Effects of methanol on styrene metabolism among workers occupationally exposed at low concentrations

A survey was conducted in the second half of a work week on 39 male workers who were occupationally exposed to styrene in combination with methanol and methyl acetate during the production of plastic buttons. Time-weighted average exposure during an 8-h shift to styrene (Sty-A) and methyl acetate was monitored by carbon cloth-equipped personal samplers and to methanol by water-equipped ones. Urine samples were collected near the end of the shift and analyzed for mandelic (MA-U) and phenylglyoxylic acids (PhGA-U) by HPLC. Geometric mean styrene concentration was 12.4 ppm (micrograms/g) with the maximum of 46 ppm, whereas the values for methanol and methyl acetate in combination were 23.5 ppm and 229 ppm, respectively. The relationship of MA-U and PhGA-U with Sty-A was examined by linear regression analysis. The equations for the regression lines were compared with the results from a previous survey (Ikeda et al. 1983) in which workers were exposed only to styrene, and the methods employed were identical with that in the present study. The comparison showed no evidence to suggest that styrene metabolism is suppressed by coexposure to methanol and methyl acetate at low concentrations below the current occupational exposure limit of 200 ppm.

Urinary methylchloroform rather than urinary metabolites as an indicator of occupational exposure to methylchloroform

In order to compare methylchloroform (MC, or 1,1,1-trichloroethane) per se and its metabolites in urine as indicators of occupational exposure to this solvent, 50 male solvent workers were studied in the second half of a working week to evaluate the exposure-excretion relationship. The time-weighted average intensity of solvent exposure of individuals during an 8-h shift was monitored by personal diffusive sampling. Urine samples were collected near the end of the shift and were analyzed for MC and its metabolites [i.e., trichloroacetic acid (TCA), trichloroethanol (TCE) and total trichloro-compounds (TTC; the sum of TCA and TCE)] by head-space gas chromatography. MC per se, TCA, TCE, and TTC in urine correlated significantly (P < 0.01) with MC in ambient air, and among the four the correlation coefficient was highest for MC. The same result were obtained by multiple regression analysis in which ambient air MC was taken as the dependent variable and either the three indicators urinary MC, TCA, and TCE or the two indicators urinary MC and TTC were taken as independent variables. Taking the specificity and selectivity of the analyte as well as the simple and hazardous chemical-free procedure of analysis into consideration, it is concluded that MC is the analyte of choice as an indicator of occupational exposure to MC, when urine is selected as a specimen available by noninvasive sampling.

Toluene in blood as a marker of choice for low-level exposure to toluene

The validity of two new biological exposure markers of toluene in blood (TOL-B) and toluene in urine (TOL-U) was examined in comparison with that of the traditional marker of hippuric acid in urine (HA-U) in 294 male workers exposed to toluene in workroom air (TOL-A), mostly at low levels. The exposure was such that the geometric mean for toluene was 2.3 ppm with a maximum of 132 ppm; the workers were also exposed to other solvents such as hexane, ethyl acetate, styrene, and methanol, but at lower levels. The chance of cutaneous absorption was remote. Higher correlation with TOL-A and better sensitivity in separating the exposed workers from the nonexposed subjects were taken as selection criteria. When workers exposed to TOL-A at lower concentrations (< 50 ppm, < 10 ppm, < 2 ppm, etc.) were selected with correlation with TOL-A was examined, TOL-B showed the largest correlation coefficient which was significant even at TOL-A of < 1 ppm, whereas correlation of HA-U was no longer significant when TOL-A was < 10 ppm. TOL-U was between the two extremes. The sensitivities of TOL-B and TOL-U were comparable; HA-U showed the lowest sensitivity. Thus, it was concluded that TOL-B is the indicator of choice for detecting toluene exposure at low levels.

Nodular lesions in renal tuberculosis

We retrospectively studied the CT findings of renal tuberculosis in 27 cases (32 kidneys). As a characteristic CT finding, nodular lesions were recognized in 20 kidneys. Low density nodules were found in three kidneys, isodensity nodules in seven, and high density nodules in 10. In a case examined by follow-up five years later, the low and isodensity nodules changed to high density nodules with decreasing volume. Ultrasound demonstrated the high density nodules as low-echo mass lesions. These nodular lesions corresponded with the localized foci in the renal parencyma and/or pyocalyx. We consider that the density differences in nodular lesions reflect the process of water absorption from the caseous necrotizing materials of tuberculosis.

