Analysis of worldwide regulatory guidance values for the most commonly regulated elemental surface soil contamination

Guidance values are used worldwide to regulate exposure to surface soil contamination. This analysis examines values applied to element 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 71 other United Nations member states. A total of 5949 guidance values for 57 elements have been identified. These values are characterized, and detailed analyses are provided for the eight most frequently regulated elements (Pb, Cd, As, Ni, Cr, Hg, Cu, and Zn). More than 300 guidance values available for each of these are tabulated. These values span from 3.6 orders of magnitude for lead to 6.9 orders of magnitude for arsenic and are distributed in patterns that resemble those of lognormal random variables. However, nonrandom value clusters are also identified in each distribution. On average, the values used in the U.S. are higher than those used elsewhere around the world for noncarcinogenic contaminants, but are lower for carcinogenic contaminants. Approximately 31.4% of all values fall within uncertainty bounds computed from the U.S. Environmental Protection Agency cancer or noncancer risk model, but only 12.9% of carcinogenic arsenic and 7.5% of carcinogenic chromium (Cr-VI) guidance values fall within cancer risk model uncertainty bounds.