Cardiopulmonary effects of overnight indoor air filtration in healthy non-smoking adults: A double-blind randomized crossover study

BACKGROUND

More than 90% of the world's population lives in areas where outdoor air pollution levels exceed health-based limits. In these areas, individuals may use indoor air filtration, often on a sporadic basis, in their residences to reduce exposure to respirable particles (PM_2.5). Whether this intervention can lead to improvements in health outcomes has not been evaluated.

METHODS

Seventy non-smoking healthy adults, aged 19 to 26 years, received both true and sham indoor air filtration in a double-blinded randomized crossover study. Each filtration session was approximately 13 h long. True and sham filtration sessions were separated by a two-week washout interval. The study was carried out in a suburb of Shanghai.

RESULTS

During the study period, outdoor PM_2.5 concentrations ranged from 18.6 to 106.9 μg/m³, which overlapped with levels measured in Western Europe and North America. Compared to sham filtration, true filtration on average decreased indoor PM_2.5 concentration by 72.4% to 10.0 μg/m³ and particle number concentration by 59.2% to 2316/cm³. For lung function measured immediately after the end of filtration, true filtration significantly lowered airway impedance at 5 Hz (Z₅) by 7.1% [95% CI: 2.4%, 11.9%], airway resistance at 5 Hz (R₅) by 7.4% [95% CI: 2.4%, 12.5%], and small airway resistance (R₅-R₂₀) by 20.3% [95% CI: 0.1%, 40.5%], reflecting improved airway mechanics especially for the small airways. However, no significant improvements for spirometry indicators (FEV₁, FVC) were observed. True filtration also significantly lowered von Willebrand factor (VWF) by 26.9% [95% CI: 7.3%, 46.4%] 24 h after the end of filtration, indicating reduced risk for thrombosis. Stratified analysis in male and female participants showed that true filtration significantly decreased pulse pressure by 3.3% [95% CI: 0.8%, 7.4%] in females, and significantly reduced VWF by 42.4% [95% CI: 17.4%, 67.4%] and interleukin-6 by 22.6% [95% CI: 0.4%, 44.9%] in males. Effect modification analyses indicated that filtration effects in male and female participants were not significantly different.

CONCLUSION

A single overnight residential air filtration, capable of reducing indoor particle concentrations substantially, can lead to improved airway mechanics and reduced thrombosis risk.

Combined use of an electrostatic precipitator and a high-efficiency particulate air filter in building ventilation systems: Effects on cardiorespiratory health indicators in healthy adults

High-efficiency particulate air (HEPA) filtration in combination with an electrostatic precipitator (ESP) can be a cost-effective approach to reducing indoor particulate exposure, but ESPs produce ozone. The health effect of combined ESP-HEPA filtration has not been examined. We conducted an intervention study in 89 volunteers. At baseline, the air-handling units of offices and residences for all subjects were comprised of coarse, ESP, and HEPA filtration. During the 5-week long intervention, the subjects were split into 2 groups, 1 with just the ESP removed and the other with both the ESP and HEPA removed. Each subject was measured for cardiopulmonary risk indicators once at baseline, twice during the intervention, and once 2 weeks after baseline conditions were restored. Measured indoor and outdoor PM2.5 and ozone concentrations, coupled with time-activity data, were used to calculate exposures. Removal of HEPA filters increased 24-hour mean PM2.5 exposure by 38 (95% CI: 31, 45) μg/m3 . Removal of ESPs decreased 24-hour mean ozone exposure by 2.2 (2.0, 2.5) ppb. No biomarkers were significantly associated with HEPA filter removal. In contrast, ESP removal was associated with a -16.1% (-21.5%, -10.4%) change in plasma-soluble P-selectin and a -3.0% (-5.1%, -0.8%) change in systolic blood pressure, suggesting reduced cardiovascular risks.

