Air Partition Coefficients Research Articles

One-dimensional consolidation analysis of layered unsaturated soils: An improved model integrating interfacial flow and air contact resistance effects

Layered unsaturated soils exhibit complex mechanical and physical properties. Owing to the roughness between unsaturated soil interfaces and the presence of irregularly distributed micro-pores, this study explores the laminar flow of pore water and counter-cyclonic flow of pore air through these channels at low velocities. In response to the complex consolidation behavior of unsaturated soils influenced by the flow and air contact resistance, an improved model is developed. The model incorporates the flow contact transfer coefficient (Rω), flow partition coefficient (ηω), air contact transfer coefficient (Ra) and air partition coefficient (ηa). Semi-analytical solutions for pore water pressure, pore air pressure and settlement in layered unsaturated soils are derived by employing the Laplace transform and its inverse transform. The rationality of the model is validated through comparative analysis with existing solutions. Analysis of the improved model yields critical insights: the presence of flow and air contact resistance leads to the development of relative pore pressure and air pressure gradients at interfaces, which diminishes the influence of the permeability coefficients of the water phase (kω) and air phase (ka) on the consolidation process. Moreover, neglecting the flow and air contact resistance effects may lead to an overestimation of settlement.

Field study on the uptake pathways and their contributions to the accumulation of organophosphate esters, phthalates, and polycyclic aromatic hydrocarbons in upland rice

Plant uptake of organic contaminants generally occurs through either root, gas-phase foliar, or particle-phase foliar uptake. Understanding these pathways is essential for food-system practitioners to reduce human exposures, and to clean contaminated-sites with phytoremediation. Herein, we conducted a field-based experiment using an improved specific exposure chamber to elucidate the uptake pathways of organophosphate esters, phthalates, and polycyclic aromatic compounds, and quantitatively assessed their contributions to organic contaminant accumulations in field-grown rice. For most target compounds, all three uptake pathways (root, foliar gas, and foliar particle uptakes) contributed substantially to the overall contaminant burden in rice. Compounds with lower octanol–water partition coefficients (Kow) were more readily translocated from roots to leaves, and compounds with higher octanol−air partition coefficients (Koa) tended to enter rice leaves mostly through particle deposition. Most compounds were mostly stored in the inner leaves (55.3–98.2 %), whereas the relatively volatile compounds were more readily absorbed by the waxy layer and then transferred to the inner leaves. Air particle desorption was a key process regulating foliar uptake of low-volatility compounds. The results can help us to better understand and predict the environmental fate of those contaminants, and develop more effective management strategies for reducing their human exposure through food ingestion.

Characterization and health risks of short- and medium-chain chlorinated paraffins in the gas and size-fractionated particulate phases in ambient air

Short-chain and medium-chain chlorinated paraffins (SCCPs and MCCPs) have garnered significant attention because they have persistence and potential toxicity, and can undergo long-distance transport. Chlorinated paraffins (CPs) inhaled in the size-fractionated particulate phase and gas phase can carry different risks to human health due to their ability to accumulate in different regions of the respiratory tract and exhibit varying deposition efficiencies. In our study, large-volume ambient air samples in both the size-fractionated particulate phase (Dp < 1.0 μm, 1.0–2.5 μm, 2.5–10 μm, and Dp ≥ 10 μm) and gas phase were collected simultaneously in Beijing using an active sampler. The overall levels of SCCPs and MCCPs were relatively high, the ranges being 57–881 and 30–385 ng/m3, respectively. SCCPs tended to be partitioned in the gas phase (on average 75% of the ΣSCCP concentration), while MCCPs tended to be partitioned in the particulate phase (on average 62% of the ΣMCCP concentration). Significant correlations were discovered between the logarithm-transformed gas–particle partition coefficients (KP) and predicted subcooled vapor pressures (PL0) (p < 0.01 for SCCPs and MCCPs) and between the logarithm-transformed KP values and octanol–air partition coefficients (KOA) (p < 0.01 for SCCPs and MCCPs). Thus, the slopes indicated that organic matter absorption was the dominant process involved in gas–particle partitioning. We used the ICRP model to calculate deposition concentrations for particulate-associated CPs in head airways region (15.6–71.4 ng/m³), tracheobronchial region (0.8–4.8 ng/m³), and alveolar region (5.1–21.9 ng/m³), then combined these concentrations with the CP concentrations in the gas phase to calculate estimated daily intakes (EDIs) for inhalation. The EDIs for SCCPs and MCCPs through inhalation of ambient air for the all-ages group were 67.5–184.2 ng/kg/day and 19.7–53.7 ng/kg/day, respectively. The results indicated that SCCPs and MCCPs in ambient air do not currently pose strong risks to human health in the study area.

