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

Part C, Section 4
4.2 Absorption of Chemicals into the Body
The health risk posed by a particular inhalation, ingestion, or dermal exposure depends on the absorbed
dose, which reflects properties of both the chemical and body surfaces involved. There is opportunity
to apply information on absorption efficiency (i.e., absorption factors) during criterion development
provided that the absorbed dose in the primary toxicological study(ies) is known. However, most often
only an administered dose or exposure is documented in the toxicological study. Where the critical
toxicological study has used a different medium than that under investigation, sometimes an absorption
factor is applied to account for the difference in absorption of the contaminant by the body in the two
different media, when this information is available. For the purposes of criterion development, it is
usually assumed that absorption efficiency in an environmental exposure is equal to that of the
toxicological study. In such cases, the absorption rate has been accounted for in the development of the
NO(A)EL or slope factor and no adjustment for absorption is necessary.
For each chemical, the data on its absorption into the body will be evaluated. When delivered doses
are known, available scientific information will be consulted to assess the feasibility of assigning an
absorption factor for the relevant exposure pathway(s).
4.3 Receptors, Exposure Pathways, and Land Uses
4.3.1 General
The development of the soil quality criterion is a two step process. The first step considers all direct soil
exposure pathways, including the ingestion of soil/dust, dermal contact, and inhalation of soil particles
into lungs. The actual inclusion of each pathway in the guidelines derivation equation is based on the
quality of the scientific evidence that a pathway is contributing to exposure. For cases where exposure
pathways have been excluded, this decision will be reassessed as new scientific data becomes available.
The second step in the soil quality criterion derivation is the consideration of indirect soil exposure
pathways through the use of check models. The indirect soil exposure is evaluated through the use of
simplified models which utilize conservative generic input values for site-specific characteristics. The
following indirect pathways are considered:
For all land uses:
• Contamination of Groundwater used as Drinking Water (Section 5.3.2)
• Contamination of Indoor Air via Volatilization into Basements (Section 5.3.4)
For agricultural land use:
• Contamination of Produce, Milk, and Meat Produced On-site (Section 5.3.3)
For residential land use with a garden:
• Contamination of Produce Grown On-site (Section 5.3.3)
89