EXPOSURE ANALYSIS -CHAPTER 1 pptx

Part I Exposure Concepts © 2007 by Taylor & Francis Group, LLC 3 1 Exposure Analysis: A Receptor- Oriented Science Wayne R. Ott Stanford University CONTENTS 1.1 Synopsis 3 1.2 Introduction 4 1.3 Full Risk Model 4 1.4 Total Human Exposure Concept 6 1.4.1 Indirect Approach 10 1.5 Receptor-Oriented Approach 12 1.6 Indoor Air Quality 14 1.7 Activities That Increase Exposures 17 1.7.1 p-DCB in Residential Microenvironments 19 1.8 Source Apportionment of Exposure 21 1.9 Public Education 24 1.10 Exposurist as a Profession 26 1.11 Conclusions 27 1.12 Questions for Review 28 References 28 1.1 SYNOPSIS Exposure science differs from past approaches in the environmental sciences, because, instead of beginning with an assumed source of pollution and then trying to find out who or what may be affected, exposure science works from both directions — not just from the source but also backward from the receptor. In the past, environmental policy analysts have assumed some obvious source, such as a smokestack or a leaky drum, may be important and then tried to trace where the pollutant goes, often losing its complicated trail long before the much-diluted pollutant ever reaches any real people, plants, or animals. By following this older source-oriented approach, it has been difficult to show in epidemiological studies that traditional sources actually affect anyone’s health or that these assumed sources cause adverse exposure of humans to harmful concentrations. Exposure science, on the other hand, begins with the target itself, measuring the pollutant concentrations that actually reach people by using, for example, personal monitors worn by individuals. Then the analyst works backward from the personal exposure to find the actual source. By following this receptor-oriented approach and measuring pollutant concentrations at the contact boundary of the person, new sources have been discovered, and some sources originally thought to be important were found to make negligible contributions to exposure. Using direct measurements of exposure, many significant new indoor sources — consumer products, building materials, and personal activities — emerge as the main contributors to human exposure and thus are more likely to be © 2007 by Taylor & Francis Group, LLC 4 Exposure Analysis the causes of environment-related illness than traditional outdoor sources. Activity pattern surveys show that people spend on average more than 90% of their time indoors or in a vehicle, and efforts to protect public health from environmental pollution and to reduce personal exposure must consider both indoor air quality and outdoor air quality as well as other routes of exposure, such as dermal contact, drinking water, nondietary contact, and food. 1.2 INTRODUCTION Historically, environmental risk problems often were discussed without identifying the target of the risk. As noted in definitions of the concepts of exposure and related terms (see Chapter 2), risk assessors must always answer a critically important question, “Whose risk is to be reduced?” If the goal is to protect public health, then the target of the risk becomes the human being. If the goal is to protect an ecological system, then the target may become some organism within the system — for example, an animal or a plant. Failure to identify the target of the risk in environmental problems causes much confusion. In this book, we are concerned primarily with the risks of pollutants to public health, so the target of concern is the human being. In particular, we are more interested in the risks caused by environmental pollution to the general public than in the risks faced by workers in certain occu- pational settings that are protected by occupational health and safety laws. Environmental protection laws, unlike occupational health laws, are intended to protect the general public. The science of exposure analysis has provided important insight by focusing more clearly than ever before on individual members of the general public and the manner in which pollutants reach and adversely affect them. Included, of course, are those persons in special high-risk occupations, but worker exposure constitutes a special subset of the general population. 