A SPME‐based method for rapidly and accurately measuring the characteristic parameter for DEHP emitted from PVC floorings

Semivolatile organic compounds (SVOCs) are present in many indoor materials. SVOC emissions can be characterized with a critical parameter, y₀, the gas‐phase SVOC concentration in equilibrium with the source material. To reduce the required time and improve the accuracy of existing methods for measuring y₀, we developed a new method which uses solid‐phase microextraction (SPME) to measure the concentration of an SVOC emitted by source material placed in a sealed chamber. Taking one typical indoor SVOC, di‐(2‐ethylhexyl) phthalate (DEHP), as the example, the experimental time was shortened from several days (even several months) to about 1 day, with relative errors of less than 5%. The measured y₀ values agree well with the results obtained by independent methods. The saturated gas‐phase concentration (y_sat) of DEHP was also measured. Based on the Clausius–Clapeyron equation, a correlation that reveals the effects of temperature, the mass fraction of DEHP in the source material, and y_sat on y₀ was established. The proposed method together with the correlation should be useful in estimating and controlling human exposure to indoor DEHP. The applicability of the present approach for other SVOCs and other SVOC source materials requires further study.     

The effect of ventilation on indoor exposure to semivolatile organic compounds

A mechanistic model was developed to examine how natural ventilation influences residential indoor exposure to semivolatile organic compounds (SVOCs) via inhalation, dermal sorption, and dust ingestion. The effect of ventilation on indoor particle mass concentration and mass transfer at source/sink surfaces, and the enhancing effect of particles on mass transfer at source/sink surfaces are included. When air exchange rate increases from 0.6/h to 1.8/h_, the steady‐state SVOC (gas‐phase plus particle phase with log K_OA varying from 9 to 13) concentration in the idealized model decreases by about 60%. In contrast, for the same change in ventilation, the simulated indoor formaldehyde (representing volatile organic compounds) gas‐phase concentration decreases by about 70%. The effect of ventilation on exposure via each pathway has a relatively insignificant association with the K_OA of the SVOCs: a change of K_OA from 10⁹ to 10¹³ results in a change of only 2–30%. Sensitivity analysis identifies the deposition rate of PM_2.5 as a primary factor influencing the relationship between ventilation and exposure for SVOCs with log K_OA = 13. The relationship between ventilation rate and air speed near surfaces needs to be further substantiated.     

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.     

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

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

Sources and dynamics of semivolatile organic compounds in a single‐family residence in northern California

Semivolatile organic compounds (SVOCs) emitted from building materials, consumer products, and occupant activities alter the composition of air in residences where people spend most of their time. Exposures to specific SVOCs potentially pose risks to human health. However, little is known about the chemical complexity, total burden, and dynamic behavior of SVOCs in residential environments. Furthermore, little is known about the influence of human occupancy on the emissions and fates of SVOCs in residential air. Here, we present the first‐ever hourly measurements of airborne SVOCs in a residence during normal occupancy. We employ state‐of‐the‐art semivolatile thermal‐desorption aerosol gas chromatography (SV‐TAG). Indoor air is shown consistently to contain much higher levels of SVOCs than outdoors, in terms of both abundance and chemical complexity. Time‐series data are characterized by temperature‐dependent elevated background levels for a broad suite of chemicals, underlining the importance of continuous emissions from static indoor sources. Substantial increases in SVOC concentrations were associated with episodic occupant activities, especially cooking and cleaning. The number of occupants within the residence showed little influence on the total airborne SVOC concentration. Enhanced ventilation was effective in reducing SVOCs in indoor air, but only temporarily; SVOCs recovered to previous levels within hours.     

