[Use of comet assay for the risk assessment of oil- and chemical-industry workers]. / Comet assay alkalmazása olaj- és vegyipari exponált dolgozók kockázatbecslésében.

INTRODUCTION: The comet assay is a fluorescent microscopic method that is able to detect DNA strand-breaks even in non-proliferative cells in samples with low cell counts. AIM: The aim of the authors was to measure genotoxic DNA damage and assess oxidative DNA damage caused by occupational exposure in groups exposed to benzene, polycyclic aromatic carbohydrates and styrene at the workplace in order to clarify whether the comet assay can be used as an effect marker tool in genotoxicology monitoring. METHOD: In addition to the basic steps of the comet assay, one sample was treated with formamido-pirimidine-DNA-glycolase restriction-enzyme that measures oxidative DNA damage. RESULTS: An increase was observed in tail moments in each group of untreated and Fpg-treated samples compared to the control. CONCLUSIONS: It can be concluded that occupational exposure can be detected with the method. The comet assay may prove to be an excellent effect marker and a supplementary technique for monitoring the presence or absence of genotoxic effects.

Health hazards among workers in plastic industry.

Styrene is a basic building block for manufacturing thousands of products throughout the world. The present study aimed to (1) detect the presence of styrene and/or its metabolites in the workers in one of the Egyptian plastic factories; (2) demonstrate some common health effects of styrene exposure among the same group by some laboratory investigations and compare them with the unexposed healthy individuals; and (3) correlate the duration of styrene exposure and its level in the blood with the severity of the demonstrated health effects. This study was conducted in one of Egyptian plastic factories. The exposed group was 40 male workers, ranging in age from 18 to 33 years (23.20 ± 4.09), working 12 h/day with 1 day off, and working without any protective equipment. A control group of 50 unexposed healthy males matched with the exposed group for age (21-35 yrs (23.40 ± 4.05)), sex, socioeconomic status, and smoking habit is selected. Written individual consent is obtained from all participants followed by (a) a full medical and occupational history and full clinical examination; (b) ventilatory function tests: forced vital capacity (FVC), slow vital capacity, forced expiratory volume in the 1st second (FEV1)%, FEV1/FVC%, peak expiratory flow, and mid-expiratory flow 25-75%; (c) analyses of ß2 microglobulin; blood styrene level; and urinary mandelic acid; and (d) cytogenetic study. The study results showed a statistically significant difference between the exposed and the control groups as regard the blood styrene level, urinary mandelic acid level, ß2 microgloblin in urine, and chromosomal study. The study also showed a statistically significant correlation between the duration of styrene exposure and ventilatory function parameters, also between the duration of styrene exposure and some detectable chromosomal aberrations. Our study recommends the implementation of preemployment and periodic medical examinations and health education programs using personal protective equipments and following the recommended allowable concentrations of styrene exposure.

Modulation of DNA repair capacity and mRNA expression levels of XRCC1, hOGG1 and XPC genes in styrene-exposed workers.

Decreased levels of single-strand breaks in DNA (SSBs), reflecting DNA damage, have previously been observed with increased styrene exposure in contrast to a dose-dependent increase in the base-excision repair capacity. To clarify further the above aspects, we have investigated the associations between SSBs, micronuclei, DNA repair capacity and mRNA expression in XRCC1, hOGG1 and XPC genes on 71 styrene-exposed and 51 control individuals. Styrene concentrations at workplace and in blood characterized occupational exposure. The workers were divided into low (below 50 mg/m³) and high (above 50 mg/m³)) styrene exposure groups. DNA damage and DNA repair capacity were analyzed in peripheral blood lymphocytes by Comet assay. The mRNA expression levels were determined by qPCR. A significant negative correlation was observed between SSBs and styrene concentration at workplace (R=-0.38, p=0.001); SSBs were also significantly higher in men (p=0.001). The capacity to repair irradiation-induced DNA damage was the highest in the low exposure group (1.34±1.00 SSB/109 Da), followed by high exposure group (0.72±0.81 SSB/109 Da) and controls (0.65±0.82 SSB/109 Da). The mRNA expression levels of XRCC1, hOGG1 and XPC negatively correlated with styrene concentrations in blood and at workplace (p<0.001) and positively with SSBs (p<0.001). Micronuclei were not affected by styrene exposure, but were higher in older persons and in women (p<0.001). In this study, we did not confirm previous findings on an increased DNA repair response to styrene-induced genotoxicity. However, negative correlations of SSBs and mRNA expression levels of XRCC1, hOGG1 and XPC with styrene exposure warrant further highly-targeted study.

Blood BTEXS and heavy metal levels are associated with liver injury and systemic inflammation in Gulf states residents.

INTRODUCTION: Exposures to volatile organic compounds and metals have previously been associated with liver diseases including steatohepatitis, although more data are needed. Benzene, toluene, ethylbenzene, xylenes, styrene (BTEXS) and metals were measured in blood samples collected between May 2012-July 2013 from volunteers participating in home visits for the Gulf Long-term Follow-up (GuLF) Study. This cross-sectional analysis evaluates associations of exposure biomarkers with serum liver injury and adipocytokine biomarkers in a sample of 214 men. METHODS: Adult nonsmoking men without a history of liver disease or heavy alcohol consumption were included. The serologic disease biomarkers evaluated were the hepatocellular injury biomarker, cytokeratin 18 [whole (CK18 M65) and caspase-cleaved fragment (CK18 M30)]; and adipocytokines. Confounder-adjusted beta coefficients were determined using linear regression models for the overall sample (primary endpoints) and for obesity-classified sub-groups (secondary endpoints). A product interaction term between the exposure of interest and a dichotomized indicator of obesity was included to determine the disease modifying effects of obesity on the biomarker associations. RESULTS: The study sample was 57% white and 51% obese. In the overall sample, lead was positively associated with CK18 M30 (ß = 21.7 ± 6.0 (SE), p = 0.0004); IL-1ß (ß = 32.8 ± 5.2, p < 0.0001); IL-6 (ß = 72.8 ± 18.3, p = 0.0001); and IL-8 (ß = 140.8 ± 42.2, p = 0.001). Cadmium exposures were associated with increased IL-1ß (ß = 77.8 ± 26.3, p = 0.003) and IL-8 (ß = 419.5 ± 201.2, p = 0.04). There were multiple significant interactions between obesity and exposure to lead, cadmium, benzene and toluene in relation to outcome biomarkers. Among obese participants (n = 108), benzene, lead, and cadmium were each positively associated with CK18 M30, IL-1ß, IL-6, and IL-8. In obese subjects, lead was also inversely associated with leptin, and toluene was positively associated with IL-1ß. CONCLUSION: For the overall sample, heavy metal exposures were associated with liver injury (lead only) and/or systemic inflammation (lead and cadmium). Obesity modified the associations between BTEXS and heavy metal exposures on several of the outcome variables. In the obesity subgroup, liver injury was positively associated with lead, cadmium and benzene exposures; systemic inflammation was increased with lead, cadmium, benzene, and toluene exposures; and leptin was inversely associated with lead exposures. The cross-sectional design of this study makes it difficult to determine causality, and all results should be interpreted cautiously. Nonetheless, the potential impact of exposures to lead, cadmium, benzene and toluene in steatohepatitis, an obesity-associated inflammatory liver disease, warrants further investigation.

Occupational styrene exposure and hearing loss: a cohort study with repeated measurements.

