Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

47 mg/m³

Most sensitive endpoint:

repeated dose toxicity

Overall assessment factor (AF):

6

Modified dose descriptor starting point:

NOAEC

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

12 mg/m³

Most sensitive endpoint:

skin irritation/corrosion

Overall assessment factor (AF):

1

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

6.6 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

Overall assessment factor (AF):

6

Modified dose descriptor starting point:

NOAEL

Trichloro(ethyl)silaneis a volatile liquid whichhydrolyses very rapidly in moist air and in contact with tissues to form hydrogen chloride (HCl) and ethylsilanetriol (half-life <1 min at pH 4, 7 and 9 and 1.5°C). Local effects (corrosion) are therefore influenced by the formation of HCl, while systemic effects may occur following exposure to the silanol hydrolysis product.

Hydrogen chloride (HCl)

An EU long-term inhalation Occupational Exposure Limit (OEL) has been set for HCl as 8 mg/m³(8 h TWA) in Commission Directive2000/39/EC.

The SIDS Initial Assessment Report (SIAR) for HCl 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 by the author of this CSR 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 has 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 HCl as the starting point to quantify local DNELs fortrichloro(ethyl)silane.

Typical worker exposure involveslow levels of exposure on a repeated basis (below the OEL for HCl). 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 HCl is neutralised 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.

Trichloro(ethyl)silane (read-across from trimethoxy(methyl)silane)

There are no repeated dose toxicity data on trichloro(ethyl)silane or its hydrolysis product, ethylsilanetriol, so good quality data for the read-across substance trimethoxy(methyl)silane (MTMS; CAS 1185-55-3), hydrolyses to methanol and methylsilanetriol) have been used to assess the general systemic toxicity of trichloro(ethyl)silane. No read-across data are available for the dermal route.Local effects from the other hydrolysis product, hydrogen chloride (HCl) are not addressed by these data ontrimethoxy(methyl)silane.

In an oral OECD 422 study, exposure of rats for 28-29 days to MTMS was associated with organ weight and/or histomorphological changes in males (liver, thymus, thyroid, duodenum, jejunum, and red blood cell) and females (liver, thyroid, duodenum, jejunum, and adrenal gland) at dose levels at or above 250 mg/kg bw/day (Jean, PA (2005)) . A marked increase in prothrombin time was observed for males at 250 and 1000 mg/kg bw/day whereas females were unaffected. Exposure was also associated with increased blood platelet concentration for males and females at 1000 mg/kg bw/day. These data support a NOAEL for the toxicity phase of the study of 50 mg/kg bw/day.

There is also a 90-day inhalation study on MTMS(Jean, PA (2007)). Based on the increased incidence of grossly observed urinary bladder calculi along with kidney dilation at the 400 ppm exposure level, the NOAEC for MTMS vapour administered for a 90-day interval via whole-body inhalation exposure to male and female Sprague-Dawley rats was 100 ppm (equivalent to 560 mg/m³). Test animals were exposed for 6 hours per day, 7 days per week.

It is unlikely that the effects observed were due to methanol.

There are no reproductive or developmental toxicity data for trichloro(ethyl)silane or its hydrolysis product, ethylsilanetriol, so good quality data for the related substancetrimethoxy(methyl)silane (MTMS)have been used to assess the reproductive and developmental toxicity of trichloro(ethyl)silane.

Exposure of rats to MTMS for 28 days (males) or up to day 3 post partum (females) was not associated with reproductive or developmental toxicity in the oral OECD 422 study previously referred to, for 28 days (males) or up to day 3 post partum (females) (Jean, PA (2005)). The findings support a NOAEL of at least 1000 mg/kg bw/day.