A general mechanistic model for predicting the fate and transport of phthalates in indoor environments

A mechanistic model that considers particle dynamics and their effects on surface emissions and sorptions was developed to predict the fate and transport of phthalates in indoor environments. A controlled case study was conducted in a test house to evaluate the model. The model‐predicted evolving concentrations of benzyl butyl phthalate in indoor air and settled dust and on interior surfaces are in good agreement with measurements. Sensitivity analysis was performed to quantify the effects of parameter uncertainties on model predictions. The model was then applied to a typical residential environment to investigate the fate of di‐2‐ethylhexyl phthalate (DEHP) and the factors that affect its transport. The predicted steady‐state DEHP concentrations were 0.14 μg/m³ in indoor air and ranged from 80 to 46 000 μg/g in settled dust on various surfaces, which are generally consistent with the measurements of previous studies in homes in different countries. An increase in the mass concentration of indoor particles may significantly enhance DEHP emission and its concentrations in air and on surfaces, whereas increasing ventilation has only a limited effect in reducing DEHP in indoor air. The influence of cleaning activities on reducing DEHP concentration in indoor air and on interior surfaces was quantified, and the results showed that DEHP exposure can be reduced by frequent and effective cleaning activities and the removal of existing sources, though it may take a relatively long period of time for the levels to drop significantly. Finally, the model was adjusted to identify the relative contributions of gaseous sorption and particulate‐bound deposition to the overall uptake of semi‐volatile organic compounds (SVOCs) by indoor surfaces as functions of time and the octanol‐air partition coefficient (K_oa) of the chemical. Overall, the model clarifies the mechanisms that govern the emission of phthalates and the subsequent interactions among air, suspended particles, settled dust, and interior surfaces. This model can be easily extended to incorporate additional indoor source materials/products, sorption surfaces, particle sources, and room spaces. It can also be modified to predict the fate and transport of other SVOCs, such as phthalate‐alternative plasticizers, flame retardants, and biocides, and serves to improve our understanding of human exposure to SVOCs in indoor environments.     

From air to clothing: characterizing the accumulation of semi‐volatile organic compounds to fabrics in indoor environments

Uptake kinetics of semi‐volatile organic compounds (SVOCs) present indoors, namely phthalates and halogenated flame retardants (HFRs), were characterized for cellulose‐based cotton and rayon fabrics. Cotton and rayon showed similar accumulation of gas‐ and particle‐phase SVOCs, when normalized to planar surface area. Accumulation was 3–10 times greater by rayon than cotton, when normalized to Brunauer–Emmett–Teller (BET) specific surface area which suggests that cotton could have a longer linear uptake phase than rayon. Linear uptake rates of eight consistently detected HFRs over 56 days of 0.35–0.92 m³/day.dm² planar surface area and mass transfer coefficients of 1.5–3.8 m/h were statistically similar for cotton and rayon and similar to those for uptake to passive air sampling media. These results suggest air‐side controlled uptake and that, on average, 2 m² of clothing typically worn by a person would sequester the equivalent of the chemical content in 100 m³ of air per day. Distribution coefficients between fabric and air (K′) ranged from 6.5 to 7.7 (log K′) and were within the range of partition coefficients measured for selected phthalates as reported in the literature. The distribution coefficients were similar for low molecular weight HFRs, and up to two orders of magnitude lower than the equilibrium partition coefficients estimated using the COSMO‐RS model. Based on the COSMO‐RS model, time to reach 95% of equilibrium for PBDEs between fabric and gas‐phase compounds ranged from 0.1 to >10 years for low to high molecular weight HFRs.     

A quantitative structure‐property relationship (QSPR) for estimating solid material‐air partition coefficients of organic compounds

The material‐air partition coefficient (K_ma) is a key parameter to estimate the release of chemicals incorporated in solid materials and resulting human exposures. Existing correlations to estimate K_ma are applicable for a limited number of chemical‐material combinations without considering the effect of temperature. The present study develops a quantitative structure‐property relationship (QSPR) to predict K_ma for a large number of chemical‐material combinations. We compiled a dataset of 991 measured K_ma for 179 chemicals in 22 consolidated material types. A multiple linear regression model predicts K_ma as a function of chemical's K_oa, enthalpy of vaporization (?H_v), temperature, and material type. The model shows good fitting of the experimental dataset with adjusted R² of 0.93 and has been verified by internal and external validations to be robust, stable and has good predicting ability ( > 0.78). A generic QSPR is also developed to predict K_ma from chemical properties and temperature only (adjusted R² = 0.84), without the need to assign a specific material type. These QSPRs provide correlation methods to estimate K_ma for a wide range of organic chemicals and materials, which will facilitate high‐throughput estimates of human exposures for chemicals in solid materials, particularly building materials and furniture.     