OBJECTIVE: Associations between occupational styrene exposure and impairment of hearing function were investigated, guided by three questions: are there hearing losses concerning high frequency and standard audiometric test? Are there dose-response relationships and measurable thresholds of effects? Are there signs of reversibility of possible effects if the workers are examined during times of improvement from their work? METHODS: A group of workers from a boat building plant, some of whom were laminators, were examined in subgroups of current low (n = 99, mean mandelic acid MA + phenylglyoxylic acid PGA = 51 mg/g creatinine), medium (n = 118, mean 229 mg/g creat.) and high (n = 31, mean 970 mg/g creat.) exposure to styrene. In addition, subgroups chronically exposed to high-long (n = 17) and low-short (n = 34) styrene levels were analysed. The examinations were carried out during normal work days and during the company holidays. Hearing thresholds and transient evoked otoacoustic emissions (TEOAE) were measured. Statistics included multiple co-variance analyses with repeated measures, linear regressions, and logistic regressions. RESULTS: The analyses of all participants demonstrated no clear exposure effects. Particularly no sufficient proof of dose-response relationship measured against parameters of current exposure (MA + PGA, styrene/blood) and of chronic exposure (cumulative and average life time exposure resp.) was found. The analyses of groups exposed to high levels show elevated thresholds at frequencies up to 1,500 Hz among the subgroup exposed to high styrene levels (e.g. 40-50 ppm as average) for a longer period of time (e.g. more than 10 years). These participants also demonstrated signs of "improvement" at frequencies above 2,000 Hz during work holidays, when they were not exposed to styrene. A significantly elevated odds ratio for cases of hearing loss (more than 25 dB (A) in one ear, 3,000-6,000 Hz) was found among the group exposed to high levels (above 30 ppm as average) for a longer period of time (more than 10-26 years). The measurements of TEOAE did not exhibit significant results related to exposure. CONCLUSION: This study found, that chronic and intensive styrene exposure increases the hearing thresholds. At levels of about 30-50 ppm as an average inhaled styrene per work day over a period of about 15 years with higher exposure levels above 50 ppm in the past, an elevated risk for impaired hearing thresholds can be expected. The formerly published results on ototoxic effects below 20 ppm could not be confirmed. With few exceptions (at frequencies of 1,000 and 1,500 Hz) no dose-response relationship between threshold and exposure data was found. Improvements of hearing thresholds during work- and exposure-free period are possible.

Human plasma and liver concentrations of styrene estimated by combining a simple physiologically based pharmacokinetic model with rodent data.

Long-term exposure to certain volatile organic compounds is a significant public health concern. A variety of food containers and drinking cups prepared from polystyrene or polystyrene-related plastics could contain styrene monomer. In the current study, the concentrations of styrene in plasma and liver were surveyed and determined after oral doses of 25 mg/kg to rats and 200 mg/kg to control and humanized-liver mice. Plasma concentrations of styrene in rats were still detected 2 hr after 10-25 mg/kg oral doses. In contrast, after an order of magnitude higher oral dose of styrene (200 mg/kg) to mice, styrene in mouse plasma was rapidly cleared within 15 min to the limit-of-detection level. However, unmetabolized styrene was detected in mouse liver 24 hr after oral treatment. A simple physiologically based pharmacokinetic (PBPK) model capable of estimating blood and liver concentrations of styrene was established for rats. A human PBPK model was then set up for styrene by using the same intrinsic hepatic clearances in rats and humans and by applying allometric scaling to rat parameters obtained from the plasma concentrations of styrene in rats. By reverse dosimetry analysis (from concentrations to doses), we found that the 95th percentile values of styrene concentrations (0.132 ng/mL) reported in United States biomonitoring data of more than 1000 human blood samples may imply exposure to repeated oral doses of styrene of 2.89 µg/kg/day. These results suggest that styrene biomonitoring data in human blood samples imply exposures roughly similar to or lower than the established tolerable daily intake level of 7.7 µg/kg/day.

Synthesis and evaluation of styrene-maleic acid copolymer conjugated amphotericin B.

