Determination of styrene and styrene-7,8-oxide in human blood by gas chromatography-mass spectrometry

A Review of Extraction Methods and Analytical Techniques for Styrene and its Metabolites in Biological Matrices

We reviewed the toxicokinetics of styrene to introduce reliable surrogates for biological monitoring of styrene workers. Also, extraction techniques and analytical methods for styrene and its metabolites have been discussed. Sample preparation is the main bottleneck of the analytical techniques for styrene and its metabolites. While some microextraction methods have been developed to overcome such drawbacks, some still have limitations such as long extraction time, fiber swelling and breakage, and the cost and the limited lifetime of the fiber. Among all, microextraction by packed sorbents coupled with high performance liquid chromatography with ultraviolet detection (MEPS-HPLC-UV) can be the method of choice for determining styrene metabolites. Few studies investigated unchanged styrene in breath samples. Chemical determination in exhaled breath provides new insights into organ toxicity in workers with inhalation exposures and can be considered as a fascinating tool in risk assessment strategies. Taking blood samples is invasive and less accepted by workers than other samples. In contrast, breath analysis is the most attractive method for workers because breath samples are easy to collect and non-invasive, and does not require worker transfer to health facilities. Therefore, developing selective and sensitive methods for determining styrene in breath samples is recommended for future studies.

An integrated approach to biomonitoring exposure to styrene and styrene-(7,8)-oxide using a repeated measurements sampling design

The aim of this work was to investigate urinary analytes and haemoglobin and albumin adducts as biomarkers of exposure to airborne styrene (Sty) and styrene-(7,8)-oxide (StyOX) and to evaluate the influence of smoking habit and genetic polymorphism of metabolic enzymes GSTM1 and GSTT1 on these biomarkers. We obtained three or four air and urine samples from each exposed worker (eight reinforced plastics workers and 13 varnish workers), one air and urine samples from 22 control workers (automobile mechanics) and one blood sample from all subjects. Median levels of exposure to Sty and StyOX, respectively, were 18.2 mg m(-3) and 133 microg m(-3) for reinforced plastics workers, 3.4 mg m(-3) and 12 microg m(-3) for varnish workers, and <0.3 mg m(-3) and <5 microg m(-3) for controls. Urinary levels of styrene, mandelic acid, phenylglyoxylic acid, phenylglycine (PHG), 4-vinylphenol (VP) and mercapturic acids (M1+M2), as well as cysteinyl adducts of serum albumin (but not those of haemoglobin) were significantly associated with exposure status (controls<exposed workers). Also, levels of VP and M1+M2 were significantly affected by smoking, and levels of M1+M2 were significantly affected by GSTM1 polymorphisms. Multiple linear regression analyses of the subject-specific (logged) metabolite levels across exposed workers showed that Sty was a significant predictor for all urinary analytes while StyOX was a significant predictor of PHG only. Interestingly, the log scale regression coefficients for Sty in these models were significantly less than one for all metabolites except M1+M2. This suggests that the natural scale relationships between levels of all Sty metabolites, except M1+M2, displayed downward concavity with increasing Sty exposure, suggestive of saturable metabolism. Levels of the protein adducts were not associated with exposure to either Sty or StyOX among exposed subjects.

Comparison of genotoxic potency of styrene 7,8-oxide with gamma radiation and human cancer risk estimation of styrene using the rad-equivalence approach

Styrene is suspected to cause lympho-hematopoietic malignancies through the formation of styrene 7,8-oxide. However, we are still unable to calculate the cancer risk for workers exposed to styrene using epidemiological data. The aims of this study were to determine the blood dose after styrene exposure and to compare the genotoxic potency of styrene 7,8-oxide and gamma radiation in order to calculate the cancer risk by means of the rad-equivalence approach. Leucocytes of 20 individuals were exposed to 0, 0.1, 0.2 or 0.3 mM styrene 7,8-oxide (1 h) or 1, 2 or 3 gray (=100, 200, 300 rad) gamma radiation. Genotoxicity was evaluated with the cytokinesis-block micronucleus assay. Comparison of the two slopes of the regression lines between micronuclei and dose revealed a genotoxic potency for styrene 7,8-oxide of 37 rad/mMh, corresponding with a median value derived from mutagenicity studies (1, 37, 208 rad/mMh). At exposure levels of 1 ppm styrene, a blood styrene 7,8-oxide concentration between 0.03 x 10(-)(6) and 0.42 x 10(-)(6) mM is to be expected using data of toxicokinetic models and human exposure studies. With the cancer risk per unit dose of gamma radiation as benchmark, we calculated a lifetime risk of acquiring a fatal lympho-hematopoietic cancer of 0.17 in 10(3) workers (between 0.037 x 10(-)(3) and 5.0 x 10(-)(3)) exposed to 20 ppm styrene during 40 years.

