Protocol for the Derivation of Environmental and Human ... - CCME

Part C, Section 1
Section 1
Derivation of Human Health Soil Quality Guidelines
1.1 Introduction
The derivation of human health soil quality guidelines involves:
• assessing the toxicological hazard or risk posed by a chemical;
• determining estimated daily intake (EDI) of that chemical, unrelated to any specific contaminated site
(i.e., "background" exposure);
• defining generic exposure scenarios for each land use;
• integrating exposure and toxicity information to set a soil quality guidelines. These guidelines must
ensure that total exposure to a contaminant (EDI and on-site exposure) will present no appreciable
human health risk.
The CCME Subcommittee submits that the steps employed to derive soil remediation guidelines are
similar to those used for site-specific risk assessment, and recognizes that the process used to derive
Environmental Quality Guidelines is subject to several sources of uncertainty (Section 1.3). Application
of risk assessment methodology to establish numerical soil quality guidelines requires that several basic
assumptions are made in lieu of site-specific information. Assumptions about the nature of chemical
exposure for specified land uses are documented in Section 2.0. A defined exposure scenario was
therefore chosen which details a sensitive receptor (child or adult) for a specified land use, the reference
characteristics of that receptor (weight, amount of soil ingested/day, amount of water ingested/day, and
other reference values, including those related to exposure duration) and specific pathways of exposure.
Few distinctions have been made for differing soil type, differing soil chemical, or physical composition,
all of which might be incorporated at a site-specific objective level.
The Subcommittee divided its guidelines development into two steps. The starting point for soil quality
guidelines is the equation dealing specifically with direct soil exposure pathways (soil ingestion, soil
dermal contact, and inhalation of soil particulate). The input values for exposure variables depend on
the assumptions for each generic land use scenario, and include the choice of sensitive human receptor,
exposure duration, frequency, and intensity.
The second step involves "check mechanisms" that attempt to quantify and respond to cross-media
transfer of soil contaminants (e.g., from soil to groundwater). This step ensures that preliminary generic
soil quality guidelines do not lead to unacceptable exposures from other media. These check
mechanisms require additional input values for site-specific characteristics. Since this protocol develops
generic guidelines, assumptions have been made about certain "generic" site conditions. However, at
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