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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
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 aquatic algae has been assessed in one algae toxicity study to assess aquatic toxicity to freshwater algae/cyanobacteria. Accordingly, data do indicate that racemic tetramethrin and thus also d-tetramethrin is not affecting growth of algae. The highest achievable concentration in the study did not affect algal growth 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 algae 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:
72 h
Dose descriptor:
NOEC
Effect conc.:
1.36 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Remarks:
initially measured concentration
Basis for effect:
growth rate
Conclusions:
The mean algal cell density in the test medium was at the end of the test after 72 hours equal to those in the parallel solvent control and control cultures. Thus, the test item racemic tetramethrin and its degradation products had no inhibitory effect on the growth of Scenedesmus subspicatus after the exposure period of 72 hours at a concentration of 1.36 mg/L (mean measured concentration of 0.72 mg/L). This test concentration was therefore determined as the 72-hour NOEC (highest concentration tested without toxic effects after a test period of 72 hours), and this value can also be used for the assessment of the d-enantiomer being part of the racemic mixture.

Description of key information

The mean algal cell density in the test medium was at the end of the test after 72 hours equal to those in the parallel solvent control and control cultures. Thus, the test item tetramethrin and its degradation products had no inhibitory effect on the growth of Scenedesmus subspicatus after the exposure period of 72 hours at a concentration of 1.36 mg/L (mean measured concentration of 0.72 mg/L). This test concentration was therefore determined as the 72-hour NOEC (highest concentration tested without toxic effects after a test period of 72 hours).

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
1.36 mg/L

Additional information