Gas–particle partitioning and dry deposition of atmospheric parent, alkylated, nitrated and hydroxyl polycyclic aromatic hydrocarbons over the Bohai sea and northern Yellow sea in autumn

To elucidate the gas–particle partitioning characteristics and dry deposition contributions of polycyclic aromatic hydrocarbons (PAHs) in the marine environment, 23 integrated air samples were collected during a research cruise in the northern Yellow Sea (NYS) and Bohai Sea (BS) in mid-autumn 2020. The atmospheric concentrations of 23 parent PAHs (PPAHs), 18 alkylated PAHs (APAHs), five nitrated PAHs (NPAHs), and seven hydroxyl PAHs (OPAHs) in gaseous and particulate phases were measured simultaneously. The total concentrations of 53 PAHs varied from 8.77 to 348 ng/m3. The 2-ring and 3-ring PPAHs and APAHs had lower particle-bound fractions than those of the NPAHs and OPAHs. For the gas–particle partitioning of the PAHs, the gas–particle partitioning coefficients (Kp) estimated using an octanol–air partition coefficient (KOA)–based model and KOA/soot–air partition coefficient (KSA) dual model (KOA–KSA dual model) were lower than the Kp measured in the field. Underestimation of the Kp commonly occurred with these models, but the KOA–KSA dual model was more suitable than the KOA–based model for gas–particle partitioning of the 53 atmospheric PAHs in the BS and NYS. The estimated atmospheric dry deposition fluxes of the 53 PAHs ranged from 631 to 14,345 ng/m2/day. The BS receives a PAHs load of up to 117 tons/year. The study provides background information on the occurrence and environmental fate of PAHs and could be vitally important for environmental safety management for the Northwest Pacific Ocean.

Characterizing novel brominated flame retardants in the coastal atmosphere of the northern Bohai and Yellow Seas

To enrich knowledge concerning occurrence and behavior of novel brominated flame retardants (NBFRs) in the Chinese marine environment, a group of 11 NBFRs were measured in the atmosphere over the northern Bohai and Yellow Seas. Samples were taken downwind of the primary NBFR production and application areas in North China. The total NBFR air concentrations (ΣNBFRs) varied from 80.9 to 934 pg/m3, with decabromodiphenyl ethane (DBDPE) being the most abundant component. The high spatial variability of ΣNBFRs and relatively weak correlations among individual compounds indicated the diverse impact of anthropogenic activities in the coastal regions. The KOA-based absorption model predicted the distributions of low-mass NBFRs, while a steady state model was more applicable for heavier compounds such as DBDPE. The partitioning of NBFRs between the gas and particle phases were significantly related with octanal–air partition coefficient (KOA) only for the notable pollution locations, suggesting absorptive contribution to NBFR sorption. The resulting relationships characterized by event differences possibly pointed out the influences including the sources of NBFRs and aerosol particles, the continental impact, and the sorption kinetics on NBFR partitioning behaviors. Dry particle-bound deposition estimations indicated that the NBFR inputs to the sea from the air was significant.

Determination of blood:air, urine:air and plasma:air partition coefficients of selected microbial volatile organic compounds