Measurement of semi-volatile organic compounds emitted from various types of indoor materials by thermal desorption test chamber method

This paper presents measurements on semi-volatile organic compounds (SVOCs) emitted from building materials, household electric appliances, and indoor products. It is extremely difficult to apply the emission test chamber method to the accurate measurement of SVOCs because they are absorbed by the internal walls of the chamber. The authors have reported on the development of the thermal desorption test chamber method that can measure correctly the emission rates of SVOCs emitted from materials under actual room-air temperature conditions. This method is composed of two measurement steps. In the first step we capture organic compounds emitted as gaseous matter. After removing the test piece from the chamber, in the second step we continuously gather the organic compounds absorbed by the chamber's internal walls while heating the chamber. We have used this method to measure emissions from various objects, and have confirmed that most SVOCs are caught in the second step. In this paper, we also report on our verification of the accuracy of SVOC measurements taken using an emission chamber and describe the emission characteristics of SVOCs.     

Dispersion in flow from a continuous source at sea

Diffusion experiments, using a continuous release of fluorescent dye from an anchored source, were carried out in the Holy Loch and two coastal areas of the Irish Sea. In each case the dye distribution was sampled by a vessel making a series of crossings of the plume. The data were analysed in terms of σ_y, the standard deviation of the dye distribution at right angles to the axis of the plume, as a function of the diffusion time t₁ and the corresponding eddy diffusion coefficient K_y. In general the value of K_y increased with t up to a diffusion time of at least 2 h. In many cases the relation between K_y and t was approximately linear, corresponding to spreading with a constant diffusion velocity B such that K_y = B²t. The observed median values of B for the Holy Loch, Red Wharf Bay and the area of the Irish Sea off the Cumberland coast were 0·4, 1·1 and 1·4 cm s⁻¹ respectively. The vertical diffusion was also analysed, but in less detail, and other features of the plumes, including their variability, are discussed. In general the rates of diffusion in the Holy Loch are similar to those reported by other workers for the Great Lakes and for coastal sea areas with weak currents and high stability. In the two Irish Sea areas the diffusion rates are similar to one another but considerably greater than in the Holy Loch.     

Sorption of emerging trace organic compounds onto wastewater sludge solids

This work examined the sorption potential to wastewater primary- and activated-sludge solids for 34 emerging trace organic chemicals at environmentally relevant concentrations. These compounds represent a diverse range of physical and chemical properties, such as hydrophobicity and charge state, and a diverse range of classes, including steroidal hormones, pharmaceutically-active compounds, personal care products, and household chemicals. Solid-water partitioning coefficients (K_d) were measured where 19 chemicals did not have previously reported values. Sludge solids were inactivated by a nonchemical lyophilization and dry-heat technique, which provided similar sorption behavior for recalcitrant compounds as compared to fresh activated-sludge. Sorption behavior was similar between primary- and activated-sludge solids from the same plant and between activated-sludge solids from two nitrified processes from different wastewater treatment systems. Positively-charged pharmaceutically-active compounds, amitriptyline, clozapine, verapamil, risperidone, and hydroxyzine, had the highest sorption potential, log K_d = 2.8-3.8 as compared to the neutral and negatively-charged chemicals. Sorption potentials correlated with a compound’s hydrophobicity, however the higher sorption potentials observed for positively-charged compounds for a given log D_ow indicate additional sorption mechanisms, such as electrostatic interactions, are important for these compounds. Previously published soil-based one-parameter models for predicting sorption from hydrophobicity (log K_ow > 2) can be used to predict sorption for emerging nonionic compounds to wastewater sludge solids.     

Assessment of K0 correlation to strength for granular materials

The coefficient of lateral stress at rest K₀ is a state soil variable, yet is well correlated to strength. As different types of friction angles can be defined, it is important to examine the applicability of K₀-strength correlation and further clarify the mechanism of K₀-stress state. In this study, the values of K₀ were experimentally investigated for different types of granular materials, focusing on its correlation to material strength and the effect of particle shape and surface roughness. For this purpose, laboratory tests were conducted to directly measure K₀ of natural sand, spherically shaped glass bead, and surface-etched glass bead packings under various stress and soil conditions. Triaxial and other basic property tests were also conducted to characterize the test granular materials. It was revealed that the effect of material density on K₀ differed depending on the stress history whereas the effect of particle surface roughness, within the range considered in this study, was relatively small. Test results highlight that the values of the friction angle employed into Jaky's K₀ equation to match measured K₀ values are not unique, showing a state-dependent aspect. Inter-particle stress analysis was introduced to assess the correlation of K₀ to the friction angle as postulated by Jaky's K₀ equation.     

