© 1997 by CRC Press, Inc. Section II Applications of Risk Analysis L1130chII.1.fm Page 123 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. CHAPTER II.1 Assessment of Residential Exposures to Chemicals Gary K. Whitmyre, Jeffrey H. Driver, and P. J. (Bert) Hakkinen SUMMARY Individuals in and around residences come in contact with a variety of chemicals from various potential sources, including outdoor sources that enter the residence, and from combustion sources and consumer products. Among the factors that deter - mine the extent of exposure to a chemical are human exposure factors (e.g., body weight, types, frequencies and durations of various daily activities) and residential exposure factors (e.g., design and properties of a residence, including air exchanges per hour for the residence or the area of interest within the residence). The goal of this chapter is to provide readers with an overview of the assessment of residential exposures to chemicals. The chapter is organized as follows: Key Words, Introduc - tion, Overview of General Issues, Lessons from the TEAM Studies, Assessment of Inhalation Exposures in the Residence, Assessment of Dermal Exposures in the Residence, Assessment of Ingestion Exposures in the Residence, Assessment of Exposures to Chemicals in Indoor Sources: Principles and Case Studies, Assessment of Exposures to Chemicals in Outdoor-Use Products: Principles and Case Studies, Data Sources for Residential Exposure Assessment, Discussion and Conclusions, References, Questions for Students to Answer. Key Words: combustion appliances, consumer products, heating, ventilation, and air conditioning system (HVAC), human exposure factors, microenvironment, residential building factors, source characteristics, total exposure assessment methodology (TEAM), volatile organic compounds (VOCS) L1130chII.1.fm Page 125 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. 1. INTRODUCTION The general public is repeatedly in contact with time-varying amounts of envi- ronmental chemicals in air, water, food, and soil. On a daily basis, individuals are exposed in a variety of microenvironments that correspond to the daily activities that place persons in contact with environmental chemicals (e.g., soil contaminants during gardening, lawn chemicals during and following application, in-transit expo - sures to benzene from gasoline, environmental tobacco smoke [ETS] in residences and office buildings, volatile organic compounds [VOCs] from consumer products used in the residence). In response to the need to characterize multiple chemical exposures from multiple environmental media (e.g., soil, air, food, water), a number of ongoing efforts have been undertaken to develop methodologies to aid in quan - tifying these exposures (McKone 1991, Cal-EPA 1994). In recent assessments of the human health impact of airborne pollutants, there has been increasing focus on the contribution of various microenvironments (e.g., indoors, outdoors, in transit) and sources (e.g., consumer products, combustion appliances, outdoor sources) to total human exposure to a given chemical. During the past 15 years, a number of studies, most notably the total exposure assessment methodology (TEAM) studies sponsored by the U.S. Environmental Protection Agency (EPA), have demonstrated that for a variety of contaminants, residential indoor air is often a more significant source of exposure than outdoor air (Thomas et al. 1993, Wallace 1993, Pellizzari et al. 1987). Some of the studies conducted in the past have found elevated indoor concentrations of certain pollutants, which raised questions concerning the types, sources, levels, and human health implications of indoor exposures (Spengler et al. 1983, Melia et al. 1978, Dockery and Spengler 1981). Assessment of potential consumer exposures has also been recognized by industry as a key part of the overall risk evaluation process for consumer products (Hakkinen et al. 1991). For example, several studies of potential indoor air exposures from use of consumer products have been conducted and published by industry and trade associations to support and confirm the safety of these particular products (Hendricks 1970, Wooley et al. 1990, Gibson et al. 1991). 