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Toxicity to microorganisms

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Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
assessment report
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
125 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
other: EC20
Effect conc.:
>= 270 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 2 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Details on results:
The test item showed inhibition values which were not correlated to its concentration. At concentrations 2000 and 1000 mg/L, approx. the same inhibition was found. It is believed that the test system, consisting of a wide variety of microorganisms, is not uniformly affected by the test item.
Results with reference substance (positive control):
results considered valid
Reported statistics and error estimates:
none

In the two studies, the inhibition which was caused by the test item did not rise above 30 %, which were observed in the treatments with 2000 and 1000 mg/L. At the lowest concentration of 125 mg/L, 15.6 % inhibition was observed.

It might be possible that the test item shows inhibitory action only to part of the microorganisms which are present in the activated sludge, so that respiration of these microorganisms is nearly completely inhibited by approximately 500 mg/L test item concentration. The microorganisms which are not susceptible to toxic effects of the test item are not inhibited at all up to the highest concentrations tested. Therefore, no exact 3h EC50 value and no exact NOEC value could be determined. The 3 h EC50 value is given as > 2000 mg/L and the NOEC is stated as 125 mg/L.

Validity criteria fulfilled:
yes
Conclusions:
The following results for the test item were determined:
3h NOEC = below 125 mg/L
3h EC20 = 270 mg/L (95 % confidence interval: 110 - 430 mg/L)
EC50 (3h) > 2000 mg/L
Executive summary:

The inhibition of the respiration rate towards microorganisms of the source substance has been assessed in a GLP compliant study according to OECD Guideline 209.

First, a limit-test with two replicates using the nominal concentration 1000 mg/L was performed. Duration of the test was three hours. Activated sludge was used as inoculum. It was taken from a domestic sewage treatment plant and washed before usage. The dry matter was determined as 4.3 g suspended solids/L, giving a concentration of 1.72 g suspended solids/L in the test.

3,5-Dichloro-phenoIe was used as reference item. Five concentrations were tested; an EC50 of 8.8 mg/L (95 % confidence interval: 7.2 - 10.5 mg/L) was determined, which lies within the range of 5 - 30 mg/L. The treatment 1000 mg/L showed a mean inhibition of the respiration rate of the activated sludge of 31 %.

Then, a main study was performed using five concentrations ranging from 2000 to 125 mg/L. The dry matter of the activated sludge was determined as 3.8 g suspended solids/L, giving a concentration of 1.52 g suspended solids/L in the test. The EC50 of the reference item was determined as 6.8 mg/L (95 % confidence interval: 5.9 - 7.7 mg/L).

The following inhibitions of the respiration rate of the activated sludge were detected: At 2000 mg/L 29.5 %, at 1000 mg/L 30.0 %, at 500 mg/L 24.5 %, at 250 mg/L 19.5 % and at 125 mg/L 15.8 % inhibition were detected.

The following results for the source test item  were determined:

NOEC (3h) = below 125 mg/L

EC20 (3h) = 270 mg/L (95% confidence interval: 110 - 430 mg/L)

EC50 (3h) > 2000 mg/L

The source substance contains the major organic moieties of the target substance. Therefore, the results of this study can be attributed to the organic moieties of the target substance.

Endpoint:
activated sludge nitrification inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
assessment report
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
3.82 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
inhibition of nitrification rate
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
13.39 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
inhibition of nitrification rate
Duration:
3 h
Dose descriptor:
other: IC20
Effect conc.:
6.12 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
inhibition of nitrification rate

The target substance contains 16.5 % Zn ions. Therefore, the hazard value for Zn ion is converted to the target substance considering a Zn content of 16.5 %.

IC50 (Zn ion) = 2.21 mg/L

IC50 (target substance) = 2.21/0.165 = 13.39 mg/L

IC20 (Zn ion) = 1.01 mg/L

IC20 (target substance) = 1.01/0.165 = 6.12 mg/L

NOEC (Zn ion) = 0.63 mg/L

NOEC (target substance) = 0.63/0.165 = 3.82 mg/L

Conclusions:
The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. Consequently, the % inhibition increases as the concentration of heavy metals increases. The no observed effect concentration is 0.1 mg Zn/L, the IC20 is reached at 0.16 mg/L Zn2+ and the IC50 is reached at 0.35 mg/L Zn2+.
As the target substance contains 16.5 % Zinc ion the no observed effect concentration for the target substance is 3.82 mg/L, the IC20 is reached at 6.12 mg/L and the IC50 is reached at 13.39 mg/L.
Executive summary:

In this study the ISO 9509 test was used to assess the inhibitory effect of Zn2+ ion nitrification of municipal wastewater samples using activated sludge collected from a municipal wastewater treatment plant. The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. The no observed effect concentration is 0.1 mg Zn/L, the IC20 is reached at 0.16 mg/L Zn2+ and the IC50 is reached at 0.35 mg/L Zn2+.