Indoor Chemistry

This review aims to encapsulate the importance, ubiquity, and complexity of indoor chemistry. We discuss the many sources of indoor air pollutants and summarize their chemical reactions in the air and on surfaces. We also summarize some of the known impacts of human occupants, who act as sources and sinks of indoor chemicals, and whose activities (e.g., cooking, cleaning, smoking) can lead to extremely high pollutant concentrations. As we begin to use increasingly sensitive and selective instrumentation indoors, we are learning more about chemistry in this relatively understudied environment.

Dermal uptake of nicotine from air and clothing: Experimental verification

This study aims to elucidate in greater detail the dermal uptake of nicotine from air or from nicotine-exposed clothes, which was demonstrated recently in a preliminary study. Six non-smoking participants were exposed to gaseous nicotine (between 236 and 304 μg/m³ ) over 5 hours while breathing clean air through a hood. Four of the participants wore only shorts and 2 wore a set of clean clothes. One week later, 2 of the bare-skinned participants were again exposed in the chamber, but they showered immediately after exposure instead of the following morning. The 2 participants who wore clean clothes on week 1 were now exposed wearing a set of clothes that had been exposed to nicotine. All urine was collected for 84 hours after exposure and analyzed for nicotine and its metabolites, cotinine and 3OH-cotinine. All participants except those wearing fresh clothes excreted substantial amounts of biomarkers, comparable to levels expected from inhalation intake. Uptake for 1 participant wearing exposed clothes exceeded estimated intake via inhalation by >50%. Biomarker excretion continued during the entire urine collection period, indicating that nicotine accumulates in the skin and is released over several days. Absorbed nicotine was significantly lower after showering in 1 subject but not the other. Differences in the normalized uptakes and in the excretion patterns were observed among the participants. The observed cotinine half-lives suggest that non-smokers exposed to airborne nicotine may receive a substantial fraction through the dermal pathway. Washing skin and clothes exposed to nicotine may meaningfully decrease exposure.

Human symptom responses to bioeffluents, short-chain carbonyls/acids, and long-chain carbonyls in a simulated aircraft cabin environment

Occupants of aircraft have reported an array of symptoms related to general discomfort and irritation. Volatile organic compounds (VOCs) have been suggested to contribute to the reported symptoms. VOCs are from products used, bioeffluents from people and oxidation reaction products. Thirty-six healthy, young female subjects rated symptoms and environmental quality during an eight-hour exposure to groups of compounds often present in aircraft: (i) long-chain carbonyls, (ii) simulated bioeffluents, and (iii) short-chain carbonyls/organic acids. Statistically more symptoms were identified for the simulated bioeffluents and, to a lesser extent, short-chain carbonyls/organic acids compared to a control condition, although they remained in the acceptable range. There were three temporal patterns in the environmental quality and symptom reports: (i) an adaptive response (immediate increases followed by a decline); (ii) an apparent physiological effect (increases one to three hours into the exposure that remained elevated); and (iii) no statistical differences in reported environmental quality or symptom severity compared to the control air conditions. Typical concentrations found in aircraft can cause transitory symptoms in healthy individuals questioning the adequacy of current standards. Understanding the effects on individuals sensitive to air pollutants and methods to remove the compounds causing the greatest symptom responses are needed.

Linking a dermal permeation and an inhalation model to a simple pharmacokinetic model to study airborne exposure to di(n-butyl) phthalate

Six males clad only in shorts were exposed to high levels of airborne di(n-butyl) phthalate (DnBP) and diethyl phthalate (DEP) in chamber experiments conducted in 2014. In two 6 h sessions, the subjects were exposed only dermally while breathing clean air from a hood, and both dermally and via inhalation when exposed without a hood. Full urine samples were taken before, during, and for 48 h after leaving the chamber and measured for key DnBP and DEP metabolites. The data clearly demonstrated high levels of DnBP and DEP metabolite excretions while in the chamber and during the first 24 h once leaving the chamber under both conditions. The data for DnBP were used in a modeling exercise linking dose models for inhalation and transdermal permeation with a simple pharmacokinetic model that predicted timing and mass of metabolite excretions. These models were developed and calibrated independent of these experiments. Tests included modeling of the "hood-on" (transdermal penetration only), "hood-off" (both inhalation and transdermal) scenarios, and a derived "inhalation-only" scenario. Results showed that the linked model tended to duplicate the pattern of excretion with regard to timing of peaks, decline of concentrations over time, and the ratio of DnBP metabolites. However, the transdermal model tended to overpredict penetration of DnBP such that predictions of metabolite excretions were between 1.1 and 4.5 times higher than the cumulative excretion of DnBP metabolites over the 54 h of the simulation. A similar overprediction was not seen for the "inhalation-only" simulations. Possible explanations and model refinements for these overpredictions are discussed. In a demonstration of the linked model designed to characterize general population exposures to typical airborne indoor concentrations of DnBP in the United States, it was estimated that up to one-quarter of total exposures could be due to inhalation and dermal uptake.

