NTP-CERHR monograph on the potential human reproductive and developmental effects of styrene. (73/204)

The National Toxicology Program (NTP) Center for the Evaluation of Risks to Human Reproduction (CERHR) conducted an evaluation of the potential for styrene to cause adverse effects on reproduction and development in humans. Styrene was selected for evaluation because of (1) public concern about styrene exposure and (2) recently available exposure studies. Styrene (ethenylbenzene; CAS RN: 100-42-5) is a high production volume chemical (a million pounds or more produced each year) and is used in the production of polystyrene resins and as a co-polymer with acrylonitrile and 1,3-butadiene. Styrene is found in items such as foam cups, dental fillings, matrices for ion exchange filters, construction materials, and boats. It is also used in protective coatings, reinforced glass fiber, agricultural products, and as a food additive. The Food and Drug Administration regulates styrene for use as a synthetic flavoring substance and as a component of polymers in contact with dry food, and also regulates the amount of residual styrene monomer allowed in polystyrene intended for use in contact with food. The public can be exposed to styrene by ingesting food or drink that has been in contact with styrene polymers or through inhalation of polluted air and cigarette smoke. The results of this evaluation on styrene are published in a NTP-CERHR monograph that includes: (1) the NTP Brief, (2) the Expert Panel Report on the Reproductive and Developmental Toxicity of Styrene, and (3) public comments received on the expert panel report. The NTP reached its conclusion of negligible concern for adverse developmental and reproductive effects resulting from styrene exposures in humans based on information presented in the NTP-CERHR Expert Panel Report on the Reproductive and Developmental Toxicity of Styrene and the public comments on that report. This conclusion is based on estimated exposures in both the general population and in people whose occupation involves styrene exposure. The expert panel estimated styrene exposure in the general U.S. population to be less than 0.3 microg/kg body weight/day in nonsmokers and 3.51 and 2.86 microg/kg body weight/day in smokers ages 12-19 years and 20-70 years, respectively. Average occupational exposures are estimated to range from 1,400-52,000 microg/kg body weight/day. Studies in humans show no evidence that occupational exposures or exposure of the general population to styrene adversely affect reproduction or development. Further, data from experimental animal studies show no adverse reproductive or developmental effects at styrene doses far above human exposure levels. The NTP will transmit the NTP-CERHR monograph on styrene to federal and state agencies, interested parties, and the public and it will be available in electronic PDF format on the CERHR web site http://cerhr.niehs.nih.gov and in printed text or CD-ROM from the CERHR: M.D. Shelby, Ph.D., Director, CERHR, NIEHS, P.O. Box 12233, MD EC-32, Research Triangle Park, NC 27709, 919-541-3455 [phone], 919-316-4511 [fax], [email protected] [email].  (+info)

Styrene induced alterations in biomarkers of exposure and effects in the cochlea: mechanisms of hearing loss. (74/204)

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.  (+info)

Audiological findings in workers exposed to styrene alone or in concert with noise. (75/204)

Audiological testing, interviews and exposure measurements were used to collect data on the health effects of styrene exposures in 313 workers from fiberglass and metal-product manufacturing plants and a mail terminal. The audiological test battery included pure-tone audiometry, distortion product otoacoustic emissions (DPOAE), psychoacoustic modulation transfer function, interrupted speech, speech recognition in noise and cortical response audiometry (CRA). Workers exposed to noise and styrene had significantly poorer pure-tone thresholds in the high-frequency range (3 to 8 kHz) than the controls, noise-exposed workers and those listed in a Swedish age-specific database. Even though abnormalities were noted on DPOAE and CRA testing, the interrupted speech and speech recognition in noise tests were the more sensitive tests for styrene effects. Further research is needed on the underlying mechanisms to understand the effects of styrene and on audiological test batteries to detect changes in populations exposed to solvents.  (+info)

Enhanced stability and bioconjugation of photo-cross-linked polystyrene-shell, Au-core nanoparticles. (76/204)

Encapsulating Au nanoparticles within a shell of photo-cross-linked block copolymer surfactant dramatically improves the physical and chemical stability of the nanoparticles, particularly when they are applied as bioconjugates. Photo-cross-linkable block copolymer amphiphiles [polystyrene-co-poly(4-vinyl benzophenone)]-block-poly(acrylic acid) [(PS-co-PVBP)-b-PAA] and [poly(styrene)-co-poly(4-vinyl benzophenone)]-block-poly(ethylene oxide) [(PS-co-PVBP)-b-PEO] were assembled around Au nanoparticles ranging from 12 to 108 nm in diameter. UV irradiation cross-linked the PVBP groups on the polymer to yield particles that withstood extremes of temperature, ionic strength, and chemical etching. Streptavidin was attached to [PS-co-PVBP]-b-PAA-coated particles using the same noncovalent and covalent conjugation protocols used to bind biomolecules to divinylbenzene-cross-linked PS microspheres. We expect that these particles will be useful as plasmonic, highly light-scattering and light-absorbing analogs to fluorescently labeled PS nanospheres.  (+info)

Evaluation of long-term occupational exposure to styrene vapor on olfactory function. (77/204)

