Dichloromethylbenzene

Endpoint summary

Additional information

Toxicity to fish:

SHORT TERM TOXICITY

Key study

In a 96-h acute toxicity study, Danio rerio were exposed to the dichloromethylbenzene mixture at nominal concentrations of 2.8 - 44 mg/L under semi-static conditions. Analytical monitoring was performed. The authors determined the 96-h LC0 to be 2.2 mg/L and the LC100 to be 4.3 mg/L.

 

The LC0 and LC100 values were recalculated during dossier preparation as geometric-mean values based on the measured concentrations, resulting in an LC0 of 1.8 mg/L and an LC100 of 2.6 mg/L. The geometric mean was determined to be 2.2 mg/L.

 

The study was performed according to GLP and followed a method which is comparable with the required guideline and is therefore considered to fulfil the requirements for a key study.

Reference: Caspers & Müller, 1992

 

Supporting studies

In a 96-h acute toxicity study,Oryzias latipes were exposed to 2,4-dichlorotoluene at nominal concentrations of 1.0 - 10 mg/L under semi-static conditions. The OECD-Guideline 203 was followed. Analytical monitoring was not performed.

A 96-h LC50 of 2.7 mg/Lwas determined based on nominal concentrations.

Reference: EA Japan, 1992

 

In a 96-h acute toxicity study,Pimephales promelas were exposed to 3,4-dichlorotoluene. It was a flow-through system and the tested concentrations were between 0.85 and 6.59 mg/L (nominal) and between 0.7 and 5.35 mg/L (mean measured).

A 96-h LC50 of 2.91 mg/Lwas determined based on mean measured concentrations.

Reference: Brooker, 1984

 

In a 96-h acute toxicity study,Danio rerio were exposed to 2,3-dichlorotoluene. It was a static system. Due to a very steep dose-response curve, an LC50 could not be estimated. A 96-h LC0 of 42.2 mg/L and an LC100 of 56.2 mg/L were determined based on nominal concentrations.

The geometric mean of these values was calculated to be 48.7 mg/L.

Reference: Bernhofen-Klinke, 1985

 

In a 96-h acute toxicity study,Oryzias latipes were exposed to 2,6 -dichlorotoluene.

A 96-h LC50 of 6.4 mg/Lwas determined.

Reference: Ueda, 1993

 

In a 96-h acute toxicity study,Danio reriowere exposed to an isomeric mixture with a higher amount of 2,6 - dichlorotoluene. It was a flow-through test system and analytical monitoring was performed.

A 96-h LC50of 3.24 mg/Lwas determined.

Reference: FhG, 1989

 

LONG TERM TOXICITY

 

Key study

The 31 - 33 d (28 day-post hatched) toxicity of 3,4-dichlorotoluene was determined in a flow-through test with Pimephales promelasfollowing a method equivalent to the OECD Guideline 210. Analytical monitoring was performed. The following parameters were determined: percent hatch, percent abnormal, dead fry immediately after hatch, percent survival of transferred fry throughout the exposure period, length and weight of juvenile fish at the exposure end.

The NOEC was determined to be 0.078 mg/L (33 d) for all above parameters. The LOEC was determined to be 0.148 mg/L (28 d) based on the parameters fry survival and standard length (measured values).

Reference: Call et al, 1985

 

Toxicity to Daphnids:

 

SHORT TERM TOXICITY

 

Key study:

The 48-hr-acute toxicity of 2,4-dichlorotoluene to Daphnia magna was studied under static conditions. Daphnids were exposed to a minimum of 5 concentrations with a spacing factor of 1.2 to 1.8. Immobilization was observed at 48h. All validity criteria are fulfilled. The 48-hour EC50 was 1.26 mg/L.

Reference: Marchini, 1999

 

Supporting studies:

The 48-hr-acute toxicity of 2,4-dichlorotoluene to Ceriodaphnia cf. dubia was studied under static conditions with analytical monitoring. The 48-hour EC50 was 1.0 mg/L (based on initial measured concentrations). The reliability is 2, nevertheless lower than the reliability of the key study because based on the information provided in the report only compliance with one of the three validity criteria can be proven. Therefore, uncertainty remains as to whether the other two validity criteria have been fulfilled. The study is therefore not chosen as key study, but nevertheless confirms the results of the key study. The slightly lower EC50 may be explained by the closed system and the use of a vehicle.

Reference: Rose, 1998

 

The 48-hr-acute toxicity of 2,4-dichlorotoluene to Daphnia magna was determined under semi-static conditions in a 21 -d study. The 48-hour EC50 was 6.5 mg/L.

Reference: EA Japan, 1992 (21d)

 

 

LONG TERM TOXICITY

 

Weight of evidence:

A weight-of-evidence approach is presented as a combination of a reliable experimental daphnia magna reproduction test for a homologue substance (4-monochlorotoluene) with a reliable QSAR result for 3,4-dichlorotoluene. The 16-d log IC50 (reproduction) was calculated from a clog Poc of 3.98 for 3,4-dichloromethylbenzene to be 0.18 µmol/L, corresponding to an IC50 of 0.24 mg/L. This result confirms the conclusion drawn from the acute aquatic studies that there are no relevant differences in sensitivity between the trophic levels.

Reference: Hermens, 1984

NITE 1999 

 

Toxicity to algae:

 

Key study:

In order to test acute toxicity to algae of the substance,Desmodesmus subspicatuswas exposed to five different nominal concentrations of the substance, and blank control solution for a period of 72 h under static conditions. The method used was the OECD Guideline 201 (Alga, Growth Inhibition Test). The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions.

The results were expressed in terms of geometric mean measured concentrations. A 72h-EC50 of 2.8 mg/L and a 72h-NOEC of 0.42 mg/L were obtained.