1.3 FULL RISK MODEL To reduce the risks of environmental pollutants to human beings, a relationship between the sources of pollution and their effects must be found. If the risk is to be assessed accurately, then all the sources of the pollutant must be included. The sources considered cannot be limited to just the traditional or more obvious ones (smokestacks, sewage outfalls, hazardous waste sites, etc.) but need to include the nontraditional sources as well (for example, building materials in indoor settings, consumer products, food, drinking water, and house dust). Establishing the links between a particular target and a particular agent, or pollutant, requires a knowledge of five fundamental components that may be viewed as links in a chain — from source to effect — comprising the full risk model (Figure 1.1). Such a link sometimes is called a route of exposure. In this full risk model, each of the five components is linked to the others and is dependent on the one before it. Thus, the pollutant output from one component is the input into the next component. Therefore, if information on one component of the model is lacking, then it is not possible to fully characterize the relationship between the sources of pollutants and the resulting effects. With a missing component, the effect of controlling a source on the exposure received by the target cannot be determined. The sources in this conceptual model are all sources of a particular pollutant that may cause risk, regardless of whether the sources are found indoors, outdoors, or in-transit, or whether they are carried to the target by air, water, food, or dermal contact. Despite the importance of each of the five components in Figure 1.1 for determining the public health risk associated with environmental pollution, historically our scientific understanding of all five components has not been equal. Usually, environmental pollution has come to the attention of public officials because traditional pollutant sources, such as smokestack plumes or leaking drums, have caused alarm because they were so obvious. The obviousness of certain traditional sources has caused an overemphasis on this source category in the complete risk model. Consequently, a © 2007 by Taylor & Francis Group, LLC Exposure Analysis: A Receptor-Oriented Science 5 great body of knowledge exists today about source abatement and control of traditional sources, and many of the environmental laws deal with direct regulation of traditional sources, regardless of whether their contribution to health risks is large or small. By comparison, nontraditional sources, which release pollutants that reach people by nontraditional routes of exposure (for example, consumer products emitting pollutants in the home), have received relatively little attention either from regulators or the public. Once a traditional source of pollution is known and identified, environmental analysts usually focus on the manner in which it moves from its source — sometimes called its fate and transport — until it ultimately is converted into other harmless chemicals or reaches humans. Like the source component (first box in Figure 1.1), the pollutant movement component (second box) has received considerable research attention. Meteorologists have developed atmospheric dispersion models, and water quality and groundwater specialists have developed geophysical models for the movement of pollutants in streams, groundwater, surface water, soil, and the food chain. Research on the movement, or fate and transport, of pollutants has dealt primarily with traditional routes of exposure, tracing the movement of pollutants through geophysical carrier media on a large physical scale (1–100 km), while nontraditional routes of exposure (for example, microenvironments with sources within 30 m of the person) usually have been overlooked. As with the first two components, the fifth component in Figure 1.1 — the effects of a pollutant on the target — also has received considerable past research attention. Numerous studies have looked at the effects on animals and humans of specific concentration levels, often without knowing whether suspected sources can create these same high exposure levels. Because research on the health effects of each pollutant is difficult, much uncertainty still remains despite years of studies of the effect of a given exposure level on rats and other animals in the laboratory, humans in clinical experimental settings, and community epidemiology studies. In contrast with the source, movement, and effect components of the full risk model, very little knowledge has been available up until the last 20 years for the remaining two components — exposure and dose. As the science advances, exposure and dose, because they have been neglected, are proving to be the two components of the full risk model for which major contributions to knowledge are possible. Without accurate knowledge of human exposure (the middle box), it is often impossible to determine which sources should be controlled and by how much, or the likely effect on public health of controlling a source. The shaded zone in Figure 1.1 shows the main areas of emphasis in exposure analysis. Filling the critical gaps in the full risk model is necessary for implementing