Dermal uptake of organic vapors commonly found in indoor air

Concentrations, Profiles, and Potential Sources of Liquid Crystal Monomers in Residential Indoor Dust from the United States

Liquid crystal monomers (LCMs) are biphenyl- or cyclohexane-based organic chemicals used in electronic digital displays, and several of them possess bioaccumulative and toxic properties. Little is known about their occurrence in indoor dust from the United States. We analyzed 60 LCMs in 104 residential indoor dust samples collected from 16 states across the United States. Forty-seven of 60 LCMs were detected in dust samples at a median ∑LCM concentration of 402 ng/g (range: not detected to 4300 ng/g). Trans-4-propylcyclohexyl trans,trans-4'-propylbicyclohexyl-4-carboxylate (MPVBC) and (trans,trans)-4-fluorophenyl 4'-pentyl-[1,1'-bi(cyclohexane)]-4-carboxylate (FPeBC) were frequently detected in dust samples. We investigated potential sources of LCMs in dust by determining concentrations and profiles of these chemicals in smartphone screens, desktop and laptop computer monitors, and displays of other electronic devices and found that profiles in smartphones matched closely with those found in dust. The calculated median daily intake of ∑LCM through dust ingestion was 1.19 ng/kg bw/d for children, whereas that through dermal absorption was 0.18 ng/kg bw/d for adults in the United States.

Monitoring human exposure to four parabens and triclosan: comparing silicone wristbands with spot urine samples as predictors of internal dose

BACKGROUND

People are exposed to a variety of chemicals each day as a result of their personal care product (PCP) use.

OBJECTIVE

This study was designed to determine if silicone wristbands provide a quantitative estimate of internal dose for phenols commonly associated with PCPs, with a focus on triclosan and four parabens: methyl-, ethyl-, propyl-, and butylparaben. Uptake of these compounds into wristbands and correlations with internal dose were assessed.

METHODS

Ten adults from central North Carolina wore five silicone wristbands, with one wristband removed each day for 5 days. Each participant provided a 24 h urine sample and a random spot urine sample each day, in which paraben and triclosan metabolites were evaluated.

RESULTS

All parabens and triclosan were detected frequently in wristbands and, except for butylparaben, in urine samples. Wristband and spot urine concentrations of parabens and triclosan were both compared to a measurement of internal dose (i.e., the total metabolite mass excreted over 5 days as a measurement of internal dose).

IMPACT STATEMENT

The two most hydrophobic compounds investigated, butylparaben and triclosan, displayed significant linear uptake in wristbands over 5 days, whereas concentrations of methyl- and ethylparaben displayed a steady state concentration. In general, wristbands and spot urine samples were similarly correlated to internal dose for frequently detected parabens and triclosan.  However, wristbands have additional advantages including higher detection rates and reduced participant burden that may make them more suitable tools for assessing exposure to PCPs.

Dermal bioavailability of perfluoroalkyl substances using in vitro 3D human skin equivalent models

Perfluoroalkyl substances (PFAS) have been identified in various products that come in contact with human skin, ranging from school uniforms to personal care products. Despite this, knowledge on human dermal uptake of PFAS is lacking. Thus, the human dermal absorption of 17 PFAS was assessed, for the first time, using in vitro 3D-human skin equivalent models exposed to 500 ng/cm2 PFAS dissolved in methanol over 24-36 h. The distribution of target PFAS is presented, based on three fractions: absorbed, un-absorbed, and retained within skin tissue (absorbable dose). Perfluoropentanoic acid (PFPeA) and perfluorobutane sulfonate (PFBS) had the highest absorbed fraction, 58.9 % and 48.7 % respectively, with the absorbed fraction decreasing with increasing carbon chain length of the studied perfluorocarboxylic acids (PFCAs) (r = 0.97, p = 0.001) and perfluorosulfonic acids (PFSAs) (r = 0.97, p = 0.004). Interestingly, while longer chain PFAS (Cn ≥ 9) were not directly absorbed, a large fraction of the exposure dose was detected within the skin tissue at the end of the exposure. This was most apparent for perfluoroundecanoic acid (PFUnDA) and perfluorononane sulfonate (PFNS) for which 66.5 % and 68.3 % of the exposure dose was found within the skin tissue, while neither compound was detected in the absorbed fraction. For compounds with a carbon chain length > 11, the fraction found within the skin tissue, decreases with increasing chain length. Physicochemical properties played a role in dermal permeation of PFAS, with a clear inverse correlation between logKOW and absorbed fraction for both PFCAs (r = -0.97; p ≤ 0.001) and PFSAs (r = -0.99; p ≤ 0.001). Steady-state flux (JSS) and permeation coefficients (Papp) were determined for target compounds with significant permeation after 36 h exposure (C5-C8 PFCAs and C4-C7 PFSAs). In general, both the flux and permeation coefficient decreased with increasing chain length.

Flame Retardant Exposure in Vehicles Is Influenced by Use in Seat Foam and Temperature

Flame retardants (FRs) are added to vehicles to meet flammability standards, such as US Federal Motor Vehicle Safety Standard FMVSS 302. However, an understanding of which FRs are being used, sources in the vehicle, and implications for human exposure is lacking. US participants (n = 101) owning a vehicle of model year 2015 or newer hung a silicone passive sampler on their rearview mirror for 7 days. Fifty-one of 101 participants collected a foam sample from a vehicle seat. Organophosphate esters (OPEs) were the most frequently detected FR class in the passive samplers. Among these, tris(1-chloro-isopropyl) phosphate (TCIPP) had a 99% detection frequency and was measured at levels ranging from 0.2 to 11,600 ng/g of sampler. TCIPP was also the dominant FR detected in the vehicle seat foam. Sampler FR concentrations were significantly correlated with average ambient temperature and were 2-5 times higher in the summer compared to winter. The presence of TCIPP in foam resulted in ∼4 times higher median air sampler concentrations in winter and ∼9 times higher in summer. These results suggest that FRs used in vehicle interiors, such as in seat foam, are a source of OPE exposure, which is increased in warmer temperatures.

Aromatic amine antioxidants (AAs) and p-phenylenediamines-quinones (PPD-Qs) in e-waste recycling industry park: Occupational exposure and liver X receptors (LXRs) disruption potential

Recently, evidence of aromatic amine antioxidants (AAs) existence in the dust of the electronic waste (e-waste) dismantling area has been exposed. However, there are limited studies investigating occupational exposure and toxicity associated with AAs and their transformation products (p-phenylenediamines-quinones, i.e., PPD-Qs). In this study, 115 dust and 42 hand wipe samples collected from an e-waste recycling industrial park in central China were analyzed for 19 AAs and 6 PPD-Qs. Notably, the median concentration of ∑6PPD-Qs (1,110 ng/g and 1,970 ng/m2) was significantly higher (p < 0.05, Mann-Whitney U test) than that of ∑6PPDs (147 ng/g and 34.0 ng/m2) in dust and hand wipes. Among the detected analytes, 4-phenylaminodiphenylamine quinone (DPPD-Q) (median: 781 ng/g) and 1,4-Bis(2-naphthylamino) benzene quinone (DNPD-Q) (median: 156 ng/g), were particularly prominent, which were first detected in the e-waste dismantling area. Occupational exposure assessments and nuclear receptor interference ability, conducted through estimated daily intake (EDI) and molecular docking analysis, respectively, indicated significant occupational exposure to PPD-Qs and suggested prioritized Liver X receptors (LXRs) disruption potential of PPDs and PPD-Qs. The study provides the first evidence of considerable levels of AAs and PPD-Qs in the e-waste-related hand wipe samples and underscores the importance of assessing occupational exposure and associated toxicity effects.

Quantitative characterization of resident' exposure to typical semi-volatile organic compounds (SVOCs) around a non-ferrous metal smelting plant

To comprehensively characterize residents' exposure to major semi-volatile organic compounds (SVOCs), samples of indoor floor wipes, size-segregated airborne particles, gaseous air, food, and paired skin wipes were simultaneously collected from residential areas around a large non-ferrous metal smelting plant as compared with the control areas, and three typical SVOCs (including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and halogenated PAHs (HPAHs)) were determined. Comparison and correlation analysis among matrices indicated PAHs were the major contaminants emitted from metal smelting activities compared to HPAHs and PCBs, with naphthalene verified as the most important characteristic compound, and their accumulation on skin may be a comprehensive consequence of contact with floor dust and air. While patterns of human exposure pathways for the SVOCs were found to be clearly correlated to their vapor pressure, dermal absorption was the major contributor (51.1-76.3%) to total carcinogenic risk (TCR) of PAHs and HPAHs for surrounding residents, especially for low molecular weight PAHs, but dietary ingestion (98.6%) was the dominant exposure pathway to PCBs. The TCR of PAHs exceeded the acceptable level (1 × 10-4), implying smelting activities obviously elevated the health risk. This study will serve developing pertinent exposure and health risk prevention measures.