Partition coefficients (PCs) are essential parameters for understanding the toxicokinetics of chemicals in the human body since they are used in the description of different processes of absorption, distribution, and excretion in physiologically based pharmacokinetic (PBPK) models used in chemical exposure and risk assessment. The goal of this study was to determine urine:air, blood:air and plasma:air partition coefficients (PCs) of microbial volatile organic compounds (mVOCs) previously selected as having high potential as biomarkers of indoor mold exposure. To achieve this goal, the vial-equilibration technique was used, and quantification was performed using headspace gas chromatography tandem mass spectrometry (HS-GC-MS/MS) analysis. Matrix:air PCs of 19 different mVOCs have been successfully determined and their values ranged between 14 and 3586 for urine:air, 78 and 4721 for blood:air and 64 and 5604 for plasma:air PCs. Water:air PCs were also determined, and their values varied between 16 and 2210, showing a good correlation with urine:air PCs for 17 compounds of the selected mVOCs (R2 = 0.97, slope close to unity) indicating that water:air PCs below 103 may be a good surrogate for urine:air PCs. All studied mVOCs have high blood:air PCs (greater than 78) indicating strong pulmonary uptake. Due to their high blood:urine PCs, some mVOCs may be more easily measured in blood than in urine. This work is an important preliminary step toward the use of mVOCs as potential biomarkers of indoor mold exposure. The data obtained in this study will help to determine the most appropriate matrix to use in this biomonitoring approach and will eventually facilitate the development of PBPK models for these chemicals.

Recalibrating polyparameter linear free energy relationships and reanalyzing mechanisms for partition of nonionic organic compounds to low-density polyethylene passive sampler

Equilibrium passive sampling techniques based on the low-density polyethylene (LDPE) film are increasingly used for determining the concentration of contaminants in water and air. Reliable models capable of predicting LDPE–water and LDPE–air partition coefficients (KiLDPEw and KiLDPEa) would be very useful. In previous studies, polyparameter linear free energy relationships (PP-LFERs) based on Abraham's solute descriptors were calibrated for LDPE–water and LDPE–air systems. Unfortunately, a portion of unreliable partition coefficients and solute descriptors were included in the calibration sets of these previous studies, leading to unexpected system parameters and predictive performance in the regression results. In this study, more reliable PP-LFERs were recalibrated for LDPE–water and LDPE–air systems (20‒25 °C) using carefully collected reliable partition coefficients and solute descriptors of various polar and nonpolar compounds (over one hundred and with low redundancy) from the literature, as well as the robust regression method. The PP-LFERs performed well with root-mean-square errors of 0.15–0.25 log units and successfully predicted KiLDPEw and KiLDPEa values spanning over 10 orders of magnitude for compounds with reliable descriptors. The partitioning mechanisms of compounds to LDPE were also reanalyzed and compared in detail with n-alkanes (C6–C16). Generally, LDPE is more prone to form dispersion interactions with solutes than n-alkanes, while it is more difficult to form cavities in LDPE. In addition, the crystallinity of LDPE is not the sole reason for the distinct constant terms presenting in PP-LFERs for LDPE–water and n-hexadecane–water systems.

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 (Klg ), dust-air (Kd ), and PM2.5 -air (Kp ) partition coefficients of DiBP, DnBP, and DEHP. The median values of log(Klg ) 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 Klg was significantly higher in the winter. The median Kd (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, Kd was associated with material of surface and residence time of dust. The Kp 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 Klg , 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.

Investigating the Effects of Temperature, Relative Humidity, Leaf Collection Date, and Foliar Penetration on Leaf–Air Partitioning of Chlorpyrifos

Leaf-air partition coefficient (Kleaf-air) values are needed to understand and predict pesticide volatilization and persistence in agroecosystems. The objectives of this work were to measure Kleaf-air values and foliar penetration for the insecticide chlorpyrifos (as an active ingredient alone and in a pesticide formulation) on alfalfa (lucerne) leaves at a range of temperatures and relative humidities and when using leaves collected in different summer months. Kleaf-air values were measured using a solid-phase fugacity meter. A portion of the leaves were also used for foliar penetration experiments. Kleaf-air values for chlorpyrifos as an active ingredient alone decreased with temperature, while the effects of temperature on chlorpyrifos in the formulation were negligible. No correlations between Kleaf-air values and relative humidity were observed. Foliar penetration increased with temperature for chlorpyrifos both as an active ingredient and in the formulation. Increasing foliar penetration with temperature is attributed to increasing diffusion into inner leaf layers. Both volatilization and foliar penetration affect the measured Kleaf-air values, so understanding the link between these processes is necessary to predict Kleaf-air values. The leaf collection date had a substantial effect on the measured Kleaf-air values, highlighting the need for a better understanding of the role of leaf properties on Kleaf-air.

