D-tetramethrin

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance is highly insoluble in water

Reference 2

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The source substance is the racemic form of the target substance d-tetramethrin. Tetramethrin does consist of 50% d- and l-form, and both do exist as cis and trans isomers. Hence, the target substance does consist of d-cis-tetramethrin, d-trans-tetramethrin, l-cis-tetramethrin and l-trans-tetramethrin, whereas the target substance only contains the first two (i.e. d-cis-tetramethrin, d-trans-tetramethrin).
Both, the source as well as the target substance, do have a cis/trans ratio of approximately 1/4 and obviously do share same molecular mass and other properties. Thus, the source substance by definition does contain ~50% of the d-form and the l-form is not expected to be significantly different with respect to its solubility and hydrolysis behaviour. Hydrolysis is by no means dependent on enantiomeric variations and thus read-across from the racemic form to its d-enantiomer is scientifically justified. Hence, it can be reasonably assumed that the hydrolysis data for racemic tetramethrin is representative for d-tetramethrin too.
The d-tetramethrin with a purity > 80 % does contain its corresponding l-form as an impurity in the range of < 7%, other impurities from the manufacturing process are individually below 1% (w/w) each. The source substance that has been tested was having a purity of approx. 98% as tetramethrin with a cis/trans ratio of 1/4 and a d-form/l-form ratio of ~50/50.

3. ANALOGUE APPROACH JUSTIFICATION
Source and Target substance do share identical structure and molecular weight, only differentiating by the fact that the source substance is a racemic mixture, whereas the target substance represents almost pure d-form. Thus, physico-chemical parameters, not being affected significantly by stereochemistry, are fully comparable, thus justifying using available data on hydrolysis properties on the racemic form for supportive read-across to the d-enantiomer.
4. DATA MATRIX
Composition comparison
D-tetramethrin (target) tetramethrin (source)
D-trans tetramethrin 70 - 80% 40 – 50%
D-cis tetramethrin 10 - 20% 7 – 11 %
L-trans tetramethrin 0 – 5% 35 – 40%
L-cis tetramethrin 0 – 2% 7 – 11%

Reason / purpose for cross-reference:

read-across source

Details on results:

The results of pH 4.0, pH 7.0 and pH 9.0 showed a degradation of TETRAMETHRIN at 50 °C. The degradation of TETRAMETHRIN at pH 4.0 was about 34% after 120 hours. During the pH 7.0 test the test item was detected at the beginning of the experiment. After 2.4 hours over 50% of TETRAMETHRIN was hydrolysed. At pH 9.0 the hydrolysis was very fast. No test item was detected in the sample solutions.
The solubility of TETRAMETHRIN in the respective buffer solutions is very low. With the use of acetonitrile as solubilizer it was not possible to increase the solubility significantly. As the solubility is at highest 2 µg/ml (see pH 4.0), it is hard to follow the degradation of TETRAMETHRIN.
According to the EEC Directive 92/69, Section C.7, the method is applicable only to water soluble substances. The test item shows no significant solubility in the different solvent systems. Therefore, no further testing could be performed with TETRAMETHRIN at pH 4.0, pH 7.0 and pH 9.0.

Conclusions:

The test item racemic tetramethrin shows no significant solubility in the different solvent systems. Therefore, same is assumed for d-tetramethrin and no further testing can be performed with d-tetramethrin at pH 4.0, pH 7.0 and pH 9.0.

Description of key information

The study assessing hydrolysis does not need to be conducted because the substance is highly insoluble in water. An attempt had already been made before, investigating the racemic mixture of d-tetramethrin and l-tetramethrin, showing to abiotic degradation, in a pre-test but also showing that water solubility was too low to perform the final test. Findings in the pre-test showed that hydrolysis at 50 °C is fast at pH 9, ~50% after 2.4 hours at neutral pH (pH 7) and slow (34% after 120 hours) at pH 4.