Dichloromethylbenzene

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil, other

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

1993

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Justification for type of information:

The substance described in this dossier is an isomeric mixture of five position isomers of dichlorotoluene. The similarities concerning chemical structure and key intrinsic properties such as log Kow and water solubility lead to the assumption that the other intrinsic values and values for ecotoxicological endpoints will also be very similar for the individual isomers and the mixture of isomers and that therefore results obtained with isomers can be useful for the assessment of the mixture.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

The anaerobic metabolism was evaluated in soil slurry microcosms under anaerobic, methanogenic conditions. The substances and their metabolites were extracted with pentane and analysed by GC.

GLP compliance:

not specified

Test type:

laboratory

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
Not reported

Radiolabelling:

no

Oxygen conditions:

anaerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

clay loam

% Org. C:

5.38

pH:

7.2

Details on soil characteristics:

The used soil contained 37.0 ppm nitrogen and 16.5 ppm phosphorus . The pH was 7.2, the organic matter content was 5.38%.
The soil was air dried, passed through a 3.25-mm-pore-diameter sieve, and immediately transferred to an anaerobic glove box before use.

Soil No.:

#1

Duration:

150 d

Soil No.:

#1

Initial conc.:

800 other: µM 2,4 DCT, corresponding to 129 mg/L

Soil No.:

#1

Initial conc.:

1 000 other: µM 2,5 - DCT, corresponding to 161 mg/L

Soil No.:

#1

Initial conc.:

1 000 other: µM 3,4 - DCT; corresponding to 161 mg/L

Soil No.:

#1

Initial conc.:

1 000 other: µM 2,6 - DCT, corresponding to 161 mg/L

Soil No.:

#1

Initial conc.:

750 other: µM 2,3 - DCT, corresponding to 121 mg/L

Parameter followed for biodegradation estimation:

test mat. analysis

other: monitoring of primary degradation products

Soil No.:

#1

Temp.:

not reported

Humidity:

not reported

Microbial biomass:

10% soil microbial culture

Details on experimental conditions:

Preparation of soil slurries: 50 g soil and 70 mL of sterile anaerobic mineral medium were placed into 150-mL serum bottles. All bottles received 1 mM sodium sulfitde and resazurin as an anaerobic indicator. The bottles were sealed with Teflon-lined butyl rubber stoppers and crimped. A H2-to CO2 head-space ratio of 80:20 was set for the methanogenic conditions. The DCT-mixture was amended and inoculated with a 10% slurry microbial culture.
To determine the degradation capabilities of the endogeneous soil microbiota, one set of soil slurry was not inoculated. Further, one set of poisoned controls was run with 15 mM sodium azide (Na N3).

Soil No.:

#1

% Degr.:

ca. 100

Parameter:

other: test material analysis of 2,4-DCT, 2,5-DCT and 3,4-DCT

Sampling time:

130 d

Soil No.:

#1

DT50:

ca. 90 d

Remarks on result:

other: 2,4-DCT; 2,5-DCT and 3,4-DCT

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Biotransformation of 2,4-DCT and 3,4-DCT resulted predominantly in the formation of 4-Chlorotoluene (4 -CT) and subsequently of toluene.

2,5-DCT was transformed to toluene via 2-CT with small amounts of 3-CT.

2,3-DCT and 2,6-DCT were found to be not susceptible to the microorganisms.

The initial concentrations and the DT50 - and DT 100 values were determinated visually from the graphs provided in the publication for the citation in HSDB.

Executive summary:

The anaerobic metabolism of a mixture of isomers was evaluated in soil slurry microcosms under anaerobic, methanogenic conditions. The substances and their metabolites were extracted with pentane and analysed by GC. Results:

- The DT50 for microbial transformation of 2,4 -DCT, 2,5 -DCT and 3,4-DCT was determined to be ca. 90 d under the test conditions.

Transformation products were 4 -, 3 - and 2-chlorotoluene 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 declined from 780 to 500 µmole and 2,6 -DCT from 1000 to 600 µmole 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 might be assumed that the test concentrations negatively influenced the metabolisation of the DCT isomers in soil slurry.

Reference: Ramanand, 1993

Description of key information

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-and 2,6-DCT (according to study author “not susceptible to microorganisms”).
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. 

Key value for chemical safety assessment

Half-life in soil:

90 d

Additional information

The anaerobic metabolism of individual isomers was evaluated in soil slurry microcosms under methanogenic conditions. The substances and their metabolites were extracted with pentane and analysed by GC. Results:

- The DT50 for microbial transformation of 2,4-DCT, 2,5-DCT and 3,4-DCT was determined to be ca. 90 d under the test conditions. Transformation products were 4 - , 3 - and 2 - chlorotoluene 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 might be assumed that the test concentrations negatively influenced the metabolisation of the DCT isomers in soil slurry.

Based on this result the substance is not persistent and not highly persistent (half life in soil >180 days) according to REACH guidance document Table R. 7.11-2 (ECHA 2012).