Dichloromethylbenzene

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

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

Adequacy of study:

key study

Study period:

1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

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 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

Principles of method if other than guideline:

The growth inhibition of Tetrahymena pyriformis was studied in a static 40-hour test. The population density was quantified spectrophotometrically.

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
PHYSICO-CHEMICAL PROPERTIES
- log Pow: 3.95

Analytical monitoring:

not specified

Details on sampling:

Not indicated

Vehicle:

not specified

Details on test solutions:

Not indicated

Test organisms (species):

Tetrahymena pyriformis

Details on inoculum:

- strain: GL-C
- Laboratory culture: yes

Test type:

static

Water media type:

freshwater

Total exposure duration:

40 h

Post exposure observation period:

Not indicated

Hardness:

Not reported

Test temperature:

27+/- 1°C

pH:

7.4 (of the medium)

Dissolved oxygen:

Not reported

Salinity:

Not applicable

Nominal and measured concentrations:

Following range finding, three replicates of six to eight concentrations of the chemicals were tested. 2 controls were run: one without test substance and with T. pyriformis and the other (blank) without test substance and T. pyriformis.

Details on test conditions:

TEST SYSTEM
- Test vessel: foam-stoppered 250 mL Erlenmeyer flasks, containing 50 mL of sterile, semidefined proteose-peptone-based medium
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 2
- Biomass loading rate: 1000 to 5000 cells/mL

TEST MEDIUM / WATER PARAMETERS
1000 mL distilled water
5 g Proteose peptone
5 g D-Glucose
1 g Yeast extract
1.2114 g Tris-HCl
10 mL each of the following salt solutions and pH to 7.35 with saturated NaOH:
Salt 1 (chlorides):
100 mL H20
0.5 g CaCl2 x 2 H20
0.05 g CuCl2 x 2 H20
0.0125 g FeCl3 x 6 H2O
Salt 2 (sulfates):
100 mL H2O
1 g MgSO4 x 7 H2O
0.25 g Fe (NH4)2(SO4)2 x 6 H2O
0.005 g MnCl2 x 6 H20
0.0005 g ZnCl2

OTHER TEST CONDITIONS
- Adjustment of pH: yes, medium was buffered to pH 7.40 prior to sterilisation.
Control cultures, reared in growth medium become acidic, reaching a pH of 5.5 following 40 to 44 h of growth. At this pH, doubling time approaches infinity, with a cell density of approx. half a million per mL.


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : the population density was quantified spectrophotometrically at 540 nm as its end points.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: Not provided
- Range finding study: yes

OTHER
The test protocol allows for eight to nine cell cycles in controls.
Only replicates with control absorbency values of > 0.6 but < 0.75 were used in the analyses.

Reference substance (positive control):

not specified

Duration:

40 h

Dose descriptor:

other: log (IGC50exp-1)

Effect conc.:

1.07 other: dimensionless

Duration:

40 h

Dose descriptor:

other: IGC50 exp-1

Effect conc.:

11.75 other: dimensionless

Duration:

40 h

Dose descriptor:

other: IGC50

Effect conc.:

0.085 mmol/L

Duration:

40 h

Dose descriptor:

other: IGC50

Effect conc.:

13.7 mg/L

Details on results:

Further details not provided

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

The 50% growth inhibitory concentration (IGC50) was determined by Probit Analysis of Statistical Analysis System (SAS) software. The Y values were absorbencies normalised as a percentage of the control.The X values were the toxicant concentrations in mg/L.

No remarks

Validity criteria fulfilled:

not applicable

Conclusions:

The 40-h EC50 of 3,4 - dichloromethylbenzene was 13.7 mg/L.

Executive summary:

The growth inhibition of Tetrahymena pyriformis was studied in a static 40-hour test. The population density was quantified spectrophotometrically. 6 to 8 concentrations were tested in triplicate.

The 40-h EC50 of 3,4 - dichloromethylbenzene was 13.7 mg/L.

