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Toxicity to microorganisms

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Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)
Deviations:
not specified
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
not specified
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge
Details on inoculum:
- activated sludge: 6.0 g/l dry mass per liter
- inoculum: 50 ml sludge/ l test volume
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20.5 - 22.4°C
pH:
7.5 - 8.3
Dissolved oxygen:
2.0-8.4 mg/l
Nominal and measured concentrations:
Nominal concentrations:
- test substance: 100, 1000, and 10000 mg/l
- reference substance: 1 and 20 mg/l
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
Duration:
3 h
Dose descriptor:
EC0
Effect conc.:
>= 10 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
On 3.5-dichlorophenol (20 mg/l) an inhibition of 78% was obtained.

In sewage treatment plant, large amount of test substance might be present in both dissolved and undissolved form. To represent a more realistic situation, the tested concentrations are much higher than the water solubility of the test substance (i.e. 88 mg/l at pH 5 and 49mg/l at pH 9). Therefore the reported concentrations represent the combined effect of dissolved and undissolved test substance on the activity of microorganism in the sewage treatment plant.

Conclusions:
Toxicity of MBTS to activated sludge was evaluated and no toxic effect was observed up to the highest nominal concentration tested (10000 mg/l) during 3 hours exposure at a pH 7.5 - 8.3 and temperature of 20.5 - 22.4 °C.
Executive summary:

Toxicity of MBTS to activated sludge was evaluated by Bayer AG (1988) according to the ISO 8192 -1986/B and no toxic effect was observed up to the highest nominal concentration tested (10000 mg/l) during 3 hours exposure at a pH 7.5 - 8.3 and temperature of 20.5 - 22.4 °C.

Endpoint:
activated sludge nitrification inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
No guideline available at the moment of testing. Inhibition of nitrification process.
GLP compliance:
no
Vehicle:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Test type:
static
Water media type:
freshwater
Limit test:
no
Remarks on exposure duration:
2-4 h test period
Test temperature:
25°C
pH:
7.6 - 7.8
Dissolved oxygen:
> 1 mg/l
Salinity:
50 - 80 mg/l ammonia
0.003 mol/l NaHCO3
Details on test conditions:
pre-cleaned activated sludge in particle-free communal waste water
Dose descriptor:
other: EC75
Effect conc.:
38 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of nitrification rate
Remarks on result:
other: reported test duration: 2-4 hours

the reported test duration was 2 - 4 hours

Conclusions:
To the nitrification inhibition by 2,2'-disulfanediylbis(1,3-benzothiazole) an EC75 of 38 mg/L during a 2 -4 h incubation period was obtained.
Executive summary:

To the nitrification inhibition by 2,2'-disulfanediylbis(1,3-benzothiazole) an EC75 of 38 mg/L during a 2 -4 h incubation period was obtained. (Tomlinson, Boon, and Trotman, 1966).

Description of key information

Toxicity of MBTS to activated sludge was evaluated by Bayer AG (1988) according to the ISO 8192 -1986/B and no toxic effect was observed up to the highest nominal concentration tested (10000 mg/l) during 3 hours exposure at a pH 7.5 - 8.3 and temperature of 20.5 - 22.4 °C. To the nitrification inhibition by 2,2'-disulfanediylbis(1,3-benzothiazole) an EC75 of 38 mg/L during a 2 -4 h incubation period was obtained (Tomlinson, Boon, and Trotman, 1966).

Key value for chemical safety assessment

Additional information

In sewage treatment plant, large amount of test substance might be present in both dissolved and undissolved form. To represent a more realistic situation, the tested concentrations in Bayer AG study (1988) are much higher than the water solubility of the test substance (i.e. 88 mg/l at pH 5 and 49mg/l at pH 9). Therefore the reported concentrations represent the combined effect of dissolved and undissolved test substance on the activity of microorganism in the sewage treatment plant.

From the different inocula tested, the nitrification inhibition on non-adapted sludge was most sensitive and should be taken for further risk assessment.