Registration Dossier

Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Testing was conducted between 17 December 2009 and 08 April 2010.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Study conducted in compliance with agreed protocols, with the following minor deviation. EC Method C7 gives no direction for the continuation of testing where the apparent reduction in test material concentration does not demonstrate pseudo-first order kinetics. Therefore, in order to generate data for environmental assessment, an additional test was initiated directly at 25°C This exception is considered not to affect the purpose or integrity of the study or the quality of the relevant results. The study report was conclusive, done to a valid guideline and the study was conducted under GLP conditions.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report date:
2010

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
additional test at 25°C for 22 days
Principles of method if other than guideline:
EC Method C7 gives no direction for the continuation of testing where the apparent reduction in test material concentration does not demonstrate pseudo-first order kinetics. Therefore, in order to generate data for environmental assessment, an additional test was initiated directly at 25°C. Sample solutions were removed periodically over a 22 day period and no significant hydrolysis was evident, with the final timepoint concentrations equating to 102, 98.5 and 104% of the mean initial concentration at pH 4, pH 7 and pH 9 respectively when monitoring the 2,2’-oxybisbutane component.
GLP compliance:
yes (incl. QA statement)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Radiolabelling:
no

Study design

Analytical monitoring:
yes
Details on sampling:
The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test. Also these solutions were subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.

Preparation of samples

Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 0.500 g/l in the three buffer solutions. A 1% co-solvent of acetonitrile was used to aid solubility.

For the additional test performed at 25.0 ± 0.5°C, the nominal sample solution concentration was reduced to 0.250 g/l. For these samples, the buffer solution was pre-warmed to 25°C to aid dissolution/homogenisation of the solutions.

The test solutions were split into individual vessels for each data point.

The solutions were shielded from light whilst maintained at the test temperature.

Preliminary test

Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5°C for a period of 120 hours.

Additional test at 25°C

Results from the Preliminary Test indicated non-pseudo-first order kinetics, the quantification of which was beyond the scope of the method guideline. To generate data for environmental consideration, an additional test was performed at pH 4, pH 7 and pH 9, with solutions being maintained at directly at 25.0 ± 0.5°C for a period of 22 days.
Buffers:
Buffer Solution (pH 4)
Components: Potassium hydrogen phthalate
Concentration (mMol dm-3): 2.5

Buffer Solution (pH 7)
Components: Disodium hydrogen orthophosphate (anhydrous), Potassium dihydrogen orthophosphate, Sodium chloride
Concentration (mMol dm-3): 1.5, 1 and 1 respectively

Buffer Solution (pH 9)
Components: Disodium tetraborate, Sodium chloride
Concentration (mMol dm-3): 0.5 and 1 respectively

The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test. Also these solutions were subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.



Details on test conditions:
As previously detailed.
Duration of testopen allclose all
Duration:
120 h
pH:
4
Initial conc. measured:
0.223 g/L
Duration:
120 h
pH:
7
Initial conc. measured:
0.252 g/L
Duration:
120 h
pH:
9
Initial conc. measured:
0.224 g/L
Duration:
527 h
pH:
4
Initial conc. measured:
0.178 g/L
Duration:
527 h
pH:
7
Initial conc. measured:
0.179 g/L
Duration:
527 h
pH:
9
Initial conc. measured:
0.17 g/L
Number of replicates:
Duplicate aliquots (A and B) of sample solution were diluted by a factor of 5 using propan-2-ol at each timepoint for analysis.
Positive controls:
no
Negative controls:
no
Statistical methods:
Not applicable

Results and discussion

Preliminary study:
pH 4: Although apparent pseudo-first order kinetics were indicated by an approximately first order, linear plot, this was considered coincidental, the rate of concentration reduction being influenced by the cumulative total peak area of multiple components. On extraction of the data for the dominant 2,2’ oxybisbutane component peak areas, second order kinetics were again confirmed, the quantification of which was beyond the scope of the method guideline

pH 7: Apparent second order kinetics, the quantification of which was beyond the scope of the method guideline. On extraction of the data for the dominant 2,2’ oxybisbutane component peak areas, second order kinetics were again confirmed.

pH 9: Apparent second order kinetics, the quantification of which was beyond the scope of the method guideline. On extraction of the data for the dominant 2,2’ oxybisbutane component peak areas, second order kinetics were again confirmed.
Test performance:
Equivalent test material concentrations based on the 2,2’-oxybisbutane peak areas only were also determined at each timepoint as this component was identified as the dominant soluble component at lower, more environmentally relevant concentrations.
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
No significant hydrolysis occurred for the testing performed directly at 25°C for environmental assessment. For the preliminary test at 50°C, although a significant reduction in test material concentration was observed, in particular for the dominant 2,2’ oxybisbutane component which was quantified individually, this was attributed to oxidation. This conclusion was based on the second order nature of the reaction, available literature references and information supplied by the Sponsor cautioning about the potential formation of peroxides. Although no additional peak was identified by GC analysis for possible investigation by GC-MS for example, again with reference to literature, the proposed oxidation product can be readily predicted.
Ethers are relatively inert compounds being stable to bases and dilute acids (further supporting hydrolytic stability); however they are prone to auto-oxidation with atmospheric oxygen to form peroxides, with the extremely similar structure isopropyl ether being especially renowned for this process.
Dissipation DT50 of parent compound
Remarks on result:
hydrolytically stable based on preliminary test
Remarks:
No significant hydrolysis occurred. Although a significant reduction in test material concentration was observed, this was attributed to oxidation.
Other kinetic parameters:
With the exception of the plot originating from the pH 4 total peak areas, hydrolysis data from the preliminary test performed at 50°C indicated non-pseudo-first order kinetics both when considered as the total peak area of all components and also when specifically addressing the 2,2’-oxybisbutane component alone. The pseudo-first order plot at pH 4 was considered to be coincidental, the rate of concentration reduction being influenced by the cumulative total peak area of multiple components.

