Variability of North American Regulatory Guidance for Heavy Metal Contamination of Residential Soil

Article excerpt

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.

Resume : Les repercussions sur la sante et les obligations de restauration des sols urbains contamines sont des questions importantes dans plusieurs villes nord-americaines. Les guides de restauration des sols evoluent et vont de valeurs basees sur les approximations du fond geochimique vers des valeurs basees sur les risques pour la sante. Cette analyse examine la variabilite des guides pour les sols residentiels parmi les etats et les provinces de l'Amerique du Nord pour le Cd, le Cr, le Cu, le Ni, le Pb et le Zn. Pour certains metaux, ces valeurs variaient jusqu'a 5 ordres de grandeur. Les comparaisons non parametriques sont utilisees pour illustrer le niveau de variation des normes actuelles et pour examiner la distribution spatiale des differences. L'analyse statistique des parametres est utilisee pour examiner l'importance des variations et determiner si des correlations peuvent etre etablies dans la structure des valeurs de guide. L'analyse de l'indice de risques est egalement utilisee pour evaluer l'impact des differences de valeurs sur le site. Les resultats montrent que la plus grande partie de la variation actuelle peut etre expliquee par un caractere aleatoire plausible si la determination des expositions maximales aux sols est un procede aleatoire. Les differences entre les proprietes statistiques des guides du Cd, du Cr, du Cu, du Ni et du Zn ainsi que celle du Pb demontrent egalement l'influence que le leadership national peut avoir sur les guides de stabilisation.

Mots cles : metaux lourds, valeurs guides pour la restauration, contamination des sols residentiels, analyse de risques, analyse de l'indice de risques.

[Traduit par la Redaction]

Introduction

The purpose of this study is to examine the variability of current regulatory guidance for heavy metal contamination of residential soil. The analysis will concentrate on current U.S., and Canadian state and provincial environmental agency guidance provided to protect human health.

The motivation for this analysis originated with a 2001 field survey of Cleveland, Ohio area brownfields. The study was designed to identify "old contamination" soils with multicomponent contamination (Jennings et al. 2002a, 2002b). However, because of the extent of contamination identified, (Cd, Cr, Cu, Pb, Ni, Zn maximums of 216, 574, 22500, 15170, 837, and 13400 mg/kg, respectively) the study was expanded to measure contamination at additional brownfields and commons (parks, city gardens, school yards, etc.) distributed throughout the survey area. …