As the target substance contains 16.5 % Zinc ion the no observed effect concentration is 3.82 mg/L, the IC20 is reached at 6.12 mg TP 1646/L and the IC50 is reached at 13.39 mg/L.

IC50 (TP 1646) = 13.39 mg/L

IC20 (TP 1646) = 6.12 mg/L

NOEC (TP 1646) = 3.82 mg/L

Description of key information

Read-across : WoE, FF6, OECD 209, GLP, activated sludge, EC50 (3h) > 2000 mg/L, NOEC (3h) < 125 mg/L

Read-Across: WoE, Zn ion, ISO 9509, activated sludge, 3 h, IC50 = 13.39 mg/L (converted to the target substance taking into account the Zn content of 16.5 %), NOEC = 3.82 mg/L (converted to the target substance taking into account the Zn content of 16.5 %).

Key value for chemical safety assessment

EC50 for microorganisms:
13.39 mg/L
EC10 or NOEC for microorganisms:
3.82 mg/L

Additional information

Read-across - FF6

The inhibition of the respiration rate towards microorganisms of the source substance has been assessed in a GLP compliant study according to OECD Guideline 209.

First, a limit-test with two replicates using the nominal concentration 1000 mg/L was performed. Duration of the test was three hours. Activated sludge was used as inoculum. It was taken from a domestic sewage treatment plant and washed before usage. The dry matter was determined as 4.3 g suspended solids/L, giving a concentration of 1.72 g suspended solids/L in the test.

3,5-Dichloro-phenoIe was used as reference item. Five concentrations were tested; an EC50 of 8.8 mg/L (95 % confidence interval: 7.2 - 10.5 mg/L) was determined, which lies within the range of 5 - 30 mg/L. The treatment 1000 mg/L showed a mean inhibition of the respiration rate of the activated sludge of 31 %.

Then, a main study was performed using five concentrations ranging from 2000 to 125 mg/L. The dry matter of the activated sludge was determined as 3.8 g suspended solids/L, giving a concentration of 1.52 g suspended solids/L in the test. The EC50 of the reference item was determined as 6.8 mg/L (95 % confidence interval: 5.9 - 7.7 mg/L).

The following inhibitions of the respiration rate of the activated sludge were detected: At 2000 mg/L 29.5 %, at 1000 mg/L 30.0 %, at 500 mg/L 24.5 %, at 250 mg/L 19.5 % and at 125 mg/L 15.8 % inhibition were detected.

The following results for the source test item  were determined:

NOEC (3h) = below 125 mg/L

EC20 (3h) = 270 mg/L (95 % confidence interval: 110 - 430 mg/L)

EC50 (3h) > 2000 mg/L

In a supporting study the following values for the source substance were determined:

The growth inhibition of the aerobe bacterium Pseudomonas putida has been assessed by comparing the growth under the influence of different concentrations of the test item for 16 hours with the growth of a control culture according to EN ISO 10712:1995 and in compliance with GLP. The following concentrations of the source substance have been assessed: 31.5, 100, 312.5, 1000, 3125, 10000 mg/L.

The results are as follows:

EC10 (16 h) = 2600 mg/L

EC50 (16 h) = 7500 mg/L

The test item is not acute toxic for bacteria.

The source substance contains the major organic moieties of the target substance. Therefore, the results of these studies cover the organic moieties of the target substance.

Read-across - Zinc Ion

Juliastuti et al., 2003

In this study the ISO 9509 test was used to assess the inhibitory effect of Zn2+ ion nitrification of municipal wastewater samples using activated sludge collected from a municipal wastewater treatment plant. The nitrite and nitrate production in nitrification decreases as the concentration of heavy metals increases. The no observed effect concentration is 0.1 mg Zn/L, the IC20 is reached at 0.16 mg/L Zn2+ and the IC50 is reached at 0.35 mg/L Zn2+.

As the target substance contains 16.5 % Zinc ion (worst case) the no observed effect concentration for the target substance corresponds to 3.82 mg/L, the IC20 is reached at 6.12 mg/L and the IC50 is reached at 13.39 mg/L

IC50 (target substance) = 13.39 mg/L

IC20 (target substance) = 6.12 mg/L

NOEC (target substance) = 3.82 mg/L