2-Butanol has not been monitored individually since although it dominated water solubility solutions at higher loading levels, it contained no hydrolysable functional groups. Alcohols are common products of hydrolysis reactions but are not themselves open to hydrolysis.

Supported by the non-pseudo-first order kinetics, the reduction in the concentration of the 2,2’-oxybisbutane component may be attributable to auto-oxidation to the peroxide, however no additional peaks were observed on GC analysis, neither was the relative composition of any component detected seen to increase over the timescale of the test.

EC Method C7 gives no direction for the continuation of testing where the apparent reduction in test material concentration does not demonstrate pseudo-first order kinetics. Therefore, in order to generate data for environmental assessment, an additional test was initiated directly at 25°C. Sample solutions were removed periodically over a 22 day period and no significant hydrolysis was evident, with the final timepoint concentrations equating to 102, 98.5 and 104% of the mean initial concentration at pH 4, pH 7 and pH 9 respectively when monitoring the 2,2’-oxybisbutane component.
Details on results:
Due to the quantity of data generated and the relevance of direct reference to graphical information which can not be entered into this field, all results data is presented in the attachment "Hydrolysis Results".

Any other information on results incl. tables

Due to the quantity of data generated and the relevance of direct reference to graphical information which can not be entered into this field, all results data is presented in the attachment "Hydrolysis Results".

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Remarks:
EXAMPLE:The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 200 mg/l. This was satisfactory with a correlation coefficient of 1.00 being obtained.
Conclusions:
Testing was initiated according to EC Method C7, however preliminary testing at 50°C resulted in pseudo second order kinetics, the quantification of which are beyond the scope of the method guideline. Such a reduction in test material concentration was attributed to an auto-oxidation mechanism for the ether containing dominant component, although significant steps have also been taken, as required by the method guideline, to exclude oxygen from the test systems including:

• Degassing of buffers by purging with nitrogen and vacuum filtration prior to use.
• Use of nitrogen headspace in all test vessels during incubation.
• Use of individual vessels for each timepoint in order to prevent exposure to air when sampling

However, if any degree of oxidation remained irrespective of these steps, then it highlights the role of such a process for the environmental fate/transformation of the test material on accidental release into the environment.

To therefore generate data for environmental assessment, an additional test was performed directly at 25°C. Sample solutions were removed periodically over a 22 day period and no significant hydrolysis was evident, with the final timepoint mean concentration equating to 102, 98.5 and 104% of the mean initial concentration at pH 4, pH 7 and pH 9 respectively when monitoring the 2,2’ oxybisbutane component.

Assessment of hydrolytic stability was based on the 2,2’-oxybisbutane component of the test material only as this was determined to be the dominate dissolved component in aqueous solutions originating from the lower, more environmentally relevant nominal saturation concentration during the water solubility testing. In addition the 2 butanol component contained no hydrolysable functional groups.
Executive summary:

Testing was initiated according to Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008, however preliminary testing at 50°C resulted in pseudo second order kinetics, the quantification of which are beyond the scope of the method guideline. Such a reduction in test material concentration was attributed to an auto-oxidation mechanism for the ether containing dominant component, although significant steps have also been taken, as required by the method guideline, to exclude oxygen from the test systems including:

·      Degassing of buffers by purging with nitrogen and vacuum filtration prior to use.

·      Use of nitrogen headspace in all test vessels during incubation.

·      Use of individual vessels for each timepoint in order to prevent exposure to air when sampling

However, if any degree of oxidation remained irrespective of these steps, then it highlights the role of such a process for the environmental fate/transformation of the test material on accidental release into the environment.

Therefore in order to generate data for environmental assessment, an additional test was performed directly at 25°C. Sample solutions were removed periodically over a 22 day period and no significant hydrolysis was evident, with the final timepoint mean concentration equating to 102, 98.5 and 104% of the mean initial concentration at pH 4, pH 7 and pH 9 respectively when monitoring the 2,2’-oxybisbutane component.

Assessment of hydrolytic stability was based on the 2,2’-oxybisbutane component of the test material only as this was determined to be the dominant dissolved component in aqueous solutions originating from the lower, more environmentally relevant nominal saturation concentration during the water solubility testing. In addition the 2-butanol component contained no hydrolysable functional groups.