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EC number: 261-596-8 | CAS number: 59086-80-5
Table 1. Cell concentrations [cells/mL] when methanol was used as a solvent
10^4 cells/mL corrected for background
red value: was excluded from the calculation due to negative cell number
Table 2.Cell concentrations [cells/mL] when TBA was used as a solvent
96 h -EC10 values mentioned in the report were 11 mg/L when TBA was used as a solvent and 7 mg/L when methanol was used as a solvent. No effects causing 50% inhibition of the growth rate were observed. The EC values were calculated by means of a parametric model developed by Kooijman et al. 1983.
Re-evaluation of data:
The 72 -h effect concentrations were calculated in retrospect according to the current OECD 201 (2011) guideline and the original cell numbers given in the report.
No differences were observed between the control and the solvent control. However since only duplicates were used, no statistical analysis could be performed. The solvent control was used as a worst case for the calculation of the growth rate inhibition rates.
1) Results on growth rate inhibition when methanol was used as a solvent:
Table 3: % Inhibition of growth rate at 72 h when methanol was used as a solvent, as calculated in retrospect according to the current OECD 201 standards using the original cell densities from the study report.
No growth rate inhibition up to 10% was observed after 72 h when methanol was used as a solvent resulting in an ErC10 (72 h) >= 31.8 mg/L.
2) Results on growth rate inhibition when TBA was used as a solvent:
Table 4: % Inhibition of growth rate at 72 h when TBA was used as a solvent, as calculated in retrospect according to the current OECD 201 standards using the orginal cell densities from the study report.
The EC10 value was calculated based on the dose-response curve. The ErC10 (72 h) was 20.914 mg/L (nominal) when TBA was used as a solvent.
No growth rate inhibition up to 50% was observed after 72 h of exposure when TBA was used as a solvent resulting in an ErC50 (72 h) > 29.5 mg/L (nominal).
Table 1.Cell concentrations [cells/mL] (TBA was used as a solvent)
A 96 h EC50 value of >10 mg/L and 96 h NOEC of 0.32 mg/L (both nominal) have been determined for both growth rate and biomass effects in the study. The EC50 value were calculated in accordance with the methods described in the OECD test guideline while the NOEC values were determined by visual comparison of the growth curves for the treated cultures and the control cultures.
Re-evaluation of data:
Since no cell numbers at timepoint 0 were adressed for the test item vessels in the report (see table 1), the mean of the control values being 1.05 x 10^4 cells/mL was used as a starting value.
Table 2: % Inhibition of growth rate at 72 h when TBA was used as a solvent, as calculated in retrospect according to the current OECD 201 standards using the orginal cell densities from the study report.
The EC10 value was calculated based on the dose-response curve. The ErC10 (72 h) was 3.4 mg/L (nominal).
No growth rate inhibition up to 50% was observed after 72 h of exposure resulting in an ErC50 (72 h) > 10 mg/L (nominal).
ErC50 (72 h) > 31.8 mg/L and ErC10 (72 h) = 31.8 mg/L (nominal, methanol as solvent, OECD 201, Scenedesmus subspicatus) based on read across from CAS 16415-12-6
ErC50 (72 h) > 29.5 mg/L and ErC10 (72 h) = 20.91 mg/L (nominal, TBA as solvent, OECD 201, Scenedesmus subspicatus) based on read across from CAS 16415-12-6
No data on the toxicity of dichloromethyltetradecylsilane (CAS 59086-80-5) towards algae are available. In accordance with Regulation (EC) No. 1907/2006 Annex XI, 1.5 “Grouping of substances and read across” and in accordance with the read across assessment framework (RAAF, ECHA 2017) a read across from the analogue substance hexadecyltrimethoxysilane (CAS 16415-12-6) has been applied to support the environmental hazard assessment of the substance. Details on the read across justification can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.
The toxicity of hexadecyltrimethoxysilane (CAS 16415-12-6) was studied in two growth inhibition tests. Both studies followed a protocol based on the OECD guideline 201 (1984) and GLP standards. Scenedesmus subspicatus was used as the test organism.
It should be noted, that only two parallels were used for both control and test series. Thus no thorough statistical assessment of effect values is possible. The study duration was 96 hours, which is not in accordance with the guideline standards. Thus a recalculation of the effect values for 72 h has been performed in retrospect in order to meet CLP and OECD standards.
The key study was initiated based on remaining uncertainties of a previous study. There was an uncertainty on the storage stability of the samples tested in the first test. Furthermore, the influence of solvent was investigated more thoroughly in the second test by adding methanol as a second solvent in addition to tertiary butanol (TBA). Therefore the chronologically second study was chosen as the key and the first study was used as supporting information.
In the key study, the test item solutions were prepared with methanol and tertiary butanol as solvents. Two stock solutions (nominally 300 g/L) were initially prepared in methanol and tertiary butanol (TBA) and subsequently added to the algal culture medium to produce the desired test concentrations. Nominal concentrations of 0 (control), 0.01, 0.032, 0.10, 0.32, 1.0, 3.2, 10.2 and 31.8 mg test item/L with methanol as a solvent and 0 (control), 0.009, 0.029, 0.094, 0.29, 0.94, 2.9, 9.4 and 29.5 mg test item/L with TBA as a solvent, were tested. The study resulted in ErC50 (96 h) values of >31.8 mg/L and > 30 mg/L with methanol and TBA as solvents, respectively. Furthermore ErC10 (96 h) values of 7 mg/L and 11 mg/L when methanol or TBA was used as a solvent, respectively, were determined. The 72 h effect values were calculated in retrospect using the original cell numbers presented in the report. When methanol was used as a solvent the 72 h ErC50 and ErC10 were both = 31.8 mg/L (nominal). When TBA was the solvent, the ErC50 (72 h) was > 29.5 mg/L while the ErC10 (72 h) was calculated to be 20.91 mg/L (nominal).
In the supporting study, the test series comprised the following concentrations: 0.0032, 0.010, 0.032, 0.10, 0.32, 1.0, 3.2 and 10 mg test item/L in addition to a control and solvent control. Tertiary butanol was used as a solvent. The 72 h effect values were calculated in retrospect using the original cell numbers presented in the report. The ErC50 (72 h) was > 10 mg/L while the ErC10 (72 h) was calculated to be 3.4 mg/L (nominal).
As the substance hydrolyses rapidly, it is very likely that the test organisms were mainly exposed to the hydrolysis products of the substance retained in the test media. Furthermore due to the use of solvents, the tested concentration largely exceeded the water solubility of the silanol hydrolysis product.
Based on the results of the analogue substance, dichloromethyltetradecylsilane (CAS 59086-80-5) is not assumed to cause adverse effects toward algae.
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