Toluene and Styrene in Urine as Biological Exposure Indices

Comparison between urinary o-cresol and toluene as biomarkers of toluene exposure

The characteristics of urinary o-cresol (o-C) and urinary toluene (TOL-U) as biomarkers of occupational exposure to toluene were comparatively evaluated. One hundred healthy male rotogravure printing workers and 161 male and female control subjects were studied. Personal exposure to airborne toluene (TOL-A) during the shift was determined as a time-weighted average. Simple analytical procedures based on solid phase microextraction followed by gas chromatography/mass spectometry analysis were applied to the determination of end-shift o-C and TOL-U. Median TOL-A was 48 (6.0-162.0) mg/m3 in printers and 0.021 (<0.003-0.137) mg/m3 in controls. o-C was 0.185 (0.032-0.948) mg/g creatinine in printers and 0.027 (<0.006-0.330) mg/g creatinine in the controls. TOL-U was 7.6 (1.8-23.9) microg/L in printers and 0.140 (0.094-0.593) microg/L in the controls. According to all indices, exposure to toluene was higher in printers than in the controls. Nevertheless, the distribution of o-C in the two groups partially overlapped, whereas such behavior was not found in TOL-U. Both o-C and TOL-U in printers were correlated with TOL-A (Pearson's on log10-transformed variables r = 0.704 and 0.844, respectively) and with each other (r = 0.683). Smoking habits significantly increased the excretion of o-C but not of TOL-U. From the point of view of sampling conditions and analytical requirements, TOL-U and o-C showed similar properties, but comparison of their intrinsic characteristics showed that TOL-U had higher specificity and sensitivity, lower background values, was better correlated with airborne exposure, and was not influenced by cigarette smoking. Therefore TOL-U may be considered superior to o-C as a biomarker of occupational exposure to toluene.

Human neurobehavioral effects of long-term exposure to styrene: a meta-analysis

Many reports in the literature suggest that long-term exposure to styrene may exert a variety of effects on the nervous system, including increased choice reaction time and decreased performance of color discrimination and color arrangement tasks. Sufficient information exists to perform a meta-analysis of these observations quantifying the relationships between exposure (estimated from biomarkers) and effects on two measures of central nervous system function: reaction time and color vision. To perform the meta-analysis, we pooled data into a single database for each end point. End-point data were transformed to a common metric of effect magnitude (percentage of baseline). We estimated styrene concentration from biomarkers of exposure and fitted linear least-squares equations to the pooled data to produce dose-effect relationships. Statistically significant relationships were demonstrated between cumulative styrene exposure and increased choice reaction time as well as increased color confusion index. Eight work-years of exposure to 20 ppm styrene was estimated to produce a 6.5% increase in choice reaction time, which has been shown to significantly increase the probability of automobile accidents. The same exposure history was predicted to increase the color confusion index as much as 1.7 additional years of age in men.

Biological monitoring in occupational exposure to low levels of 1,3-butadiene

Exposure to 1,3-butadiene (BD), a probable carcinogen to humans, was investigated in two groups of subjects working in a petrochemical plant where BD is produced and used to prepare polymers: 42 occupationally exposed workers and 43 internal non-occupationally exposed controls. BD personal exposure was very low but significantly different in the two groups (median airborne BD 1.5 and 0.4 microg/m(3) in exposed and controls, respectively). Similarly, BD in blood and urine, but not in exhaled air, was higher in the exposed workers than in controls (blood BD 3.7 ng/l versus <1.8 ng/l, urinary BD 2.4 ng/l versus <1.0 ng/l). These three biomarkers correlated significantly with personal exposure ( 0.283 < or = Pearson's r < or = 0.383) and between them (0.780 < or = r < or = 0.896). Excretion of urinary mercapturic acids N-acetyl-S-(3,4-hydroxybutyl)-l-cysteine (MI), N-acetyl-S-(1-hydroxymethyl-2-propenyl)-l-cysteine and N-acetyl-S-(2-hydroxy-3-butenyl)-l-cysteine (MII), chromosomal aberrations (CA), and sister chromatid exchanges (SCE) in peripheral blood lymphocytes were not influenced by occupational exposure. Our results show that unmetabolised BD in biological fluids, and particularly urinary BD, represents the biomarker of choice for assessing occupational exposure to low airborne concentrations of BD.