Predictors of occupational exposure to styrene and styrene-7,8-oxide in the reinforced plastics industry

OBJECTIVE

To identify demographic and work related factors that predict blood levels of styrene and styrene-7,8-oxide (SO) in the fibreglass reinforced plastics (FRP) industry.

METHODS

Personal breathing-zone air samples and whole blood samples were collected repeatedly from 328 reinforced plastics workers in the Unuted States between 1996 and 1999. Styrene and its major metabolite SO were measured in these samples. Multivariable linear regression analyses were applied to the subject-specific levels to explain the variation in exposure and biomarker levels.

RESULTS

Exposure levels of styrene were approximately 500-fold higher than those of SO. Exposure levels of styrene and SO varied greatly among the types of products manufactured, with an 11-fold range of median air levels among categories for styrene and a 23-fold range for SO. Even after stratification by job title, median exposures of styrene and SO among laminators varied 14- and 31-fold across product categories. Furthermore, the relative proportions of exposures to styrene and SO varied among product categories. Multivariable regression analyses explained 70% and 63% of the variation in air levels of styrene and SO, respectively, and 72% and 34% of the variation in blood levels of styrene and SO, respectively. Overall, air levels of styrene and SO appear to have decreased substantially in this industry over the last 10-20 years in the US and were greatest among workers with the least seniority.

CONCLUSIONS

As levels of styrene and SO in air and blood varied among product categories in the FRP industry, use of job title as a surrogate for exposure can introduce unpredictable measurement errors and can confound the relation between exposure and health outcomes in epidemiology studies. Also, inverse relations between the intensity of exposure to styrene and SO and years on the job suggest that younger workers with little seniority are typically exposed to higher levels of styrene and SO than their coworkers.

Review of the genotoxicity of styrene in humans

Styrene (CAS No. 100-42-5) is an important industrial chemical for which positive results have been reported in in vitro and in vivo genotoxicity assays. Styrene-exposed workers have been studied extensively over two decades for the induction of various types of genotoxic effects. The outcomes of these studies have been conflicting, and where positive responses have been reported, it has proved difficult to demonstrate clear relationships between levels of damage reported and exposure levels. In this review, we have assessed studies addressing mutagenicity (chromosome aberrations, micronuclei and gene mutations) and other endpoints (sister chromatid exchanges, DNA breaks and DNA adducts) using criteria derived from the IPCS guidelines for the conduct of human biomonitoring studies. Based on the re-evaluated outcomes, the data are not convincing that styrene induces gene mutations. The evidence for induction of clastogenicity in occupationally exposed workers is less clear, with a predominant lack of induction of micronuclei in different studies, but conflicting responses in chromosome aberration assays. The results of numerous studies on sister chromatid exchanges do not provide evidence of a clear positive response, despite these being induced in animals exposed to styrene at high concentrations. However, there is evidence that both DNA adducts and DNA single strand breaks are induced in styrene workers. These types of damage are considered indicative of exposure of the target cells and interaction with cellular DNA but do not necessarily result in heritable changes. There is evidence that the metabolism of styrene in humans is affected by genetic polymorphisms of metabolizing genes and that these polymorphisms affect the outcome of in vitro mutagenicity studies on styrene. Therefore, studies that have addressed the potential of this factor to affect in vivo responses were considered. To date, there are no consistent relationships between genetic polymorphisms and induction of genotoxicity by styrene in humans, but further work is warranted on larger samples. The analyses of individual studies, together with a consideration of dose-response relationships and the lack of a common profile of positive responses for the various endpoints in different studies, provide no clear evidence that styrene exposure in workers results in detectable levels of mutagenic damage. However, evidence of exposure to genotoxic metabolites is demonstrated by the formation of DNA adducts and strand breaks.

