Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p22
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 22/24)
Character Range: 1001336–1004275

vitro methods for other contaminants though further research may provide adequate validation in the future.

In vivo methods are available for the resolution of contaminated land issues though these methods are not likely to be practical due to their expense.

There are a number of in vitro methods that may be considered as a surrogate measure of arsenic and lead relative bioavailability. These may include Relative Bioavailability Leaching Procedure (RBALP) (US EPA 2007b), the Solubility Bioavailability Research Consortium (SBRC) (Kelley et al. 2002) or the in vitro gastrointestinal method (IVG). However it is noted that the selection and use of any in vitro method should be conducted on a contaminant-specific basis where the availability, validity and limitations of available methods are considered at the time of the assessment.

There do not appear to be any validated analytical methods for estimating inhalation bioaccessibility, especially for particulates. For the assessment of vapours, given that these chemicals tend to cross the lung membranes fairly easily, assuming 100% relative bioavailability is appropriate.

In risk assessments, the dermal pathway has a well-established mechanism for considering absorption and relative bioavailability. The lack of dermal-specific TRVs means that a dermal dose is compared to the ingestion TRV. However the dermal dose represents an absorbed dose rather than applied dose (as is commonly the case in establishing ingestion TRVs). Hence it may be necessary to modify the ingestion TRV. This is commonly done by applying a gastrointestinal absorption factor (GAF) to the ingestion TRV, which modifies the TRV by a factor that addresses absorption of the chemical across the gastrointestinal tract in the critical toxicity study. There are limitations with this simplistic approach as it does not address metabolism in the gut wall or skin or first-pass effects associated with orally administered doses. In some cases it may be more appropriate to use a dermal specific TRV.

For soil-bound contaminants, there is little data on the influence of matrix on dermal absorption. A common approach to address this issue is to apply a dermal absorption fraction (ABS, described in Section 4.7.3) to modify the applied dose in soil to calculate the dermally absorbed dose. It represents the proportion of the contaminant in soil that is considered to be absorbed into the bloodstream through the skin.

    4.8.3          The approach for petroleum hydrocarbons
Petroleum products have a high degree of variability in their physical properties and chemical compositions. Products such as gasoline, diesel, fuel oil and jet fuel each have their own chemical signatures and the composition of the same product can vary depending on where it was distilled and the source of its crude oil. This makes environmental assessment of these products difficult and an approach has been developed