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

Section 5
Exposure Pathways and Key Receptors According to Land
Use and Data Availability
Land use, by definition, implies a human measure of a portion of the earth's surface to sustain some
human activity, not necessarily an ecological one. However, the maintenance of primary ecological
functions is usually required for most land use activities (except some commercial and industrial
processes). The decision to derive environmental soil quality guidelines according to selected human
land uses within the NCSRP in no way subordinates the protection of ecological values to human
values. The following sections describe the receptor and exposure scenarios for agricultural,
residential/parkland, commercial, and industrial land use.
5.1 Agricultural Land Use
In general, the primary activities associated with agricultural land use include the ability to grow crops
and raise livestock. Although agricultural land use varies, the development of soil quality guidelines
must protect key receptors that permit or maintain crop growth and livestock production against
adverse effects. (Note: guidelines selection may include organisms that are subject to pesticide control.)
Protection must also be offered to resident and transitory wildlife and native flora because, in some
areas (e.g., agroecosystems), this may be the only viable habitat for these organisms. A generic
exposure scenario considered for the derivation of soil quality guidelines for agricultural land use is
provided in Figure 5.
5.1.1 Growth of Crops and Plants
To ensure crop production at agricultural sites, it is essential to maintain soil-dependent biota whose
ecological function sustains crop and plant growth. Contact of crops and native plants directly with
contaminated soil must also be considered in guidelines development (Figure 5).
Sufficient toxicological information exists to consider dermal soil contact by microbes (and their effect
on nutrient cycling), soil invertebrates (e.g., decomposers), and crops and plants (e.g., seeds and roots)
for guidelines derivation for the protection of crop and plant growth. Currently, there is not enough
information to incorporate dermal absorption and translocation of contaminants by crops and plants via
aerial deposition into guidelines derivation, but this pathway should be examined where information is
available. Root uptake and accumulation of contaminants by crops grown on-site and used as feed, or
native flora used as pasture, must also be examined when they relate to livestock and wildlife ingestion
scenarios (Figure 5).
5.1.2 Maintenance of Livestock and Wildlife
To ensure adequate soil quality for the maintenance of grazing and feedlot livestock, potential adverse
effects from the incidental ingestion of contaminated soil and ingestion of contaminated food must be
considered for guidelines derivation. These pathways of exposure are the most significant source of
contaminant uptake by livestock (Thorton and Abrahams, 1983, Fries, 1987, Paustenbach, 1989).
Sufficient toxicological information exists to consider
32