2,11-Dioxa-3,10-disiladodecane, 3,3,10,10-tetramethoxy-

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.074 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.74 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.007 mg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

74 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.27 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.027 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.01 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

1,6-Bis(trimethoxysilyl)hexane (CAS 87135-01-1) has a high water solubility of 526 mg/l and a low predicted log K_ow of 1.27. It has a hydrolysis half-life of approximately 5.2 hours at 25.1⁰C and pH 7; the substance will therefore undergo rapid hydrolysis in contact with water to form 1,6-bis(trihydroxysilyl)hexane and methanol. 1,6-Bis(trihydroxysilyl)hexane has high predicted water solubility (1E+06 mg/l) and very low predicted log K_ow (-3.5).

REACH guidance (ECHA 2012, R.16) states that “for substances where hydrolytic DT₅₀ is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. TGD guidance, (EC 2003) and R.16 (2012) also suggests that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Therefore, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the silanol hydrolysis product in accordance with REACH guidance. As described in Section 1.3, condensation reactions of the silanols are possible.

The registration substance is part of a class of low-functionality compounds acting via a non-polar narcosis mechanism of toxicity. The group of organosilicon substances in this group contain alkyl, aryl, alkoxy or hydroxy groups attached to the silicon atom when present in aqueous solution. Secondary features may be present in the alkyl chain (e.g. halogen, nitrile, unsaturated bonds) that do not affect the toxicity of the substances. The silanol hydrolysis products may be susceptible to condensation reactions, see Section 4.8 of IUCLID and 1.3 of the CSR.

Methanol is well characterised in the public domain literature and it is not hazardous at the concentrations relevant to the studies; the short-term EC₅₀ and LC₅₀ values are in excess of 1000 mg/l (OECD 2004 - SIDS for methanol, CAS 67-56-1).

Conclusion on classification

The substance has reliable short-term E(L)C₅₀values of >100 mg/l in fish, >100 mg/l in invertebrates and >100 mg/l in algae. It has reliable NOEC ≥100 mg/l in algae.

The substance hydrolyses rapidly in water. The silanol hydrolysis product is not expected to be readily biodegradable, but has a log K_ow<<3.

These data are consistent with the following classification under Regulation (EC) No 1272/2008 (as amended) (CLP):

Acute toxicity: Not classified.

Chronic toxicity: Not classified.