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At least 667 records · Page 37Linked to original sources
PubMed2006

On the difficulties of predicting the adsorption of volatile organic compounds at low pressures in microporous solid: the example of ethyl benzene.

Adsorption isotherms of toluene and ethyl benzene, at 25 degrees C and 40 degrees C, were determined in two microporous activated carbons and one zeolite. Significant differences were found in the adsorption behavior, at low pressures, between the two vapors on the same adsorbent material. The quantities of adsorbed ethyl benzene at 25 degrees C, in the low-pressure region, were lower than what was observed at 40 degrees C in all the studied adsorbents, contrary to what was found for toluene. This fact was not related to kinetic effects at the two temperatures nor to vapor swelling of the adsorbents structure. Also, there was no molecular sieving since at high pressures the toluene and ethyl benzene occupied the same adsorption space. The differences found in the ethyl benzene adsorption at the two temperatures pose difficulties in the analysis of the adsorption data and, therefore, in the prediction of results. This is discussed in the analysis of the results with the application of the Dubinin-Astakhov equation and in the estimation of the isosteric heats of adsorption. The adsorption potentials of two possible ethyl benzene conformations were estimated for the adsorption in the pores of activated carbon from the Horvath and Kawazoe model, and the values compared with those found experimentally. The results were interpreted in terms of the ethyl benzene conformation effects when the molecule is confined in pores that are about the same size of one of the conformations.

Journal Article↗
PubMedDate not supplied

Reference range concentrations of N-acetyl-S-(2-hydroxyethyl)-L-cysteine, a common metabolite of several volatile organic compounds, in the urine of adults in the United States.

N-acetyl-S-(2-hydroxyethyl)-L-cysteine (2-hydroxyethyl mercapturic acid, HEMA) is a urinary metabolite of several hazardous chemicals, including vinyl chloride (VC), ethylene oxide (EO), and ethylene dibromide (EDB). Information about the levels of HEMA in the general population is useful for assessing human exposures to HEMA parent compounds, including VC, EO, and EDB. To establish reference range concentrations for HEMA, we analyzed urine samples from 412 adult participants in the Third National Health and Nutrition Examination Survey (NHANES II) by using isotope-dilution high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). HEMA was detected in 71% of the samples examined. Creatinine-corrected concentrations ranged from less than 0.68 microg/g creatinine to 58.7 microg/g creatinine; the 95th percentile concentration was 11.2 microg/g creatinine; and the geometric mean and median creatinine-corrected concentrations were both 1.6 microg/g creatinine. We observed a statistically significant difference (P=0.0001) in the creatinine-corrected geometric mean concentration values of HEMA between smokers (2.8 microg/g creatinine) and nonsmokers (1.1 microg/g creatinine). The high levels of HEMA seen among smokers likely originated from HEMA-producing chemicals known to be present in tobacco smoke.

Acetylcysteine↗
PubMedDate not supplied

Worker exposure to aromatic volatile organic compounds in dry cleaning stores.

This study evaluated worker exposure to aromatic compounds and perchloroethylene (PERC) in dry cleaning stores relative to four different solvents. For benzene and toluene, there was no significant difference among the indoor air concentrations of the four different solvents. For ethylbenzene, m,p-xylene, and o-xylene, the air concentrations were significantly higher in the dry cleaning stores using Solvent V, YuClean, and Super New Cleaner than in those using a PERC mixture. Breath concentrations measured prior to and immediately after work were not significantly different for benzene and toluene, whereas breath concentrations of ethylbenzene, m,p-xylene, and o-xylene were significantly higher (p<0.05) in the samples collected immediately after work compared with those collected prior to work. The breath concentrations of benzene and toluene both prior to and immediately after work showed no upward or downward trend for 7 consecutive days excluding Sunday, starting from Monday. In contrast, the breath concentrations of ethylbenzene, m,p-xylene, and o-xylene measured immediately after work showed a slight upward trend in three subjects. However, this trend was most likely not due to an accumulated body burden from repeated daily work, but rather was the result of the amount of solvent used each day. It is concluded that dry cleaning workers using the aromatics-contained solvents are exposed to elevated levels of some aromatic compounds compared with the dry cleaning workers using PERC. Further study is recommended to examine the presence of other air toxics inside dry cleaning stores using these solvents.

Air Pollution, Indoor↗
PubMed1990

Assessment of population exposure and carcinogenic risk posed by volatile organic compounds in indoor air.

A number of air pollutants are being found in low concentrations in indoor and outdoor air. Several studies have measured these concentrations for a large number of compounds in hundreds of residences. The concentrations range over several orders of magnitude over time and space. The log-normal distributions that are found make it possible to assess the impact on the health of populations, especially for genotoxic effects for which a threshold concentration is not expected to exist. Spreadsheets can be constructed which incorporate the unit risk of a substance for cancer, the distribution of concentrations of the substance in the population, and the size of the population into an assessment of the expected excess cases of cancer that can be attributed to the population exposure to such a toxicant. This approach allows for the evaluation of population risk for different substances as found in different environments, and for the evaluation of the relative efficacy of different strategies for population risk reduction.

Air Pollutants↗
PubMed1999

Chamber testing of adsorption of volatile organic compounds (VOCs) on material surfaces.