Subcortical low intensity in early cortical ischemia

PURPOSE

To describe subcortical low intensity on T2- and proton density-weighted MR images in early cortical ischemia and to discuss a cause of these findings.

METHODS

Nine patients with early cortical ischemia were studied with proton density- and T2-weighted images, and T1-weighted images at 1.5 T. Gadolinium enhancement was added in six cases.

RESULTS

In all cases there was high to intermediate intensity in the cortex and low intensity in the subcortical white matter (subcortex) on the proton density- and T2-weighted images. No significant signal abnormalities were shown on T1-weighted images in the subcortex; gyriform enhancement was seen in the affected cortex in all of the six patients studied with gadolinium. Of the four patients with follow-up MRs, the subcortical low intensity changed to high intensity in two and remained low in two patients in the chronic stage. Neither hemorrhage nor calcification was seen on CT.

CONCLUSION

Iron accumulation in the subcortex caused by disruption of the axonal transportation and continuous production of free radicals caused by the hypoxic-ischemic state most likely reduces the signal intensity of the subcortex on the proton density- and T2-weighted images. The subcortical low intensity on the proton density- and T2-weighted images is an important diagnostic sign of early cortical ischemia.

Exposure monitoring and health effect studies of workers occupationally exposed to cyclohexane vapor

A survey was conducted in the second half of a working week on 33 women who either applied glue (with cyclohexane as an almost exclusive solvent component) or worked in the vicinity of glue application. Carbon cloth-equipped diffusive samplers were used for personal measurement of time-weighted average intensity of exposure to the solvent. The geometric mean and the highest cyclohexane concentration observed in air were 27 ppm and 274 ppm, respectively. Concentrations of cyclohexanol in urine samples and cyclohexane in whole blood and serum collected at the end of a shift showed significant correlations with the solvent exposure levels. Urinary cyclohexanone also correlated, but with a smaller correlation coefficient. The observation suggests that cyclohexanol in urine and cyclohexane in blood or serum collected at the end of a shift are useful indicators of occupational exposure to cyclohexane vapor. Quantitative estimation of balance at the end of the shift suggested that only a minute portion (< 1%) of cyclohexane absorbed is excreted in the urine as cyclohexanol, almost exclusively as a glucuronide. A survey of subjective symptoms revealed an increase in the prevalence of "dimmed vision " and "unusual smell", but hematology and serum biochemistry testing did not indicate any specific signs.

Absence of mutagenicity in peripheral lymphocytes of workers occupationally exposed to methyl methacrylate

Chromosome aberration rates and sister chromatid exchange frequency were examined in the peripheral lymphocytes of 38 male workers who were engaged in organic glass production and exposed to methyl methacrylate (MMA) vapors at the concentrations of 0.9 ppm to 71.9 ppm. The results were compared with the findings in the concurrent nonexposed male subjects. Comparison of the exposed group with the nonexposed controls showed that there were no exposure-related changes in chromosome aberration rate. SCE frequency was higher in the exposed group than in the controls, but this was considered to be due to higher ages of the former group than that of the latter. In fact, selection of nonsmokers and further classification of the exposed nonsmokers into two groups of those with exposure below and above a median MMA concentration (ca. 4 ppm) failed to show any difference among the three nonsmoking groups in cytogenetic parameters, or any dose-dependency. The present results, although in a limited number of subjects, indicate that occupational methyl methacrylate exposure under the conditions studied is not associated with mutagenicity. This conclusion confirms the absence of mutagenicity of methyl methacrylate in humans, and is in general agreement with a majority of the results of studies on mutagenicity in vitro, animal carcinogenicity and occupational cancer epidemiology of methyl methacrylate.

