Isodecyl 3,5,5-trimethylhexanoate

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

27 April 2017 to 9 October 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

OECD Guideline 301B, Ready Biodegradability
(Adopted 1981, Revised 1992)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Test Substance
The following details for the test substance, Isotridecyl 3,5,5-trimethylhexanoate, were supplied by the Sponsor:
Test substance name: Isotridecyl 3,5,5-trimethylhexanoate
Synonym: Isotridecyl Isononanoate
Molecular formula: C22H44O2
Molecular weight: 340.59 g/mol
Purity: 100.2%
Date received: 1 March 2017
Storage conditions: Room temperature (15-30°C) protected from light
All test substance details were supplied by the Sponsor. An analysis report is presented in report Appendix 1.
The carbon content, 78%, was calculated from the molecular weight provided by the Sponsor. This carbon content was used in setting the test concentration of Isotridecyl 3,5,5-trimethylhexanoate. No allowance was made for purity.
A solubility trial was performed by weighing a sub-sample (290 mg calculated quantity to ensure 225 mg carbon) of Isotridecyl 3,5,5-trimethylhexanoate into a suitable container and making up to 100 mL with reverse osmosis (RO) water. The test substance did not appear to be in solution and was sonicated for 5 minutes and stirred for 10 minutes. As the test substance was not in solution, it was deemed insufficiently soluble to be added as an aqueous stock solution. Isotridecyl 3,5,5trimethylhexanoate was therefore added directly to the test vessels.

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

A sample of activated sludge was collected from one of the return lines at Burley Menston sewage treatment works (West Yorkshire, UK), which has a predominantly domestic waste-water catchment. The sample was transported in a closed container, but with an adequate headspace, to prevent the sample becoming anaerobic. On arrival, the sample was aerated by means of a compressed air supply.
The suspended solids concentration of the activated sludge was determined by filtering a subsample (25 mL) through a pre-dried and pre-weighed glass microfibre filter (Whatman GF/C). The filter and retained solids were then dried in an oven (nominally 105°C) and re-weighed. The weight of the sludge solids was determined from the difference in the weights before and after drying. The concentration of suspended solids was calculated to be 6.2 g/L.
The activated sludge used in this study was not deliberately acclimatised or adapted to Isotridecyl 3,5,5-trimethylhexanoate before exposure under test conditions.

Duration of test (contact time):

ca. 29 d

Initial conc.:

ca. 15 mg/L

Based on:

IC (inorganic carbon)

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

Preparation of Test Vessels
The study consisted of four treatment groups as described in the following table:

Treatment Group Vessel Contents
Blank control inoculated mineral salts medium
Test substance inoculated mineral salts medium and test substance
Reference substance inoculated mineral salts medium and sodium benzoate
Toxicity control inoculated mineral salts medium, test substance and sodium benzoate

The purpose of the toxicity control was to assess the biodegradation of the reference substance in the presence of the test substance.
Duplicate vessels were prepared for the test substance, reference substance and blank control groups. A single vessel was prepared for the toxicity control.
Preparation of Test Medium.

The test was conducted in an aqueous, synthetic, mineral salts medium. A test medium concentrate was prepared in RO water containing 30 mL/L solution (a) and 3 mL/L of each of solutions (b), (c) and (d). Solutions (a) to (d) were prepared as follows:

(a) potassium dihydrogen phosphate (8.50 g, VWR); dipotassium hydrogen phosphate(21.75 g, VWR); disodium hydrogen phosphate dihydrate (33.40 g, Fisher); ammonium chloride (0.50 g, Fisher), all dissolved in and made up to 1 L with RO water.
(b) calcium chloride dihydrate (36.40 g, VWR), dissolved in and made up to 1 L withRO water.
(c) magnesium sulphate heptahydrate (22.50 g, Sigma-Aldrich), dissolved in andmade up to 1 L with RO water.
(d) ferric chloride hexahydrate (0.25 g, Sigma-Aldrich) and concentrated hydrochloricacid (1 drop, VWR), dissolved in and made up to 1 L with RO water.

On the basis of the suspended solids determined to be 6.2 g/L, the medium was inoculated with activated sludge (116 mL in a total volume of 8 L) to give a suspended solids concentration of 90 mg/L. This provided a nominal final solids concentration of 30 mg/L in each test vessel (500 mL added to a total volume of 1.5 L).