Growth of organic films on indoor surfaces

We present a model for the growth of organic films on impermeable indoor surfaces. The model couples transport through a gas-side boundary layer adjacent to the surface with equilibrium partitioning of semivolatile organic compounds (SVOCs) between the gas phase and the surface film. Model predictions indicate that film growth would primarily be influenced by the gas-phase concentration of SVOCs with octanol-air partitioning (K_oa ) values in the approximate range 10≤log K_oa ≤13. Within the relevant range, SVOCs with lower values will equilibrate with the surface film more rapidly. Over time, the film becomes relatively enriched in species with higher log K_oa values, while the proportion of gas-phase SVOCs not in equilibrium with the film decreases. Given stable airborne SVOC concentrations, films grow at faster rates initially and then subsequently diminish to an almost steady growth rate. Once an SVOC is equilibrated with the film, its mass per unit film volume remains constant, while its mass per unit area increases in proportion to overall film thickness. The predictions of the conceptual model and its mathematical embodiment are generally consistent with results reported in the peer-reviewed literature.

Dermal Uptake of Benzophenone-3 from Clothing

Benzophenone-3 (also known as BP-3 or oxybenzone) is added to sunscreens, plastics, and some coatings to filter UV radiation. The suspected endocrine disruptor BP-3 has been detected in the air and settled dust of homes and is expected to redistribute from its original sources to other indoor compartments, including clothing. Given its physical and chemical properties, we hypothesized that dermal uptake from clothing could contribute to the body burden of this compound. First, cotton shirts were exposed to air at an elevated concentration of BP-3 for 32 days; the final air concentration was 4.4 μg/m³. Next, three participants wore the exposed shirts for 3 h. After 3 h of exposure, participants wore their usual clothing during the collection of urine samples for the next 48 h. Urine was analyzed for BP-3, a metabolite (BP-1), and six other UV filters. The rate of urinary excretion of the sum of BP-1 and BP-3 increased for all participants during and following the 3 h of exposure. The summed mass of BP-1 and BP-3 excreted during the first 24 h attributable to wearing exposed t-shirts were 12, 9.9, and 82 μg for participants 1, 2, and 3, respectively. Analysis of these results, coupled with predictions of steady-state models, suggest that dermal uptake of BP-3 from clothing could meaningfully contribute to overall body burden.

Association of Ozone Exposure With Cardiorespiratory Pathophysiologic Mechanisms in Healthy Adults

Importance

Exposure to ozone has been associated with cardiovascular mortality, but the underlying biological mechanisms are not yet understood.

Objective

To examine the association between ozone exposure and cardiopulmonary pathophysiologic mechanisms.

Design, Setting, and Participants

A longitudinal study involving 89 healthy adult participants living on a work campus in Changsha City, China, was conducted from December 1, 2014, to January 31, 2015. This unique quasiexperimental setting allowed for better characterization of air pollutant exposure effects because the participants spent most of their time in controlled indoor environments. Concentrations of indoor and outdoor ozone, along with the copollutants particulate matter, nitrogen dioxide, and sulfur dioxide, were monitored throughout the study period and then combined with time-activity information and filtration conditions of each residence and office to estimate 24-hour and 2-week combined indoor and outdoor mean exposure concentrations. Associations between each exposure measure and outcome measure were analyzed using single-pollutant and 2-pollutant linear mixed models controlling for ambient temperature, secondhand smoke exposure, and personal-level time-varying covariates.

