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

Part B, Section 4
Section 4
Potential Ecological Receptors and Exposure Pathways of
Soil Contamination
4.1 Ecological Receptors of Soil Contamination
As a first step in the development of environmental soil quality guidelines, it is essential to identify the
ecological component(s) potentially at threat from contamination. This protocol addresses adverse
effects posed by chemical stressors to the biotic component (receptors) of a terrestrial ecosystem. By
characterizing potential receptors of contaminated soil it is possible to identify those requiring protection
from soil contamination as well as evaluating potential exposure scenarios. A simplified exposure
scenario identifying potential receptors of contaminated soil in a greatly simplified terrestrial ecosystem is
illustrated in Figure 4. It is evident that exposure spans a range of trophic levels including soildependent
organisms (plants, soil invertebrates, soil microbes) and higher order consumers (wildlife,
livestock).
Ideally, the selection of receptors should be compatible with, and reflect important characteristics of the
ecosystem (i.e., ecologically relevant). Because of the paucity of ecological effects information for
terrestrial organisms, however, the selection of ecological receptors for this protocol must focus on key
receptors that maintain land use activities. It is also necessary to devise an array that includes
ecologically relevant receptors that are sensitive to chemical stressors, so that guidelines derived through
this protocol reflect sensitive measurement endpoints. In this sense, the receptors of choice serve as
predictive sentinel species from which guidelines can be derived. The ecological receptors selected for
this protocol are summarized in Table 1 and discussed in more detail for each land use in Sections 5.1
to 5.4.
4.2 Exposure Pathways to Soil Contamination
Once the receptor array has been identified, soil exposures for these receptors must be evaluated. For
the purposes here, evaluation depends on the production of a set of facts, assumptions, and inferences
about how exposure to ecological receptors from contaminated soil takes place. In the scenario
depicted in Figure 4, soil-dependent organisms and their consumers are exposed to contamination
directly from the soil, water, and air through the food chain. Those organisms dependent on soil for
survival (e.g., plants, soil invertebrates, soil microbes) come into contact with the soil directly as a
function of their life cycle and therefore will likely receive the greatest threat from contaminated soil.
Higher trophic level consumers receive their largest exposure through consumption of contaminated
food and ingested soil particles, although absorption of contaminants from dermal contact with soil and
inhalation of vapours and suspended soil may also occur.
Ideally, it would be desirable to consider all influential variables for all potential exposure pathways at all
trophic levels (as might be done at the site level). This is not possible in a generic protocol and therefore
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