Registration Dossier
Registration Dossier
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EC number: 249-854-8 | CAS number: 29797-40-8
Biodegradation in water and sediment: simulation tests
Administrative data
Link to relevant study record(s)
Description of key information
A weight-of-evidence approach is presented using a OECD 309 test yielding half-lifes and a separate test investigating the metabolism of dichlorotoluenes wiht specific bacteria. The OECD 309 test used a lake water system amended with sediment. Dichlormethylbenzene (mixture of isomers) degrades in water with a half-life of 31.7 days at 12°C in the dark. Individual isomers were evaluated showing half-lives of 25 to 55 days. The 2,3-DCT isomer was the only component showing a half-life above 40 days. This fact was explained by the second test: Primary biodegradation patterns of dichlorotoluenes are hydroxylation of the methyl group or dihydroxylation at the aromatic ring. Whereas the hydroxylation of the methyl group was found for all dichlorotoluenes, ring hydroxylation was not found for 2,3-DCT and 3,5-DCT. This explains why the half-life of 2,3-DCT is higher: This component can only be degradet by one metabolic route whereas the most other isomers have an additional second route.
Key value for chemical safety assessment
- Half-life in freshwater:
- 31.7 d
- at the temperature of:
- 12 °C
Additional information
Although the substance as such shows a half-life of 31.7 days at 12°C thus not fulfilling the P-criterion. However, there is one isomer (2,3 -DCT,
content about 9%) which shows a longer half-life of 55 days at 12°C.
| Table: Degradation behaviour of individual isomers | ||||
| Isomer | DT50 (day) | chi2 err (%) | kinetics | Temp. (°C) |
| 2,4-DCT + 2,6-DCT (sum) | 30.6 | 8.5 | SFO | 12 |
| 2,5-DCT | 35.4 | 7.9 | SFO | 12 |
| 2,3-DCT | 55.8 | 6.3 | SFO | 12 |
| 3,4 -DCT | 25.3 | 9.2 | SFO | 12 |
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