Biological monitoring and possible health effects in workers occupationally exposed to methyl methacrylate

Monitoring by means of blood and urine analysis for methanol was successfully applied in 32 male workers who were exposed to methyl methacrylate (MMA) monomer at 6 ppm as a geometric mean and at 112 ppm as the maximum. Measurement of time-weighted average (TWA) intensity of the vapor exposure was successfully conducted with a diffusive sampler with activated carbon cloth as an adsorbent. Methanol concentrations in whole blood, serum, and urine samples were measured by headspace gas chromatography. The methanol concentrations in the three biological samples collected at the end of 8-h workshifts related linearly with the TWA MMA vapor concentrations, with correlation coefficients of 0.8-0.9. Quantitative evaluation of MMA in vapor and of methanol in urine suggests that only 1.5% of MMA inhaled will be excreted in urine as methanol. There were no significant clinical symptoms or abnormal hematological or serum biochemical findings at this exposure level, except that some workers complained throat irritation and frequent cough and sputa. The results indicate that biological monitoring by analysis for methanol is sensitive enough to detect MMA exposure at levels at which no serious health effects are to be expected.

Exposure-excretion relationship of styrene and acetone in factory workers: a comparison of a lipophilic solvent and a hydrophilic solvent

A factory survey was conducted in the second half of a working week on 41 exposed male workers, who were engaged in fiber-reinforced plastics work and exposed to the mixed vapors of styrene and acetone. Nonexposed workers, 20 men, were recruited from the same factory. Styrene and acetone in respiratory zone air were monitored for a 8-h shift with carbon cloth- and water-equipped personal diffusive samplers, respectively. Blood and urine samples were collected at the shift-end. Acetone and styrene concentrations in whole blood, serum and urine were measured by head-space gas chromatography, and phenylglyoxylic acid in urine by high-performance liquid chromatography. All biological exposure indicators analyzed correlated significantly with the intensity of exposure to the corresponding solvent during the shift. The slopes of the regression lines indicate that a very small fraction of styrene absorbed will be excreted into urine as styrene per se, and that styrene is quite effectively excreted into urine after metabolic conversion. In contrast, the slopes of regression lines for acetone suggest that acetone distributes both in the blood and urine quite evenly. When the distribution of the solvent in serum was compared with that in the whole blood, it was found that almost all of styrene in blood is present in the serum, whereas acetone distributed very evenly in the cellular and noncellular fractions of the blood.

Comparative evaluation of blood and urine analysis as a tool for biological monitoring of n-hexane and toluene

Blood and urine samples were collected from 57 male Japanese solvent workers [exposed to n-hexane (Hex-A), ethyl acetate, and toluene (Tol-A) at 1.5, 2.3, and 2.3 ppm as GM-TWA, respectively] and also from 20 male nonexposed workers at the end of a 8-h shift, and analyzed for n-hexane (Hex-B) and toluene (Tol-B) in blood, and n-hexane (Hex-U), toluene (Tol-U), 2,5-hexanedione [both with (HD-U/cHYD) and without hydrolysis (HD-U/sHYD)] and hippuric acid (HA-U) in urine. Regression analysis showed that both Hex-B and Tol-B correlated significantly with corresponding exposure to the solvents. Solvents in urine (Hex-U and Tol-U) also correlated with solvents in air but with smaller correlation coefficients than the solvents in blood. Both HD-U/cHYD and HD-U/sHYD showed significant correlation with Hex-A, but HA-U failed to do so with Tol-A. Based on the correlation among biological exposure indicators and solvent concentration in air, sensitivity as an exposure indicator was compared between the solvent in blood and the metabolite in urine in terms of the lowest solvent concentration at which the exposed can be separated (with statistical significance) from the nonexposed (the lowest separation concentration; LSC). The LSC was 3.9 ppm for Hex-B, 1 to 2 ppm for HD-U/sHYD and 10 to 30 ppm for HD-U/cHYD, suggesting that HD-U/sHYD is superior even to Hex-B in detecting low n-hexane exposure; this high sensitivity of HD-U/sHYD is due to the absence of HD-U/sHYD in the urine from the nonexposed.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological monitoring of acrylonitrile exposure through a new analytical approach to hemoglobin and plasma protein adducts and urinary metabolites in rats and humans

A new, simple and fast procedure of measuring acrylonitrile (ACN) in ACN derived mercapturic acids such as S-(2-cyanoethyl)-L-cysteine(CyEC), and in hemoglobin (Hb) and plasma protein adducts and urinary metabolites in rats and humans exposed to ACN was developed. ACN in mercapturic acids or proteins was analyzed by capillary gas chromatography (GC) by liberating ACN at a high-temperature in the injector port of GC with or without oxidizing sulfur atoms of the ACN-bound cysteines into sulfoxide form by hydrogen peroxide in vitro. At 350 degrees C, more than 90% of ACN in authentic CyEC was recovered by this method. Increasing a single ip dose of ACN from 5 to 50 mg/kg produced proportional increases in ACN bound to Hb 24 hr after the treatment. The alkylation of plasma protein with ACN was about 1/10 as low as that of Hb. After repeated daily ip doses of 1-10 mg/kg, ACN in Hb decreased with a half-life of about 9 days. ACN was also detected in the blood of workers exposed to ACN for 1 to 10 years at a Siberian synthetic rubber factory.

Urinalysis vs. blood analysis, as a tool for biological monitoring of solvent exposure

Blood and urine samples were collected at the end of an 8-h workshift from 30 male workers exposed to a mixture of n-hexane, ethyl acetate and toluene (each being about 2 ppm as geometric means) and also from 20 nonexposed male workers. Blood samples were analyzed for n-hexane and toluene, and urine samples were analyzed for n-hexane, toluene, 2,5-hexanedione (both with and without hydrolysis) and hippuric acid. Based on the correlation between biological exposure indicators and solvent concentrations in air, sensitivity as an exposure indicator was compared between solvents in blood and solvents or metabolites in urine in terms of the lowest solvent concentration at which the exposed subjects can be statistically separated from the nonexposed. Both n-hexane and toluene in blood were sensitive enough to detect the exposure at 6.1 ppm and 1.4 ppm, respectively. n-Hexane exposure below 2 ppm was detectable also by urinalysis for 2,5-hexadione without hydrolysis. Urinary hippuric acid, however, failed to detect low toluene exposure under the conditions studied. Of additional interest is the fact that toluene in urine correlated significantly with toluene in air, which apparently deserves further study for confirmation.

Formic acid excretion in comparison with methanol excretion in urine of workers occupationally exposed to methanol

A semiautomated head-space gas chromatographic (GC) method was developed for measuring formic acid in urine. The method consists of heating 1 ml urine sample in a 20-ml air-tight vial in the presence of 1 ml sulfuric acid and 2 ml ethanol at 60 degrees C for 30 min for ethyl esterification and air-liquid equilibrium, followed by automatic injection of 1 ml head-space air into a flame ionization detector GC. The detection limit was 1 mg/l for formic acid. The method was applied to measure formic acid in the shift-end urine samples from 88 workers exposed to methanol at 66.6 ppm (as geometric mean) and in urine samples from 149 nonexposed controls. Methanol concentrations were also determined. Regression analysis showed that urinary formic acid concentrations, as observed or corrected for either creatinine concentration or specific gravity of urine (1.016), correlated significantly with time-weighted average intensities of exposure to methanol vapor. Men excreted significantly more formic acid than women. Comparison with methanol excretion suggested, however, that urinary formic acid is less sensitive than urinary methanol as an indicator of methanol vapor exposure, primarily because the background level for formic acid (26 mg/l as arithmetic mean, or 23 mg/l as geometric mean) is more than ten times higher than the level for methanol (1.9 mg/l as arithmetic mean, or 1.7 mg/l as geometric mean). After theoretical methanol exposure at infinite concentration, the urinary formic acid/methanol ratio should be about 0.4.

Comparative evaluation of urinalysis and blood analysis as means of detecting exposure to organic solvents at low concentrations

One hundred and forty-three workers exposed to one or more of toluene, xylene, ethylbenzene, styrene, n-hexane, and methanol at sub-occupational exposure limits were examined for the time-weighted average intensity of exposure by diffusive sampling, and for biological exposure indicators by means of analysis of shift-end blood for the solvent and analysis of shift-end urine for the corresponding metabolite(s). Urinalysis was also performed in 20 nonexposed control men to establish the "background level." Both solvent concentrations in blood and metabolite concentrations in urine correlated significantly with solvent concentrations in air. Comparison of blood analysis and urinalysis as regards sensitivity in identifying low solvent exposure showed that blood analysis is generally superior to urinalysis. It was also noted that estimation of exposure intensity on an individual basis is scarcely possible even with blood analysis. Solvent concentration in whole blood was the same as that in serum in the case of the aromatics, except for styrene. It was higher in blood than in serum in the case of n-hexane, and lower in the cases of styrene and methanol.