Amphotericin B (AmB), which plays a central role in the treatment of systemic fungal infections, is difficult to formulate because it's sparingly soluble in water and organic solvents. We previously prepared AmB-loaded micelles using styrene-maleic acid copolymer (SMA). Although solubilization was achieved by this formulation, stability in the blood circulation was as insufficient as that of Fungizone®, which is a conventional formulation of AmB. Meanwhile, it is well known that polymer-drug conjugates are more stable in circulation than drug-loaded micelles. Therefore, in this study, we developed covalently conjugated SMA-AmB (SMA-AmB conjugate). The SMA-AmB conjugate was found to be soluble and present as micelles in aqueous solution. Furthermore, it was revealed that this micelle behaves as a larger molecule by forming a complex with albumin. The circulation in the blood increased significantly compared to that of Fungizone®, which was suggested to be due to this complex-forming ability. Although in vitro and in vivo antifungal activity of the SMA-AmB conjugate against Saccharomyces cerevisiae was reduced by 1/3 compared to that of Fungizone®, hemolysis decreased to 1/40 or less, and the LD50 decreased to 1/10. In conclusion, it is expected that the SMA-AmB conjugate can be a polymer-therapeutic agent with high antifungal selectivity.

Determination of volatile organic compounds in biological samples using headspace solid-phase microextraction and gas chromatography: toluene and styrene.

Epidemiological and laboratory investigations have shown that toluene and styrene are toxic compounds that lead to impairment of the nervous system. To quantitate toluene and styrene in biological samples, liquid-liquid phase, headspace (HS), and solid-phase microextraction (SPME) methods are generally used. Most of these methods are not sensitive enough for applications involving small sample volumes. Here, we present a method for quantitative analysis of low concentrations of styrene and toluene in very small volumes of biological samples using HS-SPME and gas chromatography (GC) equipped with a flame-ionization detector. The method was developed by optimizing operating parameters that affect the HS-SPME-GC process [i.e., desorption time (30 s), depth of the fiber in the GC injection port (3.7 cm), adsorption time (4 min), and adsorption temperature (room temperature)]. It has a wide range of linearity (0.5-500 ng/10 microL), high precision (coefficient of variation < 5%), good accuracy (deviation < 11%), and low detection limits of 0.13 and 0.08 ng/10 microL for styrene and toluene in serum, respectively. This analytical technique can be applied to the estimation of styrene and toluene in small volumes of biological fluids (blood, serum, and perilymph) and tissues of low lipid content (cochlea).

Styrene induced alterations in biomarkers of exposure and effects in the cochlea: mechanisms of hearing loss.

It is known that styrene is ototoxic and causes cochlear damage starting from the middle turn. However, the cellular mechanism underlying styrene ototoxicity is still unclear. In this study, rats were exposed to styrene by gavage at different doses once a day for varying periods. Styrene levels in the cochlear tissues, styrene-induced permanent hearing loss, cochlear disruptions, and cell death pathways were determined. Styrene concentration in the cochlea varied along with the basilar membrane with the lowest level in the basal turn being consistent with the lowest styrene-induced threshold shift and hair cell loss in this region. After 3 weeks of exposure (5 days per week), a dose-dependent permanent hearing loss and a hair cell loss, especially in the midfrequency region, were observed. The styrene exposure at a dose of 200 mg/kg, which induced a blood level of 6.0 +/- 1.0 microg/g, caused an average of 4.4 +/- 0.5% OHC (outer hair cell) loss and 2-5 dB threshold shift in the cochlear region of 20-70% from the apex. A significant OHC loss was not observed until 7 days of exposure at a dose of 800 mg/kg. Deiters cells appeared to be the most vulnerable target of styrene. When condensed nuclei were observed in Deiters cells after a few days of styrene exposure (800 mg/kg), other cells were still intact. Apoptotic cell death appeared to be the main cell death pathway in the cochlea after styrene exposure. In the styrene-induced apoptotic OHCs, histochemical staining detected activated caspases-9 and 8, indicating that both mitochondrial-dependent pathway and death receptor-dependent pathway were involved in the styrene-induced cell death.

