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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
15 February - 6 March 2001
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study has been performed according to OECD and EC guidelines and according to GLP principles.
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Version / remarks:
(1984)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: 87/302/EEC, Part C, Publication No. L133 (1988)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
- The test substance appeared to be hardly soluble in test medium. An initial volume of 300 ml of test solution (containing approx. 50 mg SPS-100 plus 16 ml sysnthetic sewage feed) was prepared in Milli-RO water (tap water purified by reverse osmosis; Millipore Corp., Bedford, Mass., USA) using 1 L glass bottles. Subsequently, 200 ml of sludge was added to obtain a final test concentration of 100 mg SPS-100/L.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Source: Municipal sewage treatment plant, "Waterschap de Maaskant", 's-Hertogenbosh, the Netherlands.
- Preparation of inoculum for exposure:
The sludge were coarsely sieved, washed and diluted with tap-water. The amount of suspended solids was 3.5 g/L of sludge (pH before use was 7.8). The batch of sludge was used on subsequent days (maximum 4 days), therefore 50 ml of synthetic sewage feed was added to each litre of activated sludge at the end of each working day. The sludge was kept areated. It was not specified on which day (ranging from day 0 to day 4) the current test was performed.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
30 min
Post exposure observation period:
After the 30-min contact time the oxygen consumption was measured and recorded for a period of approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer. The pH and temperature was determined in the remaining part of the reaction mixture. This procedure was repeated for duplicate concentration and controls.
Test temperature:
21.5 degrees C
pH:
At the start:7.8
At the end: 7.2-7.4
Dissolved oxygen:
Controls at the start: 7.4-8.2 mg O2/L
Test substance at the start: 7.9- 8.6 mg O2/L
Nominal and measured concentrations:
Nominal concentrations: 0 (control) and 100 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 1 L glass bottle
- Material, size, headspace, fill volume: glass, 1 L filled with 500 ml of test solution
- Aeration: yes
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 2
- No. of vessels per reference substance control (replicates): 1 per concentration
- The amount of suspended solids was 2.1 g/L of sludge (pH before use was 7.8)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap water purified by reverse osmosis (Milli-RO)
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
30 min
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
- No significant inhibition in respiration rate of of the sludge was recorded at 100 mg SPS-100/L (NOEC).
- Acceptability of the test:
Mean respiration rate in controls was 46 mg O2/L and the difference between controls was 9%.
Results with reference substance (positive control):
The EC50 for 3,5-dichlorophenol was 8 mg/L
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this present test, the test substance was not toxic to waste water (activated sludge) bacteria at a nominal concentration of 100 mg SPS-100/L.
Executive summary:

The toxicity of SPS-100 to microorganisms was determined in a 30 min activated sludge respiration inhibition study.

In the test microorganisms in activated sludge from a municipal sewage treatment plant were exposed to the test substance at a concentration of 100 mg/L under static conditions. Under the choosen test conditions SPS-100 did not significantly inhibited the respiration rate of the waste water bacteria. The EC50 exceeded the test nominal concentration of 100 mg/L.

The present toxicity study is classified as reliable without restrictions according to the OECD guideline No. 209 since the criteria for acceptability of the test were met.

Description of key information

The toxicity of SPS-100 to microorganisms was determined in a 30 min activated sludge respiration inhibition study. Under the choosen test conditions SPS-100 did not significantly inhibited the respiration rate of waste water bacteria (activated sludge) at concentrations as high as 100 mg/L (NOEC). Therefore, it was concluded that the test substance it is not toxic up to the solubility limit. The study is considered to be reliable without restrictions according to the OECD guideline No. 209 sincethe criteria for acceptability of the test were met.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
100 mg/L

Additional information

The toxicity of SPS-100 to microorganisms was determined in a 30 min activated sludge respiration inhibition study.

In the test microorganisms in activated sludge from a municipal sewage treatment plant were exposed to the test substance at a concentration of 100 mg/L under static conditions. Under the choosen test conditions SPS-100 did not significantly inhibited the respiration rate of the waste water bacteria. The EC50 exceeded the test nominal concentration of 100 mg/L.

The study is considered to be reliable without restrictions according to the OECD guideline No. 209 sincethe criteria for acceptability of the test were met.