In vitro hydrolysis of methyl acetate, a limitation in application of head-space gas-chromatography in biological monitoring of exposure

Stoichiometric conversion of methyl acetate to methanol in vitro was detected when methyl acetate was incubated with blood for 2 to 8 h. The velocity of the reaction was so fast that almost all of methyl acetate disappeared in 8 h. The methanol formation was further confirmed by means of gas-chromatography-mass spectrometry. The capacity to hydrolyze methyl acetate was evenly distributed in cellular and noncellular fractions of blood, but not in urine. The significance of the observation is discussed in relation to biological monitoring of exposure to industrial ester solvents by means of head-space gas-chromatography of blood samples.

Curvi-linear relation between acetone in breathing zone air and acetone in urine among workers exposed to acetone vapor

An occupational health study was conducted on 45 acetone-exposed male workers in combination with 343 non-exposed men to examine the quantitative relationship between the intensity of acetone vapor exposure and the concentration of acetone in urine. The time-weighted average acetone concentrations were measured by means of diffusive samplers with water as absorbent, whereas urine samples were collected at the end of the shift as well as before the shift on the next morning. Acetone concentration in shift-end urine did not increase when the workers were exposed to acetone up to approx. 15 ppm, and this was followed by a gradual increase at a higher atmospheric acetone concentration, in a manner dependent to acetone vapor concentration. The comparison in acetone concentrations between the urine samples collected at the shift-end and those before the shift of the next morning showed that the levels in two sets of samples were the same among those exposed to 15 or less ppm acetone, whereas acetone in the shift-end samples was significantly higher than the counterpart levels in the pre-shift samples among those exposed to acetone at more than 15 ppm.

Monitoring of workers exposed to a mixture of toluene, styrene and methanol vapours by means of diffusive air sampling, blood analysis and urinalysis

Exposure of 34 male workers to combined toluene, styrene and methanol was monitored by personal diffusive sampling of solvent vapours in breathing zone air, analysis of shift-end blood for the 3 solvents and analysis of shift-end urine for hippuric, mandelic and phenylglyoxylic acids and methanol. The exposure of most of the workers was below current occupational exposure limits. Regression analysis showed that a linear correlation exists for each of the 3 solvents between any pairs of the concentrations in air, blood and urine. Namely, toluene, styrene and methanol concentrations in blood obtained at the end of a shift are linearly related to the time-weighted average intensity of exposure to corresponding solvents, and also hippuric, mandelic and phenylglyoxylic acids as well as methanol in shift-end urine. The concentrations of hippuric, mandelic and phenylglyoxylic acids as well as methanol in urine correlated with the respiratory exposure intensity. Comparison of the present results with the exposure--excretion relationship after occupational exposure to the individual solvent showed that no modification in metabolism is induced by the combined exposure when exposure is low, as in the present case.

Occupational dimethylformamide exposure. 2. Monomethylformamide excretion in urine after occupational dimethylformamide exposure

The relationship between the 8-h time-weighted average (TWA) intensity of exposure to N,N-dimethylformamide (DMF) vapor (with little possibility of skin contact with liquid DMF) and the subsequent excretion of N-monomethylformamide (MMF) precursor in shift-end urine samples was examined in 116 workers exposed to DMF and 92 workers exposed to DMF in combination with toluene. Urinary MMF level was examined also in 42 non-exposed subjects. The TWA vapor concentration in breathing zone air of each worker was successfully measured by means of a recently developed diffusive sampler in which water was used as an absorbent. The examination of gas chromatographic (GC) conditions for MMF determination showed that the formation of MMF was not saturated when the injection port temperature was set at 200 degrees C, reached a plateau at 250 degrees C, and showed no additional increase at 300 degrees C. There was a linear relationship between DMF in air and MMF in urine with a regression equation of y = 1.65 x + 1.69 (r = 0.723, P less than 0.01), where y is MMF (unit; mg/l, uncorrected for urine density) in urine and x is DMF (ppm) in air, when only those exposed to DMF were selected, and the injection port temperature was set at 250 degrees C. From this equation, it was possible to estimate that about 10% of the DMF absorbed will be excreted into urine as the MMF precursor. The slope of the regression line was significantly smaller among those exposed to DMF and toluene in combination as compared with those with DMF exposure only.

