Variability of North American regulatory guidance for heavy metal contamination of residential soil

Abstract

The health implications and remediation obligations of contaminated urban soils are significant issues in many North American cities. Remediation guidance for soils is evolving and shifting from values based on geochemical background approximations to values based on health risks. This analysis examines residential-soil guidance variability among the states and provinces of North America for Cd, Cr, Cu, Ni, Pb, and Zn. For some metals, values vary by as much as 5 orders of magnitude. Nonparametric comparisons are used to illustrate the degree to which current standards differ and to examine the spatial distribution of differences. Parametric statistical analysis is used to examine the significance of variations, and to determine if correlations exist in the structure of guidance values. Hazard index analysis is also used to examine how guidance value differences impact site risk assessments. Results indicate that most of the current variation can be explained as plausible randomness if determining maximum acceptable soil exposures is a random process. Differences between the statistical properties of Cd, Cr, Cu, Ni, and Zn guidance and that of Pb also demonstrate the influence that national leadership can have on stabilizing guidance. Key words: heavy metals, remediation guidance values, residential soil contamination, risk analysis, hazard index analysis.