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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
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 formula and mass, functional groups 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 toxic properties. Acute toxicity to invertebrates has been assessed in one acute daphnia toxicity study and one daphnia reproduction study, forming a solid foundation for assessing aquatic toxicity to freshwater invertebrates. Accordingly, data do indicate that racemic tetramethrin and thus also d-tetramethrin is very toxic to invertebrates and results of d-tetramethrin are not expected to significantly differ from the racemic mixture, considering that this contained the d-enantiomer as the main component.
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, behaviour regarding toxicity to freshwater invertebrates is expected not being affected significantly by stereochemistry, and being fully comparable, thus justifying using available data on daphnia toxicity properties 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
Duration:
24 h
Dose descriptor:
EC50
Effect conc.:
0.54 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
0.47 mg/L
Nominal / measured:
meas. (TWA)
Conc. based on:
test mat.
Basis for effect:
mobility
Conclusions:
Results found for acute toxicity to daphnia of racemic tetramethrin were 24h-EC50: 0.54 mg/L and 48h-EC50: 0.47 mg/L, considered adequate also for the d-enantiomer d-tetramethrin.

Description of key information

The acute toxicity of the test item tetramethrin to Daphnia magna was determined in a 48-hour static test according to the EU Commission Directive 92/69/EEC, Part C.2 (1992), and the OECD Guideline for Testing of Chemicals, No. 202, Part I (1984).

The biological test results are:

24-hour EC50: 0.54 mg/L (95% confidence limits: 0.48 - 0.60 mg/L)

48-hour EC50: 0.47 mg/L (95% confidence limits: 0.43 - 0.51 mg/L)

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
0.47 mg/L

Additional information