Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 4 (2000) / Chapter Skim
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B7 Polydimethylcyclosiloxanes
B7 Polydimethylcyclosiloxanes
Pages 151-174
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From page 151... ...
B 7 Polydimethylcyclosilaxanes John T.~James, Ph.D. Johnson Space Center Toxicology Group Medical Operations Branch Houston, Texas PHYSICAL AND CHEMICAL PROPERTIES Name: Hexamethylcyclo- Octamethylcyclo- Decamethylcyclo trisiloxane tetrasiloxane pentasiloxane (HMCTS)
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in testing of three other silicone oils on five human subjects, Hobbs et al.
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1996~. TOXICITY SUMMARY The toxicity data base consists mostly of studies conducted on OMCTS because it is used often in cosmetics and other products that contact human skin.
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Gavage studies of rats given up to 1600 mg/kg/d for 28 ~ showed increased liver weights at concentrations as low as 400 mg/kg/~; however, none ofthe rats showed histopathological lesions associated with the hepatomegaly. In the LET inhalation study, Sprague-Dawley rats of both sexes were exposed to actual concentrations of 0.0S, 0.94, and 9.0 mg/L (nominal concentrations were 1.1, 6.9, and 34.7 mg/L)
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The animals were killed 14 ~ after exposure ended. Observations included clinical signs, body weights, food consumption, clinical chemistry, hematology, urinalysis, gross pathology, and histopathology.
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The observations included body weights, food consumption, clinical signs, gross pathology, selected organ weights, and selected histopathology. Clinical chemistry and hematology were not reported and the chamber temperatures reported (26-27 °C)
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Observations included the following: clinical signs, body weights, food consumption, hematology, clinical chemistry, urinalysis, gross pathology, organ weights, and histopathology. At the terminal sacrifice, females in the 8.4-mg/L group showed statistically increased red-blood-cell (RBC)
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and high-concenkation groups for recovery studies. The end points included in this study were as follows: clinical signs, body weights, food consumption, ophthalmological examination, clinical chemistry, hematology, urinalysis, gross pathology, organ weights, and histopathology.
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. OMCTS was tested in cultured mouse lymphoma cells for induction of SCEs, point mutations, chromosomal aberrations, end primary DNA damage, with and without microsomal activation (Dow Corning 1 995b)
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. Reproductive Toxicology Few studies of the reproductive toxicity of dimethy~cyclosiloxanes could be found; however, structurally related organosiloxanes produce adverse reproductive effects on mate and female rats.
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cd CON lo, so in ~ ~= ~(~\ ch, ~ ~- ~ at 'a ~.- ~c: ~· c)
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RATIONALE FOR ACCEPTABLE CONCENTRATIONS The toxicological data base, much of it not peer reviewed, on these three siloxanes suggests that they are relatively nontoxic compounds. Clinical signs indicating CNS depression have been noted in high-concentration exposures and only hepatomegaly, without histopathological change, respiratory irritation, and possibly injury to the ovaries or testis have been noted after prolonged exposures to high concentrations.
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. The summary report describes microscopically observed inflammatory changes in the nasal cavities and an increased incidence of pulmonary perivascular infiltration in the highexposure rats.
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,6 in/d, 5 d/w (120 h total) for 4 w showed morphological changes in their nasal cavities as a result of irritation and sTight inflammation in the Jung paranchyma (Kelly et al.1995, Dow Corning 1995a)
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1995~. The 7-d AC for gonad effects was based on the lack of effects reported in rats exposed at 200 ppm 6 in/d, 5 d/w for 4 w (Kelly et al.
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170 an Ct x o ._ CQ Ct o Cd o o Ct C)
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171 lo.
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Roverts.1984. Sub-Acute Inhalation Toxicity Study of Silicone Oil KF 994 in Rats.
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in male and female rats following repeated nose-only vapor inhalation exposure. Toxicologist 16: 16.
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1991. Thirteen-week subchronic inhalation toxicity study on octamethylcyclotetrasiloxane (D4)
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