The legalization of cannabis may result in increased indoor exposure to Δ9-tetrahydrocannabinol

Cannabis is a genus of plants in the Cannabaceae family that contains tetrahydrocannabinolic acid. When heated or burned, the acid decarboxylates to form tetrahydrocannabinol (THC). Its (-)-trans-Δ9-THC isomer is a psychoactive substance that has been used as a drug for centuries. In most countries, both the private sale of cannabis products and their use for non-medical purposes are still prohibited by law. However, for some time now there has been societal and political pressure to at least partially legalize cannabis products. It can be expected that such a measure will lead to a significant increase in the consumption of cannabis. However, this also increases the possibility of involuntary passive exposure to THC and contamination of the indoor environment. In indoor sciences, THC is still a largely unknown or underrepresented substance. In this perspective paper, THC will therefore first be presented on the basis of its physical properties. Then, the distribution of THC in different indoor compartments and potential routes of passive exposure are discussed. Finally, an assessment of the future importance of THC for indoor use is made. Previous experience has shown that early monitoring is always advantageous so that preventive and protective measures can be taken quickly if necessary.

Screening and Evaluation of Children's Sensitively Toxic Chemicals in New Mosquito Repellent Products Based on a Nationwide Investigation

New mosquito repellent products (NMRPs) are emerging popular repellents among children. There are increasing reports on children's sensitization reactions caused by NMRPs, while regulations on their productions, sales, or usage are still lacking. One of the reasons could be the missing comprehensive risk assessment. We first conducted a nationwide investigation on children's NMRP usage preferences. Then, we high-throughput screened volatile or semivolatile organic chemicals (VOCs/SVOCs) in five representative NMRPs by the headspace gas chromatography-orbitrap high-resolution mass spectrometry analytical method. After that, toxic compounds were recognized based on the toxicity forecaster (ToxCast) database. A total of 277 VOCs/SVOCs were recognized, and 70 of them were identified as toxic compounds. In a combination of concentrations, toxicities, absorption, distribution, metabolism, and excretion characteristics in the body, 28 chemicals were finally proposed as priority-controlled compounds in NMRPs. Exposure risks of recognized toxic chemicals through NMRPs by inhalation and dermal intake for children across the country were also assessed. Average daily intakes were in the range of 0.20-7.31 mg/kg/day for children in different provinces, and the children in southeastern coastal provinces were found to face higher exposure risks. By controlling the high-priority chemicals, the risks were expected to be reduced by about 46.8% on average. Results of this study are therefore believed to evaluate exposure risks, encourage safe production, and promote reasonable management of NMRPs.

Atmospheric fate of typical liquid crystal monomers in the tropospheric gas, liquid, and granular phases

Mineral aerosol particles significantly impact environmental risk prediction of liquid crystal monomers (LCMs). In this work, we investigated the reaction mechanisms and kinetics of three typical LCMs (4-cyano-3,5-difluorophenyl 4-ethylbenzoate (CEB-2F), 4-cyano-3-fluorophenyl 4-ethylbenzoate (CEB-F), and 4-cyanophenyl 4-ethylbenzoate (CEB)) with ozone (O3) in the atmospheric gas, liquid, and particle phases employing density functional theory (DFT). Here, O3 is prone to add to the benzene ring without F atom(s) in the selected LCMs. The ozonolysis products are aldehydes, carboxylic acids, epoxides, and unsaturated hydrocarbons containing aromatic rings. Those products undergo secondary ozonolysis to generate small molecular compounds such as glyoxal, which is beneficial for generating secondary organic aerosol (SOA). Titanium dioxide (TiO2), an essential component of mineral aerosol particles, has good adsorption properties for LCMs; however, it slightly reduces the reactivity with O3. At 298 K, the reaction rate constant of the selected LCMs reacting with O3 in the gas and atmospheric liquid phases is (2.74‒5.53) × 10-24 cm3/(mol·sec) and 5.58 × 10-3‒39.1 L/(mol·sec), while CEB-2F reacting with O3 on (TiO2)6 cluster is 1.84 × 10-24 cm3/(mol·sec). The existence of TiO2 clusters increases the persistence and long-distance transportability of LCMs, which enlarges the contaminated area of LCMs.

Particle size-dependent and route-specific exposure to liquid crystal monomers in indoor air: Implications for human health risk estimations

In indoor environments, liquid crystal monomers (LCMs) released from display devices is a significant concern, necessitating a comprehensive investigation into their distribution behaviors and potential health risks. Herein, we examined various LCMs in educational and workplace air and compared their associated health risks through inhalation and dermal absorption routes. 4-propyl-4'-vinylbicyclohexyl (3VbcH) and 4,4'-bis(4-propylcyclohexyl) biphenyl (b3CHB) with median concentrations of 101 and 1460 pg m-3, were the predominant LCMs in gaseous and particulate phases, respectively. Composition and concentration of LCMs differed substantially between sampling locations due to the discrepancy in the quantity, types, and brands of electronic devices in each location. Three models were further employed to estimate the gas-particle partitioning of LCMs and compared with the measured data. The results indicated that the HB model exhibited the best overall performance, while the LMY model provided a good fit for LCMs with higher log Koa (>12.48). Monte Carlo simulation was used to estimate and compared the probabilistic daily exposure dose and potential health risks. Inhalation exposure of LCMs was significantly greater than the dermal absorption by approximately 1-2 orders of magnitude, implying that it was the primary exposure route of human exposure to airborne LCMs. However, certain LCMs exhibited comparable or higher exposure levels via the dermal absorption route due to the significant overall permeability coefficient. Furthermore, the particle size was discovered to impact the daily exposure dose, contingent on the particle mass-transfer coefficients and accumulation of LCMs on diverse particle sizes. Although the probabilistic non-carcinogenic risks of LCMs were relatively low, their chronic effects on human beings merit further investigations. Overall, this study provides insights into the contamination and potential health risks of LCMs in indoor environments, underscoring the importance of considering particle sizes and all possible exposure pathways in estimating human health risks caused by airborne organic contaminants.

Aquatic toxicity, ecological effects, human exposure pathways and health risk assessment of liquid crystal monomers

Liquid crystal monomers (LCMs), one of the key materials for liquid crystal displays, have been considered as emerging pollutants in recent years. However, the environmental behaviors of LCMs have not yet been well investigated. The toxicity data of 1173 LCMs were calculated by integrated computational simulation methods in this study. It showed that 64.6% LCMs exhibited PBT (persistent, bioaccumulative, and toxic) properties. Based on the results, 1173 LCMs were identified as molecules possessing the highest level of acute toxicity to aquatic organisms. Among which, and a human health risk priority control list about LCMs was generated in this study, among which 435 were classified as requiring priority control LCMs. It was confirmed that LCMs could eventually accumulate in the human body along the aquatic food chain or penetrate the bloodstream through the dermis, thereby causing harm to health by identifying the exposure pathways of LCMs in humans. Additionally, the electronegativity of the side chain group of LCMs is the main factor causing toxicity differences; therefore, the LCMs containing halogens presented significant acute and chronic toxic effects. This study provided a more comprehensive understanding of LCMs for the public and scientific strategies for controlling LCMs.

Concentration identification and endpoint-oriented health risk assessments on a broad-spectrum of organic compounds in atmospheric fine particles: A sampling experimental study in Beijing, China

Understanding the complicate chemical components in atmospheric fine particulate matter (PM2.5) helps policy makers for pollutants control track progress and identify disparities in overall health risks. However, till now, information on accurate component detection, source identification, and effect-oriented risk assessment is scarce, especially for the simultaneous analysis of a broad-spectrum of compounds. In this study, a high-throughput target method was employed to distinguish the occurrence and characteristics of 152 chemicals: phthalate esters (PAEs), organophosphate esters (OPEs), carboxylic acid esters (CAEs), nitrophenols (NPs), nitrogen heterocyclic compounds (NHCs), per- and poly-fluoroalkyl substances (PFASs), triclosan and its derivatives (TCSs), and organosulfates (OSs) in ambient PM2.5 collected from Beijing, China. Detection frequencies of 77 targeted compounds were >50 %. Total concentrations of all compounds ranged from 33.1 to 745 ng/m3. The median concentration of ∑PAEs (108 ng/m3) was the highest, followed by ∑CAEs (12.2 ng/m3) and ∑NPs (10.1 ng/m3). Organophosphate diesters (di-OPEs) and TCSs were reported for the first time in ambient PM2.5. The pollutants mainly originated from the local industrial production, release of building materials, and environmental degradation of parent compounds. Based on absorption, distribution, metabolism, excretion, and toxicity (ADMET)-oriented risk evaluations, we found that bis (2-ethylhexyl) phthalate, diisobutyl phthalate, dibutyl phthalate, and di (2-ethylhexyl) adipate have high health risks. Additionally, the high oxidative stress potential of 4-nitrocatechol and the strong blood-brain barrier penetration potential of triclosan cannot be ignored. Our study will facilitate the evaluations of specific health outcomes and mechanisms of pollutants, and suggestion of pollutants priority control to reduce human health hazards caused by atmospheric particles.

Methods for the characterisation of dermal uptake: Progress and perspectives for organophosphate esters

Organophosphate esters (OPEs) are a group of pollutants that are widely detected in the environment at high concentrations. They can adversely affect human health through multiple routes of exposure, including dermal uptake. Although attention has been paid to achieving an accurate and complete quantification of the dermal uptake of OPEs, existing evaluation methods and parameters have obvious weaknesses. This study reviewed two main categories of methodologies, namely the relative absorption (RA) model and the permeability coefficient (PC) model, which are widely used to assess the dermal uptake of OPEs. Although the PC model is more accurate and is increasingly used, the most important parameter in this model, the permeability coefficient (Kp), has been poorly characterised for OPEs, resulting in considerable errors in the estimation of the dermal uptake of OPEs. Thus, the detailed in vitro methods for the determination of Kp are summarised and sorted. Furthermore, the commonly used skin membranes are identified and the factors affecting Kp and corresponding mechanisms are discussed. In addition, the experimental conditions, conclusions, and available data on Kp values of the OPEs are thoroughly summarised. Finally, the corresponding knowledge gaps are proposed, and a more accurate and sophisticated experimental system and unknown Kp values for OPEs are suggested.

