Ultrafine, fine, and black carbon particle concentrations in California child-care facilities.

Although many U.S. children spend time in child care, little information exists on exposures to airborne particulate matter (PM) in this environment, even though PM may be associated with asthma and other respiratory illness, which is a key concern for young children. To address this data gap, we measured ultrafine particles (UFP), PM2.5 , PM10 , and black carbon in 40 California child-care facilities and examined associations with potential determinants. We also tested a low-cost optical particle measuring device (Dylos monitor). Median (interquartile range) concentrations for indoor UFP, gravimetric PM2.5 , real-time PM2.5 , gravimetric PM10 , and black carbon over the course of a child-care day were 14 000 (11 000-29 000) particles/cm3 , 15 (9.6-21) µg/m3 , 15 (11-23) µg/m3 , 48 (33-73) µg/m3 , and 0.43 (0.25-0.65) ng/m3 , respectively. Indoor black carbon concentrations were inversely associated with air exchange rate (Spearman's rho = -.36) and positively associated with the sum of all Gaussian-adjusted traffic volume within a one-kilometer radius (Spearman's rho = .45) (P-values <.05). Finally, the Dylos may be a valid low-cost alternative to monitor PM levels indoors in future studies. Overall, results indicate the need for additional studies examining particle levels, potential health risks, and mitigation strategies in child-care facilities.

Model framework for integrating multiple exposure pathways to chemicals in household cleaning products.

We present a screening-level exposure-assessment method which integrates exposure from all plausible exposure pathways as a result of indoor residential use of cleaning products. The exposure pathways we considered are (i) exposure to a user during product use via inhalation and dermal, (ii) exposure to chemical residues left on clothing, (iii) exposure to all occupants from the portion released indoors during use via inhalation and dermal, and (iv) exposure to the general population due to down-the-drain disposal via inhalation and ingestion. We use consumer product volatilization models to account for the chemical fractions volatilized to air (fvolatilized ) and disposed down the drain (fdown-the-drain ) during product use. For each exposure pathway, we use a fate and exposure model to estimate intake rates (iR) in mg/kg/d. Overall, the contribution of the four exposure pathways to the total exposure varies by the type of cleaning activities and with chemical properties. By providing a more comprehensive exposure model and by capturing additional exposures from often-overlooked exposure pathways, our method allows us to compare the relative contribution of various exposure routes and could improve high-throughput exposure assessment for chemicals in cleaning products.

Formaldehyde and acetaldehyde exposure and risk characterization in California early childhood education environments.

Little information is available about air quality in early childhood education (ECE) facilities. We collected single-day air samples in 2010-2011 from 40 ECE facilities serving children ≤6 years old in California and applied new methods to evaluate cancer risk in young children. Formaldehyde and acetaldehyde were detected in 100% of samples. The median (max) indoor formaldehyde and acetaldehyde levels (µg/m3 ) were 17.8 (48.8) and 7.5 (23.3), respectively, and were comparable to other California schools and homes. Formaldehyde and acetaldehyde concentrations were inversely associated with air exchange rates (Pearson r = -0.54 and -0.63, respectively; P < 0.001). The buildings and furnishings were generally >5 years old, suggesting other indoor sources. Formaldehyde levels exceeded California 8-h and chronic Reference Exposure Levels (both 9 µg/m3 ) for non-cancer effects in 87.5% of facilities. Acetaldehyde levels exceeded the U.S. EPA Reference Concentration in 30% of facilities. If reflective of long-term averages, estimated exposures would exceed age-adjusted 'safe harbor levels' based on California's Proposition 65 guidelines (10-5 lifetime cancer risk). Additional research is needed to identify sources of formaldehyde and acetaldehyde and strategies to reduce indoor air levels. The impact of recent California and proposed U.S. EPA regulations to reduce formaldehyde levels in future construction should be assessed.

VOC exposures in California early childhood education environments.

