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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: inherent biodegradability
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 biodegradability. Biodegradability of the l-form is expected being identical to the d-form, that made up half of the substance tested (racemic form) and thus, the results from the racemic form are expected being not different from those of the d-tetramethrin. Accordingly, data do indicate that also the d-tetramethrin is inherently biodegradable, as shown in a ready biodegradability study and an inherent biodegradability study.
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 biodegradability is expected not being affected significantly by stereochemistry, and being fully comparable, thus justifying using available data on biodegradability 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
Reason / purpose for cross-reference:
read-across source
Parameter:
% degradation (O2 consumption)
Value:
20
Sampling time:
28 d
Remarks on result:
other: results from inherent biodegradtion study
Parameter:
% degradation (test mat. analysis)
Value:
26
Sampling time:
28 d
Remarks on result:
other: results from ready biodegradation study, without nitrification
Conclusions:
The test item racemic tetramethrin had no inhibitory effect on activated sludge microorganisms because the biodegradation rate in the toxicity control was >25% within 14 days. In a ready biodegradability study 26% degradation was observed and in an inherent biodegradation study 20% (measured as O2 consumption) was found indicative of inherent biodegradability of racemic tetramethrin but also d-tetramethrin.

Description of key information

READY BIODEGRADABILITY TEST: The test item had no inhibitory effect on activated sludge microorganisms because the biodegradation rate in the toxicity control was >25% within 14 days. Tetramethrin was found to be moderately biodegradable under the test conditions within 28 days.

INHERENT BIODEGRADABILITY TEST: After 28 days of incubation, the test item tetramethrin was found to be ultimately biodegradable by about 20% based on BOD measurement

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable
Type of water:
freshwater

Additional information