United States Environmental Protection Agency Office of Health and Environmental Assessment Washington DC 20460 Research and Development EPA/600/S8-85/010 Mar. 1989 &EPA Project Summary Development of Statistical Distributions or Ranges of Standard Factors Used in Exposure Assessments E. Anderson, N. Browne, S. Duletsky, J. Ramig, and T. Warn This summary provides information on how to calculate human exposure to toxic substances and ranges of values for body weight, skin surface area, and ventilation rates. Percentile distribution of body weight were computed from the Second National Health and Nutrition Examination Survey (NHANES II) data base computer program. Distribu- tions of skin surface areas were similarly calculated from NHANES height and weight data by applying regression equations. Insufficient data precluded the development of distributions of ventilation rates. Activity pattern information is presented to permit the calculation of time-weighted average ventilation rates. This Project Summary was devel- oped by EPA's Office of Health and Environmental Assessment, Wash- ington, DC, to announce key findings of the research project that is fully documented in a separate report of the same title (See Project Report ordering information at back). Introduction Using standard factors in exposure assessments promotes consistency among various exposure assessment activities in which the Environmental Protection Agency (EPA) is involved. Consistency with respect to common physical, chemical, and biological factors, to assumptions about typical exposure situations, and to the presen- tation of the possible ranges of estimates, enhances the comparability of results and encourages gains in state-of-the-art exposure assessment techniques. Current practice for estimating human exposures typically involves the assumption of average values for such factors as body weight, liquid con- sumption, and respiration rates. The full report presents statistical distributions or ranges of values for these factors. Where sufficient data are available, percentile distributions are developed. Where insufficient data precluded the development of statistical distributions, ranges of values were compiled from measurements reported in the literature. In a few instances, unpublished data obtained through correspondence with researchers have been used to develop ranges or distributions. All data, including these unpublished data, are presented in the Appendices of the full report. A glossary of terms is also presented. Body Weight Published percentile distributions for body weight for men and women and male and female children are based primarily on data gathered in the first National Health and Nutrition Examination Survey during 1970 and 1974. The source of data used in this study is the more recent, second National Health and Nutrition Examination Survey , NHANES II, for which published percentiles are not yet available. NHANES II was conducted on a nationwide probability sample of ap- ------- proximately 28,000 persons, aged 6 months to 74 years, from the civilian, noninstitutionalized population of the United States. The survey started in February 1976 and was completed in February 1980. The sample was selected so that certain population groups thought to be at high risk of malnutrition (persons with low incomes, preschool children and the elderly) were oversampled. NHANES II provides information on 20,322 interviewed and examined indi- viduals. Weight was measured with a scale that mechanically prints weight to quarter- pound intervals directly onto the permanent record. In the full report, percentiles (and their standard errors) of the distribution of body weight have been computed from the NHANES II data using the computer program QNTLS. Surface Area of the Human Body Two approaches can be used to determine the surface area (SA) of the body: direct measurement of the skin area or estimating the SA by geometrical approximation. Several direct measurement tech- niques have been used to measure SA, including direct coating, triangulation, and surface integration. The coating methods consist of coating either the whole body or specific regions with a substance of known or measured area. In some instances the pieces of coating were placed on cross- section paper and the area measured by counting the squares covered. In others, the areas of the pieces of coating were calculated by weighing the coating or weighing duplicates cut from a substance of uniform thickness. Triangulation consists of marking the area of the body into geometric figures then calculating the figure areas from their linear dimen- sions. Surface integration is performed by running a planimeter over the body in parallel strips of equal width. The SA is calculated by adding the areas of all the strips measured. Directly measuring body SA by any method described above is a difficult and time consuming task. Consequently, existing direct measurement data are limited. Body SA can be estimated using geometric methods by assuming the parts of the body resemble geometric solids, then calculating the surface area of the solids based on a few measurements of length and circum- ference. For example, the SA of the trunk may be estimated by measuring the length from the groove of the neck to the tip of the coccyx and taking circum- ferences just under the arms, at the level of the pubis. A linear method has been proposed in which estimates are made on the principle that the surface area of the parts of the body are proportional, rather than equal, to the surface area of the solids they resemble, so that estimates of SA made from lengths and circum- ferences need to be corrected by con- stants obtained from direct measure- ments of SA. Several formulae have been proposed for estimating body SA from measure- ments of other major body dimensions. Generally, the formulae are based on the principles that body density and shape are roughly the same and that the relation of SA to any dimension may be represented by the curve of central tendency of their plotted values or by the algebraic expression for the curve. Most formulae for estimating SA relate height to weight. The first such equation derived can be expressed by: SA = KW 2/3 where SA is surface area in square meters, W is weight in kilograms, and K is a constant. While the equation has been criticized because the specific gravities of human bodies are not equal and because the surface area per unit volume differs for individuals with different body builds, it gives a reasonably good estimate of SA. A formula that has found wide acceptance and use is: SA = a0 H3-, Wa2 where SA is surface area in square meters, H is height in centimeters, and W is weight in kilograms. The value of an (0.007182), a, (0.725), and a2 (0.425) were estimated from a sample of only nine individuals for which SA was directly measured. More recently, values of the model parameters were solved for the rela- tionship between SA and height and weight by multiple regression analysis. The least squares best fit for this equation yielded the following values for the three coefficients: an = 0.024265, a-| = 0.3964, and 82 =0.5378. The result is this equation for estimating