2. OVERVIEW OF GENERAL ISSUES Exposures to chemicals, in general, occur principally because humans engage in normal activities in various microenvironments that bring them into relatively close proximity with a number of chemical substances every day. These activities and concurrent sources of chemicals occur in outdoor air (i.e., via ambient levels of air pollutants such as nitrogen oxides, carbon monoxide, and particulates), in the work setting (e.g., exposure to industrial chemicals in factory jobs and exposure to carpet adhesive VOCs in office buildings), from pollutant exposures in vehicles while in transit or refueling (e.g., passenger-compartment benzene levels), and from chemical exposures in the residence. For the purpose of this chapter, the residential microenvironment is defined as indoor (i.e., inside the residence) as well as outdoor backyard areas. L1130chII.1.fm Page 126 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. There are a number of sources of residential exposures, including (1) consumer products such as cleaners, waxes, paints, pesticides, adhesives, paper products/print - ing ink, clothing/furnishings (e.g., which can off-gas VOCs); (2) building sources, which include combustive products from appliances and attached garages, building materials (e.g., which can release formaldehyde), and HVAC systems; (3) personal sources such as tobacco smoke and biological contaminants (e.g., allergens) of human, animal, and plant origin; and (4) outdoor sources of chemicals leading to infiltration of the residential environment. The latter include ambient combustive pollutants, contaminated soil particles that can infiltrate or be tracked into the home, drinking water (which can release volatile organics during showering or other use in the home), and contaminated subsurface water (e.g., infiltration of VOCs into basement areas). The residential environment should be thought of in very dynamic terms. VOCs that enter the residential environment can be absorbed to surfaces, or “sinks,” and then later be released as airborne levels that are depleted by various mechanisms, including air exchange with other rooms of the house and with outdoor air and with chemical/physical transformations in residential air. There is evidence that particu - late contaminants, whether generated inside the residence or tracked in/infiltrated from the outdoor environment, are resuspended and recycled within the house by walking on floors and rugs, sweeping and dusting, and vacuuming (see Figure 1). Thus, the residence is the exposure unit. There are a number of noninhalation exposure pathways that need to be addressed in characterizing and quantifying human residential exposures to chemicals. These include dermal exposure to dislodgeable residues on surfaces (such as pesticides on floors and carpeting and chemicals resulting from use of hard surface cleaners) and ingestion exposure to surface contaminants (such as that due to hand-to-mouth activity, particularly in infants and toddlers). There are several examples of studies and reviews that have addressed and provided examples of noninhalation residential exposures (Calvin 1992, CTFA 1983, ECETOC 1994, Turnbull and Rodricks 1989, Vermeire et al. 1993). 3. LESSONS FROM THE TEAM STUDIES Since 1980, the U.S. EPA’s Office of Research and Development has conducted a series of studies on human exposure to different classes of pollutants. These are commonly referred to as the total exposure assessment methodology (TEAM) stud - ies. These studies have dealt with VOCs, carbon monoxide, pesticides, and partic- ulates, often comparing indoor and outdoor exposures to these contaminants. When total personal exposures to VOCs (i.e., concentrations in the breathing zone) were measured via the presence of chemicals in exhaled breath, personal exposures most often exceeded outdoor air exposures. Median personal concentrations of VOCs were on the order of 2 to 5 times outdoor levels; maximum personal concentrations were roughly 5 to 70 times the highest outdoor levels (Wallace 1993). This observed variability in exposures indicates (1) the role of various human activities in bringing individuals into contact with chemicals indoors and (2) the importance of specific L1130chII.1.fm Page 127 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. sources of exposures that may not be present in residential settings for all individuals. For example, (1) smokers had 6 to 10 times the personal benzene exposures of nonsmokers; (2) persons regularly wearing or storing freshly dry-cleaned clothes in the residence had significantly higher personal exposures to tetrachloroethylene; and (3) persons using mothballs and solid deodorizers in the residence were observed to have greatly elevated exposures to p-dichlorobenzene than nonusers (Wallace 1993). The most recent study, known as PTEAM, focused on measuring personal exposures to inhalable particles (PM 10 ) of approximately 200 residents from River- side, California, using specially designed indoor sampling devices. A major finding from this work is that personal exposures to particles in the daytime are 50% greater than either general indoor or outdoor concentrations. It has been hypothesized that these data suggest that individuals are exposed to a “personal cloud” of particles as they go about their daily activities, (Wallace 1993). Resuspension of household dust via walking in the residence, such as contaminated soil particles tracked into the home, and certain household activities such as vacuuming and cooking or sharing a home with a smoker, lead to significant particle exposures. The