Propyltriacetoxysilane

Toxicity to aquatic algae and cyanobacteria

Description of key information

Key study:  OECD Guideline 201. GLP study. The EC50 (72h) on green algae (Pseudokirchenriella subpicata) based on growth rate for Propyltriacetoxysilane was determined to be 24.41 mg/L without pH adjustment and > 1562.50  mg/L with pH adjustment. The NOEC (72h) based on growth rate was determined to be 18 mg/L without pH adjustment and 40 mg/L whit pH adjustment. 

Key value for chemical safety assessment

EC50 for freshwater algae:

24.41 mg/L

EC10 or NOEC for freshwater algae:

18 mg/L

Additional information

Key study: Experimental data on Propyltriacetoxysilane

An Algae Growth Inhibition Test was performed according to OECD Guideline 201 (GLP study) on test item Propyltriacetoxysilane. The EC50 value (based on growth) rate for Pseudokirchenriella subpicata at 72 hour exposure period was 24.42 mg/L without pH adjustment and > 1562.50 mg/L with pH adjustment. The NOEC (72h and based on growth rate) was determined to be 18 mg/L without pH adjustment and 40 mg/L with pH adjustment. Based on microscopic observations performed at test termination in all test concentrations no differences in size and shape of algal cells were reported as compared to the algae cells in the control.

Supporting studies: Read-across from experimental data on supporting substance acetic acid

In the study by Bringmann and Kühn 1980 (klimisch 3) performed with acetic acid, the 8 days Toxicity Threshold for Scenedermus quadricauda was determined to be 4000 mg/L based on growth rate. Based on this result, the read-across approach was applied and the 8 days Toxicity Threshold for propyltriacetoxysilane was calculated to be 5513.41 mg/L.

In the study by Krebs, 1991 (klimisch 2) conducted on acetic acid, the EC50 at 24 hours of green algae exposure was 156 mg/L based on growth inhibition. The read-across was applied and EC50 (24h) for propyltriacetoxysilane was calculated to be 215 mg/L.

Based on the experimental results obtained by Bringmann and Kühn 1978 (klimisch 3) with acetic acid for Microcystis aeruginosa (8d Toxicity threshold = 90 mg/L, basis for effect: cell multiplication), the read-across approach was applied and the 8 days Toxicity Threshold for propyltriacetoxysilane was calculated to be 124.05 mg/L.

In the publication by Hoare et al., 1967 (klimisch 3) the EC50 at 60 hours of Anacystis nidularis (blue-green algae exposure) was determined to be 1640 mg/L based on growth inhibition. Taking into account this result, the read-across approach was applied and EC50 (60h, basis for effect: growth inhibition) for Propyltriacetoxysilane was calculated to be 1654.73 mg/L.

Discussion:

Taking into account the growth inhibition test performed on propyltriacetoxysilane and the supporting studies on acetic acid and sodium acetate, should be pointed out that the toxicity of propyltriacetoxysilane seems to be caused by the pH effect of acetic acid since the effect concentration obtained in the studies conducted without pH adjustment of propyltriacetoxysilane solution and with supporting acetic acid (EC50 (72h): 24.42 mg/L, EC50 (24h): 215 mg/L; TT (8d): 124.05 mg/L) are much lower than those obtained in the studies conducted with pH adjustment of propyltriacetoxysilane solution and with the supporting sodium acetate (EC50 (72h) > 1562.50 mg/, EC50 (60h): 1654.73 mg/L). In fact, as mentioned before, propyltriacetoxysilane polymerizes triggered by hydrolysis (half-life < 37.5 seconds) in contact with water into polymers with molecular weight high enough to be considered biologically unavailable and the toxicity of the substance is due to the degradation product acetic acid which decreases the pH of test solution.