A simple test chamber method to quantify adsorption and desorption of organic compounds on material surfaces is described. Important environmental parameters such as temperature, relative humidity and air velocity were varied and controlled independently around typical indoor values. Experiments were performed with alpha-pinene and toluene in concentrations of 160-300 micrograms/m3. The measurements show adsorption on and desorption from wool carpet, nylon carpet, polyvinyl chloride (PVC) floor coverings, cotton curtain material and the empty chamber. The ranking of the materials, with respect to their sorption capacity, is as mentioned above. The adsorption of alpha-pinene was higher than the adsorption of toluene for all the materials. Air velocity was not found to influence the sorption of alpha-pinene and toluene on wool carpet, tested with air velocities at 0, 10 and 20 cm/s. The experiments were carried out during both the adsorption and the desorption phase. The uncertainty of the experiments was lowest during the desorption phase. Based on the results obtained, it can be recommended that sorption experiments should be performed as desorption phase experiments. A one-sink model, based on the Langmuir adsorption isotherm, appears adequate to describe the results.

Adsorption↗
PubMed1991

Neuropsychological assessment for detecting adverse effects of volatile organic compounds on the central nervous system.

Because there are no direct biological markers for the substances implicated in indoor air exposure, it is impossible to directly measure if an individual or group of individuals has been exposed to a potentially neurotoxic substance in the workplace. Behavioral changes may be the earliest and only manifestation of central nervous system (CNS) effects and are often too subtle to be revealed by routine physical or neurological examination. Neuropsychological techniques are sensitive to subtle behavioral/cognitive changes that can result from exposure to neurotoxins. These techniques consist of oral and written tests that are administered by a trained examiner on a one-to-one basis. In general, a wide variety of cognitive domains are evaluated. The typical battery generally includes assessing orientation, attention, intelligence, language, visual memory, verbal memory, perception, visuoconstruction, simple motor speed, psychomotor speed, and mood. As with most assessment techniques, the neuropsychological methods have limitations. One major drawback is the availability of appropriate norms that are used to compare the results of a specific individual. Because these tasks are greatly affected by age, intelligence, and in some instances sex, the availability of appropriate norms is mandatory to determine if the CNS has been effected. Although neuropsychological tests are sensitive to the presence of CNS involvement, they are not specific. Patterns of performance seen with specific instances of neurotoxic exposure may also be seen with a number of other diseases of the CNS such as dementia, cerebrovascular disease, hydrocephalus, or normal aging. In addition, neuropsychiatric symptoms such as anxiety and/or depression are often manifested as cognitive difficulties that will mimic the cognitive dysfunction seen with toxicity of the CNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain↗
PubMed1995

Recent advances in measuring exhaled breath and estimating exposure and body burden for volatile organic compounds (VOCs).

An improved portable breath measurement method has been developed that allows 1-min sampling times. The equipment has been successfully tested in field and chamber studies. Results of these studies suggest that breath levels following known exposures are predictable and reproducible across a small number of volunteers. The residence times in the body and the distribution in body compartments of several common air toxics have been determined. A simple four-compartment linear model is capable of fitting the observed data. The main parameters of the model include the fraction f of the parent compound exhaled under steady-state conditions and the residence times tau i, in the tau ith compartment. The values of these parameters for several VOCs and for the four body compartments (blood, vessel-rich tissues, vessel-poor tissues, and fat) are provided.

Body Burden↗
PubMed1984

The role of skin absorption as a route of exposure for volatile organic compounds (VOCs) in drinking water.

Assessments of drinking water safety rely on the assumption that ingestion represents the principal route of exposure. A review of the experimental literature revealed that skin penetration rates for solvents are remarkably high, and that the stratum corneum is a less effective barrier to penetration than traditionally assumed. Based on published skin absorption rates, we used Fick's law (Jos = Kop delta Cos) to determine permeability constants for selected compounds. We then calculated dose per kilogram for nine different exposure situations and compared this to the oral dose per kilogram. We found that skin absorption contributed from 29-91 per cent of the total dose, averaging 64 per cent. Dose per kilogram body weight ranged from .0002 mg/kg-.18 mg/kg, with an average of .03 mg/kg. In weak aqueous solutions, flux of the solute is directly proportional to concentration. Laboratory approaches differ markedly from environmental exposures and can underestimate absorption. We conclude that skin absorption of contaminants in drinking water has been underestimated and that ingestion may not constitute the sole or even primary route of exposure.

Administration, Oral↗
PubMed2003

[Screenings of 23 plant species in Beijing for volatile organic compound emissions].

The VOCs emissions from plants are mainly isoprene and monoterpenes, which account for 2/3 of the total emissions from biosphere. 23 kinds of typical plants in Beijing area were screened to estimate the emission rates of isoprene and monoterpenes by adopting a bag-enclosure sampling method followed by a GC-FID analysis. It was found that such deciduous trees as Sophora japnica and Salix babyloniaca etc. were mainly emitting isoprene and coniferous trees as Pinus tabulaetormis mainly released monoterpenes. The study also showed that the emission of isoprene were affected by both temperature and Photosynthetic Active Radiation (PAR), while monoterpene emissions were mainly temperature-dependent.

Butadienes↗