recent Valdez Air Health Study in Valdez, Alaska (Goldstein et al. 1993) generally supports the findings of the TEAM studies in terms of the importance of personal sources of exposure Figure 1 Potential pathways of human contact with contaminated soils. (Adapted from Mc- Kone, T.E. 1993. Understanding and Modeling Multipathway Exposures in the Home. Reference House Workshop II: Residential Exposure Assessment for the ‘90s. Society for Risk Analysis, 1993 Annual Conference, Savannah, Georgia.) L1130chII.1.fm Page 128 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. relative to outdoor sources. In the Valdez study, mean personal concentrations of benzene were roughly three to four times higher than outdoor levels, despite the presence of a significant outdoor source of benzene in the community (i.e., a petro - leum storage and loading terminal). 4. ASSESSMENT OF INHALATION EXPOSURES IN THE RESIDENCE An overview of factors that are commonly considered in assessing inhalation exposures to chemicals in the residence is provided in Figure 2. These factors include • Source characteristics — Perhaps the most important factors determining the impact of chemical sources in the residence on inhalation exposures are the nature of the source (e.g., consumer product or residential construction material such as floor or wall surface), how it is released (fine respirable aerosols, nonrespirable coarse aerosols, vapor release [e.g., solid air freshener]), and the source strength (roughly proportional to the concentration of the chemical in the source or product). • Human exposure factors — These include body weight, which varies between and within age and gender categories, and inhalation rates, which vary primarily by age, gender, and activity level. • Physical-chemical properties — These include factors such as molecular weight and vapor pressure that determine the rate of evaporation into air of a chemical in an applied material (e.g., paint), or the release from aqueous solution (e.g., the role of the Henry’s law constant in determining the release of volatile organics from tap water used in the home). • Residential building factors — The basic characteristics of the room(s) and building in which residential exposures occur, as well as the ventilation configuration (i.e., number of windows and doors open, the rate of mechanical ventilation and air mixing, rate of infiltration of outside air), will determine the extent and rate of dilution of the chemical of interest in a specific indoor air setting. • Exposure frequency and duration — The exposure frequency (i.e., the number of days per year, years per lifetime) and duration of exposure (i.e., minutes or hours of exposure to a chemical for a given day on which exposure occurs) are critical variables for estimating residential exposures to chemicals. These are a function of product-use patterns, human activities that bring individuals in contact with areas that may contain a chemical, and the nature of the population’s mobility which limit the total number of years an individual may be exposed to a site- specific contaminated residence (e.g., radon). As discussed in Whitmyre et al. (1992a,b), a number of these factors are asso- ciated with a wide range of variability across an affected population, resulting in a wide band of uncertainties; thus, the true distribution of exposures across the pop - ulation would likely span several orders of magnitude. A number of indoor air modeling tools are available for use in assessing inha- lation exposures to a variety of contaminants from a variety of sources. Some are more oriented toward assessment of exposures to chemicals from consumer products when the specific emission term is not known, such as with the Screening-Level Consumer Inhalation Exposure Software (SCIES) developed by the Exposure L1130chII.1.fm Page 129 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. Assessment Branch of the U.S. EPA’s Office of Pollution Prevention and Toxics (U.S. EPA 1994). Another exemplary model is MAVRIQ, which can be used to estimate indoor inhalation exposures to organic chemicals due to volatilization from indoor uses of water (Wilkes and Small 1992). A number of validated U.S. EPA modeling tools exist to address indoor airborne levels of chemicals from many types of emission sources. An example of an indoor air model that can be used when the emission term is known (e.g., aerosol product released at a rate of 1.5 g/sec for 3 min) is the Multi-Chamber Concentration and Exposure Model (MCCEM) developed for the Environmental Monitoring Systems Laboratory, U.S. EPA, Las Vegas (U.S. EPA 1991a). MCCEM is a user-friendly computer program that estimates indoor concentrations for, and inhalation exposures to, chemicals released from products or materials used indoors. Concentrations can be modeled in as many as four zones (e.g., rooms) in a building. The user provides values for emission