Heavy metals, as environmental contaminants of terrestrial ecosystems, are not a recent phenomenon. They are ubiquitous in trace concentrations in soils and vegetation, and if fact many are required by plants and animals as micronutrients. In addition, naturally occurring surface mineralizations can produce metal concentrations in soils and vegetation that are as high, or higher, than those found around man-made sources. The searches by prospectors for such metal deposits, frequently using biogeochemical techniques, are a part of our history. These cases of natural ‘pollution’ are, however, relatively localized, and it was not until the recent era of industrialization that widespread contaminations by heavy metals (and other classes of pollutants as well) have occurred.

Sources of Metal and Elemental Contamination of Terrestrial Environments

Evaluation of trace elements in U.S. coals using the USGS COALQUAL database version 3.0. Part I: Rare earth elements and yttrium (REY)

Selenium excess and deficiency have been established as the cause of various health problems in man and animals. Combustion of fossil fuels, especially coal, may be a major source of the anthropogenic introduction of selenium in the environment. Coal is enriched in selenium relative to selenium's concentration in most other rocks and relative to selenium in the Earth's crust. Data from almost 9,000 coal samples have been used to determine the concentration and distribution of selenium in US coals. The geometric mean concentration of selenium in US coal is 1.7 ppm. The highest mean selenium value (geometric mean 4.7 ppm) is in the Texas Region. Atlantic Coast (Virginia and North Carolina) and Alaska coals have the lowest geometric means (0.2 and 0.42 ppm, respectively). All western coal regions have mean selenium concentrations of less than 2.0 ppm. In contrast, all coal basins east of the Rocky Mountains (except for several small basins in Rhode Island, Virginia, and North Carolina) have mean selenium values of 1.9 or greater. Generally, variations in selenium concentration do not correlate with variations in ash yield, pyritic sulphur, or organic sulphur concentrations. This may be the result of multiple sources of selenium; however, in some non-marine basins with restricted sources of selenium, selenium has positive correlations with other coal quality parameters. Selenium occurs in several forms in coal but appears to be chiefly associated with the organic fraction, probably substituting for organic sulphur. Other important forms of selenium in coal are selenium-bearing pyrite, selenium-bearing galena, and lead selenide (clausthalite). Water-soluble and ion-exchangeable selenium also have been reported.

Distribution and mode of occurrence of selenium in US coals

Lichens and mosses as monitors of industrial activity associated with uranium mining in northern Ontario, Canada—Part 2: Distance dependent uranium and lead accumulation patterns☆

Plant Community Characteristics and Responses

Trace-metal variation in soils and sagebrush in the Powder River Basin, Wyoming and Montana

/pdf/geochemical-survey-of-the-western-coal-regions-first-annual-2daxu313qv.pdf

John R. Keith

Papers

Trace-metal variation in soils and sagebrush in the Powder River Basin, Wyoming and Montana

Geochemical survey of the western coal regions; first annual progress report, July 1974