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Toxicity to microorganisms

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Endpoint:
toxicity to microorganisms, other
Remarks:
cell multiplication inhibition test
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Principles of method if other than guideline:
Method: other: Cell multiplication inhibition test
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
a stock solution was prepared; to achive the test concentrations a defined amount of the stock solution was dissolved
Test organisms (species):
Pseudomonas putida
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
16 h
Test temperature:
25°C
Duration:
16 h
Dose descriptor:
other: TT
Effect conc.:
33 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth inhibition

TT = Toxicity threshold; determined at 3 % effect compared to control

Conclusions:
For Pseudomonas putida a NOEC of 33 mg/l was obtained in a cell multiplication inhibition test during 16 hours of exposure
Executive summary:

The toxicity of o-cresol to Pseudomonas putida was assessed in a cell multiplication inhibition test according to Bringmann (1976). Bacteria were exposed for 16 hours at a temperature of 25°C to the test substance. A toxicity threshold concentration of 33 mg/l was determined after 16 hours exposure. The result is equivalent to an EC3 or a NOEC. The endpoint biomass is measured by turbidity determination with a photometric detector.

Endpoint:
toxicity to microorganisms, other
Remarks:
cell multiplication inhibition test
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Principles of method if other than guideline:
cell multiplication inhibition test
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
a stock solution was prepared; to achive the test concentrations an defined amount of the stock solution was dissolved
Test organisms (species):
Entosiphon sulcatum
Details on inoculum:
holozoic bacteriovorous flagellate
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
25°C
pH:
initial pH 6.9
Duration:
72 h
Dose descriptor:
other: TT
Effect conc.:
17 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth inhibition

TT = Toxicity threshold; determined at 5 % effect compared to control

Validity criteria fulfilled:
not specified
Conclusions:
In a cell multiplication inhibition test conducted with Entosiphon sulcatum a 72h-NOEC of 17 mg/l is determined.
Executive summary:

According to Bringmann (1978), the protozoa Entosiphon sulcatum was exposed to o-cresol for 72 hours using the cell multiplication inhibition test method. A toxicity threshold of 17 mg/l was obtained which is equivalent to a NOEC or an EC3.

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:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
no guideline available
Principles of method if other than guideline:
No guideline available at the moment of testing. Inhibition of nitrification process
GLP compliance:
no
Analytical monitoring:
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 incubation period
Test temperature:
25 °C
pH:
7.6 - 7.8
Dissolved oxygen:
> 1mg/L
Salinity:
BOD 250 mg/L
50-80 mg/L ammonia
0.003 mol/L NaHCO3
0.002 mol/L (NH4)2SO4
Details on test conditions:
pre-cleaned activated sludge in particle-free communal waste water (BOD5: 250 mg/l; NH4-N/l: 50-80 mg)
Dose descriptor:
other: EC75
Effect conc.:
12.8 mg/L
Nominal / measured:
not specified
Conc. based on:
test mat.
Basis for effect:
inhibition of nitrification rate
Remarks on result:
other: duration 2-4h

major scope of study was to develop method

Validity criteria fulfilled:
not specified
Conclusions:
Nitrification inhibition by o-cresol was measured by a similar method yielding an EC75 of 12.8 mg/L during a 2 -4 h incubation period.
Executive summary:

Tomlinson (1966) described the influence of o-cresol on the nitrification process in domestic wastewater. A purified activated sludge was incubated for 2 to 4 hours to the wastewater (BSB5 = 250 mg/l, 50 to 80 mg NH4-N/l) fortified with different concentrations of o-cresol. The effect on the inhibition of the nitrification was determined by photometric analysis of nitrite and nitrate. An EC75-value of 12.8 mg/l is given for the inhibition of the reaction step of ammonia to nitrite.

Description of key information

Regarding all available test on toxicity to microorganisms, the most relevant test resulting in the lowest PNEC value is used for assessment.
Nitrification inhibition by o-cresol was measured by a similar method yielding an EC75 of 12.8 mg/L during a 2 -4 h incubation period . In a cell multiplication inhibition test conducted with Entosiphon sulcatum a 72h-NOEC of 17 mg/l is determined. For Pseudomonas putida a NOEC of 33 mg/l was obtained in a cell multiplication inhibition test during 16 hours of exposure. In order to protect the efficiency of sewage treatment plants, inhibition of nitrification is identified to be the most sensitive test system.

Key value for chemical safety assessment

EC50 for microorganisms:
12.8 mg/L

Additional information

No standard tests concerning the respiration inhibition on microorganisms in sewage treatment systems are available. However, several tests are available to evaluate the toxicity of o-cresol to microorganisms.

The influence of o-cresol on the nitrification process in domestic wastewater is described in an experiment. A purified activated sludge was incubated for 2 to 4 hours to the wastewater (BSB5 = 250 mg/l, 50 to 80 mg NH4-N/l) fortified with different concentrations of o-cresol. The effect on the inhibition of the nitrification was determined by photometric analysis of nitrite and nitrate. An EC75-value of 12.8 mg/l is given for the inhibition of the reaction step of ammonia to nitrite.

Concerning toxicity towards single species, the toxicity of o-cresol to Pseudomonas putida was assessed in a cell multiplication inhibition test according to Bringmann. Bacteria were exposed for 16 hours at a temperature of 25°C to the test substance. A toxicity threshold concentration of 33 mg/l was determined after 16 hours exposure. The result is equivalent to an EC3 or a NOEC. The endpoint biomass is measured by turbidity determination with a photometric detector.

The protozoa Entosiphon sulcatum was exposed to o-cresol for 72 hours using the cell multiplication inhibition test method. A toxicity threshold of 17 mg/l was obtained which is equivalent to a NOEC or an EC3.