Gaschromatographic determination of butoxyacetic acid after hydrolysis of conjugated metabolites in urine from workers exposed to 2-butoxyethanol

Free and total urinary 2-butoxyacetic acid following dermal and inhalation exposure to 2-butoxyethanol in human volunteers

OBJECTIVES

To assess excretion kinetics of free and total (free + conjugated) 2-butoxyacetic acid (BAA) following dermal and inhalation exposure to butoxyethanol (BE).

METHODS

Six male volunteers were dermally exposed for 4 h to a 50% aqueous solution of BE on an area of 40 cm(2) of the volar forearm. Six other male volunteers were exposed by inhalation (mouth only) to 93 mg m(-3) BE for 30 min. As biological indices of exposure, BE in blood and total and free BAA in urine were measured.

RESULTS

Following inhalation exposure, the 24-h cumulative excretion of free and total BAA in urine amounted to 5.5 +/- 2.7 and 12.8 +/- 4.0 mg, respectively. After dermal exposure, 147.1 +/- 61.0 and 346 +/- 52 mg, respectively, of free and total BAA were excreted in urine up to 48 h after the onset of exposure. The proportion of conjugated BAA in single urine samples increased after dermal exposure in time from 45+/-30% in the first collection period to 92+/-2% after 48 h. The elimination half-life of total BAA following dermal exposure was longer than that of free BAA (5.1 +/- 0.6 and 3.8 +/- 0.4 h, respectively). The interindividual variation in the cumulative excreted amount after inhalatory exposure was higher (49%) for free BAA than for total BAA (31%). The average dermal flux amounted to 3.5 mg cm(-2) h(-1) independently of whether free or total BAA was used for the calculation, and, again, the interindividual variation in the estimated fluxes was higher for free BAA than for total BAA (41% and 15%, respectively).

CONCLUSION

The interindividual variation in the extent of conjugation is large, and the degree of conjugation increases with time. Due to lower interindividual variability, total BAA is superior to free BAA as a biomarker of exposure.

A human exposure study to investigate biological monitoring methods for 2-butoxyethanol

2-Butoxyethanol is a glycol ether widely used in printing inks, varnishes and cleaning fluids. As skin absorption can be significant, biological monitoring is useful in monitoring worker exposure. A number of analytes and matrices have been used previously, including 2-butoxyethanol in blood and free and total 2-butoxyacetic acid in urine. Using a combination of a volunteer study and samples from exposed workers, we compared the applicability of some of the biological monitoring markers available. We conclude that 2-butoxyethanol in blood is not a suitable marker for biological monitoring due to sampling problems. In view of the low-level exposures reported in occupational surveys, 2-butoxyethanol in breath is also unsuitable because of a lack of sensitivity. Measuring 2-butoxyacetic acid in blood is possible, although non-invasive urine samples are preferred. Free 2-butoxyacetic acid in urine has previously been widely used; however, we found that the extent of conjugation of 2-butoxyacetic acid in urine varied from 0 to 100% both within and between individuals and is not related to time, concentration or urine pH. Data from 48 exposed workers suggested that an estimated 57% (95% confidence interval 44-70%) of the total 2-butoxyacetic acid is excreted in the conjugated form, and that conjugation may be activated above a certain exposure level. Using total 2-butoxyacetic acid significantly reduced inter-individual variation. Elimination half-lives for free and total 2-butoxyacetic acid were similar ( approximately 6 h) and there was no delay in excretion of the conjugated metabolite (peak excretion for both free and total was between 6 and 12 h after the end of exposure). In conclusion, we propose that total butoxyacetic acid (after acid hydrolysis) in urine is the biomarker of choice for monitoring exposure to 2-butoxyethanol. Urine samples should be collected post-shift towards the end of the working week.

Synthesis, characterization, and use of 2-[(2H(9))butoxy]acetic acid and 2-(3-methylbutoxy)acetic acid as an internal standard and an instrument performance surrogate, respectively, for the gas chromatographic-mass spectrometric determination of 2-butoxyacetic acid, a human metabolite of 2-butoxyethanol

2-[(2H(9))Butoxy]acetic acid and 2-(3-methylbutoxy)acetic acid were synthesized, mixed with 2-butoxyacetic acid, and separated by capillary gas chromatography on a fused-silica column with a length of 50 m, inside diameter of 0.200 mm, and a "free fatty acid phase" wall coating of 0.3 microm film. 2-[(2H(9))Butoxy]acetic acid, 2-butoxyacetic acid, and 2-(3-methylbutoxy)acetic acid were baseline resolved at retention times of 13.55, 13.78, and 15.20 min; 2-(3-methylbutoxy)acetic acid having a peak efficiency of 360,000. Mass spectrometric detection using selected ion monitoring at m/z 66, 57, and 71 showed linear analytical responses from 0.04 ng to at least 200 ng with a limit of detection of 0.04 ng for 2-butoxyacetic acid.