a risk-based approach to environmental management. Completing the full risk model allows an analyst to determine if traditional source control efforts are actually reducing the risks to public health in the manner expected and to the degree needed. If we do not know whether the right sources (or other contributors to exposure and risk) are being controlled, or whether they are being controlled by FIGURE 1.1 Five components of the conceptual full risk model. To determine how much a change in a source causes a corresponding change in an effect, it is necessary to know: (a) all five components and (b) the linkage between each pair of components. The shaded zone indicates the primary emphasis of the science of exposure analysis. (From Ott 1985. With permission.) Source Movement of Pollutants Dose EffectExposure © 2007 by Taylor & Francis Group, LLC 6 Exposure Analysis the correct amount, then our environmental programs will become ineffective and inefficient in reducing public health risks. Fortunately, exposure research completed over two decades has demonstrated for a handful of pollutants that the all-important missing exposure and dose data can be obtained and that the full risk model can be completed, thus making possible a true risk-based approach to environmental management. This exposure research also has identified a variety of new nontraditional pollutant sources and other important contributors to exposure that environmental programs currently are not addressing adequately, and the data show that many of these newly identified sources contribute more to public health risk than many traditional sources now subject to environmental laws and regulations. As a consequence of these new findings, some observers believe that our environmental priorities and policies need to be reshaped and our laws revised. Although it is important to link sources to exposures to effects in the full risk model, even linking sources to exposures (but not necessarily to dose or effects) provides a great new body of practical knowledge that is important to regulators, decision makers, public health officials, and the general public. If an accurate source-exposure relationship can be established for a particular environmental pollutant, then it is possible to discover the most economical and efficient way to reduce risk by reducing exposures, with a consequent reduction in potential risk. This benefit is possible because it is reasonable to assume that a monotonic relationship exists between exposure and risk — that is, decreases in exposure lead to corresponding decreases in health risk, even though the exact form of the relationship may not be known. Indeed, by completing even the partial risk model between sources (first box) and exposure (middle box) — that is, finding the relationships for just the first three boxes — we may discover that our mitigation activities are placing too much emphasis on the wrong sources and that other overlooked nonregulatory approaches may be more effective in reducing exposures than the ones we have chosen. Indeed, the evidence from some exposure research findings points toward many simple steps not usually associated with environ- mental laws that can be taken by individuals to reduce their own risks. 1.4 TOTAL HUMAN EXPOSURE CONCEPT The total human exposure concept seeks to provide the missing component in the full risk model: estimates of the total exposure of the population to an environmental pollutant with known accuracy and precision, usually averaged over a time period of interest, such as 24 hours. Ideally, the exposure information needed is not for just one member of the population, nor is it the average exposure of the entire population. Rather, what usually is sought is a frequency distribution of all members of the population, giving not only the population mean exposure but also the highest 1%, 5%, and 10% of the exposures of the population. 1 This measurement methodology has been completely developed and demonstrated successfully for one major pollutant, carbon monoxide (CO; see Chapter 6), and the total human exposure methodology also has been applied effectively to a number of other toxic environmental pollutants. The total human exposure approach begins first by applying the conceptual definitions of exposure that can be described quantitatively (Chapter 2). A target must be identified, and a contact boundary also must be identified, even though it might not be formally stated in a real-life exposure analysis. Any pollutant in any carrier medium that comes into contact with this conceptual contact boundary — either through the air, food, water, or dermal route — is considered to be an exposure to that pollutant at that instant of time (Figure 1.2). The instantaneous