Main Outcomes and Measures

Biomarkers indicative of inflammation and oxidative stress, arterial stiffness, blood pressure, thrombotic factors, and spirometry were measured at 4 sessions.

Results

Of the 89 participants, 25 (28%) were women and the mean (SD) age was 31.5 (7.6) years. The 24-hour ozone exposure concentrations ranged from 1.4 to 19.4 parts per billion (ppb), corresponding to outdoor concentrations ranging from 4.3 to 47.9 ppb. Within this range, in models controlling for a second copollutant and other potential confounders, a 10-ppb increase in 24-hour ozone was associated with mean increases of 36.3% (95% CI, 29.9%-43.0%) in the level of platelet activation marker soluble P-selectin, 2.8% (95% CI, 0.6%-5.1%) in diastolic blood pressure, 18.1% (95% CI, 4.5%-33.5%) in pulmonary inflammation markers fractional exhaled nitric oxide, and 31.0% (95% CI, 0.2%-71.1%) in exhaled breath condensate nitrite and nitrate as well as a -9.5% (95% CI, -17.7% to -1.4%) decrease in arterial stiffness marker augmentation index. A 10-ppb increase in 2-week ozone was associated with increases of 61.1% (95% CI, 37.8%-88.2%) in soluble P-selectin level and 126.2% (95% CI, 12.1%-356.2%) in exhaled breath condensate nitrite and nitrate level. Other measured biomarkers, including spirometry, showed no significant associations with either 24-hour ozone or 2-week ozone exposures.

Conclusions and Relevance

Short-term ozone exposure at levels not associated with lung function changes was associated with platelet activation and blood pressure increases, suggesting a possible mechanism by which ozone may affect cardiovascular health.

Characterizing Aggregated Exposure to Primary Particulate Matter: Recommended Intake Fractions for Indoor and Outdoor Sources

Exposure to fine particulate matter (PM_2.5) from indoor and outdoor sources is a leading environmental contributor to global disease burden. In response, we established under the auspices of the UNEP/SETAC Life Cycle Initiative a coupled indoor-outdoor emission-to-exposure framework to provide a set of consistent primary PM_2.5 aggregated exposure factors. We followed a matrix-based mass balance approach for quantifying exposure from indoor and ground-level urban and rural outdoor sources using an effective indoor-outdoor population intake fraction and a system of archetypes to represent different levels of spatial detail. Emission-to-exposure archetypes range from global indoor and outdoor averages, via archetypal urban and indoor settings, to 3646 real-world cities in 16 parametrized subcontinental regions. Population intake fractions from urban and rural outdoor sources are lowest in Northern regions and Oceania and highest in Southeast Asia with population-weighted means across 3646 cities and 16 subcontinental regions of, respectively, 39 ppm (95% confidence interval: 4.3-160 ppm) and 2 ppm (95% confidence interval: 0.2-6.3 ppm). Intake fractions from residential and occupational indoor sources range from 470 ppm to 62 000 ppm, mainly as a function of air exchange rate and occupancy. Indoor exposure typically contributes 80-90% to overall exposure from outdoor sources. Our framework facilitates improvements in air pollution reduction strategies and life cycle impact assessments.

Exposure to SVOCs from Inhaled Particles: Impact of Desorption

Inhaled semivolatile organic compounds (SVOCs) are simultaneously present in gas and particle phases. Particles desorb a fraction of their SVOCs moving through the human respiratory tract (RT). Quantifying such desorption is challenging but important since gas- and particle-phase SVOCs deposit in different locations in the RT, encountering different cell populations with varying health consequences. This paper presents a mass transfer model to quantify this desorption process in the head, tracheobronchial, and alveolar regions of the RT. The desorption of SVOCs from inhaled particles can be gauged using the ratio of particle residence time to the time required to achieve particle/gas equilibrium. Results indicate that the larger this ratio is, the more likely particles desorb the SVOCs they carry. For particles smaller than 0.5 μm diameter and SVOCs with a particle/gas partition coefficient (unitless) of 10¹⁰, accounting for desorption reduces the estimated particle-phase SVOC concentrations in the alveolar region by more than 35%; the reduction is almost 700% for 0.05 μm diameter particles. In hypothetical scenarios representing common indoor and outdoor situations, neglecting desorption significantly overestimates the concentration of ultrafine particle associated SVOCs in the alveolar region. This model is a preliminary step toward more nuanced estimates of exposure to inhaled SVOCs.

