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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

The toxicity of 2,3-dichlorobutadiene-1,3 to activated sewage sludge was investigated in a respiration inhibition test according to EU Method C11 Activated sludge respiration inhibition 2008. Following three hours exposure to 2,3-dichlorobutadiene-1,3 the EC50was observed to be > 1000 mg/L (based on nominal exposure concentrations), the corresponding EC10was calculated to be 163.8 mg/L.

Key value for chemical safety assessment

Additional information

Read-across justification

- Group: 2-Chlorobuta-1,3-dien (CAS 126-99-8) and 2,3-Dichlorobuta-1,3-dien (CAS 1653-19-6)

- Justification: REACH regulation EC 1907/2006 and ECHA guidance document R.6 give that substances whoses physicochemical, toxicological and ecotoxicological properties are likely to be similar, or follow a regular pattern as a result of structural similarity, may be considered as a group / category of substances.

- Chemical similarity: Both substances show the same chemical structure only differing in the degree of chlorination that is one and two chlorine atoms.

- Physical behaviour: Both substances are organic, share the range of melting and boiling points as well as vapour pressure.

- Fate and ecotoxicology: 2,3-Dichlorobuta-1,3-dien shows higher lower biodegradability and higher acute toxicities than the reference substance 2,3-Dichlorobuta-1,3-dien.

Concluding, using 2,3-Dichlorobuta-1,3-dien for read-across of “Toxicity to microorganisms” is possible and is not expected to underestimate toxic effects. Rather it can be expected that toxicity to microorgan-isms is overrated and, therefore, may act as worst-case scenario.