Dichloromethylbenzene

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

weight of evidence

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 values for ecotoxicological endpoints will also be very similar for the individual isomers and the mixture of isomers and that therefore these results obtained with 4-chlorotoluene can be useful for the assessment of the mixture.

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

GLP compliance:

yes

Analytical monitoring:

not specified

Vehicle:

not specified

Test organisms (species):

Daphnia magna

Test type:

not specified

Water media type:

freshwater

Total exposure duration:

21 d

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.32 mg/L

Nominal / measured:

not specified

Basis for effect:

reproduction

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

1.6 mg/L

Nominal / measured:

not specified

Basis for effect:

reproduction

Conclusions:

The long-term toxicity of 4-chlorotoluene towards daphnids is characterized by a NOEC(21 d) of 0.32 mg/L as well as an EC50(21 d) of 1.6 mg/L.

Executive summary:

The long-term toxicity of 4-chlorotoluene towards daphnids is characterized by a NOEC(21 d) of 0.32 mg/L as well as an EC50(21 d) of 1.6 mg/L referring to the reproduction of the test animals (Nite, 1999).

Reference 2

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Study period:

1984

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

Well documented and reliable QSAR, which can not be alone a key- study.
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 these results obtained with 3,4-dichlortoluene can be useful for the assessment of the mixture.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: Concept NEN 6502, 1980

Deviations:

yes

Remarks:

: Number of organisms per group and exposure time for reproduction results

Principles of method if other than guideline:

Two different QSARs were used for the calculation of an 16-LC50 (mortality) and an 16-d IC50 (reproduction) value for Daphnia from the log Poct. The results for other substances, not described here, were compared with experimentally estimated values. The experiments followed the Dutch concept NEN 6502; Determination of the chronic toxicity with Daphnia magna. Dutch Standard Organization, Delft. EIFAC, 1980.

GLP compliance:

no

Analytical monitoring:

yes

Vehicle:

no

Test organisms (species):

Daphnia magna

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

16 d

Duration:

16 h

Dose descriptor:

EC50

Effect conc.:

1.5 µmol/L

Nominal / measured:

nominal

Basis for effect:

reproduction

Remarks on result:

other: ca. 16 days (3-4 broods); Log EC50=0.18 (Log Poct=3.98)

Duration:

16 d

Dose descriptor:

EC50

Effect conc.:

0.24 mg/L

Nominal / measured:

nominal

Basis for effect:

reproduction

Remarks on result:

other: ca. 16 days (3-4 broods); Log EC50=0.18 (Log Poct=3.98)

Duration:

16 d

Dose descriptor:

LC50

Effect conc.:

5.24 µmol/L

Nominal / measured:

nominal

Basis for effect:

mortality

Remarks on result:

other: Log LC50=0.72 (Log Poct=3.98)

Duration:

16 d

Dose descriptor:

LC50

Effect conc.:

0.85 mg/L

Nominal / measured:

nominal

Basis for effect:

mortality

Remarks on result:

other: Log LC50=0.72 (Log Poct=3.98)

# experimental EC50- and LC50-values were determined by log/probit plots

# 16-d LC50 (mortality) was calculated with the following QSAR: log 1/LC50 = (0.64 +/- 004) log Poct - 3.27 n = 5, r = 0.995, s = 0.08

# 16-d EC50 (reproduction) was calculated with the following QSAR: log 1/EC50 = (0.72 +/- 0.06) log Poct - 3.05 n = 5, r = 0.990, s = 0.14 (n = number of compounds, r = correlation coefficient, s = standard error

# Log Poct values (3.98 for 3,4 - DCT) was calculated according to Rekker, 1977: The hydrophobic fragmental constant, Elsevier, Amsterdam, 389 pp.

Conclusions:

The 16-d log IC50 (reproduction) was calculated for 3,4 - dichlorotoluene to be 0.18 µmol/L, corresponding to a IC50 of 0.24 mg/L.
The 16-d log EC50 (mortality) was calculated to be 0.72 µmol/L, corresponding to a LC50 of 0.85 mg/L.

Executive summary:

Two different QSARs were used for the calculation of an 16-LC50 (mortality) and an 16-d IC50 (reproduction) value for Daphnia from the log Poct. The results for other substances, not described here, were compared with experimentally estimated values. The experiments followed the Dutch concept NEN 6502; Determination of the chronic toxicity with Daphnia magna.

The 16-d log IC50 (reproduction) was calculated for 3,4 - dichlorotoluene from a calculated log Poct of 3.98 to be 0.18 µmol/L, corresponding to a an IC50 of 0.24 mg/L.

The 16-d log EC50 (mortality) was calculated to be 0.72 µmol/L, corresponding to an EC50 of 0.85 mg/L.

The good correlation of the QSARs may be confirmed by comparing the results obtained with the respective experimental results of five other substances with log Poct values ranging from 2.81 to 5.69.

The QSAR is well documented and considered to be reliable, but cannot be a alone a key-study.

The study is mentioned in the SIDS for 2,4 - dichlormethylbenzene, but the results are not considered in the SIDS summary, presumably as representing read-across from another isomer and further as being determined by QSARs.

Reference: Hermens, 1984

Description of key information

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.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

0.24 mg/L

Additional information

The weight-of evidence approach (4 -monochlorotoluene vs. dichlorotoluene) is based on similar structure, relevant PC data and ecotox data:

Structural similariy: The common moiety for the substances is the monochloro-toluene structure. The difference consist in the replacement of 1 chlor atom by one hydrogene atom.

Similarity of PC data

The following table shows that the relevant PC data of both substances are in the same order of magnitude:

	4 -Monochlorotoluene	Dichlorotoluenes
vapour pressure (hPa)	3.1	0.6
logKow	3.33	4.2 -4.3
water solubility (mg/L)	40	11.2

Similarity of ecotox data (key values)

	4-Monochlorotoluene	Dichlorotoluenes
acute Daphnia EC50 (mg/L)	1.7	1.26
chronic Daphnia NOEC (mg/L)	0.32	0.24 (QSAR)

Conclusion on read-across:

The read-across approach is justified by similarities in structure, relevant physicochemical data and ecotox results.

QSAR study:

A reliable QSAR result is available for Daphnia magna: The 16-d log IC50 (reproduction) was estimated from a calculated log Kow of 3.98 for 3,4-dichlorotoluene to be 0.18 µmol/L, corresponding to an IC50 of 0.24 mg/L. This value is by the factor of three higher than the other available chronic value, i.e. the NOEC of 0.078 mg/L determined in the 33-day FELS study, thus confirming the conclusion drawn from the acute aquatic studies that there are no relevant differences in sensitivity between the trophic levels.

Reference: Hermens, 1984

 

The similarities between the dichlorotoluene 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".

Further study:

In a study on the long-term toxicity of 2,4 -dichloromethylbenzene to Daphnia magna the EA Japan determined a 21-d NOEC (reproduction) of 2 mg/L (p < 0.05). Since not all validity criteria may be assessed, the reliability is not assignable. Despite of the data lacks, the SIDS summary for 2,4-dichloromethylbenzene is based on this study with the argument, that no other ecotoxicological data are available, even if the QSAR for 3,4-dichloromethylbenzene is mentioned in the SIDS dossier scarcely.

Reference: EA Japan, 1992