2.12 SHORELINE DERMAL CONTACT
This pathway involves contact with contaminated sediments
during shoreline recreational activities. Contaminants in surface water
are transferred to shoreline sediments over a period of time. The pollutants
in sediment may result in exposure by dermal contact with sediments, inadvertent
ingestion of sediments (discussed in Subsection 2.13), and external exposure
to radionuclides in sediments (discussed in Subsection 2.22). The analysis
for these exposure pathways begins with the pollutant concentration in
surface water at the location of the shoreline being used for recreational
activities. For the dermal contact with sediment exposure pathway, the
following considerations are given to the exposure evaluation.
- Transport Medium:
- surface water concentration in the water at the shoreline location, Cswi, pCi/L or mg/L, expressed as a 70-year average value
- Special Process:
- loss of pollutants during transport in the surface water body by volatilization or decaytransfer of pollutant from water to shoreline sediment accumulation of pollutant in sediment over time contact of individuals with shoreline sediment absorption through the skin
- Exposure Factors:
- area of skin exposed, shoreline event frequency, and exposure duration.
The loss of pollutants during transport in the surface
water body is evaluated using Equation (3). The transfer and accumulation
of pollutants in sediments is estimated from the model developed by (Soldat
et al. 1974) relating water concentration to shoreline sediment concentration
following a long period of deposition. The pollutant concentration in sediment
is given by the expression below. The equation provides an effective surface
contamination (pCi/m2) for use in calculating gamma exposure
rates from radionuclides to persons standing on sediment. This surface
contamination rate can be converted to a sediment concentration for use
in calculating dermal exposure and ingestion exposure for chemical and
radionuclide pollutants. The sediment surface contamination level is estimated
as follows:
(75)
where
CSi = surface concentration of pollutant i in shoreline sediment (mg/m2 or pCi/m2)
100 = empirical constant for transfer of pollutants from water to sediment (L/m2/d).
Cswi = concentration of pollutant i in surface water at the location of the shoreline (mg/L or pCi/L)
lsi = loss or decay rate constant for pollutant i in surface waters (d-1)
TEl = period over which shoreline sediment has accumulated (yr).
The value of the transfer constant was derived for several radionuclides
by using data obtained from an analysis of water and sediment samples taken
from the Columbia River at Richland, Washington, and at Tillamook Bay,
Oregon, 75 km south of the river mouth (Nelson 1965; Toombs and Cutler
1968).
The surface sediment concentration can be converted
to a sediment mass concentration using the sediment density and an assumed
sediment thickness, as follows:
(76)
where
Cssi = shoreline sediment concentration for pollutant i at the location of recreational shoreline use (mg/kg or pCi/kg)
10-6 = units conversion factor (m3/cm3)
103 = units conversion factor (g/kg).
tss = thickness of shoreline sediments (m)
rss = density of shoreline sediments (g/cm3) and CSi is as previously defined.
The intake of pollutants from dermal contact with
sediments is estimated using a soil adherence factor (mg/cm2)
and a total absorption fraction per contact event. The average daily dose
of chemical pollutants is estimated, as follows:
(77)
where
Dhdi = average daily dose for chemical pollutant i from dermal contact with shoreline sediment (mg/kg/d)
10-6 = units conversion factor (kg/mg)
FEsl = shoreline contact event frequency (events/d)
AD = adhesion factor for contact with soil or sediment (mg/cm2 skin)
Ahd = area of skin contacted by sediment (cm2/event)
ABdi = fraction of pollutant i on skin that is absorbed into the body during one soil or sediment contact event (dimensionless)
Fhd = fraction of days per year that shoreline exposure occurs (dimensionless)
EDhd = exposure duration for the shoreline sediment dermal contact pathway (yr)
AThdi = averaging time for pollutant i for the shoreline sediment dermal contact pathway (yr)
BWhd = body weight of exposed individual for the shoreline sediment dermal contact pathway (kg)
f1i = fraction of ingested pollutant absorbed by the gut from ingestion intake (dimensionless).
The total lifetime dose from radionuclide pollutants is estimated as follows:
(78)
where
Dhdi = total lifetime dose for radionuclide pollutant i from dermal contact with shoreline sediment (rem)
DFdi = dose conversion factor for radionuclide i for the dermal absorption intake route (rem/pCi intake)
and other terms are as previously defined.