Dermal uptake of phthalates from clothing: Comparison of model to human participant results

In this research, we extend a model of transdermal uptake of phthalates to include a layer of clothing. When compared with experimental results, this model better estimates dermal uptake of diethylphthalate and di-n-butylphthalate (DnBP) than a previous model. The model predictions are consistent with the observation that previously exposed clothing can increase dermal uptake over that observed in bare-skin participants for the same exposure air concentrations. The model predicts that dermal uptake from clothing of DnBP is a substantial fraction of total uptake from all sources of exposure. For compounds that have high dermal permeability coefficients, dermal uptake is increased for (i) thinner clothing, (ii) a narrower gap between clothing and skin, and (iii) longer time intervals between laundering and wearing. Enhanced dermal uptake is most pronounced for compounds with clothing-air partition coefficients between 10⁴ and 10⁷ . In the absence of direct measurements of cotton cloth-air partition coefficients, dermal exposure may be predicted using equilibrium data for compounds in equilibrium with cellulose and water, in combination with computational methods of predicting partition coefficients.

The Essential Role for Laboratory Studies in Atmospheric Chemistry

Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues. Laboratory studies provide rich opportunities to expand our understanding of the atmosphere via collaborative research with the modeling and field measurement communities, and with neighboring disciplines.

Measurements of dermal uptake of nicotine directly from air and clothing

In this preliminary study, we have investigated whether dermal uptake of nicotine directly from air or indirectly from clothing can be a meaningful exposure pathway. Two participants wearing only shorts and a third participant wearing clean cotton clothes were exposed to environmental tobacco smoke (ETS), generated by mechanically "smoking" cigarettes, for three hours in a chamber while breathing clean air from head-enveloping hoods. The average nicotine concentration (420 μg/m³ ) was comparable to the highest levels reported for smoking sections of pubs. Urine samples were collected immediately before exposure and 60 hour post-exposure for bare-skinned participants. For the clothed participant, post-exposure urine samples were collected for 24 hour. This participant then entered the chamber for another three-hour exposure wearing a hood and clothes, including a shirt that had been exposed for five days to elevated nicotine levels. The urine samples were analyzed for nicotine and two metabolites-cotinine and 3OH-cotinine. Peak urinary cotinine and 3OH-cotinine concentrations for the bare-skinned participants were comparable to levels measured among non-smokers in hospitality environments before smoking bans. The amount of dermally absorbed nicotine for each bare-skinned participant was conservatively estimated at 570 μg, but may have been larger. For the participant wearing clean clothes, uptake was ~20 μg, and while wearing a shirt previously exposed to nicotine, uptake was ~80 μg. This study demonstrates meaningful dermal uptake of nicotine directly from air or from nicotine-exposed clothes. The findings are especially relevant for children in homes with smoking or vaping.

Fungal and bacterial growth in floor dust at elevated relative humidity levels

Under sustained, elevated building moisture conditions, bacterial and fungal growth occurs. The goal of this study was to characterize microbial growth in floor dust at variable equilibrium relative humidity (ERH) levels. Floor dust from one home was embedded in coupons cut from a worn medium-pile nylon carpet and incubated at 50%, 80%, 85%, 90%, 95%, and 100% ERH levels. Quantitative PCR and DNA sequencing of ribosomal DNA for bacteria and fungi were used to quantify growth and community shifts. Over a 1-wk period, fungal growth occurred above 80% ERH. Growth rates at 85% and 100% ERH were 1.1 × 10⁴ and 1.5 × 10⁵ spore equivalents d^-1 mg dust^-1 , respectively. Bacterial growth occurred only at 100% ERH after 1 wk (9.0 × 10⁴ genomes d^-1 mg dust^-1 ). Growth resulted in significant changes in fungal (P<.00001) and bacterial community structure (P<.00001) at varying ERH levels. Comparisons between fungal taxa incubated at different ERH levels revealed more than 100 fungal and bacterial species that were attributable to elevated ERH. Resuspension modeling indicated that more than 50% of airborne microbes could originate from the resuspension of fungi grown at ERH levels of 85% and above.

