Propane-1,2,3-triyl 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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Data based on the inhibition control of a ready biodegradability study. This approach is in accordance with the Guidance on information requirements and chemical safety assessment (Chapter R.7b: Endpoint specific guidance, ECHA 2008).

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: OECD 301 B (Ready Biodegradability: CO2 Evolution Test)

Qualifier:

equivalent or similar to guideline

Guideline:

other: EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Qualifier:

equivalent or similar to guideline

Guideline:

other: EPA OPPTS 835.3110 (Ready Biodegradability)

GLP compliance:

yes (incl. QA statement)

Remarks:

The Department of Health of the Government of the United Kingdom

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source of inoculum/activated sludge: A mixed population of activated sludge microorganisms was obtained from the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK on 30 July 2012.
- Preparation of inoculum for exposure: the activated sludge was washed twice by settlement and resuspension in mineral medium to remove any excessive amounts of dissolved organic carbon (DOC) that may have been present. The washed sample was then maintained on continuous aeration at approximately 21 °C and used on the day of collection.
- Suspended solids concentration: 2.9 g/L prior to use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

14 d

Details on test conditions:

TEST CONDITIONS
- Composition of medium: According to OECD Guideline:
Solution a KH2PO4 8.50 g/L
K2HPO4 21.75 g/L
Na2HPO4.2H2O 33.40 g/L
NH4Cl 0.5 g/L

Solution b CaCl2 27.5 g/L
Solution c MgSO4.7H2O 22.5 g/L
Solution d FeCl3.6H20 0.25 g/L
10 mL of solution a and 1 mL of solutions b, c and d were added to 1 L of purified water
- Solubilising agent (type and concentration if used): Due to the low solubility of the test substance in water (< 0.05 mg/L) a pre-study on the solubility and stability of the substance was performed to establish the most suitable mode of preparation, which turned out to be the preparation of the solution in a volatile solvent. Therefore, for the final test, chloroform was used to prepare the stock solution. An amount of test item (1065 mg) was dissolved in 10 mL of chloroform to give a 1065 mg/10 mL solvent stock solution. An aliquot (400 μL) of this solvent stock solution was dispensed onto a filter paper and the solvent allowed to evaporate to dryness for approximately 15 minutes. The filter paper was dispersed in approximately 400 mL of mineral medium with the aid of high shear mixing (approximately 7500 rpm, 5 minutes) prior to addition to inoculated mineral medium. The volume was then adjusted to 3 liters.
- Test temperature: ca. 22 °C
- pH: 7.4 ± 0.2
- pH adjusted: yes
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 5 L test culture vessels, each containing 3 L of solution.
- Number of culture flasks/concentration: 2 per blank control, reference control and test item vessels. Only one replicate in the toxicity control
- Method used to create aerobic conditions: the test vessels were sealed and CO2-free air bubbled through the solution at a rate of 30-100 mL/min per vessel and stirred continuously by magnetic stirrer.
- Measuring equipment: TOC analyzer. Samples (50, 135, 180, 300 or 540 μL) were injected into the IC (Inorganic Carbon) channel of the TOC analyzer. Inorganic carbon analysis occurs by means of the conversion of an aqueous sample to CO2 by orthophosphoric acid using zero grade air as the carrier gas. Calibration was by reference solutions of sodium carbonate (Na2CO3). Each analysis was carried out in triplicate.
- Details of trap for CO2 and volatile organics if used: the CO2 produced by degradation was collected in two 500 mL Dreschel bottles containing 350 mL of 0.05 M NaOH. The CO2 absorbing solutions were prepared using purified de-gassed water

SAMPLING
- Sampling frequency: Samples (2 mL) were taken from the first CO2 absorber vessels on Days 0, 2, 6, 8, 10, 14, 21, 28 and 29. The second absorber vessels were all sampled on Days 0 and 29.
- Sampling method: The samples taken on Days 0, 2, 6, 8, 10, 14, 21, 28 and 29 were analyzed for CO2 immediately. On Day 28, 1 mL of concentrated hydrochloric acid was added to each vessel to drive off any inorganic carbonates formed. The vessels were resealed, aerated overnight and the final samples taken from both absorber vessels on Day 29.
- Inorganic Carbon/Total Carbon Analysis: Samples (30 mL) were removed from the test item vessels on Day 0 prior to the addition of the test item in order to calculate the Inorganic Carbon content in the test media. The samples were filtered through 0.45 μm Gelman AcroCap filters (first approximate 5 mL discarded in order to pre-condition the filter) prior to DOC analysis. Samples (30 mL) were also removed from the inoculum control vessels on Day 0 and filtered through 0.45 μm Gelman AcroCap filters (first approximate 5 mL discarded in order to pre-condition the filter) prior to DOC analysis. IC/TC analysis of the test item dispersions after dosing was not possible due to the insoluble nature of the test item in water.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 2 replicates
- Reference control: yes, 2 replicates
- Toxicity control: yes, 1 replicate

Reference substance (positive control):

yes

Remarks:

sodium benzoate

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

>= 14.2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Result of toxicity control from ready biodegradability test

Results with reference substance (positive control):

Sodium benzoate reached 96% biodegradation after 14 days of exposure

Biodegradation in the toxicity control vessel reached 62% within 14 days.

“If in a toxicity test, containing both the test and reference substance, less than 35% degradation (based on total DOC) or less than 25% (based on total ThOD or ThCO2) occurred within 14 days, the test substance can be assumed to be inhibitory.” (OECD guideline 301)

Since more than 60% degradation occurred in the toxicity control, the substance is with high probability not toxic to aquatic microorganisms. The test item concentration in the toxicity control of 14.2 mg/L can be used as NOEC value for the toxicity to aquatic microorganisms.

Description of key information

NOEC = 14.2 mg/L (from ready biodegradation test, 62% biodegradation in toxicity control within 14 days)

Additional information

No standard studies evaluating the effect of propane-1,2,3-triyl 3,5,5-trimethylhexanoate (CAS No. 56554-53-1) on respiration inhibition of aquatic microorganisms are available. Therefore, a ready biodegradability study is used to derive a NOEC for this endpoint. If a compound degrades well in a ready biodegradability test, or does not inhibit the degradation of a positive control at a certain concentration, this concentration can be used as a NOEC value. This approach is in accordance with the Guidance on information requirements and chemical safety assessment, Chapter R.7b (ECHA, 2012).

A substance can be assumed to be not inhibitory of the activity of aquatic microorganisms if, in the toxicity control of a ready biodegradation test, more than 25% biodegradation occurs within a period of 14 days (OECD Guideline 301). For propane-1,2,3-triyl 3,5,5-trimethylhexanoate a biodegradation screening test according to OECD 301B is available (Bayliss, 2012). This test includes a toxicity control containing 14.2 mg/L of test material and 17.1 mg/L reference substance (sodium benzoate). Within 14 days, 62% biodegradation took place in this toxicity control clearly indicating the lack of toxic potential of propane-1,2,3-triyl 3,5,5-trimethylhexanoate to aquatic microorganisms, and therefore, the test item concentration of 14.2 mg/L can be used as a NOEC value.

Based on the above information it is considered that propane-1,2,3-triyl 3,5,5-trimethylhexanoate is not inhibitory of aquatic microorganisms activity and further testing for this endpoint is not deemed necessary.

Reference

European Chemicals Agency (ECHA, 2012). Guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance