2-ethylhexyl 3,5,5-trimethylhexanoate

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:

July - December 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

The test item was first weighed onto glass slides. The glass slides were then transferred to the designated test flasks and test water was added. No emulsifiers or solvents were used.
The reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control. A stock solution containing 2.5 g sodium benzoate per liter test water was prepared by completely dissolving 250 mg sodium benzoate in
100 mL test water. From this stock solution, 10 mL aliquots were added to the corresponding test flasks containing test water.
Accordingly, a mixture of test item (100 mg/L) and procedure control (100 mg/L) was prepared as toxicity control.
Finally, activated sludge was added to each test flask. The final test volume was 250 mL per test flask.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The study was performed with aerobic activated sludge from a wastewater treatment plant (ARA Ergolz II, Füllinsdorf, Switzerland) treating predominantly domestic wastewater. The sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated.
Based on this ratio, calculated amounts of wet sludge were suspended in test water to obtain a concentration equivalent to 4 g dry material per liter. During the holding period of one day prior to use, the sludge was aerated at room temperature. Prior to use, the sludge was first thoroughly mixed and then diluted with test water to a concentration of 1 g per liter (dry weight basis). Based on the determined dry weight of this diluted activated sludge, defined amounts were added to test water to obtain a final concentration of 30 mg dry material per liter.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

28 d

Test temperature:

22 °C, maintained with a built-in thermostat and checked weekly

pH:

adjusted to 7.9 - 7.4 (7.4 at start of test, 8.0 at end of test after 28 days)

Dissolved oxygen:

Electro-chemical analysis process: The biodegradation process consumes the dissolved oxygen in the test medium and generates CO2. The CO2 is adsorbed by soda lime, which results in a decrease of the total pressure in the airtight test flasks. The pressure drop is detected and converted into an electrical signal by means of an electrode type manometer. The consumed oxygen is replaced by electrolytically generated oxygen from a copper sulfate solution.

Salinity:

no data

Nominal and measured concentrations:

nminal concentrations tested

Details on test conditions:

Inhibitory effect of test substance was measured as toxicity control with a test for ready biodegradability.

Reference substance (positive control):

yes

Remarks:

sodium benzoate

Key result

Duration:

28 d

Dose descriptor:

NOEC

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:

The percent biodegradation in the toxicity control, containing both test item and sodium benzoate, was calculated based on the sum of the ThOD of the test item and the reference item.
In the toxicity control, the run of the curve of the oxygen consumption over the 28-day exposure period correlated very well with the oxygen demand of the two added substances, i.e. test item and reference item. Within 14 days of exposure, biodegradation amounted to 37%.
Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L because biodegradation in the toxicity control was >25% within 14 days.

Validity criteria fulfilled:

yes

Conclusions:

According to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L.

Executive summary:

In the toxicity control, the run of the curve of the oxygen consumption over the 28-day exposure period correlated very well with the oxygen demand of the two added substances, i.e. test item and reference item. Within 14 days of exposure, biodegradation amounted to 37%. Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L because biodegradation in the toxicity control was >25% within 14 days. the NOEC is reported as 100 mg/l.

Description of key information

The NOEC of test substance is reported as 100 mg/L

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

According to the ECHA Guidance document R7b, no further test on the toxicity to microorganisms has to be conducted if the toxicity control in a ready biodegradability test shows no inhibitory effects on microorganisms. As the toxicity control in the Closed Bottle Ready biodegradability test showed no inhibition of the microbial activity at a substance concentration of 100 mg/L, no further test is necessary to evaluate the respiration inhibition of activated sludge. The concentration used in the toxicity control (100 mg/L) can be used as NOEC value.