2.15 SOIL DERMAL CONTACT
Normal daily activities generally involve contact
with small amounts of soil from which dermal contact and absorption may
occur. This pathway is considered for the atmospheric deposition to soil
transport pathway and the user- defined measured soil concentration pathway.
The considerations given to estimation of the exposure
from contact with soil from atmospheric transport and deposition are as
follows.
- Transport Medium:
- soil concentration at the location of the exposed individual, Casi, pCi/m2 or mg/m2, expressed as an annual deposition accumulation value
- Special Process:
- accumulation of pollutants in soil over the exposure duration for the soil dermal contact pathway transfer of contaminated soil particles onto skin of the exposed individual transfer of contaminant through skin
- Exposure Factors:
- soil contact event frequency and exposure duration.
The soil concentration is provided from the transport
analysis as an average annual deposition amount averaged over a 70-year
exposure period. The accumulation of pollutants in soil over a multi-year
exposure duration is estimated using the deposition and accumulation Equations
(19) and (20) given in Subsection 1.2.4. The amount transferred to skin
is estimated using a soil adherence factor (as for the shoreline sediment
dermal contact pathway) and the area of skin contaminated. This transfer
through skin is estimated using a pollutant specific total absorption fraction
applicable to each soil contact event.
The average daily dose for chemical pollutants from
soil dermal contact is evaluated as follows for the atmospheric transport
and deposition pathway:
(85)
where
Dddi = average daily dose for chemical pollutant i from dermal contact with soil, equivalent to ingestion intake (mg/kg/d)
10-6 = units conversion factor (m3/cm3)
10-3 = units conversion factor (g/mg)
SAFi = soil deposition and accumulation factor for the soil ingestion pathway exposure duration (d)
Fdd = fraction of days per year that soil dermal contact occurs (dimensionless)
FEdd = soil contact event frequency (events/d)
AD = adherence factor for contact with soil or sediment (mg/cm2 skin)
Add = area of skin contacted by soil (cm2)
ABdi = fraction of pollutant i on skin that is absorbed into the body during one soil or sediment contact event (fraction/event)
f1i = fraction of pollutant i absorbed in passing through the GI tract following ingestion (mg absorbed/mg ingested)
DPsi = average annual deposition rate to soil for pollutant i (mg/m2/d)
tdd = thickness of soil layer that atmospherically deposited pollutant is uniformly distributed within (m)
rdd = density of soil that atmospherically deposited pollutant is distributed within (g/cm3)
EDdd = exposure duration for the soil dermal contact pathway (yr)
ATddi = averaging time for pollutant i for the soil dermal contact pathway (yr)
BWdd = body weight of exposed individual for the soil dermal contact pathway (kg).
For radionuclide pollutants, the total lifetime dose
from soil contact following atmospheric deposition is evaluated as follows:
(86)
where
Dddi = total lifetime dose for radionuclide pollutant i from soil dermal contact (rem)
DFdi = dose conversion factor for dermal absorption of radionuclide i (rem/pCi absorbed)
DPsi = annual average deposition rate to soil for radionuclide pollutant i (pCi/m2/d).
and other terms are as previously defined.
When measured soil concentrations are defined by
the user, the exposed individuals are assumed to be exposed directly to
the soil with the average soil concentrations evaluated using Equation
(32). The average daily dose from dermal contact with soil for the measured
soil pathway is evaluated as follows for chemical pollutants:
(87)
where
Dddi = average daily dose for chemical pollutant i from dermal contact with soil (mg/kg/d)
SMFi = average soil concentration for pollutant i (mg/kg).
and other terms are as previously defined. The averaging time for noncarcinogenic
chemicals is set to the exposure duration, and the averaging time for carcinogenic
chemicals is fixed at 70 years.
For radionuclide pollutants, the total lifetime dose
from dermal contact with measured soil is evaluated as follows:
(88)
where
Dddi = total lifetime dose for radionuclide pollutant i from ingestion of soil (rem)
SMFi = average soil concentration for radionuclide pollutant i (pCi/kg)
and other terms are as previously defined. The average soil concentration
is evaluated using Equation (32).