exposure usually is expressed as a pollutant concentration (for example, mass/volume) in a particular carrier medium at a particular instant of time. Some pollutants, such as CO, can reach humans through only one carrier medium, 1 These percentages are based on the quantiles of the distribution of population exposures. For example, if we rank all the population exposures we have from highest to lowest, and 99% of the exposures are found to be below 65 µg/m 3 of some pollutant, then can we say that 1% of the population of our sample have exposures at or above 65 µg/m 3 . © 2007 by Taylor & Francis Group, LLC Exposure Analysis: A Receptor-Oriented Science 7 the air inhaled. Other pollutants, such as lead and chloroform, can reach humans through two or more routes of exposure in multiple carrier media (for example, air, food, dermal, and drinking water). If multiple routes of exposure are involved, then the total human exposure approach seeks to determine a person’s exposure (concentration in each carrier medium at a particular instant of time) through all routes of exposure from all the sources of that pollutant (Figure 1.3). Once applied, the total human exposure methodology seeks to provide information, with known precision and accuracy, about the exposures of the general public through all environmental media, regardless of whether the pathways of exposure are air, drinking water, food, or dermal contact. It seeks to provide reliable, quantitative data on the number of people exposed and their levels of FIGURE 1.2 Exposure occurs when any pollutant makes direct contact with the human being through one of four possible carrier media. FIGURE 1.3 Full risk model when there is more than one source of the same agent. Here the movement of the pollutant from the source to the target (a human being) is shown as an “exposure pathway” for each source. The entire journey of a pollutant from a source to a target is a “route of exposure.” HUMAN BEINGWATER AIR SOIL FOOD GUT GUT SKIN LUNG SKIN GUT SKIN CONCEPTUAL MODEL OF TOTAL HUMAN EXPOSURE Source 1 Source 2 Source n Exposure Pathway 1 Exposure Pathway 2 Exposure Pathway n Human Being E x p o s u r e D o s e © 2007 by Taylor & Francis Group, LLC 8 Exposure Analysis exposure, as well as the sources and other contributing factors responsible for these exposures, including the reasons for the individual person-to-person differences in exposure. Ideally, these exposure data are presented in an exposure distribution — a frequency distribution showing the proportion of the population exposed to different concentration level intervals over a specific time period. Placing the human being at the center of attention makes the total human exposure approach different from the older and more traditional environmental analysis approaches — total human exposure is a receptor-oriented approach, because it begins with the receptor, the human being. The total human exposure approach first considers all routes of exposure by which a pollutant may reach a target. Then, it focuses on those particular routes that are relevant for the pollutant of concern, developing measurements of the concentrations reaching the target. Activity pattern infor- mation from diaries maintained by respondents can help identify those activities and microenvi- ronments that are of greatest importance, which, in many cases, helps to identify the contributing sources. Body burden, the amount of pollutant present in the person’s body — for example, blood concentrations of lead (Pb) or breath concentrations of volatile organic compounds (VOCs) — often is included in exposure studies as an indication of previous exposure, thereby helping to confirm and strengthen our understanding of the exposure measurements. The direct approach consists of direct measurements of exposures of the general population to the pollutants of concern, such as the U.S. Environmental Protection Agency’s (USEPA) Total Exposure Assessment Methodology (TEAM) studies. In a TEAM study, a representative random sample of the population is selected based on a carefully planned statistical design using the probability sampling methods outlined in Chapter 3. Then, for the particular pollutant (or class of pollutants) under study, the pollutant concentrations reaching the respondents selected according to this statistical design are measured from all sources and for all relevant carrier media. A sufficient number of people are sampled using statistical sampling techniques — sometimes called a multi- stage probability design — to permit inferences to be drawn, with known precision, about the exposures of the larger population from which the sample is drawn. Often a stratified random sample is used to select a greater number of those persons who are