Registration Dossier

Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Administrative data

Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2017-01-10 - 2017-03-09 (experimental phase)
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
see target record
Cross-reference
Reason / purpose:
read-across source
Remarks:
link to target
Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Klimisch 1 source record, but performed on read-across substance
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
There is data available on the hydrolysis behaviour of the registered substance 5-Mercapto-1,3,4-thiadiazole-2-thiol-benzoate in unbuffered water at room temperature, hence posing the same conditions as test on aquatic toxicity. The hydrolytic degradation of 5-mercapto-1,3,4-thiadiazole-2-thiol-benzoate can be described as a pseudo-first order kinetic and the half-life of 5-mercapto-1,3,4-thiadiazole-2-thiol-benzoate was determined to be 1.91 h. 1,3,4-Dimercapto-thiadiazol (DMTD, CAS 1072-71-5) and benzoic acid (CAS 65-85-0) were identified as degradation products as expected by hydrolytical cleavage of the thioester group. It can be concluded that the substance hydrolyzes very rapidly in water, i.e. the half life is max. 1/25 of the test duration when put into aqueous test systems, e.g. daphnia or algae acute toxicity tests. Hence, the substance as such does not need to be tested in those systems, it is sufficient for hazard assessment to use data gained with 1,3,4-Dimercapto-thiadiazol (DMTD, CAS 1072-71-5) and benzoic acid (CAS 65-85-0).


2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Target chemical: Benzenecarbothioic acid, S-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) ester, CAS 51988-14-8, SMILES Code O=C(Sc(nnc1S)s1)c(cccc2)c2
Source chemical 1: Benzoic acid, CAS 65-85-0, SMILES Code O=C(O)c(cccc1)c1
Source chemical 2: 1,3,4-Thiadiazolidine-2,5-dithione, CAS 1072-71-5, SMILES Code N(NC(=S)S1)C1=S
All substances do not contain impurities to an extent which is expected to alter the outcome of the experimental results or read-across approach.


3. ANALOGUE APPROACH JUSTIFICATION
5-Mercapto-1,3,4-thiadiazole-2-thiol-benzoate was shown to hydrolyze rapidly in unbuffered water at room temperature, which simulates rather closely the conditions in aquatic toxicity tests. The hydrolytic degradation of 5-mercapto-1,3,4-thiadiazole-2-thiol-benzoate can be described as a pseudo-first order kinetic and the half-life of 5-mercapto-1,3,4-thiadiazole-2-thiol-benzoate was determined to be 1.91 h. 1,3,4-Dimercapto-thiadiazol (DMTD, CAS 1072-71-5) and benzoic acid (CAS 65-85-0) were identified as degradation products as expected by hydrolytical cleavage of the thioester group. No further assessment of the hydrolysis of benzoic acid and DMTD has been conducted because these substances are known to be hydrolytically stable.

According to ECHA’s Guidance R.6, “in the context of risk assessment, (Q)SAR and read-across approaches have been used to: … estimate environmental fate data, especially partitioning behaviour and abiotic degradation (e.g. atmospheric oxidation and hydrolysis);“ Further, for data collection, as a first step, a „Preliminary analysis of reactivity, uptake and fate“ should be performed. „A preliminary assessment of expected reactivity, uptake and fate is performed on the basis of the information for the abiotic and biotic reactions involving the parent compound. The following considerations should be taken into account: …
- what chemical reactivity (what type(s) of reactions) is expected for the parent compound
- which metabolites and reaction products (i.e. hydrolysis products) are generated“ „The preliminary analysis of uptake and fate is used to determine which compound(s) (parent compound and/or reaction products and/or metabolites) are suitable for modelling the endpoint of interest.
Especially in the context of a category development for read-across, not only Metabolic pathways may serve to establish a category, but also, as a kind of sub-group, degradation processes. „On the other hand the same concept underlying the metabolic pathways can be used for environmental degradation processes. For example, for a substance which hydrolyses very rapidly in aquatic test systems (half-life <1 hour), the aquatic toxicity endpoints can be covered by the test results with the degradation product(s). However, the referenced guidance document (OECD (2000). Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures No. 23, ENV/JM/MONO(2000)6) already lists substances as difficult for testing with a half-life < 24h („Data profile for review of test substance properties and indicator values of difficulties for media preparation and testing… Hydrolysis half-life at 25°C and pH=7 = <24 hours“).

