McKay, Donald. "Front matter" Multimedia Environmental Models ...

mated again in mg/day. Food, the other vehicle, is more difficult to estimate. A typical
diet may consist of 1 kg/day of solids broken down as shown in Table 8.5. Fish
concentrations can be estimated directly from water concentrations, but meat, vegetable,
and dairy product concentrations are still poorly understood functions of the
concentrations of chemical in air, water, soil, and animal feeds, and of agrochemical
usage. Techniques are emerging for calculating food-environment concentration
ratios, but at present the best approach is to analyze a typical purchased “food
basket.” This issue is complicated by the fact that much food is grown at distant
locations and imported. Beverages, food, and water may also be treated for chemical
removal commercially or domestically by washing, peeling, or cooking. An example
illustrates this method of estimating dose.
Worked Example 8.4
A chemical of molar mass 181.5 g/mol has partitioned into the air, water, soil,
and sediment resulting in the concentrations given in Table 8.6 below. As a result
of contact with these abiotic media, fish, vegetation, and meat (and correspondingly,
dairy products) are estimated to have the concentrations tabulated.
Using these data and the exposure rates from Table 8.5 for an adult, calculate
the dose to an adult human. Assume that the density of food is 1000 kg/m 3 .
Table 8.6 Illustration of Calculation of Human Dose
Concentration
C (mol/m 3 )
In this case, inhalation in air causes 75% of the dose, and consumption of
vegetation causes another 21%.
Significant chemical exposure may also occur in occupational settings (e.g.,
factories), in institutional and commercial facilities (e.g., schools, stores, and cinemas),
and at home, but these exposures vary greatly from individual to individual
and depend on lifestyle.
There emerges a profile of relative exposures by various routes from which the
dominant route(s) can be identified. If desired, appropriate measures can be taken
to reduce the largest exposures. The advantage of this approach is that it places the
spectrum of exposure routes in perspective. There is little merit in striving to reduce
an already small exposure.
©2001 CRC Press LLC
Intake Rate
I (m 3 /day)
Amount
Consumed
(C*I) (mol/day)
Amount Consumed
(C*I*181.5) (g/day)
Vegetation 4.02 ¥ 10 –7 6.57 ¥ 10 –4 2.64 ¥ 10 –10 4.79 ¥ 10 –8
Fish 2.75 ¥ 10 –6 1.40 ¥ 10 –5 3.85 ¥ 10 –11 6.99 ¥ 10 –9
Meat 1.02 ¥ 10 –9 1.23 ¥ 10 –4 1.26 ¥ 10 –13 2.28 ¥ 10 –11
Dairy 3.23 ¥ 10 –10 2.50 ¥ 10 –4 8.06 ¥ 10 –14 1.46 ¥ 10 –11
Water 1.16 ¥ 10 –9 1.50 ¥ 10 –3 1.74 ¥ 10 –12 3.16 ¥ 10 –10
Soil 1.69 ¥ 10 –7 6.50 ¥ 10 –8 1.10 ¥ 10 –14 1.99 ¥ 10 –12
Air 6.80 ¥ 10 –11 13.5 ¥ 100 9.18 ¥ 10 –10 1.67 ¥ 10 –7
Total dose = 2.22 ¥ 10 –7 g/day = 0.222 mg/day