A physiologically based pharmacokinetic model of diethyl phthalates in humans

Phthalates are a family of industrial and consumer product chemicals, among which diethyl phthalate (DEP) has been widely used. DEP is metabolized into the active metabolite monoethyl phthalate (MEP) and exposure to DEP may induce male reproductive toxicity, developmental toxicity and hepatotoxicity. To better assess the toxicity of DEP and MEP, it is important to understand and predict their internal concentrations, especially in reproductive organs. Here we present a human physiologically based pharmacokinetic (PBPK) model of DEP. Implemented in R, the PBPK model consists of seven tissue compartments, including blood, gut, liver, fat, skin, gonad, and rest of body (RB). In the blood both DEP and MEP partition into free and bound forms, and tissue distribution is considered as blood flow-limited. DEP is metabolized in the gut and liver into MEP which is further glucuronidated and cleared through the urine. The chemical-specific parameters of the model were predicted in silico or estimated based on published human urinary MEP data after exposure to DEP in the air at 250 or 300 μg/m3 for 3 or 6 h through inhalation and dermal absorption. Sensitivity analysis identified important parameters including partition coefficients of DEP for fat, RB, and skin compartments, and the rate constants for glucuronidation of MEP and urinary excretion, with regard to Cmax, area under the curve (AUC), and clearance half-lives of DEP and MEP. A subset of the sensitive parameters was then included in hierarchical population Bayesian Markov chain Monte Carlo (MCMC) simulations to characterize the uncertainty and variability of these parameters. The model is consistent with the notion that dermal absorption represents a significant route of exposure to DEP in ambient air and clothing can be an effective barrier. The developed human PBPK model can be utilized upon further refinement as a quantitative tool for DEP risk assessment.

Reducing Transdermal Uptake of Semivolatile Plasticizers from Indoor Environments: A Clothing Intervention

Models and laboratory studies suggest that everyday clothing influences the transdermal uptake of semivolatile organic compounds, including phthalate plasticizers, from indoor environments. However, this effect has not been documented in environmental exposure settings. In this pilot study, we quantified daily excretion of 17 urinary metabolites (μg/day) for phthalates and phthalate alternatives in nine participants during 5 days. On Day 0, baseline daily excretion was determined in participants' urine. Starting on Day 1, participants refrained from eating phthalate-heavy foods and using personal care products. On Days 3 and 4, participants wore precleaned clothing as an exposure intervention. We observed a reduction in the daily excretion of phthalates during the intervention; mono-n-butyl phthalate, monoisobutyl phthalate (MiBP), and monobenzyl phthalate were significantly reduced by 35, 38, and 56%, respectively. Summed metabolites of di(2-ethylhexyl)phthalate (DEHP) were also reduced (27%; not statistically significant). A similar reduction among phthalate alternatives was not observed. The daily excretion of MiBP during the nonintervention period strongly correlated with indoor air concentrations of diisobutyl phthalate (DiBP), suggesting that inhalation and transdermal uptake of DiBP from the air in homes are dominant exposure pathways. The results indicate that precleaned clothing can significantly reduce environmental exposure to phthalates and phthalate alternatives.

Gas-Phase and Surface-Initiated Reactions of Household Bleach and Terpene-Containing Cleaning Products Yield Chlorination and Oxidation Products Adsorbed onto Indoor Relevant Surfaces

The use of household bleach cleaning products results in emissions of highly oxidative gaseous species, such as hypochlorous acid (HOCl) and chlorine (Cl2). These species readily react with volatile organic compounds (VOCs), such as limonene, one of the most abundant compounds found in indoor enviroments. In this study, reactions of HOCl/Cl2 with limonene in the gas phase and on indoor relevant surfaces were investigated. Using an environmental Teflon chamber, we show that silica (SiO2), a proxy for window glass, and rutile (TiO2), a component of paint and self-cleaning surfaces, act as a reservoir for adsorption of gas-phase products formed between HOCl/Cl2 and limonene. Furthermore, high-resolution mass spectrometry (HRMS) shows that the gas-phase reaction products of HOCl/Cl2 and limonene readily adsorb on both SiO2 and TiO2. Surface-mediated reactions can also occur, leading to the formation of new chlorine- and oxygen-containing products. Transmission Fourier-transform infrared (FTIR) spectroscopy of adsorption and desorption of bleach and terpene oxidation products indicates that these chlorine- and oxygen-containing products strongly adsorb on both SiO2 and TiO2 surfaces for days, providing potential sources of human exposure and sinks for additional heterogeneous reactions.

Cloth-Air Partitioning of Neutral Per- and Polyfluoroalkyl Substances (PFAS) in North Carolina Homes during the Indoor PFAS Assessment (IPA) Campaign

Partitioning of per- and polyfluoroalkyl substances (PFAS) to indoor materials, including clothing, may prolong the residence time of PFAS indoors and contribute to exposure. During the Indoor PFAS Assessment (IPA) Campaign, we measured concentrations of nine neutral PFAS in air and cotton cloth in 11 homes in North Carolina, for up to 9 months. Fluorotelomer alcohols (i.e., 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH) are the dominant target species in indoor air, with concentrations ranging from 1.8 to 49 ng m-3, 1.2 to 53 ng m-3, and 0.21 to 5.7 ng m-3, respectively. In cloth, perfluorooctane sulfonamidoethanols (i.e., MeFOSE and EtFOSE) accumulated most significantly over time, reaching concentrations of up to 0.26 ng cm-2 and 0.24 ng cm-2, respectively. From paired measurements of neutral PFAS in air and suspended cloth, we derived cloth-air partition coefficients (Kca) for 6:2, 8:2, and 10:2 FTOH; ethylperfluorooctane sulfonamide (EtFOSA); MeFOSE; and EtFOSE. Mean log(Kca) values range from 4.7 to 6.6 and are positively correlated with the octanol-air partition coefficient. We investigated the effect of the cloth storage method on PFAS accumulation and the influence of home characteristics on air concentrations. Temperature had the overall greatest effect. This study provides valuable insights into PFAS distribution, fate, and exposure indoors.

Ozone Loss: A Surrogate for the Indoor Concentration of Ozone-Derived Products

Ozone concentrations tend to be substantially lower indoors than outdoors, largely because of ozone reactions with indoor surfaces. When there are no indoor sources of ozone, a common condition, the net concentration of gaseous products derived from indoor ozone chemistry scales linearly with the difference between outdoor and indoor ozone concentrations, termed "ozone loss." As such, ozone loss is a metric that might be used by epidemiologists to disentangle the adverse health effects of ozone's oxidation products from those of exposure to ozone itself. The present paper examines the characteristics, potential utility, and limitations of the ozone loss concept. We show that for commonly occurring indoor conditions, the ozone loss concentration is directly proportional to the total rate constant for ozone removal on surfaces (ksum) and inversely proportional to the net removal of ozone by air exchange (λ) plus surface reactions (ksum). It follows that the ratio of indoor ozone to ozone loss is equal to the ratio of λ to ksum. Ozone loss is a promising metric for probing potential adverse health effects resulting from exposures to products of indoor ozone chemistry. Notwithstanding its virtues, practitioners using it should be mindful of the limitations discussed in this paper.

Characterization of chemical transport in human skin and building material

Volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) are ubiquitous in indoor environment. They can emit from source into air, and subsequently penetrate human skin into blood through dermal uptake, causing adverse health effects. This study develops a two-layer analytical model to characterize the VOC/SVOC dermal uptake process, which is then extended to predict VOC emissions from two-layer building materials or furniture. Based on the model, the key transport parameters of chemicals in every skin or material layer are determined via a hybrid optimization method using data from experiments and literature. The measured key parameters of SVOCs for dermal uptake are more accurate than those from previous studies using empirical correlations. Moreover, the association between the absorption amount of studied chemicals into blood and age is preliminarily investigated. Further exposure analysis reveals that the contribution of dermal uptake to the total exposure can be comparable with that of inhalation for the examined SVOCs. This study makes the first attempt to accurately determine the key parameters of chemicals in skin, which is demonstrated to be critical for health risk assessment.

