2,4-diethyl-9H-thioxanthen-9-one

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

2018-05-11

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

1. SOFTWARE
EPIWIN v4.1

2. MODEL (incl. version number)
ECOSAR v1.11

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
CCc1cc(CC)c2Sc3ccccc3C(=O)c2c1

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
please refer to attached QMRF

5. APPLICABILITY DOMAIN
please refer to attached QPRF

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Guideline:

other: ECHA Guidance R.6

Specific details on test material used for the study:

Smiles: CCc1cc(CC)c2Sc3ccccc3C(=O)c2c1

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

0.02 mg/L

Nominal / measured:

not specified

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

Having a log Kow of > 5, it is very likely that no effects at saturation are expected for the substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0).

Sublethal observations / clinical signs:

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Values used to Generate ECOSAR Profile

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Log Kow: 6.500      (User Entered)

Wat Sol: 0.66       (mg/L, User Entered)

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ECOSAR v1.11 Class-specific Estimations

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Neutral Organics

                                                                   Predicted

ECOSAR Class                 Organism            Duration  End Pt   mg/L (ppm)

===========================  ==================  ========  ======   ==========

Neutral Organics           : Fish                96-hr     LC50        0.020

Neutral Organics           : Daphnid             48-hr     LC50        0.017

Neutral Organics           : Green Algae         96-hr     EC50        0.072

Neutral Organics           : Fish                          ChV         0.003

Neutral Organics           : Daphnid                       ChV         0.005

Neutral Organics           : Green Algae                   ChV         0.047

Neutral Organics           : Fish (SW)           96-hr     LC50        0.026

Neutral Organics           : Mysid               96-hr     LC50     0.000914

Neutral Organics           : Fish (SW)                     ChV         0.044

Neutral Organics           : Mysid (SW)                    ChV     2.08e-005

Neutral Organics           : Earthworm           14-day    LC50      159.329 *

Note:  * = asterisk designates: Chemical may not be soluble enough to

       measure this predicted effect. If the effect level exceeds the

       water solubility by 10X, typically no effects at saturation (NES)

       are reported.

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Class Specific LogKow Cut-Offs

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If the log Kow of the chemical is greater than the endpoint specific cut-offs

presented below, then no effects at saturation are expected for those endpoints.

Neutral Organics:

----------------

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50)

Maximum LogKow: 6.0 (Earthworm LC50)

Maximum LogKow: 6.4 (Green Algae EC50)

Maximum LogKow: 8.0 (ChV)

Validity criteria fulfilled:

not applicable

Conclusions:

- (96h) LC50 = 0.02 mg/L estimated with ECOSAR v1.11
- no effects at saturation are expected for the substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0) as the experimentally determined log Kow of the chemical (> 6.5) is greater than the endpoint specific cut-off (5.0 for fish 96h LC50).

Executive summary:

The LC50 (96 h) was predicted with the QSAR model ECOSAR v1.11, which is implemented in EPIWIN v4.11. A LC50 (96 h) value of 0.02 mg/L was derived. This prediction does not fall completely in the applicability domain of this model, because the measured logKow exceeds the maximum logKow of 5 in the training set; with an experimentally determined log Kow of greater than 6.5 it is very likely that no effects at saturation are expected for the substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0).

Description of key information

- 96 hour LC50 (calculated using ECOSAR Version 1.11): 0.02 mg/L [test material: registration substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0)].

 - 96 hour LC50 (calculated using ECOSAR Version 1.11): 0.125 mg/L [test material: closely related substance 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) for which experimental daphnia and algae data (incl. analytical verifications) are available].

- Predicted water solubilities (using WSKOWWIN programme v1.42 by US EPA), which seem to be appropriate values according to analytical findings on the closely related substance ITX in the algae and daphnia study can demonstrate that both thioxanthones, especially, the registration substance 2,4-diethyl-9H-thioxanthen-9-one, are not sufficiently soluble under environmentally relevant conditions to ever reach the calculated values:

a) registration substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0): 0.0041 mg/L at 25°C;

b) closely related read-across substance 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9): 0.0292 mg/L at 25°C.

- The acute toxicity of both thioxanthones to fish is considered to be no effects at the water solubility limit (saturation).

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.02 mg/L

Additional information

Using the modelling software ECOSAR Version 1.11, the supporting substance 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9) - from which experimental data for daphnia and algae is available - has been calculated to have an EC50 to fish of 0.125 mg/L, the less water soluble registration substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0) an EC50 of 0.02 mg/L.

In tests conducted under GLP conditions to the appropriate EC and OECD guidelines, the closely related substance ITX was demonstrated not to have effects at its level of solubility. As such the EC50 of the substance were determined to be > 0.028 mg/L (daphnia) and > 0.047 mg/L (algae) and similarly the NOEC in those studies were determined to be 0.028 mg/L (daphnia) and 0.0050 mg/L (algae).

Although the test material ITX has been shown to have a water solubility of 0.34 mg/L in distilled water (using EU method A.6), its solubility in the test media used for the acute toxicity to daphnia study and the algal growth inhibition study has been demonstrated to be significantly lower, whereby this finding (dependency of the test media on water solubility) is surely applicable for the registration substance DETX as well [that has a water solubility < 0.66mg/L (below the LOD) using EU method A.6].

The predicted water solubilities of both thioxanthones (using WSKOWWIN programme v1.42 by US EPA) point out the very low water solubility of the thioxanthones, especially of the registration substance:

- registration substance 2,4-diethyl-9H-thioxanthen-9-one ("DETX", CAS 82799-44-8, EC 280-041-0): 0.0041 mg/L at 25°C;

- closely related read-across substance 2-Isopropylthioxanthone ("ITX", CAS 5495-84-1, EC 226-827-9): 0.0292 mg/L at 25°C.

Whilst there are subtle differences in the compositions of the media used in the tests on the different species these test media can be considered more representative of the conditions in the environment.

As such it is considered unlikely that the substance ITX and also the less water soluble registration substance DETX would be sufficiently soluble under environmentally relevant conditions to ever reach the calculated values.

Consequently, the registrant considers it justified to omit the acute toxicity to fish study on DETX and that the available data is adequate to fully conclude on the classification and labelling of the substance and that those available data are conclusive, but not sufficient for classification.