Tetradecamethylhexasiloxane

Endpoint summary

Description of key information

The key study for skin irritation is read across from a structurally analogous substance octamethyltrisiloxane (CAS 107-51-7). The study, conducted according to OECD TG 406, and in compliance with GLP, reports the test material to be not sensitising to skin (RCC, 1999).

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

The key study for skin sensitisation is read across from a structurally analogous substance octamethyltrisiloxane (L3, CAS 107-51-7). The study, conducted according to OECD TG 406, and in compliance with GLP, reports the test material to be not sensitising to skin (RCC, 1999).

At induction, 0.3 ml of undiluted test material was applied epidermally onto the scapular area of 10 guinea pigs. The area was shaved prior to application. The test material was kept in contact to the skin by occlusive dressing for 48 hours. The reaction sites were assessed for erythema and oedema 24 and 48 hours after removal of the dressing, using the numerical grading system according to Draize. 0.3 ml of olive oil was applied onto the skin of the 5 control guinea pigs.

At challenge, 0.2 ml of 50 % of the test material in olive oil was applied onto the flanks of 10 test guinea pigs and kept in contact to the skin under occlusive dressing for 24 hours. The area was shaved prior to application. Approximately 24 and 48 hours after the removal of the dressing the application sites were assessed for erythema and oedema using the numerical scoring system according to Draize. Olive oil was applied onto the skin of the 5 control guinea pigs. No signs of erythema or oedema were observed at 24 and 48 hours post-application. Expected reactions were observed in the positive and negative control groups.

READ-ACROSS JUSTIFICATION

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint. In the case of sensitisation relevant properties are structural similarity, hydrolysis rate and the physical-chemical parameters in the same range. In the following paragraphs the proposed read-across is discussed. Further information can be found in the supporting report (PFA, 2013u) attached in Section 13 of the IUCLID 6 dossier.  

Read-across hypothesis

The hypothesis is that the target (registered) source substance and the (read-across) substances have similar toxicological properties because they are linear siloxanes with similar physicochemical properties and are structurally similar with similar hydrolysis rates so have similar toxicological properties.

a) Structural similarity

Tetradecamethylhexasiloxane (L6) is a methyl-substituted linear siloxane, with six silicon atoms connected by five oxygen atoms, in which the Si-O bonds are susceptible to hydrolysis. Octamethyltrisiloxane (L3) is also a methyl substituted linear siloxane, with three silicon atoms and two oxygen atoms.

b) Similar physicochemical properties

The linear siloxanes all have high log K_ow (increasing with increasing chain length) and low water solubility.

c) Similar hydrolysis rates

The linear siloxanes all hydrolyse slowly at neutral pH.

Summary of key sensitisation data for linear siloxanes

Substance	L2	L3	L4	L5	L6
Chemical name	Hexamethyl disiloxane	Octamethyl trisiloxane	Decamethyl tetrasiloxane	Dodecamethyl pentasiloxane	Tetradecamethyl hexasiloxane
CAS number	107-46-0	107-51-7	141-62-8	141-63-9	107-52-8
Skin sensitising result	Not sensitising (Dow Corning Corporation, 1992)	Not sensitising (RCC, 1999)	-	-	-

Reference

Dow Corning Corporation (1992). Human repeated insult patch test with hexamethyldisiloxane. TKL Research, USA. Report no.: 1992-I0000-37036. Report date: 1992-03-11.

PFA, 2013u, Peter Fisk Associates, Analogue report - mammalian toxicity of linear and branched siloxanes, PFA.300.002.008

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available information on the read across substance, octamethyltrisiloxane (CAS 107-51-7), no classification for skin sensitisation is required according to Regulation (EC) No 1272/2008.