Air Partition Coefficients Research Articles

Measurements of Octanol−Air Partition Coefficients (KOA) for Polybrominated Diphenyl Ethers (PBDEs): Predicting Partitioning in the Environment

Octanol−air partition coefficients (KOA) are reported for 13 polybrominated diphenyl ethers (PBDEs) over the temperature range (15−45) °C. KOA exhibited a log−linear relationship with inverse absolute temperature, and values at 25 °C range from 9.3 (PBDE-17) to 12.0 (PBDE-126). These are approximately 1 to 2 orders of magnitude greater than those measured for the counterpart polychlorinated biphenyls (PCBs). PBDEs also showed a strong temperature dependence. The enthalpy of phase change from octanol to air, ΔHOA, was (≈70 to ≈120) kJ mol-1. This corresponds to a 20−100 times higher KOA value at 5 °C versus 35 °C. A method is presented for estimating KOA at any temperature for additional PBDEs using relative retention times. Log KOA values were compared against two sets of recently published subcooled liquid vapor pressures (poL) that show significant discrepancies. Activity coefficients in octanol (γO) for PBDEs ranged from 1 to 10 when one set of vapor pressures was used. This was consistent with other c...

Quantitative relationships between molecular structures, environmental temperatures and octanol–air partition coefficients of PCDD/Fs

A concise quantitative model that incorporates information on both environmental temperature ( T) and molecular structures, for logarithm of octanol–air partition coefficient ( K OA) to base 10 (log K OA) of PCDDs, was developed. Partial least squares (PLS) analysis together with 14 quantum chemical descriptors were used to develop the quantitative relationships between structures, environmental temperatures and properties (QRSETP) model. It has been validated that the obtained QRSETP model can be used to predict log K OA of other PCDDs. Molecular size, environmental temperature ( T), q + (the most positive net atomic charge on hydrogen or chlorine atoms in PCDD molecules) and E LUMO (the energy of the lowest unoccupied molecular orbital) are main factors governing log K OA of PCDD/Fs under study. The intermolecular dispersive interactions and thus the size of the molecules play a leading role in governing log K OA. The more chlorines in PCDD molecules, the greater the log K OA values. Increasing E LUMO values of the molecules leads to decreasing log K OA values, implying possible intermolecular interactions between the molecules under study and octanol molecules. Greater q + values results in greater intermolecular electrostatic repulsive interactions between PCDD and octanol molecules and smaller log K OA values.

SELECTING INTERNALLY CONSISTENT PHYSICOCHEMICAL PROPERTIES OF ORGANIC COMPOUNDS

Methods are presented for selecting values of chemical properties of vapor pressure, water solubility, Henry's law constant, and octanol—water and octanol—air partition coefficients, which are subject to thermodynamic constraints, while taking advantage of all measurements. The aim of the mathematical procedures is to find the one set of internally consistent partitioning parameters that is minimally divergent from the experimental values. Information about the reliability or uncertainty of reported values can be accounted for by weighing factors. A similar approach is applied to the temperature dependence of these properties. The influence of partial miscibility of the octanol—water system is discussed and a correction is suggested for this effect. The selection method is applied to 50 mostly aromatic chemicals for which multiple measured partitioning data are available. The resulting sets of consistent property data are presented and discussed.

Measurement of particle-bound polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs) in Arctic air at Alert, Nunavut, Canada