Co-occurrence and distribution of organophosphate tri- and di-esters in dust and hand wipes from an e-waste dismantling plant in central China

Electronic waste (e-waste) dismantling facilities are a well-known source of emerging contaminants including organophosphate esters (OPEs). However, little information is available regarding the release characteristics and co-contaminations of tri- and di-esters. This study, therefore, investigated a broad range of tri- and di-OPEs in dust and hand wipe samples collected from an e-waste dismantling plant and homes as comparison. The median ∑tri-OPE and ∑di-OPE levels in dust and hand wipe samples were approximately 7- and 2-fold higher than those in the comparison group, respectively (p < 0.01). Triphenyl phosphate (median: 11,700 ng/g and 4640 ng/m²) and bis(2-ethylhexyl) phosphate (median: 5130 ng/g and 940 ng/m²) were the dominant components of tri- and di-OPEs, respectively. The combination of Spearman rank correlations and the determinations of molar concentration ratios of di-OPEs to tri- OPEs revealed that apart from the degradation of tri-OPEs, di-OPEs could originate from direct commercial application, or as impurities in tri-OPE formulas. Significant positive correlations (p < 0.05) were found for most tri- and di-OPE levels between the dust and hand wipes from dismantling workers, whereas this was not observed in those from the ordinary microenvironment. Our results provide robust evidence that e-waste dismantling activities contribute to OPEs contamination in the surroundings and further human exposure pathways and toxicokinetics are needed to be elucidated.

Evaluating Neutral PFAS for Potential Dermal Absorption from the Gas Phase

Exposures to per- and polyfluoroalkyl substances (PFAS) are of increasing concern. Assessments typically focus only on ingestion and inhalation exposure due to a lack of generally accepted approaches for estimating dermal absorption. Prior work indicates limited dermal absorption of ionic PFAS, but absorption of neutral PFAS has not been examined from the liquid vehicle or from vapor. Partitioning of semivolatile organic compounds from the gas phase to the skin surface (i.e., stratum corneum) is well known, but the potential for partitioning of neutral PFAS from the gas phase to the stratum corneum has yet to be estimated. The SPARC-estimated physicochemical properties were used to calculate transdermal permeability coefficients (k_{p_g}) and dermal-to-inhalation (D/I) exposure ratios for two groups of neutral PFAS, including those on a U.S. Environmental Protection Agency PFAS list. 11 neutral PFAS gave calculated D/I ratios >5, indicating that direct transdermal absorption may be an important exposure pathway compared to inhalation. Data on consumer products or indoor air is needed for the 11 neutral PFAS, followed by possible biomonitoring to experimentally verify dermal absorption from air. Additional PFAS should be estimated by the protocol used here as they are identified in commercial products.

Seasonal variations of airborne phthalates and novel non-phthalate plasticizers in a test residence in cold regions: Effects of temperature, humidity, total suspended particulate matter, and sources

As a class of plasticizers widely used in consumer products, some phthalate esters (PAEs) have been restricted due to their adverse health effects and ubiquitous presence, leading to the introduction of alternative non-phthalates plasticizers (NPPs) to the market. However, few studies focus on the influence of environmental parameters on the presence of these plasticizers and the potential human health risks for people living in poorly ventilated indoor spaces in cold regions. We investigated the trends of PAEs and NPPs in air in a typical indoor residence in northern China for over one year. The air concentrations of PAEs were significantly higher than those of NPPs (p < 0.05), indicating that PAEs are still the dominant plasticizers currently being used in the studied residence. PAEs showed seasonal fluctuation patterns of the highest levels found in summer and autumn. The temperature and relative humidity dependence for most PAEs and NPPs decreased with decreasing vapor pressure. Concentrations of the high molecular weight NPPs and PAEs positively correlated with total suspended particles (TSP). It is worth noting that the peak concentrations of PAEs and NPPs were found when the haze occurred in autumn. Principal component analysis (PCA) suggested the diverse applications of PAEs and NPPs in the indoor environment. The hazard index (HI) values observed in this study were all below international guidelines (<1); however, the average carcinogenic risk (CR) values for some compounds exceeded acceptable levels (One in a million), which raised concerns about the possibility of carcinogenicity for people living indoors for long periods of time in cold regions.

Metabolic profiling of the fluorinated liquid-crystal monomer 1-ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene

1-Ethoxy-2,3-difluoro-4-(trans-4-propylcyclohexyl)benzene (EDPrB) is a typical fluorinated liquid-crystal monomer (LCM). LCMs contaminants are becoming increasingly concerning due to their potential persistence, bioaccumulation, toxicity, and broad prevalence in environmental and human samples. However, LCM metabolism is poorly understood. Herein, by introducing selected EDPrB into the appropriate liver microsomes in vitro, we examined the metabolic pathways of LCM in humans, rats, pigs, Cyprinus carpio, crucian carp, and Channa argus. A total of 20 species-dependent metabolites were identified and structurally elucidated by gas and liquid chromatography-high resolution mass spectrometry for the first time. Dealkylation, H-abstraction, and hydroxylation reactions are the primary metabolic pathways. Half of these in vitro metabolites were found in the urine, serum, and fecal samples of Sprague-Dawley rats exposed to EDPrB. Toxicity predictions indicate that 17 metabolites can be classified as toxic. According to the Ecological Structure Activity Relationships (ECOSAR), a number of metabolites exhibit equivalent or greater aquatic toxicity to that of EDPrB. Toxicity Estimation Software Tool (T.E.S.T.) predicts that some metabolites exhibit developmental toxicity and mutagenicity in rats. These findings suggest that biotransformation should be particularly emphasized, and more toxicological and monitoring studies should be performed to assess the ecological and human safety of LCMs.

Endocrine-Disrupting Chemicals and Their Effects in Pet Dogs and Cats: An Overview

Over the past few decades, several pollutants classified as environmental endocrine-disrupting chemicals (EDCs) have become a matter of significant public health concern. Companion animals play a major role in human society, and pet ownership is substantially increasing worldwide. These intimate human-pet relationships imply sharing much of the same environment, thus including exposure to similar levels of EDCs in daily routine. Here, we review the current knowledge on the sources and routes of exposure to EDCs in domestic indoor and outdoor environments and discuss whether endocrine disruption is a health concern in pets. We summarize the phenomenon of endocrine disruption, providing examples of EDCs with a known impact on dog and cat health. Then, we propose an overview of the literature on the adverse effects of EDCs in domestic pets, with a special focus on the health of reproductive and thyroid systems. Finally, we explore the potential role of companion animals as unintentional sentinels of environmental exposure to EDCs and the implications for public health risk assessment in a "shared risk" scenario. Overall, this review supports the need for an integrated approach considering humans, animals, and the environment as a whole for a comprehensive assessment of the impact of EDCs on human and animal health.

Inhalation and dermal absorption as dominant pathways of PCB exposure for residents of contaminated apartment buildings

Applications of polychlorinated biphenyls (PCBs) in buildings and their persistence in indoor environments have led to cases of current and highly elevated exposure in humans, despite the global cease of production decades ago. Personal exposure to PCBs was assessed among residents in a social housing estate in Denmark containing both contaminated (n = 67) and non-contaminated (n = 23) apartments. Samples and estimated daily intakes (EDIs) were assessed for 15 PCB congeners, and body burden, which was limited by the dietary data availability, was compared across 7 indicator PCBs, with its sum (PCB_sum7) often applied in European regulation of PCBs. Median PCB_sum7 EDI across measured pathways for exposed residents was 101 ng· (kg bodyweight)^-1· day^-1, with the majority of exposure (60%) coming from inhalation of contaminated indoor air. Calculated from both PCBs measured in indoor air and on hand wipes, dermal absorption estimates showed comparable results and served as a secondary exposure pathway, accounting for 35% of personal exposure and considering selected assumptions and sources of physical-chemical parameters. Estimates revealed that diet was the primary PCB source among the reference group, accounting for over 75% of the PCB_sum7 EDI across exposure routes. When evaluating overall EDIs across the two study groups and including dietary estimates, PCB exposure among exposed residents was around 10 times higher than the reference group. Solely within the exposed population, pathway-specific body burdens were calculated to account for exposure across years of residence in contaminated apartments, where lower chlorinated PCBs were dominant in indoor air. Among these dominant congeners, estimated body burdens of PCB-28 and -52 were significantly correlated with measured serum (r_s = 0.49, 0.45; p < 0.001). This study demonstrates that inhalation and dermal absorption serve as dominant exposure pathways for residents of apartments contaminated with predominantly lower chlorinated PCBs and suggest that predictions of body burden from indoor environment measurements may be comparable to measured serum PCBs.

Distribution of flame retardants among indoor dust, airborne particles and vapour phase from Beijing: spatial-temporal variation and human exposure characteristics

The occurrence and distribution of 10 brominated flame retardants (BFRs) and 10 organophosphate flame retardants (OPFRs) were investigated in indoor dust, total suspended particles (TSP), and vapour phase from offices (n = 10), homes (n = 9), and day-care centres (n = 10) in Beijing, China. Three types of samples were collected biweekly from one office and one home over a year to examine temporal trends. BFRs in dust significantly correlated with those in TSP, while OPFRs significantly correlated among all three matrices. In addition, BFRs in dust (ng/g) and TSP (pg/m³) exhibited similar temporal trends with higher levels in the cold season, whereas OPFRs in TSP and vapour phase (pg/m³) showed similar temporal trends with higher levels in the warm season. The geometric mean concentrations of BFRs and OPFRs in the three matrices from the above mentioned three types of indoor microenvironments were used for exposure and health risk estimation, and ∑₇OPFRs showed much higher hazard index (HI) values than ∑₁₀BFRs for all subpopulations, and inhalation of OPFRs was a major risk source. With the volatility of flame retardants (FRs) decreasing, the contribution of dust ingestion and dermal absorption showed an increasing trend, and the contribution of inhalation exhibited a gradual decreasing trend, which implied the dominant exposure pathway to FRs is strongly related to the vapour pressure (25 °C, Pa) of these substances. Using a single type of microenvironment or the collection of samples at a single point in time can lead to overestimation or underestimation of overall exposure and risk for people to some extent. The correlations of FRs in dust, TSP, and vapour phase from indoor microenvironments, as well as their temporal trends were first reported in this study, which will provide a basis for more accurate FR exposure assessments in the future.