It can be concluded that the substance hydrolyzes very rapidly in water, i.e. with 1.91h the half life is max. 1/25 of the test duration when put into aqueous test systems, e.g. daphnia or algae acute toxicity tests. It is well noted that ECHA’s guidance mentions a half-life <1 hour for the qualification as rapid in terms of hydrolysis, but as this can be considered as guidance value and the original OECD publication mentions < 24h as a boundary value for substances difficult to test, the registrant concludes that, with a half life of 1.91h, the substance already qualifies to hydrolyze rapidly.

Further, with regard to the available data on aquatic toxicity, for better comparison the estimated values are regarded first, it can be shown that the presence of the parent compound (less than 50% of the initial quantity after 2h) has no impact on the results of the aquatic toxicity tests, at least none which may underestimated the actual hazard. Besides, it can be assumed that the target substance already degrades to a certain extend during preparation of the hypothetical test solutions, even if precautions as cited in ENV/JM/MONO(2000)6 are taken. As can be seen in the section 4 Data matrix, the EC50 or LC50 values vary over a broad range. However, the lowest values were estimated for the hydrolysis product 1,3,4-Dimercapto-thiadiazol, so only this product is most relevant for a possible classification, not the parent compound. Although no actual test data on the parent compound is available, available test data on the hydrolysis products indicate that DMTD is the more toxic one, which supports the above-mentioned conclusion, as estimated data reveal the same trend in magnitudes.

Hence, the substance as such does not need to be tested in those systems, it is sufficient for hazard assessment to use data gained with 1,3,4-Dimercapto-thiadiazol (DMTD, CAS 1072-71-5) and benzoic acid (CAS 65-85-0).


4. DATA MATRIX
The following information was estimated via US EPA EpiSuite estimation tool or taken from actual data sources:

Property CAS 51988-14-8 (target) CAS 65-85-0 (source 1) CAS 1072-71-5 (source 2)
Water solubility (EpiSuite) 395.1 mg/L 2493 mg/L 2.638e+005 mg/L
logPow (EpiSuite) 2.05 1.87 -0.6349
Biodegradability (EpiSuite) not readily biodegradable readily biodegradable not readily biodegradable
Acute toxicity fish, 96h LC50 (EpiSuite) 31.672 mg/l (Esters) 1300.781 mg/l (Neutral Organics-acid) 12.705 mg/l (Hydrazines)
8.588 mg/l (Thiols and Mercaptans) 0.624 mg/l (Thiocarbamate, Di(Substit))
187.325 mg/l (Neutral Organic SAR) 28692.277 mg/l (Neutral Organic SAR)
Acute toxicity daphnids, 48h LC50 (EpiSuite) 65.467 mg/l (Esters) 730.075mg/l (Neutral Organics-acid) 109.112 mg/l (Hydrazines)
1.073 mg/l (Thiols and Mercaptans) 1.754 mg/l (Thiocarbamate, Di(Substit))
106.884 mg/l (Neutral Organic SAR) 12773.367 mg/l (Neutral Organic SAR)
Acute toxicity algae, 96h EC50 (EpiSuite) 27.631 mg/l (Esters) 518.374 mg/l (Neutral Organics-acid) 2.622 mg/l (Hydrazines)
0.748 mg/l (Thiols and Mercaptans) 0.190 mg/l (Thiocarbamate, Di(Substit))
81.240 mg/l (Neutral Organic SAR) 3479.678 mg/l (Neutral Organic SAR)
Acute toxicity daphnids, 48h EC50 (test data) 860 mg/l 5.95 mg/L
Acute toxicity algae (test data) Inhibition starts at 1630 mg/l (96 hr) (pH = 7)
EC50 (14d) = >10 mg/l EC50 (72h) > 160 mg/L
Reason / purpose:
read-across source
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Version / remarks:
Version dated 13-Apr-2004
Deviations:
yes
Remarks:
Instead of storage at freezing conditions, t0 specimens were stored at 2-8°C until analysis – this represents a deviation of the study plan which is not considered to have an influence on the integrity of the results and of the test
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: At room temperature

Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0, 1.0, 2.0, 4.0, 8.0, 10 mg/L
- Sampling method: Specimens were drawn from freshly prepared treatments and those incubated for 48 hr.
- Sample storage conditions before analysis: The supporting analysis of the specimens could not be performed on the same day of collection of the specimens. Therefore, the specimens were stored at 2-8°C and then analysed.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item was weighed in ELENDT M4 dilution water followed by stirring on a magnetic stirrer for 10 min (screening test) / 5 min (main test) being necessary to dissolve the test item sufficiently in the test medium. pH of the treatments was not adjusted.
- Controls: ELENDT M4 dilution water without any test item
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): none stated
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: water flea
- Strain/clone: Daphnia magna STRAUS (clone 5)
- Source: obtained from Dr. M. Bergtold, BASF, D-67117 Limburgerhof; the strain originally derived from the Institut National de Recherche Chimique Appliquee, France in 1978
- Feeding during test: During the test the daphnia were not fed.