Occupational dimethylformamide exposure. 1. Diffusive sampling of dimethylformamide vapor for determination of time-weighted average concentration in air

A diffusive sampling method with water as absorbent was examined in comparison with 3 conventional methods of diffusive sampling with carbon cloth as absorbent, pumping through National Institute of Occupational Safety and Health (NIOSH) charcoal tubes, and pumping through NIOSH silica gel tubes to measure time-weighted average concentration of dimethylformamide (DMF). DMF vapors of constant concentrations at 3-110 ppm were generated by bubbling air at constant velocities through liquid DMF followed by dilution with fresh air. Both types of diffusive samplers could either absorb or adsorb DMF in proportion to time (0.25-8 h) and concentration (3-58 ppm), except that the DMF adsorbed was below the measurable amount when carbon cloth samplers were exposed at 3 ppm for less than 1 h. When both diffusive samplers were loaded with DMF and kept in fresh air, the DMF in water samplers stayed unchanged for at least for 12 h. The DMF in carbon cloth samplers showed a decay with a half-time of 14.3 h. When the carbon cloth was taken out immediately after termination of DMF exposure, wrapped in aluminum foil, and kept refrigerated, however, there was no measurable decrease in DMF for at least 3 weeks. When the air was drawn at 0.2 l/min, a breakthrough of the silica gel tube took place at about 4,000 ppm.min (as the lower 95% confidence limit), whereas charcoal tubes could tolerate even heavier exposures, suggesting that both tubes are fit to measure the 8-h time-weighted average of DMF at 10 ppm.

Occupational dimethylformamide exposure. 3. Health effects of dimethylformamide after occupational exposure at low concentrations

A factory survey was conducted in a plant where N,N-dimethylformamide (DMF) was in use during the production of polyurethane plastics and related materials. In all, 318 DMF-exposed workers (195 men and 123 women) and 143 non-exposed controls (67 men and 76 women) were examined for time-weighted average exposure (to DMF and other solvents by diffusive sampling), hematology, serum biochemistry, subjective symptoms, and clinical signs. Most of the exposed workers were exposed only to DMF, whereas others were exposed to a combination of DMF and toluene. DMF exposure in the former group was up to 7.0 ppm (geometric mean on a workshop basis), whereas it was up to 2.1 ppm in combination with 4.2 ppm toluene. Both hematology and serum biochemistry, results (including aspartate and alanine aminotransferases, gamma-glutamyl transpeptidase and amylase) were essentially comparable among the 3 groups. There was, however, a dose-dependent increase in subjective symptoms, especially during work, and in digestive system-related symptoms such as nausea and abdominal pain in the past 3-month period. The prevalence rate of alcohol intolerance complaints among male (assumedly) social drinkers was also elevated in relation to DMF dose.

Methanol in urine as a biological indicator of occupational exposure to methanol vapor

The exposure-excretion relationship and possible health effects of exposure to methanol vapor were studied in 33 exposed workers during the second half of 2 working weeks. Urinary methanol concentrations were also determined in 91 nonexposed subjects. The geometric mean value for methanol in urine samples from the latter was less than 2 mg/l (95% upper limit of normal, less than 5 mg/l) when log-normal distribution was assumed. Among the exposed workers, the methanol level in urine samples collected prior to the work shift exceeded the 95% upper limit of normal. The time-weighted average intensity of exposure to methanol vapor was measured using personal sampling devices (in which water severed as an absorbent) in 48 cases of methanol exposure (i.e., 2 of the 33 exposed workers failed to provide urine samples, whereas 17 subjects were examined twice). Methanol concentrations in urine were determined in samples collected at the end of the shift from the 48 exposed cases as well as from 30 nonexposed controls. There was a significant correlation between the exposure to methanol vapor at concentrations of up to 5,500 ppm and the levels of methanol measured in the shift-end urine samples. The calculation indicated that a mean level of 42 mg methanol/l urine (95% confidence range, 26-60 mg/kg) was excreted in the shift-end urine sample following 8 h exposure to methanol at 200 ppm (the current occupational exposure limit). Dimmed vision and nasal irritation were among the most frequent symptoms complained during work. Three cases showing clinical signs of borderline significance were identified.

