Analysis of worldwide Regulatory Guidance Values for less frequently regulated elemental surface soil contaminants

Guidance values are used to regulate exposure to surface soil contamination. In the United States, element guidance values have been promulgated by at least 6 federal agencies, 46 states, and several regional, city, county, territorial, and autonomous Native American jurisdictions. Guidance values have also been promulgated in at least 74 other United Nations member states. A companion manuscript examined the values applied to the eight most frequently regulated elements (Pb, Cd, As, Ni, Cr, Hg, Cu, and Zn) each for which there are at least 300 guidance values. This manuscript extends analysis to the second tier of contaminants (Sb, Ba, Be, Co, F, Mn, Mo, Se, Ag, Tl, Sn, and V) each for which there are at least 100 guidance values. These values span from 3.4 (for Sn) to 6.1 (for Be) orders of magnitude. Their distributions resemble those of lognormal random variables, but also contain non-random value clusters. On average, with the exception of cobalt, the values used in the U.S. are higher (less conservative) than those used elsewhere. Only about 44% of U.S. values and 31% of all values fall within uncertainty bounds computed for the U.S. Environmental Protection Agency health risk model applied to the elements considered.