Desorption of SVOCs from Heated Surfaces in the Form of Ultrafine Particles

Ultrafine particles (UFP) produced by electric heating of stoves and metal cooking pans, absent food, have been hypothesized to be created from a surface film of semivolatile organic compounds (SVOCs) sorbed from the surrounding air. This study tests that hypothesis by size-resolved measurements extending the lower range of the UFP studied from 10 to 2.3 nm, and including other surfaces (glass, aluminum, and porcelain). Heating glass Petri dishes or squares of aluminum foil to about 350-400 °C for 4-6 min removed all sorbed organic substances completely. Subsequent exposure of these "clean" Petri dishes and foil squares to indoor air in two different residences for successively longer periods (1 h to 281 days), followed by heating the materials for 4-6 min, indicated a strong relationship of the number, size distribution, and mass of the UFP to the time exposed. Estimates of the accumulation rate of SVOCs on surfaces were similar to those in studies of organic film buildup on indoor windows. Transfer of skin oils by touching the glass or foil surfaces, or after washing the glass surface with detergent and bare hands, was also observed, with measured particle production comparable with that produced by long-term exposure to indoor air.

Dermal uptake directly from air under transient conditions: advances in modeling and comparisons with experimental results for human subjects

To better understand the dermal exposure pathway, we enhance an existing mechanistic model of transdermal uptake by including skin surface lipids (SSL) and consider the impact of clothing. Addition of SSL increases the overall resistance to uptake of SVOCs from air but also allows for rapid transfer of SVOCs to sinks like clothing or clean air. We test the model by simulating di-ethyl phthalate (DEP) and di-n-butyl phthalate (DnBP) exposures of six bare-skinned (Weschler et al. 2015, Environ. Health Perspect., 123, 928) and one clothed participant (Morrison et al. 2016, J. Expo. Sci. Environ. Epidemiol., 26, 113). The model predicts total uptake values that are consistent with the measured values. For bare-skinned participants, the model predicts a normalized mass uptake of DEP of 3.1 (μg/m² )/(μg/m³ ), whereas the experimental results range from 1.0 to 4.3 (μg/m² )/(μg/m³ ); uptake of DnBP is somewhat overpredicted: 4.6 (μg/m² )/(μg/m³ ) vs. the experimental range of 0.5-3.2 (μg/m² )/(μg/m³ ). For the clothed participant, the model predicts higher than observed uptake for both species. Uncertainty in model inputs, including convective mass transfer coefficients, partition coefficients, and diffusion coefficients, could account for overpredictions. Simulations that include transfer of skin oil to clothing improve model predictions. A dynamic model that includes SSL is more sensitive to changes that impact external mass transfer such as putting on and removing clothes and bathing.

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

Exposure to fine particulate matter (PM_2.5 ) is a major contributor to the global human disease burden. The indoor environment is of particular importance when considering the health effects associated with PM_2.5 exposures because people spend the majority of their time indoors and PM_2.5 exposures per unit mass emitted indoors are two to three orders of magnitude larger than exposures to outdoor emissions. Variability in indoor PM_2.5 intake fraction (iF_in,total ), which is defined as the integrated cumulative intake of PM_2.5 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 PM_2.5 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 iF_in,total were compiled. In addition to providing data for the calculation of iF_in,total in various indoor environments and for a range of geographic regions, this paper discusses remaining limitations to the incorporation of PM_2.5 -derived health impacts into life cycle assessments and makes recommendations regarding future research.