Since the publication is very detailed and since, according to the endpoint specific guidance document (R7.8.17.1), the sensitivity of Tetrahymena-tests is comparable to the sensitivity of respiration inhibition tests, it is concluded that this test fulfils the requirements for a reliable key- study.

Reference: Schultz, 1999

Description of key information

The 40-h EC50 of 3,4-dichlorotoluene to Tetrahymena pyriformis was 13.7 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

13.7 mg/L

Additional information

Key study

The growth inhibition of Tetrahymena pyriformis was studied in a static 40-hour test. The population density was quantified spectrophotometrically. 6 to 8 concentrations were tested in triplicate. The 40-h EC50 of 3,4-dichlorotoluene was 13.7 mg/L. Since the publication is very detailed and since, according to the endpoint specific guidance document (R7.8.17.1), the sensitivity of Tetrahymena-tests is comparable to the sensitivity of respiration inhibition tests, it is concluded that this test fulfils the requirements for a reliable key- study.

Reference: Schultz, 1999

The similarities between the isomers concerning chemical structure and key intrinsic properties such as log kow and water solubility as well as nearly identical results for acute fish toxicity obtained for the mixture and individual isomers justify read across from tests results obtained with the individual isomers 2,4-DCT and 3,4-DCT to the mixture. A more detailed argumentation for read-across is given in the Summary "Aquatic toxicity".

Disregarded studies

The bioluminescence inhibition of Photobacterium phosphoreum was measured with a Beckman instrument, Model 2055. Five test concentrations with a spacing factor of 2 were incubated with the bacteria at 15°C for 15 min. Further details are not provided.

The 15-min EC50 of 3,4-dichlorotoluene was 1.4 mg/L.

Though MICROTOX tests should be considered of low relevance for the STP according to the endpoint specific guidance (R7.8.17.1), the result is almost comparable to the key result. As the reliability is not assignable, the result is disregarded, despite of the lower value.

Reference: Hermens, 1985

The bioluminescence inhibition of Photobacterium phosphoreum after 15 min exposure was determined by using the DXY-2 toxicity analyzer of the Institute of Soil Science, Academia Sinica, Nanjing. Further details are not provided.

The 15-min EC50 of 2,5-dichlorotoluene was 6.71 mg/L.

Though MICROTOX tests should be considered of low relevance for the STP according to the endpoint specific guidance (R7.8.17.1), the result is comparable to the key result. As the reliability is not assignable, the result is disregarded, despite of the lower value.

Reference: Huang, 1996

Further studies

The respiration inhibition of activated sludge from predominantly industrial sewage was tested with the dichloromethylbenzene isomeric mixture according to the German ISO guideline 8192 (1986). Test duration was 3 hours.

The EC50 was determined to be 11 g/L.

Since no information is available on possible adaption, the reliability is not assignable.

Reference: Caspers & Müller, 1991

The respiration inhibition of activated sludge from predominantly industrial sewage was tested with 2,3-dichlorotoluene according to the OECD-guideline 209. Test duration was 3 hours.

The EC50 was determined to be 70 mg/L.

Since no information is available on possible adaption, the reliability is not assignable.

Reference: Bayer, 1985

The respiration inhibition of activated sludge (source not reported) was tested with another isomeric mixture of dichloromethylbenzene isomers containing considerably more 2,6-dichlorotoluene. Test method was the German ISO guideline 8192. Test duration was 3 hours.

The EC50 was determined to be > 10 g/L.

Since only a short is abstract available, the reliability is not assignable.

Reference: Bayer, 1989

The acute toxicity of 2,4- dichlorotoluene to Pseudomonas putida was determined in a 30 minutes flow-through test. The EC0 was determined to be 125 mg/L.

An EC50 > 125 mg/L may be derived from this result.

Since only a short abstract available, the reliability is not assignable.

Reference: Bayer, 1991