Detection rates, trends in and factors affecting observed levels of selected volatile organic compounds in blood among US adolescents and adults.

Data from National Health and Nutrition Examination Survey were analyzed to evaluate detection rates, trend in and factors affecting the observed levels of 1,4-dichlorobenzene, benzene, ethylbenzene, o-xylene, styrene, toluene, and m/p-xylene among US adolescents and adults over 2005-2012. Over 2005-20102, among adolescents, detection rates declined by more than 50% for benzene, ethylbenzene, and o-xylene, and among adults, detection rates declined by more than 50% for ethylbenzene and o-xylene and by a little less than 50% for benzene. Among adults, adjusted levels of 1, 4-dichlorobenzene, benzene, ethylbenzene, o-xylene, toluene, and m/p-xylene decreased by 13.7%, 17.1%, 20%, 17.7%, 23.2%, and 18.7% respectively for every two-year survey cycle. Among adolescents, percentage decline in the levels of 1, 4-dichlorobenzene, benzene, ethylbenzene, o-xylene, styrene, toluene, and m/p-xylene was 15.2%, 21.4%, 19.3%, 16.1%, 47.8%, and 17.7% respectively for every two year survey period. The ratio of adjusted geometric means for adult smokers as compared to adult nonsmokers was 10.7 for benzene, 3.5 for ethylbenzene, 2.0 for o-xylene, 3.4 for styrene, 3.5 for toluene, and 2.2 for m/p-xylene. Among adolescents, gender did not affect the adjusted levels of any of the seven VOCs, and the order in which adjusted levels for 1, 4-dichlorobenzene by race/ethnicity was observed was: non-Hispanic white (0.038ng/mL)

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.

An evaluation of concentrations of styrene-7,8-oxide in rats and humans resulting from exposure to styrene or styrene-7,8-oxide and potential genotoxicity.

There is potential for oral exposure of humans to styrene (ST) such as from migration of residual levels in polystyrene food containers. After absorption, ST is metabolised to styrene-7,8-oxide (SO), an alkylating epoxide. Hence, a comparison of blood burdens of SO resulting from oral exposures to ST was made with SO burdens possibly warranting genotoxic concern. A validated physiological toxicokinetic model was used for the assessment. Model calculations predicted for exposures to ST that maximum concentrations of SO in venous blood of rats and humans should not exceed 0.33 µg/ml and 0.036 µg/ml, respectively, because of saturation of the SO formation from ST. The daily area under the concentration-time curve of SO in venous blood (AUCSO) was directly proportional to the dose of ST (mg/kg body weight; BW), independent of the exposure route (inhalation or oral exposure). In resting humans, the daily AUCSO was about half that in rats at the same amount of ST/kg BW (calculated up to 100mg ST/kg BW in humans). Taking into account the results of cytogenetic studies in ST-exposed rats, it was deduced that no genotoxic effects of SO are to be expected in ST-exposed humans, at least up to a daily amount of 100mg ST/kg BW, which is equivalent to 100 times the amount originating from the Overall Migration Limit in the EU for ST migrating from food contact plastics. Therefore, no potential genotoxic concern is predicted for ST uptake from food packaging, based on the reported combined measured and modelled data.

Physiological modeling of the relative contributions of styrene-7,8-oxide derived from direct inhalation and from styrene metabolism to the systemic dose in humans.

