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

Part A, Section 2
2.2 Limitations of the Protocol
While it is recognized that contaminants are likely to occur in mixtures, not enough is known about
contaminant mixtures for them to be considered in the protocol. The protocol does not indicate the
depth of soil to which these generic guidelines apply. However, health-based guidelines theoretically
apply to the practical depth (i.e., 0 to 5 cm from the surface) for direct soil exposure, and to a greater
depth (> 5 cm) for potential indirect exposure routes (to prevent ground water contamination, or
infiltration of contaminants into indoor air).
The defined exposure scenarios used to develop the soil quality guidelines do not cover the full spectrum
of the types of sites, environments, and organism-site interactions that can exist (see Figure 3).
However, based on experience, and on contaminated site literature, the vast majority of hazardous and
potentially hazardous scenarios have been considered.
Every chemical has peculiarities that cannot be adequately documented in this protocol. These
peculiarities will be identified and discussed in individual supporting documents. There may also be some
contaminants where the criterion derivation process described in the protocol is not suitable. Deviations
from the protocol will be fully documented. New data will come to light as the science of soil
contaminant toxicology and exposure develops. Each responsible agency will have to decide how and
when to best incorporate new data and information into generic guidelines.
2.3 Guiding Principles
Soil is a complex heterogeneous medium consisting of variable amounts of minerals, organic matter,
water and air, and is capable of supporting organisms, including plants, bacteria, fungi, protozoans,
invertebrates and other animal life. Ideally, soil at the guideline levels will provide a healthy functioning
ecosystem capable of sustaining the current and likely future uses of the site by ecological receptors and
humans.
2.3.1 Protecting Human Health
Human health soil quality guidelines provide concentrations of contaminants in soil, at or below which no
appreciable human health risk is expected. This protocol considers direct soil exposure pathways, and
accounts for indirect soil exposure through air, water, and food, via simplified, generic models. Key
components of the risk based generic human health guidelines include:
• a multimedia exposure assessment of background exposure unrelated to contaminated sites;
• considering a generic human exposure scenario relevant to each land use.
In the multimedia exposure assessment, total background exposure by all pathways (i.e., air, water,
food, soil, and consumer products when appropriate) and all routes (i.e., inhalation,
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