Direct measurements of reaeration rates using noble gas tracers in the River Lagan, Northern Ireland

Dissolved oxygen (DO) in river systems is often depleted by polluting substances, sometimes rendering the water unfit for habitats and human use. The natural mass transfer of oxygen from the atmosphere can help to alleviate this. The reaeration coefficient, K₂, which describes the rate of oxygen absorption, is an important parameter in water‐quality modelling. Owing to difficulties in the direct measurement of K₂, values for use in water quality models are typically derived using predictive equations, but these are notoriously inaccurate. This paper presents a field method for the direct measurement of K₂ by two alternative analysis methods and includes the results of eight tests conducted on a reach of the River Lagan, in Northern Ireland. The method is based on a long‐established protocol but replaces a now‐unacceptable radioactive tracer (⁸⁵Kr) with stable noble gases. K₂₍₂₀₎ values between 3 and 80/day are reported for the test reach.     

Electrostatic dust collectors compared to inhalable samplers for measuring endotoxin concentrations in farm homes

Paired electrostatic dust collectors (EDCs) and daily, inhalable button samplers (BS) were used concurrently to sample endotoxin in 10 farm homes during 7‐day periods in summer and winter. Winter sampling included an optical particle counter (OPC) to measure PM_2.5 and PM_2.5–10. Electrostatic dust collectors and BS filters were analyzed for endotoxin using the kinetic chromogenic Limulus amebocyte lysate assay. Optical particle counter particulate matter (PM) data were divided into two PM categories. In summer, geometric mean (geometric standard deviation) endotoxin concentrations were 0.82 EU/m³ (2.7) measured with the BS and 737 EU/m² (1.9) measured with the EDC. Winter values were 0.52 EU/m³ (3.1) for BS and 538 EU/m² (3.0) for EDCs. Seven‐day endotoxin values of EDCs were highly correlated with the 7‐day BS sampling averages (r = 0.70; P < 0.001). Analysis of variance indicated a 2.4‐fold increase in EDC endotoxin concentrations for each unit increase of the ratio of PM_2.5 to PM_2.5–10. There was also a significant correlation between BS and EDCs endotoxin concentrations for winter (r = 0.67; P < 0.05) and summer (r = 0.75; P < 0.05). Thus, EDCs sample comparable endotoxin concentrations to BS, making EDCs a feasible, easy to use alternative to BS for endotoxin sampling.     

Sediment desorption of PCB congeners and their bio-uptake by dipteran larvae

Sediment desorption of PCB congeners and their bio-uptake by Chironomus tentans Fabricus were investigated in a continuous flow system. The desorption of 71 congeners (in Aroclors 1221, 1016, 1254 and 1260) determined by glass capillary gas chromatography could be described by a first order function. The release rate of the individual congeners was inversely related to their octanol/water partition coefficients (K_ow). The depth of mobilization generally decreased with the number of chlorine substitutions and was inversely related to K_ow.Bio-uptake of the congeners by Chironomus tentans Fabricus was selective with the bio-uptake factor being highest for those with 2–4 chlorines. There was no correlation between the factor and either K_ow or desorption rate from the sediments.     

Measurements and modeling of absorptive partitioning of volatile organic compounds to painted surfaces

Partitioning to surfaces is an important sink for volatile organic compounds (VOCs) indoors, but the mechanisms are not well understood or quantified. Here, a mass spectrometer was coupled to a portable surface reactor and a flow tube to measure partitioning of VOCs into paint films coated onto glass or wallboard, and their subsequent diffusion. A model was developed to extract values of the effective absorbing organic mass concentration of the film, C_w, which is a measure of absorption capacity, and VOC diffusion coefficients, D_f, from VOC time profiles measured during film passivation and depassivation. Values of C_w agreed well with the value estimated from the paint film mass and flow tube air volume, and D_f values (also measured using attenuated total reflectance-Fourier transform infrared spectroscopy) correlated well with VOC vapor saturation concentrations, C*, estimated using a group contribution method. The value of these relationships for estimating key parameters that control VOC partitioning into paint and the fate of VOCs indoors was demonstrated using a house model, which indicated that >50% of VOCs with C* ≤10⁸ μg/m³ (C* of octane, hexanone, and propanol) that contacted a paint film of typical thickness fully permeated the film regardless of emission duration.     