Per- and polyfluoroalkyl substances (PFAS) in the Three-North Shelter Forest in northern China: First survey on the effects of forests on the behavior of PFAS

Per- and polyfluoroalkyl substances (PFAS) are a family of anthropogenic chemicals, that have attracted increasing attention since the early 2000 s. Although forests have been shown to act as a filter and important sink for nonpolar persistent organic pollutants (POPs), relevant reports on PFAS are lacking. Air, soil, and leaf samples were collected inside and outside the forest from two regions of the Three-North Shelter Forest in northern China between 2017 and 2018. Twenty-seven PFAS were analyzed to study the effect of forest on the transport and fate of PFAS. The average ratios of PFAS in the air outside to inside the forest (Qair) ranged from 2.83 ± 0.78–10.6 ± 3.1. A significant positive correlation was found between Qair and the n-octanol−air partition coefficient of individual PFAS (p = 0.041). Higher Qair values for most ionic PFAS were found in broad-leaved forests than in coniferous forests. Soil samples outside the forests showed higher PFAS levels than those inside. The measured concentrations of 8:2 fluorotelomer alcohol, a volatile neutral PFAS, in leaf samples were two orders of magnitude higher than those estimated using the equilibrium leaf−air partition of nonpolar POPs, indicating that it may not fit the case of PFAS with surface activity.

Effects of temperature and relative humidity on soil−air partition coefficients of organophosphate flame retardants and polybrominated diphenyl ethers

The soil−air partition coefficients (KSA) of polybrominated diphenyl ethers (PBDEs) and organophosphate flame retardants (OPFRs) is important for determining their fate in soil and air media. However, KSA values of OPFRs and PBDEs are not available from the current literature, and the effects of environmental factors such as temperature and relative humidity (RH) on KSA values are not clear. In this study, a solid-phase fugacity meter was used to measure the KSA values of PBDEs and OPFRs at different temperatures (25, 30, 35, 40, and 45 °C) and relative humidity (RH) conditions (<3 and 100% RH), the relationships between KSA and octanol−air partition coefficients (KOA) for OPFRs and PBDEs were analyzed. The results showed that an increase in temperature and RH resulted in a decrease of all KSA values for PBDEs and OPFRs. Furthermore, the effects of RH on the soil−air partitioning behavior of PBDEs were larger than that of OPFRs. In addition, a significant correlation (p < 0.0001) was observed between log KSA and log KOA. The experimental KSA values of OPFRs and PBDEs were quite different from the predicted KSA, when calculated with their KOA values. Overall, this study provides a better understanding for predicting the behavior and fate of OPFRs and PBDEs in soil−air systems.

Application of multimedia models for understanding the environmental behavior of volatile methylsiloxanes: Fate, transport, and bioaccumulation.

Multimedia fate and transport models (MFTMs) describe how chemicals behave in the environment based on their inherent properties and the characteristics of receiving systems. We critically review the use of MFTMs for understanding the behavior of volatile methylsiloxanes (VMS). MFTMs have been used to predict the fate of VMS in wastewater treatment, rivers, lakes, marine systems, and the atmosphere, and to assess bioaccumulation and trophic transfers. More widely, they have been used to assess the overall persistence, long‐range transport potential (LRTP), and the propensity for atmosphere–surface exchange. The application of MFTMs for VMS requires particularly careful selection of model inputs because the properties of VMS differ from those of most organic compounds. For example, although n‐octanol/water partition coefficient (K OW) values are high, air:water partition coefficient (K AW) values are also high and n‐octanol/air partition coefficient (K OA) values are relatively low. In addition, organic carbon/water partition coefficient (K OC) values are substantially lower than expectations based on K OW. This means that most empirical relationships between K OC and K OW are not appropriate. Good agreement between modeled and measured concentrations in air, sediment, and biota indicates that our understanding of environmental fate is reasonable. VMS compounds are “fliers” that principally partition to the atmosphere, implying high LRTP, although they have low redeposition potential. They are degraded in air (half‐lives 3–10 days) and, thus, have low overall persistence. In water, exposure can be limited by hydrolysis, volatilization, and partitioning to sediments (where degradation half‐lives are likely to be high). In food webs, they are influenced by metabolism in biota, which tends to drive trophic dilution (i.e., trophic magnification factors are often but not always <1). Key remaining uncertainties include the following: (i) the strength and direction of the temperature dependence for K OC; (ii) the fate of atmospheric reaction products; and (iii) the magnitude of emissions to wastewater. Integr Environ Assess Manag 2022;18:599–621. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Measurement of octanol–air partition coefficients for liquid crystals based on gas chromatography-retention time and its implication in predicting long-range transport potential

