Dichloromethylbenzene

Endpoint summary

Additional information

Stability

Hydrolysis:

As reported in SIDS, the main isomer 2,4-dichlorotoluene was found to be hydrolytically stable at pH 4, 7, and 9 in an OECD 111 test performed by MITI,(Reference: MITI, 1993). In this dossier, the DT50 of this isomer is therefore indicated to be >1 year. This DT50 is also applicable to the DCT mixture.

Photo transformation in air:

The following half lives were calculated (Reference: Lanxess, 2009):

- 12.2 days for 2,3- and 2,6-dichlorotoluene

- 13.6 days for 2,5-, 2,3- and 3,4-dichlorotoluene.

For the DCT mixture, the longer half life of 13.6 days is applied as worst-case value.

Biodegradation

Ready biodegradability:

No degradation (0 %) of DCT mixture was found in a 28-d manometric respirometry test according to the OECD 301F, showing that DCT mixture is not readily biodegradable (Reference: Caspers & Müller, 1991).

 

Biodegradation in soil:

A microcosms study in soil slurry under anaerobic, methanogenic test conditions (Reference: Ramanand, 1993) provided the following results:

- DT50 of ca. 90 days for the three main isomers 2,4-DCT, 2,5-DCT and 3,4-DCT. Transformation products were 4-CT, 3-CT and 2-CT as well as toluene.

- Slower degradation was found for 2,3 -DCT and 2,6-DCT (according to the authors "not susceptible to the microorganisms"). Reading from the graphs, 2,3 -DCT and 2,6 -DCT declined by about 40% within 120 to 150 days.

The concentrations at which the DCT isomers were tested (121, 129 or 161 mg/L) are about 10 times higher than the LC50 determined for 3,4 -DCT in the "toxicity to microorganisms test" by Schultz, 1999. Therefore, it must be assumed that the test concentrations negatively influenced the metabolisation of the DCT isomers in soil slurry.

 

Biodegradation in water and sediment:

A simulation test in surface water according to OECD 309 showed a half-live of 31.7 days at 12°C for the whole mixture of isomers. The four main isomers have half-lives of 25 to 35 days. However, there is one isomer (2,3 -DCT, content about 9%) which has a half life of 55 days at 12°C. Biodegradation occurs via 1. hydroxylation of the methyl group ("benzyl alcohols") and/or 2.di-hydroxylation of the aromatic ring. The higher half-life of 2,3 -DCT is explained by the fact that the ring-hydroxylation does not occur with this isomer.

Bioaccumulation

Bioaccumulation:

For one of the main isomers, 2,4-DCT, in a study in fish, the BCF was determined to be 606 – 939 (Reference: Database NITE, <=1995).

By QSAR, the BCF for this isomer was calculated to be 1000 (Reference: Database HSDB, 2009).

For DCT mixture, BCF values of 274-319 were calculated based on experimentally determined log Koc values ranging from 4.2 to 4.3 (Reference: Keller, 2010).

 

For the risk assessment, the experimentally determined value of 939 is chosen. It is concluded that DCT mixture has a moderate bioaccumulation potential.

 

Transport and distribution

Adsorption/desorption on soil or sediment:

A log Koc of 3.36 was determined for DCT mixture according to OECD 121 (Reference: Neuland, 2010), indicating that DCT mixture is slightly mobile in soil.

Henry´s Law Constant:

The Henry´s Law Constant was calculated with EUSES on the basis of experimental values for the water solubility and vapour pressure of the dichloromethylbenzene mixture to be 876 Pa m3/mol at 25°C and 420 Pa m3/mol at 12 °C.