Weekly filter samples, representing air-borne particles, at Alert, Nunavut, (82°30′N, 62°20′W) collected during the winter of 2000/2001 have been analysed for polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs). The sampling period coincided with the occurrence of the Arctic Haze (December–April) when air-borne particulate concentrations are generally high at Alert. Atmospheric phase distribution at average ambient temperature (−28.2°C) estimated using the Junge–Pankow adsorption model and the adsorption model based on octanol–air partition coefficients have shown that most PCDD/F congeners would be particle-bound under such conditions; with particle fractions >90%. The concentrations of both ΣPCDDs and ΣPCDFs observed were lower than those found at Ny-Ålesund (78°55′N, 11°56′E) and other locations worldwide. This is attributable to the remoteness of the site and the absence of anthropogenic activities nearby. An apparent peak in concentrations occurred during the third week of 2001 (15–22/1/2001). Weekly averaged 5-day Lagrangian back trajectories have shown that Alert was mainly affected by air originated from North Atlantic and North America during the first week of 2001. The origin of the airmass shifted eastwards further into Russia and Eurasia during the second and third weeks when the air concentrations of PCDD/Fs peaked at Alert. Then, the influence from Eurasia decreased while the North Atlantic sector regained dominance when the concentrations tapered off during the fourth and fifth weeks. In spite of the remoteness of Alert, congener profiles in most samples were enriched with PCDFs, corresponding to “source” profiles as suggested by Wagrowski and Hites (Environ. Sci. Technol. 34 (2000) 2952). Similar profiles were observed in air and tree bark at other Arctic locations. These profiles were probably the result of PCDD/F physical–chemical properties, which influence their transport behaviour between sources and receptors, as well as the unique Arctic environmental conditions. Therefore, the “source” and “sink” homologue profiles generally applicable to sample collected at temperate sites cannot be applied to those collected in the high Arctic.

Measurement of octanol–air partition coefficients using solid-phase microextraction (SPME)—application to hydroxy alkyl nitrates

Multifunctional organic compounds are thought to constitute a major component of the organic matter found in atmospheric particles. Their partitioning into the organic matter depends on their structure, their chemical properties and the properties of the absorbing matrix. It was recently shown that octanol is a suitable surrogate for organic particles and the octanol–air partition coefficient ( K OA) was suggested as a useful tool for estimating the partitioning of organic compounds into atmospheric particles that contain high organic mass fractions. In this paper, we present a new and simple technique for the determination of K OA using solid phase microextraction (SPME) relative to a known Henry's law constant. We apply the technique for the determination of K OA of β-, γ- and δ-C 3–C 5 hydroxy alkyl nitrates. The temperature dependence of K OA for some of the compounds is also measured. It is shown that the solubility constants of these compounds are higher in octanol than in water and that the solubility in octanol increases with the length of the hydrophobic chain and with increasing distance between the hydroxy and the nitrooxy groups. Partition coefficients between the gas and particulate phase ( K p) are calculated using the determined K OA values and their atmospheric implications are discussed.

Human Physiologic Factors in Respiratory Uptake of 1,3-Butadiene

1,3-Butadiene (BD), a suspected human carcinogen, is used as the raw material in industries to make synthetic butyl rubber and plastics. Simulation models using experimental animal data have shown that physiologic factors play an important role in the kinetic behavior of BD. However, human data are limited. The aim of this inhalation study was to identify influential human physiologic factors in the respiratory uptake of BD. We recruited 133 healthy volunteers in Boston, Massachusetts, into this study and tested them under an approved human subjects protocol. Each subject was exposed to 2 ppm (4.42 mg/m3) BD for 20 min, followed by purified air for another 40 min. Five exhaled breath samples collected during exposure were used to determine the respiratory uptake of BD, which was defined as absorbed BD (micrograms) per kilogram of body weight during exposure. Although subjects were given identical administered doses (40 ppm x min), there was a wide range of uptake, 0.6-4.9 microg/kg. Of the studied physiologic factors, the blood:air partition coefficient and alveolar ventilation were most significant in determining the respiratory uptake (p < 0.001 for each). In addition, in the multiple regression analysis, females had significantly higher respiratory uptake of BD than males on a weight basis. For all subjects, increasing age and cigarette smoking led to significantly decreased respiratory uptake of BD. The results of this human study are consistent with previous kinetic simulations and animal studies. The findings also suggest that interindividual variation in human physiologic factors that affect the exposure-internal dose relationship should be considered while also exploring exposure-disease associations in future epidemiologic research.

Human physiologic factors in respiratory uptake of 1,3-butadiene.

