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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key 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 vapour pressure, having been determined in a GLP compliant guideline study to be as low as < 0.027 mPa.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
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 vapour pressure data on the racemic form for 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:
read-across source
Test no.:
#1
Temp.:
25 °C
Vapour pressure:
< 0 Pa
Conclusions:
The experimentally determined vapour pressure for racemic tetramethrin ( at 25 °C is P < 0.027 mPa) is considered reliabel for read-across to d-tetramethrin. Thus, the vapour pressure is considered negligible.

Description of key information

The vapour pressure of test item racemic tetramethrin (technical grade) has been determined according to test method OECD 104 and OJEC A.4, following the gas saturation method.

The vapour pressure tests were performed on the test article sample at 25 °C (298 K) with a 20 mL/min nitrogen flow rate. Since in the test solution the tetramethrin peak area was lower than the LOD, the vapour pressure of the test article at 25 °C is P < 0.027 mPa (log P < -1.571).

Key value for chemical safety assessment

Vapour pressure:
0 Pa
at the temperature of:
25 °C

Additional information