Determination of residual styrene monomer in polystyrene granules by gas chromatography–mass spectrometry

Polystyrene is widely used in formulations intended for children use. The main problem with this plastic is the residual styrene, which can migrate from the product, and therefore, be in contact with children. The acute toxicity of styrene is well known, raising the need of an efficient and fast method of analysis for this compound. Several extraction methods have been evaluated and compared for the determination of residual styrene monomer in polystyrene granules used in toys: supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), Soxhlet extraction, headspace emission and dissolution-precipitation. The analyte was subsequently detected by gas chromatography (GC) with MS detection. The results indicated that the most efficient method was dissolution-precipitation giving even higher extraction efficiency than SFE. For validating the method, PS samples spiked with known quantities of styrene at three concentration levels were prepared to calculate the extraction recovery. The founded validation data proved the suitability of the proposed method.

A novel approach based on solid phase microextraction gas chromatography and mass spectrometry to the determination of highly reactive organic compounds in cells cultures: styrene oxide

A solid phase microextraction (SPME) gas chromatography/mass spectrometry (GC/MS) method was developed to assess actual doses of highly reactive organic compounds like styrene oxide (SO) in exposed cell cultures. Using SPME, we set up a method to measure accurately extracellular SO concentrations as well as to obtain an approximate assessment of intracellular levels. The SPME-GC/MS method was developed and validated using two different coating materials, carboxen-PDMS and polyacrylate. In cell-free systems, linearity was established over 3 orders of magnitude for both fibers, but carboxen-PDMS showed higher extraction efficiency and a lower limit of detection (0.5 x 10(-7) vs 10(-6) M for polyacrylate). Precision calculated as % RSD was within 4-16% for all intra- and interday determinations. Experiments performed to study SO stability in cell-free medium showed a time-dependent decrease in SO concentration (11% of initial the concentration after 24 h), mostly due to the spontaneous hydrolysis of SO into styrene glycol, which was measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS). When the neuronal cell line (SK-N-MC) was exposed to a nominal concentration of 0.3 x 10(-4) M SO, the actual concentration measured in the supernatant was considerably lower and was found to decrease during incubation. Intracellular SO was estimated indirectly, by difference between the amount measured in the medium without cells and in the supernatant of the cell-containing medium.

Temporal association between serum prolactin concentration and exposure to styrene

BACKGROUND

Previous studies have suggested that occupational exposure to styrene is associated with increased serum levels of the anterior pituitary hormone prolactin (PRL).

AIMS

To test the hypotheses that: (1) the effect of styrene exposure on PRL secretion is an acute effect, not a subchronic or chronic effect; (2) blood styrene, as a measure of absorbed dose, is a stronger predictor of serum PRL level than personal breathing zone air styrene concentration.

METHODS

Subjects were recruited from 17 workplaces in the reinforced plastics industry. Personal breathing zone air styrene, whole blood styrene, and serum PRL were measured during one to three sessions, approximately one year apart. Linear multiple regression was used to model the relations between acute (air styrene or blood styrene obtained at same time as PRL), subchronic (average air or blood styrene over two or three sessions), and chronic (years of work in industry or facility times average air styrene over all sessions) indices of styrene exposure and serum PRL.

RESULTS

Acute blood styrene concentration was the strongest predictor of serum PRL concentration, with the model predicting a 2.06-fold increase in PRL (95% CI 1.11 to 3.84) for every 10-fold increase in blood styrene. Serum PRL tended to increase with increasing styrene exposure in both men and women; however, women tended to have higher PRL levels. For women, the change in blood styrene between sessions 1 and 2 was a significant predictor of the change in serum PRL between sessions.

CONCLUSIONS

Results confirm that styrene exposure enhances serum PRL concentrations and support an acute effect of styrene on PRL secretion.