1,3-Butadiene (BD), a suspected human carcinogen, is used as the raw material in industries to make synthetic butyl rubber and plastics. Simulation models using experimental animal data have shown that physiologic factors play an important role in the kinetic behavior of BD. However, human data are limited. The aim of this inhalation study was to identify influential human physiologic factors in the respiratory uptake of BD. We recruited 133 healthy volunteers in Boston, Massachusetts, into this study and tested them under an approved human subjects protocol. Each subject was exposed to 2 ppm (4.42 mg/m3) BD for 20 min, followed by purified air for another 40 min. Five exhaled breath samples collected during exposure were used to determine the respiratory uptake of BD, which was defined as absorbed BD (micrograms) per kilogram of body weight during exposure. Although subjects were given identical administered doses (40 ppm x min), there was a wide range of uptake, 0.6-4.9 microg/kg. Of the studied physiologic factors, the blood:air partition coefficient and alveolar ventilation were most significant in determining the respiratory uptake (p < 0.001 for each). In addition, in the multiple regression analysis, females had significantly higher respiratory uptake of BD than males on a weight basis. For all subjects, increasing age and cigarette smoking led to significantly decreased respiratory uptake of BD. The results of this human study are consistent with previous kinetic simulations and animal studies. The findings also suggest that interindividual variation in human physiologic factors that affect the exposure-internal dose relationship should be considered while also exploring exposure-disease associations in future epidemiologic research.

Quantitative structure–pharmacokinetic relationship modelling

This article presents the current methods in quantitative structure–pharmacokinetic relationship (QSPkR) modelling along with examples using chemicals of toxicological significance. The common method involves: (i) collecting pharmacokinetic data or determining pharmacokinetic parameters (e.g. elimination half-life, volume of distribution) by fitting to experimental data; and (ii) associating them with the structural features of chemicals using a Free–Wilson model. Such QSPkRs have been developed for a few series of chemicals but their usefulness is limited to the exposure scenario and conditions under which the experimental data were originally collected. The alternative approach involves the development of quantitative structure–property relationship (QSPR) models for parameters, blood:air partition coefficient, tissue:blood partition coefficient, maximal velocity for metabolism and Michaelis affinity constant, of physiologically-based pharmacokinetic (PBPK) models which are useful for conducting species, route, dose and scenario extrapolations of the tissue dose of chemicals. Mechanistic QSPRs are available for predicting tissue:blood and blood:air partition coefficients from molecular structure information of chemicals, whereas such approaches are not currently available for hepatic metabolism parameters. However, at the present time, the pharmacokinetics of inhaled volatile organic chemicals can be simulated adequately by considering the physiological limits of the hepatic extraction ratio (0–1) and molecular structure-based estimates of partition coefficients in the PBPK model. This current state-of-the-art of structure-based modelling of pharmacokinetics will advance with the development of QSPRs for other chemical-specific parameters of PBPK models. Integrated QSPR–PBPK modelling should facilitate the identification of chemicals of a family that possess desired properties of bioaccumulation and blood concentration profile in both test animals and humans.

Blood:air partition coefficients of individual and mixtures of trihalomethanes

The objective of the present study was to determine the rat blood:air partition coefficients ( P b:a) of chloroform, bromodichloromethane, dibromochloromethane and bromoform present in vitro individually or as mixtures. The experimentally determined P b:a of chloroform, bromodichloromethane, dibromochloromethane and bromoform present individually corresponded to ( mean± SD, n=8 ) 21.3±1.8, 41.8±6.2, 97.5±4.1 , and 187±7.4, respectively. The P b:a of these trihalomethanes (THMs) showed a decreasing trend during mixed in vitro exposures to 0.138±0.002 or 0.273±0.002 μmol of each of the four THMs. In general, the P b:a determined during mixed exposures differed by ⩽15% of the average P b:a determined for THMs present individually. The results of this study suggest that an alteration of P b:a of the individual THMs is unlikely to occur at the blood concentrations of THMs observed during mixed exposures in rats.

