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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of 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: GLP study done according to OECD Guideline 209.
Justification for type of information:
Hydrocarbons, C9-C10, aromatics, >1% Naphthalene are a combination of Hydrocarbons, C9 Aromatics and Hydrocarbons, C10-C12 Aromatics. Read across data is available for Hydrocarbons, C9 Aromatics and Hydrocarbons, C10-C12 Aromatics and the worst case scenario for each end point has been presented.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
Due to the high vapor pressure of the test substance, the substance would have been lost to volatilization during the standard 3 hr exposure. Instead the test substance was injected directly into the oxygen uptake for an exposure duration of 10 min.
GLP compliance:
yes (incl. QA statement)
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
90% domestic sewage from Chester Sewage Works (Welsh Water) collected on day of the test. The mixed liquor suspended solids content was 3.64 g dry solids/l.
Test type:
static
Limit test:
yes
Total exposure duration:
10 min
Test temperature:
20 +/- 0.6°C
pH:
7.5-7.7
Nominal and measured concentrations:
Nominal: 1.1, 3.3, 9.9, 33, 99 mg/l
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Key result
Duration:
10 min
Dose descriptor:
NOEC
Effect conc.:
> 99 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
10 min
Dose descriptor:
EC50
Effect conc.:
> 99 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
- Effect concentrations exceeding solubility of substance in test medium: yes
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: 3-hr EC50 = 14 mg/l

 Concentration Respiration Rate (mg O2/g dry solids/h)  Inhibition % 
Control  17.8 
1.1   18.8 
3.3  18.6 
9.9  18.6 
33  18.0 
99  18.0 
Validity criteria fulfilled:
yes
Conclusions:
Hydrocarbons,C9, Aromatics is not expected to be toxic to aerobic sewage treatment. The NOEC is >99 mg/L (nominal). The EC50 is also > 99 mg/L (nominal).
Executive summary:

This study was done to determine if Shellsol A had an inhibitory effect on the respiration rate of activated sludge. Activated sludge was exposed to 1.1, 3.3, 9.9, 33, or 99 mg/L of test substance. The exposure duration, 10 min, was much less than the normal duration of 3 hrs. However, due to the high volatility of the substance, it would be rapidly lost to volitization during the vigorous aeration of the activated sludge process. The test substance showed no inhibition of respiration as compared to negative controls. The positive control substance inhibited respiration up to 93.2%. Therefore, the results of the study are considered valid, and the substance is not expected to be toxic to aerobic sewage treatment, and the NOEC and EC50 are both >99 mg/L (nominal).

Description of key information

There is no data available for this substance. However, key data is available for a structural analogue C9 aromatics. The data is read across to this substance based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13. Key information is summarised below:

Hydrocarbons,C9, Aromatics is not expected to be toxic to aerobic sewage treatment. The NOEC is >99 mg/L (nominal). The EC50 is also > 99 mg/L (nominal).

Key value for chemical safety assessment

Additional information