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Ecotoxicological information

Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
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 microorganisms has been assessed in one OECD 209 study to assess toxicity to freshwater microorganisms from a sewage treatment plant. Accordingly, data do indicate that racemic tetramethrin and thus also d-tetramethrin is not affecting growth of freshwater microorganisms. The highest achievable concentration in the study did not affect growth of microorganisms 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 microorganisms 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:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks on result:
not determinable
Remarks:
The 3-hour EC20, EC50 and EC80 could not be calculated, but were clearly higher than 1000 mg/L
Duration:
3 h
Dose descriptor:
other: EC15
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks on result:
other: Up to and including the concentration of 1000 mg/L the test item tetramethrin had no significant inhibitory effect (<15%) on the respiration rate of activated sludge after the incubation period of three hours
Conclusions:
The 3-hour NOEC (EC15) of racemic tetramethrin to activated sludge microorganisms was at least 1000 mg/L. This value might even be higher, but concentrations in excess of 1000 mg/L were not tested. The 3-hour EC20, EC50 and EC80 could not be calculated, but were clearly higher than 1000 mg/L. Considering that d-tetramethrin is a major component of racemic tetramethrin mixture, the data can be used also to prove that d-tetramethrin will not be affecting respiration of microorganisms significantly.

Description of key information

The 3-hour NOEC (EC15) of Tetramethrin to activated sludge microorganisms was at least 1000 mg/L. This value might even be higher, but concentrations in excess of 1000 mg/L were not tested. The 3-hour EC20, EC50 and EC80 could not be calculated, but were clearly higher than 1000 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information