ACCLIMATION
- Acclimation period: The cultivation of the daphnia is performed in a way that the animals are transferred in new test medium at an interval of 1 to 3 days followed by feeding.
- Acclimation conditions (same as test or not): same as test
- Type and amount of food: Desmodesmus subspicatus- and/or Chlorella-cells
- Feeding frequency: following each transfer in new test medium
- Health during acclimation (any mortality observed): no mortality stated

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES:
Daphnias used for the test are not older than 24 hr. Therefore, in every case, daphnia are transferred into fresh medium one day before starting of the daphnia test in order to get daphnia for the test younger than 24 hr.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Post exposure observation period:
none
Hardness:
250 mg/L CaCO3
Test temperature:
19.3 - 20.6 °C during the definitive main test (20.0 - 20.3 °C during the screening test)
pH:
8.24 - 9.28 during the definitive main test (5.75 - 8.30 during the screening test)
Dissolved oxygen:
8.3 - 8.9 mg O2/L during the definitive main test (8.2 - 8.7 during the screening test)
Nominal and measured concentrations:
Nominal: 0, 1.0, 2.0, 4.0, 8.0, 10 mg/L (definitive main test)
Found (t0): 0.0, 1.05, 2.11, 4.22, 8.37, 10.69 mg/L
Found (t48h): 0.0, 0.99, 1.97, 4.04, 8.16, 10.43 mg/L
Mean (t0 - t48h): 0.0, 1.02, 2.04, 4.13, 8.27, 10.56 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: carboys
- Material, size, headspace, fill volume: glass, 100mL volume
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4 (definitive main test), 2 (screening test)
- No. of vessels per control (replicates): 4 (definitive main test), 2 (screening test)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Elendt M4 (test medium according to OECD 202); the stock solutions with the macronutrients were individually prepared in ultrapure water (for each salt a separate solution). From these individual stock solutions, the medium was prepared.
- Culture medium different from test medium: no

OTHER TEST CONDITIONS
- Photoperiod: 16 hr of light and 8 hr of darkness

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : immobility, daily

VEHICLE CONTROL PERFORMED: yes, medium only

RANGE-FINDING STUDY
- Test concentrations: 1, 10, 100 mg/L
Reference substance (positive control):
yes
Remarks:
To verify the sensitivity of the test system towards toxic items the effect of potassium dichromate towards different animals of this breed was tested prior to beginning of the test.
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
5.95 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
other: EC20
Effect conc.:
4.46 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC10
Effect conc.:
3.83 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
LOEC
Effect conc.:
4 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
- Mortality of control: no immobilisation noted
- Other adverse effects control: none stated
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: none stated
- Effect concentrations exceeding solubility of substance in test medium: no
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Limit test: no
- Dose-response test: yes
- ECx: EC50 (24 hr) = 0.95 mg/L
- Other: In order to verify the sensitivity of the test system towards toxic items the effect of potassium dichromate towards different animals of this breed was tested prior to beginning of the test. The value of the EC50 (24 hr) in this period of time was at 0.95 mg/L potassium dichromate. This value is in accordance with the recommendations of 0.6 to 2.1 mg/L K2Cr2O7 given in OECD Guideline 202 (Daphnia sp., Acute Immobilisation Test).
Reported statistics and error estimates:
Statistical evaluation was done using the commercial computer program ToxRat Professional Version 3.2.1.
Validity criteria fulfilled:
yes
Conclusions:
The study was performed according to OECD TG 202 without deviations which may have impact on the validity of the study. Thus, the results were so obtained via a scientifically reasonable method. Hence, there is no doubt that the obtained results are not reliable:
Under the conditions used for the test, there was a significant immobilisation of the daphnias at concentrations >2.0 mg/L (definitive main test).
As a conclusion of the analytical part of this study, it can be stated that the concentrations of the test item remained sufficiently stable during incubation. Based on this, the reported effect concentrations should refer to the nominal concentrations tested. The following EC-values were determined accordingly after 48 hours:
Mobility:
LOEC = 4.0 mg/L
NOEC = 2.0 mg/L
EC50 = 5.95 mg/L
Based on these results, the test item does not need to be classified as acute toxic to the aquatic environment. With regard to chronic toxicity, taking into account the facts that the test item is soluble in water, i.e. above the determined EC50 value, and not readily biodegradable, the test item should be classified as aquatic chronic Cat. 2. As 5-Mercapto-1,3,4-thiadiazol-2-thiol-benzoate hydrolyzes into a mixture of hydrolysis products, which contains DMTD > 25%, the registered substance as such should be classified as aquatic chronic Cat. 2, applying the rules for classification as mixtures under Regulation 12072/2008.
Executive summary:

2,5-Dimercapto-1,3,4-thiadiazole (“DMTD”) was tested for acute toxicity towards daphnia according to OECD-Test Guideline 202 (version dated 13-Apr-2004) in compliance with GLP. In order to investigate the influence of the test item towards the daphnia, the swimming behaviour of the animals was recorded. Under the conditions used for the test, there was an immobilisation of the daphnia at concentrations >2 mg/L. As a conclusion of the analytical part of this study, it can be stated that the concentrations 2,5-Dimercapto-1,3,4-thiadiazole (“DMTD”) remained sufficiently stable during incubation of 48hr. As a result of the supporting analysis it can be stated that the results of the biological part should be based on the nominal concentrations applied because the recoveries of the nominal concentrations were all >80%.

The following EC-values (effective concentrations) were determined accordingly:

Basis: Nominal Concentrations [mg/L]

t24hr

t48hr

NOEC

≥ 10.00

2.00

LOEC

>10.00

4.00

                      EC10

7.57

3.83

                      EC20

11.71

4.46

                      EC50

n.d. (>10.00)

5.95

n.d. = not determined for mathematical reasons.

The test is considered valid as all conditions for validity were met.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2017
Report Date:
2017

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Version / remarks:
Version dated 13-Apr-2004
Deviations:
yes
Remarks:
Instead of storage at freezing conditions, t0 specimens were stored at 2-8°C until analysis – this represents a deviation of the study plan which is not considered to have an influence on the integrity of the results and of the test
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid
Specific details on test material used for the study:
STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: At room temperature

Sampling and analysis

Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0, 1.0, 2.0, 4.0, 8.0, 10 mg/L
- Sampling method: Specimens were drawn from freshly prepared treatments and those incubated for 48 hr.
- Sample storage conditions before analysis: The supporting analysis of the specimens could not be performed on the same day of collection of the specimens. Therefore, the specimens were stored at 2-8°C and then analysed.

Test solutions

Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item was weighed in ELENDT M4 dilution water followed by stirring on a magnetic stirrer for 10 min (screening test) / 5 min (main test) being necessary to dissolve the test item sufficiently in the test medium. pH of the treatments was not adjusted.
- Controls: ELENDT M4 dilution water without any test item
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): none stated

Test organisms

Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: water flea
- Strain/clone: Daphnia magna STRAUS (clone 5)
- Source: obtained from Dr. M. Bergtold, BASF, D-67117 Limburgerhof; the strain originally derived from the Institut National de Recherche Chimique Appliquee, France in 1978
- Feeding during test: During the test the daphnia were not fed.


ACCLIMATION
- Acclimation period: The cultivation of the daphnia is performed in a way that the animals are transferred in new test medium at an interval of 1 to 3 days followed by feeding.
- Acclimation conditions (same as test or not): same as test
- Type and amount of food: Desmodesmus subspicatus- and/or Chlorella-cells
- Feeding frequency: following each transfer in new test medium
- Health during acclimation (any mortality observed): no mortality stated

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES:
Daphnias used for the test are not older than 24 hr. Therefore, in every case, daphnia are transferred into fresh medium one day before starting of the daphnia test in order to get daphnia for the test younger than 24 hr.

