Benzene Uptake Research Articles

Shape-selective adsorption of aromatic molecules from water by tetramethylammonium–smectite

The adsorption of aromatic compounds by smectite exchanged with tetramethylammonium (TMA) has been studied. Aromatic compounds adsorbed by TMA–smectite are assumed to adopt a tilted orientation in a face-to-face arrangment with the TMA tetrahedra. The sorptive characteristics of TMA–smectite were influenced strongly by the presence of water. The dry TMA–smectite showed little selectivity in the uptake of benzen, toluene and xylene. In the presence of water, TMA–smectite showed a high degree of selectivity based on molecular size/shape, resulting in high uptake of benzene and progressively lower uptake of larger aromatic molecules. This selectivity appeared to result from the shrinkage of interlamellar cavities by water.

Determination of S-phenylmercapturic acid in the urine--an improvement in the biological monitoring of benzene exposure.

In an inhalation study rats were exposed to different doses of benzene, ranging from 1 to 500 p.p.m. The urine was sampled during the inhalation period of 8 h and for 24 h after exposure. S-Phenylmercapturic acid (S-PMA) in the urine was determined by amino acid analysis. Phenol was measured by gas chromatography/mass spectrometry. In both cases the correlation between benzene uptake and the excretion of the urinary metabolites was significant at the level of P = 0.01. The same significant correlation (P = 0.01) was demonstrable after i.p. administration of benzene at doses between 0.7 and 140.0 microliters/kg body weight. In the case of two collectives of workers who were exposed to air concentrations of up to 0.15 p.p.m. for 8 h and of up to 1.13 p.p.m. for 12 h respectively, the amount of S-PMA in the first urine samples after the shift was significantly higher than in samples collected at the beginning of the shift (P = 0.01). In the first collective the mean values and the standard deviations of the S-PMA concentrations in the samples at the beginning of the shift were 12.0 +/- 16.7 compared with 48.5 +/- 64.5 micrograms/g creatinine at shift end. In the second collective they were 25.1 +/- 25.1 compared with 70.9 +/- 109.2 micrograms/g creatinine. The level of significance of the difference between the concentration values of S-PMA at the beginning and end of the shift was P = 0.01. The phenol concentration did not differ significantly. These results suggest that S-PMA can be regarded as a useful indicator for monitoring individuals and collectives exposed to benzene at levels even less than 1 p.p.m.

Sorption Characteristics of Organic Compounds on hexadecyltrimethylammonium‐Smectite

AbstractWhen hexadedyltrimethylammonium (HDTMA) ion is exchanged for metal cations like calcium in smectite, the sorptive properties of the clay are greatly modified. The resultant HDTMA‐smectite complex behaves as a dual sorbent, in the sorption of organic compounds, in which the mineral fraction functions as a solid adsorbent and the organic (HDTMA) phase as a partition medium. Capacities of mineral adsorption and partition uptake by HDTMA in the HDTMA‐smectites are illustrated by sorption of benzene, trichloroethene (TCE), and water as vapors on the dry sample and by sorption of benzene and TCE from water. The exchanged HDTMA in clay is found to be a much more powerful partition medium than ordinary soil organic matter in the uptake of benzene and TCE. Based on this finding, HDTMA‐smectite appears to be an effective sorbent for removing organic contaminants from water. It is suggested that such sorptive organo‐clay complexes could be used to enhance the containment capabilities of clay landfill liners and bentonite slurry walls.

A method for repeated evaluation of benzene uptake in rats and mice during a six hour inhalation period.

Benzene uptake measurements and respiratory minute volume (RMV) were assessed in rats and mice during a 6-hour inhalation exposure to 300 ppm (v/v) of benzene vapor. The values for benzene uptake and RMV were used to compare predictions of inhaled dose in both species. The theoretical prediction assumed an unchanging RMV. The next prediction allowed adjustments for changes in RMV during exposure. The final prediction addressed benzene uptake directly. The uptake characteristics of benzene in both species were different from the theoretical prediction, from the prediction adjusted for changing RMV and from each other. The greatest difference was seen in rats where the observed benzene dose was only 28% of the theoretical value. The experiment was not designed to elucidate the causes for the difference between the predictions, nor was the data sufficient to suggest whether the rat or the mouse was a suitable model of benzene uptake in humans.

