Geochemical and Mineralogical Maps, with Interpretation, for Soils of the Conterminous United States

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Antimony (Sb) is a metalloid, meaning this element has properties between those of a typical metal and nonmetal. It is used in the production of storage batteries, flame retardants, alloys, ceramic and glass, plastics, and brake linings. Exposure to Sb at high concentrations can result in numerous adverse health effects. The element is not considered essential for humans. More information about the toxicity of Sb (or other elements and substances) and its potential negative human health impacts can be found at the Agency for Toxic Substances and Disease Registry (ATSDR) website, or click to download a fact sheet about Sb. Antimony has a strong affinity for sulfur (S) and stibnite (Sb₂S₃) is the primary Sb ore mineral. Minor amounts of Sb can also occur in the more common sulfide minerals such as galena (PbS), sphalerite ((Zn,Fe)S), and pyrite (FeS₂). In soils, Sb can sorb onto iron (Fe) oxides and hydroxides, clay minerals, and organic matter.

The distribution of mineral resource deposits with Sb as a commodity (major or minor) in the United States, extracted from the U.S. Geological Survey (USGS) Mineral Resource Data System (MRDS) website, can be seen by hovering the mouse here. Statistics and information on the worldwide supply of, demand for, and flow of Sb–containing materials are available through the USGS National Minerals Information Center (NMIC) website. The average abundance of Sb in the upper continental crust is estimated to be 0.75 milligrams per kilogram (mg/kg) (Hu and Gao, 2008). Among the common rock types, shales contain the highest Sb concentrations, averaging about 1 mg/kg. Other common sedimentary and igneous rocks have concentrations ranging from 0.1 to 0.3 mg/kg. Coal can have elevated concentrations of Sb with averages of about 2 mg/kg.

In our data, the median Sb concentration varies little for the three sample types collected. The median concentration of Sb is 0.57 mg/kg for the top 0- to 5-cm layer and for the soil A horizon, and 0.58 mg/kg for the soil C horizon (see the summary statistics [open in new window]). In general, the geochemical maps for the three sample types are quite similar for Sb.

The distribution of Sb in soils of the conterminous United States is primarily controlled by the composition of underlying soil parent materials. Areas of elevated Sb concentrations include:

• Eastern Montana, North Dakota, South Dakota, eastern Nebraska, eastern Kansas, southern Iowa, northern Missouri, Kentucky, Ohio, and Pennsylvania where parent materials for soils are dominantly marine shale, clayey till, or glacial deposits containing a significant amount of shale. In Pennsylvania, coal may also comprise a portion of the parent material; and
• Western Montana, northern Idaho, Nevada, central and northern Arizona, and south–central Colorado where Sb is present as a constituent of sulfide minerals in areas of historical or current mining activities. Soils in these areas may be formed on mineralized bedrock containing elevated concentrations of Sb. In areas of extensive mining and mineral processing, it is also possible that there may be a component of Sb contamination from these activities superimposed on elevated background concentrations.

The Gulf and Atlantic Coastal Plain (Fenneman and Johnson, 1946) is bisected by the Southern Mississippi River Alluvium and the Southern Mississippi Valley Loess (USDA, 2006). Alluvial sediments have deposited in the Mississippi River valley as the river flooded in recent geologic time. When these sediments dried, winds picked up the fine material and deposited it in thick loess sheets, mainly along the east side of the river valley. The youngest loess sheets are about 10,000 years old. A pattern of higher Sb in soils developed on these young sediments reflects long–range transport of Sb–bearing material from the upper part of the Mississippi River drainage basin

Areas of relatively low Sb concentrations in soils include:

• Atlantic Coastal Plain and the Piedmont (Fenneman and Johnson, 1946) where soil parent materials are dominantly quartz–rich rocks and unconsolidated sediments
• Nebraska Sand Hills (USDA, 2006), where soil parent materials are quartz– and plagioclase–rich sand dunes and sand sheets;
• Parts of the Southern High Plains (USDA, 2006) of Texas and New Mexico where soil parent materials consist of quartz–rich eolian sands and alluvial sediments; and
• Northern and western Michigan where the soil parent materials are comprised of quartz–rich glacial deposits

Statistics - 0 TO 5 CM

Histogram

Boxplot

Empirical cumulative distribution function

Statistics - A Horizon

Histogram

Boxplot

Empirical cumulative distribution function

Statistics - C Horizon

Histogram

Boxplot

Empirical cumulative distribution function