Workers in the reinforced plastics industry are exposed to large quantities of styrene and to small amounts of the carcinogen, styrene-7,8-oxide (SO), in air. Since SO is also the primary metabolite of styrene, we modified a published physiologically based pharmacokinetic (PBPK) model to investigate the relative contributions of inhaled SO and metabolically derived SO to the systemic levels of SO in humans. The model was tested against air and blood measurements of styrene and SO from 252 reinforced plastics workers. Results suggest that the highly efficient first-pass hydrolysis of SO via epoxide hydrolase in the liver greatly reduces the systemic availability of SO formed in situ from styrene. In contrast, airborne SO, absorbed via inhalation, is distributed to the systemic circulation, thereby avoiding such privileged-access metabolism. The best fit to the model was obtained when the relative systemic availability (the ratio of metabolic SO to absorbed SO per unit exposure) equaled 2.75 x 10(-4), indicating that absorbed SO contributed 3640 times more SO to the blood than an equivalent amount of inhaled styrene. Since the ratio of airborne styrene to SO rarely exceeds 1500 in the reinforced plastics industry, this indicates that inhalation of SO presents a greater hazard of cytogenetic damage than inhalation of styrene. We conclude that future studies should assess exposures to airborne SO as well as styrene.

Characterization of hepatocellular resistance and susceptibility to styrene toxicity in B6C3F1 mice.

Short-term inhalation exposure of B6C3F1 mice to styrene causes necrosis of centrilobular (CL) hepatocytes. However, in spite of continued exposure, the necrotic parenchyma is rapidly regenerated, indicating resistance by regenerated cells to styrene toxicity. These studies were conducted to test the hypothesis that resistance to repeated styrene exposure is due to sustained cell proliferation, with production of hepatocytes that have reduced metabolic capacity. Male mice were exposed to air or 500 ppm styrene (6 h/day); hepatotoxicity was evaluated by microscopic examination, serum liver enzyme levels, and bromodeoxyuridine (BrdU)-labeling index (LI). Metabolism was assessed by measurement of blood styrene and styrene oxide. Both single and repeated exposures to styrene resulted in mortality by Day 2; in mice that survived, there was CL necrosis with elevated BrdU LI at Day 6, and complete restoration of the necrotic parenchyma by Day 15. The BrdU LI in mice given a single exposure had returned to control levels by Day 15. Re-exposure of these mice on Day 15 resulted in additional mortality and hepatocellular necrosis, indicating that regenerated CL cells were again susceptible to the cytolethal effect of styrene following a 14-day recovery. However, in mice repeatedly exposed to styrene for 14 days, the BrdU LI remained significantly increased on Day 15, with preferential labeling of CL hepatocytes with enlarged nuclei (karyomegaly). If repeated exposures were followed by a 10-day recovery period, CL karyomegaly persisted, but the BrdU LI returned to control level and CL hepatocytes became susceptible again to styrene toxicity as demonstrated by additional mortality and acute necrosis after a challenge exposure. These findings indicated a requirement for continued styrene exposure and DNA synthesis in order to maintain this resistant phenotype. Analyses of proliferating-cell nuclear-antigen (PCNA) labeling were conducted to further characterize the cell cycle kinetics of these hepatocytes. The proportion of cells in S-phase was increased by repeated exposure. However, PCNA analysis also revealed an even larger increase in the G1 cell compartment with repeated exposures, without a concurrent increase in G2 phase or in mitotic cell numbers. These data indicate that resistance to styrene-induced necrosis under conditions of repeated exposure is not due to sustained cell turnover and production of new, metabolically inactive cells, but rather is due to some other, as yet unknown, protective phenotype of the regenerated cells.

Neurobehavioral effects of experimental exposures to low levels of styrene.

Two experimental studies were conducted with the intention to simulate exposure characteristics of work places with styrene exposure and to investigate the risk for neurobehavioral impairments. In experiment I 16 volunteers (8 in the morning, 8 in the afternoon) were exposed to 0.5 and 20 ppm styrene on a constant level for 3h. In experiment II 24 volunteers (12 in the morning, 12 in the afternoon) were exposed for 4h to 0.5 and 20 ppm styrene on a constant level as well as to a changing exposure between 0.5 and 40 ppm with a TWA of 14 ppm. Simple reaction, choice reaction, attention, acute symptoms, and ratings for well-being were measured. Exposure related performance effects could not be detected. However, 6h time change resulted in delayed choice reactions in the morning hours. Analysing acute symptoms and the state of well-being the impact of styrene did not reach adverse extents of impaired well-being.

