Dichloro(diphenyl)silane

Endpoint summary

Additional information

The registered substance dichloro(diphenyl)silane (CAS 80-10-4) hydrolyses very rapidly in contact with water (DT50 = 10 sec at pH 7 and 1.5 °C) to diphenylsilanediol and hydrochloric acid. REACH guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). TGD (EC, 2003) and REACH guidance R.16 (ECHA, 2016) also suggest that when the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity testing.

Therefore, the aquatic toxicity was assessed based on read-across to the silanol hydrolysis product diphenylsilanediol (CAS 947-42-2). For the assessment of toxicity to activated sludge microorganism read-across to trichloro(phenyl)silane (CAS 98-13-5) was performed. Additional information is given in a supporting justification attached in IUCLID Section 13 (PFA, 2016).

 

Acute toxicity studies evaluating the short-term toxicity of the silanol hydrolysis product diphenylsilanediol to aquatic organisms are available for all three trophic levels (fish, aquatic invertebrates, algae). All studies were performed according to accepted standard guidelines and GLP. Acute effects were observed towards the tested organisms among all three trophic levels.

The second hydrolysis product hydrochloric acid is well characterised in the public domain literature and effects on aquatic organisms arising from exposure to hydrochloric acid are thought to result from a reduction in the pH of the ambient environment (arising from an increase in the H+ concentration) to a level below their tolerable range. Aquatic ecosystems are characterized by their ambient conditions, including the pH, and resident organisms are adapted to these conditions. The pH of aquatic habitats can range from 6 in poorly-buffered ‘soft’ waters to 9 in well-buffered ‘hard’ waters. The tolerance of aquatic ecosystems to natural variations in pH is well understood and has been quantified and reported extensively in ecological publications and handbooks (e.g. OECD SIDS for CAS 7647-01-0, hydrochloric acid). It is not considered appropriate or useful to derive a single aquatic PNEC for hydrochloric acid because any effects will not be a consequence of true chemical toxicity and will be a function of, and dependent on, the buffering capacity of the environment. Generally the changes in pH of the receiving water should stay within the natural range of the pH, and for this reason, adverse effects on the aquatic environment are not expected due to anthropogenic or naturally occurring hydrochloric acid (OECD SIDS, 2002). Thus, hydrochloricacid is not considered to contribute to the overall aquatic toxicity of the target substance. In consequence, data for hydrochloric acid are not presented specifically for each environmental toxicity endpoint within this dossier.

 

Table: Overview on aquatic effect values for Diethoxy(dimethyl)silane and its hydrolysis products.

	Parent	Silanol hydrolysis product	Other hydrolysis product^a
CAS	80-10-4	947-42-2	7647-01-0
	Dichloro(diphenyl)silane	Diphenylsilanediol	Hydrochloric acid
Acute fish (LC50)	RA CAS 947-42-2	39 mg/L	4.92 mg/L (pH 4.3)
Acute Invertebrates (EC50)	RA CAS 947-42-2	24 mg/L	0.492 mg/L (pH 5.3)
Algae (EC50)	RA CAS 947-42-2	9 mg/L	0.492 mg/L (pH 5.3)
Algae (NOErC)	RA CAS 947-42-2	1.1mg/L	0.097 mg/L (pH 6)

^aSource = OECD SIDS (2002)

No effects on activated sludge microorganisms were recorded up to a concentration of 1000 mg/L with the read-across substance trichloro(phenyl)silane. The NOEC (3 h) was found to be≥1000 mg/L, which is equivalent to≥ 740 mg/L phenylsilanetriol. On this basis, no toxic effects are anticipated by the target substance and the degradation process in sewage treatment plants is not considered to be inhibited.

References:

OECD, 2002. Hydrogen Chloride - SIDS Initial Assessment Report for SIAM 15, Boston, USA: UNEP Publications.