Factor interactions and aquatic toxicity testing

Hypothesizing that experimental variables constituting an exposure situation act independently when in combination, we have reviewed two published data sets dealing with effects of metal mixtures on aquatic animals in order to assess the potential practical significance of factor interactions and their implication to the design of aquatic toxicity tests. Both data sets were re-analyzed using each of the following predictive models: (1) simple-additive, y = a_x + b_y, where y is an estimated response, a_x is the observed response to a concentration of toxicant x when y = 0, and b_y is the observed response to a level of toxicant y when x = 0; (2) linear-additive, y = a + b₁x₁ + b₂x₂, in which y is a predicted value, a and b are pooled estimates involving all treatments in the exposure assay; (3) quadratic response, y = a + b₁x₁ + b₂x₂ + b₁₂x₁x₂ + b₁₁x₁² + b₂₂x₂², which provides for estimates of interactions and non-linear effects. The relative effectiveness of each model in predicting joint effects of independent test variables was evaluated in terms of calculated mean-square error and goodness-of-fit (R²) values, as well as by how well predicted treatment effects compared with responses observed by original investigators.Our analyses show that in one case all three models provided similar estimates that closely approximated observed responses, despite the presence of a statistically significant two-factor metal interaction. In comparison, in the second instance, the quadratic response model was the most effective predictor and was appreciably better than the linear-additive model in terms of the calculated parameters. The simple-additive model on the other hand, tended to over-estimate treatment effects, by as much as 80% in some instances, and was least effective of the three models examined. Our re-analyses show that the working hypothesis is rejected, i.e. an assumption of factor independence is not to be accepted a priori.A sequential testing protocol is presented which would permit an evaluation of the existence of factor interactions.     

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.     

Effects of dissolved humic materials on acute toxicity of some organic chemicals to aquatic organisms

The influence of dissolved humic materials (DHM) on the acute toxicity of diazinon, tetrabromobisphenol-A (TBP), 4-chloroanilin (4-CA) and pentachlorophenol (PCP) was evaluated using the zebrafish (Brachydanio rerio Hamilton-Buchanan) and waterflea (Daphnia magna Straus). The 96-h LC₅₀ (zebrafish) and 48-h EC₅₀ values for four chemicals were determined in the presence of 0, 0.5, 5.0 and 50 TOC mg/l. The effects of DHM on the toxicity of four test chemicals to B. rerio were not observed in all of the DHM treatments. In the daphnid toxicity test, DHM significantly reduced the toxicity of diazinon and 4-CA, while no reduction of the toxicity of TBP and PCP was observed. These results indicate that the interaction between DHM and chemicals can alter the toxicity of some chemicals to D. magna.     

Semi‐volatile organic compounds in the air and dust of 30 French schools: a pilot study

The contamination of indoor environments with chemical compounds released by materials and furniture, such as semi‐volatile organic compounds (SVOCs), is less documented in schools than in dwellings—yet children spend 16% of their time in schools, where they can also be exposed. This study is one of the first to describe the contamination of the air and dust of 90 classrooms from 30 nursery and primary schools by 55 SVOCs, including pesticides, phosphoric esters, musks, polycyclic aromatic hydrocarbons (PAHs), polychlorobiphenyls (PCBs), phthalates, and polybromodiphenylethers (PBDEs). Air samples were collected using an active sampling method, and dust samples were collected via two sampling methods (wiping and vacuum cleaning). In air, the highest concentrations (median >100 ng/m³) were measured for diisobutyl phthalate (DiBP), dibutyl phthalate (DBP), diethyl phthalate (DEP), bis(2‐ethylhexyl) phthalate (DEHP), and galaxolide. In dust, the highest concentrations (median >30 μg/g) were found for DEHP, diisononyl phthalate (DiNP), DiBP, and DBP. An attempt to compare two floor dust sampling methods using a single unit (ng/m²) was carried out. SVOC concentrations were higher in wiped dust, but frequencies of quantification were greater in vacuumed dust.