PHYSIOLOGICALLY BASED CLEARANCE/EXTRACTION MODELS FOR COMPOUNDS METABOLIZED IN THE NOSE: An Example with Methyl Methacrylate

Airstream clearance (with units of volume/time) is the volumetric flow from which chemical would have to be completely removed to account for the net loss in the nose. Extraction is the proportion of airflow from which the chemical is completely removed. Over the past several years we have developed physiologically based clearance-extraction (PBCE) models for the nose to assess the physiological, biochemical, and anatomical factors that control airstream clearance. A generic clearance equation was derived for single airway/tissue compartments that had a separate air region and either one, two, or three underlying tissue regions. For all of these structures, airstream clearance (Cl(sys)) has a common form-Equation (1)-related to tissue clearance (Cltot), gas-phase diffusional clearance (PAgas), airflow (Q), and the mucus air partition coefficient (Hmuc:a). Clsys = CltotHm:aPAgasQ/CltotHm:a(Q + PAgas) + PAgasQ. A physiologically based clearance-extraction (PBCE) model for the whole nose combined three separate nasal tissue regions, each with a four-compartment tissue stack (air, mucus, epithelial tissue, and submucosal region). A steady-state solution of the PBCE model successfully described literature results on the steady-state extraction of methyl methacrylate (MMA) and several other metabolized vapors. Model-derived tissue dosimetry estimates, that is, the amount of MMA metabolized in the target epithelial compartment of the olfactory region, for rats and humans provide dosimetric adjustment factors (DAFs) required in calculating a human reference concentration (RfC) from rodent studies. Depending on the assignment of esterase activities to sustentacular and submucosal regions, the DAFs from the PBCE model varied between 1.6 and 8.0, compared to the default value of 0.145. From the experience with MMA, a minimal data set could be defined for building the PBCE model. It consists of mucus:air and blood:air partition coefficients, metabolic constants for enzymatic hydrolysis in nasal tissues from rat and human tissues, immunohistochemistry of the distribution of these activities in rats and human olfactory tissues, and extraction studies in anesthetized rats to assess the total nasal metabolism of the test compound.

OVERVIEW OF UPPER RESPIRATORY TRACT VAPOR UPTAKE STUDIES

This review is aimed at highlighting toxicologically relevant physiological and biochemical factors that influence the delivery of inhaled vapors to nasal tissues. Numerous experiments in rodents have shown that vapor uptake efficiencies are dependent on vapor solubility (as measured by blood:air partition coefficient) and inspiratory flow rate. Nasal tissues are rich in xenobiotic metabolizing enzymes, and it has been shown experimentally through the use of metabolic inhibitors that inspired vapors are metabolized in nasal tissue and that this process serves to enhance inspired vapor uptake efficiency in that site. Metabolism-based species differences in vapor uptake have been observed among rodent species. Concentration-dependent changes in vapor uptake have also been observed and related to saturation of local metabolic pathways at high exposure concentrations. Therefore, appropriate consideration of local metabolism is necessary for comprehensive high- to low-dose or species extrapolations of nasal toxicity data. Recent studies have provided evidence of sensory nerve-mediated reflex responses that alter nasal vascular function and may alter nasal inspired vapor dosimetric relationships. In toto, these studies also indicate the need to define uptake behavior for a vapor of interest over a wide range of exposure concentrations due to the possibility of nonlinear metabolism kinetics or the induction of nasal reflex and/or toxic responses. Such data are required for the formulation of a robust nasal dosimetry model.

Physiological modeling reveals novel pharmacokinetic behavior for inhaled octamethylcyclotetrasiloxane in rats.

