[3-(trimethoxysilyl)propyl]urea

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Data waiving:

other justification

Justification for data waiving:

the study does not need to be conducted because the substance has a low octanol water partition coefficient and the adsorption potential of this substance is related to this parameter

Description of key information

log Koc (parent substance) = 1.63 (pH 7)

log Koc (silanol hydrolysis product) = 0.48 (pH 7)

Key value for chemical safety assessment

Koc at 20 °C:

3.01

Additional information

The registered (parent) substance 1 -[3 -(trimethoxysilyl)propyl]urea (CAS No. 23843-64-3) decomposes fast in the environment, due to rapid hydrolysis in contact with water forming the corresponding hydrolysis products [3-(trihydroxysilyl)propyl]urea and methanol. The hydrolysis half-life at 20-25°C and pH 7 was calculated to be 2.8 h while a hydrolysis half-life of 0.2 and 0.1 h was calculated for pH 4 and 9, respectively (for more information refer to the hydrolysis section). The parent substance has an octanol-water partitioning coefficient of -0.2 while the hydrolysis product has a very low octanol–water partition coefficient of -3.3 and thus low potential for adsorption. In accordance with Column 2 of REACH Annex VIII, the adsorption/desorption screening test does not need to be conducted, since the parent substance decomposes rapidly and the hydrolysis product has a very low log Kow value.  

Further information on the adsorption behavior of the parent substance and its hydrolysis product was collected by an appropriate calculation method. Considering the ionizing properties of the compounds, the adsorption potential has been calculated using Franco and Trapp ‘s expressions (2008) on estimation of the organic carbon-water partitioning coefficient of ionisable organic substances. More detail on the derived octanol-water partitioning coefficient of its non-ionised (log Kow) and ionized forms (log D) as well as the pKa values can be found in the chapter referring to the partitioning coefficient.

The following equation was used for Koc calculation as suggested by the authors:

 

Koc =Fn x 10^{0.37xlogPn+1.70}+Fion x 10^{pKa^0.65xf^0.14}

Where:

 

Fn = 1/(1+10^(pH-pKa))

Pn: Kow of the neutral molecule (EpiWin)

pKa: 1.06 (parent substance), 1.77 (hydrolysis product) (more information in chapter “partitioning coefficient”)

Fion = 1- Fn

f: Ratio of concentration in octanol to total concentration: Kow (overall)/(Kow (overall) + 1)

 

The log Koc of the parent compound 1 -[3-(trimethoxysilyl)propyl]urea was calculated to be 1.63 at pH 4, 7 and 9.

However, since the parent compound is in most environmental pH ranges not stable, the log Koc values of the silanol hydrolysis product [3-(trihydroxysilyl)propyl]urea was considered more relevant and was calculated with the same method. The log Koc of the hydrolysis product was calculated to be 0.48 at pH 4; 0.48 at pH 7 and 0.48 at pH 9. These values indicate the low adsorption potential of the silanol hydrolysis product in soils and sediments. 

Since the hydrolysis of the parent compound 1-[3-(trimethoxysilyl)propyl]urea (CAS No. 23843-64-3) at pH 4, 7 and 9 was identified to be very fast we assume that under environmental conditions the hydrolysis product will be the dominant species present and therefore its log Koc values are considered more appropriate for the chemical safety assessment.

 

Reference:

Franco A. & Trapp S., 2008: Estimation of the soil-water partition coefficient normalized to organic carbon for ionizable organic chemicals. Environmental Toxicology and Chemistry, Vol. 27, No. 10, pp. 1995–2004.

[LogKoc: 0.48]