Little information exists about exposures to volatile organic compounds (VOCs) in early childhood education (ECE) environments. We measured 38 VOCs in single-day air samples collected in 2010-2011 from 34 ECE facilities serving California children and evaluated potential health risks. We also examined unknown peaks in the GC/MS chromatographs for indoor samples and identified 119 of these compounds using mass spectral libraries. VOCs found in cleaning and personal care products had the highest indoor concentrations (d-limonene and decamethylcyclopentasiloxane [D5] medians: 33.1 and 51.4 µg/m³, respectively). If reflective of long-term averages, child exposures to benzene, chloroform, ethylbenzene, and naphthalene exceeded age-adjusted "safe harbor levels" based on California's Proposition 65 guidelines (10-5 lifetime cancer risk) in 71%, 38%, 56%, and 97% of facilities, respectively. For VOCs without health benchmarks, we used information from toxicological databases and quantitative structure-activity relationship models to assess potential health concerns and identified 12 VOCs that warrant additional evaluation, including a number of terpenes and fragrance compounds. While VOC levels in ECE facilities resemble those in school and home environments, mitigation strategies are warranted to reduce exposures. More research is needed to identify sources and health risks of many VOCs and to support outreach to improve air quality in ECE facilities.

Estimated effect of ventilation and filtration on chronic health risks in U.S. offices, schools, and retail stores.

We assessed the chronic health risks from inhalation exposure to volatile organic compounds (VOCs) and particulate matter (PM2.5) in U.S. offices, schools, grocery, and other retail stores and evaluated how chronic health risks were affected by changes in ventilation rates and air filtration efficiency. Representative concentrations of VOCs and PM2.5 were obtained from available data. Using a mass balance model, changes in exposure to VOCs and PM2.5 were predicted if ventilation rate were to increase or decrease by a factor of two, and if higher efficiency air filters were used. Indoor concentrations were compared to health guidelines to estimate percentage exceedances. The estimated chronic health risks associated with VOC and PM2.5 exposures in these buildings were low relative to the risks from exposures in homes. Chronic health risks were driven primarily by exposures to PM2.5 that were evaluated using disease incidence of mortality, chronic bronchitis, and non-fatal stroke. The leading cancer risk factor was exposure to formaldehyde. Using disability-adjusted life years (DALYs) to account for both cancer and non-cancer effects, results suggest that increasing ventilation alone is ineffective at reducing chronic health burdens. Other strategies, such as pollutant source control and the use of particle filtration, should also be considered.

Indoor inhalation intake fractions of fine particulate matter: review of influencing factors.

Exposure to fine particulate matter (PM2.5 ) is a major contributor to the global human disease burden. The indoor environment is of particular importance when considering the health effects associated with PM2.5 exposures because people spend the majority of their time indoors and PM2.5 exposures per unit mass emitted indoors are two to three orders of magnitude larger than exposures to outdoor emissions. Variability in indoor PM2.5 intake fraction (iFin,total ), which is defined as the integrated cumulative intake of PM2.5 per unit of emission, is driven by a combination of building-specific, human-specific, and pollutant-specific factors. Due to a limited availability of data characterizing these factors, however, indoor emissions and intake of PM2.5 are not commonly considered when evaluating the environmental performance of product life cycles. With the aim of addressing this barrier, a literature review was conducted and data characterizing factors influencing iFin,total were compiled. In addition to providing data for the calculation of iFin,total in various indoor environments and for a range of geographic regions, this paper discusses remaining limitations to the incorporation of PM2.5 -derived health impacts into life cycle assessments and makes recommendations regarding future research.

Determining source strength of semivolatile organic compounds using measured concentrations in indoor dust.

UNLABELLED: Consumer products and building materials emit a number of semivolatile organic compounds (SVOCs) in the indoor environment. Because indoor SVOCs accumulate in dust, we explore the use of dust to determine source strength and report here on analysis of dust samples collected in 30 US homes for six phthalates, four personal care product ingredients, and five flame retardants. We then use a fugacity-based indoor mass balance model to estimate the whole-house emission rates of SVOCs that would account for the measured dust concentrations. Di-2-ethylhexyl phthalate (DEHP) and di-iso-nonyl phthalate (DiNP) were the most abundant compounds in these dust samples. On the other hand, the estimated emission rate of diethyl phthalate is the largest among phthalates, although its dust concentration is over two orders of magnitude smaller than DEHP and DiNP. The magnitude of the estimated emission rate that corresponds to the measured dust concentration is found to be inversely correlated with the vapor pressure of the compound, indicating that dust concentrations alone cannot be used to determine which compounds have the greatest emission rates. The combined dust-assay modeling approach shows promise for estimating indoor emission rates for SVOCs. PRACTICAL IMPLICATIONS: The combined dust-assay modeling approach in this study can be used to predict the source strength of indoor released compounds, integrating emissions from consumer products, building materials, and other home furnishings. Our findings show that estimated emission rates are closely related to not only the level of compounds on dust, but also the vapor pressure of the compound. Thus, a fugacity-based indoor mass balance model and measured dust concentrations can be used to estimate the whole-house emission rates from all sources in actual indoor settings, when individual sources of emissions are unknown.