Liquid crystals (LCs) are widely used in the modern society, but their environmental fate and related human health effects remain inadequately recognized. To assist in better understanding the environmental fate of LCs, the octanol–air partition coefficients (KOA) of 21 target LCs were determined with a gas chromatography-retention time (GC-RT) approach. Four classes of traditional organic pollutants, including polycyclic aromatic hydrocarbons, organochlorides, polybrominated diphenyl ethers, and polychlorinated biphenyls were employed as reference or calibration compounds. Cluster analysis indicated that the reference and calibration compounds somewhat influenced the relative and absolute magnitudes of GC-RT results. A quantitative structure-property relationship (QSPR) model was constructed from the experimental results and outperformed a widely-used model, KOAWIN, in estimating log KOA of LCs. This model was used to predict log KOAs for 116 LCs with the same element compositions and similar structures as the target LCs. Overall persistence and long-range transport potential were predicted based on the measured and estimated log KOA values, yielding consistent results. Several LCs were shown to have comparable characteristic travel distances and transport efficiencies as the traditional organic pollutants, suggesting they are potential environmental pollutants and the QSPR model is applicable in predicting the environmental fate of LCs.

In silico prediction of polyethylene-aqueous and air partition coefficients of organic contaminants using linear and nonlinear approaches

Low-density polyethylene (LDPE) passive sampling is very attractive for use in determining chemicals concentrations. Crucial to the measurement is the coefficient (KPE) describing partitioning between LDPE and environmental matrices. 255, 117 and 190 compounds were collected for the development of datasets in three different matrices, i.e., water, air and seawater, respectively. Further, 3 pp-LFER models and 9 QSPR models based on classical multiple linear regression (MLR) coupled with prevalent nonlinear algorithms (artificial neural network, ANN and support vector machine, SVM) were performed to predict LDPE-water (KPE-W), LDPE-air (KPE-A) and LDPE-seawater (KPE-SW) partition coefficients. These developed models have satisfying predictability (R2adj: 0.805–0.966, 0.963–0.991 and 0.817–0.941; RMSEtra: 0.233–0.565, 0.200–0.406 and 0.260–0.459) and robustness (Q2ext: 0.840–0.943, 0.968–0.984 and 0.797–0.842; RMSEext: 0.308–0.514, 0.299–0.426 and 0.407–0.462) in three datasets (water, air and seawater), respectively.In particular, the reasonable mechanism interpretations revealed that the molecular size, hydrophobicity, polarizability, ionization potential, and molecular stability were the most relevant properties, for governing chemicals partitioning between LDPE and environmental matrices. The application domains (ADs) assessed here exhibited the satisfactory applicability. As such, the derived models can act as intelligent tools to predict unknown KPE values and fill the experimental gaps, which was further beneficial for the construction of enormous and reliable database to facilitate a distinct understanding of the distribution for organic contaminants in total environment.

Addressing uncertainty in mouthing-mediated ingestion of chemicals on indoor surfaces, objects, and dust