A Method for Repeated Evaluation of Benzene Uptake in Rats and Mice During a Six Hour Inhalation Period

Benzene uptake measurements and respiratory minute volume (RMV) were assessed in rats and mice during a 6-hour inhalation exposure to 300 ppm (v/v) of benzene vapor. The values for benzene uptake and RMV were used to compare predictions of inhaled dose in both species. The theoretical prediction assumed an unchanging RMV. The next prediction allowed adjustments for changes in RMV during exposure. The final prediction addressed benzene uptake directly. The uptake characteristics of benzene in both species were different from the theoretical prediction, from the prediction adjusted for changing RMV and from each other. The greatest difference was seen in rats where the observed benzene dose was only 28% of the theoretical value. The experiment was not designed to elucidate the causes for the difference between the predictions, nor was the data sufficient to suggest whether the rat or the mouse was a suitable model of benzene uptake in humans.

Effects of sublethal concentrations of zinc and benzene on striped bass, Morone saxatilis (Walbaum), infected with larval Anisakis nematodes

Young of the year striped bass, Morone saxatilis, were exposed to sublethal concentrations of zinc and benzene and infected with larval Anisakis nematodes to determine the effects of these stressors on various physiological parameters. Results indicated that both pollutants and parasites significantly decreased haematocrit values. Parasites alone increased the liver somatic index, decreased haematocrits and, in the initial phase of the experiment, lowered antibody titres. Pollutants alone did not appear to significantly affect antibody titres, nor was there any difference in zinc and benzene uptake in the livers of infected and non‐infected fish.

The effects of ethanol ingestion and repeated benzene exposures on benzene pharmacokinetics

Two groups of C57B1 6J mice were exposed to 300-ppm benzene vapor, 6 hr/day, 5 days/week for 20 exposures. One group received 10% ethanol (EtOH) in the drinking water commencing 20 hr prior to the initial exposure and continuing 5 days/week throughout the study. The second group received tap water. The uptake and clearance of benzene was followed in the blood during and after the 1st and 20th exposures. During the first benzene exposures, the mean steady state benzene concentrations in benzene/EtOH-treated mice and benzene/water-treated mice were 5.2 and 10.7 μg/ml, respectively. The mean elimination rate constants for the benzene/EtOH- and benzene/water-treated groups were 0.124 and 0.042 min −1, respectively. By 20 exposures, the benzene/EtOH group showed no change in mean blood steady state concentration (Css); however, the Css of the benzene/water group was reduced to 7.9 μg/ml. The mean elimination rate constants for the two groups were not different after the 20th exposure. The benzene/water mice exhibited a shift from mono- to biexponential clearance between the 1st and 20th exposures. Monoexponential clearances were observed for the benzene/EtOH group at both time points. These results indicate that 1 day of 10% EtOH consumption causes dramatic effects on benzene kinetics. After 20 days of treatment, the benzene/water and benzene/EtOH animals are kinetically similar. These changes in kinetics can be explained by the ability of ethanol and benzene to alter benzene metabolism.

Experimental evidence of the influence of sorption-heat release processes on the sorption kinetics of benzene in NaX zeolite crystals

Under constant-volume–variable-pressure conditions the sorption uptake of benzene by NaX zeolite crystals has been investigated with respect to the influence of external thermal conditions on the uptake rate. The information obtained permits quantitative conclusions concerning the influence of the sorption heat generated on the uptake rate, i.e. the decrease in apparent diffusivities calculated under the erroneous presumption of the isothermicity of the sorption process considered. A corresponding tentative mechanism which takes into account the generation of thermal interface barriers is proposed. Furthermore, there are experimental conditions for which the uptake of benzene by NaX zeolite crystals should be considered as an isothermic process. Within that parameter region agreement was obtained between the sorption diffusion data (corrected by the Darken equation) and the n.m.r. self-diffusivities, as reported earlier.

