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EC number: 700-717-5 | CAS number: -
The DNEL for long-term exposure - local effects via the inhalation route is determined on the basis of read-across to the most chlorinated constituent in MS-Silane, silicon tetrachloride (CAS 10026-04-7). Silicon tetrachloride (SiCl4) is a volatile, inorganic liquid which hydrolyses very rapidly in moist air and in contact with tissues to form hydrogen chloride (HCl) and silicic acid, which may precipitate as silica at sufficiently high concentrations. Local effects (corrosion) are therefore influenced by the formation of hydrogen chloride, while systemic effects may occur following exposure to silicic acid.
An EU long-term inhalation Occupational Exposure Limit (OEL) has been set for Hydrogen chloride as 8 mg/m3 (8 h TWA) in Commission Directive 2000/39/EC. The SIDS Initial Assessment Report (SIAR) for Hydrogen chloride describes a systemic NOAEL of 20 ppm from a 90-day repeated dose inhalation study (OECD, 2002). However, since the NOAEL for local effects in the same study was 10 ppm it is considered for the purposes of the CSA that the observed effects at 20 ppm were secondary to corrosion and were not indicative of true systemic toxicity. The OECD SIAR (2002) reports the following: For repeated dose toxicity, 13 inhalation and 7 oral dose studies have been reported. Among those, only the inhalation studies reported by CIIT (1984) were reliable. They were performed in compliance with FDA-GLP, and they are considered to be the critical studies for assessment. Four groups of 10 males and 10 females (mice: B6C3F1; rats: SD and F344) individually housed were exposed to hydrogen chloride gas at concentrations of 0, 10, 20 and 50 ppm for 90 days (6 hours/day, 5 days/week). For male and female mice at 50 ppm, a decrease in body weight gain, food consumption and liver weight (male) was noted. For male SD rats at 50 ppm, a decrease in food consumption was observed. For F344 rats, a decrease in body weight gain was observed in males at 50 ppm and a decrease in food consumption was observed in both sexes at 20 and 50 ppm. No biologically significant difference was observed in urinalysis, haematology and serum chemistry. Inflammatory histopathological changes in lips or nasal cavity were observed in B6C3F1 mice and F344 rats above 10 ppm or in SD rats above 20 ppm. In addition, the histopathological examination of reproductive organs (testis, epididymis, prostate, seminal vesicle; ovary, uterus, oviduct, mammary glands) could not find any exposure related effects. The NOAEL for repeated dose inhalation toxicity, except for the local effects of irritation, is considered to be 20 ppm for rats and mice. It is therefore considered appropriate to use the existing EU OEL for Hydrogen chloride as the starting point to quantify local DNELs for silicon tetrachloride.
Any exposure will result in hydrolysis to silanol, hydrogen ions and chloride ions; the ions will enter the body's natural buffering and homeostatic processes independently of the silanol. The silanol hydrolysis product must therefore be considered for systemic DNELs because it is expected that this substance will be systemically available. This might be particularly important in situations when inhalation occurs and Hydrogen chloride is neutralized before it reaches the lower respiratory tract, so the silanol hydrolysis product is available for absorption, but there is no irritation from which secondary effects could arise. Also, a systemic DNEL based on the silanol must be considered to allow for situations when the exposure to the silanol is below the local DNEL, but could still cause systemic effects.
The DNEL for long-term exposure - systemic effects for MS-Silane via the dermal and inhalation routes was derived using the DNEL for the hydrolysis product of two structurally similar constituents of MS-Silane [dichloro(dimethyl)silane, CAS 75 -78 -5; 20 - 35% concentration in MS-Silane and dichloro(methyl)silane; CAS 75 -54 -7; 0 - 20% concentration in MS-Silane]. This DNEL was also chosen as it was the most conservative DNEL identified for the four MS-Silane constituents for which DNELs have been derived (see Table 1).
Table 1. Available DNELs for MS-Silane Constituents
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