The inorganic carbon (IC) concentration of the inoculated mineral salts medium was determined using an InnovOx carbon analyser. In this analysis, IC in the samples was released as CO2 by acidification with hydrochloric acid. The CO2 was then passed to a non-dispersive infra-red (NDIR) detector. The concentration of carbon dioxide was determined in the NDIR detector, by measuring the amount of infra-red energy absorbed by the sample. A calibration check was performed on each occasion by injecting a series of sodium hydrogen carbonate standards. The existing calibration curve was used to quantify the IC present in the samples. Each sample was analysed in triplicate/quadriplicate.
Treatment of Test Vessels

Isotridecyl 3,5,5-trimethylhexanoate was accurately weighed (29.03 to 29.14 mg) for direct addition to test substance and toxicity control vessels, to give a nominal test substance concentration corresponding to 15 mg carbon/L.
A reference substance stock solution (2.25 g carbon/L) was prepared by dissolving sodium benzoate (1.93 g) in RO water (500 mL). Reference and toxicity control vessels were treated with the stock solution (10 mL), to give a nominal sodium benzoate concentration corresponding to 15 mg carbon/L.

Test Initiation

Following all test and reference substance treatments and addition of the inoculated medium concentrate, the volume in each vessel (including the blank control vessels) was made up to 1.5 L by addition of RO water. Each vessel was sealed, connected to a series of three traps containing aqueous barium hydroxide (nominally 0.0125 M), and the carbon dioxide-free air supply initiated.
Incubation Conditions

The test vessels were incubated in the dark under the conditions below.

Temperature
The incubation and test measurements were conducted at a target temperature range of 22 ± 2°C. During the course of the study, the temperature decreased to 17.6°C. Thereafter temperature settled back to target range. This did not appear to affect the study integrity.

Measurement of pH
Measurements of pH were made in the blank control and reference substance vessels at the start of incubation and in all vessels at the end of the test prior to the addition of the hydrochloric acid. Measured pH values ranged from pH 7.54 to pH 7.66 on Day 0 and pH 7.44 to pH 7.61 on Day 28 (Table 1).

Air Flow
The air used in this study was delivered from a cylinder of CO2-free air (Air Products) and was regulated in two stages. Initial control was provided by a gas regulator and the air flow to each vessel controlled by individual needle valves. Measurements of the flow rate exiting each test vessel were made at intervals not exceeding seven days, with a bubble flow meter and stopwatch. Adjustments were made as necessary to maintain a flow rate of ca 50 mL per minute.

Reference substance:

benzoic acid, sodium salt

Preliminary study:

The inorganic carbon content of the test medium was determined to be 1.93 mg carbon/L, corresponding to 4.29%.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

<= 47

Sampling time:

29 d

Details on results:

Measured CO2 Yields as a Percentage of Theoretical
Carbon dioxide evolution and percentage biodegradation data are presented in Table 2, Table 3 and Figure 1. The mean total carbon dioxide production in the blank control vessels was 43 mg/L (Test end), satisfying the validity criterion of less than 70 mg/L.
Isotridecyl 3,5,5-trimethylhexanoate
To be considered readily biodegradable, a test substance must achieve 60% biodegradation by the end of the test. Additionally, the test substance must biodegrade by at least 60% within 10 days of having degraded by 10%.
Isotridecyl 3,5,5-trimethylhexanoate showed limited biodegradation during the study with a maximum mean biodegradation of 47%. Isotridecyl 3,5,5-trimethylhexanoate cannot, therefore, be considered readily biodegradable.
Percent biodegradation values at each sampling interval, for the two replicates containing Isotridecyl 3,5,5-trimethylhexanoate did not vary by more than 14%, therefore satisfying the validity criterion of less than 20% difference.
Sodium Benzoate
Rapid carbon dioxide generation commenced immediately and declined to a more gradual rate over the period of the incubation as shown in Figure 1. The mean percentage biodegradation had exceeded 60% by Day 7 (66%), 85% by the end of the incubation phase on Day 28 and 86% by the end of the study on Day 29. The validity criterion of 60% biodegradation at 14 days was therefore met.
Toxicity Control
Assessment of biodegradation in the toxicity control was confined to the sodium benzoate fraction. The rate of biodegradation of the reference substance in the presence of Isotridecyl 3,5,5-trimethylhexanoate (63% at Day 7, 75% at the end of the incubation phase on Day 28 and 76% by the end of the test on Day 29) was higher than that of the reference substance alone. This suggests that Isotridecyl 3,5,5 trimethylhexanoate had no inhibitory effect on the sludge microorganisms under the test, the test was considered to be valid.

