Appendix B
Human Anatomical and Intake Factors Used in the Exposure Assessment Calculations
In constructing dose models one needs to define the characteristics of individuals in various age/gender categories and the characteristics of the microenvironments in which they live or from which they obtain water and food. Appendix B defines the types of anatomical and activity data needed to carry out the exposure/dose assessment and explains how these data are obtained. For all factors used in this assessment, we define both an arithmetic mean value and a coefficient of variation (CV), which is the arithmetic standard deviation divided by the arithmetic mean.
We calculate the arithmeticmean body weight and CV of body weight for three age groups—infant, child, and adult. The body weight for infants is needed for estimating exposures to contaminants in breast milk. Body weight for adults and children are needed to calculate lifetimeaverage contact rates per unit body weight and contact rates for an exposure duration of less than a full lifetime. The child age category applies to ages 0 to 15 years, but excludes breastfed babies. General data on bodyweight distributions by age and gender are available from the ICRP [1975], the U.S. EPA [1985, 1989a] and Najjar and Roland [1987]. Because it provides more details on agespecific variations, we used the Najjar and Roland [1987] data set to develop the mean value and CV of body weight for ages 0 to 1, 0 to 15, 15 to 70, and for lifetime. These values are listed in Table B1.
Table B1
Values of Human Anatomical and Intake Properties Used in the Exposure Calculations^{(a)}
Parameter, symbol 
Child^{(b)} 
Adult^{(b)} 
Combined^{(b)} 
Units 

Body weight of infants 
7.2 
(0.3) 
 

 
 
kg 
Body weight, BW 
29 
(0.24) 
71 
(0.2) 
62 
(0.2) 
kg 
Surface area, SA_{b} 
0.032 
(0.09) 
0.024 
(0.06) 
0.026 
(0.07) 
m^{2}/kg 
Working breathing rate, BR_{w} 
 
 
0.030 
(0.3) 
 
 
m^{3}/kgh 
Active breathing rate, BR_{a} 
0.023 
(0.3) 
0.018 
(0.3) 
0.019 
(0.3) 
m^{3}/kgh 
Resting breathing rate, BR_{r} 
0.008 
(0.3) 
0.006 
(0.2) 
0.0064 
(0.2) 
m^{3}/kgh 
Fluid intake, I_{fl} 
0.029 
(0.2) 
0.020 
(0.2) 
0.022 
(0.2) 
L/kgd 
Breast milk intake^{(c)}, I_{bm} 
0.11 
(1) 
 