of special interest from an exposure standpoint (for example, long-distance commuters if a vehicular air pollutant is under investigation), and then sample weights are used in the subsequent data analysis to adjust for the over-sampling. From statistical analyses of the diaries (activities and locations visited), it often is possible to identify the likely sources, microenvironments, and human activities that contribute most to pollutant exposures, including both traditional and nontraditional sources. Many of these large-scale exposure field studies, such as the TEAM studies (Table 1.1), have been made possible because of new compact personal exposure monitors (PEMs) capable of measuring exposure to some air pollutants with high precision (see Chapters 5–8 and Chapter 15). An exposure field study of this kind typically samples 25 to 800 respondents and includes the following four basic elements: 1. Use of a representative probability sample of the population 2. Direct measurement of the pollutant concentrations reaching these people through all carrier media (air, food, water, and dermal contact) 3. Direct measurement of body burden to infer dosage 4. Direct recording of each person’s daily activities through diaries For volatile pollutants that are readily absorbed and given up by the blood, it is possible to determine with reasonable precision the concentration of that pollutant present in the blood by asking respondents to exhale their deep-lung breath into a sampling bag and then to analyze the contents of the bag. This is basically the same method that is used by police officers who stop drivers on the highway to measure the concentration of their blood alcohol using a breath analyzer test. Breath measurement works satisfactorily for a number of other pollutants of interest besides alcohol (ethanol) that are absorbed by the blood (for example, CO and benzene). The resulting © 2007 by Taylor & Francis Group, LLC Exposure Analysis: A Receptor-Oriented Science 9 concentrations of the pollutant in the breath can be used to assess the concentration of the pollutant in the blood and is a useful measure of body burden at that time. Measurements of body burden in some bodily fluids, such as breath or urine, have the advantage that they provide a useful indicator of previous exposure and are noninvasive — they do not require a sample of blood or tissue from the person. In addition, pharmacokinetic models have been developed that express the mathematical relationship between prior exposure and predicted blood and breath concentrations. Although the final sample sizes for some of the TEAM studies in Table 1.1 were not extremely large, the representative probability designs of the larger studies enable the analyst to make inferences about the exposures of the much larger populations from which these samples were drawn, such as the population of an entire community. The TEAM studies were the first to show for large populations that indoor sources of toxic chemicals not only greatly outnumber outdoor TABLE 1.1 Locations of Total Exposure Assessment Methodology (TEAM) Studies City Pollutants Date No. of Households Chapel Hill, NC VOCs 1980 6 Beaumont, TX VOCs 1980 11 Elizabeth–Bayonne, NJ (3 seasons) VOCs 1980 9 Research Triangle Park, NC (3 seasons) VOCs 1980 3 Los Angeles, CA CO 1981 9 Elizabeth–Bayonne, NJ (3 seasons) VOCs 1981–83 355 Greensboro, NC VOCs 1982 25 Devils Lake, ND VOCs 1982 25 Denver, CO CO 1982-83 450 Washington, DC CO 1982-83 712 Los Angeles, CA (3 seasons) VOCs 1984 120 Antioch–Pittsburg, CA (3 seasons) VOCs 1984 75 Jacksonville, FL Pesticides 1985 9 Jacksonville, FL (3 seasons) Pesticides, House dust 1986–87 200 Springfield, MA (3 seasons) Pesticides 1987 100 Baltimore, MD VOCs 1987 150 Los Angeles, CA VOCs 1987 50 Bayonne–Elizabeth, NJ VOCs 1987 11 Azusa, CA Particles, metals 1989 9 Riverside, CA Particles, metals 1991 178 Valdez, AK 1 VOCs, benzene 1990–91 58 Toronto, Ontario 2 Particles, metals 1995–96 750 Indianapolis, IN 2 Particles, metals 1996 240 1 Study with personal monitors by Alyeska Pipeline Service Co. through research contractors. 