surface area: SA = 0.024265 H° 3964 W° 5378 expressed logarithmically as: In SA = In 0.024265 + 0.3964 In H 0.5378 In W. The coefficients for this equation agr remarkably with those obtained in earl measurements. A graphical method has been propos whereby SA could be read from diagram relating height and weight surface areas. However, it does not gi an explicit model for calculating SA. T graph was developed empirically bas on 252 cases, 127 of which were fr( 401 direct measurements report earlier. In the other 125 cases the SA w estimated using the linear method. Several investigators who have work in determining body surface area ha reported their results in terms of surfa areas (SA) of different parts of the bo as well as total surface area. T literature contains SA of body parts b( as direct measurements and estimates. Data on body part SA ha been reported for both sexes, for seve ethnic groups, and for ages ranging frc newborn to elderly. This study presents the largest sint group of direct measurements made any SA investigator, involving a balanc sample of individuals according to s age group, and compares the results Japanese measurements with Germa and Americans, however, only averag for each age group and sex a presented, which limits the usefulness the data for determining ranges percentages for each body part or regie Our recent study proposed a hum skin surface model based on a geomet method of estimating SA. Various bo dimensions for a "50th percentile ma were used with a mensuration formula geometric solids to calculate the SA the geometric solid most closely relat to the body part. The results were ported as a percentage of total ! associated with each body part, whi shows the author's comparison of I model with three earlier publish methods. Available direct measurement d« were analyzed using the Statistic Processing System (SPS) softwe package to generate equations tt calculate SA as a function of height a weight. These equations were then us to calculate SA distributions of the U population with NHANES II height a weight data using the computer progn QNTLS. ------- Ventilation Rates Pulmonary ventilation data and activity pattern data permit the calculation of time-weighted average ventilation rates. Pulmonary ventilation is the mass movement of gas in and out of the lungs. The volumes of inhaled and exhaled air usually are not exactly equal; the volume of inspired oxygen is typically larger than the volume of expired carbon dioxide. Pulmonary ventilation is generally represented by the minute volume (^e), the volume of gas expired in liters per minute at BTPS (gas volume at normal body temperature and ambient barometric pressure, saturated with water vapor). Minute volume is the product of tidal volume (the volume of gas moved during each respiratory cycle) and respiratory frequency. Minute volume is usually measured accurately with a water-filled spirom- eter. The spirometer uses one-way valves to funnel expired air into a col- lection system or alternatively, directly into a spirometer. There have been several formulae proposed in the literature to calculate minute ventilation of humans at rest from anthropometric data. Resting ventilation is directly related to the resting metabolic rate. With exercise, minute volume increases in response to the increase in metabolic demand. There is an abrupt increase in ventilation with the onset of exercise, followed by a further, more gradual increase. With moderate exercise, the increase is due primarily to an increase in tidal volume; this is accompanied by an increase in respiratory frequency when the exercise becomes more strenuous. When exer- cise ceases, there is an abrupt decrease in ventilation, followed by a more gradual decline to preexercise values. Review of the literature failed to identify equations that would enable the development of statistical distributions of minute ventila-tion at all activity levels for male and female children and adults. Therefore, ranges of measured values were compiled from the available data, which are tabulated in the full report. Many of these measurements are from early studies. Most of the available minute ventilation measurements are from studies ex- pressing the associated activity levels in terms of kilogrammeters per minute. In other studies, the activity level was given qualitatively by the type of activity (e.g., walking at 3 miles per hour); the asso- ciated breathing rates were categorized based on representative activities. For each age-sex-activity level category for which data were available, minimum, maximum, and mean minute volumes were determined. These values were derived from both individual measurements and reported mean values, for which the raw data were not presented. Weighted means were cal- culated by assigning each individual measurement a weight of one and each mean value a weight corresponding to the number of subjects the mean repre- sented; the weighted data were then summed and divided by the total number of subjects. The standard deviations for the age-sex-activity level groups were not calculated because many of the mean values used were reported without any measure of distribution variance. In addition, many groups had very few data points, making standard statistical sum- maries difficult to interpret. In some cases, means were presented without the minimum and maximum values of the original data sets; therefore, the minima and maxima for age-sex-activity level groups are representative only of the available individual measurements. Activity pattern data may be used in conjunction with minute volume data to estimate ventilation rates. In addition to providing information on exercise levels, available activity pattern studies also describe the amount of time spent in different microenvironments. Such de- tailed information is desirable if the ambient concentration of a pollutant differs significantly from one microenvi- ronment to another, as may happen with particulate filtration from the outdoor to the indoor microenvironment. More detailed activity pattern data are available in the Appendices of the full report which presents in its entirety a document describing activity patterns for 56 population subgroups. This document is a supplement to a report on the application of the National Ambient Air Quality Standard Exposure Model to carbon monoxide. Hourly assignments to locations, microenvironments, and activ- ity levels are presented for each popu- lation subgroup. ------- £ Anderson, N. Browne, S. Duletsky, J. Ramig, and T. Warn are with GCA Corporation, Chapel Hill, NC 27514, Tom McLaughlin is the EPA Project Officer (see below). The complete report, entitled, "Development of Statistical Distributions or Ranges of Standard Factors Used in Exposure Assessments," (Order No. PB 85-242 667/AS; Cost: $21.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Office of Health and Environmental Assessment U.S. Environmental Protection Agency Washington, DC 20460 United States Center for •Environm.&ntat Research Environmental Protection Information ' Vs,:>,":"'Yi Agency CincinnatTOH 4$268^5 \-& VrXAT^i 1J^£ jl'-j ~ n Official Business Penalty for Private Use $300 EPA/600/S8-85/010 CHICAGO ------- |