Octamethylcyclotetrasiloxane (D4) is an ingredient in selected consumer and precision cleaning products. Workplace inhalation exposures may occur in some D4 production operations. In this study, we analyzed tissue, plasma, and excreta time-course data following D4 inhalation in Fischer 344 rats (K. Plotzke et al., 2000, Drug Metab. Dispos. 28, 192-204) to assess the degree to which the disposition of D4 is similar to or different from that of volatile hydrocarbons that lack silicone substitution. We first applied a basic physiologically based pharmacokinetic (PBPK) model (J. C. Ramsey and M. E. Andersen, 1984, Toxicol. Appl. Pharmacol. 73, 159-175) to characterize the biological determinants of D4 kinetics. Parameter estimation techniques indicated an unusual set of characteristics, i.e., a low blood:air (P(b:a) congruent with 0.9) and a high fat:blood partition coefficient (P(f:b) congruent with 550). These parameters were then determined experimentally by equilibrating tissue or liquid samples with saturated atmospheres of D4. Consistent with the estimates from the time-course data, blood:air partition coefficients were small, ranging from 1.9 to 6.9 in six samples. Perirenal fat:air partition coefficients were large, from 1400 to 2500. The average P(f:b) was determined to be 485. This combination of partitioning characteristics leads to rapid exhalation of free D4 at the cessation of the inhalation exposure followed by a much slower redistribution of D4 from fat and tissue storage compartments. The basic PK model failed to describe D4 tissue kinetics in the postexposure period and had to be expanded by adding deep-tissue compartments in liver and lung, a mobile chylomicron-like lipid transport pool in blood, and a second fat compartment. Model parameters for the refined model were optimized using single-exposure data in male and female rats exposed at three concentrations: 7, 70, and 700 ppm. With inclusion of induction of D4 metabolism at 700 ppm (3-fold in males, 1-fold in females), the parameter set from the single exposures successfully predicted PK results from 14-day multiple exposures at 7 and 700 ppm. A common parameter set worked for both genders. Despite its very high lipophilicity, D4 does not show prolonged retention because of high hepatic and exhalation clearance. The high lipid solubility, low blood:air partition coefficient, and plasma lipid storage with D4 led to novel distributional characteristics not previously noted for inhaled organic hydrocarbons. These novel characteristics were only made apparent by analysis of the time-course data with PBPK modeling techniques.

The relevance of physical activity for the kinetics of inhaled gaseous substances.

Inhalation is the most important route of absorption for many volatile substances. The inhaled chemical is distributed via the bloodstream into the organs and tissues. It is eliminated mainly unchanged by exhalation and also via metabolism. The blood concentration can be considered as a surrogate for the body burden of the chemical. It depends on the rate of uptake and on the rate of elimination. The rate of uptake by inhalation is determined by the blood:air partition coefficient of the gaseous compound, the actual concentration of the chemical already in the blood entering the lungs, the blood flow through the lungs, and the alveolar ventilation. The latter is greatly influenced by physical activity, which thus has a crucial impact on the rate of uptake. Consequently, the blood concentration of an inhaled chemical and the resulting alveolar retention, representing the rate of metabolism at steady-state, are dependent on the intensity of physical work. Both parameters can be calculated for steady-state conditions using simple algebraic equations, if one assumes that the rate of metabolic elimination is limited by the blood flow through the metabolizing organs. This assumption is valid for many rapidly metabolized inhaled gases and vapours at low concentrations present under workplace conditions. The derived equations give the theoretical background for the observations presented from a series of experimental studies which demonstrate that physical activity can be a major determinant of the toxicokinetics of inhaled compounds. Practical examples illustrate the procedure. We conclude that workplace-related physical activity should be taken into account for compounds with blood:air partition coefficients above 6 in the determination of occupational limit concentrations in air.

Gas--particle partitioning of organic compounds and its interpretation using relative solubilities.

A review is presented of the current understanding of the partitioning phenomena of relatively low vapor pressure organic chemicals between the gas phase and atmospheric particulates. The phenomena have been interpreted as adsorption, absorption, or a combination of both and corresponding theoretical equations suggested to quantify partitioning. Empirical correlations involving the chemical's vapor pressure and octanol--air partition coefficient are discussed. It is suggested that insights into selecting preferred correlations and into the nature of the partitioning phenomena can be enhanced by treating the partition coefficient as a ratio of a solubility or pseudo-solubility of the chemical in the aerosol particle to that in air. Such particle solubilities when calculated for PCBs, alkanes, and PAHs show remarkable constancy and are generally consistent with near-ideal absorption into organic matter. An exception occurs when the PAH is generated simultaneously with the aerosol and unusually high solubilities are observed, indicative of adsorption to active carbon surfaces. Recommendations are made for interpreting experimental partitioning data and for the use of correlations for predictive purposes.

