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Ecotoxicological information

Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study, performed under GLP using linalool, a close chemical analogue of the test item with similar physico-chemical properties.
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
Instead of using centrifuged sludge, settled sludge was used.
GLP compliance:
yes
Analytical monitoring:
not specified
Vehicle:
not specified
Details on test solutions:
Nutrient solution was prepared by dissolving the following in 1 litre of dechlorinated drinking water:
- 16 g peptone
- 11 g meat extract
- 3 g urea
- 0.7 g NaCl
- 0.4 g CaCl2.2H2O
- 0.2 g MgSO4.7H2O
- 2.8 g K2HPO4
Test organisms (species):
activated sludge
Details on inoculum:
The activated sludge was obtained from the sewage treatment plant of CH-4153 Reinach. The pH of the sludge after collection was measured as 7.3
The activated sludge was prepared for used as described in the OECD 209 guideline, with the exception that the sludge was separated from the aqueous layer by settling rather than centrifugation.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Remarks on exposure duration:
Results were also recorded for a 30 minute duration
Test temperature:
20 +/- 2 degrees C
Nominal and measured concentrations:
Nominal test concentrations: 1.01, 3.22, 10.07, 32.22, 100.7 mg/l
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 ml BOD flask
- No. of organisms per vessel: sludge concentration used was 1.6 g/l (dry weight)
- No. of vessels per concentration (replicates):1
- No. of vessels per control (replicates): 3 (reference)
- No. of vessels per vehicle control (replicates): 2 (blank)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Dechlorinated drinking water



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
Duration:
3 h
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:
See table 1 in 'Any other information on results incl. tables' field.
Results with reference substance (positive control):
Graphically determined: EC50 (30 min) = 24.0 mg/l; 3 hour = 19.9 mg/l).

Table 1. Inhibition concentrations

    Oxygen consumption rate (mg/l/h) % Inhibition
Sample Concentration (mg/l) 30 min 3 hour 30 min 3 hour
Blank 1 0 45.42 43.06 0 3
Blank 2 0 45.39 45.43 0 -3
Reference 1 32 15.24 13.53 66 69
Reference 2 10 41.31 36.14 9 18
Reference 3 3.2 43.35 42.38 4 4
Test conc. 1 100.7 43.67 44.96 4 -2
Test conc. 2 32.22 45.82 45.31 -1 -2
Test conc. 3 10.07 46.37 44.86 -2 -1
Test conc. 4 3.22 45.6 44.61 0 -1
Test conc. 5 1.01 45.28 44.79 0 -1
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this study the EC50 at 30 mins and 3 hours are determined to be > 100 mg/l.
Executive summary:

In a OECD 209 guideline study, activated sludge (treating predominantly domestic waste) was exposed to linalool at nominal test concentrations of 1.01, 3.22, 10.07, 32.22, 100.7 mg/l for 30 minutes and 3 hours. No microbial inhibition of respiration was observed at test concentrations used in this study. The results of this study show that linalool is of low toxicity to microorganisms, with an EC50 value of >100 mg/l for respiration inhibition (at both 30 minute and 3 hour exposure periods).

   

       

Description of key information

One key study has been identified which adequately assessed the toxicity of the close the test item analogue, linalool, to microorganisms. This study followed the OECD 209 guideline and was GLP-compliant.

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information

Linalool is a close chemical analogue of the test item, with similar physico-chemical properties. Results of its testing for microbial toxicity are therefore deemed suitable to assess the equivalent toxicity of dihydromyrcenol.

No microbial inhibition of respiration was observed at the test concentrations used in the linalool key study, suggesting dihydromyrcenol is of low toxicity to microorganisms, with an EC50 value of >100 mg/l for respiration inhibition (at both 30 minute and 3 hour exposure times).