In indoor environments, humans ingest chemicals present as surface residues and bound to settled particles (dust), through mouthing hands (hand-to-mouth transfer) and objects (object-to-mouth transfer). Here, we introduce a novel modeling approach in support of systematic investigation into the mouthing-mediated ingestion of chemicals present in indoor environments. This model explicitly considers the indoor dynamics of dust and chemicals, building on mechanistic links with physicochemical properties of chemicals, features of the indoor environment, and human activity patterns. The evaluation of this model demonstrates that it satisfactorily reproduces chemical hand loadings and exposure data reported in the literature. We then use the evaluated model to investigate the response of mouthing-mediated ingestion to chemical partitioning between the gas phase and solid phases, expressed as the octanol–air partition coefficient (KOA). Assuming a unit emission rate to the indoor environment, we find that low-volatility chemicals (with a KOA greater than 109) are more efficiently enriched in hand skin, resulting in higher mouthing-mediated ingestion than other compounds. For individuals living in a room with a typical level of dustiness, more than half of the chemical mass found in their hands comes from dust transfer, whereas more than half of the chemical mass ingested is the fraction present as residues on hands. We also use the new model to explore how the mouthing-mediated ingestion of chemicals is dependent on factors describing the indoor environment and human behavior. The model predicts that less frequent cleaning leads to higher accumulation of dust on indoor surfaces, thereby transferring more chemicals to hands and mouth in each contact. Introducing more dust into the room, but maintaining the same cleanup frequency, increases the dustiness of indoor surfaces, which promotes the transfer of relatively volatile chemicals (with a KOA lower than 109) to hands and mouth but decreases the transfer of chemicals with low volatility. More frequent hand contact with indoor surfaces increases both the hand loading and mouthing-mediated ingestion of chemicals, but the increases are more remarkable for adults than children because the higher surface contact frequency of children “saturates” hand loadings. An increase in handwashing frequency lowers the hand loading and mouthing-mediated ingestion of chemicals and this mitigating process is more prominent for relatively volatile chemicals. The new evaluated modeling approach can facilitate the prediction of mouthing-mediated ingestion for various age groups and the model predictions can be used to aid future fate and (bio)monitoring studies focusing on indoor contamination.

Determination of environmental properties and toxicity of octyl-dimethyl-para-aminobenzoic acid and its degradation products

Octyl-dimethyl-para-aminobenzoic acid (ODPABA) is one of compounds of emerging concern. It undergoes transformations under the influence of oxidizing or chlorinating agents and UV radiation forming products with different properties. There is very little experimental data concerning the environmental fate of ODPABA and its transformation products. Therefore, the purpose of the studies was to determine environmental parameters: water solubility, soil – water partition coefficient, octanol – air partition coefficient, bioconcentration factor as well as half-life in air, water and soil. Based on the results obtained, the persistence and migration possibilities of ODPABA and its transformation products in the aquatic environment were estimated. Moreover, the ecological toxicity of oxidation and chlorination products was investigated. Microtox®, Daphtoxkit F® and Artoxkit M® tests were used to determine toxicity. LC50 for Fish and Daphnia magna was calculated by Ecosar module. Studies have shown that as a result of ODPABA transformations, chloroorganic products are formed, which are lipophilic, are bioconcentrated in organic matter, are characterized by significant environmental persistence, can spread over considerable distances and are toxic. Oxidation products have significantly smaller impact on the environment. They are characterized by higher water solubility, lower bioconcentration factor and are less toxic.

Predicting Sorbent-Air Partition Coefficients for Terpenoids at Multiple Temperatures.

Partition coefficients describe the relative concentration of a chemical equilibrated between two phases. In the design of air samplers, the sorbent-air partition coefficient is a critical parameter, as is the ability to extrapolate or predict partitioning at a variety of temperatures. Our specific interest is the partitioning of plant-derived terpenes (hydrocarbons formed from isoprene building blocks) and terpenoids (with oxygen-containing functional groups) in polydimethylsiloxane (PDMS) sorbents. To predict as a function of temperature for compounds containing carbon, hydrogen, and oxygen, we developed a group contribution model that explicitly incorporates the van't Hoff equation. For the 360 training compounds, predicted values strongly correlate (R2 > 0.987) with values measured at temperatures from 60 °C to 200 °C. To validate the model with available literature data, we compared predictions for 50 additional C10 compounds, including 6 terpenes and 22 terpenoids, with values measured at 100 °C and determined an average relative error of 3.1 %. We also compared predictions with values measured at 25 °C. The modeling approach developed here is advantageous for properties with limited experimental values at a single temperature.