Butoxyethanol ingestion with prolonged hyperchloremic metabolic acidosis treated with ethanol therapy

BACKGROUND

Severe toxic ingestions of butoxyethanol (CAS No. 111-76-2) are rare despite the prevalence of this glycol ether in products such as glass and surface cleaners. Manifestations of acute butoxyethanol toxicity include metabolic acidosis, hemolysis, hepatorenal dysfunction, and coma, but vary widely in reported cases. Furthermore, the optimal therapeutic approach is not yet established. Much of the toxicity of butoxyethanol has been ascribed to its aldehyde and acid metabolites which are similar to those produced by oxidative metabolism of methanol and ethylene glycol. Although the roles of alcohol dehydrogenase inhibition with ethanol or fomepizole and hemodialysis are clear in the case of toxic ingestions of methanol and ethylene glycol, they remain poorly defined for butoxyethanol poisoning.

CASE REPORT

We report the case of a 51-year-old female who ingested up to 8 ounces of Sanford Expo White Board Cleaner (butoxyethanol and isopropanol). She developed prolonged hyperchloremic metabolic acidosis and mental status depression and was treated with ethanol therapy but not hemodialysis. This patient recovered without apparent sequelae. The kinetics of butoxyethanol metabolism in this case are described and the potential therapeutic options are discussed.

Urinary 2-methoxy acetic acid accumulation in response to 2-methoxy ethanol exposure

Urinary 2-methoxy acetic acid reportedly has a long half-life (77.1 hr) in humans. The authors studied urinary 2-methoxy acetic acid in a group of 18 workers exposed to 2-methoxy ethanol from Monday to Saturday following a 7-d cease in production. The weekly time-weighted average exposure concentration of 2-methoxy ethanol was 4.5 ppm. The urinary 2-methoxy acetic acid of exposed workers was increased significantly, from 18.5 microg/ml (10.6 mg/gm creatinine) on Monday (prior to work) to 48.4 microg/ml (46.5 mg/gm creatinine) on Friday (after work), to 51.2 microg/ml (45.6 mg/gm creatinine) on Saturday after work. These levels occurred, despite that fact that the daily mean time-weighted average 2-methoxy ethanol exposures were very consistent and were close to the current Taiwan Permissible Exposure Limit of 5 ppm. These urinary 2-methoxy acetic acid levels were much higher than levels that occur with inhalation only, and they demonstrate that skin absorption is a significant contributor to 2-methoxy ethanol exposure. The high background concentrations of 2-methoxy acetic acid in the preshift urine samples following a 7-d production halt confirm that there is a long half-life of 2-methoxy acetic acid in humans. The determination of urinary 2-methoxy acetic acid is recommended for exposure assessment of 2-methoxy ethanol.

Improved method to measure urinary alkoxyacetic acids

OBJECTIVES

To simplify the current preparation of samples, and to improve the specificity and reliability of the conventional analytical methods to measure urinary alkoxyacetic acids.

METHODS

Samples containing alkoxyacetic acids including methoxy, ethoxy, and butoxyacetic acids (MAA, EAA, and BAA) were acidified with HCl and extracted with a mixed solvent of methylene chloride and isopropyl alcohol, then analysed by gas chromatography/mass spectrometry (GC/MS).

RESULTS

Optimal results were obtained when pH was 1.05-1.45, the ratio of methylene chloride and isopropyl alcohol was 2:1, and when extraction time was 10 minutes. Over the concentration range 0.3-200 micrograms/ml, MAA, EAA, and BAA could be determined with a pooled coefficient of variation (nine concentrations, six replicate samples) of 5.55%, 6.37%, and 6.41%, respectively. Urine samples were stable for at least 5 months and 3 freeze-thaw cycles at -20 degrees C. The limits of detection of MAA, EAA, and BAA were 0.055, 0.183, and 0.009 microgram/ml, respectively. The matrix effect of urine samples was negligible for MAA and EAA, but were marginally significant for BAA. The average recoveries of alkoxyacetic acids were 99%-101%. In urine samples MAA from 15 exposed workers showed a strong linear correlation (r = 0.999, slope = 1.01) between the new GC/MS method and Sakai's GC method.

CONCLUSIONS

The simplified non-derivatisation pretreatment of samples coupled with GC/MS can provide a specific, sensitive, simple, safe, and reliable method for the biological monitoring of occupational exposure of ethylene glycol ethers.