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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:
2008-01-28 to 2008-02-21
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Qualifier:
according to
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
For measurement of the respiration rate a well-mixed sample of each test medium was poured into a BOD-flask after three hours incubation time, and was not further aerated.
Details on test solutions:
Based on the results of a pre-test, the test item was soluble at a concentration of at least 5 g/L in tap water.A stock solution with a nominal concentration of 5 g/L was prepared by dissolving 1250.1 mg of the test item in 250 mL tap water by intense stirring for fifteen minutes. Adequate volumes of this stock solution were diluted with tap water to prepare the test media with the lower test item concentrations. The final nominal concentrations tested were 10, 32, 100, 320 and 1000 mg/L.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Sampling site: ARA Ergolz II, Füllingsdorf, Switzerland- Concentration of suspended solid: 3 g per liter- Method of cultivation: prior to use the sludge was fed daily with 50 mL synthetic wastewater per liter and kept at room temperature under continuous aeration.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Hardness:
no data
Test temperature:
20+-2°C
pH:
8.1 to 8.4
Dissolved oxygen:
8.2 to 9.4 mg O2/L
Salinity:
no data
Nominal and measured concentrations:
The final nominal concentrations tested were 10, 32, 100, 320 and 1000 mg/L.
Details on test conditions:
TEST SYSTEM
- Test vessel: >500 ml- Volume of the test solution: 500 ml
- Test temperature: 20+-2°C
- Dissolved oxygen analyzer: oxygen electrode (WTW TriOxmatic 300) oxygen meter (WTW Oxi 539)
- Aeration: yes
- Preparation of synthetic sewage (filled up to 1 liter deionized water)16 g peptone11 g meat extract3 g urea0.7 g NaCl0.4 g CaCl2*2H200.2 g MgSO4*7H202.8 g K2HPO4
-Preparation of activated sludge: The sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated.
-Preparation of stock solution of test item: A stock solution with a nominal concentration of 5 g/L was prepared by dissolving 1250.1 mg of the test item in 250 ml tap water by intense stirring for fifteen minutes. In this way a clear solution was obtained. Adequate volumes of this stock solution were diluted with tap water to prepare test media with the lower test item concentrations. Then, 16 ml synthetic wastewater and 200 ml activated sludge inoculum were added.
- Preparation of stock solution of reference control: 0.5 g 3,5-dichlorophenol was dissolved in 10 ml 1M NaOH and diluted to about 30 mL with purified water. Excess NaOH was neutralized with 0.5 M H2SO4 to the point of incipient precipitation. Thereafter, the mixture was diluted to 1 liter with purified water. The final pH was determined and to be in the range of 7 to 8.
TEST CONCENTRATIONS
- Test concentrations: 10, 32, 100, 320, 1000 mg/L
- Test concentrations reference control: 5, 16, 50 mg/L
- Replicates: Duplicates
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 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:
other: EC80
Effect conc.:
> 1 000 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:
other: EC20
Effect conc.:
933 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: 95% CL = 913 to 947 mg/L
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
847 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: determined as the calculated 3-hour EC15; 95% CL = 805 to 874 mg/L
Results with reference substance (positive control):
EC50 = 20 mg/L (3 hours)

Influence of Hyoscine Butylbromide and 3,5-Dichlorophenol on the Oxygen Consumption of Activated Sludge              

   Nominal Concentration (mg/L)  Oxygen consumption rate (mg O2 L-1 min-1)  Inhibition (%)
 Test item              10  1.365 3.2 
 32  1.423  -0.9
 100  1.409  0.1
 320  1.420  -0.7
 1000  1.069  24.2
 Reference control        5  1.517  -7.6
 16  0.836  40.7
 50  0.169  88.0
 Blank control     0  1.373  
 0  1.446  
 Mean    1.410  
 Deviation    5.3  

Up to and including the concentration of 320 mg/L the test item had no significant inhibitory effect (=15%) on the respiration rate of activated sludge after the incubation period of 3 hours. At the highest test item concentration of 1000 mg/L the inhibitory effect increased only slightly to 24%.

Validity criteria fulfilled:
yes
Conclusions:
It is considered that the respiration inhibition of (-)-scopolamine butylbromide is low because EC50 was > 1000 mg/L and the NOEC is 847 mg/L under this test conditions.

Description of key information

The read-across substance Hyoscine butylbromide was assessed for its toxicological potential to activated sludge in an aerobic respiration inhibition test over 3 hours according to OECD 209. Under this test conditions an EC50 of > 1000.0 mg/L was determined. A 3-hours NOEC of 847 mg/L was determined.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
847 mg/L

Additional information