Hazard assessment of chemical air contaminants measured in residences.

UNLABELLED: Identifying air pollutants that pose a potential hazard indoors can facilitate exposure mitigation. In this study, we compiled summary results from 77 published studies reporting measurements of chemical pollutants in residences in the United States and in countries with similar lifestyles. These data were used to calculate representative mid-range and upper-bound concentrations relevant to chronic exposures for 267 pollutants and representative peak concentrations relevant to acute exposures for five activity-associated pollutants. Representative concentrations are compared to available chronic and acute health standards for 97 pollutants. Fifteen pollutants appear to exceed chronic health standards in a large fraction of homes. Nine other pollutants are identified as potential chronic health hazards in a substantial minority of homes, and an additional nine are identified as potential hazards in a very small percentage of homes. Nine pollutants are identified as priority hazards based on the robustness of measured concentration data and the fraction of residences that appear to be impacted: acetaldehyde; acrolein; benzene; 1,3-butadiene; 1,4-dichlorobenzene; formaldehyde; naphthalene; nitrogen dioxide; and PM(2.5). Activity-based emissions are shown to pose potential acute health hazards for PM(2.5), formaldehyde, CO, chloroform, and NO(2). PRACTICAL IMPLICATIONS: This analysis identifies key chemical contaminants of concern in residential indoor air using a comprehensive and consistent hazard-evaluation protocol. The identification of a succinct group of chemical hazards in indoor air will allow for successful risk ranking and mitigation prioritization for the indoor residential environment. This work also indicates some common household activities that may lead to the acute levels of pollutant exposure and identifies hazardous chemicals for priority removal from consumer products and home furnishings.

Household exposure models.

Human exposure to volatile organic compounds (VOCs) in tap water is often assumed to be dominated by ingestion of drinking water. This paper addresses the relative importance of inhalation and dermal exposure in a typical household. A three-compartment model is used to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes as a result of tap water use. Mass transfers from water to air are derived from measured data for radon and used to estimate mass-transfer properties for VOCs. The model is used to calculate a range of concentrations and human exposures in U.S. dwellings. The estimated ratio of household-inhalation uptake to ingestion uptake is in the range of 1-6 for VOCs. A dermal absorption model is used to assess exposure across the skin boundary during baths and showers. The ratio of dermal exposure to ingestion exposure is in the range 0.6-1.

Linking a PBPK model for chloroform with measured breath concentrations in showers: implications for dermal exposure models.

Four issues are addressed in this paper. First, both dermal uptake models and a revised PBPK model are developed and combined into a form appropriate for simulating chloroform breath levels in individuals exposed in showers by inhalation and dermal routes and by the inhalation route only. Second, experimentally measured and previously reported ratios of chloroform concentrations in air and breath to tap-water concentration are used to evaluate the model predictions. Particular attention is given to the implied dermal uptake as measured by these experiments and to whether this is consistent with the recommended value for skin uptake of chloroform that is calculated using EPA guidance. This analysis indicates that the ratio of chloroform dermally absorbed in the shower relative to tap-water concentration is between 0.25 and 0.66 mg per mg/L and that the effective permeability of the skin during a 10-min. shower exposure is between 0.16 and 0.42 cm/hr. Third, the model is used to assess the relationship of dermal and inhalation exposure to metabolized dose in the liver. It is found that, for dermal and inhalation exposures in the shower and under conditions of linear metabolism, the ratio of metabolized dose to water concentration is on the order of 0.41 mg per mg/L. Fourth, the model is used to determine the chloroform concentration at which dermal and inhalation exposures to chloroform would begin to result in nonlinear metabolism. This concentration is found to be in the range of 60 to 100 mg/L.

