Acute Exposure Guideline Levels for Selected Airborne Chemicals Volume 13 (2012) / Chapter Skim
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7 Trimethoxysilane and Tetramethoxysilane
7 Trimethoxysilane and Tetramethoxysilane
Pages 202-241
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Both the document and the AEGL values were then reviewed by the National Research Council (NRC) Committee on Acute Exposure Guideline Levels.
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A factor of 3 was applied for interspecies differences, because similar effects were observed in rats, mice, and hamsters exposed at the same concentration in a 5-day inhalation study (Dow Corning Corp.
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An uncertainty factor of 3 was used for interspecies differences because in a 5day inhalation study with trimethoxysilane, a structural analog of tetramethoxysilane, effects were similar in rats, mice, and hamsters (Dow Corning Corp.
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(2.7 mg/m3) for lethality (Dow Corning Corp.
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Reacts slowly; reacts with Reacts, generating methanol water liberating methanol Vapor pressure 57 mm Hg at 20°C 10.1 mm Hg at 20°C Specific gravity 0.95 at 20°C 1.03 g/cc at 20°C Explosive limits Lower limit: 4.3% at 34°C No data available (volume % in air) Upper limit: 40.1% at 62°C Conversion factors 1 ppm = 5.0 mg/m3 1 ppm = 6.2 mg/m3 1 mg/m3 = 0.2 ppm 1 mg/m3 = 0.16 ppm
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From page 207... ...
and tetramethoxysilane (BIBRA 1988) cause ocular irritation; however, primary sources describing such effects were not available.
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. The following clinical signs were observed post exposure mostly beginning about day 5: unkempt fur, perinasal encrustation, decreased respiratory rate, body weight loss, and audible respiration.
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The study author and the pathologist for the study both concluded that pulmonary lesions increased in severity with increasing concentration and exposure duration with animal death caused by lung dysfunction. Pathologic findings in the lungs of the rats exposed to trimethoxysilane for 1 h included: 643 ppm: four males and four females; marked to severe necrotic bronchiolitis in all lungs, squamous metaplasia of bronchiolar epithelium in three lungs, and marked to severe vascular changes (congestion, edema)
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Pathologic findings in the lungs of rats exposed to trimethoxysilane for 4 h included: 166 ppm: three males and four females; marked to severe necrotic bronchiolitis in all lungs, and moderate to marked vascular/inflammatory changes in all lungs. 71 ppm: one male; necrotic bronchiolitis, congestion, and edema.
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In a study by Union Carbide (1991) , Fisher 344 rats were exposed to trimethoxysilane vapor at 0 (control)
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hamsters, and New Zealand White rabbits were exposed to trimethoxysilane at concentrations of 0, 10, 25, or 50 ppm for 7 h/day for 5 consecutive days, with a 14-day observation period post exposure (Dow Corning Corp.
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Rats exposed to trimethoxysilane had 1- and 4-h LC50s of 154 ppm and 60 ppm, respectively (Nachreiner and Dodd 1988)
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. In another repeat exposure study, hamsters, mice, and rats had similar clinical signs following exposure to trimethoxysilane for 5 days and mortality occurred at 10 ppm or greater in the mice and rats (Dow Corning Corp.
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A statistically significant difference was observed in food consumption, body weight, and clinical parameters in rats exposed at 30 ppm. Males exposed at 15 ppm had only a decrease in total protein.
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Lethality was reported in a study of rats exposed nose-only to tetramethoxysilane at 50 ppm. The only other study was a repeat exposure study in which rats were exposed to tetramethoxysilane at concentrations up to 45 ppm for 28 days.
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That value was derived using the ten Berge formula and the rat mortality data from the acute rat inhalation studies by Nachreiner and Dodd (1988)
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7.2. Summary of Animal Data Relevant to AEGL-2 Only one acute inhalation study on trimethoxysilane was found (Nachreiner and Dodd 1988)
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. For tetramethoxysilane, LC50 data were available from a study in rats exposed nose-only to tetramethoxysilane at concentrations of 31, 50 or 88 ppm for 4 h (Dow Corning Corp.
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A factor of 3 was used for interspecies differences because similar effects were observed in rats, mice, and hamsters exposed at the same concentrations in a 5-day inhalation study (Dow Corning Corp.
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the point of departure was based on a repeated exposure study. A default value of 10 was used for intraspecies variability because there were no data to estimate human variability and it was not clear that tetramethoxysilane acts as a simple chemical irritant in the lungs (NRC 2001)
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b (0.25 mg/m3) a ERPG (emergency response planning guidelines, American Industrial Hygiene Association [AHIA 2005]
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d (6 mg/m3) a ERPG (Emergency Response Planning Guidelines, American Industrial Hygiene Association [AHIA 2005]
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American Conference of Governmental Industrial Hygienists, Cincinnati, OH. AIHA (American Industrial Hygiene Association)
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with Cover Letter Dated 040992. Dow Corning Corp., Midland, MI, EPA Document No.
