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EC number: 219-784-2 | CAS number: 2530-83-8
24 hr LC50 = 58 mg/l (30-100) 48 hr LC50 = 55 mg/l (30-100) 72 hr LC50 = 55 mg/l (30-100) 96 hr LC50 = 55 mg/l (30-100)
Short-term toxicity to fish: 96-hour LC50 55 mg/l (nominal) (OECD 203). The LC50 is equivalent to 45 mg/l when expressed in terms of [3-(2,3-epoxypropoxy)propyl]silanetriol.
A 96 hour LC50 value of 55 mg/l (nominal) has been determined for the effects of the registration substance on the mortality of the freshwater fish Cyprinus carpio (Infracor Degussa Group, 1996). In view of the test media preparation method and exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance.
DOC analysis of filtered stock solution confirmed very high recoveries, although the concentration of substance was sufficiently high that silanol hydrolysis products could have begun to oligomerise and theoretically, precipitate. The concentration-response relationship in this study was very steep with 0% and 100% mortality observed at successive concentration levels. No sublethal effects were reported. 90% mortality was observed by the 24 h time point in the upper concentration level with 100% mortality by 48 h. It is therefore considered that the effects are predominantly due to the toxicity of the substance (and its soluble hydrolysis products) rather than physical effects associated with undissolved materials. Therefore the effects seen in the test are attributed to a mixture of the parent substance, the [3-(2,3-epoxypropoxy)propyl]silanetriol hydrolysis product, and soluble oligomers.
The results may be expressed in terms of concentration of the hydrolysis product, [3-(2,3-epoxypropoxy)propyl]silanetriol, by applying a molecular weight correction: (MW of silanol = 194.26 / MW of parent = 236.34) * 55 mg/l = 45 mg/l.
This study is selected as Key as it is the lowest value among the reliable studies.
Several supporting studies on the short-term toxicity of the substance to fish are available:
A 96 hour LC50 value of 237 mg/l (nominal concentration) has been determined for the effects of the test substance on mortality of Oncorhynchus mykiss (Dow Corning, 1978).
A 96 hour LC50 value of 276 mg/l (nominal concentration) has been determined for the effects of the test substance on mortality of Lepomis macrochirus (Dow Corning, 1978).
A 96 hour LC50 value of 349 mg/l (nominal concentration) has been determined for the effects of the test substance on mortality of Pimephales promelas (Evonik, 1988).
Ecotoxicity testing for this substance is complicated by the hydrolysis and condensation reactions of the substance. 3-(2,3-Epoxypropoxy)propyltrimethoxysilane is susceptible to hydrolysis of both the trimethoxy and epoxide groups. The silanetriol formed by hydrolysis of the methoxy groups will undergo condensation reactions to form siloxane dimers, oligomers and polymers, which may precipitate and cause physical effects on the test organisms.
One study reported an LC50 value of 4.9 mg/l (Evonik, 1994). However, this study has been disregarded due to major methodological deficiencies. A very high stock loading rate was used (10.2 g/l). Oligomers would have formed and it is therefore unclear as to whether the effects were physical or toxicological. The study is therefore not considered for the assessment.
[3-(2,3-Epoxypropoxy)propyl]silanetriol is susceptible to further hydrolysis reactions and the ultimate hydrolysis product 3-[3-(trihydroxysilyl)propoxy]propane-1,2-diol is considered unlikely to exhibit significant ecotoxic effects based on QSAR estimated E(L)C50s >>100 mg/l (ECOSAR).
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