The pharmacokinetics of repetitive benzene exposures at 300 and 100 ppm in AKR Mice and Sprague-Dawley rats

Groups of AKR Mice and Sprague-Dawley rats were exposed to either 300 or 100 ppm benzene for 6 hr/day × 5 days/week for 20 days. The uptake and clearance of benzene was followed in blood during and after the 1st, 6th and 20th exposures. In rats, the maximum concentrations of benzene in blood (C max) were proportional to the exposure concentrations, that is the C max values at 300 ppm were three times the C max values at 100 ppm. This was not the case with the mice which showed C max values at 300 ppm equal to five to eight times the C max values at 100 ppm. At both exposure levels mice exhibited larger elimination rate constants than rats. Both rats and mice showed larger elimination rate constants at 100 ppm than at 300 ppm. At 300 ppm, the mice showed progressive increases in elimination rate constants, progressive decreases in C max and an unusual shift from monoexponential clearance to biexponential clearance between the 6th and 20th exposures. It is postulated that the induction of benzene-metabolizing enzymes and/or an increase in lipid tissue mass are responsible for the progressive changes of the kinetic parameters of the mice.

Benzene in blood and phenol in urine in monitoring benzene exposure in industry.

Determinations of benzene concentration in blood and of phenol in urine were made by head-space gas chromatography techniques on samples taken near the end of the work day from two groups of workers potentially exposed to low levels of benzene in the work-place atmosphere. Preliminary results suggest that benzene in blood is more reliable than phenol tests for assessing both exposure and uptake of benzene. Normal values of phenol in urine (10 mg/liter or less) were found in nearly all those cases in which benzene was detected in the blood.

The analysis and control of volatile hydrocarbon concentrations (e. g. benzene) during oil bioassays

It is well known that volatile hydrocarbons such as benzene, toluene, and xylene, which are abundant in many refined oils, affect phytoplankton growth. However, experiments to determine these effects in many cases have been improperly designed resulting in questionable conclusions. Experiments presented in this paper indicate that ambient benzene concentrations reported in the published literature may be lower than stated by an order of 10 to 100. By continuous monitoring the benzene concentration decrease was observed and it was possible to determine whether the loss was due to degassing because of loose closures or biological uptake. Unless tight closures are used benzene is quickly lost to the atmosphere (exponential decay rate ≌ 1.2d-1). Experiments demonstrated that benzene is quickly lost from cotton stoppered bioassay flasks that are typically used. Rubber stoppered flasks with little gaseous headspace showed minimum benzene loss. Biological uptake of benzene can be demonstrated when closures are secure and the effect of certain concentrations on growth can be correctly interpreted. Benzene concentrations above 10 to 20 ppm significantly reduce the growth rate of Skeletonema sp. The benzene concentration decreased quickly in 10 to 20 ppm benzene solutions implying metabolic uptake. These experiments indicate that proper closures and analysis of the volatile pollutant concentration during bioassay experiments increase the likelihood of correct interpretation and may yield additional insights into the causation factors.

The adsorption of benzene vapour from an air stream, by beds of charcoal: I. The most efficient physical arrangement of the bed

AbstractAir is often cleaned by passing contaminated air through a granular bed of an adsorbent such as charcoal. In such a situation the rate of flow of air is fixed and there is an upper limit to the physical size of the bed and an upper limit to the resistance of the bed to air‐flow through it. The problem considered is the optimum size of granule to be used in the bed and the optimum shape of the granule, leading to the longest life‐time of the bed. An empirical answer to the problem is given for the uptake of benzene by a BCNU steam‐activated charcoal; apparatus, experiments and results used are described. The method of working and the conclusion are applicable to any vapour/solid system.

Some Physical and Chemical Properties of Bovine Saliva which May Affect Rumen Digestion and Synthesis

Summary An investigation was conducted on 77 samples of saliva from dairy cattle to ascertain some of this secretion's chemical and physico-chemical properties. The average water content of 36 specimens was 99.12 per cent. The average pH of 54 samples protected by neutral paraffin oil from carbon dioxide loss was 8.53, whereas the average pH for the unprotected samples was 8.71. No appreciable variation was noted in the pH of saliva collected at 6-hour intervals over a 24-hour period, and the time of collection relative to the feeding time had no apparent effect on the reaction of the saliva. An analysis of 75 saliva samples showed an average ascorbic acid concentration of 0.15 mg. per cent, while the average plasma ascorbic acid level of the same animals was 0.47 mg. per cent. The deodorizing and surface active properties of cow's saliva were demonstrated. The surface tention of 55 samples was 47.10 dynes per cm. at 29° C., while typical adsorption curves were derived from the uptake of benzene by saliva. since dried cow's saliva took up benzene in a manner characteristic of adsorption, it was believed that the absorbent materials of saliva were altered in some way by drying, resulting in the loss of the adsorbing property.