2 Approach similar to TEAM by Ethyl Corp. under a contract with Research Triangle Institute, NC. © 2007 by Taylor & Francis Group, LLC 10 Exposure Analysis sources but also cause the bulk of human exposures, often two to five times the amount caused by outdoor sources (Figure 1.4). For example, tetrachloroethylene (sometimes called perchloroethyl- ene, or PERC) comes from clothes recently brought home from the dry cleaners; chloroform is emitted by water boiled during cooking and released when showering; bathroom and kitchen deodorizers and mothballs are sources of para-dichlorobenzene (p-DCB); solvents stored in the home and cleaning fluids are sources of 1,1,1-trichloroethane and tetrachloroethylene; automobiles and gasoline stored in attached garages emit benzene; aerosol sprays release a variety of organic compounds, including p-DCB; other organic pollutants arise from paints, glues, varnishes, turpen- tine, and adhesives, as well as furniture polish, carpets, and building materials. Finally, pesticides and herbicides stored in homes or applied indoors can be important sources of personal exposure, in addition to house dust tracked in from outdoors. There is a greater likelihood of receiving a high exposure from sources that are nearby (usually indoors), while the lower probability of receiving an elevated exposure from a traditional source suggests that the outdoor sources depicted in Figure 1.4 should be shown in the far distance and should be smaller than they are now depicted. Indoor exposures are significant for a number of reasons. A great variety and number of chemicals are present indoors close to people, and the small physical scale (under 30 m) limits dilution, causing relatively high concentrations. Also, the infiltration of outdoor air into indoor settings is relatively slow, causing a low air change rate and a long residence time — the time required for the volume of air equal to the volume of the indoor setting to be fully replaced. Air change rates in homes typically range from 0.2 to 1 air change per hour, giving residence times (the reciprocal of the air change rate) of 1–5 hours. These factors — intensity and variety of sources combined with low dilution and low air change rate — make indoor air pollutants especially important contributors to the total exposure of occupants. Finally, activity pattern, or time budget, studies based on large representative probability samples in which participants completed 24-hour diaries show that people spend most of their time indoors (Klepeis et al. 2001), as discussed briefly in the following sections. All these factors combine to make indoor air pollution an important contributor to total exposure and to total risk. 1.4.1 I NDIRECT A PPROACH The direct approach described above is valuable for measuring directly the distribution of exposures across a population by using personal exposure monitors to measure air exposure and other methods to measure dermal, food, and drinking water exposure, making it possible to draw inferences from a representative sample to a much larger population. By contrast, the indirect approach seeks to measure and understand the basic relationships between causative factors and the resulting expo- sures in the small settings called microenvironments, such as homes or motor vehicles. By combining microenvironmental air pollutant concentrations with diary-based activity patterns in an exposure model, it is possible to predict population exposure distributions. Similar approaches are applicable to dermal exposure. Thus, the indirect approach is basically a modeling approach combining measurements from small-scale microenvironmental experiments with large-scale activity pattern data in order to predict population exposure distributions. The resulting exposure model is intended to complement the direct approach field studies by helping to translate their findings to other locales and to other situations. These models also are designed to allow the analyst to consider “what if” questions and to predict how exposures might change in response to different policies and regulatory (and nonregulatory) actions. Exposure models are not the same as the traditional outdoor pollutant transport models for predicting outdoor concentrations in ambient air, surface water, or groundwater. Rather, they are designed to predict human exposure of a rather mobile human being (see Chapter 19 and Chapter 20). Thus, they require information on typical personal activities, locations visited during the day, and time budgets of people, as well as information on the likely concentration © 2007 by Taylor & Francis Group, LLC Exposure Analysis: A Receptor-Oriented Science 11 FIGURE 1.4 Examples of traditional (outdoor) and nontraditional (indoor) sources of exposure, based on findings from the total exposure measurement studies. (From Ott 1990. With permission.) Pesticide Application Industry Refineries Automobile Exhaust Industry Discharges Toxic Wastes, Chemicals Fresh Dry Cleaning Bathroom Cleaners, Room Deodorizers, Hair Products Outdoor Indoor Lighter Fluid, Solvents, Cleaning Fluids Automobile Exhaust, Oil, Gasoline, Antifreeze Insecticides, Herbicides, Pool Chemicals Furniture Polish, Furniture Stuffing, Paneling Cigarette Smoke Paint, Glue, Varnish, Tu rpentine Gas Stove Aerosol Sprays Kitchen Cleaners Hot Showers © 2007 by Taylor & Francis Group, LLC [...]