Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p18
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 18/24)
Character Range: 990132–993281

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 x AF x ABS
For water, the calculation of DAevent is dependent on the exposure duration.
For short duration exposures (tevent ≤ t*):
For long duration exposures:

Table 2. Variables description for dermal contact intake calculation
Variable  Units         Description
DAevent   mg/cm2-event  Dermal absorbed dose per event per unit exposed skin area
EF        days/year     Exposure frequency
EV        events/day    Event frequency
ED        years         Exposure duration
SA        cm2           Skin surface area available for contact
BW        kg            Body weight
AT        days          Averaging time
CS        mg/kg         Concentration in soil
CW        mg/cm3        Concentration in water
CF        10-6 kg/mg    Unit conversion factor
AF        mg/cm2-event  Adherence factor of soil to skin
ABS       -             Dermal absorption fraction (chemical-specific)
FA        -             Fraction absorbed from water
Kp        cm/hour       Dermal permeability coefficient of compound in water (chemical –specific)
τevent    hours/event   Lag time per event (chemical-specific, refer to Appendix B of US EPA (2004b))
t*        hours         Time to reach steady state = 2.4 τevent
tevent    hour/event    Event duration
B         -             Ratio of the permeability coefficient of a compound through the stratum corneum relative to its permeability coefficient across the viable epidermis (refer to Equation A.1 in Appendix A of US EPA (2004b))

    4.7.4          Inhalation intakes
Inhalation intakes can be estimated for the following pathways:
    * inhalation of vapours in indoor air
    * inhalation of vapours in outdoor air
    * inhalation of dust particles.
The mechanism for deriving the vapour and dust concentration in air for the above pathways is described in an earlier section of this Schedule. The quantitative approach outlined in US EPA (1989) was developed before the US EPA issued the Inhalation Dosimetry Methodology (US EPA 1994). In this regard, US EPA (2009) updates the inhalation dosimetric approach to be compatible with the Inhalation Dosimetry Methodology, which represents the US EPA's current methodology for inhalation dosimetry and the derivation of inhalation toxicity reference values.

Risk Assessment Guidance (RAGS) Part F (US EPA 2009) recommends that when estimating risk via inhalation, risk assessors should use the concentration of the chemical in air as the exposure metric (e.g. mg/m3), rather than inhalation intake of a contaminant in air based on inhalation rate (IR) and body weight (BW) (e.g., mg/kg-day). The US EPA "recommends that the intake equation presented in RAGS, Part A (US EPA (1989), Exhibit 6-16) should no longer be used when evaluating risk from the inhalation pathway". Hence for the quantification of exposures via inhalation of dust or vapours, it is appropriate that guidance available from US EPA (2009) is considered.