 

Supporting study:

The 72-hr toxicity of 2,4-dichlorotoluene to Pseudokirchnerella subcapitata was studied in an open system, a vehicle was used.

The EU-method C3 (1984) was followed.

The 72-h EbC50 was 9.7 mg/L (based on biomass). This value is comparable to the key result.

Reference: EA Japan, 1992

  

Toxicity to microorganisms:

 

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

  

Justification for read-across from studies with individual isomers to the isomer mixture:

 

The substance described in this dossier is an isomeric mixture of five position isomers of dichlorotoluene.

 

As further shown in the following table, the log Kow of DCT mixture (experimental, Neuland) is nearly identical to the modelled values for 2,4- and 2,6- DCT (QSAR, Hansch). Since the calculation of the log kow values for all isomers with kowWin provided the same value of 3.83 for all isomers, which comes close to the value of 4.2 -4.3 experimentally determined for the mixture, it is concluded that the experimentally determined log kow of 4.2 - 4.3 is a reliable value for all isomers.

 

The experimental value for the water solubility of 8 mg/L for 2,4-dichlorotoluene (Bayer) is very similar to the experimental value of 11.2 mg/L for the mixture (Schödel). As shown in the following table, the calculated water solubility values of the individual isomers are within the same magnitude and therefore comparable (KowWIn and ChemID plus).

 

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 read across to the mixture.

 

This assumption is supported by the results obtained in acute fish toxicity studies performed with the isomers: 2,4 -, 3,4 -, 2,3 - and 2,6 - DCT as well as with two different mixtures including the one which is to be assessed in this dossier (see following table). The results are nearly identical for all tested isomers with the exception of the result obtained for 2,3-DCT, which is considerable higher. However, this study is attributed a reliability of only 4.

 

Consequently, read-across from one individual isomer to the whole mixture seems to be reliable. Values obtained for 2,4-DCT or 3,4-DCT are therefore read across to the DCT-mixture as summarised in the following table:

 

Key and supporting studies in the aquatic toxicity performed with dichloromethylbenzene mixture or with individual isomers :

	DCT-mixture	2,4-DCT	3,4-DCT	2.,3-DCT	2,6-DCT	2,5-DCT
Mean % in the mixture (range)	100%	26 ( 20 - 30)	14 (10 - 20)	10 (5 - 15)	7 (5 - 10)	44 (30 - 50)
Structure formula (in print as graphics may not be inserted here)	mixture of 5 position isomers of dichlorotoluene	The Cl-atoms are positioned at nos. 2 and 4 on the toluene ring	The Cl-atoms are positioned at nos. 3 and 4 on the toluene ring	The Cl-atoms are positioned at nos. 2 and 3 on the toluene ring	The Cl-atoms are positioned at nos. 2 and 6 on the toluene ring	The Cl-atoms are positioned at nos. 2 and 5 on the toluene ring
Molecular weight [g/mol]	161.03	161.03	161.03	161.03	161.03	161.03
Log Kow	4.2 -4.3, exp. Neuland 3.95 - 4.24, exp, ChemID (KOWWIN not possible)	4.1 exp., Verschueren 4.24 QSAR, Hansch 3.83 KOWWIN	3.83 KOWWIN	3.83 KOWWIN	4.29 QSAR, Hansch 3.83 KOWWIN	3.83 KOWWIN
Water solubility	11.2 mg/L,experimentally, (Schödel, RL 1)	8 mg/L (exp., Bayer, RL1) 16.2 mg/L (EPIWIN derived from kow RL2, and ChemID, calculated, RL2)	26 mg/L (ChemID, experimentally, RL2) 28.7 mg/L (EPIWIN derived from kow, RL2)	28.1 mg/L (EPIWIN derived from kow, RL2 and ChemID, calculated, RL2)	26.49 mg/L (EPIWIN derived from kow, RL2) 18.5 mg/L (ChemID, calculated, RL2)	27.6 mg/L (EPIWIN derived from kow, RL2, and ChemID, calculated, RL2)
Fish, acute	2.2 mg/L (geo-mean of LC0 and LC100, 96h, Caspers, RL2)	27 mg/L (96 -h LC50, EA Japan, RL2 )	2.91 mg/L (96-h LC50, Brooke, RL2)	48.7 mg/L (geo-mean of LC0 and LC100, 96h, Bernhofen-Klinke, RL4)	6.4 mg/L (96-h LC50, Ueda, RL4)
	3.24 mg/L (96h-LC50 mixture containing 40.3% 2,5-DCT, 36.3 % 2,6-DCT and 22.2% 2,4-DCT, FhG, RL4)
Fish, long-term	0.078 mg/L (read across from 3,4–DCT)		0.078 mg/L (33-d NOEC, reproduction, FELS, Call, RL2)
Invertebrates, acute	1.26 mg/L (read across from 2,4–DCT)	1.26 mg/L (48-h EC50, D. magna, Marchini, RL2)
		1.0 mg/L (48h EC50, C. cf. dubia, vehicle, closed system, Rose, RL 2 but lower than key study)
		6.5 mg/L (48h-LC50, D. magna, EA Japan, 21d-test, RL 4)
Daphnia, long-term	0.24 mg/L (read across from 3,4–DCT)		0.24 mg/L (16-d EC50 (reproduction, Hermens, RL2, QSAR)
Algae, acute	2.8 mg/L (Currenta 2010)	9.7 mg/L(72-h EbC50, open system, vehicle, EA Japan, RL2)
Algae, chronic	0.42 mg/L (Currenta 2010)
Microorganisms	13.7mg/L (read across from 3,4–DCT)		13.7mg/L (40-h EC50, Tetrahymena, Schultz, RL2)