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Ecotoxicological information

Toxicity to microorganisms

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Reference
Endpoint:
toxicity to microorganisms, other
Type of information:
experimental study
Adequacy of study:
key study
Study period:
27 July 1990 - 24 August 1990
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Study performed according to OECD Guideline 301B in compliance with GLP. However, the results of this key study are compiled in a summary report only representing the most crucial results, lacking information on the blanks and reference substance.
Reason / purpose:
reference to same study
Qualifier:
equivalent or similar to
Guideline:
other: OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Principles of method if other than guideline:
The study was conducted in accordance to draft Ecotoxicology SOP 158 01. However, the ferric chloride stock solution contained 0.25g not 0.2 g and the EDTA stock solution contained 0.4g (as recommended in the 1988 OECD Ring Test) and not 0.5g as advised by the draft SOP 158 01.
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Remarks:
Measurement of CO2/DIC
Details on sampling:
- Sampling frequency: Day 4, 7, 11, 14, 18, 21, 25 and 28
- Sampling method: At each interval a vessel is removed and the carbon dioxide concentration of the headspace gas determined. The seal of the vessel is then broken and the concentration of inorganic carbon in the test medium measured.
Vehicle:
no
Details on test solutions:
APPLICATION OF TEST SOLUTION
The test substance was added directly to the appropriate vessels with a high quality liquid delivery syringe. The volume added( 1-2 μl) is negligible compared to the total volume of 100 m in each vessel and is not taken into consideration when determining the results.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Source of inoculum/activated sludge: Secondary effluent from an unacclimatised activated sludge plant at URL North
- Preparation of inoculum for exposure: 10% by volume of activated sludge plant secondary effluent was filtered through Whatman filter paper (541) to remove coarse particulate matter.
- Pretreatment: The level of dissolved inorganic carbon (DIC) was reduced by sparging the filtered effluent with nitrogen after prior adjustment of the pH to 6.5.
Test type:
static
Water media type:
freshwater
Total exposure duration:
28 d
Test temperature:
Air temperature 18-21°C
Temperature in the liquid medium 21.5-23°C
pH:
6.5
Nominal and measured concentrations:
10 mg/L organic carbon corresponding to 14.2 mg/L test substance (nominal)
Details on test conditions:
TEST SYSTEM
- Culturing apparatus: 160mL vessels (hypovials) containing 100mL mineral salts medium inoculated with secondary effluent and the respective test of reference substance
- Method used to create aerobic conditions: headspace of vessels filled with air (60mL), containing approx. 6 times the mass of oxygen required for the complete oxidation of the substance.
- Test performed in closed vessels due to significant volatility of test substance: yes

TEST CONDITIONS
- Composition of medium: mineral salts medium (as recommended in the 1988 OECD Ring test)
- Test temperature: Air temperature 18-21°C; Temperature in the liquid medium 21.5-23°C
- pH: 6.5
- pH adjusted: yes
- Other: EDTA stock solution (for the preparation of the mineral salts medium) contained 0.4g instead of 0.5g as recommended in the draft Ecotoxicology SOP 158 01; Nominal Carbon added to medium: 940 µg (assuming 100% purity of compound)
Reference substance (positive control):
not specified
Key result
Duration:
28 d
Dose descriptor:
NOEC
Effect conc.:
14.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
Biodegradation of the test substance during 28d
Details on results:
Substance was found to be readily biodegradable hence no toxic or other inhibitory effect on microorganisms is concluded.
Results with reference substance (positive control):
The test does not mention inclusion of a toxicity control.

Percentage Biodegradation of the test substance Litsea cubeba:

Day No.

% Biodegradation (a)

R488 (b)

4

52.2

7

71.2

11

82.4

14

89.7

18

89.2

21

93.2

25

100.7

28

103.9

95% confidence interval

102.6 – 105.3

(a) Based on nominal carbon concentration which assumes 100% purity of the named test substance unless specified otherwise

(b) Actual percentage biodegradation

Validity criteria fulfilled:
not specified
Remarks:
no information on difference between replicates and CO2 evolution in blank, toxicity control not applicable as substance was found to be readily biodegradable.
Conclusions:
Based on the results of a ready biodegradability screening test (OECD TG301B), the substance is not considered to be toxic or inhibit micro-organisms when dosed 14.2 mg/L Litsea cubeba.
Executive summary:

The toxicity of Litsea cubeba to microorganisms can be inferred from a study conducted in accordance to GLP and to an equivilant guideline with OECDTG 301B (carbon dioxide evolution test -modified Sturm test, closed vessel). In this study, activated sludge was exposed to 14.2 mg/L test substance for 28 days. Analysis for CO2/DIC in the liquid medium was analyzed on day 4, 7, 11, 14, 18, 21, 25 and 28.

Litsea cubeba was biodegraded by 71.2 % at day 14 and completely biodegraded at day 28. However as there was complete biodegradation, the test substance is not considered to inhibit mcirobial activity. It can therefore be concluded that Litsea cubeba is non-toxic to microorganisms at the nominal tested concentration of 14.2 mg/L which is therefore considered the NOEC.

Description of key information

The toxicity of Litsea cubeba to microorganisms can be inferred from a study conducted in accordance to GLP and to an equivilant guideline with OECDTG 301B (carbon dioxide evolution test -modified Sturm test, closed vessel). In this study, activated sludge was exposed to 14.2 mg/L test substance for 28 days. Analysis for CO2/DIC in the liquid medium was analyzed on day 4, 7, 11, 14, 18, 21, 25 and 28.

Litsea cubeba was biodegraded by 71.2 % at day 14 and completely biodegraded at day 28. However as there was complete biodegradation, the test substance is not considered to inhibit mcirobial activity. It can therefore be concluded that Litsea cubeba is non-toxic to microorganisms at the nominal tested concentration of 14.2 mg/L which is therefore considered the NOEC.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
14.2 mg/L

Additional information