 
kg/kgd 

Water intake during recreation, I_{flr} 
0.0007 
(1) 
0.0007 
(1) 
0.0007 
(1) 
L/kgh 
Ingestion of homegrown exposed produce, I_{ep} 
0.0016 
(0.7) 
0.00078 
(0.7) 
0.00096 
(0.7) 
kg/kgd 
Ingestion of homegrown unexposed produce, I_{up} 
0.00095 
(0.7) 
0.00053 
(0.7) 
0.00062 
(0.7) 
kg/kgd 
Notes to Table B1:
^{(a)} Listed are the arithmeticmean value and (in parentheses) the estimated coefficient of variation (CV), equal to the standard deviation divided by the mean. Body weights are from Najjar and Roland [1987], breathing rates are from ICRP [1975], tap water intakes are from Yang and Nelson [1986] and Ershow and Cantor [1989] and food intakes are from Yang and Nelson [1986].
^{(b)} The child category covers ages 0 to 15, the adult category covers ages 16 to 70, the combined category is used to represent lifetime equivalent exposure and is obtained by multiplying the child category by 15/70, the adult category by 55/70, and then summing these products.
^{(c)} Breastmilk intakes are from Butte et al. [1984] and Whitehead and Paul [1981].
Information on the relation between human body weight and surface area has been published by the ICRP [1975] and the U.S. EPA [1989b]. The EPA [1989b] reports that surface area (SA) in m^{2} can be estimated as 0.1 times body weight (BW) in kg raised to the 2/3 power. Using this formula, along with methods described in Bevington [1969], we estimate the mean value and standard deviation of surface area per unit body weight, SA_{b}, in m^{2}/kg for children and adults using the formula
, (B1)
where the second term is the standard deviation of the surface areabody weight ratio. The resulting surfacearea values and CVs are given in Table B1.
General data on breathing rates by age and gender are available from the EPA [1985, 1989a] and the ICRP [1975]. Values in Table B1 are taken primarily from the ICRP [1975] with variances estimated by McKone and Daniels [1991]. The working breathing rate is for 8 hours of work and, when combined with 8 hours of breathing at the active rate and 8 hours at the resting rate, gives a daily equivalent intake of 30 m^{3} for an adult [EPA, 1989b]. Layton [1992] has derived breathing rates that are consistent with the quantities of oxygen needed to metabolize reported dietary intakes of fats, carbohydrates, and proteins. He has shown that the values in Table B1 could be high by a factor of from 20% to 30%, but this is within the CV reported here.
Tapwater intake includes all household tap water that is consumed as a beverage or used to prepare foods and beverages. Yang and Nelson [1986] have published tapwater and totalfluid intakes in mL/d for the U.S. population by age, sex, and region of the country. Ershow and Cantor [1989] have published populationbased estimates of sex, region, and seasonaveraged tapwater intakes per unit body weight by the U.S. population in mL/kgd. From these two papers, we have derived intakes of tap water in L/kgd for children, adults, and lifetime equivalent. We also need to determine the amount of incidental ingestion that occurs during water recreation. Based on EPA [1989b] data, we use 0.0007 L/kgh (CV equal to 1) as the ingestion rate of any surface water during recreational use. The mean values and CVs of tapwater intake and surface water intake are listed in Table B1.
Data on ingestion of breast milk by infants are available in Butte et al. [1984] and Whitehead and Paul [1981]. We calculate the breastmilk ingestion per unit body weight for infants ages 0 to 12 months as 0.11 kg/kgd with a CV of 0.2. This CV is based on other ingestion factors.
Ingestion of homegrown foods obtained from gardens in the vicinity of the NTLF are included in the risk assessment. For the food intakes included in the exposure assessment, we calculate here the arithmetic mean and standard deviation of homegrown food intakes per unit body weight for children, adults, and lifetime equivalent exposure, all on bodyweight basis. We consider homegrown foods to be those produced on the land associated with a household and consumed within that household. The following food groups are considered in the exposure assessment:
Total intake of foods in each of these groups is obtained from data compiled by the Nationwide Food Consumption Survey (NFCS) [USDA, 1983]. In this survey, the U.S. Department of Agriculture (USDA) used a stratified probability sample of households in the 48 conterminous states and the District of Columbia in each of four seasons from April 1977 through March 1978. The samples were designed to be representative of the United States and were classified according to geographic regions of the country, geographic divisions within each of the regions, and central city, suburban, and nonmetropolitan populations. We calculate total annual average food intakes using results compiled by Yang and Nelson [1986], who analyzed the data from the USDA survey. The variance of intakeperbodyweight ratio used to determine the CV is calculated under the assumption that food intake correlates with body weight to the twothirds power. The mean and variance of body weight used in this estimate are taken from Table B1. Listed first in Table B1 is our estimated total annual average population intake of fruits and vegetables and of grains expressed on a bodyweight and agespecific basis.
Limited data are available on the amount of homegrown food that is produced and consumed in California or in the U.S. The U.S. EPA [1989a] has compiled for U.S. households data on the fractions of consumed produce that come from home gardens. For all categories of fruits and vegetables reported in this study, the fraction that is homegrown is in the range 0.04 to 0.75, and for the one grain listed (corn), the average fraction that is homegrown is 0.45 for the 25% of the individuals surveyed who consumed homegrown corn. From these data we estimated that the fraction of consumed fruits and vegetables that are homegrown is 0.24 with a CV of 0.7, and that the fraction of consumed grains (mostly corn) that are homegrown is 0.11 also with a CV of 0.7. These values represent households with home gardens and not necessarily the average of total homegrown consumption in either the U.S. or California.
According to Yang and Nelson (1986), 47% of all consumed produce (fruits and vegetables) consists of leafy vegetables and other exposed produce, which intercept contaminants from the atmosphere. The remaining 53% of fruits and vegetables consists of protected produce or root crops, in which contaminant transfer to the edible portion is primarily by root uptake. All grain crops are assumed to be exposed primarily to air contaminants.
Based on the information provided in the previous paragraphs, we estimated the mean and CV of the ingestion of exposed (aboveground) and unexposed homegrown produce in households near the NTLF. Table B1 lists our estimates of the mean average annual ingestion of both exposed and unexposed homegrown foods on a bodyweight basis for children, for adults, and for a lifetime of exposure. As is the case for other contact rates, both the mean value and the CV are provided.