... ND 12 6 24 ND 1 2 14 220 52 QL 220 52 11 11 ND 5.8 1 1 13 26 12 ND 26 12 QL 11 ND 6.3 18 25 1 14 12 7.9 32 QL 23 23 32 11 9 11 5.6 QL 12 9.9 1 14 26 ND 26 QL -11 -ND -13 1 6 410 16 410 420 -6 -10 -13 0 Exposure Analysis: A Receptor-Oriented Science 19 TABLE 1. 4 (CONTINUED) Activities Associated with Increased Personal Exposures or Indoor Air µ Concentrations (µg/m3) Personal Exposure Chemical/Activity... Driving No activities 1 23 14 Median Indoor Air Concentration Median Maximum Maximum N 54 6.6 QL 54 24 12 11 QL 1 6 1 23 14 800 18 50 4.5 QL 800 470 50 17 10 -6 11 -8.6 QL 1 6 1 23 10 970 44 15 0 15 10 970 12 00 15 0 75 26 -6 8 -29 11 -300 22 15 0 350 53 7.4 9 2 -8 44 10 2 -5.7 16 0 200 -16 280 280 43 12 2 9 -8 32 70 -3.6 60 290 -16 17 6 18 10 25 48 10 3.3 6 17 18 10 30 34 7.8 QL 11 -12 0 6.9 N = Number... Median 12 16 5 10 330 33 12 2.4 5 4 13 10 36 ND 2 2 3 1 3 6 8 675 86 24 260 64 44 QL 4 14 3 2 3 17 17 93 60 5.5 Maximum Indoor Air Concentration N Median Maximum 500 84 28 6.6 6 9 3 6 340 37 25 2.6 630 59 30 5.2 23 57 2.4 3 2 10 23 48 ND 25 59 QL 10 00 10 0 63 260 11 0 11 0 16 -1 3 6 6 -380 82 40 4.8 -380 94 380 14 24 36 95 11 0 12 4 14 3 20 24 QL 44 44 5 43 ND 15 2 1 8 20 75 220 ND 69 11 0 220 ND 12 ... et al 20 01 With permission.) 19 87; Wallace 19 86, 19 91a,b, 19 93a,b,c, 19 97, 20 01; Wallace et al 19 82, 19 84, 19 85, 19 86, 19 87a,b,c, 19 88a, 19 89; Zweidinger et al 19 82; see Chapter 7), particles (Clayton et al 19 93; Özkaynak et al 19 96; Pellizzari et al 19 93a,b; Thomas et al 19 93b; Wallace 19 96; Yakovleva, Hopke, and Wallace 19 99; see Chapter 8), and pesticides (Whitmore et al 19 94; see Chapter 15 ), as... 4 Person 3 Person 4 1 2 3a 4 5 6 7 8 9 3.7 8.2 11 .6 4.0 12 .0 8.6 3.5 11 .5 8.5 1 2 65 250 12 0 19 0 430 450 630 1 2 8 240 300 220 425 470 450 1 3 43 250 330 -b 340 410 500 1 2 4 8 (7) 17 (17 ) 20 (19 ) 28 (23) 34 (34) 39 (39) 1 2 7 27 (10 ) 15 (25) 28 (26) 44 (30) 44 (45) 54 (55) Note: ( ) Predicted value using the model described in Wallace et al (19 86), CALV = CALV (0) e-t/τ + fA (1 – e-t/τ), where CALV... (Behar et al 19 79; Lioy 19 90; Ott 19 82, 19 85, 19 90, 19 95a; Ott et al 19 86; Ott and Roberts 19 98; Spengler and Sexton 19 83; Spengler and Soczek 19 84; Smith, 19 88a,b, 19 93; Wallace 19 93a, 19 95, 19 96, 2000; Wallace and Ott 19 82; Weselowski, 19 84) For an everyday example of an RSAE approach, consider benzene exposure to nonsmokers in a local community, the San Francisco Bay Area (Benzene exposure to smokers... Ott 19 95a With permission.) TABLE 1. 2 Time Budgets for Persons Aged 12 and Older Californiaa Location Indoors In-vehicle Outdoors Total a b c Minutes per Day Percent of Day Minutes per Day Percent of Day 12 56 98 86 14 40 87% 7% 6% 10 0% 12 52 79 10 9 14 40 87% 5.5% 7.6% 10 0%c Jenkins et al (19 92) Klepeis et al (20 01) Does not add to 10 0.0% due to rounding © 2007 by Taylor & Francis Group, LLC U.S.b 16 Exposure. .. for Assessing Exposure to Environmental Pollutants, Journal of Exposure Analysis and Environmental Epidemiology, 11 : 2 31 252 Levy, D (19 91) New Rules Target Toxics in the Air: 50% Cut in Emissions by Businesses, San Francisco Chronicle, 8 August 19 91 Lioy, P.G (19 90) Assessing Total Human Exposure to Contaminants, Environmental Science & Technology, 24: 938–945 Lioy, P.G (19 91) Human Exposure Assessment:... al 19 85; Hartwell et al 19 84; Johnson 19 83; Ott et al 19 88; Ott, Mage, and Thomas 19 92; Wallace et al 19 88b; Wallace and Ott 19 82; see Chapter 6), volatile organic compounds (VOCs) (Pellizzari et al 19 87a,b; Wallace and O’Neill © 2007 by Taylor & Francis Group, LLC Exposure Analysis: A Receptor-Oriented Science 15 midnight 12 :00 3:00 TIME OF DAY 6:00 9:00 Noon 3:00 6:00 ▼ 9:00 12 :00 midnight 0 10 20... L.A (19 87) The TEAM Study: Summary and Analysis: Volume I, Report No EPA 600/6-87/002a, NTIS PB 88 -10 0060, U.S Environmental Protection Agency, Washington, DC Wallace, L.A (19 89) Major Sources of Benzene Exposure, Environmental Health Perspectives, 82: 16 5 16 9 Wallace, L.A (19 90) Major Sources of Exposure to Benzene and Other Volatile Organic Compounds, Risk Analysis, 10 (1) : 59–64 Wallace, L.A (19 91a) . source 1 150 15 0 Driving 23 15 75 No activities 10 10 26 8 11 22 Decane Unknown indoor source 17 25 15 0 9 44 16 0 Painting 6 48 350 2 10 2 200 Driving 18 10 53 No activities 10 3.3 7.4 8 5.7 16 Undecane Painting. Microenvironments 19 1. 8 Source Apportionment of Exposure 21 1.9 Public Education 24 1. 10 Exposurist as a Profession 26 1. 11 Conclusions 27 1. 12 Questions for Review 28 References 28 1. 1 SYNOPSIS Exposure. 6.3 Benzene Smoking cigarettes 18 12 23 9 5.6 12 Driving 25 7.9 23 Lawn mower exhaust 1 32 32 No activities 14 QL 11 11 QL 9.9 Styrene Cleaning carburetor 1 26 26 No activities 14 ND QL 11 ND 13 o-Xylene Cleaning