Partition of phthalates among air, PM2 .5 , house dust and skin in residential indoor environments

As a group of typical endocrine disrupters, phthalates are simultaneously present in a variety of environmental media and enter human body through multiple exposure pathways. In this study, field monitoring data were used to characterize the skin-air (K_lg ), dust-air (K_d ), and PM_2.5 -air (K_p ) partition coefficients of DiBP, DnBP, and DEHP. The median values of log(K_lg ) in the summer and winter were 7.654 and 7.932, 7.265 and 7.902, 9.419 and 9.015 for DiBP, DnBP, and DEHP, respectively, and K_lg was significantly higher in the winter. The median K_d (m³ /mg) in the summer (0.036-0.151 for DiBP, 0.021-0.036 for DnBP and 1.479-4.069 for DEHP) were significantly higher than the counterparts in the winter (0.027-0.065 for DiBP, 0.022-0.245 for DnBP, and 0.140-3.250 for DEHP). In addition, K_d was associated with material of surface and residence time of dust. The K_p values (m³ /μg) of DiBP, DnBP, and DEHP in the summer (0.053, 0.015, and 0.021) were also significantly higher than the counterparts in the winter (0.011, 0.004, and 0.025). The partition of phthalates was influenced by built environment, such as temperature, humidity, ventilation, indoor chemistry, smoking, and building age. Except K_lg , there was substantial discrepancy between the estimates of K with empirical equations and the values of K based on field monitoring data in our study.

A novel set of volatile urinary biomarkers for late-life major depressive and anxiety disorders upon the progression of frailty: a pilot study

Mood and anxiety disorders are frequent in the elderly and increase the risk of frailty. This study aimed to identify novel biomarkers of major depressive disorder (MDD) and anxiety in the elderly. We examined 639 participants in the community-dwelling Otassha Study (518 individuals considered healthy control, 77 with depression, anxiety, etc.), mean age 75 years, 58.4% of female. After exclusion criteria, we analyzed VOCs from 18 individuals (9 healthy control, 9 of MDD/agoraphobia case). Urinary volatile and semi-volatile organic compounds (VOCs) were profiled using solid-phase microextraction and gas chromatography-mass spectrometry. Six urinary VOCs differed in the absolute area of the base peak between participants with MDD and/or agoraphobia and controls. High area under the receiver-operating characteristic curve (AUC) values were found for phenethyl isothiocyanate (AUC: 0.86, p = 0.009), hexanoic acid (AUC: 0.85, p = 0.012), texanol (AUC: 0.99, p = 0.0005), and texanol isomer (AUC: 0.89, p = 0.005). The combined indices of dimethyl sulfone, phenethyl isothiocyanate, and hexanoic acid, and texanol and texanol isomer showed AUCs of 0.91 (p = 0.003) and 0.99 (p = 0.0005) and correlated with the GRID-HAMD and the Kihon Checklist (CL score), respectively. These VOCs may be valuable biomarkers for evaluating MDD and/or agoraphobia in the elderly.

Thirdhand Exposures to Tobacco-Specific Nitrosamines through Inhalation, Dust Ingestion, Dermal Uptake, and Epidermal Chemistry

Tobacco-specific nitrosamines (TSNAs) are emitted during smoking and form indoors by nitrosation of nicotine. Two of them, N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), are human carcinogens with No Significant Risk Levels (NSRLs) of 500 and 14 ng day^-1, respectively. Another TSNA, 4-(methylnitrosamino)-4-(3-pyridyl) butanal (NNA), shows genotoxic and mutagenic activity in vitro. Here, we present additional evidence of genotoxicity of NNA, an assessment of TSNA dermal uptake, and predicted exposure risks through different pathways. Dermal uptake was investigated by evaluating the penetration of NNK and nicotine through mice skin. Comparable mouse urine metabolite profiles suggested that both compounds were absorbed and metabolized via similar mechanisms. We then investigated the effects of skin constituents on the reaction of adsorbed nicotine with nitrous acid (epidermal chemistry). Higher TSNA concentrations were formed on cellulose and cotton substrates that were precoated with human skin oils and sweat compared to clean substrates. These results were combined with reported air, dust, and surface concentrations to assess NNK intake. Five different exposure pathways exceeded the NSRL under realistic scenarios, including inhalation, dust ingestion, direct dermal contact, gas-to-skin deposition, and epidermal nitrosation of nicotine. These results illustrate potential long-term health risks for nonsmokers in homes contaminated with thirdhand tobacco smoke.

Characterizing firefighter's exposure to over 130 SVOCs using silicone wristbands: A pilot study comparing on-duty and off-duty exposures

Firefighters are occupationally exposed to an array of hazardous chemicals, and these exposures have been linked to the higher rates of some cancer in firefighters. However, additional research that characterizes firefighters' exposure is needed to fully elucidate the impacts on health risks. In this pilot study, we used silicone wristbands to quantify off-duty and on-duty chemical exposures experienced by 20 firefighters in Durham, North Carolina. By using each firefighter's off-duty wristband to represent individual baseline exposures, we assessed occupation-related exposures (i.e. on-duty exposures). We also investigated the influence of responding to a fire event while on-duty. In total, 134 chemicals were quantified using both GC-MS and LC-MS/MS targeted methods. Seventy-one chemicals were detected in at least 50% of all silicone wristbands, including 7 PFAS, which to our knowledge, have not been reported in wristbands previously. Of these, phthalates were generally measured at the highest concentrations, followed by brominated flame retardants (BFRs) and organophosphate esters (OPEs). PFAS were measured at lower concentrations overall, but firefighter PFOS exposures while on-duty and responding to fires were 2.5 times higher than off-duty exposures. Exposure to polycyclic aromatic hydrocarbons (PAH), BFRs, and some OPEs were occupationally associated, with firefighters experiencing 0.5 to 8.5 times higher exposure while on-duty as compared to off-duty. PAH exposures were also higher for firefighters who respond to a fire than those who did not while on-duty. Additional research with a larger population of firefighters that builds upon this pilot investigation may further pinpoint exposure sources that may contribute to firefighters' risk for cancer, such as those from firefighter gear or directly from fires. This research demonstrates the utility of using silicone wristbands to quantify occupational exposure in firefighters and the ability to disentangle exposures that may be specific to fire events as opposed to other sources that firefighters might experience.

Indoor Secondary Pollutants Cannot Be Ignored: Third-Hand Smoke

Smoking has been recognized by the World Health Organization (WHO) as the fifth highest threat to humanity. Smoking, a leading disease promoter, is a major risk factor for non-communicable diseases (NCDs) such as cancer, cardiovascular disease, diabetes, and chronic respiratory diseases. NCDs account for 63% of all deaths worldwide. Passive smoking is also a health risk. Globally, more than a third of all people are regularly exposed to harmful smoke. Air pollution is a common global problem in which pollutants emitted into the atmosphere undergo a series of physical or chemical reactions to produce various oxidation products, which are often referred to as secondary pollutants. Secondary pollutants include ozone (O₃), sulfur trioxide (SO₃), nitrogen dioxide (NO₂), and respirable particulate matter (PM). It is worth mentioning that third-hand smoke (THS), formed by the reaction of nicotine with second-hand smoke (SHS) caused by indoor O₃ or nitrous acid (HONO), is a major indoor secondary pollutant that cannot be ignored. As a form of indoor air pollution that is relatively difficult to avoid, THS exists in any corner of the environment where smokers live. In this paper, we summarize the important research progress on the main components, detection, and toxicity of THS and look forward to future research directions. Scientific understanding of THS and its hazards will facilitate smoking bans in indoor and public places and raise public concern for how to prevent and remove THS.

Recognition and Health Impacts of Organic Pollutants with Significantly Different Proportions in the Gas Phase and Size-Fractionated Particulate Phase in Ambient Air

The distributions of organic pollutants in the gas phase and size-fractionated particle phases can largely affect human health risks posed by them. Gas-particle partitioning and particle-size distributions of some known pollutants have been investigated. However, the pollutants which are more likely to enter the human body and cause strong adverse effects may be neglected. In this study, a nontargeted screening approach combining comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry and chemometrics was developed. Eighty-eight compounds with markedly different proportions in the gas phase and PM₁, as well as 50 contaminants with significant differences in PM₁ and particles with diameters of 1-2.5 μm, were identified. Of these compounds, 18 were found in the air for the first time. There were obvious discrepancies between the measured and predicted gas-particle partitioning coefficients for some pollutants, suggesting unexpected environmental fates and health risks. The human daily intakes through inhalation and dermal exposure to these pollutants were estimated with the International Commission on Radiological Protection deposition model and transdermal permeability model. A risk-based prioritization was performed. The results indicated that adverse effects posed by 9H-fluoren-9-one, 2-ethylhexyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, p-cumenol, 2,4-diisocyanato-1-methyl-benzene, bis(2-ethylhexyl) phthalate, perylene, (E)-cinnamaldehyde, 4-methyl-2-nitro-phenol, benzoic acid, and bis(2-methylpropyl) ester hexanedioic acid in ambient air may be more severe than those posed by conventionally monitored pollutants. The findings would facilitate raising concerns about these pollutants before they cause further severe and widespread impacts.