The primary sensory neurons of the olfactory system are chronically exposed to the ambient environment and may therefore be susceptible to damage from occupational exposure to many volatile chemicals. To investigate whether occupational exposure to styrene was associated with olfactory impairment, we examined olfactory function in 2 groups: workers in a German reinforced-plastics boat-manufacturing facility having a minimum of 2 years of styrene exposure (15-25 ppm as calculated from urinary metabolite concentrations, with historical exposures up to 85 ppm) and a group of age-matched workers from the same facility with lower styrene exposures. The results were also compared with normative data previously collected from healthy, unexposed individuals. Multiple measures of olfactory function were evaluated using a standardized battery of clinical assessments from the Monell-Jefferson Chemosensory Clinical Research Center that included tests of threshold sensitivity for phenylethyl alcohol (PEA) and odor identification ability. Thresholds for styrene were also obtained as a measure of occupational olfactory adaptation. Styrene exposure history was calculated through the use of past biological monitoring results for urinary metabolites of styrene (mandelic acid [MA], phenylglyoxylic acid [PGA]); current exposure was determined for each individual using passive air sampling for styrene and biological monitoring for styrene urinary metabolites. Current mean effective styrene exposure during the day of olfactory testing for the group of workers who worked directly with styrene resins was 18 ppm styrene (standard deviation [SD] = 14), 371 g/g creatinine MA + PGA (SD = 289) and that of the group of workers with lower exposures was 4.8 ppm (SD = 5.2), 93 g/g creatinine MA+PGA (SD = 100). Historic annual average exposures for all workers were greater by a factor of up to 6x. No differences unequivocally attributable to exposure status were observed between the Exposed and Comparison groups or between performance of either group and normative population values on thresholds for PEA or odor identification. Although odor identification performance was lower among workers with higher ongoing exposures, performance on this test is not a pure measure of olfactory ability and is influenced by familiarity with the stimuli and their sources. Consistent with exposure-induced sensory adaptation, however, elevated styrene thresholds were significantly associated with higher occupational exposures to styrene. In summary, the present study found no evidence among a cross-section of reinforced-plastics workers that current or historical exposure to styrene was associated with a general impairment of olfactory function. When taken together with prior studies of styrene-exposed workers, these results suggest that styrene is not a significant olfactory toxicant in humans at current exposure levels.  (+info)

Roles of ring-hydroxylating dioxygenases in styrene and benzene catabolism in Rhodococcus jostii RHA1. (78/204)

Proteomics and targeted gene disruption were used to investigate the catabolism of benzene, styrene, biphenyl, and ethylbenzene in Rhodococcus jostii RHA1, a well-studied soil bacterium whose potent polychlorinated biphenyl (PCB)-transforming properties are partly due to the presence of the related Bph and Etb pathways. Of 151 identified proteins, 22 Bph/Etb proteins were among the most abundant in biphenyl-, ethylbenzene-, benzene-, and styrene-grown cells. Cells grown on biphenyl, ethylbenzene, or benzene contained both Bph and Etb enzymes and at least two sets of lower Bph pathway enzymes. By contrast, styrene-grown cells contained no Etb enzymes and only one set of lower Bph pathway enzymes. Gene disruption established that biphenyl dioxygenase (BPDO) was essential for growth of RHA1 on benzene or styrene but that ethylbenzene dioxygenase (EBDO) was not required for growth on any of the tested substrates. Moreover, whole-cell assays of the delta bphAa and etbAa1::cmrA etbAa2::aphII mutants demonstrated that while both dioxygenases preferentially transformed biphenyl, only BPDO transformed styrene. Deletion of pcaL of the beta-ketoadipate pathway disrupted growth on benzene but not other substrates. Thus, styrene and benzene are degraded via meta- and ortho-cleavage, respectively. Finally, catalases were more abundant during growth on nonpolar aromatic compounds than on aromatic acids. This suggests that the relaxed specificities of BPDO and EBDO that enable RHA1 to grow on a range of compounds come at the cost of increased uncoupling during the latter's initial transformation. The stress response may augment RHA1's ability to degrade PCBs and other pollutants that induce similar uncoupling.  (+info)

Development and initial application of a hybridization-independent, DNA-encoded reaction discovery system compatible with organic solvents. (79/204)

We have developed and applied an approach to reaction discovery that takes advantage of DNA encoding, DNA-programmed assembly of substrate pairs, in vitro selection, and PCR amplification, yet does not require reaction conditions that support DNA hybridization. This system allows the simultaneous evaluation of >200 potential bond-forming combinations of substrates in a single experiment and can be applied in a range of solvent and temperature conditions. In an initial application, we applied this system to explore Au(III)-mediated chemistry and uncovered a simple, mild method for the selective Markovnikov-type hydroarylation of vinyl arenes and trisubstituted olefins with indoles.  (+info)

Syntheses, characterization and study of the use of cobalt (II) Schiff-base complexes as catalysts for the oxidation of styrene by molecular oxygen. (80/204)

Schiff-Base complexes of bis-5-phenylazosalicylaldehyde ethylenediimine and bis-5-phenylazosalicylaldehyde-O-phenylenediimine ligands with Co(II) (I and II) have been synthesized and characterized by their IR spectra and elemental analyses. These complexes catalyze the oxidation of styrene in the presence of dioxygen and excess pyridine. The effect of the reaction conditions on the oxidation of styrene was studied by varying solvent, nature and amount of the catalyst and substrate. The catalytic behavior of the studied complexes was shown to be dependent on the conditions applied. In all reactions, acetophenone and 1- phenylethanol were the only observed products.  (+info)