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Environmental fate & pathways

Hydrolysis

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Description of key information

In accordance with Section 2 of Annex XI of Regulation (EC) No. 1907/2006 (REACH), it is considered justified to omit the hydrolysis study required under point 9.2.2.1 of Annex VIII on the grounds that testing is not technically feasible. 
Although the test material was determined to have a water solubility value of less than or equal to 1.19 x 10^-3 g/L, it has been considered that this value was a significant over-estimation, especially when contrasting the result with the calculated value of 4.7 x 10^-8 g/L, which suggests that the test material has a very low water solubility. Therefore, it was considered that the solution concentration required for the test, which would be half the saturated level at most, would be impractically low to perform the study as a sufficiently sensitive analytical method was not available.
The main functional groups in the components of the test material were a tin-ester complex, ester and alkene. The alkene groups would be unlikely to hydrolyse, especially as delocalisation with the ester groups would stabilise the double bond. Ester groups do undergo hydrolysis, but as for the alkene, they may be stabilised with the delocalisation effect. The tin-ester complex may have the potential to hydrolyse (dissociate) at environmentally relevant temperatures and pH, but as the test material has a very low solubility hydrolytic attack would be reduced.

Key value for chemical safety assessment

Additional information

Supporting information is provided in the form of four read across studies.

 

The first piece of supporting information is an internal company study conducted to a good scientific standard with a reasonable level of reporting, Yoder (2003). The study used a non-standard technique measuring the behaviour of dioctyltins in water by electrospray ionisation mass spectrometry (ESI/MS). Although the registered substance was a point of interest in the study, the poor solubility in both water and suitable solvents meant that the test substance was not present at a detectable level, and it was not possible to use a surrogate substance to create standards. No conclusions on the hydrolysis of the test substance could be drawn from the available data. The test material DOTO (di-n-octyltin oxide) is in the same category of substances as the registration substance, as such it is considered acceptable to use a read-across approach to provide supporting information to address this endpoint. In accordance with the criteria detailed by Klimisch (1997) the report was assigned a reliability score of 2 as it was performed and reported to a high standard.

In the second supporting study, hydrolysis as a function of pH was investigated in accordance with the standardised guidelines OECD 111 and EU Method C.7, Lange, 2012. Testing was performed at pH 4, 7 and 9 at 20 ± 0.5 °C. The test material was applied at 0.1 % (v/v) in test systems. Immediately after application, a reaction of the test material with the buffer was visually observed by formation of a white amorphous precipitate. Samples were taken at test initiation and every 10 minutes thereafter until a plateau phase was reached. As a direct analysis of the test material from aqueous solution was not possible, the known transformation product 2,4-pentadione was analysed via HPLC-DAD. Quantification was performed against an external standard. The analytical method was validated with satisfactory results in regard to linearity, repeatability of injection, accuracy and specificity. Analyses indicated a plateau phase for the 2,4-pentadione content for all tested conditions after at least 10 minutes. A mass balance, based on analysed 2,4-pentadione could not be established. It was assumed that the reduced, but reproducible, 2,4-pentadione content was caused by adsorption to the employed filter material, necessary for the elimination of the precipitate. This was confirmed by representative IR measurements performed in a separate study. Reaction rate constants and half lives for all tested conditions could not be assessed, as the hydrolysis reaction was completed within the first two analyses. Taking visual observation of the immediate precipitation into account, it could be assumed that the hydrolytical half life is significantly lower than the time needed for the first sampling (10 minutes). Based on chemical deliberation, the transformation product (precipitate) was assumed to be n-dioctyl oxide. The identity was confirmed by X-ray spectroscopy in a separate study.

 

The study report was conclusive, done to valid guidelines and was conducted under GLP conditions with a high level of reporting. Since the study was conducted with the read across substance dioctylbis(pentane-2,4-dionate-O,O’)tin it has been assigned a reliability score of 2 in accordance with the criteria of Klimisch (1997). As the test material is in the same category of substances as the registration substance, it is considered acceptable to use a read-across approach to provide supporting information to address this endpoint.

In the third uppoting study, hydrolysis as a function of pH was investigated in accordance with standardised guidelines OECD 111 and EU Method C.7. Testing was performed at pH 4, 7 and 9 at 20, 30 and 50 °C. The test material, di-n-octyltin dilaurate, was applied at 400 mg/L (v/v) in each test system. For pH 4, 7 and 9, samples were taken at test initiation and at 8 spaced points. Buffer solutions were analysed at test initiation and at test termination and there was no analytical interference with the test material.

At the start of the study (0 h sampling) very high concentrations of the transformation products were observed. Analysis of 0 h samplings were performed within 4.5 hours after application. For the C12 carboxylic acid, transformation rates significantly above 50 % of the applied test material were calculated indicating a rapid aqueous transformation. On further sampling intervals, a steady state or even a reduction of the carboxylic acid concentrations were observed. In all samples a white precipitate was observed and removed before analysis. Therefore, it could be concluded that the test material will immediately be hydrolysed in the presence of water, therefore no reaction rate constants or half life values could be calculated. Based on the results obtained it could be concluded that the half life of the test material is below 4.5 hours for the main compound (C12 carboxylic acid homologue) and slightly above for the longer chain homologues.

The study report was conclusive, done to valid guidelines and was conducted upder GLP conditions with a high level of reporting. Since the study was conducted with the read across substance di-n-octyltin dilaurate it has been assigned a reliability score of 2. As the test material is in the same category of substances as the registration substance, it is considered acceptable to use a read-across approach to provide supporting information to address this endpoint.

 

In the fourth supporting study, the hydrolysis products of the test material, tin, dioctylbis(2,4-pentanedionato-kO2,k)4)-, were investigated using IR and NMR spectroscopy. During the study 10 g of test material was added to 90 g of distillated water and stirred for 48 hours at room temperature. On the border of the beaker and on the top of the water phase a white substance was formed. This substance was filtered out and washed several times with distilled water and later with n-hexane. After drying the substance for 24 hours at 50 °C in a vacuum it was analysed by IR and 119Sn-NMR spectroscopy.

The IR spectrum of the hydrolysis product of the test material was analogous to that of dioctyltin oxide thereby confirming it as a hydrolysis product. The resolution of the NMR spectra was found to be insufficient.

Therefore, under the conditions of the study dioctyltn oxide was found to be a hydrolysis product of tin, dioctylbis(2,4-pentanedionato-kO2,k)4)-, the condensation product of di-n-octyltin oxide den 2,4-pentanedione.

These data are taken from an internal company study conducted to a good scientific standard with a reasonable level of reporting. Since the study was conducted with the read across substance dioctylbis(pentane-2,4-dionate-O,O’)tin, and has been assigned a reliability score of 2. As the test material is in the same category of substances as the registration substance, it is considered acceptable to use a read-across approach to provide supporting information to address this endpoint.