Study design

Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Post exposure observation period:
none

Test conditions

Hardness:
250 mg/L CaCO3
Test temperature:
19.3 - 20.6 °C during the definitive main test (20.0 - 20.3 °C during the screening test)
pH:
8.24 - 9.28 during the definitive main test (5.75 - 8.30 during the screening test)
Dissolved oxygen:
8.3 - 8.9 mg O2/L during the definitive main test (8.2 - 8.7 during the screening test)
Nominal and measured concentrations:
Nominal: 0, 1.0, 2.0, 4.0, 8.0, 10 mg/L (definitive main test)
Found (t0): 0.0, 1.05, 2.11, 4.22, 8.37, 10.69 mg/L
Found (t48h): 0.0, 0.99, 1.97, 4.04, 8.16, 10.43 mg/L
Mean (t0 - t48h): 0.0, 1.02, 2.04, 4.13, 8.27, 10.56 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: carboys
- Material, size, headspace, fill volume: glass, 100mL volume
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4 (definitive main test), 2 (screening test)
- No. of vessels per control (replicates): 4 (definitive main test), 2 (screening test)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Elendt M4 (test medium according to OECD 202); the stock solutions with the macronutrients were individually prepared in ultrapure water (for each salt a separate solution). From these individual stock solutions, the medium was prepared.
- Culture medium different from test medium: no

OTHER TEST CONDITIONS
- Photoperiod: 16 hr of light and 8 hr of darkness

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : immobility, daily

VEHICLE CONTROL PERFORMED: yes, medium only

RANGE-FINDING STUDY
- Test concentrations: 1, 10, 100 mg/L
Reference substance (positive control):
yes
Remarks:
To verify the sensitivity of the test system towards toxic items the effect of potassium dichromate towards different animals of this breed was tested prior to beginning of the test.

Results and discussion

Effect concentrationsopen allclose all
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
5.95 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
other: EC20
Effect conc.:
4.46 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC10
Effect conc.:
3.83 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
LOEC
Effect conc.:
4 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
- Mortality of control: no immobilisation noted
- Other adverse effects control: none stated
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: none stated
- Effect concentrations exceeding solubility of substance in test medium: no
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Limit test: no
- Dose-response test: yes
- ECx: EC50 (24 hr) = 0.95 mg/L
- Other: In order to verify the sensitivity of the test system towards toxic items the effect of potassium dichromate towards different animals of this breed was tested prior to beginning of the test. The value of the EC50 (24 hr) in this period of time was at 0.95 mg/L potassium dichromate. This value is in accordance with the recommendations of 0.6 to 2.1 mg/L K2Cr2O7 given in OECD Guideline 202 (Daphnia sp., Acute Immobilisation Test).
Reported statistics and error estimates:
Statistical evaluation was done using the commercial computer program ToxRat Professional Version 3.2.1.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
The study was performed according to OECD TG 202 without deviations which may have impact on the validity of the study. Thus, the results were so obtained via a scientifically reasonable method. Hence, there is no doubt that the obtained results are not reliable:
Under the conditions used for the test, there was a significant immobilisation of the daphnias at concentrations >2.0 mg/L (definitive main test).
As a conclusion of the analytical part of this study, it can be stated that the concentrations of the test item remained sufficiently stable during incubation. Based on this, the reported effect concentrations should refer to the nominal concentrations tested. The following EC-values were determined accordingly after 48 hours:
Mobility:
LOEC = 4.0 mg/L
NOEC = 2.0 mg/L
EC50 = 5.95 mg/L
Based on these results, the test item does not need to be classified as acute toxic to the aquatic environment. With regard to chronic toxicity, taking into account the facts that the test item is soluble in water, i.e. above the determined EC50 value, and not readily biodegradable, the test item should be classified as aquatic chronic Cat. 2.
Executive summary:

2,5-Dimercapto-1,3,4-thiadiazole (“DMTD”) was tested for acute toxicity towards daphnia according to OECD-Test Guideline 202 (version dated 13-Apr-2004) in compliance with GLP. In order to investigate the influence of the test item towards the daphnia, the swimming behaviour of the animals was recorded. Under the conditions used for the test, there was an immobilisation of the daphnia at concentrations >2 mg/L. As a conclusion of the analytical part of this study, it can be stated that the concentrations 2,5-Dimercapto-1,3,4-thiadiazole (“DMTD”) remained sufficiently stable during incubation of 48hr. As a result of the supporting analysis it can be stated that the results of the biological part should be based on the nominal concentrations applied because the recoveries of the nominal concentrations were all >80%.

The following EC-values (effective concentrations) were determined accordingly:

Basis: Nominal Concentrations [mg/L]

t24hr

t48hr

NOEC

≥ 10.00

2.00

LOEC

>10.00

4.00

                      EC10

7.57

3.83

                      EC20

11.71

4.46

                      EC50

n.d. (>10.00)

5.95

n.d. = not determined for mathematical reasons.

The test is considered valid as all conditions for validity were met.