A holistic modeling framework for estimating the influence of climate change on indoor air quality

The IPCC 2021 report predicts rising global temperatures and more frequent extreme weather events in the future, which will have different effects on the regional climate and concentrations of ambient air pollutants. Consequently, changes in heat and mass transfer between the inside and outside of buildings will also have an increasing impact on indoor air quality. It is therefore surprising that indoor spaces and occupant well-being still play a subordinate role in the studies of climate change. To increase awareness for this topic, the Indoor Air Quality Climate Change (IAQCC) model system was developed, which allows short and long-term predictions of the indoor climate with respect to outdoor conditions. The IAQCC is a holistic model that combines different scenarios in the form of submodels: building physics, indoor emissions, chemical-physical reaction and transformation, mold growth, and indoor exposure. IAQCC allows simulation of indoor gas and particle concentrations with outdoor influences, indoor materials and activity emissions, particle deposition and coagulation, gas reactions, and SVOC partitioning. These key processes are fundamentally linked to temperature and relative humidity. With the aid of the building physics model, the indoor temperature and humidity, and pollutant transport in building zones can be simulated. The exposure model refers to the calculated concentrations and provides evaluations of indoor thermal comfort and exposure to gaseous, particulate, and microbial pollutants.

Modeling di (2-ethylhexyl) Phthalate (DEHP) and Its Metabolism in a Body's Organs and Tissues through Different Intake Pathways into Human Body

Phthalate esters (PAEs) are ubiquitous in indoor environments as plasticizers in indoor products. Residences are often exposed to indoor PAEs in the form of gas, particles, settled dust, and surface phases. To reveal the mechanism behind the accumulation of PAEs in different tissues or organs such as the liver and the lungs when a person exposed to indoor PAEs with different phases, a whole-body physiologically based pharmacokinetic model for PAEs is employed to characterize the dynamic process of phthalates by different intake pathways, including oral digestion, dermal adsorption, and inhalation. Among three different intake pathways, dermal penetration distributed the greatest accumulation of DEHP in most of the organs, while the accumulative concentration through oral ingestion was an order of magnitude lower than the other two doses. Based on the estimated parameters, the variation of di-ethylhexyl phthalate (DEHP) and mono (2-ethylhexyl) phthalate (MEHP) concentration in the venous blood, urine, the liver, the thymus, the pancreas, the spleen, the lungs, the brain, the heart, and the kidney for different intake scenarios was simulated. The simulated results showed a different accumulation profile of DEHP and MEHP in different organs and tissues and demonstrated that the different intake pathways will result in different accumulation distributions of DEHP and MEHP in organs and tissues and may lead to different detrimental health outcomes.

Temperature and indoor environments

From the thermodynamic perspective, the term temperature is clearly defined for ideal physical systems: A unique temperature can be assigned to each black body via its radiation spectrum, and the temperature of an ideal gas is given by the velocity distribution of the molecules. While the indoor environment is not an ideal system, fundamental physical and chemical processes, such as diffusion, partitioning equilibria, and chemical reactions, are predictably temperature-dependent. For example, the logarithm of reaction rate and equilibria constants are proportional to the reciprocal of the absolute temperature. It is therefore possible to have non-linear, very steep changes in chemical phenomena over a relatively small temperature range. On the contrary, transport processes are more influenced by spatial temperature, momentum, and pressure gradients as well as by the density, porosity, and composition of indoor materials. Consequently, emergent phenomena, such as emission rates or dynamic air concentrations, can be the result of complex temperature-dependent relationships that require a more empirical approach. Indoor environmental conditions are further influenced by the thermal comfort needs of occupants. Not only do occupants have to create thermal conditions that serve to maintain their core body temperature, which is usually accomplished by wearing appropriate clothing, but also the surroundings must be adapted so that they feel comfortable. This includes the interaction of the living space with the ambient environment, which can vary greatly by region and season. Design of houses, apartments, commercial buildings, and schools is generally utility and comfort driven, requiring an appropriate energy balance, sometimes considering ventilation but rarely including the impact of temperature on indoor contaminant levels. In our article, we start with a review of fundamental thermodynamic variables and discuss their influence on typical indoor processes. Then, we describe the heat balance of people in their thermal environment. An extensive literature study is devoted to the thermal conditions in buildings, the temperature-dependent release of indoor pollutants from materials and their distribution in the various interior compartments as well as aspects of indoor chemistry. Finally, we assess the need to consider temperature holistically with regard to the changes to be expected as a result of global emergencies such as climate change.

Emission Rates of Volatile Organic Compounds from Humans

Human-emitted volatile organic compounds (VOCs) are mainly from breath and the skin. In this study, we continuously measured VOCs in a stainless-steel environmentally controlled climate chamber (22.5 m³, air change rate at 3.2 h^-1) occupied by four seated human volunteers using proton transfer reaction time-of-flight mass spectrometry and gas chromatography mass spectrometry. Experiments with human whole body, breath-only, and dermal-only emissions were performed under ozone-free and ozone-present conditions. In addition, the effect of temperature, relative humidity, clothing type, and age was investigated for whole-body emissions. Without ozone, the whole-body total emission rate (ER) was 2180 ± 620 μg h^-1 per person (p^-1), dominated by exhaled chemicals. The ERs of oxygenated VOCs were positively correlated with the enthalpy of the air. Under ozone-present conditions (∼37 ppb), the whole-body total ER doubled, with the increase mainly driven by VOCs resulting from skin surface lipids/ozone reactions, which increased with relative humidity. Long clothing (more covered skin) was found to reduce the total ERs but enhanced certain chemicals related to the clothing. The ERs of VOCs derived from this study provide a valuable data set of human emissions under various conditions and can be used in models to better predict indoor air quality, especially for highly occupied environments.

Gas-particle partition and size-segregated distribution of flame retardants in indoor and outdoor air: Reevaluation on the role of fine particles in human exposure

In this study, we investigated the distribution of brominated and organophosphate flame retardants (BFRs and OPFRs) in the paired gaseous and nine size-segregated particulate samples collected from 8 typical indoor compartments and monthly outdoor in Xinxiang, China, respectively. For the indoor environments, total concentrations of FRs (Σ₁₉FRs) in bulk air ranged from 3.9 ng/m³ to 37.5 ng/m³, with that in children recreation center (37.5 ng/m³) and furniture store (28.7 ng/m³) showing highest levels. In the outdoor air, Σ₁₉FRs ranged from 3.1 ng/m³ to 13.6 ng/m³ among the 12 months, with that from late spring and summer being the highest. OPFRs had higher concentration than BFRs, with the total concentration of OPFRs accounting for 77%-99% of ∑₁₉FRs. TCIPP (tris(chloroiso-propyl) phosphate), TCEP (tris(2-chloroethyl) phosphate), TEP (triethyl phosphate) and DBDPE (decabromodiphenyl ethane), BDE-209 (decabromodiphenyl ether) were the predominant analogs. Specifically, BFRs tended to enrich in gas phase indoors and coarse particles (aerodynamic diameters >3.3 μm) outdoors, but OPFRs mainly distributed in coarse particles both indoors and outdoors. The size distribution patterns varied among FRs, with the higher volatile FRs (e.g., TCEP, TCIPP) distributed more uniformly across particulate size. Although the distribution patterns of FRs in air were driven by multiple factors, organic carbon and element carbon in particulate matter had an influence to a certain extent. Health risks from exposure to FRs were characterized via the hazard quotient approaches. The total noncarcinogenic risks of ∑₁₆FRs from inhalation were higher than that from air to skin transport, and the risks resulted from coarse particle-bound ∑₁₆FRs (>3.3 μm) and gas phase were both significantly higher than that from fine fraction (<3.3 μm) in all scenarios, implying that FRs in coarse particles should not be underestimated.

Occupational Exposure of Canadian Nail Salon Workers to Plasticizers Including Phthalates and Organophosphate Esters

Personal exposure of nail salon workers to 10 phthalates and 19 organophosphate esters (OPEs) was assessed in 18 nail salons in Toronto, Canada. Active air samplers (n = 60) and silicone passive samplers, including brooches (n = 58) and wristbands (n = 60), were worn by 45 nail salon workers for ∼8 working hours. Diethyl phthalate (median = 471 ng m^-3) and diisobutyl phthalate (337 ng m^-3) were highest in active air samplers. Most abundant OPEs in active air samplers were tris(2-chloroisopropyl)phosphate or TCIPP (303 ng m^-3) and tris(2-chloroethyl)phosphate or TCEP (139 ng m^-3), which are used as flame retardants but have not been reported for use in personal care products or nail salon accessories. Air concentrations of phthalates and OPEs were not associated with the number of services performed during each worker's shift. Within a single work shift, a combined total of 16 (55%) phthalates and OPEs were detected on passive silicone brooches; 19 (66%) were detected on wristbands. Levels of tris(2-chloroisopropyl)phosphate, tris(1,3-dichloro-2-propyl)phosphate or TDCIPP, and triphenyl phosphate or TPhP wristbands were significantly higher than those worn by e-waste workers. Significant correlations (p < 0.05) were found between the levels of some phthalates and OPEs in silicone brooches and wristbands versus those in active air samplers. Stronger correlations were observed between active air samplers versus brooches than wristbands. Sampler characteristics, personal characteristics, and chemical emission sources are the three main factors proposed to influence the use of passive samplers for measuring semi-volatile organic compound exposure.

