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Toxicity to aquatic algae and cyanobacteria

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Description of key information

EC50 (72 h): >25 mg/l; NOEC: 2.5 mg/l  (expressed in terms of [3-(2,3-epoxypropoxy)propyl]methylsilanediol).

Key value for chemical safety assessment

EC50 for freshwater algae:
25 mg/L
EC10 or NOEC for freshwater algae:
2.5 mg/L

Additional information

A 72 h ErC50 nominal value of 280 mg/L, equivalent to 2.7 to 6.8 mg/l parent substance (geometric mean), and a NOEC nominal value of 1.0 mg/l (geometric mean not available) have been determined for the effects of [3-(2,3-epoxypropoxy)propyl]diethoxy(methyl)silane (CAS 2897-60-1) on the growth rate of the freshwater algae Scenedesmus subspicatus. In all the test concentrations bright green dispersions were observed by the end of the test period and in the highest 3 concentrations clumps of algal cells were noted. It cannot be excluded that the observed effects are related to undispersed test material. Therefore the results of the study should be treated with caution, however the results are taken forward for use in the chemical safety assessment as they represent a conservative worst case. At the nominal concentrations of 32 mg/l and below no algal clumps were recorded. Therefore a more reliable EC50 should be based on these concentrations. A 72 h ErC50 value of >32 mg/l nominal, equivalent to >17 mg/l measured initial (geometric mean not possible), and a NOEC of 3.2 mg/l nominal, 1.8 mg/l, measured initial, have thus been estimated by the current reviewer; where 19% and 7% inhibition were recorded at 17 and 1.8 mg/l respectively.

Epoxides are known to have the potential for enhanced toxicity due to a specific mode of action to higher organisms (e.g. by Lipnick, 1991); therefore even though the available experimental data provide an assessment limited to a relatively low concentration, the assessment is driven by the data on invertebrates and the uncertainties in interpretation of this test result are not considered critical to the data set.

Due to the rapid hydrolysis rate of the test substance it is likely that the test organisms were predominantly exposed to the hydrolysis products of the test substance.

The results may be expressed in terms of concentration of the hydrolysis product, (2,3-epoxypropoxy)propyl]methylsilanediol, by applying a molecular weight correction: (MW of silanol = 192.28 / MW of parent = 248.40) * >32 mg/l = >25 mg/l. The NOEC value is converted using the same method.

[3-(2,3 -Epoxypropoxy)propyl]methylsilanediol is susceptible to further hydrolysis reactions and the ultimate hydrolysis product 3-{3-[dihydroxy(methyl)silyl]propoxy}propane-1,2-diol is considered unlikely to exhibit significant ecotoxic effects based on QSAR estimated E(L)C50s >>100 mg/l (ECOSAR). The rate of reaction under environmental conditions is uncertain.

Refer to IUCLID Section 6 endpoint summary for further discussion of the approach to chemical safety assessment and justification for read across.

Reference

Lipnick RL. 1991. Outliers: their origin and use in the classification of molecular mechanisms of toxicity. Sci. Total. Environ. 109-110:131153.