N-[3-(methoxydimethylsilyl)propyl]ethylenediamine

Toxicity to aquatic algae and cyanobacteria

Description of key information

(72-h) EC50: 8.8 mg/l growth rate Pseudokirchneriella subcapitata, reliability 2 (Springborn Smithers, 2002b)
(72-h) NOEC: 3.1 mg/l growth rate Pseudokirchneriella subcapitata, reliability 2 (Springborn Smithers, 2002b)

Additional information

Experimental data was not available for N-[3-(methoxydimethylsilyl)propyl]ethylenediamine (CAS 3069-33-8), therefore read across from the comparable substance, N-(3-(trimethoxysilyl)propyl)ethylenediamine (CAS 1760-24-3) was deemed acceptable for assessment.

In order to reduce animal testing read-across is proposed to fulfill up to REACH Annex IX requirements for the registered substance from substances that have similar structure and physicochemical properties. Ecotoxicological studies are conducted in aquatic medium or in moist environments; therefore the hydrolysis rate of the substance is particularly important since after hydrolysis occurs the resulting product has different physicochemical properties and structure.

In moist medium, N-[3-(methoxydimethylsilyl)propyl]ethylenediamine (CAS 3069-33-8) hydrolyses very rapidly (half-life of approximately 0.7 hours at pH 7 and 25°C) to N-[3-(hydroxydimethylsilyl)propyl]ethylenediamine and methanol. The non-silanol hydrolysis product, methanol, is not expected to contribute to any adverse effects at the relevant dose levels. Methanol is well characterised in the public domain literature and is not hazardous at the concentrations relevant to the studies; the short-term EC50 and LC50 values for this substance are in excess of 1000 mg/l (OECD,2004 - SIDS for methanol, CAS 67-56-1, OECD, 2004).

 

Both, the registered substance and the read across substance N-(3-(trimethoxysilyl)propyl)ethylenediamine hydrolyse rapidly and have similar hydrolysis products. Apart from comparable hydrolysis products, other phys.-chem. data suppose that similar behaviour can also be expected for the parent constituents, as their molecular weights and log Kow are comparable.

A 72-hour EC50 value of 8.8 mg/l and NOEC of 3.1 mg/l have been determined for the effects of the test substance on growth rate of Pseudokirchneriella subcapitata in the key study (Springborn Smithers, 2002). The results are expressed relative to nominal concentrations of the test substance. However the substance is subject to rapid hydrolysis and under the test conditions it is therefore likely that exposure will have been to its hydrolysis products methanol and n-(3-(trihydroxysilyl)propyl)ethylenediamine. This result has been selected as the lowest EC50 value for effects on growth rate from four reliable studies. The other reliable EC50 value was 126 mg/l and the corresponding NOEC is 20 mg/l.

Another report to which it is not possible to assign a reliability score determined EC50 values in the range of 31 to 175 ppm and corresponding NOEC value of <1 to <125 ppm. The study with the lowest reliable EC50 and NOEC values has been selected as key study as a worst case scenario. 

Considerations on the non-silanol hydrolysis products:

Methanol is well characterised in the public domain literature and is not hazardous at the concentrations relevant to the studies; the short-term EC50 and LC50 values for this substance are in excess of 1000 mg/l (OECD,2004 - SIDS for methanol, CAS 67-56-1, OECD, 2004).

Reference: OECD (2004). SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.