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Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2013-12-12 until 2014-01-02 and 2014-01-16 until 2014-02-27
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The data are derived from work involving two non-GLP OECD 301F studies with the aim to minimize inhibition of the inoculum by means of testing several concentrations of the test item and using silica gel to enable biodegradation.
Qualifier:
equivalent or similar to guideline
Guideline:
other: OECD 301F
GLP compliance:
no
Remarks:
The laboratory complies the general requirements for the competence of testing and calibration laboratories.
Analytical monitoring:
not required
Vehicle:
no
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Source of activated sludge: Escatawpa Wastewater Treatment Plant (ESC), Mississippi. secondary biological wastewater treatment system utilizing the activated sludge process.
- Laboratory culture: not applicable
- Method of cultivation: not applicable
- Storage conditions: not applicable
- Storage length: not applicable (settling immediately started)
- Preparation of inoculum for exposure:
The sludge after arrival is settled and decanted with mineral water added back. This settling procedure is repeated twice more and aerated over night prior to use. The day of the test, the air is turned off and inoculate settled in an Imhoff cone. The settled concentrate is drained into beaker and solids concentration determined.
- Concentration of sludge: 30mg/L of suspended solids (SS)
Test type:
static
Water media type:
freshwater
Total exposure duration:
1 d
Test temperature:
22±1 °C
Nominal and measured concentrations:
10, 20 and 40 mg/L
Details on test conditions:
TEST CONDITIONS
- Composition of medium: according to OECD 301F guideline
- Additional substrate: no (test 1December 2013) and yes (silica gel in test 2 January 2014).
- Solubilising agent (type and concentration if used): In test 2, approximately 500 mg of silica gel (Aldrich, Merck grade 9385) with a mesh size of 230-400 angstrom was weighed out and added to all test bottles (including blanks, reference compound and test material) after addition of the test compound and before the inoculate concentrate is added.
- Test temperature: 22±1 °C
- pH: not specified
- Suspended solids concentration: 30 mg/L
- Continuous darkness: not specified

TEST SYSTEM
- Culturing apparatus: 1-liter vessels
- Number of culture flasks/concentration: triplicates for test 1 and quadruplicates in test 2
- Measuring equipment: Coordinated Environmental Services (CES) Ltd (Cornwell, UK) aerobic electrolytic respirometer unit consisting of 20 one-liter
vessels fitted with heads containing O2 and CO2 sensors.
- Measurement frequency: CO2 generation and O2 uptake data is recorded by the instrument every six hours during the 28-day test.
- Other: Stirring is adjusted to 300-400rpm.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Blank 1-liter vessels are prepared identical to the samples (i.e. test medium, inoculate, and silica gel when present).
- Reference substance and control: Sodium benzoate, silica gel when present is also included in the reference 1-liter vessels.
- Abiotic sterile control: not applicable
- Toxicity control: no
Reference substance (positive control):
yes
Remarks:
benzoic acid, sodium sal
Key result
Duration:
6 h
Dose descriptor:
IC50
Effect conc.:
10.97 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
12 h
Dose descriptor:
IC50
Effect conc.:
11.7 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
18 h
Dose descriptor:
IC50
Effect conc.:
13.28 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
24 h
Dose descriptor:
IC50
Effect conc.:
14.54 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Conclusions:
The concentrations of Benzenesulfonic acid, 4-C15-16-sec-alkyl derivs. required to inhibit oxygen uptake by 50% were 10.97 mg/L, 11.70 mg/L, 13.28 mg/L and 14.54 mg/L at 6, 12, 18 and 24 hours, respectively. The mean IC50 for the 24 hour time period was 12.62 mg/L.
Executive summary:

As an add-on to an OECD 301F ready biodegradability study, the respiratory inhibition potential of Benzenesulfonic acid, 4-C15-16-sec-alkyl derivs. was measured. All concentrations of the substance tested produced some inhibition of oxygen uptake. The concentrations of Benzenesulfonic acid, 4-C15-16-sec-alkyl derivs. required to inhibit oxygen update by 50% were 10.97 mg/L, 11.70 mg/L, 13.28 mg/L and 14.54 mg/L at 6, 12, 18 and 24 hours, respectively.

Endpoint:
toxicity to microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline Study without detailed documentation
Principles of method if other than guideline:
Method: other
GLP compliance:
not specified
Analytical monitoring:
not specified
Test organisms (species):
activated sludge
Duration:
30 min
Dose descriptor:
EC50
Effect conc.:
> 261 mg/L

Test item

respiration

% of blank

[mg/L]

[mg O2/g TS]

1.3

12

115

3.9

12

115

13

13

125

39

16

154

130

18

173

261

11

106

The test item does not inhibit respiration

Conclusions:
The 30 minute EC50 of MIPA to activated sludge respiration was greater than 261 mg/L.

Description of key information

The concentrations of the read across substance Benzenesulfonic acid, 4-C15-16-sec-alkyl derivs. required to inhibit oxygen uptake by 50% were 10.97 mg/L, 11.70 mg/L, 13.28 mg/L and 14.54 mg/L at 6, 12, 18 and 24 hours, respectively.

The mean IC50 for the 24 hour time period was 12.62 mg/L.

For the second read across substance (MIPA), the 30 minute EC50 to activated sludge respiration was greater than 261 mg/L.

As the toxicity to microorganisms value for Benzenesulfonic acid, 4 -C15 -16 -sec-alkyl derivs. was significantly lower than that for MIPA, it will be used for Benzenesulfonic acid, 4 -C15 -16 -sec-alkyl derivs. MIPA-salt.

Key value for chemical safety assessment

EC50 for microorganisms:
12.62 mg/L

Additional information

Due to suspected microorganism toxicity, the respiratory inhibition potential of Benzenesulfonic acid, 4-C15-16-sec-alkyl derivs. was measured as an add-on to an OECD 301F ready biodegradability study. All concentrations of the substance tested produced some inhibition of oxygen uptake. The concentrations of Benzenesulfonic acid, 4-C15-16-sec-alkyl derivs. required to inhibit oxygen update by 50% were 10.97 mg/L, 11.70 mg/L, 13.28 mg/L and 14.54 mg/L at 6, 12, 18 and 24 hours, respectively. The mean IC50 for the 24 hour time period was 12.62 mg/L.