A sensitive gas chromatographic-tandem mass spectrometric method for detection of alkylating agents in water: application to acrylamide in drinking water, coffee and snuff

A sensitive analytical method for the analysis of acrylamide and other electrophilic agents in water has been developed. The amino acid L-valine served as a nucleophilic trapping agent. The method was applied to the analysis of acrylamide in 0.2-1 mL samples of drinking water or Millipore-filtered water, brewed coffee, or water extracts of snuff. The reaction product, N-(2-carbamoylethyl)valine, was incubated with pentafluorophenyl isothiocyanate to give a pentafluorophenylthiohydantoin (PFPTH) derivative. This derivative was extracted with diethyl ether, separated from excess reagent and impurities by a simple extraction procedure, and analyzed by gas chromatography-tandem mass spectrometry. (2H3)Acrylamide, added before the reaction with L-valine, was used as internal standard. Acrylamide and the related compound, N-methylolacrylamide, gave the same PFPTH derivative. The concentrations of acrylamides were < or = 0.4 nmol L(-1) (< or = 0.03 microg acrylamide L(-1)) in water, 200 to 350 nmol L(-1) in brewed coffee, and 10 to 34 nmol g(-1) snuff in portion bags, respectively. The precision (the coefficient of variation was 5%) and accuracy of the method were good. The detection limit was considerably lower than that of previously published methods for the analysis of acrylamide.

A toxicokinetic model for styrene and its metabolite styrene-7,8-oxide in mouse, rat and human with special emphasis on the lung

Styrene (ST) occurs ubiquitously in the environment and it is an important industrial chemical. After its uptake by the exposed mammalian organism, ST is oxidized to styrene-7,8-oxide (SO) by cytochrome P450 dependent monooxygenases. This reactive intermediate is further metabolized by epoxide hydrolase (EH) and glutathione S-transferase (GST). In long-term animal studies, ST induced lung tumors in mice but not in rats. Considering the lung to be the relevant target organ for ST induced carcinogenicity in mice, we extended a previously developed physiological toxicokinetic model in order to simulate the lung burden with ST and SO in the ST exposed mouse, rat and human. The new model describes oral and pulmonary uptake of ST, its distribution into various tissues, its exhalation and its metabolism to SO in lung and liver. It also simulates the distribution of the produced SO into the tissues and its EH and GST mediated metabolism in liver and in lung. In both organs the ST induced GSH consumption is described together with the formation of adducts to hemoglobin and to DNA of lymphocytes in ST exposed mice, rats and humans. The model includes compartments for arterial, venous and pulmonary blood, liver, muscle, fat, richly perfused tissues and lung. The latter organ is represented by two compartments, namely by the conducting and the alveolar zone. The physiological description of the pulmonary compartments relies on measured alveolar retentions, literature values of surface area of capillary endothelium, of the thickness of the tissue 'air-to-plasma', of the partition coefficient lung:blood and of metabolic parameters of ST and SO measured in pulmonary cell fractions of rodents and humans. Simulations of average pulmonary GSH levels in ST exposed rodents agree with measured data. The model predicts a significant GSH depletion (40%) in the conducting zone of mice exposed for 6 h to a ST concentration of only 20 ppm. In the conducting zone of rats, exposure to 200 ppm ST results in a loss of GSH of about 15% only. In humans, a pulmonary GSH reduction does not occur. The highest average pulmonary SO concentrations are predicted for mice, somewhat lower values for rats and by far the lowest ones for humans. Following steady state exposure to 20 ppm ST, the average SO concentration in mouse lungs is expected to be only three times higher than in rats. This difference diminishes to a factor of less than two at 70 ppm. In humans exposed to 20 ppm ST for 8 h, the average pulmonary SO burden of 0.016 micromol/kg is predicted to be about 17 and 50 times smaller than the corresponding values for rat and mouse. In agreement with reported values, pulmonary DNA adduct levels in rodents exposed to 160 ppm ST were simulated to be similar in rats and mice. In summary, there was no dramatic difference in the calculated average pulmonary SO burden between both animal species. However, pulmonary GSH loss was by far more expressed in ST exposed mice than rats. Since the model was validated on all available ST/SO data in mice, rats and humans, we consider it to be useful for estimating the risk resulting from exposure to ST.