Benzene in urine

Analytical Methods for Determining Benzene in Biological Samples 6-2 Analytical Methods for Determining Metabolites of Benzene in Urine... 

Screening methods are available for analysis of benzene in feces and urine (Ghoos et al. 1994) and body fluids (Schuberth 1994). Both employ analysis by capillary GC with an ion trap detector (ITD). Benzene in urine has been determined by trapping benzene stripped from the urine on a Carbotrap tube, followed by thermal desorption GC/flame ionization detection (FID). The detection limit is 50 ng/L and the average recovery is approximately 82% (Ghittori et al. 1993). Benzene in urine has also been determined using headspace analysis with capillary GC/photoionization detection (PID). The detection limit is 40 ng/L (Kok and Ong 1994). 

Methods are also available for determining metabolites of benzene in urine. A summary of available methods is shown in Table 6-2. Both GC/FID or GC/MS and high-performance liquid chromatography (HPLC) with ultraviolet detection (UV) have been used to measure urinary metabolites. 

Ljungkvist, G., Larstad, M., Mathiasson, L. Specific determination of benzene in urine using dynamic headspace and mass-selective detection. J. Chromatogr. B 721, 39 6 (1999)... 

ETHYL BENZENE Mandelic acid in urine End of shift at end of 1.5 g/g creatinine Ns... 

N-Methylformamide in urine Ethyl benzene End of shift 40 mg/g creatinine ... 

Human exposure to low levels of phenol is widespread because it is contained in many consumer products including mouthwashes, gargles, tooth drops, throat lozenges, and ointments (Douglas 1972 EPA 1980). Phenol is a normal product of protein metabolism, and it is also a metabolite of benzene. In persons not exposed to phenol or benzene, the total phenol concentration in the urine generally does not exceed 20 mg/L and is usually <10 mg/L (ACGIH 1991). 

Popp W, Rauscher D, Muller G et al. 1994. Concentrations of benzene in blood and S-phenylmercapturic acid and l, /-muconic acid in urine in car mechanics. Int Arch Occup Environ Health 66 1-6. 

Methods for Determining Biomarkers of Exposure and Effect. Exposure to 1,4-dichloro-benzene may be evaluated by measuring the levels of this compound in blood, breath, milk, and adipose tissue, and by measuring the level of 2,5-dichlorophenol, a metabolite of 1,4-dichlorobenzene, in urine (Bristol et al. 1982 Erickson et al. 1980 Jan 1983 Langhorst and Nestrick 1979 Pellizzari et al. 1985). Sensitive analytical methods are available for measurements in blood. Development of methods with improved specificity and sensitivity for other tissues and breath would be valuable in identifying individuals with low-level exposure. Development of standardized procedures would permit comparison of data and facilitate the study of correlations between exposure and measured levels biological samples. Interlaboratory studies are also needed to provide better performance data for methods currently in use. 

S. Myung, S. Yoon and M. Kim, Analysis of benzene ethylamine derivatives in urine using the programmable dynamic liquid-phase microextraction (LPME) device. Analyst, 2003,128(12), 1443-1446. 

Tests for phenol levels in urine have been used as an index of benzene exposure urinary phenol concentrations of 200mg/l are indica-... 

WalkleyJE, Pagnotto LD, Elkins HB The measurement of phenol in urine as an index of benzene exposure. Am Ind Hyg Assoc 7 22 362-367, 1961... 

Tardif et al. (1992, 1993 a, 1997) have developed a physiologically based toxicokinetic model for toluene in rats (and humans—see Section 4.1.1). They determined the conditions under which interaction between toluene and xylene(s) occurred during inhalation exposure, leading to increased blood concentrations of these solvents, and decreased levels of the hippurates in urine. Similar metabolic interactions have been observed for toluene and benzene in rats (Purcell et al., 1990) toluene inhibited benzene metabolism more effectively than the reverse. Tardif et al. (1997) also studied the exposure of rats (and humans) to mixtures of toluene, we/a-xylene and ethylbenzene, using their physiologically based pharmacokinetic model the mutual inhibition constants for their metabolism were used for simulation of the human situation. 

Gad El Karim, M.M.. Ramanujam, V.M.S. Legator, M.S. (1986) Correlation between the induction of micronuclei in bone marrow by benzene exposure and the excretion of metabolites in urine of CD-I mice. Toxicol, appl. Pharmacol., 85, 464 77... 

The biomarker should be specific for the chemical or metabolites of interest that is, it needs to be an unambiguous marker of exposure. Measurement of the unchanged parent chemical may have greater specificity than that of the metabolite, which may be common to several substances (Bernard and Lauwerys 1986). For example, if the metabolite of the parent chemical is being measured, the result may be equivocal if the same metabolite is produced endogenously or formed after exposure to other compounds. Occupational exposure to high air concentrations of benzene was formerly monitored by testing for its metabolite, phenol, in urine. However, the use of phenol to measure small environmental exposures to benzene is problematic in that many foods contain phenol, and the normal... 

Regarding styrene, the variety of controlled human oral and inhalation studies that relate dose to urinary concentration and the existence of a pharmacokinetic model (Droz and Guillemin 1983) could facilitate interpretation of mandelic acid concentration in urine. A caveat in this regard is that other chemical exposures can produce mandelic acid in urine, such as ethyl benzene, acetophenone, and phenylglycine (ACGIH 1991). Those background sources would be more likely to confound low-level general-population biomarker results than workplace end-of-shift results. 

Phase 1 oxidation products of benzene, including phenol, hydroquinone, catechol, 1,2,4-trihy-droxybenzene, and trans,Irans-muconic acid in urine, are evidence of exposure to benzene. Another substance observed in urine of individuals exposed to benzene is S-phenylmercapturic acid,... 