Comparison of multi-media transport and transformation models: regional fugacity model vs. CalTOX.

Two multimedia environmental transport and transformation computer models are summarized and compared. The regional fugacity model published by Mackay and Paterson (1991), termed Fug3ONT, is a four compartment steady-state model designed to simulate the relative distribution of nonionic organic chemicals in a multimedia system. CalTOX is a seven compartment multimedia total exposure model for hazardous waste sites. Both models are based on the principles of fugacity. CalTOX, however, separates the soil into three layers (surface, root, and vadose) and uses a different approach to estimate the diffusive mass transfer rate in soil. These differences result in lower estimates of the steady-state contaminant concentrations of six environmentally relevant chemicals in the root soil of CalTOX as compared to the bulk soil of Fug3ONT. The difference is greatest for compounds with low mobility in soil such as 2,3,7,8-Tetrachlorodibenzo-p-dioxin and Benzo(a)pyrene where estimates from CalTOX and Fug3ONT differ by more than 3 orders of magnitude. Otherwise, the models provide similar estimates for the distribution of the six chemicals among the air, water, sediment and surface soil.

Geographical scenario uncertainty in generic fate and exposure factors of toxic pollutants for life-cycle impact assessment.

In environmental life-cycle assessments (LCA), fate and exposure factors account for the general fate and exposure properties of chemicals under generic environmental conditions by means of 'evaluative' multi-media fate and exposure box models. To assess the effect of using different generic environmental conditions, fate and exposure factors of chemicals emitted under typical conditions of (1). Western Europe, (2). Australia and (3). the United States of America were compared with the multi-media fate and exposure box model USES-LCA. Comparing the results of the three evaluative environments, it was found that the uncertainty in fate and exposure factors for ecosystems and humans due to choice of an evaluative environment, as represented by the ratio of the 97.5th and 50th percentile, is between a factor 2 and 10. Particularly, fate and exposure factors of emissions causing effects in fresh water ecosystems and effects on human health have relatively high uncertainty. This uncertainty is mainly caused by the continental difference in the average soil erosion rate, the dimensions of the fresh water and agricultural soil compartment, and the fraction of drinking water coming from ground water.

Estimating skin permeation. The validation of five mathematical skin permeation models.

This study provides an analysis of the reliability of five mathematical models, simulating permeation of substances through the skin from aqueous solutions. An extensive database was generated, containing data on 123 measured permeation coefficients of 99 different chemicals and their physicochemical properties. In addition, in this database all relevant experimental conditions are included. The coefficients of the different skin permeation models were estimated by non-linear multiple regression, using the octanol-water partition coefficient and the molecular weight as independent parameters. The reliability of the models was evaluated by testing variation of regression coefficients and of residual variance for subsets of data, randomly selected from the complete database. Three models were considered to provide reliable estimations of the skin permeation coefficient. These are based on the McKone and Howd model, the Guy and Potts model and the Robinson model. The last-mentioned two models were adaptations, because MW0.5 as independent parameter provided a better fit than MW (MW = molecular weight) in the original models. The McKone and Howd model and the Robinson model have the advantage, that they predict more precisely the skin permeation of highly hydrophilic and highly lipophilic chemicals compared to the Guy and Potts model. The revised Robinson model resulted always in the smallest residual variance.

Human toxicity potentials for life-cycle assessment and toxics release inventory risk screening.

The human toxicity potential (HTP), a calculated index that reflects the potential harm of a unit of chemical released into the environment, is based on both the inherent toxicity of a compound and its potential dose. It is used to weight emissions inventoried as part of a life-cycle assessment (LCA) or in the toxics release inventory (TRI) and to aggregate emissions in terms of a reference compound. Total emissions can be evaluated in terms of benzene equivalence (carcinogens) and toluene equivalents (noncarcinogens). The potential dose is calculated using a generic fate and exposure model, CalTOX, which determines the distribution of a chemical in a model environment and accounts for a number of exposure routes, including inhalation, ingestion of produce, fish, and meat, and dermal contact with water and soil. Toxicity is represented by the cancer potency q1* for carcinogens and the safe dose (RfD, RfC) for noncarcinogens. This article presents cancer and noncancer HTP values for air and surface-water emissions of 330 compounds. This list covers 258 chemicals listed in U.S. Environmental Protection Agency TRI, or 79 weight-% of the TRI releases to air reported in 1997.

