N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane

Toxicity to aquatic algae and cyanobacteria

Description of key information

Toxicity to algae: 72 hour ErC₅₀ 125 mg/l (nominal initial concentration in terms of parent substance) (OECD TG 201). The test was conducted using a mixed pre-hydrolysed solution prepared from the registration substance. The observations in this study are attributed to the exposure of test organisms to the hydrolysis products in the test system. The geometric mean concentration of 3-(dihydroxymethylsilyl)propylamine at the ErC₅₀ was determined as 41 mg/l. The geometric mean concentration of trimethylsilanol at the EC₅₀ was determined as 58 mg/l (note: hydrolysis product concentrations at the LC₅₀ measured in the mixed pre-hydrolysed solution).

Key value for chemical safety assessment

EC50 for freshwater algae:

125 mg/L

EC10 or NOEC for freshwater algae:

77 mg/L

Additional information

72 h ErC₅₀ = 125 (mg initial nominal concentration of parent/L) 72 h ErC₅₀ = 41 (mg dihydroxy hydrolysis product (geo mean)/L) 72 h ErC₅₀ = 58 mg trimethylsilanol hydrolysis product (geo mean)/L); 72 h ErC₁₀ = 77 (mg initial nominal concentration of parent/L) 72 h ErC₁₀ = 22 (mg dihydroxy hydrolysis product (geo mean)/L) 72 h ErC₁₀ = 30 mg trimethylsilanol hydrolysis product (geo mean)/L). Note: NOECs from this study appear to be more representative of the AUC effects examined in the study alongside growth rate, hence it is recommended that ErC₁₀ values are used in classification and labelling.

These results have been determined for the effects of the registration substance on growth rate of Selenastrum capricornutum. In view of the test media preparation method and exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance.The nominal test concentrations are supported by substance-specific analysis of two of the hydrolysis products and concentrations ranged between 50 -100% (in fresh media) to 90 -100% of nominal equivalent (after 72 h), consistent with the expectations of extensive hydrolysis in the test media prior to and during the test. 

The relevent 72 hour geometric mean measured ErC₅₀ and ErC₁₀ values for two of the the hydrolysis products are:

41 mg/l and 22 mg/l, respectively, for 3-(dihydroxymethylsilyl)propylamine

58 mg/l and 30 mg/l, respectively, for trimethylsilanol (TMS)

 

Above a concentration of approximately 1000 mg/l, dimeric / oligomeric, cyclic or cross-linked condensation products could potentially form over time in the aqueous test media. No evidence of undissolved material (parent substance or precipitated products) is mentioned in the study report for this test. pH was ruled out as a significant contributor to effects in this study based on insignificant difference between pH-adjusted replicates at the highest concentration level and non-adjusted replicates at the same concentration level.

There is no basis to expect that ethanol present in the test system would have significantly influenced the results of the test.