Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p17
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 17/24)
Character Range: 987467–990367

EA 2002)
    * Eating poultry, meat or fish (US EPA 1989)
    * Drinking contaminated water (US EPA 1989)
    * Incidental ingestion of surface water while swimming (US EPA 1989)
    * NHMRC Guidelines for managing risks in recreational water (NHMRC 2008).
The equations available to estimate these intakes are generally of the form shown below and detailed in Table 1 for the direct soil ingestion pathway (US EPA 1989).

Intake (mg/kg-day) = CS x IRS x CF x FI x EF x ED
     BW x AT
All currently available exposure models for contaminated land assessment use equations of this form, although there may be variations in detail. Values for the variables in Table 1 (and similar variables for other ingestion pathways) should be derived during the stages of exposure assessment described earlier in this section.
Table 1. Variables description for soil ingestion intake calculation
Variable  Units        Description
CS        mg/kg        Concentration in soil
IRS       mg soil/day  Soil ingestion rate
CF        10-6 kg/mg   Unit conversion factor
FI        -            Fraction ingested from contaminated source
EF        days/year    Exposure frequency
ED        years        Exposure duration
BW        kg           Body weight
AT        days         Averaging time

    4.7.3          Dermal intakes
Dermal intakes can be estimated for the following pathways:
    * dermal contact with soil and dust
    * dermal contact with non-aqueous phase liquid
    * dermal contact with chemicals in water (swimming, showering, bathing or incidental contact).
Dermal contact with vapour phase contaminants is not generally assessed since it is likely to be insignificant in comparison with other pathways (US EPA 1989).

Dermal absorbed dose or dermal intake is estimated using the concept of absorbed dose per event (US EPA 2004b). The overall absorbed dose depends on the number of events, the adherence factor (AF) and the fraction of contaminant absorbed (ABS).

It is noted that there are a number of uncertainties inherent in the estimation of both AF and ABS. US EPA (2004b) provides estimates of ABS for eleven substances or groups of substances and provides guidance on the treatment of uncertainty for the assessment of substances where specific ABS values are not available. AF is dependent on soil type, activity type and exposed population age, and values are provided for a range of circumstances in Exhibit C-2 in Appendix C of US EPA (2004b). Because soil type is so important to the value of AF, additional guidance is provided for sediment (although the method is the same). Wet soil and fine-grained soil have much higher values of AF than dryer and coarser soil.

The equation for dermal intakes is published as follows and detailed in Table 2.
Dermal intake (mg/kg-day)  =  DAevent x EF x EV x ED x SA
                                         BW x AT

For soil, DAevent = CS x CF