Disulfiram

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

30 September 1999- 05 November 1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

GLP - Guideline study, tested with the source substance tetramethylthiuram disulfide (CAS No. 137-26-8). In accordance to the ECHA guidance document “Practical guide 6: How to report read-across and categories (March 2010)”, the reliability was changed from RL1 to RL2 to reflect the fact that this study was conducted on an read-across substance

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

- A stock solution of 10.4 mg/L was prepared by dissolving 5.2 mg test substance in 500 mL demineralised water.
The respiration rate of activated sludge was measured in solutions containing the following nominal concentrations : 0.104 , 0.329, 1.04, 3.29 , 10.6, 32.8 and 100.4 mg Thiram/L. The first four solutions were prepared by diluting the stock solution : respectively 5 , 15.8, 50 and 158 mL of the stock solution was made up to 500 mL inoculated test medium. The other three solutions were prepared by adding respectively 5.3, 16.4 and 50.2 mg Thiram directly to the test vessels, containing the inoculated test medium.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Laboratory culture: No
- Method of cultivation: not reported
- Preparation of inoculum for exposure: The domestic sewage sludge was sieved through a 0.5 mm sieve in order to remove large particles and aerated until use. The mixed liquor had a pH of 7.21. A small amount of the mixed liquor was dried and weighed: the suspended solids level was 4.09 g/L (n = 2, 4.20 and 3.98 g/L). This level corresponds to a concentration of 1.6 g/L in the final test solution.
- Pretreatment: No
- Initial biomass concentration: Not reported

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

17.6 – 18.5 °C

pH:

7.57 – 7.94

Nominal and measured concentrations:

Nominal initial: 0.104, 0.329, 1.04, 3.29, 10.6, 32.8 and 100.4 mg Thiram/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 1 L borosilicate glass beakers. The measuring vessel was a flat-bottomed BOD flask (250 mL)
- Aeration: Clean, oil-free air
- No. of vessels per concentration (replicates): 1/treatment
- No. of vessels per control (replicates): 2/control

TEST MEDIUM / WATER PARAMETERS
- Dilution water: Aerated tap water.
- Synthetic sewage
A synthetic sewage feed was prepared by dissolving the following amounts of nutrients in
1000 mL deionised water:
16 g peptone;
11 g meat extract;
3 g urea;
0.7 g NaCI;
0.49 CaCI2.2 H2O;
0.2 g MgS04.7 H2O;
2.8 g K2HPO4.

EFFECT PARAMETERS MEASURED: After the 3 hour incubation period the content of each test vessel was transferred to a flat-bottomed BOD flask (250 mL) equipped with a magnetic stirrer and the dissolved oxygen concentration in this sealed bottle was monitored for 10 minutes.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

< 0.1 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

3.11 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: 0.5-6.43

Duration:

3 h

Dose descriptor:

other: EC80

Effect conc.:

16.2 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: 6.43 - 40.2

Results with reference substance (positive control):

Tested concentrations: 3, 9, 27 and 81 mg/L of 3,5-dichlorophenol
3 h-EC50 = 6.05 mg/L (95% confidence interval: 3.71 – 9.87 mg/L)

Validity criteria fulfilled:

yes

Conclusions:

Thiram has a high toxicity towards aquatic bacteria.
The test is considered to be valid because the two control respiration rates were within 15% of each other and the 3 h EC50 of the reference substance 3,5-dichlorophenol was in the range of 5 to 30 mg/L.

Executive summary:

Materials and methods:The inhibition of activated sludge respiration by Thiram was investigated according to OECD test guideline No. 209 (1981) and Directive 87/302/EEC, Part C in a study designed to determine the 3 hour median effective concentration (EC50) of the test substance using activated sludge.

The test was performed at around 20 °C under static conditions with two controls, seven concentrations of test substance and four concentrations of the reference substance 3,5-dichlorophenol. Nominal concentrations of Thiram were used for all calculations.Sludge was obtained from the waste water treatment plant of Zonhoven (Belgium).

Results and discussion:The test substance inhibited activated sludge respiration in the tested range, resulting in the following respiration rates after 3 hour incubation periods:

Concentration of Thiram (mg/L) / Respiration rate (mg O2/L/h)
               0 (control 1)        24.07
               0 (control 2)         24.26
               0.104      22.25
               0.329      18.22
               1.04        18.13
               3.29        13.77
               10.6        3.62
               32.8        2.32
               100.4      2.53
Exposure of activated sludge to Thiram resulted in a 3 hour EC50 of 3.11 mg/L with a 95% confidence interval of 1.50 to 6.43 mg/L. The 3 hour EC20 and EC80 were 0.59 mg/L (95% confidence interval: 0.18 – 2.00 mg/L) and 16.2 mg/L (95% confidence interval: 6.56 – 40.2 mg/L).

Description of key information

EC50 (3 h) = 3.11 mg a.i./L

Additional information

No data on toxicity of disulfiram (CAS No. 97-77-8) to aquatic microorganisms were available. Therefore, conclusions for this endpoint had to be drawn based on the toxicity data of an analogue substance. The toxicity of tetramethylthiuram disulfide (CAS No. 137-26-8), substance structurally and composition related to tetraethylthiuram disulfide, to microorganisms was investigated in one study (Van der Kerken, 1999b). This test was conducted according to OECD Guideline 209 (1984): Activated Sludge, Respiration Inhibition test, under GLP conditions. After 3 hours exposure to the test compound, an EC50 value of 3.11 mg a.i./L was obtained. The resulting NOEC was determined to be below the lowest concentration tested.

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