Ozone, Electrostatic Precipitators, and Particle Number Concentrations: Correlations Observed in a Real Office during Working Hours

This study investigates the impacts of outdoor and indoor ozone concentrations, ESP operation and occupancy on particle number concentrations within a modern office in Changsha, China. The office's one-pass air handling system contains a mini-bag filter (MERV 12) followed by an electrostatic precipitator (ESP) and high efficiency particulate air (HEPA) filter. Over a five-week period the system was operated either without the ESP (Stage 1, first-third week) or with the ESP (Stage 2, fourth and fifth week). Ozone and particle number concentrations were measured on working days. During both stages, indoor ozone and particle number concentrations tracked the outdoor ozone concentration. When operating, the ESP produced approximately 29 mg h(-1) of ozone, increasing supply air ozone by 15 ppb and steady-state indoor ozone by about 3 ppb. Occupancy tended to decrease indoor ozone and increase particle levels. During occupancy, indoor particle levels were low (∼2600 particle/cm(3)) when the supply air ozone level was less than 18 ppb. Above this threshold, the supply air ozone concentration and indoor particle number concentration were linearly related, and ESP operation increased the average indoor particle level by about 22 000 particles/cm(3). The implications for worker exposure to both ozone and particles are discussed.

Organophosphate esters in dust samples collected from Danish homes and daycare centers

Organophosphates are used in a wide range of materials and consumer products and are ubiquitous in indoor environments. Certain organophosphates have been associated with various adverse health effects. The present paper reports mass fractions of organophosphates in dust samples collected from 500 bedrooms and 151 daycare centers of children living in Odense, Denmark. The identified compounds include: tris(isobutyl) phosphate (TIBP), tri-n-butyl phosphate (TNBP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(1,3-dichloroisopropyl) phosphate (TDCIPP), tris(2-butoxyethyl) phosphate (TBOEP), triphenylphosphate (TPHP), 2-ethylhexyl-diphenyl phosphate (EHDPP), tris(2-ethylhexyl) phosphate (TEHP) and tris(methylphenyl) phosphate (TMPP). Both the number of organophosphates with median values above the limit of detection and the median values were higher for samples from daycare centers than for samples from homes. Organophosphates with median mass fractions above the limit of detection were: TCEP from homes (6.9 μg g(-1)), and TCEP (16 μg g(-1)), TCIPP (5.6 μg g(-1)), TDCIPP (7.1 μg g(-1)), TBOEP (26 μg g(-1)), TPHP (2.0 μg g(-1)) and EHDPP (2.1 μg g(-1)) from daycare centers. When present, TBOEP was typically the most abundant of the identified OPs. The sum of the organophosphate dust mass fractions measured in this study was roughly in the mid-range of summed mass fractions reported for dust samples collected in other countries. On a global scale, the geographical distribution of organophosphates in indoor dust is quite variable, with higher concentrations in industrialized countries. This trend differs from that for phthalate esters, whose geographic distribution is more homogeneous. Exposure to organophosphates via dust ingestion is relatively low, although there is considerable uncertainly in this assessment.

Impact of Clothing on Dermal Exposure to Phthalates: Observations and Insights from Sampling Both Skin and Clothing

Clothing can either retard or accelerate dermal exposure to phthalates. To investigate the impact of clothing on dermal exposure to six phthalates (DMP/DEP/DiBP/DnBP/BBzP/DEHP) in real environments, two sets of experiments have been conducted: (1) Skin wipes were collected from 11 adults to examine the phthalate levels on both bare-skin (hand/forehead) and clothing-covered body locations (arm/back/calf); (2) Five adults were asked to wear just-washed jeans for 1 day (1(st) experiment), 5 days (2(nd) experiment), and 10 days (3(rd) experiment). Phthalate levels on their legs were measured on selected days during the wearing period, and phthalate levels in the jeans were measured at the end of each experiment and again after washing. Measured phthalate levels on body locations covered by clothing were lower than those on uncovered locations, but still substantial. Dermal uptake would be underestimated by a factor of 2 to 5 if absorption through body locations covered by clothing were neglected. Phthalate levels in the jeans and on the legs increased with the wearing time. However, the levels in the jeans and on the legs were not strongly correlated, indicating that other pathways, e.g, contact with bedding or bedclothes, likely contribute to the levels on the legs. The efficiency with which laundering washing removed phthalates from the jeans increased with decreasing Kow; median values ranged from very low (<5%) for DEHP to very high (∼75%) for DMP.

