconsolidated sand and gravel; (2) glacial unconsolidated sand and gravel; (3) semi-consolidated sand; (4) sandstone; (5) sandstone and carbonate rock; (6) carbonate rock; (7) basaltic and other volcanic rock; and (8) crystalline rock. The majority of groundwater samples and the largest percentages of exceedences of HHBs were in the glacial and nonglacial unconsolidated sand and gravel aquifers; in these aquifers, As, Fe, Mn, and U are the most common trace elements exceeding HHBs.
Overall, 19 percent of wells (962 of 5,097) exceeded an HHB for at least one trace element. The trace elements with HHBs included in this summary were Sb, As, Ba, Be, B, Cd, Cr, Cu, Pb, Mn, Mo, Ni, Se, Ag, Sr, Tl, U, and Zn. Mn occurred most often at concentrations greater than its human-health benchmark (12 percent), followed by As (7.0 percent), Sr (4.3 percent), U (4.0 percent), B (1.9 percent), and Mo (1.5 percent). Rn occurred at concentrations greater than the U.S. Environmental Protection Agency (USEPA) proposed maximum contaminant level of 300 pCi/L in more than 65 percent of water samples, and concentrations of Rn in 2.7 percent of samples were greater than the USEPA-proposed alternate maximum contaminant level of 4,000 pCi/L. There were more exceedences of HHBs in the dry-region groundwater than in the humid-region groundwater.
Groundwater pH and redox conditions were significant factors for the occurrence of many trace elements. Low pH (less than 7) was a significant factor in the occurrence of many cationic metals, such as Al, Fe, Mn, and Ni; these metals, as well as Cu, Pb, and Zn, adsorb more strongly to aquifer materials as pH increases. Anoxic conditions often were related to the increased occurrence of many oxyanion-forming elements, such as As, Cr, and Mo, whereas oxic conditions often were related to higher Se occurrence. Groundwater redox and pH effects were evident for As, Cr, Mo, and Se. Based on all samples, As occurrence generally increased as geochemical conditions became increasingly anoxic for groundwater with pH less than 7, but was consistently high for samples with pH greater than 7. A similar pattern was evident for Mo and, to a lesser extent, Cr. For groundwater in aquifers in glacial unconsolidated sand and gravel, however, As occurrence increased as groundwater became increasingly anoxic and as pH increased, indicating that redox is an important process throughout the range of pH. Al, Cu, Pb, and Zn occurred more often in low-pH groundwater and, except for Al, in oxic conditions.
In general, older waters (mostly pre-1953) had more occurrences of trace elements, greater pHs, were from deeper wells, and had lower concentrations of dissolved oxygen than younger waters (defined as waters containing a fraction younger than 1953). Most oxyanion-forming trace elements occurred more frequently in old groundwater. However, although U occurrence was greater in older water collected from dry-region aquifers, U occurred more often in young water in humid-region aquifers. This difference may be related to old, humid-region groundwater having lower concentrations of dissolved oxygen, a condition which can inhibit U mobility.
Overall, As co-occurred primarily with silica (SiO2) and Mo in water with slightly high pH. About 12 percent of water samples without SiO2 or Mo had concentrations of As greater than or equal to 1 μg/L. This number increased to about 45 percent if either Mo or silica were present and to about 85 percent if both Mo and SiO2 were present. From a subset of water samples selected from 2,714 wells for co-occurrence analysis, samples from 572 wells (21.1 percent) had HHB exceedences of one or more trace elements. Of the 2,714 samples, 62 (2.3 percent) had two or more trace elements that exceeded HHBs. Fifty of the 62 (80 percent) were from unconsolidated sand and gravel aquifers and involved at least As and Mn, Mn and U, or As and U.