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EC number: 240-465-9 | CAS number: 16415-13-7
Table 1: Appearances of the test solutions
At the initiation of culturing
Water + test substance
Test substance was not dissolved.
Sludge + test substance
At the termination of culturing
Test solution was white cloudy.
Test solution was white cloudy and growth of the sludge was observed.
Table 2: The percentage biodegradation after 28 days.
Table 1: Validity criteria
Criterionfrom the guideline
Validity criterion fulfilled
Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.
6% difference on day 28 and 13% on day 60
Percentage degradation of the reference compound has reached the pass levels by day 14.
60% after 3 d
The oxygen uptake of the inoculum blank is normally 20-30 mg O2/L and should not be greater than 60 mg/L in 28 days.
mean oxygen depletion in the inoculum control was 8 mg O2/L on day 28 and 10.8 mg O2/L on day 60
Both test item replicates reached the 10% biodegradation level on day 4. The 60% pass level was reached by the mean of replicates on day 39. The mean biodegradation on day 60 was 65%.
Table 2: % biodegradation over time.
Triethoxy(hexadecyl)silane (CAS 16415-13-7) is inherently biodegradable (57% after 28 d and 65% after 60 d, OECD 301F) based on read across from CAS 18643-08-8.
One experimental study with triethoxy(hexadecyl)silane (CAS 16415-13-7) is available. The study was performed according to OECD 301 C (GLP). A mixture of activated sludge and samples from different natural locations (e.g. lakes, rivers) was used as inoculum. The test item was degraded to 43% (BOD analysis) and 74% (HPLC analysis). Based on the hydrolytic half-life of 58.4 h at pH7 the substance is expected to hydrolyse within the timescale of a ready biodegradation study. During hydrolysis ethanol and hexadecylsilanetriol are formed. It is expected that ethanol was completely degraded by microorganisms, and that the silanol hydrolysis product was partially degraded by microorganisms. A complete degradation, however, was not reached under the present test conditions.
In order to verify if the substance is at least inherently biodegradable and thus not persistent in the environment a read-across to the suitable source substance chloro(dimethyl)octadecylsilane (CAS 18643-08-8) has been applied to support the environmental hazard assessment of the substance. This read-across is 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). 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 available study investigating the biodegradation of the analogue substance chloro(dimethyl)octadecylsilane (CAS 18643-08-8) was conducted according to OECD guidance 301F and GLP conditions. The inoculum (non-adapted activated sludge from a sewage treatment plant) was exposed for 60 days to 19 mg/L test substance and biodegradation was calculated based on CO2 evolution. The substance was degraded to 57% after 28 d and 65% after 60 d. Therefore, the read across substance is considered as inherently biodegradable.
Based on the result of the analogue substance, triethoxy(hexadecyl)silane (CAS 16415-13-7) is assumed to be inherently biodegradable.
[Type of water: freshwater]
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