Roles of the human occupant in indoor chemistry

Over the last decade, influences of the human occupant on indoor chemistry have been investigated in environments ranging from simulated aircraft cabins to actual classrooms. We have learned that ozone reacts rapidly with constituents of skin surface lipids on exposed skin, hair, and clothing, substantially reducing indoor ozone concentrations but increasing airborne levels of mono- and bifunctional compounds that contain carbonyl, carboxyl, or α-hydroxy ketone groups. Moreover, occupants transfer skin oils to and shed skin flakes (desquamation) onto indoor surfaces. Evidence for the presence of skin flakes/oils has been found in airborne particles, settled dust, and wipes of indoor surfaces. These occupant residues are also anticipated to scavenge ozone and produce byproducts. Under typical conditions, occupancy is anticipated to decrease the net level of oxidants in indoor air. When occupants scavenge ozone, the level of SOA derived from ozone/terpene chemistry decreases; the fraction of SVOCs in the gas-phase increases, and the fraction associated with airborne particles decreases. Occupants also remove organic compounds, including certain chemically active species, via bodily intake. Studies reviewed in this paper demonstrate the pronounced influences of humans on chemistry within the spaces they inhabit and the consequences of these influences on their subsequent chemical exposures.

C(m)-History Method, a Novel Approach to Simultaneously Measure Source and Sink Parameters Important for Estimating Indoor Exposures to Phthalates

The concentration of a gas-phase semivolatile organic compound (SVOC) in equilibrium with its mass-fraction in the source material, y0, and the coefficient for partitioning of an SVOC between clothing and air, K, are key parameters for estimating emission and subsequent dermal exposure to SVOCs. Most of the available methods for their determination depend on achieving steady-state in ventilated chambers. This can be time-consuming and of variable accuracy. Additionally, no existing method simultaneously determines y0 and K in a single experiment. In this paper, we present a sealed-chamber method, using early-stage concentration measurements, to simultaneously determine y0 and K. The measurement error for the method is analyzed, and the optimization of experimental parameters is explored. Using this method, y0 for phthalates (DiBP, DnBP, and DEHP) emitted by two types of PVC flooring, coupled with K values for these phthalates partitioning between a cotton T-shirt and air, were measured at 25 and 32 °C (room and skin temperatures, respectively). The measured y0 values agree well with results obtained by alternate methods. The changes of y0 and K with temperature were used to approximate the changes in enthalpy, ΔH, associated with the relevant phase changes. We conclude with suggestions for further related research.

Role of clothing in both accelerating and impeding dermal absorption of airborne SVOCs

To assess the influence of clothing on dermal uptake of semi-volatile organic compounds (SVOCs), we measured uptake of selected airborne phthalates for an individual wearing clean clothes or air-exposed clothes and compared these results with dermal uptake for bare-skinned individuals under otherwise identical experimental conditions. Using a breathing hood to isolate dermal from inhalation uptake, we measured urinary metabolites of diethylphthalate (DEP) and di-n-butylphthalate (DnBP) from an individual exposed to known concentrations of these compounds for 6 h in an experimental chamber. The individual wore either clean (fresh) cotton clothes or cotton clothes that had been exposed to the same chamber air concentrations for 9 days. For a 6-h exposure, the net amounts of DEP and DnBP absorbed when wearing fresh clothes were, respectively, 0.017 and 0.007 μg/kg/(μg/m(3)); for exposed clothes the results were 0.178 and 0.261 μg/kg/(μg/m(3)), respectively (values normalized by air concentration and body mass). When compared against the average results for bare-skinned participants, clean clothes were protective, whereas exposed clothes increased dermal uptake for DEP and DnBP by factors of 3.3 and 6.5, respectively. Even for non-occupational environments, wearing clothing that has adsorbed/absorbed indoor air pollutants can increase dermal uptake of SVOCs by substantial amounts relative to bare skin.