rates, the zone where the source is located, the zone where exposure occurs, duration of exposure, air exchange rates, the nature of the building, and whether a short-term model (including average and maximum peak values) or long-term model is desired. The model contains room volume data and measured air flow rate data between different rooms for different building configurations and different geographic locations, or the user may build a hypothetical house or building, assigning the desired room (zone) volume and air exchange rates. Other examples of similar modeling tools include several U.S. EPA models, as well as the CONTAM model developed and updated regularly by the National Institute of Standards and Technology (NIST 1994). A new database/model management tool developed by the University of Nevada at Las Vegas for the Environmental Monitoring Systems Laboratory, U.S. EPA, Las Vegas, is anticipated to revolutionize the modeling of indoor air exposures. This software tool is called the Total Human Exposure Risk Database and Advanced Simulation Environment (THERdbASE). This software integrates a number of indoor air models with distributional data on variables such as demographics, time activity, food consumption, and physiological parameter data that can be subset according to the needs of the assessment (Pandian et al. 1995). THERdbASE can Figure 2 Components of indoor air residential exposure assessment. L1130chII.1.fm Page 130 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. also be used for estimating dermal and ingestion exposures and total human exposure via multiple agents and pathways, i.e., multiple agents present in more than one media and coming into contact with humans via multiple exposure pathways and routes. This software is now available for downloading via the Internet’s World Wide Web at http://eeyore.lv-hrc.nevada.edu (ISEA 1995). 5. ASSESSMENT OF DERMAL EXPOSURES IN THE RESIDENCE There are numerous opportunities for dermal exposure to chemicals in the res- idential environment. These include, but are not limited to, direct contact with cleaning/laundry products (e.g., cleanser, laundry detergent) during use, indirect contact with cleaning product residues (e.g., laundry detergent residues in washed clothing), contact with dislodgeable residues of a chemical after use (e.g., crawling infant contact with pesticide residues on rug); and direct contact with materials that are intentionally applied to the skin (e.g., soap, cosmetics). There are basically two types of approaches to assessing dermal exposures: (1) the film-thickness approach and (2) dermal permeability-based approaches (U.S. EPA 1992). The film-thickness approach assumes that a uniform layer of a material (e.g., liquid consumer product) is present on a certain area of the skin and that all of the material in that layer is available for absorption. Default film-thickness data, in the absence of data on the actual product of interest, are available from the U.S. EPA (1987). Other variables that are unique to the film-thickness approach are the density of the product (grams per cubic centimeter, g/cm 3 ) and the percent dermal absorption anticipated during each event exposure period. Absorption can be assumed to be 100% for screening-level assessments, but severe overestimation of dermal exposure is likely to occur. In contrast, dermal permeability-based methods recognize the fact that dermal absorption is a time-dependent process, and under controlled conditions, the dermal penetration can be expressed as a time-dependent parameter known as the dermal permeability coefficient (K p ). Measured and estimated dermal flux (micrograms per cubic centimeter per hour, µg/cm 2 /h) and/or permeability coefficients (centimeters per hour, cm/h) have been published for various substances (U.S. EPA 1992, Driver et al. 1993). Additional discussion/information regarding dermal exposure assess - ment and percutaneous absorption kinetics can be found in U.S. EPA 1992, Kasting and Robinson 1993, and Wilschut et al. 1995. Regardless of which general approach is taken, various additional factors must be taken into account to determine exposures. • Human exposure factors — Besides body weight, which varies between and within age and gender categories, it is necessary to build an exposure scenario that specifies the amount of skin surface area exposed. One can use total surface area statistics and take a fraction representing the exposed area, or one can specify body parts that are exposed (e.g., both hands) and use body part surface area data (U.S. EPA 1989, AIHC 1995). Because skin surface area is closely correlated with body L1130chII.1.fm Page 131 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. weight, data on the ratio of surface area to body weight should ideally be used in calculating the dermal exposure (Phillips et al. 1993). • Frequency and duration of exposure — The duration of exposure should represent the anticipated contact time with the skin prior to washing or removal. • Concentration of the chemical on the skin — It is the estimation or measurement of vapor-phase or aqueous-phase concentration of a given agent in contact with the skin. For example, aqueous-phase exposures are usually expressed as micro - grams (µg) of agent per cubic centimeter (cm 3 ) of aqueous solution. • Surface area of skin exposed — The amount of surface area exposed is proportional to the amount of a given substance that may be percutaneously absorbed. 