Human health risk assessments

Abstract

Before a site is considered contaminated, concentrations of chemicals, particularly natural elements, should be compared to data from local or regional surveys of background soil quality in uncontaminated areas, if data are available. On-site levels would be considered to be consistent with background where the maximum measured concentration of a COPC is less than or equal to a representative statistic for background concentration. If it is found that concentrations of Contaminants of Potential Concern (COPCs) at the site are representative of background levels, then the site may not be contaminated despite the fact that generic environmental quality guidelines are exceeded. In a human health risk assessment, if concentrations of a contaminant are within the range of local or regional background conditions, the contaminant should be excluded from further consideration as a COPC. The concept of background concentrations of chemicals varies among jurisdictions. Potential background levels can be derived from data taken from control sites located close to, but outside the influence of the contaminated site, or may be based on more regional values. Whichever concept is employed, there is a need for a standardized approach to assessing the availability and appropriateness of data on background levels, or evaluating the need for sampling background concentrations at a reference site. CCME Soil Quality Guidelines - Human Health Many contaminants, particularly metals, are naturally occurring, and natural levels can exceed CCME soil quality guidelines and other generic guidelines without representing anthropogenic contamination. When setting national guidelines, the CCME derives guideline values by determining the tolerable or essentially negligible concentration of a contaminant above the background (natural) level (CCME, 2006). The CCME also recognizes that natural levels in soil vary spatially, and recommends that local soil quality objectives be established that incorporate local or regional background concentrations if they are significantly different from the background value used in the derivation of the national generic guideline for a particular contaminant (CCME, 1996). In principle, for threshold contaminants, the total exposure from direct soil pathways should not generally exceed typical background soil exposures by more than 20% of the residual tolerable daily intake (RTDI), although >20% may be allotted under certain circumstances. If the chemical is identified as a non-threshold substance by Health Canada, then a guideline will be developed