Uncertainty and variability in human exposures to soil contaminants through home-grown food: a Monte Carlo assessment.

This paper presents a general model for exposure to homegrown foods that is used with a Monte Carlo analysis to determine the relative contributions of variability (Type A uncertainty) and true uncertainty (Type B uncertainty) to the overall variance in prediction of the dose-to-concentration ratio. Although classification of exposure inputs as uncertain or variable is somewhat subjective, food consumption rates and exposure duration are judged to have a predicted variance that is dominated by variability among individuals by age, income, culture, and geographical region. Whereas, biotransfer factors and partition factors are inputs that, to a large extent, involve uncertainty. Using ingestion of fruits, vegetables, grains, dairy products, and meat and soils assumed to be contaminated by hexachlorobenzene (HCB) and benzo(a)pyrene (BaP) as cases studies, a Monte Carlo analysis is used to explore the relative contribution of uncertainty and variability to overall variance in the estimated distribution of potential dose within the population that consumes home-grown foods. It is found that, when soil concentrations are specified, variances in ratios of dose-to-concentration for HCB are equally attributable to uncertainty and variability, whereas for BaP, variance in these ratios is dominated by true uncertainty.

Dermal uptake of organic chemicals from a soil matrix.

Uptake of chemicals from soil on human skin is considered. Based on a review of literature on the structure of human skin, the processes by which chemicals pass through this boundary, and experiments that reveal the rate and magnitude of this transport process; a two-layer model is presented for estimating how chemical uptake through the stratum corneum depends on chemical properties, skin properties, soil properties and exposure conditions. The model is applied to two limiting scenarios--(1) continuous deposition and removal of soil on the skin surface and (2) a one-time deposition of soil onto the skin surface. The fraction of soil-bound chemical that passes through the stratum corneum is dependent on the skin-soil layer thickness; the dimensionless Henry's law constant, Kh and the octanol-water partition coefficient, Kow of the soil-bound chemical. The nature of this dependence is discussed.

The transfer of trichloroethylene (TCE) from a shower to indoor air: experimental measurements and their implications.

Experiments were performed to measure the transfer of trichloroethylene (TCE), a volatile organic compound (VOC), from tap water in showers to indoor air. In these experiments, the loss of TCE from tap water in the shower is based on the difference between influent and effluent concentrations. We have developed and previously published a three-compartment model, which we use to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes resulting from the use of contaminated tap water. An important input to this model is the transfer efficiency of the VOC from water to air. The experiments reveal that the transfer efficiency of TCE from shower water to air has an arithmetic mean value of 61 percent and an arithmetic standard deviation of 9 percent. Analysis of the results shows that there is no statistically significant difference between the transfer efficiency measured with hot (37 degrees C) or cold (22 degrees C) shower water and that there is no statistically significant change in transfer efficiency with time during a 20-min shower. The implications for exposure assessment are considered.

Estimating human exposure through multiple pathways from air, water, and soil.

This paper describes a set of multipathway, multimedia models for estimating potential human exposure to environmental contaminants. The models link concentrations of an environmental contaminant in air, water, and soil to human exposure through inhalation, ingestion, and dermal-contact routes. The relationship between concentration of a contaminant in an environmental medium and human exposure is determined with pathway exposure factors (PEFs). A PEF is an algebraic expression that incorporates information on human physiology and lifestyle together with models of environmental partitioning and translates a concentration (i.e., mg/m3 in air, mg/liter in water, or mg/kg in soil) into a lifetime-equivalent chronic daily intake (CDI) in mg/kg-day. Human, animal, and environmental data used in calculating PEFs are presented and discussed. Generalized PEFs are derived for air----inhalation, air----ingestion, water----inhalation, water----ingestion, water----dermal uptake, soil----inhalation, soil----ingestion, and soil----dermal uptake pathways. To illustrate the application of the PEF expressions, we apply them to soil-based contamination of multiple environmental media by arsenic, tetrachloroethylene (PCE), and trinitrotoluene (TNT).