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Toxicity to microorganisms

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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:
reference to same study
Qualifier:
according to
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. certificate)
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).
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:
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.

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:
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).