1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 3: ANALYSIS
Model
The general form of the food chain model used to estimate exposure of birds and mammals
to COPECs in soil-sediment, surface water, and food items is as follows:
Where:
E t = E o + E d + E i
E t = the total chemical exposure experienced by wildlife
E o , E d , and E i =
oral, dermal, and inhalation exposure, respectively
Oral exposure occurs through the consumption of contaminated food, water, or soil-sediment.
Dermal exposure occurs when contaminants are absorbed directly through the skin. Inhalation
exposure occurs when volatile compounds or fine particulates are inhaled into the lungs.
Although methods are available for assessing dermal exposure to humans (U.S. EPA 1992f),
data necessary to estimate dermal exposure are generally not available for wildlife (U.S.
EPA 1993c). Similarly, methods and data necessary to estimate wildlife inhalation exposure
are poorly developed or generally not available (U.S. EPA 1993c). Therefore, for the
purposes of this assessment, both dermal and inhalation exposure were assumed to be
negligible. As a consequence, most exposure must be attributed to the oral exposure
pathway. By replacing E o with a generalized exposure model modified from Suter et al.
(2000), the previous equation was rewritten as follows:
Where:
N
⎡
⎤
[ j s ] ⎢∑
ij i ⎥ + [ j
× ]
Eo
= Soil × P × FIR + B × P × FIR Water WIR
⎣ i=
1
⎦
E o = total oral exposure (mg/Kg/d)
Soil j = concentration of chemical (j) in soil (mg/Kg)
P s = soil ingestion rate as proportion of diet
FIR = species-specific food ingestion rate (kg food/Kg body weight/d)
B ij = concentration of chemical (j) in biota type (i) (mg/Kg)
P i = proportion of biota type (i) in diet
Water j =
concentration of chemical (j) in water (mg/L)
WIR = species-specific water ingestion rate (L/kg body weight/d)
The end product or exposure estimate for external exposures for birds and mammals is a
dosage (amount of chemical per kilogram receptor body weight per day [mg/Kg bw/d])
rather than a media concentration as is the case for the other receptor groups (fish and other
aquatic organisms, terrestrial plants, and terrestrial invertebrates. This is a function of both
the multiple pathway approach as well as the typical methods used in toxicity testing for
birds and mammals. Sample calculations for exposure via food-chain uptake are presented
in Appendix I, along with examples of risk estimation calculations.
ERA REPORT 3-22 SAC/143368(003.DOC)
7/31/02