1,3,4-thiadiazole-2,5-dithiol

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms, other

Remarks:

Toxicity control of available OECD 301F

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-12-20 - 2017-01-23 (experimental phase)

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

Information derived from OECD 301F guideline study under GLP which is hence well-performed and reliable. Information on the parallel toxicity control is considered to suffice to fulfill scientifically reasonable the requirements of the present endpoint.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Version / remarks:

Version dated 17-Jul-92

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: direct weighing

Test organisms (species):

sewage, domestic

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: Activated sludge from the municipal sewage treatment plant at Taunusstein-Bleidenstadt, Germany
- Method of cultivation: Prior to use samples of activated sludge were washed twice with mineral nutrient solution of the “Manometric-Respirometry-Test” to eliminate organic components and carbonates from the sludge. After resolution with mineral nutrient medium the sludge was aerated for 4 hr using compressed air. Thereafter it was homogenised in a Philips mixer for 2 minutes and then filtered through a cotton filter previously carefully rinsed with deionised water. The filtrate was used as inoculum.
- Initial biomass concentration: The dry matter content of the inoculum was 113 mg/L. 10 mL of the inoculum were used per litre of test solution resulting in approximately 1.13 mg/L dry mass (being in accordance with ≤ 30 mg/L given by the guideline

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

28 d

Nominal and measured concentrations:

109.8 mg/l (nominal)

Details on test conditions:

The test item and inoculum from sewage sludge corresponding to ≈1.1 mg/L dry matter (being in accordance with ≤ 30 mg/L given by the guideline) derived from the municipal sewage treatment plant at Taunusstein-Bleidenstadt were incubated together in one litre of a mineral nutrient medium for 28d in special incubation vessels of a respirometer. The incubation took place in the dark at 25 °C of constant temperature. Upon biochemical processes in the test solutions the test item is oxidized and oxygen in the liquid is consumed. Oxygen in the space above the liquid phase is dissolved in the liquid, resulting in generation of CO2 (from carbon material of the test item) in its place. As this CO2 is absorbed by soda lime, the partial pressure of oxygen in the space and the total pressure decrease. The drop in pressure is detected and converted into an electric signal generating electrolytic oxygen from sulphuric acid copper solution contained in an electrolytic bottle by constant current. This oxygen is supplied to the cultivating bottle and restoration of pressure is detected by means of the manometer, resulting in switching off the relay circuit and stopping the electrolytic process. Thus, the upper space in the cultivating bottle is always kept under a constant pressure of oxygen and the quantity of oxygen consumed in the cultivating bottle is proportional to the quantity of electrolytic oxygen. So the oxygen uptake can be read directly from the manometer.
In order to determine a possible bacterial toxicity of the test item one test solution with 109.8 mg test item and 101.5 mg sodium benzoate per litre of test solution was tested in parallel. If there was no bacterial toxicity, the oxygen-uptake in this combined test solution should have been the same as the sum of both the oxygen-uptake of the test solutions with the test item alone (mean of the two test solutions with the highest concentration of test item) and the test solution with sodium benzoate alone, respectively, or at least the same as within the sodium benzoate control.

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

109.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

O2 consumption

Details on results:

- 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: none

Validity criteria fulfilled:

yes

Remarks:

For assessment of the endpoint "ready biodegradability"

Conclusions:

Information was derived from OECD 301F guideline study under GLP which is hence well-performed and reliable. Information on the parallel toxicity control is considered to suffice to fulfill scientifically reasonable the requirements of the present endpoint as it is not relevant for classification under Regulation 1272/2008 and the tested concentration is further sufficient to exclude any underestimation of the hazard towards sludge. The toxicity control showed 45% degradation within 28 days, therefore the test item is not considered to be inhibitory according to the OECD test guidelines 301F at a concentration of 109.8 mg/l.

Executive summary:

2,5-Dimercapto-1,3,4-thiadiazole (“DMTD”) was tested for biodegradability according to ‘Manometric Respirometry Test' (OECD Guideline 301F) under GLP. The degradation process was followed by the oxygen uptake in the test solutions using two test solutions of the test item. With respect to the theoretical oxygen demand (ThOD) of the test item and the measured BOD of the test solutions no net degradation of the test item was measured.

The toxicity control showed 45% degradation within 28 days, therefore the test item is not considered to be inhibitory according to the OECD test guidelines 301F, therefore the test item is not considered to be inhibitory according to the OECD test guidelines 301F at a concentration of 109.8 mg/l.

Description of key information

Toxicity to microorganisms: NOEC = 109.8 mg/l for activated domestic sludge (Toxicity control within OECD 301F, GLP)

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

109.8 mg/L