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EC number: 217-496-1
CAS number: 1873-88-7
A category approach is applied to this endpoint and is detailed in the
Siloxane Category report (PFA, 2017). There is a limited amount of
terrestrial toxicity data available with siloxanes. An integrated
testing strategy for the category is proposed. For low molecular weight,
volatile siloxanes, it is proposed to waive terrestrial toxicity testing
due to the test being technically not feasible.
Terrestrial studies with siloxanes such as
1,1,1,3,5,5,5-heptamethyltrisiloxane (H-L3, CAS 1873-88-7),
hexamethyldisiloxane (HMDS, CAS 107-46-0) and octamethyltrisiloxane (L3,
CAS 107-51-7) are technically difficult to conduct due to their high
volatilisation potential (as indicated by high Henry’s Law Constant and
low octanol-air partition coefficient) and the potential for degradation
in soil. Soil testing according to guideline methods does not allow for
a renewal of the substrate and hence re-application of test substance.
Therefore, there is potential for the organisms to not be exposed to the
test material for a sufficiently long period of time for effects to be
expressed, as well as the difficulty of quantifying actual exposure
concentrations. OECD TG 222 acknowledges that the test method may not be
applicable to substances for which the air/soil partition coefficient is
greater than one, or to substance with vapour pressure (VP) exceeding
300 Pa at 25°C. HMDS and L3 meet both of these criteria (for HMDS, Kair-soil
= 3.3 at 20°C (temperature for terrestrial testing), VP
5500 Pa at 25°C; for L3, Kair-soil = 1.3 at
20°C, VP 530 Pa at 25°C). The air/soil partition coefficient for H-L3 is
3.7 at 20°C and vapour pressure 850 Pa at 25°C, therefore the behaviour
of this substance in the soil test systems is expected to be similar.
Terrestrial toxicity testing with HMDS and L3 have shown that
maintaining adequate concentrations in the test system is not feasible
for these compounds.
A 28-day test of the effects of the source substance
hexamethyldisiloxane (HMDS) on nitrate formation rate of soil microflora
has been conducted in accordance with OECD TG 216. However, the
substance could not be maintained in the test system, as demonstrated by
the analytical evidence: measurements in all concentrations were below
the Limit of Quantification (LOQ) by day 3 of the test.
A stability/recovery test under OECD TG 222 conditions with the
structurally related test substance octamethyltrisiloxane (L3)
demonstrated significant loss of test item from the test system,
ascribed to volatilisation losses. The definitive test was therefore not
carried out. A nitrogen transformation test (OECD TG 216) carried out
with L3 also demonstrated significant loss of test material.
H-L3 has a Kair-soil of 3.7, and a vapour
pressure of 850 at 25°C. Based on the partitioning properties of H-L3
and the experimental findings for the source substances HMDS and L3, the
registrants believe that it is not technically feasible to conduct
terrestrial testing (OECD TG 222, OECD TG 216 and OECD TG 208) for H-L3
on the basis that the test substance is too volatile to maintain adequate
concentrations in the test system.
Due to absence of chronic or long-term effects in aquatic
organisms up to the substance solubility limit, no aquatic PNEC has been
derived. Consequently, the Equilibrium Partitioning Method (EPM) is not
Because an aquatic PNEC has not been derived and the substance
cannot be maintained in the terrestrial environment, no terrestrial
hazard is identified and a PNECsoil has not been derived.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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