3-[tris(acetoxy)silyl]propyl methacrylate

Toxicity to aquatic algae and cyanobacteria

Description of key information

Toxicity to algae based on weight of evidence: 72 hour E_rC₅₀ >100 mg/l; NOEC(growth) ≥100 mg/l (nominal) (highest concentration tested) (EU method C.3), and 72 hour E_rC₅₀ >536 mg/l; E_rC₁₀ 503 mg/l (nominal) (EU method C.3), both read-across from a structurally related substance, 3-trimethoxysilylpropyl methacrylate (CAS 2530-85-0). The E_rC₅₀ values are equivalent to >83 mg/l and >445 mg/l when expressed in terms of the silanol hydrolysis product. The quantified results from the second test are taken as the basis of PNEC, as these are the lowest results that are not limit values.

Additional information

There are no reliable algal toxicity data available for 3-[tris(acetoxy)silyl]propyl methacrylate (CAS 51772-85-1), therefore good quality data for the structurally-related substance, 3-trimethoxysilylpropyl methacrylate (CAS 2530-85-0), have been read across. Both substances share the same silanol hydrolysis product, 3-(trihydroxysilyl)propyl methacrylate. The other hydrolysis products are acetic acid and methanol, respectively.

A 72 hour E_rC₅₀ value of >100 mg/l and NOEC(growth rate) of ≥100 mg/l (nominal) (highest concentration tested) have been determined for the effects of the structurally-related substance, 3-trimethoxysilylpropyl methacrylate (CAS 2530-85-0) on growth rate of Scenedesmus subspicatus (new name: Desmodesmus subspicatus) (RCC, 2002c). Test media were prepared by direct addition with stirring for 35 minutes. However in view of the exposure regime it is likely that the test organisms were primarily exposed to the hydrolysis products of the substance. The results may be expressed in terms of concentration of the hydrolysis product, 3-(trihydroxysilyl)propyl methacrylate, by applying a molecular weight correction: (MW of silanol = 206.27 / MW of parent = 248.35) * 100 mg/l = 83 mg/l.

In a second reliable test also using 3-trimethoxysilylpropyl methacrylate (CAS 2530-85-0), a 72 hour E_rC₅₀ value of >536 mg/l and E_rC₁₀ of 503 mg/l were determined for effects on growth rate of Scenedesmus subspicatus (new name: Desmodesmus subspicatus) (Infracor, 2000). A NOEC(cell number) of 322 mg/L was established in this test. In this test, the registration substance would have been fully hydrolysed during preparation of stock solution (which was also filtered prior to the exposure period). There is potential for oligomerisation to have occurred during preparation of the stock, however, high recoveries at the end of the test indicate that precipitation did not occur to a significant extent. At the loading levels corresponding to the NOEC and EC50 the concentration of monomeric silanol should have been stable in the test medium. The results may be expressed in terms of concentration of the hydrolysis product, 3-(trihydroxysilyl)propyl methacrylate, by applying a molecular weight correction: (MW of silanol = 206.27 / MW of parent = 248.35) * 536 mg/l = 445 mg/l.

The 2002 study did not observe any effects up to 100 mg/l loading but the 2000 study did observe effects in the same species at higher loading levels. It is therefore appropriate to derive an indicative PNEC for the silanol hydrolysis product from the second study result for use in chemical safety assessment. Both of these reliable studies provide useful weight of evidence for the hazard assessment.

Refer to the discussion in the Section 6 endpoint summary (Section 7.0 of CSR) for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.