Electronic-Waste-Driven Pollution of Liquid Crystal Monomers: Environmental Occurrence and Human Exposure in Recycling Industrial Parks

Liquid crystal monomers (LCMs) in liquid crystal displays (LCDs) may be released into the environment, especially in electronic waste (e-waste) recycling industrial parks with a high pollution risk. However, little has been known about the environmental release and human exposure to LCMs until now. Herein, a total of 45 LCMs were detected in LCDs of commonly used smartphones and computers by high-resolution mass spectrometry with suspect screening analysis. Fluorinated biphenyls and their analogs were the dominant LCMs. Based on available standards of the screening results and previous studies, 55 LCMs were quantified in samples from an e-waste recycling industrial park in Central China. The LCMs were frequently detected in outdoor dust (n = 43), workshop #1 indoor dust (n = 53), and hand (n = 43) and forehead wipes (n = 43), with median concentrations of 6950 ng/g, 67,400 ng/g, 46,100 ng/m², and 62,100 ng/m², respectively. The median estimated daily intake values of the LCMs via dust ingestion and dermal absorption were 48.3 and 16.5 ng/kg body weight/day, respectively, indicating a high occupational exposure risk of these compounds. In addition, 16 LCMs were detected in the serum of eight elderly people (≥60 years old) with over 5 years of experience in e-waste dismantling operations, resulting in a total concentration range of 3.9-26.3 ng/mL.

Disposition of Fluorine on New Firefighter Turnout Gear

Firefighter turnout gear is essential for reducing occupational exposure to hazardous chemicals during training and fire events. Per-and polyfluoroalkyl substances (PFASs) are observed in firefighter serum, and possible occupational sources include the air and dust of fires, aqueous film-forming foam, and turnout gear. Limited data exist for nonvolatile and volatile PFASs on firefighter turnout gear and the disposition of fluorine on the individual layers of turnout gear. Further implications for exposure to fluorine on turnout gear are not well understood. Three unused turnout garments purchased in 2019 and one purchased in 2008, were analyzed for 50 nonvolatile and 15 volatile PFASs by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-qTOF-MS) and gas chromatography-mass spectrometry (GC-MS), respectively. Particle-induced gamma ray emission (PIGE), a surface technique, and instrumental neutron activation analysis (INAA), a bulk technique, were used to measure total fluorine. Bulk characterization of the layers by pyrolysis-GC/MS (py-GC/MS) was used to differentiate fluoropolymer (e.g., PTFE) films from textile layers finished with side-chain polymers. The outer layer, moisture barrier, and thermal layers of the turnout gear all yielded measured concentrations of volatile PFASs that exceeded nonvolatile PFAS concentrations, but the summed molar concentrations made up only a small fraction of total fluorine (0.0016-6.7%). Moisture barrier layers comprised a PTFE film, as determined by py-GC-MS, and gave the highest individual nonvolatile (0.159 mg F/kg) and volatile PFAS (20.7 mg F/kg) as well as total fluorine (122,000 mg F/kg) concentrations. Outer and thermal layers comprised aromatic polyamide-based fibers (aramid) treated with side-chain fluoropolymers and had lower levels of individual nonvolatile and volatile PFASs. Equal concentrations of total fluorine by both PIGE and INAA on the outer and thermal layers is consistent with treatment with a side-chain fluoropolymer coating. New turnout gear should be examined as a potential source of firefighter occupational exposure to nonvolatile and volatile PFASs in future assessments.

Quantum Chemical Calculation and Evaluation of Partition Coefficients for Classical and Emerging Environmentally Relevant Organic Compounds

Octanol/water (K_OW), octanol/air (K_OA), and hexadecane/air (K_HdA) partition coefficients are calculated for 67 organic compounds of environmental concern using computational chemistry. The extended CRENSO workflow applied here includes the calculation of extensive conformer ensembles with semiempirical methods and refinement through density functional theory, taking into account solvation models, especially COSMO-RS, and thermostatistical contributions. This approach is particularly advantageous for describing large and nonrigid molecules. With regard to K_OW and K_HdA, one can refer to many experimental data from direct and indirect measurement methods, and very good matches with results from our quantum chemical workflow are evident. In the case of the K_OA values, however, good matches are only obtained for the experimentally determined values. Larger systematic deviations between data computed here and available, nonexperimental quantitative structure-activity relationship literature data occur in particular for phthalic acid esters and organophosphate esters. From a critical analysis of the coefficients calculated in this work and comparison with available literature data, we conclude that the presented quantum chemical composite approach is the most powerful so far for calculating reliable partition coefficients because all physical contributions to the conformational free energy are considered and the structure ensembles for the two phases are generated independently and consistently.

Emerging investigator series: the role of chemical properties in human exposure to environmental chemicals

One of the ultimate goals of environmental exposure science is to mechanistically understand how chemical properties and human behavior interactively determine human exposure to the wide spectrum of chemicals present in the environment. This comprehensive review assembles state-of-the-art knowledge of the role of partitioning, dissociation, mass transfer, and reactive properties in human contact with and absorption of organic chemicals via oral, dermal, and respiratory routes. Existing studies have revealed that chemicals with different properties vary greatly in mass distribution and occurrence among multiple exposure media, resulting in distinct patterns of human intake from the environment. On the other hand, these chemicals encounter different levels of resistance in the passage of intestinal, dermal, and pulmonary absorption barriers and demonstrate different levels of bioavailability, due to the selectivity of biochemical, anatomical and physiological structures of these absorption barriers. Moving forward, the research community needs to gain more in-depth mechanistic insights into the complex processes in human exposure, advance the technique to better characterize and predict chemical properties, generate and leverage experimental data for a more diverse range of chemicals, and describe better the interactions between chemical properties and human behavior.

Measurement of size-segregated airborne particulate bound polycyclic aromatic compounds and assessment of their human health impacts - A case study in a megacity of southwest China

Particle size distribution of particulate polycyclic aromatic compounds (PACs) is one of the important factors controlling human exposure to PACs in air. In this study, size-segregated airborne particle samples were collected in a megacity in southwest China to analyze PACs concentrations and evaluate related health risks. Annual average concentrations of Σ₁₉PAHs (polycyclic aromatic hydrocarbons, 17.4 ng/m³) and Σ₁₀OPAHs (oxygenated PAHs, 15.3 ng/m³) were one order of magnitude higher than those of Σ₉MPAHs (methyl PAHs, 0.97 ng/m³) and Σ₂₇NPAHs (nitrated PAHs, 1.54 ng/m³). More than 55% of PACs masses were associated with fine particles (aerodynamic diameter D_ae < 2.1 μm). Inhalation exposure assessment showed that less than 60% of particulate bound PACs could deposit in the respiratory tract, which implies that the traditional model using ambient concentration of PACs would overestimate the inhalation risk. On the other hand, incremental lifetime cancer risks from dermal absorption (ILCR_derm) were comparable to those from inhalation (ILCR_inh) exposure despite the much lower daily dermal absorption dose than the daily inhalation dose, which implies that the health impact might be underestimated if only considering inhalation exposure. Cancer risks from inhalation exposure were mainly attributed to fine particles while those from dermal exposure were mostly associated with coarse particles. Although neither ILCR_derm nor ILCR_inh exceeded the threshold value of 10^-6 set by USEPA, the total ILCR exceeded this criterion, manifesting potential health risks from exposure to airborne particulate PACs in this region.

Approach to Predicting the Size-Dependent Inhalation Intake of Particulate Novel Brominated Flame Retardants

The risk of human exposure to particulate novel brominated flame retardants (NBFRs) in the atmosphere has received increasing attention from scientists and the public, but currently, there is no reliable approach to predict the intake of these compounds on the basis of their size distribution. Here, we develop a reliable approach to predict the size-dependent inhalation intake of particulate NBFRs, based on the gas/particle (G/P) partitioning behavior of the NBFRs. We analyzed the concentrations of eight NBFRs in 363 size-segregated particulate samples and 99 paired samples of gaseous and bulk particles. Using these data, we developed an equation to predict the G/P partitioning quotients of NBFRs in particles in different size ranges (K_Pi) based on particle size. This equation was then successfully applied to predict the size-dependent inhalation intake of particulate NBFRs in combination with an inhalation exposure model. This new approach provides the first demonstration of the effects of the temperature-dependent octanol-air partitioning coefficient (K_OA) and total suspended particle concentration (TSP) on the intake of particulate NBFRs by inhalation. In an illustrative case where TSP = 100 μg m^-3, inhalation intake of particulate NBFRs exceeded the intake of gaseous NBFRs when log K_OA > 11.4.

