Hexyl propionate

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

4th October 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Version / remarks:

Paris, 1992

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Commercial name: Hexyl Propionate
Givaudan Code No.: 8446841
Chemical nature Propanoic acid, hexyl ester
Empirical formula C9H1802
Molecular weight 158.24 g/mol
CAS No. 2445-76-3
Aspect colourless liquid

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

Fresh activated sludge from a biological waste water treatment plant treating predominantly domestic sewage (Bois-de-Bay, Satigny, Switzerland) was used.
The sludge is collected in the morning, washed three times in the mineral medium (by centrifuging at 1000 g for 10 minutes , discarding the supernatant and resuspending in mineral medium) and kept aerobic until being used on the same day.
The dry weight of suspended solids is determined by taking two 50 ml samples of the homogenised sludge, evaporat ing water on a steam bath, drying in an oven at 105 - 110 °C for two hours and weighing the residue.

Dry weight of suspended solids : 5.065 g/1, diluted to 1.53 g/1

To obtain a concentration of 30 mg/1 (dry weight) in 103 ml total volume (Flasks 17a and 18a), 2.00 ml of sludge was added (inoculum).

To obtain a concentration of 30 mg/1 (dry weight) in 255 ml total volume (Flasks 1a, 2a, 9a and 10a), 5.00 ml of sludge was added (inoculum).

Duration of test (contact time):

ca. 28 d

Initial conc.:

ca. 30 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

Principle

The method used is basically the one described under No. 301 F in the OECD Guidelines for Testing of Chemicals.

A measured volume of inoculated mineral medium, containing a known concentration of test substance as the nominal sole source of organic carbon, is stirred in a closed flask at a constant temperature (± 1 °C) for up to 28 days. Evolved carbon dioxide is absorbed in sodium hydroxide pellets. The consumption of oxygen is determined by measuring the pressure drop in the respirometer flask. The Biological Oxygen Demand (BOD), amount of oxygen taken up by the microbial population during biodegradation of the test chemica l (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of ThOD (Theoretical Oxygen Demand , calculated from the elemental composition , assuming that carbon is oxidized to carbon dioxide, hydrogen to water and nitrogen to ammonium, nitrite or nitrate) .

Apparatus

The respirometer used during this study is an Oxitop Control System, made by Wissenschaftlich -Technische Werkstatten (WTW), Weilheim , Germany.

Water

The water used during this study is deionised water containing less than 10 mg/1
dissolved organic carbon.

Stock solutions of mineral components The following stock solutions were prepared:

Solution A

KH2P04 8.5 g
K2HP04 21.75 g
Na2HP04 · 2 H20 33.4 g
NH4CI 0.5 g
dissolved in water and made up to 1 litre

Solution B

CaCl2 27.5 g
dissolved in water and made up to 1 litre.

Solution C

MgSO4.7H2O 22.5 g
dissolved in water and made up to 1 litre.

Solution D

FeCl3.6H2O 0.25 g
HCl (conc. one drop
dissolved in water and made up to 1 litre.

Mineral medium

Prepared by mixing 50 ml of solution A and 2000 ml deionised water, adding 5 ml of each of the solutions B, C and D and making up to 5 litres with deionised water. The pH is measured and if necessary adjusted to 7.4 ± 0.2 with phosphoric acid or potassium hydroxide.

Reference substance

Sodium benzoate (Fiuka, Buchs, Switzerland ,Art . No. 71300), purity : min. 99.0 %.

Preparation of the flasks

Test substance samples (7.65 mg, corresponding to 30.0 mg/1 in 255 ml of test medium) are weighed in small aluminium boats and added directly to the test flasks of the Oxitop, whereas reference the substance (sodium benzoate) is added as 1.00 ml of a 10.2 g/1 solution in mineral medium , to give a total volume of 103 mi.

Flasks are filled with 250 ml of mineral medium (flasks containing reference substance : 100 ml). Samples of test or reference substance are added. Then suspended sludge diluted to a concentration of 1.53 g/1 dry matter is added. Except when the test substance has an acid or alkaline character, the pH of each flask is not measured but assumed to be the same as the mineral medium (see 'Mineral medium'), in order not to remove any floating undissolved test substance from the test medium by dipping a glass electrode in it. Neutral test substances, even sodium benzoate, were shown not to affect the pH of the medium by more than 0.1 pH unit. Two sodium hydroxide pellets are placed in the quivers on top of the bottle, and the flasks are closed tightly with the measuring heads. The flasks are allowed to equilibrate to the test temperature . The measurement is started by programming the measuring unit of the Oxitop test flasks , and the test flasks are placed in the temperature controlled cupboard of the Oxitop system. After temperature equilibration , the controller of the instrument starts the data acquisition (time zero of the experiment) .

Performance of the test

Everyday the oxygen consumption of each flask is recorded and correct temperature and stirring are checked .

At the end of the test period (normally 28 days) , the pH of each flask is measured again.

Reference substance:

benzoic acid, sodium salt

Preliminary study:

An optional toxicity control as suggested by OECD guideline 301 F was not performed.
The validity of the study is not adversely affected .

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 79

Sampling time:

28 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 28

Sampling time:

2 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 70

Sampling time:

12 d

Results with reference substance:

Degradation of sodium benzoate exceeded 40 % after 7 days and 65 % after 14 days (flask 18a): the activity of the inoculum was thus verified (validity criterion).

Test temperature 22.3 °C to 22.9 °C

Deviations from guidelines, study plan and standard operating procedures

 

An optional toxicity control as suggested by OECD guideline 301 F was not performed.

The validity of the study is not adversely affected .

 

Duplicate flasks (flasks 17a and 18a) were foreseen as procedural control in the study plan. Erroneously high oxygen consumption was observed on flask 17a. Therefore the results for this flask were not taken into consideration for this study. As the OECD Guideline 301F foresees a single flask for the procedural control this does not represent a guideline deviation ,the validity of the study is not adversely affected.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

According to this OECD 301F test, Hexyl Propionate should be regarded as readily biodegradable.

Hexyl Propionate undergoes 79 % biodegradation after 28 days in the test conditions. The 10-day window criterion is also fulfilled (28 % biodegradation on day 2 and 70 % on day 12).
Hexyl Propionate did not inhibit the intrinsic respiration of the inoculum at the test concentration and was therefore considered to be non-toxic to the inoculum at the test concentration .
Thus , Hexyl Propionate should be regarded as readily biodegradable according to this test.

Executive summary:

Hexyl Propionate undergoes 79 % biodegradation after 28 days in the test conditions. The 10-day window criterion is also fulfilled (28 % biodegradation on day 2 and 70 % on day 12).

 

Hexyl Propionate did not inhibit the intrinsic respiration of the inoculum at the test concentration and was therefore considered to be non-toxic to the inoculum at the test concentration .

 

Thus , Hexyl Propionate should be regarded as readily biodegradable according to this OECD 301F test.

Description of key information

Study conducted to international testing guideline with GLP certification.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater