Worldwide regulatory guidance values for surface soil exposure to carcinogenic or mutagenic polycyclic aromatic hydrocarbons

Regulatory guidance values are used worldwide to control residential exposure to surface soil contamination. A total of 1,991 values used in 44 United Nations member states plus 4 territories or administrative regions to control exposure to seven polycyclic aromatic hydrocarbons (PAH) generally considered to be carcinogenic or mutagenic (benz(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, dibenzo(a,h)anthracene, chrysene and indeno(1,2,3-c,d)pyrene) are examined. The distributions of these values vary over 6.3–7.2 orders of magnitude and resemble the distributions of lognormal random variables. The U.S. Environmental Protection Agency (USEPA) values fall near the low end of these distributions and exert a modest influence on the values from other U.S. jurisdictions. On average, 17 additional jurisdictions use USEPA values and 21% of all guidance values fall within uncertainty bounds approximated from the USEPA risk model. An average of 62% of U.S. guidance values fall below the median value, but this varies from 43% for chrysene to 70% for dibenz(a,h)anthracene and benzo(a)pyrene. Although the magnitudes of guidance values differ, the ratios of values often reflect the relationships implied by benzo(a)pyrene Toxicity Equivalency Factors (TEFs). This influence is strongest in RGVs from U.S. jurisdictions.

► At least 44 nations have surface soil guidance values for carcinogenic PAH.
► The values are highly variable and span 6 or 7 orders of magnitude.
►  USEPA and many U.S. state values are near the low end of these distributions.
► Many values are based on benzo(a)pyrene using Toxicity Equivalency Factors.
► Value clusters may identify emerging consensus values.