6. ASSESSMENT OF INCIDENTAL INGESTION EXPOSURES IN THE RESIDENCE Ingestion of chemical residues can occur in the home beyond chemical residues (e.g., pesticides) consumed in food derived from nominally contaminated raw agri - cultural commodities (RACs) from spraying in the field. Primary examples of inci- dental residues include ingestion of cleaning agent and pesticide residues on plates and silverware following product use and ingestion of trace levels of organics (e.g., haloforms) in drinking water entering the home. Another important pathway for incidental ingestion exposure is hand-to-mouth behavior in infants and toddlers in particular; Vacarro (1992) has shown this to be actually the predominant exposure pathway (for this age group) for exposure to pesticide residues applied to carpets either directly or incidentally (e.g., through insecticide fogger use, such as a flea bomb), more so than inhalation or dermal contact through crawling on/touching contaminated surfaces. For food-related incidental contact, it will be necessary to consider the nature of the toxicological end point (e.g., short-term vs. long-term health effects) to determine which type of dietary consumption data is most appro - priate (e.g., an upper bound on the amount eaten on 1 day in which the commodity is consumed or long-term averages which would include days on which the com - modity is not consumed). 7. ASSESSMENT OF EXPOSURES TO CHEMICALS IN INDOOR SOURCES: PRINCIPLES AND CASE STUDIES During the past 15 years, a number of studies, most notably the TEAM studies sponsored by the U.S. EPA, have demonstrated that residential air is often a more significant source of exposure to various chemicals (e.g., VOCs) than outdoor air. Many of the compounds of interest in residential air are present in consumer products that are used in and around the residence. Recent studies have investigated the relationship between use period/postuse period activities and exposures to a variety of chemicals in consumer products. While the resulting residential exposures are likely to be low in most cases, nonetheless, there is a need to characterize these exposures. For certain chemicals such as pesticides, postapplication exposures in particular may require characterization of various exposure pathways/routes and L1130chII.1.fm Page 132 Friday, September 3, 2004 4:18 PM © 1997 by CRC Press, Inc. subpopulations to fully understand the magnitude of exposure associated with con- sumer uses of these chemicals. In performing such assessments, it is necessary to consider the range of approaches that can be taken, including use of body-burden modeling for intermittent exposures, use of indoor air modeling tools, incorporation of time-activity data, consideration of the form of the airborne concentration dissi - pation curve in determining postapplication exposures, and use and adjustment of emissions/concentration data for surrogate compounds to obtain an emission rate/air - borne level for the compound of interest. The following case studies are provided to suggest the variety of possible exposure scenarios, sources of exposure, and chemical contaminants to which many individuals are exposed in the residence. Case Study 1: Residential Exposure to Toluene During Use of Nail Polish. In one case study reported by Curry et al. (1994), inhalation exposures occurring during normal in-home use of nail lacquers were characterized. The study involved moni - toring of personal, area, and background levels of toluene before, during, and after application of nail lacquer products. Based on the monitoring data, total personal exposures (during application plus postapplication) ranged from 1030 to 2820 µg per person per day. The dissipation kinetics for airborne toluene associated with this activity are shown in Figure 3 for a subject in a residence with poor ventilation (all outside doors and windows closed). Based on the log-linear regression curve, the estimated half-lives for toluene in the breathing zone of this subject and in the general area of the room of nail polish use (i.e., living room) were 67 and 89 min, respec - tively. Figure 3 Log plot of area and breathing zone toluene concentrations (mg/m 3 ) as a function of time during and following nail laquer application. (From Curry, K.K., et al. 1994. Journal of Exposure Analysis and Environmental Epidemiology 4 (4): 443–456. With permission of Princeton Scientific Publishing, NJ.) L1130chII.1.fm Page 133 Friday, September 3, 2004 4:18 PM [...]