Neodecanoic acid, iron salt

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2020-03-04 to 2020-04-01

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))

Version / remarks:

adopted 22 July 2010

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

- Name of the test material: Neodecanoic acid, iron salt
- Source and lot/batch number of test material: 20009737
- Expiration date of the lot/batch: 31 October 2020
- Content: 11 +/- 1% iron
- Appearance: resinous viscous liquid
- Colour: brown
- Storage conditions: ambient temperature, in the dark

Analytical monitoring:

not required

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item has a very low water solubility. Therefore the test item was added directly into the test vessels with a test volume of 500 mL to obtain a final loading rate of 10, 100 and 1000 mg/L.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Activated sludge from the municipal wastewater treatment plant Breisgauer Bucht was used as test system. The treatment plant has a capacity of 600 000 inhabitant equivalents and clarifies predominantly domestic wastewater. Sampling date of activated sludge was 4 March 2020. The activated sludge was kept aerated until use at test temperature. The activated sludge was washed twice by settling the sludge, decanting the supernatant and resuspending the sludge in chlorine-free tap water. Dry solid of the activated sludge was determined as 5.2 g/L by weight measurements before and after drying at 105 °C (mean of triplicate measurements). Before using, the activated sludge was diluted to 3 g/L dry solids with chlorine-free tap water, in order to obtain a final concentration of 1.5 g/L dry solids in the test.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

19.4 to 21.5 °C

pH:

7.4–7.5

Dissolved oxygen:

ca. 6 up to ca. 7.5 mg/L (oxygen saturation of 60–70 %)

Nominal and measured concentrations:

10, 100 and 1000 mg/L (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: Graduated cylinder 600 mL (Schott, Mainz, Germany); 250 - 300 mL BOD bottles with adapter for oxygen electrode
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: 500 mL
- Aeration: All vessels were stirred and aerated throughout the contact time with room air to assure an oxygen saturation of 60-70% using a membrane pump.
- No. of vessels per concentration (replicates): 3 to 5
- No. of vessels per control (replicates): 6
- No. of vessels per abiotic control (replicates): 3
- Sludge concentration (weight of dry solids per volume): 3 g/L dry solids
- Weight of dry solids per volume of reaction mixture per unit of time: 1.5 g/L dry solids
- Nutrients provided for bacteria: peptone 16 g/L, meat extract 11 g/L, urea 3 g/L, NaCl 0.7 g/L, CaCl2 * 2 H2O 0.4 g/L, MgSO4* 7 H2O 0.2 g/L, K2HPO4 2.8 g/L
- Nitrification inhibitor used (delete if not applicable): none

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: chlorine-free tap wate

OTHER TEST CONDITIONS
- Adjustment of pH: yes

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): The respiration rate is calculated from oxygen measurements using the linear portion of the oxygen-time-curves. This determination was repeated for each vessel at 15-min intervals, ensuring that the contact time in each vessel was 3 h.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10
- Range finding study : Yes
- Test concentrations: 10, 100 and 1000 mg/L
- Results used to determine the conditions for the definitive study: Yes

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

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

A range finder test with the concentrations of 10, 100 mg/L (three replicates) and 1000 mg/L (five replicates) was performed. There was no inhibition observed in the treated test vessels, the test item seems to support the inoculum which leads to higher consumption rates in the treated test vessels and to negative inhibition effects. Neodecanoic acid, iron salt had no toxic effect on the total respiration rate of activated sludge micro-organism at the concentrations of 10, 100 and 1000 mg/L after the exposure period of 3 hours.

Results with reference substance (positive control):

- Results with reference substance valid? Yes
- Relevant effect levels: The EC50 of 3,5-dichlorphenol was calculated as 16.26 mg/L and was therefore within the acceptable range of 2 to 25 mg/L. The pH in the reference vessels was 7.4-7.5.

Criteria met for the validity of the study:

- The coefficient of variation (CV) of the blank respiration rates was less than 30 % (actually 8 %).

- The blank controls mean oxygen uptake rate was higher than 20 mg oxygen per one gram of activated sludge per hour (actually 25.4 mg/g*h).

- The 3-hour EC50 of the reference item was within the acceptable range of 2 to 25 mg/L (actually 16.26 mg/L).

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiration inhibition test according to OECD 209 resulted in an EC50 > 1000 mg/L and a NOEC ≥ 1000 mg/L.

Executive summary:

To investigate potential harmful effects of neodecanoic acid, iron salt, on microorganisms a range finder test with the concentrations of 10, 100 mg/L (three replicates) and 1000 mg/L (five replicates) were conducted according to OECD test guideline 209. There was no inhibition observed in the treated test vessels, the test item seems to support the inoculum which leads to higher consumption rates in the treated test vessels and to negative inhibition effects. Neodecanoic acid, iron salt had no toxic effect on the total respiration rate of activated sludge micro-organism at the concentrations of 10, 100 and 1000 mg/L after the exposure period of 3 hours.

The result is therefore:

EC50 > 1000 mg/L

NOEC ≥ 1000 mg/L

The pH in the test vessels was between 7.4 and 7.5.

Description of key information

To investigate potential harmful effects of neodecanoic acid, iron salt on microorganisms, an activated sludge respiration inhibition test was performed according to OECD 209 and under GLP.

A limit test with the concentration of 1000 mg/L was performed. The pH in the test vessels was 7.4-7.5. No inhibition was observed in the test vessels with 1000 mg/L test concentration (–31 to 19 %). The respiration rates in the test vessels were not significantly lower than the respiration rate of the controls (Student’s t-test).

Therefore, an EC50 of > 1000 mg/L and a NOEC of ≥ 1000 mg/L were determined.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L