Octyl laurate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to microorganisms

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 2017).

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Remarks:

Department of Health, United Kingdom

Analytical monitoring:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: A nominal amount of test item (855 mg) was dissolved in 10 mL of chloroform to give a 855 mg/10 mL solvent stock solution. An aliquot (456 μL) of the test item solvent stock solution was dispensed onto a filter paper and the solvent allowed to evaporate for approximately 15 min. The filter paper was dispersed in approximately 400 mL of mineral medium with the aid of high shear mixing (approximately 7500 rpm, 5 min) prior to addition to the test vessel containing inoculated mineral medium. An aliquot (51.4 mL) of the sodium benzoate stock solution was also added to the test vessel and the volume was adjusted to 3 L.

Test organisms (species):

other: activated sludge, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activated sewage sludge micro-organisms obtained on 7 December 2015 from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK.
- Laboratory culture: no
- Storage conditions: No storage, used on the day of collection.
- Pretreatment: The activated sewage sludge sample was washed twice by settlement and resuspension in mineral medium to remove any excessive amounts of dissolved organic carbon (DOC). The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approximately 21 °C.
- Suspended solids concentraiton: 3.1 g/L

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 guideline
- Solubilising agent (type and concentration if used): chloroform
- Test temperature: 20-24 °C
- pH: 7.4 - 7.7
- pH adjusted: yes; adjusted to pH 7.4 ± 0.2 using diluted hydrochloric acid or sodium hydroxide solution
- Continuous darkness: yes
- Suspended solids concentration: 30 mg/L

TEST SYSTEM
- Culturing apparatus: 5 L test vessels containing 3 L of solution
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Approximately 24 h prior to addition of the test and reference items the vessels were filled with 2400 mL of mineral medium and 29.0 mL of inoculum and aerated overnight. The test vessels were sealed and CO2-free air bubbled through the solution at a rate of 30 to 100 mL/min per vessel and stirred continuously by magnetic stirrer.
- Measuring equipment: The samples were analyzed for IC using either a Shimadzu TOC-VCSH TOC analyzer or a Shimadzu TOC-LCSH TOC analyzer. Samples (135 or 50 μL) were injected into the IC channel of the TOC analyzer. IC analysis occurs by means of the conversion of an aqueous sample to CO2 by orthophosphoric acid or 2 M HCl using zero grade air as the carrier gas. Calibration was by reference solutions of sodium carbonate (Na2CO3). Each analysis was carried out in triplicate. The pH was measured using a Hach HQ40d Flexi handheld meter.
- 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 water.
- Other: 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.

SAMPLING
- Sampling frequency: Sampled on Days 0, 2, 6, 8, 10, 14, 21, 28 and 29. The second absorber vessels were sampled on Days 0 and 29.
- Sampling method: Samples (2 mL) were taken from the first CO2 absorber vessels.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, two replicates
- Abiotic sterile control: no
- Toxicity control: yes, one replicate
- Procedure control: yes, two replicates

Reference substance (positive control):

yes

Remarks:

sodium benzoate

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

>= 13 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Result of toxicity control from ready biodegradability test

Details on results:

The toxicity control was degraded to 87% after 14 d. Thus, it can be assumed that the test item is not inhibitory to the inoculum (degradation > 25%).

Results with reference substance (positive control):

The reference substance was degraded to 76% after 28 d thus confirming the suitability of the inoculum.

The toxicity control attained 87% degradation after 14 days of incubation.

“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 35% 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 13 mg/L can be used as NOEC value for the toxicity to activated sludge microorganisms.

Description of key information

NOEC (14 d): ≥ 13 mg/L for activated sludge microorganisms (OECD 301B)

Additional information

Since no studies on the toxicity to aquatic microorganisms are available a ready biodegradability study is used to derive a NOEC for the toxicity to aquatic microorganisms. 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: Endpoint specific guidance, ECHA, 2017).

A substance can be assumed to be not inhibitory to aquatic microorganisms, if in the toxicity control of a ready biodegradation test, more than 35% degradation based on CO2 evolution occurred within 14 days (OECD guideline 301). For octyl laurate (CAS 5303-24-2) a biodegradation test conducted according to OECD guideline 301B is available. The test includes a toxicity control, which contains 13 mg/L of the test substance and 17.01 mg/L of the reference material. The toxicity control attained 87% degradation after 14 days of incubation. Hence, the substance is not toxic to aquatic microorganisms and a NOEC of ≥ 13 mg/L was derived.