Results with reference substance:

Sodium Benzoate
Rapid carbon dioxide generation commenced immediately and declined to a more gradual rate over the period of the incubation as shown in Figure 1. The mean percentage biodegradation had exceeded 60% by Day 7 (66%), 85% by the end of the incubation phase on Day 28 and 86% by the end of the study on Day 29. The validity criterion of 60% biodegradation at 14 days was therefore met.
Toxicity Control
Assessment of biodegradation in the toxicity control was confined to the sodium benzoate fraction. The rate of biodegradation of the reference substance in the presence of Isotridecyl 3,5,5-trimethylhexanoate (63% at Day 7, 75% at the end of the incubation phase on Day 28 and 76% by the end of the test on Day 29) was higher than that of the reference substance alone. This suggests that Isotridecyl 3,5,5trimethylhexanoate had no inhibitory effect on the sludge microorganisms under the test, the test was considered to be valid.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

All validity criteria were satisfied (inorganic carbon content, degradation of reference material, CO2 production from blank controls) and the results of this study are therefore considered to be valid.
No inhibitory effect was observed on the biodegradation of the reference substance in the presence of Isotridecyl 3,5,5-trimethylhexanoate.
Mean carbon dioxide evolution from Isotridecyl 3,5,5-trimethylhexanoate was < 60% of the theoretical carbon dioxide yield throughout the test. The level of biodegradation did not meet the requirements for ready biodegradability and Isotridecyl 3,5,5 trimethylhexanoate cannot, therefore, be classified as readily biodegradable.

Executive summary:

The ready biodegradability of Isotridecyl 3,5,5-trimethylhexanoate was assessed by measurement of carbon dioxide (CO₂) evolution under standard conditions. The procedure followed was that of OECD Guideline 301B, Ready Biodegradability (Adopted 1981, Revised 1992).

The test substance, Isotridecyl 3,5,5-trimethylhexanoate, was added to the test system as a direct addition. Buffered mineral salts medium was added to give a test substance concentration equivalent to 15 mg organic carbon/L. The medium was inoculated with microorganisms derived from a sample of activated sludge not previously intentionally exposed to the test substance. Test vessels were incubated in darkness at 22 ± 2°C for 28 days and their contents continuously sparged with a supply of CO₂-free air. The exhaust air from each vessel was passed through a series of traps containing a barium hydroxide solution to trap evolved CO₂.

At regular intervals during the incubation, traps were detached and their contents titrated with hydrochloric acid to determine the quantity of CO₂evolved from the respective test vessels. At the end of incubation, 28 days, the test vessel contents were acidified to release any residual CO₂that may have remained in solution. Titration of the traps was performed following overnight aeration.

The procedure and the activity of the inoculum were checked by measuring the CO₂evolved from vessels containing a reference substance, sodium benzoate. An additional vessel containing a combination of the test and reference substances served as a toxicity control to assess whether the test substance was inhibitory to biodegradation at the test concentration. Two blank control vessels were also prepared containing inoculated medium only. The results of these vessels were used to check the validity of the test and to correct the evolved CO₂values.

Isotridecyl 3,5,5-trimethylhexanoate showed < 60% biodegradation during the incubation. As a result, Isotridecyl 3,5,5-trimethylhexanoate cannot be considered readily biodegradable.

The mean total CO₂production in the blank control vessels was 43 mg/L at the end of the test, satisfying the validity criterion of < 70 mg/L.

Mean biodegradation of the reference substance had exceeded 60% by Day 7 and had reached 85% by the end of the incubation phase on Day 28 and 86% at the end of the test on Day 29. The corrected rate of biodegradation of the reference substance in the presence of Isotridecyl 3,5,5-trimethylhexanoate (63 % at Day 7, 75% by the end of the incubation phase on Day 28 and 76% at the end of the test on Day 29 test) was similar to that of the reference substance alone, suggesting that Isotridecyl 3,5,5trimethylhexanoate did not have an inhibitory effect on the sludge microorganisms under the test conditions and the test was considered to be valid.

The inorganic carbon content of the test medium was determined to be

1.93 mg carbon/L, corresponding to 4.29% satisfying the validity criterion of < 5%.

All validity criteria were satisfied, the blank controls and reference vessels performed as expected, and the results of this study are therefore considered to be valid.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

The biodegradation of the target substance will be substantially similar to the biodegradation of the source substance because the related properties (organic liquids with exceedingly low water solubility and vapour pressures) are substantially similar and there is a relationship between the biodegradation mechanism and the chemical structures. As the target substance has a shorter chain length (C10 cf C13) it is expected that the biodegradation of the source substance will potentially underestimate the biodegradation of the target substance. However, the structural and functional similarities between these 2 substances means that any differences seen between the biodegradation rates will be relatively small and that read-across is therefore appropriate.

Reason / purpose for cross-reference:

read-across source

Parameter:

% degradation (CO2 evolution)

Value:

<= 47

Sampling time:

29 d

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable, not fulfilling specific criteria

Type of water:

freshwater