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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:
2010-03-24 to 2010-03-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to OECD 209 test guideline, and in compliance with GLP.
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 100 mg/L

Vehicle:
no
Test organisms (species):
activated sludge
Details on inoculum:
- Pretreatment: The activated sludge was washed three times with tap water. The dry weight of the activated sludge was determined after filtration (paper filter).

- Initial biomass concentration: The recommended amount of wet sludge for the test vessels was then calculated to obtain a suspended solids level of 4 g/L (±10 %).
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
19.6 - 20.5 °C
Dissolved oxygen:
- Dissolved oxygen: in a range of 7.4 – 7.9 mg O2/L

Details on test conditions:
TEST SYSTEM
- Test vessel: Glass beaker

- Type (delete if not applicable): open

- Aeration: Continuous, membrane pumps

- No. of vessels per concentration (replicates): 1

- No. of vessels per control (replicates): 2

- Biomass loading rate: 100 mg/l

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


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

TEST CONCENTRATIONS
- Test concentrations: 100 mg/L of the Test item

- Results used to determine the conditions for the definitive study: The results of this preliminary WAF-study resulted in a mixing period of 24 h and a settling period of 1 h being recommended for preparation of the WAFs.
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
other: EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: confidence limit 95 %, significance level: 0.05
Results with reference substance (positive control):
- Results with reference substance valid? Yes, Deviation between respiration rates of the controls: 12.2 % (nominal value ≤ 15 %)

- Relevant effect levels: EC50 (3 h) of 3,5-Dichlorophenol: 14.4 mg/L (nominal value 5 - 30 mg/L), NOEC < 1.0 mg/L (NOEC=No Observable Effect Concentration)
Reported statistics and error estimates:
Determination of the EC50 (EC=Effective Concentration) of the Reference item 3,5-Dichlorophenol was accomplished using Probit-analysis (Finney-method, lognormal distribution; confidence limit 95 %, significance level: 0.05).

Table 2: Results of the Activated Sludge, Respiration Inhibition Test of Distilled Tall Oil

 

c / Loading rate (mg/L)

 

Respiration rate

(mg O2/L x h)

 

Inhibition (%)

Control 1

-

64.9

-

Reference

3

61.5

11.3

10

45.7

34.1

30

18.0

74.1

Test item

100

60.8

12.4 *

Control 2

-

73.9

-

 

Remark: * With reference to the validity criterion of OECD-Guideline 209, that recommends a deviation of respiration rates of the two controls of ≤15 %, the result of inhibition of the Test Item Distilled Tall Oil of 12.4 % was not regarded as a definite inhibition.

Validity criteria fulfilled:
yes
Conclusions:
A 3 hour Water Accommodated Fractions (WAFs) value EL50 of > 100 mg/L and a NOELR of 100 mg/L have been determined for Distilled Tall Oil in a test conducted according to OECD 209. The result is considered reliable.

Description of key information

A 3 h-EL50 of > 100 mg/L and a NOELR of ~100 mg/L.

Key value for chemical safety assessment

Additional information

A Water Accommodated Fractions (WAFs) of Distilled Tall Oil caused no acute toxic effects on bacteria in an Activated Sludge, Respiration Inhibition Test as a Limit Test conducted in accordance to OECD 209. A 3 h-EL50 of > 100 mg/L and a NOELR of~100 mg/L have been determined for the test substance.

PNEC for WWTP

It is not considered necessary to derive a PNEC or conduct risk characterisation for DTO in biological WWTP (sewage treatment plant) for the following reasons:

 

- DTO (and the majority of its constituents are naturally-occurring and well tolerated by environmental organisms)

- DTO has been reliably demonstrated to be readily biodegradable by activated sludge cultures

- In a typical WWTP, sewage organisms are exposed to DTO as a whole substance. Samples of DTO (tested as water-accommodated fractions) caused no acute toxic effects on microorganism in a standard activated sludge respiration inhibition (ASRI) test.

 

It is therefore very unlikely that DTO would cause inhibitory effects on microorganisms present in STP.

Calculation of PNEC for WWTP micro-organisms

PNEC for WWTP micro-organisms for DTO will not be determined based on available study since DTO does not cause inhibitory effects to microorganisms in sewage treatment plants.