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Environmental fate & pathways

Hydrolysis

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Description of key information

Under the test conditions (40 °C, 240 h), Mesamoll can be considered to be stable in aqueous solutions (Currenta, 2008).

Key value for chemical safety assessment

Additional information

The investigation of hydrolysis should provide information concerning the behaviour of the test substance under environmental relevant conditions and under conditions prevailing in biological assays. Furthermore, the identification of relevant degradation products is focused on.

The present study investigated the stability of sulfonic acid, C10-21-alkane, Ph esters in aqueous media recovering more than 80 % of representative constituents after a duration of 240 h. The observed concentration decline of about 20 % over a duration of 10 d is acceptable ruling out the occurrence of degradation processes. Sulfonic acid, C10-21-alkane, Ph esters are stable under the applied test conditions.

According to the REACh Guidance documents, hydrolysis studies performed in accordance with the OECD Guideline No 111 are preferred to accurately describe the bahaviour of a substance at various pH values and temperatures. However, older studies often deviate from that current OECD guideline, but shall also be used to provide information about the stability in aqueous media in general and relevant degradation products.

Tests according to the OECD Guideline No 111 normally encompass a pre test at three different pH values at a temperature of 50 °C over a duration of 5 days. Only in cases where the concentration decrease is greater than 10 %, additional testing becomes necessary.

The present study was not performed according to the OECD guideline 111 with the following deviations:

- tests were performed at 40 °C (instead of 50 °C) over a duration of 240 h (instead of 120 h)

- use of food simulating solvent containing 10 % (v/v) ethanol in water (instead of a buffer)

- only one pH was tested (instead of three)

The study proceeded 10 °C below the temperature, but taking twice the test duration as recommended in the guideline. According to the Van’t-Hoff-rule the reaction rate doubles when rising the temperature about 10 °C and vice versa. Therefore, the study approximately yields results comparable to that obtained for tests performed at 50 °C over a duration of 120 h.

According to the guideline, the solvent concentration should normally not exceed 1 % (v/v). If higher concentrations are applied, it has to be ensured that the solvent has no effect on the hydrolysis of the test substance. As the focus of the study was to investigate the recovery of sulfonic acid, C10-21-alkane, Ph esters under the conditions of a migration test, the aqueous phase consists of food simulating solvent consisting of 10 % (v/v) ethanol dissolved in water. In the presence of ethanol, sulfonic acids, C10-21 alkane, Ph esters might undergo a transesterification under the formation of alkane sulfonic acid alkyl esters and phenol, whereas the corresponding ethyl esters are less stable with respect to hydrolysis compared to the phenyl esters. That means, if a transesterification with ethanol would occur, the formed ethyl ester would undergo a more rapid hydrolysis causing an observable concentration decay of the parent test substance. As the recovery after 240 h was greater than 80 %, the solvent present does not influence the stability of the test substance.

The hydrolysis of esters is catalyzed by acids as well as bases, whereas the catalytic effect of bases is generally stronger (Riemscheider & Hermann, 2005). Hydrolysis in an acidic environment leads to an equilibrium mixture containing the ester, alcohol as well as the free sulfonic acid, whereas a complete hydrolysis of the ester solely occurs if the formed alcohol is removed from the mixture. Furthermore, the reaction rate in dilute acids is generally fairly low, partly based on the poor solubility of the esters in water. Concluding, it can be assumed that sulfonic acid, C10-21-alkane, Ph esters can hydrolyze under acidic conditions but the reaction is assumed to be slow and thus not relevant under environmental and physiological conditions.

Hydrolysis under alkaline conditions (saponification) will take place under the formation of the salts of the alkane sulfonic acid and phenol. The reaction rate increases with increasing pH values meaning that hydrolysis gains in importance solely at very high pH values. Furthermore, the great resistance against saponification is one main feature of sulfonic acid, C10-21-alkane, Ph esters as compared to common softeners (Product information, Lanxess) supporting the assumption that the saponification reaction solely gains in importance at very high pH values normally not occurring in natural systems.

Despite the present study deviates from the OECD guideline 111 it is able to describe the behaviour of sulfonic acids, C10-21 alkane, Ph esters in aquatic media. Based on chemical knowledge, a reaction in an acidic environment is negligible slow and under alkaline conditions solely gains in importance at very high pH values. Furthermore, a new study would not yield additional information as the possible hydrolysis products are known as well.