Development of an in vitro approach to point-of-contact inhalation toxicity testing of volatile compounds, using organotypic culture and air-liquid interface exposure

In vitro chemical risk assessment using human cells is emerging as an alternative to in vivo animal testing with reduced costs, fewer animal welfare concerns, and the possibility of greater human health relevance. In vitro inhalation toxicity testing of volatile compounds poses particular challenges. Here we report our efforts to establish a testing protocol in our own lab using the EpiAirway bronchial epithelium cell culture model and the Vitrocell 12/12 system for air-liquid interface (ALI) exposures. For purposes of method development, we used methyl iodide (MeI) as a test compound. We examined viability, cytotoxicity, and epithelial integrity responses. Dose-dependent, reproducible responses were observed with all assays. EpiAirway and BEAS-2B cytotoxicity responses to acute exposure were roughly similar, but EpiAirway was more resistant than BEAS-2B by the viability measurement, suggesting a proliferative response at low MeI concentrations. If wells were sealed to prevent evaporation, in-solution MeI concentration-response could be used to predict the response to MeI vapor within 2-fold by converting from the media- to the air-concentration at equilibrium using the blood:air partition coefficient for MeI. The long-term stability of EpiAirway cultures enabled repeated exposures over a 5-d period, which produced responses at lower concentrations than did acute exposure.

Measurement and Modeling the Phase Partitioning of Organophosphate Esters Using Their Temperature-Dependent Octanol-Air Partition Coefficients and Vapor Pressures.

Atmospheric concentrations of 11 organophosphate esters (OPEs) were measured in an urban area in Izmir, Turkey to explore their phase partitioning. Octanol-air partition coefficients (KOA) and vapor pressures (PL) of the OPEs were also measured as a function of temperature. Average Σ11OPE gas-phase concentrations were 1.77 ± 0.84 and 4.00 ± 1.77 ng/m3, while particle-phase concentrations were 1.95 ± 0.77 and 1.15 ± 0.36 ng/m3 during winter and summer, respectively. TCiPP1 dominated Σ11OPEs, followed by TnBP and TEP. OPE concentrations generally increased and shifted to gas-phase in the summer probably due to higher temperatures that favor partitioning to the gas-phase. Distribution between two phases covered a wide range from being primarily in gas-phase (TEP, TnBP) or particle-phase (EHDPP, TEHP, T2iPPP). Phase partitioning was also examined via four widely used models (KOA, Soot, Steady-State, and pp-LFER). All models underestimated the majority of particle-gas partition coefficients (KP) especially for the compounds having higher volatilities. Estimations based on the recently reported molecular weight of organic matter in urban aerosols (MWOM) and activity coefficients of OPEs in octanol (ξOCT) determined in the present study suggested that the basic assumptions of KOA-based models (i.e., ξOCT/ξOM and MWOCT/MWOM = 1) are not valid.

PBPK modeling of impact of nonalcoholic fatty liver disease on toxicokinetics of perchloroethylene in mice

BackgroundNonalcoholic fatty liver disease (NAFLD), a major cause of chronic liver disease in the Western countries with increasing prevalence worldwide, may substantially affect chemical toxicokinetics and thereby modulate chemical toxicity. ObjectivesThis study aims to use physiologically-based pharmacokinetic (PBPK) modeling to characterize the impact of NAFLD on toxicokinetics of perchloroethylene (perc). MethodsQuantitative measures of physiological and biochemical changes associated with the presence of NAFLD induced by high-fat or methionine/choline-deficient diets in C57B1/6 J mice are incorporated into a previously developed PBPK model for perc and its oxidative and conjugative metabolites. Impacts on liver fat and volume, as well as blood:air and liver:air partition coefficients, are incorporated into the model. Hierarchical Bayesian population analysis using Markov chain Monte Carlo simulation is conducted to characterize uncertainty, as well as disease-induced variability in toxicokinetics. ResultsNAFLD has a major effect on toxicokinetics of perc, with greater oxidative and lower conjugative metabolism as compared to healthy mice. The NAFLD-updated PBPK model accurately predicts in vivo metabolism of perc through oxidative and conjugative pathways in all tissues across disease states and strains, but underestimated parent compound concentrations in blood and liver of NAFLD mice. ConclusionsWe demonstrate the application of PBPK modeling to predict the effects of pre-existing disease conditions as a variability factor in perc metabolism. These results suggest that non-genetic factors such as diet and pre-existing disease can be as influential as genetic factors in altering toxicokinetics of perc, and thus are likely contribute substantially to population variation in its adverse effects.