... Feet Hands Other Lognormal Lognormal Other Other Other Other Lognormal Other Lognormal Lognormal 2. 99 1.695 0.341 0.5 82 3.905 0.8875 0.6655 3. 82 0.9 52 5.371 3.5883 128 .9568 23 .23 18 15.7106 157.6735 19 .22 19 11.009 4. 426 6 16.8134 38 .27 1 346.998 34.7596 493.8357 360.9199 381.706 903 .20 36 26 2.7404 22 1.7177 21 1.9 821 196.8466 819. 520 3 180.1404 316. 322 7 4.09 92 1.74 0.5 427 1.4 925 3.4337 1.8891 0.8 927 4. 023 7... recently-sprayed turf Journal of Environmental Science and Health B27 (1): 9 22 Harris, S.A., K.R Solomon, and G.R Stephenson 19 92 Exposure of homeowners and bystanders to 2, 4-dichlorophenoxyacetic acid (2, 4-D) Journal of Environmental Science and Health B27 (1): 23 –38 Hendricks, M.G 1970 Measurement of enzyme laundry product dust levels and characteristics in consumer use Journal of the American Oilers and. .. York: ACSH Agriculture Canada 19 92 Pesticide Information Backgrounder B 92 01 Pesticides Directorate Ames, B N 1983 Dietary carcinogens and anticarcinogens Science 22 1: 125 6– 126 3 Ames, B N., R Magaw and L S Gold 1987 Ranking possible carcinogenic hazards Science 23 6 :27 1 28 0 Ames, B N and L S Gold 1989 Pesticides, risk and applesauce Science 24 4: 755–757 Ames, B.N., M Profet and L.S Gold 1990 Dietary pesticides... regulation, and public perception, In: Risk Assessment and Management Handbook for Environmental, Health & Safety Professionals Eds Kolluru, R., S Bartell, R Pitblado, and S Stricoff New York: McGraw-Hill © 1997 by CRC Press, Inc L1130chII .2. fm Page 144 Friday, September 3, 20 04 4 :22 PM uses of pesticides The chapter is organized as follows: Introduction, Balancing Benefits Against Risks, Pesticides and Food... Residential exposures to 2, 4-D via use of herbicide formulations on lawns during application (N = 22 ) have been addressed by Harris et al (19 92) Normalized absorbed doses of 2, 4-D (i.e., milligrams of exposure per pound of active ingredient handled) were estimated in the Harris et al (19 92) study based on postapplication urinary levels of 2, 4-D Under typical-use conditions, use of the granular formulation resulted... 0.8 927 4. 023 7 1.11 62 19. 529 6 3.57 82 39.39 62 24.7973 797.0 722 42. 3376 Total derm: Obs 121 103 109 90 89 88 84 71 81 25 80 Note: 95% C.I on Mean: Dermal: [– 120 60.59 32, 13654.7376]; Number of Records: 137; Data File: MIXER/LOADER; Subset Name: OPENMIX.LIQ.DERM.MLOD As part of an ongoing effort to improve and harmonize existing guidelines, the U.S EPA is also currently revising Subdivision K of the Pesticide... S.R Baker 1992b Human exposure assessment II: quantifying and reducing the uncertainties Toxicology and Industrial Health 8 (5): 321 –3 42 Wilkes, C.R and M.J Small 19 92 Inhalation exposure model for volatile chemicals from indoor uses of water Atmospheric Environment 26 A: 22 27 22 36 Wilschut, A., W.F ten Barge, P.J Robinson, and T.E McKone 1995 Estimating skin permeation: the validation of five mathematical... Branch, Office of Pollution Prevention and Toxics U.S EPA Publication No 560/ 5-8 5-0 07 U.S EPA (U.S Environmental Protection Agency) 1989 Exposure factors handbook Washington, DC: Exposure Assessment Group, Office of Health and Environmental Assessment, Office of Research and Development U.S EPA Publication No 600/ 8-8 9-0 43 © 1997 by CRC Press, Inc L1130chII.1.fm Page 140 Friday, September 3, 20 04 4:18... during use of nail lacquers in residences: description of the results of a preliminary study Journal of Exposure Analysis and Environmental Epidemiology 4 (4): 443–456 Dockery, D.W and J.D Spengler 1981 Indoor-outdoor relationships of respirable sulfates and particles Atmospheric Environment 15: 335–343 Driver, J.H and L Milask 1995 User’s guide DietRisk — chronic dietary exposure and risk analysis Technology... Rejection Rate Analysis: Occupational and Residential Exposure EPA/738-R-9 3-0 08 Washington, D.C.: U.S EPA U.S EPA (Environmental Protection Agency) 1994a Pesticides Industry Sales and Usage: 19 92 and 1993 Market Estimates 733-K-9 4-0 01 Washington, D.C.: U.S EPA, Office of Prevention, Pesticides and Toxic Substances U.S EPA (Environmental Protection Agency) 1994b Series 875 — Occupational and Residential . absorb and retain residues). Example transfer coefficients from this study were approximately 21 ,20 0 cm 2 /h for adults, 12, 400 cm 2 /h for a 10-year-old child (extrapolated), and 920 0 cm 2 /h. California: Office of Scientific Affairs, Department of Toxic Substances Con- trol, Cal-EPA. NTIS Publication No. PB9 5-1 00467. Calvin, G. 19 92. Risk Management Case History — Detergents. In: Risk Management. Exposure of homeowners and bystanders to 2, 4-dichlorophenoxyacetic acid (2, 4-D). Journal of Environmental Science and Health B27 (1): 23 –38. Hendricks, M.G. 1970. Measurement of enzyme laundry product