A PROPOSED CONTINENTAL-SCALE SOIL GEOCHEMICAL SURVEY OF NORTH AMERICA: ESTABLISHING A DATABASE FOR THE 21ST CENTURY

In 2003, the U.S. Geological Survey (USGS) and the Natural Resources Conservation Service (NRCS), in partnership with the Geological Survey of Canada, Agriculture and Agri-Food Canada, Health Canada, and the Consejo de Recursos Minerales (Mexico), began an effort to study the feasibility of conducting a new soil geochemical survey of North America. This undertaking is being considered because the most-often-quoted data set for background concentrations of metals and other trace elements in soils of the conterminous United States consists of only 1,323 samples collected during the 1960s and 1970s by the USGS under the leadership of H.T. Shacklette. Samples from the “Shacklette data” were collected from a depth of about 1 ft, primarily from noncultivated fields having native vegetation, and analyzed for more than 40 elements. This data set represents a density of only one sample per about 6,000 km2 (2,300 mi2). The only other national-scale soil geochemical data set for the United States was generated by the NRCS and contains 3,045 samples of agricultural soil collected from major crop-producing areas of the conterminous US. These samples were only analyzed for five elements (Cu, Pb, Zn, Cd, and Ni). These two national-scale databases are inadequate to address the increasing number of questions posed by the risk assessment and regulatory community, health scientists, land managers, as well as soil and earth scientists. In addition, neither Canada nor Mexico has a national-scale soil trace-element geochemical database.

A Soil Geochemistry Workshop drawing 112 international attendees was held in March 2003 to officially initiate the feasibility study. This group made recommendations for sample design, sample collection protocols, and analytical protocols for the proposed new survey. It was recommended that the new survey include, in addition to “standard” total inorganic elemental analysis, determination of parameters such as bioavailability, selected organic compounds, and microbial characterization. Pilot studies, each of 2-year duration, will begin on 3-4 areas representing diverse geography, climate, soil types, geology, land use, and population density during late 2003 to test recommended protocols. The protocols will be finalized and the continental-scale survey will ideally begin in 2006.