Protein adducts as dosimeters of human exposure to styrene, styrene-7,8-oxide, and benzene.

Cysteinyl adducts of hemoglobin (Hb) and albumin (Alb) formed via reactions with reactive species were measured in 48 subjects exposed to styrene (0.24-55.2 ppm) and to styrene-7,8-oxide (SO) (2.65-107 ppb) in a factory producing boats in the USA. Hb and Alb adducts were also investigated among 88 workers exposed to benzene (0-138 ppm) in several Chinese factories. The particular adducts were S-(2-hydroxy-1-phenylethyl) cysteine, from reactions of SO with Alb (designated SO-Alb), and S-phenylcysteine, from reactions of the CYP450 benzene metabolite, benzene oxide (BO), with Hb and Alb (designated BO-Hb and BO-Alb, respectively). The relationships between adduct levels and exposures were investigated in both studies. The estimated slopes varied considerably among the particular combinations of adduct and agent to which the workers were exposed, ranging from 0.815 pmol BO-Hb/g Hb per ppm benzene to 24400 pmol SO-Alb/g Alb per ppm SO. We used these estimated slopes, along with kinetic constants, to predict the systemic doses of SO and BO in humans per mg of styrene, SO or benzene per kg body weight, under certain assumptions. Using RX to signify the particular electrophile (SO or BO) the doses of RX to the blood per unit of dose varied between 2.21 and 4110 nM RX-h/mg agent per kg b.w. The dose of RX to the blood arising from inhalation of SO was almost 2000 times that of styrene (i.e. 4110 vs. 2.21 nM RX/mg agent per kg b.w.) and 430-781 times that of benzene (i.e. 4110 vs. 5.26-9.55 nM RX/mg agent per kg b.w.), depending upon the study. Comparable estimates of the blood dose of BO were obtained from adducts of Hb and Alb and two independent studies of BO-Alb yielded similar dose estimates. These results point to the utility of protein adducts as dosimeters of reactive electrophilic species in occupational studies. Finally, significant levels of background adducts of SO and BO with Hb and Alb were observed among workers, among control subjects and in commercial human proteins. Levels of these background adducts were too great to have arisen from non-occupational exposures to styrene or benzene or from cigarette smoking.

Toluene and styrene intoxication route in the rat cochlea.

It is well established that organic solvents such as toluene and styrene are ototoxic in the rat; however, the intoxication route used to reach the organ of Corti is still questionable. The distribution of toluene and styrene in various tissues of Long-Evans rats (n = 2 x 8) was studied after inhalation of either 1750 ppm toluene or 1750 ppm styrene for 10 h (6 consecutive h + 4 h the following day). At the end of the solvent exposures, blood, brain, auditory nerves, the organ of Corti, cerebrospinal (CSF), and inner ear fluids (IEF) were sampled or removed to measure the rates of solvent uptake in each tissue by gas chromatography. Results indicate that CSF and IEF were free from detectable solvents, whereas the organ of Corti, the nerves, and the brain were contaminated. Therefore, both toluene- and styrene-induced hearing losses are caused by tissue intoxication rather than by fluid contamination. It is proposed that the outer sulcus is used as an intoxication route to reach the organ of Corti.

Identification of 1-adenine DNA adducts in workers occupationally exposed to styrene.

Styrene is an extensively used industrial chemical that has been classified as a possible human carcinogen. The possible carcinogenicity may be related to the covalent DNA binding properties of styrene 7,8-oxide, a major metabolite of styrene. We have developed a sensitive and a highly specific phosphorus-32-postlabeling method for the determination of 1-styrene 7,8-oxide-adenine DNA adducts. These adducts were analyzed in white blood cells from workers exposed to styrene at mean level of 76.2 mg/m3. Three of nine exposed workers showed adducts above the detection limit; the mean was 0.79 +/- 0.14 1-styrene 7,8-oxide-adenine DNA adducts/10(9) nucleotides. None of the 11 control cells showed adducts above the detection limit, which was 0.4 adducts/10(9) nucleotides. The results show a potential of 1-adenine DNA adducts for predicting risks in the workers exposed to styrene.

