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EC number: 213-914-1 | CAS number: 1066-40-6
Long-term toxicity to fish
Administrative data
Link to relevant study record(s)
Description of key information
NOEC for freshwater fish: range 20 µg/l (QSAR) - ≥27 µg/l (taken as an indicative value from the surrogate substance octamethytrisiloxane, in which no effects were observed at this loading which represented the limit of solubility in test media).
Key value for chemical safety assessment
Additional information
There are no long-term fish toxicity data available for hexamethyldisiloxane, therefore data from the structurally-related substance octamethyltrisiloxane (CAS 107-51-7), have been read across. HMDS and L3 are within the Reconsile Siloxane Category of compounds, and have high log Kow (5.1 and 6.6), high log Koc (3.0 and 4.3) and low water solubility (0.93 mg/l and 0.034 mg/l). In addition, the substances have a slow hydrolysis rate relative to the time-scale of ecotoxicity testing (t1/2 = 116 h and 329 h at pH 7 and 25°C). Environmental toxicity data for siloxanes are consistent with a non-polar narcosis mechanism (Redman 2012, Peter Fisk Associates 2017at). Given the similar properties, structural similarities, and expected mode of action, it is considered valid to read-across the results for octamethyltrisiloxane to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2017at) attached in Section 13.
A 90-day read-across NOEC of ≥27 µg/l (0.027 mg/l) has been determined for the effects of the surrogate substance octamethyltrisiloxane (L3) on embryo survival, larval hatch and growth (length and dry weight) of Oncorhynchus mykiss. The results were obtained from an early-life stage: reproduction, (sub)lethal effects flow-through test, conducted in accordance with OECD Guideline 210 (Springborn Smithers 2010). The read-across justification is discussed in Section 7.0. In the tested substance, no effects were observed at the limit of solubility. The limit of solubility of HMDS is considerably higher, so the NOEC is read across as a conservative, indicative value.
An estimated chronic NOEC of 0.020 mg/l for fish for HMDS is available using a reliable QSAR method. The method has been validated for use with volatile methyl siloxanes such as HMDS and works well (see QMRF; Peter Fisk Associates 2013bc).
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