Dose-dependent increase in 2,5-hexanedione in the urine of workers exposed to n-hexane

The concentrations of 2,5-hexanedione (2,5-HD), an n-hexane metabolite, and 2-acetylfuran (2-AF) were measured in urine samples from 123 workers who had predominantly been exposed to n-hexane vapor and 53 workers who had experienced no exposure to solvents. The time-weighted average intensity of exposure to n-hexane vapor was determined by a diffusive sampling method. For biological monitoring of exposure, urine samples were collected late in the afternoon during the second half of a working week and were analyzed in the presence and absence of acid hydrolysis (at pH less than 0.5) for 2,5-HD and 2-AF by gas chromatography on a nonpolar capillary DB-1 column. The urinary 2,5-HD concentration increased as a linear function of the intensity of exposure to n-hexane, showing a correlation coefficient of 0.64-0.77 after acid hydrolysis and that of 0.73-0.83 in the absence of hydrolysis, depending on the correction for urinary density (P less than 0.01 in all cases, with no improvement in the coefficient occurring after the corrections). In contrast, 2-AF levels were independent of n-hexane exposure. The geometric mean 2,5-HD concentration in urine samples from 53 nonexposed men was 0.26 mg/l as observed (i.e., with no correction), 0.19 mg/l after correction for a urinary specific gravity of 1.016, and 0.23 mg/g creatinine after correction for creatinine concentration, and the geometric standard deviation was approximately 2.

2-Acetylfuran, a confounder in urinalysis for 2,5-hexanedione as an n-hexane exposure indicator

The apparent amount of 2,5-hexanedione, a biomarker of n-hexane expsoure in occupational health, in the urine of both exposed and non-exposed subjects varied not only as a function of the pH at which the urine sample was hydrolyzed but also depending on the capillary column used for gas chromatographic (GC) analysis of the urinary hydrolyzates after extraction with dichloromethane. The formation of a compound, identified by gas chromatography-mass spectrometry (GC-MS) as 2-acetylfuran, following acid hydrolysis was a major cause of confounding effects. This compound was hardly separated from 2.5-hexanedione on a capillary column such as DB-WAX, whereas separation could be achieved on a DB-1 capillary column. 2-Acetylfuran was formed when a urine sample was heated at a pH of less than 2 for hydrolysis, and the amount detected in urine did not differ between exposed and non-exposed subjects, indicating that the formation of 2-acetylfuran is independent of n-hexane exposure. When urinary hydrolysis is used, hydrolysis at a pH of less than 0.5, extraction with dichloromethane, and GC analysis on a non-polar capillary column are proposed to be the best analytical conditions for 2,5-hexanedione analysis in biological monitoring of exposure to n-hexane.

Urinary methylhippuric acid isomer levels after occupational exposure to a xylene mixture

The quantitative relationship between exposure to xylene vapor and urinary excretion of methylhippuric acid (MHA) isomers were studied in the second half of a working week. The participants in the study were 121 male workers engaged in dip-coating of metal parts who were predominantly exposed to three xylene isomers. The intensity of exposure measured by diffusive sampling during an 8-h shift was such that the geometric mean vapor concentration was 3.8 ppm for xylenes (0.8 ppm for o-xylene, 2.1 ppm for m-xylene, and 0.9 ppm for p-xylene), 0.8 ppm for toluene, and 0.9 ppm for ethylbenzene. Urine samples were collected at the end of the shift and analyzed for metabolities by HPLC. The statistical analysis showed that there is a linear relationship between the intensity of exposure to xylenes and the concentration of MHA in urine, that the regression line passes very close to the origin, and that the increment in observed (i.e., noncorrected) MHA concentrations as a function of increasing xylene concentration was 17.8 mg x l-1 ppm-1. Further examination on the basis on individual xylene isomers showed that the slopes of the regression lines for o- and m-isomers were similar (i.e., 17.1 and 16.6 mg l-1 ppm-1, respectively), whereas that for p-xylene was larger (21.3 mg l-1 ppm-1).