OVERVIEW OF UPPER RESPIRATORY TRACT VAPOR UPTAKE STUDIES

This review is aimed at highlighting toxicologically relevant physiological and biochemical factors that influence the delivery of inhaled vapors to nasal tissues. Numerous experiments in rodents have shown that vapor uptake efficiencies are dependent on vapor solubility (as measured by blood:air partition coefficient) and inspiratory flow rate. Nasal tissues are rich in xenobiotic metabolizing enzymes, and it has been shown experimentally through the use of metabolic inhibitors that inspired vapors are metabolized in nasal tissue and that this process serves to enhance inspired vapor uptake efficiency in that site. Metabolism-based species differences in vapor uptake have been observed among rodent species. Concentration-dependent changes in vapor uptake have also been observed and related to saturation of local metabolic pathways at high exposure concentrations. Therefore, appropriate consideration of local metabolism is necessary for comprehensive high- to low-dose or species extrapolations of nasal toxicity data. Recent studies have provided evidence of sensory nerve-mediated reflex responses that alter nasal vascular function and may alter nasal inspired vapor dosimetric relationships. In toto, these studies also indicate the need to define uptake behavior for a vapor of interest over a wide range of exposure concentrations due to the possibility of nonlinear metabolism kinetics or the induction of nasal reflex and/or toxic responses. Such data are required for the formulation of a robust nasal dosimetry model.

PHYSIOLOGICALLY BASED CLEARANCE/EXTRACTION MODELS FOR COMPOUNDS METABOLIZED IN THE NOSE: An Example with Methyl Methacrylate

Airstream clearance (with units of volume/time) is the volumetric flow from which chemical would have to be completely removed to account for the net loss in the nose. Extraction is the proportion of airflow from which the chemical is completely removed. Over the past several years we have developed physiologically based clearance-extraction (PBCE) models for the nose to assess the physiological, biochemical, and anatomical factors that control airstream clearance. A generic clearance equation was derived for single airway/tissue compartments that had a separate air region and either one, two, or three underlying tissue regions. For all of these structures, airstream clearance (Clsys) has a common form-Equation (1)-related to tissue clearance (Cltot), gas-phase diffusional clearance (PAgas), airflow (Q), and the mucus air partition coefficient (Hmuc:a). Clsys = (CltotHm:aPAgasQ) / (CltotHm:a(Q+PAgas) + PAgasQ) A physiologically based clearance-extraction (PBCE) model for the whole nose combined three separate nasal tissue regions, each with a four-compartment tissue stack (air, mucus, epithelial tissue, and submucosal region). A steady-state solution of the PBCE model successfully described literature results on the steady-state extraction of methyl methacrylate (MMA) and several other metabolized vapors. Model-derived tissue dosimetry estimates, that is, the amount of MMA metabolized in the target epithelial compartment of the olfactory region, for rats and humans provide dosimetric adjustment factors (DAFs) required in calculating a human reference concentration (RfC) from rodent studies. Depending on the assignment of esterase activities to sustentacular and submucosal regions, the DAFs from the PBCE model varied between 1.6 and 8.0, compared to the default value of 0.145. From the experience with MMA, a minimal data set could be defined for building the PBCE model. It consists of mucus:air and blood:air partition coefficients, metabolic constants for enzymatic hydrolysis in nasal tissues from rat and human tissues, immunohistochemistry of the distribution of these activities in rats and human olfactory tissues, and extraction studies in anesthetized rats to assess the total nasal metabolism of the test compound.