Indoor Particulate Matter in Urban Households: Sources, Pathways, Characteristics, Health Effects, and Exposure Mitigation

Particulate matter (PM) is a complex mixture of solid particles and liquid droplets suspended in the air with varying size, shape, and chemical composition which intensifies significant concern due to severe health effects. Based on the well-established human health effects of outdoor PM, health-based standards for outdoor air have been promoted (e.g., the National Ambient Air Quality Standards formulated by the U.S.). Due to the exchange of indoor and outdoor air, the chemical composition of indoor particulate matter is related to the sources and components of outdoor PM. However, PM in the indoor environment has the potential to exceed outdoor PM levels. Indoor PM includes particles of outdoor origin that drift indoors and particles that originate from indoor activities, which include cooking, fireplaces, smoking, fuel combustion for heating, human activities, and burning incense. Indoor PM can be enriched with inorganic and organic contaminants, including toxic heavy metals and carcinogenic volatile organic compounds. As a potential health hazard, indoor exposure to PM has received increased attention in recent years because people spend most of their time indoors. In addition, as the quantity, quality, and scope of the research have expanded, it is necessary to conduct a systematic review of indoor PM. This review discusses the sources, pathways, characteristics, health effects, and exposure mitigation of indoor PM. Practical solutions and steps to reduce exposure to indoor PM are also discussed.

Analysis, occurrence, toxicity and environmental health risks of synthetic phenolic antioxidants: A review

The continuous improvement of living standards is related to higher requirements for the freshness and taste of food. For example, synthetic phenolic antioxidants (SPAs) are added to fats and fried foods as food additives to minimize the oxidative rancidity of oils and fats. Hence, the global use of SPAs is increasing year by year. Dibutyl hydroxytoluene is one of the widely used SPAs, often in combination with butyl hydroxyanisole or gallate SPAs. The extensive use of these compounds makes them and their transformation products to be widespread in various environmental matrices, including indoor dust, wastewater, river water, sewage sludge, and sediment, as well as human samples, such as nails and urine, at concentrations varying from nanogram per gram (ng/g) to microgram per gram (μg/g). Animal experiments have shown that high-dose SPA exposure is toxic, which may lead to DNA damage and mismatches and the development of cancerous tumors. Since the biosphere shares the same set of genetic codes, humans and animals have many identical or similar feedback mechanisms and information pathways. Therefore, the damage of SPAs to animals may also threaten human health. This review discusses the properties, occurrence, analysis, and environmental health risks of typical SPAs, including butyl hydroxyanisole, dibutyl hydroxytoluene, tert-butylhydroquinone, propyl gallate, octyl gallate, and lauryl gallate, used as food additives. In addition, AO2246, which is used in food packaging bags, is also considered. Future research directions on SPAs and their transformation products (TPs) are identified and discussed.

Evaluating Indoor Air Chemical Diversity, Indoor-to-Outdoor Emissions, and Surface Reservoirs Using High-Resolution Mass Spectrometry

Detailed offline speciation of gas- and particle-phase organic compounds was conducted using gas/liquid chromatography with traditional and high-resolution mass spectrometers in a hybrid targeted/nontargeted analysis. Observations were focused on an unoccupied home and were compared to two other indoor sites. Observed gas-phase organic compounds span the volatile to semivolatile range, while functionalized organic aerosols extend from intermediate volatility to ultra-low volatility, including a mix of oxygen, nitrogen, and sulfur-containing species. Total gas-phase abundances of hydrocarbon and oxygenated gas-phase complex mixtures were elevated indoors and strongly correlated in the unoccupied home. While gas-phase concentrations of individual compounds generally decreased slightly with greater ventilation, their elevated ratios relative to controlled emissions of tracer species suggest that the dilution of gas-phase concentrations increases off-gassing from surfaces and other indoor reservoirs, with volatility-dependent responses to dynamically changing environmental factors. Indoor-outdoor emissions of gas-phase intermediate-volatility/semivolatile organic hydrocarbons from the unoccupied home averaged 6-11 mg h^-1, doubling with ventilation. While the largest single-compound emissions observed were furfural (61-275 mg h^-1) and acetic acid, observations spanned a wide range of individual volatile chemical products (e.g., terpenoids, glycol ethers, phthalates, other oxygenates), highlighting the abundance of long-lived reservoirs resulting from prior indoor use or materials, and their gradual transport outdoors.

Effect of dermal phthalate levels on lung function tests in residential area near a petrochemical complex

Phthalates can leach into indoor and outdoor airborne particulate matter and dust, which can then be ingested or absorbed and induce lung injury. Dermal phthalate levels can be used as a matrix for exposure direct absorption from air, particle deposition, and contact with contaminated products. However, the association between dermal phthalate levels in skin wipes and lung function tests remains unknown. A total of 397 participants were included. Spirometry measurements of forced expiratory volume in 1 s (FEV1, L) and forced vital capacity (FVC, L) were calculated. Dermal phthalate levels of diethyl phthalate (DMP), diethyl phthalate (DEP), di(n-butyl) phthalate (DnBP), butyl benzyl phthalate (BBzP), di(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DiNP), and diisodecyl phthalate (DiDP) on forehead skin wipes were detected. The one-unit increases in logarithm (log) dermal DnBP (β = - 0.08; 95% CI - 0.16, - 0.003, p = 0.041), BBzP (β = - 0.09; 95% CI - 0.16, - 0.02, p = 0.009), DEHP (β = - 0.07; 95% CI - 0.14, - 0.003, p = 0.042), and DiNP (β = - 0.08; 95% CI - 0.15, - 0.02, p = 0.017) were significantly associated with decreases in FVC. For elderly participants, one-unit increases in log dermal DnBP (β = - 0.25; 95% CI - 0.46, - 0.04, p = 0.021), BBzP (β = - 0.17; 95% CI - 0.33, - 0.01, p = 0.042), and DiDP (β = - 0.19; 95% CI - 0.39, < 0.01, p = 0.052) were associated with decreases in FEV1. In conclusion, dermal phthalate levels were significantly associated with decreases in lung function tests.

Associations of dermal diethyl phthalate level with changes in lung function test value mediated by absolute eosinophil count: A panel study of adults in southern Taiwan

Phthalate concentrations in indoor and outdoor dust are associated with respiratory disease. Both immunoglobulin E (IgE) and eosinophil count are associated with airway inflammation from exposure to environmental allergens. Dermal phthalate level can be used as a matrix for assessing personal exposure through direct absorption from the air, particle deposition, or contact with contaminated products. However, the association between dermal phthalate level and changes in lung function test values, as mediated by immunological response, remains unclear. In total, 237 adults in southern Taiwan were recruited. Spirometry measurements (in L) of forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were taken on visits 1 (2016-2018) and 2 (2019). Dermal phthalate level, absolute eosinophil count, and IgE level were recorded on visit 1. Mean changes in FVC and FEV1 decrease pear year, as determined through pairwise comparisons, were significant (^diffFVC_{per year}: -0.46, 95% CI: -0.51, -0.41; p < 0.001; ^diffFEV1_{per year}: -0.37, 95% confidence interval [CI]: -0.41, -0.34; p < 0.001). For FEV1 decrease, log-unit increases in dermal diethyl phthalate (DEP) were positively associated with ^diffFEV1_{per year} (β = 0.096; 95% CI: 0.042, 0.150; p = 0.001) and negatively associated with absolute eosinophil count (β= -0.201; 95% CI: -0.380, -0.023; p= 0.027). Log-unit increases in absolute eosinophil count were negatively associated with ^diffFEV1_{per year} (β= -0.109; 95% CI: -0.150, -0.068; p < 0.001). Absolute eosinophil count mediated 19.70% of the association between dermal DEP level and ^diffFEV1_{per year}. For FVC decrease, log-unit increases in dermal DEP were positively associated with ^diffFVC_{per year} (β = 0.095; 95% CI: 0.035, 0.155; p = 0.002) and negatively associated with absolute eosinophil count (β = -0.243; 95% CI: -0.427, -0.060; p = 0.010). Log-unit increases in absolute eosinophil count were negatively associated with ^diffFVC_{per year} (β= -0.122; 95% CI: -0.168, -0.076; p < 0.001). Absolute eosinophil count mediated 29.98% of the association between dermal DEP level and ^diffFVC_{per year}. The results suggest that dermal DEP level is positively associated with changes in lung function test values and is mediated by absolute eosinophil count.

Physical-Chemical Coupling Model for Characterizing the Reaction of Ozone with Squalene in Realistic Indoor Environments

Squalene can react with indoor ozone to generate a series of volatile and semi-volatile organic compounds, some of which may be skin or respiratory irritants, causing adverse health effects. Better understanding of the ozone/squalene reaction and product transport characteristics is thus important. In this study, we developed a physical-chemical coupling model to describe the behavior of ozone/squalene reaction products, that is, 6-methyl-5-hepten-2-one (6-MHO) and 4-oxopentanal (4-OPA) in the gas phase and skin, by considering the chemical reaction and physical transport processes (external convection, internal diffusion, and surface uptake). Experiments without intervention were performed in a single-family house in California utilizing time- and space-resolved measurements. The key parameters in the model were extracted from 5 day data and then used to predict the behaviors in some other days. Predictions from the present model can reproduce the concentration profiles of the three compounds (ozone, 6-MHO, and 4-OPA) well (R² = 0.82-0.89), indicating high accuracy of the model. Exposure analysis shows that the total amount of 6-MHO and 4-OPA entering the blood capillaries in 4 days can reach 14.6 and 30.1 μg, respectively. The contribution of different sinks to ozone removal in the tested realistic indoor environment was also analyzed.