Foreman et al. [631] compared the direct method of the chelate formation with the preliminary ashing method for the analysis of beryllium in rat urine. A detailed study showed that both of the methods are satisfactory, whereas testing of column material and packings showed the best results for a PTFE column packed with SE-52. Down to 1 ng/ml of the element could be detected in urine with the use of an ECD and EDTA as a masking reagent and a 0.05 M benzene solution of trifluoroacetylacetone. 

Several tests can show if you have been exposed to benzene. Some of these tests may be available at your doctor s office. All of these tests are limited in what they can tell you. The test for measuring benzene in your breath must be done shortly after exposure. This test is not very helpful for detecting very low levels of benzene in your body. Benzene can be measured in your blood. However, since benzene disappears rapidly from the blood, measurements may be accurate only for recent exposures. In the body, benzene is converted to products called metabolites. Certain metabolites of benzene, such as phenol, muconic acid, and S-phenyl-N-acetyl cysteine (PhAC) can be measured in the urine. The amount of phenol in urine has been used to check for benzene exposure in workers. The test is useful only when you are exposed to benzene in air at levels of 10 ppm or greater. However, this test must also be done shortly after exposure, and it is not a reliable indicator of how much benzene you have been exposed to, since phenol is present in the urine from other sources (diet, environment). Measurement of muconic acid or PhAC in the urine is a more sensitive and reliable indicator of benzene exposure. The measurement of benzene in blood or of metabolites in urine cannot be used for making predictions about whether you will experience any harmful health effects. Measurement of all parts of the blood and measurement of bone marrow are used to find benzene exposure and its health effects. 

In vivo experiments on 4 human volunteers, to whom 0.0026 mg/cm2 of 14C-benzene was applied to forearm skin, indicated that approximately 0.05% of the applied dose was absorbed (Franz 1984). Absorption was rapid, with more than 80% of the total excretion of the absorbed dose occurring in the first 8 hours after application. Calculations were based on urinary excretion data and no correction was made for the amount of benzene that evaporated from the applied site before absorption occurred. In addition, the percentage of absorbed dose excreted in urine that was used in the calculation was based only on data from rhesus monkeys and may not be accurate for humans. In another study, 35-43 cm2 of the forearm was exposed to approximately 0.06 g/cm2 of liquid benzene for 1.25-2 hours (Hanke et al. 1961). The absorption was estimated from the amount of phenol eliminated in the urine. The absorption rate of liquid benzene by the skin (under the conditions of complete saturation) was calculated to be low, approximately 0.4 mg/cm2/hour. The absorption due to vapors in the same experiment was negligible. The results indicate that dermal absorption of liquid benzene is of concern, while dermal absorption from vapor exposure may not be of concern because of the low concentration of benzene in vapor form at the point of contact with the skin. No signs of acute intoxication due to liquid benzene dermally absorbed were noted. These results confirm that benzene can be absorbed through skin. However, non-benzene-derived phenol in the urine was not accounted for. 

Benzene was rapidly distributed throughout the bodies of dogs exposed via inhalation to concentrations of 800 ppm for up to 8 hours per day for 8-22 days (Schrenk et al. 1941). Fat, bone marrow, and urine contained about 20 times the concentration of benzene in blood benzene levels in muscles and organs were 1-3 times that in blood and erythrocytes contained about twice the amount of benzene found in plasma. During inhalation exposure of rats to 1,000 ppm (2 hours per/day, for 12 weeks), benzene was stored longer (and eliminated more slowly) in female and male rats with higher body fat content than in leaner animals (Sato et al. 1975). 

Data regarding metabolism of benzene in humans have come primarily from studies using inhalation exposures. Benzene is excreted both unchanged via the lungs and as metabolites in the urine. The rate and percentage of excretion via the lungs are dependent on exposure dose and route. Qualitatively, the metabolism and elimination of benzene appear to be similar in humans and laboratory animals, but no directly comparable studies are available (Henderson et al. 1989 Sabourin et al. 1988). 

Mice received a single oral dose of either 10 or 200 mg/kg radiolabeled benzene (McMahon and Bimbaum 1991). Radioactivity was monitored in urine, feces, and breath. At the low dose, urinary excretion was the major route of elimination. Hydroquinone glucuronide, phenylsulfate, and muconic acid were the major metabolites at this dose, accounting for 40%, 28%, and 15% of the dose, respectively. At 200 mg/kg, urinary excretion decreased to account for 42-47% of the administered dose, while respiratory excretion of volatile components increased to 46-56% of the administered dose. Fecal elimination was minor and relatively constant over both doses, accounting for 0.5-3% of the dose. 

The metabolic fate of benzene can be altered in fasted animals. In nonfasted rats that received an intraperitoneal injection of 88 mg of benzene, the major metabolites present in urine were total conjugated phenols (14-19% of dose), glucuronides (3-4% of dose), and free phenol (2-3% of dose). However, in rats fasted for 24 hours preceding the same exposure, glucuronide conjugation increased markedly (18-21% of dose) (Cornish and Ryan 1965). Free phenol excretion (8-10% of dose) was also increased in... 

Blood concentrations of benzene following inhalation exposure in mice and rats were adequately predicted. Bone marrow concentrations of benzene following subcutaneous injection in mice and inhalation exposure in rats were accurately predicted, as were blood concentrations of benzene in rats following intraperitoneal injection. For humans, the model slightly overestimated the data for benzene in expired air at the low concentration of 5 ppm. For the mid concentration of 25 ppm, excellent fit was obtained from the model for both benzene in expired air and blood benzene levels. Model agreement for expired benzene was also good at concentrations of 57 and 99 ppm. The model was also accurate in predicting the amount of phenol in the urine after a 5-hour exposure to 31.3 or 47 ppm. 

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