A mass transfer model for simulating VOC sorption on building materials

The sorption of volatile organic compounds (VOCs) by different building materials can significantly affect VOC concentrations in indoor environments. In this paper, a new model has been developed for simulating VOC sorption and desorption rates of homogeneous building materials with constant diffusion coefficients and material–air partition coefficients. The model analytically solves the VOC sorption rate at the material–air interface. It can be used as a “wall function” in combination with more complex gas-phase models that account for non-uniform mixing to predict sorption process. It can also be used in conjunction with broader indoor air quality studies to simulate VOC exposure in buildings.

A Comparative Study of the Gas-Particle Partitioning of PCDD/Fs, PCBs, and PAHs

Air samples were taken concurrently for four sampling events in the winter of 1998 at three contrasting sites: an urban center and two rural sites. The rural sites were characterized by the extensive usage of coal and wood for space heating. Samples were analyzed for PCDD/Fs, PCBs, and PAHs. Recently measured octanol−air partition coefficients (Koa) for PCDD/Fs enabled a comparison of the Koa-based versus the subcooled liquid vapor pressure (pL)-based partition model for all three compound classes. Both Koa and pL were found to be excellent descriptors of the gas-particle partitioning of PCDD/Fs, PCBs, and PAHs. However, regressions for log Kp-log pL gave higher regression coefficients than for log Kp-log Koa. Both models showed roughly similar relative states of equilibrium for PCDD/Fs, PCBs, and PAHs. PCBs were closest to equilibrium at the urban site. It is argued that newly released particles at the rural sites caused nonequilibrium partitioning at those sites for PCBs. PAHs were released at all site...

New Indoor Carpet as an Adsorptive Reservoir for Volatile Organic Compounds

Carpet is generally recognized as a source of volatile organic compounds (VOCs) in indoor air. However, carpet systems can also serve as adsorptive sinks with the potential for reductions in peak VOC concentrations and subsequent re-emission of VOCs over prolonged periods of time. A series of experiments involving eight VOCs, several carpet systems, and environmental conditions were completed using a set of parallel chambers to characterize the sorptive interaction between VOCs and carpet. A linear adsorption/desorption model was observed to be appropriate for short-term sorption events. New carpet fibers treated with stain protection generally accounted for only a small fraction of mass sorbed to carpet. Most of the sorbed mass was accounted for by either the underlying pad (cushion) or a combination of the pad and structural backing. Equilibrium partition coefficients were observed to be correlated to chemical vapor pressure and octanol−air partition coefficient. Variations in relative humidity (RH) had...

Development of a method for the application of solid-phase microextraction to monitor biodegradation of volatile hydrocarbons during bacterial growth on crude oil

A quantitative solid-phase microextraction, gas chromatography, flame ionization detector (SPME-GC-FID) method for low-molecular-weight hydrocarbons from crude oil was developed and applied to live biodegradation samples. Repeated sampling was achieved through headspace extractions at 30°C for 45 min from flasks sealed with Teflon Mininert. Quantification without detailed knowledge of oil–water–air partition coefficients required the preparation of standard curves. An inverse relationship between retention time and mass accumulated on the SPME fibre was noted. Hydrocarbons from C5 to C16 were dated and those up to C11 were quantified. Total volatiles were quantified using six calibration curves. Biodegradation of volatile hydrocarbons during growth on crude oil was faster and more complete with a mixed culture than pure isolates derived therefrom. The mixed culture degraded 55% of the compounds by weight in 4 days versus 30–35% by pure cultures of Pseudomonas aeruginosa, Rhodococcus globerulus or a co-culture of the two. The initial degradation rate was threefold higher for the mixed culture, reaching 45% degradation after 48 h. For the mixed culture, the degradation rate of individual alkanes was proportional to the initial concentration, decreasing from hexane to undecane. P. fluorescens was unable to degrade any of the low-molecular-weight hydrocarbons and methylcyclohexane was recalcitrant in all cases. Overall, the method was found to be reliable and cost-effective. Journal of Industrial Microbiology & Biotechnology (2000) 25, 155–162.