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2001. Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Chemicals.
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1988. Trimethoxysilane: Acute Vapor Inhalation Toxicity Study in Rats.
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228 Acute Exposure Guideline Levels Uncertainty factors: 3 for interspecies differences 10 for intraspecies variability 10-min AEGL-3: 263 ppm ÷ 30 = 8.8 ppm (44 mg/m3)
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Test Species/Strain/Number: Rat, Sprague-Dawley, 5 males and 5 females per concentration Exposure route/Concentrations/Durations: Inhalation; 19, 39, 71, or 166 ppm for 4 h and 68, 155, 342, or 643 for 1 h Effects: 19 ppm: no deaths or clinical signs; lung lesions ranged from mild infiltrate of inflammatory cells to congestion and edema. 39 ppm: 1/10 deaths; atelectasis in two lungs; bronchial lesions ranging from fibrosis to necrosis.
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. Intraspecies: 10, no data were available to estimate human variability and it was not clear that trimethoxysilane acts as a simple chemical irritant in the lungs (NRC 2001)
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1989. Subchronic inhalation toxicity of tetramethoxysilane in rats.
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8-h AEGL-2: C1 × 8 h = 90 ppm-h C1 = 11.25 ppm 11.25 ppm ÷ 30 = 0.38 ppm (2.4 mg/m3) Derivation of AEGL-3 Values Key study: Dow Corning Corp.
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Trimethoxysilane and Tetramethoxysilane 233 1-h AEGL-3: C3 × 1 h = 70,000 ppm-h C3 = 70,000 ppm C = 41 ppm 41 ppm ÷ 30 = 1.4 ppm (8.7 mg/m3)
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≤ 10 ppm: no lesions. End point/Concentration/Rationale: 15 ppm was the no-effect level for irreversible effects Uncertainty factors/Rationale: Interspecies: 3, rats, mice, and hamsters had similar clinical signs and the rate of mortality was similar among rats and mice in a subchronic study of trimethoxysilane, a structural analog of tetramethoxysilane (Dow Corning Corp.
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End point/Concentration/Rationale: Lethality; BMCL05 of 26 ppm determined using EPA Benchmark Database Software Uncertainty factors/Rationale: Interspecies: 3, rats, mice, and hamsters had similar clinical signs and the rate of mortality was similar among rats and mice in a subchronic study of trimethoxysilane, a structural analog of tetramethoxysilane (Dow Corning Corp.
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. According to this concept, exposure concentration and exposure duration may be reciprocally adjusted to maintain a cumulative exposure constant (k)
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Trimethoxysilane and Tetramethoxysilane 237 between exposure concentration and exposure duration for a given chemical and for a specific health-effect end point. Haber's Rule is the special case where n = 1.
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238 Acute Exposure Guideline Levels APPENDIX F CATEGORY PLOTS FOR TRIMETHOXYSILANE AND TETRAMETHOXYSILANE Chemical Toxicity - TSD Animal Data Trimethoxysilane 1000 No Effe c t 100 Dis c om fort ppm Dis a bl i n g 10 Som e L eth al i ty L eth al AEGL -3 1 AEGL AEGL-2 0 0 60 120 180 240 300 360 420 480 Minutes FIGURE F-1 Category plot of toxicity data and AEGL values for trimethoxysilane. Chemical Toxicity - TSD Animal Data Tetramethoxysilane 100 No Effe c t 10 Dis c om fort ppm Dis a bl i n g Som e L eth al i ty AEGL -3 1 L eth al AEGL -2 AEGL 0 0 60 120 180 240 300 360 420 480 Minutes FIGURE F-2 Category plot of toxicity data and AEGL values for tetramethoxysilane.
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Trimethoxysilane and Tetramethoxysilane 239 APPENDIX G BENCHMARK CALCULATIONS FOR TETRAMETHOXYSILANE The benchmark calculations for tetramethoxysilane are based on a 4-h acute LC50 inhalation study (Dow Corning Corp.
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Analysis of Deviance Table Model Log (likelihood) Deviance Test DF P-value Full model -9.35947 Fitted model -9.50533 0.291706 1 0.5891 Reduced model -20.1904 21.6618 2 <0.0001 AIC: 23.0107 Goodness of Fit Scaled Estimated Dose probability Expected Observed Size Residual 31.0000 0.0110 0.110 0 10 -0.3337 50.0000 0.2678 2.678 3 10 0.23 88.0000 0.9124 9.124 9 10 -0.1392 Chi-square = 0.18; DF = 1; P-value = 0.6683 Benchmark Dose Computation Specified effect = 0.05 Risk Type = Extra risk Confidence level = 0.95 BMD = 37.2855 BMDL = 25.9763
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Trimethoxysilane and Tetramethoxysilane 241 Probit Model with 0.95 Confidence Level Probit 1 0.8 Fraction Affected 0.6 0.4 0.2 0 BMDL BMD 20 30 40 50 60 70 80 90 dose 08:15 01/13 2006
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