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The registered substance N-[3-(trimethoxysilyl)propyl]butylamine (CAS No. 31024-56-3) is expected to hydrolyse rapidly in contact with water (half-life approximately 4.0 h at 25 °C and pH 7, QSAR) to form N-[3-(trihydroxysilyl)propyl]butylamine and methanol. REACH guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). TGD (EC, 2003) and REACH guidance R.16 (ECHA, 2016) also suggest that when the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity testing.

Therefore, the hazard assessment for the environment, including sediment and soil compartments, is based on the properties of the hydrolysis products, in accordance with REACH guidance.

Short-term aquatic toxicity data is available for all three trophic levels (fish, algae, aquatic invertebrates) on the registered compound. The hazard assessment showed no short-term aquatic hazard to all three trophic levels (all acute effect values > 1 mg/L). However, the highest achievable concentrations in the respective test media that still yielded fully soluble test concentrations without the formation of insoluble polymer structures (i.e. the functional water solubilities) were well below the standard testing concentration range of up to 100 mg/L as well as well below the predicted solubility of the substance (13000 mg/L). In the available experimental studies for the registered substance, the functional water solubilities in the respective testing media were determined in preliminary solubility trials, on the basis of which the definitive test concentrations of up to 50 mg/L (acute fish test), 25 mg/L (acute invertebrate test) and 1 mg/L (aquatic algae test) were defined for the definitive exposure tests. Therefore, the data on the registered substance does not provide an accurate representation of the likely toxicity of the substance.

Thus, it was considered appropriate to read across from the structurally analogue substance N-ethyl-3-trimethoxysilyl-2-methylpropanamine (CAS No. 227085-51-0). The source substance is also expected to hydrolyse rapidly in the aquatic environment (DT50 = 4.7 h at pH 7 and 20-25 °C, QSAR) to form a structurally similar silanol hydrolysis product, N-ethyl-3-trihydroxysilyl-2-methylpropanamine, and the common alcohol hydrolysis product methanol.

Short-term aquatic toxicity data is available for all three trophic levels. No short-term toxicity effects up to the highest concentrations tested were observed in any of the three organism groups (EC/LC50 > 100 mg/L, equivalent to > 81 based on molecular weight corrections). Taking into consideration the fast hydrolysis time of the source compound, the study design (static), and the duration of the acute toxicity tests (48 to 96 h), it can be assumed that the organisms were predominantly exposed to the hydrolysis products.

The second hydrolysis product 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 methanol are in excess of 1000 mg/L (OECD SIDS, 2004). Thus, methanol is not considered to contribute to the overall aquatic toxicity of the target substance. In consequence, data for methanol are not presented specifically for each environmental toxicity endpoint within this dossier.

All aquatic studies were performed according to accepted standard guidelines and GLP criteria.

Table: Overview on aquatic effect values for N-[3-(trimethoxysilyl)propyl]butylamine, the analogue substance N-ethyl-3-trimethoxysilyl-2-methylpropanamine, and the hydrolysis products.


Silanol hydrolysis product


Common non-silanol hydrolysis product






Chemical Name





Acute fish (96-h LC50)

> 50 mg/L

See parent

> 100 mg/L


> 15000 mg/L

Acute Invertebrates (48-h EC50)

> 25 mg/L

See parent

> 100 mg/L

> 10000 mg/L

Algae (72-h EC50)

> 1 mg/L

See parent

> 100 mg/L

ca. 22000 mg/L

Algae (72-h NOErC)

≥1 mg/L

See parent

22 mg/L

No data

a Source = OECD SIDS (2004)


The toxicity towards aquatic microorganisms was investigated in a study according to OECD guideline 209 and GLP criteria on the source substance N-[3-(trimethoxysilyl)propylcyclohexylamine] (CAS No. 3068-78-8). After an exposure time of 3 h an inhibition of respiration of 37.9% was recorded in the highest concentration tested, resulting in an EC50 (3 h) > 1000 mg/L (nominal). Based on the results with the source substance, the target substance N-[3-(trimethoxysilyl)propyl]butylamine (CAS No. 31024-56-3) is not expected to have inhibitory effects on aquatic microorganisms.

This assessment is supported by showing no inhibitory effects in a toxicity control, which was run in the ready biodegradation studyaccording to OECD guideline 301 B on the registered substance. A substance can be assumed to be "not inhibitory" to aquatic microorganisms, if in the toxicity control of a ready biodegradation test, more than 25% degradation based on CO2 evolution (CO2/ThCO2) occurred within 14 d (OECD guideline 301). The toxicity control tested a concentration of 41.7 mg/L test item and 34.3 mg/L sodium benzoate. The toxicity control attained 59.7% degradation within 14 d and 72.4% within 28 d (after acidification), based on CO2 -evolution. Therefore, the substance is not toxic to aquatic microorganisms. As no inhibition of the sludge microorganisms occurred, the degradation process in sewage treatment plants is not considered to be inhibited.



OECD, 2004: SIDS Initial Assessment Report for Methanol, SIAM 19, Berlin, Germany, 19-22 October 2004, Methanol, CAS 67-56-1