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Environmental fate & pathways

Hydrolysis

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Description of key information

Testing of hydrolysis of Modified Small Vinyl Ester was performed according to OECD Guideline method 111 and EC test method C.7. The determination half-life times of Modified Small Vinyl Ester is based on the hydrolysis half-life times for bisGMA and its monomaleic adduct, which are the main constituents of Modified Small Vinyl Ester, amounting ca. 57.5% and 14.5%, respectively. The ultimate hydrolysis products are estimated to be the same from these two compounds, except for maleic acid released from monomaleic adduct of bisGMA. The hydrolysis half-life times are similar for the two compounds at pH=4 and pH=9, but at pH=7 the half-life time of monomaleic adduct of bisGMA is 2-3 times that of bisGMA at the lowest test temperatures (20-50 °C). At the highest test temperature (60/70 °C) the hydrolysis half-life time is approximately the same. The hydrolysis half-life times were found to be strongly correlated to temperature and pH. BisGMA will hydrolyse more rapidly than its monomaleic adduct. At pH=7 and 20 °C, after approximately 85 days, i.e. 3 half-life times for bisGMA and 1 half-life time for its monomaleic adduct, the remainder of the two compounds amounts approximately 9%, i.e. 13% of the original amount of bisGMA and 50% of the original amount of monomaleic adduct of bisGMA. The highest obtained half-life value was used as a key value for the chemical safety assessment, i.e. 85 days at 20 °C (at pH=7).

Key value for chemical safety assessment

Half-life for hydrolysis:
85 d
at the temperature of:
20 °C

Additional information

Hydrolysis as a function of pH for Modified Small Vinyl Ester was experimentally obtained by following the guidelines; OECD Guidelines for Testing of Chemicals – Method 111 “Hydrolysis as a Function of pH” and EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a function of pH). The preliminary test (Tier 1) and main study (Tier 2) were performed for the determination of the rate of hydrolysis of Modified Small Vinyl Ester at pH values normally found in the environment (pH 4-9).

Mean recoveries were not within the range of 70 - 110% at pH 4 and at pH 9. An additional recovery test (not reported in detail) at 0.6 mg/l and 2 mg/l showed that the lower recovery at 2 mg/l is not due to limited solubility at pH 4 (monomaleic adduct of bisGMA). At pH 9, the mean accuracy was only slightly outside the range which might have been caused by a 115% value. Because the recovery was always in the same range and that hydrolysis is calculated using relative numbers, the analytical method was still found adequate.

The determination half-life times of Modified Small Vinyl Ester is based on the hydrolysis half-life times for bisGMA (Notox project 493155) and for monomaleic adduct of bisGMA (Notox project 495920). These two compounds are the main constituents of Modified Small Vinyl Ester, amounting ca. 57.5% and 14.5%, respectively. The ultimate hydrolysis products are estimated to be the same from these two compounds, except for maleic acid released from monomaleic adduct of bisGMA. The hydrolysis half-life times are similar for the two compounds at pH=4 and pH=9, but at pH=7 the half-life time of monomaleic adduct of bisGMA is 2-3 times that of bisGMA at the lowest test temperatures (20-50 °C). At the highest test temperature (60/70 °C) the hydrolysis half-life time is approximately the same. The longest hydrolysis half-life time is 85 days for monomaleic adduct of bisGMA at 20 °C and pH=7. BisGMA will hydrolyse more rapidly than its monomaleic adduct. At pH=7, after approximately 85 days, i.e. 3 half-life times for bisGMA and 1 half-life time for its monomaleic adduct, the remainder of the two compounds amounts approximately 9%, i.e. 13% of the original amount of bisGMA and 50% of the original amount of monomaleic adduct of bisGMA.

The highest obtained half-life value was used as a key value for the chemical safety assessment, i.s. 85 days at 20 °C (at pH=7).