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

Part B, Section 7
Therefore,
BCF = concentration in plants
concentration in soil
Using professional judgment, BCF values from soil to plants can be estimated with available literature
data. A technical draft report has been prepared by Environment Canada (1994c) and provides
guidance on estimation of appropriate soil-to-plant BCF values for guidelines derivation.
7.6.7 Calculation of the Soil Quality Guideline for Ingestion
An animal may be exposed to a contaminant by more than one route (i.e. through contaminated food,
direct soil ingestion, dermal exposure, inhalation of air and dust, and drinking water) (Figure 15). The
effects from the sum of these exposures should not exceed the DTED. Contributions from each media
(also called apportionment factors) to the total exposure for livestock and wildlife are discussed below.
Water
The U.S. EPA and Health and Welfare Canada agree that 20% of a human's estimated daily intake
(EDI) is contributed from water. It is assumed that the remaining 80% originates from soil, air, and
food. Due to the lack of sufficient data to estimate an inter-species apportionment factor for water, an
apportionment factor of 20% shall be used for livestock and wildlife. If apportionment information is
available for the species in question it should be used in place of the human value.
Dermal Absorption and Inhalation
Insufficient information exists to account for dermal absorption and inhalation of contaminants in
livestock. It is assumed that these two routes of exposure together do not contribute significantly to the
total contaminant exposure to livestock (i.e. approximately 5%). However, if contaminant specific
information is available for dermal absorption and inhalation (e.g. volatiles), it will be used in place of the
default 5% apportionment factor.
Ingestion
The proportion of the total exposure attributed to ingestion is the product of the dry matter intake rate
(DMIR) and contaminant concentration in that medium. Assuming that water and dermal
absorption/inhalation account for 25% of the total exposure then the remaining 75% of the total
exposure is from food and soil ingestion. Walker and MacDonald (1992) recommended an
apportionment factor of 75% in the calculation of tissue residue guidelines for the protection of wildlife
consumers of aquatic life to account for contributions of food to the total exposure.
Therefore, in order to provide protection to the animal, maximum exposure from ingestion of soil and
food combined should not exceed 75% of the DTED. The soil quality guideline for
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