1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1991-03-11 till 1991-03-12

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with acceptable restrictions.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

Principles of method if other than guideline:

A defined amount of activated sludge is mixed with synthetic nutrient solution and measured the rate of respiration. This respiration rate is compared with those measured in test preparations with different concentrations of the test substance. The sensitivity of the activated sludge is examined with 3.5-dichlorophenol as a reference.

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

other: mircoorganisms from a laboratory sewage treatment plant (OECD)

Details on inoculum:

- Type and Origin: mixed population of aquatic microorganisms (activated sludge) from a laboratory sewage treatment plant (OECD)
- Sampling: 1991-03-08
- Pretreatment: none

Test type:

static

Water media type:

freshwater

Total exposure duration:

3 h

Details on test conditions:

Test concentrations: 1000, 1800, 3200, 5600 and 10000 mg/L

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorphenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

6 620 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Test concentration (mg/L)	Respirations rate (mg/L*h)	Inhibition (%)
1000	15.0	32.4
1800	13.5	39.2
3200	13.2	40.5
5600	12.9	41.9
10000	9.0	59.5

Validity criteria fulfilled:

yes

Conclusions:

The potential toxic effect of ZMB2 was tested according to "ISO 8192 (Test for Inhibition of Oxygen Consumption by Activated Sludge)" The toxicity of microorganisms was measured by an EC50 of 6620 mg/L and showed 46 % resprition inhibition on activated sludge whitin 3 hours (Bayer AG, 1992).

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
Refer to Section 13.2 for read-across justification document.

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

10 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Validity criteria fulfilled:

not specified

Conclusions:

The test item showed 44.4 % respiration inhibition of activated sludge at the highest test item concentration of 10000 mg/L.
An EC50 of >10000 mg/L were obtained in this test. The effect value relates to nominal concentration, since no analytical monitoring was performed.

Executive summary:

In a one-to-one read-across approach, the substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (source substance) is considered appropriate for direct read-across (one-to-one) to zinc 4-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide 7-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide (target substance) for the endpoint toxicity to microorganisms. In conclusion, the 3 h EC50 of the test item to microorganisms was >10000 mg/L. A full justification for the read-across approach is presented in IUCLID Section 13.2.

Reference 3

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1990-03-02 till 1990-03-23

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study with acceptable restrictions.

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- adjusted activated sludge concentration: 6.00 g/L

Test type:

static

Water media type:

freshwater

Total exposure duration:

3 h

Hardness:

no data

Test temperature:

temperature range: 20.0 - 20.4 °C (including all test concentrations, controls and reference substance)

pH:

7.4 - 8.0

Dissolved oxygen:

no data

Salinity:

no data

Nominal and measured concentrations:

- nominal concentration of test substance: 100, 1000, 1800, 3200, 5600 and 10000 mg/L
- Nominal concentration of reference substance: 1.0 and 20.0 mg/L

Details on test conditions:

- Two controls, one at test start and one at test end
- One physico-chemical oxygen consumption control with the highest concentration of test substance

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 10 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

- No physico-chemical oxygen consumption was observed at the test item concentration of 10000 mg/L.
- The inhibitions of five nominal concentrations (1000, 1800, 3200, 5600 and 10000 mg/L) were measured at 33.3 - 44.4 %, and the respiration rate at 15 - 18 mg/L*h.
- The respiration rates in two controll experiments were tested at 19.0 mg/L*h and 21.0 mg/L*h, respectively.

Results with reference substance (positive control):

3,5-dichlorophenol as reference compount was tested at concentration of 1.0 and 20.0 mg/L, and the inhibitions were measured at 7.4 and 75 %, respectively.

Validity criteria fulfilled:

not specified

Conclusions:

The test item showed 44.4 % respiration inhibition of activated sludge at the highest test item concentration of 10000 mg/L.
An EC50 of >10000 mg/L were obtained in this test. The effect value relates to nominal concentration, since no analytical monitoring was performed.

Executive summary:

In order to test the toxicity to microorganism of the substance, activated sludge from predominantly domestic sewage plant was exposed to the test solution of five nominal concentrations of the substance (1000, 1800, 3200, 5600 and 10000 mg/L), blank control solution and solution with positive reference substance for a period of 3 hours. The respiration rates were calculated. No physico-chemical oxygen consumption was observed at the highest concentration of test substance. The test item showed 43 % respiration inhibition of activated sludge at the highest test item concentration of 10000 mg/L,and an EC50 of >10000 mg/L were obtained.. This toxicity study is classified as acceptable and satisfies the guideline requirements for the toxicity study to microoragnisms.

Description of key information

Key study:

Toxicity to microorganisms - activated sludge respiration inhibition 3 h LC50 = 6620; ISO 8192; Bayer AG (1992)

Supporting study:

Toxicity to microorganisms - activated sludge respiration inhibition 3 h LC50 = > 10 000; ISO 8192; Bayer AG (1992) (data from read-across substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, used in a one-to-one approach)

Key value for chemical safety assessment

EC50 for microorganisms:

6 620 mg/L

Additional information

In accordance with ISO 8192 (Test for Inhibition of Oxygen Consumption by Activated Sludge) ZMB2 was determined to have an EC50 of 6620 mg/L and showed 46 % respiration inhibition on activated sludge within 3 hours (Bayer AG, 1992).