Dose-related color vision impairment in toluene-exposed workers

Occupational exposure to various neurotoxic chemicals can impair color vision. We evaluated this possibility in toluene-exposed workers. Thirty-three rubber workers and 16 referents were studied. We estimated toluene exposure by measuring urinary excretion of the unmodified form of the solvent (i.e., TolU). Color vision was tested with the Lanthony D-15 desaturated panel, and the outcomes were expressed quantitatively with the Color Confusion Index and the Total Confusion Index. Toluene-exposed workers had a subclinical reduction in color vision, compared with referents. We related this effect to solvent cumulative exposure--estimated as the product of urinary excretion of unmodified toluene by previous toluene exposure duration. This approach supports the hypothesis that impairment progresses as exposure continues. In the examined group of workers, toluene exposure was within the occupational limit proposed by the American Conference of Governmental Industrial Hygienists. The observed loss in color vision raises doubts on the real protection afforded by this limit--at least for effects of the solvent on the eyes. Finally, the Total Confusion Index was a more sensitive index than the Color Confusion Index in the evaluation of toluene-related color-vision impairment, suggesting that this index should be adopted in future studies of the effects of chemicals on color perception.

The urinary excretion of solvents and gases for the biological monitoring of occupational exposure: a review

'In the field' application of the measurement of urinary excretion of unmodified solvent for the biological monitoring of exposed workers has been investigated in many recent papers. The results obtained for several solvents are reviewed. The values of correlation coefficients (r) and regression lines obtained for benzene, toluene, xylene, styrene, n-hexane, cyclohexane, 2- and 3-methylpentane, methyl chloride, tetrachloroethylene, carbon tetrachloride, methyl chloroform, p-dichlorobenzene, nitrous oxide, halothane, isoflurane, enflurane, acetone, methyl ethyl ketone and methyl isobutyl ketone are presented. The correlations observed were generally good: r values range from 0.50-0.97, and the majority are between 0.84 and 0.90. The regression lines reported for the same solvent in different studies present some variability: this is possibly due to an inadequate control of factors influencing the relationship between external dose and absorption, such as differences in body burden, work load, individual characteristics, etc. These factors are discussed. As a whole, results reported in the literature show that measuring of urinary excretion of unmodified solvents provides a highly sensitive and specific exposure index, and can also be applied for the biological monitoring of occupational exposure to low levels of solvents or to solvent mixtures. Nevertheless, for an adequate assessment of biological limit values, further studies evaluating the reproducibility of regression lines are needed, given that the aspects influencing the correlation between external dose and urinary excretion are fully controlled. Another crucial aspect is the correlation with early effects: even though this has yet to be evaluated for several solvents, for others such as styrene and perchloroethylene a good correlation was obtained, further supporting the usefulness of the measurement of urinary excretion of solvent for the biological monitoring of occupational exposure.

Variability in biological monitoring of organic solvent exposure. II. Application of a population physiological model

A physiological population model is used to study the variability associated with the biological monitoring of solvent exposure. The model consists of a combination of a physiological compartmental model and statistical simulation technique. Variable components considered are: exposure concentration, physical workload, body build, liver function, and renal function. The model is applied to six solvents: trichloroethylene, tetrachloroethylene, methylchloroform, benzene, toluene, and styrene. Biological indicators and air monitoring are compared as predictors of exposure, both external and internal (uptake, brain concentration, reactive metabolite formation). It appears that the choice of the best indicator depends on the type of exposure which is to be predicted. The effects of the various factors, environmental, physiological, or metabolic, are quantified and discussed. It is shown that fluctuation in exposure plays a large part in the final variability of biological indicator results. Further improvements and applications of this population model are considered.

Evaluation of exposure to isoflurane (Forane): environmental and biological measurements in operating room personnel

The concentration of isoflurane (Forane) in the ambient atmosphere was determined in 11 operating theaters of 5 hospitals in Italy. The concentration of isoflurane in the ambient air exceeds the recommended time-weighted average exposure levels (median value: 113 mumol/m3). Isoflurane was detected in the urine of 45 exposed subjects (anesthetists, surgeons, and nurses). A significant correlation was found between the isoflurane concentration in urine produced during the shift (Cu' nmol/l) and isoflurane environmental concentration (Cl' mumol/m3) (Cu = 0.243 X Cl + 3.712) (r = .90). The results show that the urinary isoflurane concentration can be used as an appropriate biological exposure index. The authors suggest a biological exposure index of 18 nmol/l (3.4 micrograms/l). This is the biological value obtained after 4 h of an average environmental exposure to 81 mumol/m3 (2 ppm).