Solvent ototoxicity in the rat and guinea pig.

There is clear evidence that aromatic solvents can disrupt the auditory system in humans and animals. As far as animal models are concerned, solvent-induced hearing loss seems to be species-dependent. Indeed, most published data have been obtained with the rat, which shows mid-frequency cochlear deficits, whereas the guinea pig does not show any permanent hearing loss after solvent exposure. In the current investigation, the effects of two solvents, toluene (600 ppm) and styrene (1000 ppm), were studied in both Long-Evans rats and pigmented guinea pigs exposed 6 h/day for 5 consecutive days. Cochlear function was tested by using distortion product otoacoustic emissions (DPOAE) measured prior to the solvent exposure, 20 min after the end of the exposure and successively at 2 and 4 weeks post-exposure. In addition to cochlear testing, solvent concentrations in blood and urinary metabolites were measured. A cochlear histological analysis was performed at the end of the experiment. No decrease in DPOAE amplitude was observed in the guinea pig, even immediately following the end of exposure. The rat model showed severe disruption of auditory function and cochlear pathology, whereas the guinea pig had no disruption of DPOAE or cochlear pathological alterations. Therefore, the vulnerability of the cochlear function was strictly dependent on the species. As expected, an important difference in the styrene concentration in blood was observed: the solvent concentrations were fourfold higher in the rat than in the guinea pig. Therefore, it is clear that a pharmacokinetic or an uptake difference might explain the difference in susceptibility observed between the two species. Moreover, the metabolism pathways of the solvents were different depending on the species. Attempts to explain differences of vulnerability between the rat and guinea pig are addressed in the present paper.

Analysis of styrene and its metabolites in blood and urine of workers exposed to both styrene and acetone.

A purge-and-trap gas chromatographic (PT-GC) method for determining styrene concentrations in urine and blood samples has been used in the biological monitoring of workers exposed to styrene and acetone. Blood and urine samples were collected from 34 individuals exposed to both solvents at the end of a 4-h shift and measured for styrene in urine (Su), blood (Sb), and the two major urinary metabolites, mandelic acid (MA) and phenylglyoxylic acid (PGA). A second urine sample was taken at the beginning of the next shift. Environmental exposure was measured using passive personal monitoring and GC. Urinary excretion of MA and PGA was measured by high-performance liquid chromatography. The average exposures to styrene and acetone were 70.5 mg/m3 and 370.5 mg/m3, respectively. In end-of-shift samples there was a significant correlation between concentrations of Su and Sb and the metabolites PGA, MA (r = 0.714 and 0.788, p < 0.001 for Su and r = 0.644 and 0.566, p < 0.005 for Sb). A high correlation between Sb and Su (r = 0.732, p < 0.001) also existed. Poor correlations were found between Su and metabolites in samples collected at the beginning of the next shift (r = 0.491 and 0.474 for PGA and MA, respectively, p < 0.05). There was a better correlation between the biological parameters at the end of the shift and the environmental styrene (r = 0.841 for PGA, r = 0.834 for MA, r = 0.788 for Su, and r = 0.698 for Sb; p < 0.001) compared with those at the start of the shift (r = 0.81 for PGA, 0.675 for MA, and 0.650 for Su; p < 0.001). We found that the concentration of excreted metabolites decreased significantly when environmental concentrations of acetone increased (p < 0.05), particularly at the end of the shift. Although the best correlation with environmental styrene was obtained with the sum of PGA and MA at the end of the shift (r = 0.862, p < 0.001), urine and blood styrene were shown to be more useful biological monitoring indicators because their concentrations were not affected by acetone co-exposure.