USING THE USDA-NRCS SOIL SURVEY DATABASE TO EVALUATE AMPHIBOLE CONTENT OF SOILS IN THE UNITED STATES

Currently there are health concerns regarding exposure to asbestos in its natural setting, especially asbestiform amphiboles. To evaluate the distribution of amphiboles we used soil data from the USDA-NRCS Soil Survey Laboratory database. We analyzed the optical mineralogical data from selected sand fractions of pedons within the database. The sands encompass the range in particle size from 0.02 to 0.25 mm. Results show that soils in all states contain some amount of amphiboles, except for Rhode Island.

The soil samples are from horizons within pedons, a 3-dimentional body of soils on the landscape that consists of one or more horizons with depth. Out of the 50 states, 40 had 10% or more of sampled pedons containing amphiboles. Overall, 4,396 pedons out of the 34, 326 pedons (about 13%) sampled in the United States contained some amount of amphiboles. State percentages of the number of pedons sampled containing amphiboles ranged from 0% to 49%. Excluding Rhode Island, Illinois had the lowest percentage (3%) of sampled pedons containing amphiboles. Arkansas had 49% of sampled pedons containing amphiboles. Sixteen percent or, 34,326 samples, which represent horizons within pedons, contained amphiboles out of an overall total of 212,389. Samples from each horizon varied in percentages from 1% (Florida) to 24% (Arkansas) excluding Rhode Island.

Based on these data, amphibole content in United States’ soils is somewhat evenly distributed across the country. Maps of asbestos mine locations published by USGS in the U.S. show few locations in the central U.S., while our data shows an even distribution in this area. The USGS maps show trends of asbestos mines along mountain ranges (e.g., the Appalachians) whereas our percentage maps show no correlations with these deposits. One last important point deals with the morphology of the amphiboles. We assume that the vast majority of the amphiboles found in the soils would not meet the mineralogical definition of asbestos (i.e., they would not have been derived from asbestiform amphiboles), while the majority of them would meet the regulatory criteria (i.e., are over 5 microns in length with a greater that 3 to 1 aspect ratio). Following this later definition, then we would assume 13% of the pedons and 16% of the horizons are “naturally contaminated.”