Hexyl butyrate

Biodegradation in water: screening tests

Administrative data

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

3 October 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2011

Report date:

2011

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

17 July 1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

Hexyl butyrate

EC Number:

220-136-6

EC Name:

Hexyl butyrate

Cas Number:

2639-63-6

Molecular formula:

C10H20O2

IUPAC Name:

hexyl butanoate

Test material form:

liquid

Specific details on test material used for the study:

Commercial name Hexyl Butyrate
Givaudan Code No.: 3069001
Chemical nature Butanoic acid, hexyl ester
Empirical formula C1oH2o02
Molecular weight 172.26 g/mol
CAS No. 2639-63-6
Aspect colourless liquid

Study design

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, evaporating 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 totalvolume (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,
15a and 16a), 5.00 ml of sludge was added (inoculum).

Duration of test (contact time):

ca. 28 d

Initial test substance concentration

Initial conc.:

ca. 30 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

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 oC) 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 chemical (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

Reference substance:

benzoic acid, sodium salt

Results and discussion

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 .

% Degradation

% Degradation 1

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 74

Sampling time:

28 d

% Degradation 2

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 13

Sampling time:

1 d

% Degradation 3

Key result

Parameter:

% degradation (CO2 evolution)

Value:

ca. 59

Sampling time:

11 d

BOD5 / COD results

Results with reference substance:

% biodegradation of reference substance
Days 5 7 14 21 38
% deg. 78 83 94 98 102

See attached appendices for full results.

Any other information on results incl. tables

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.

 

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable, but failing 10-day window

Conclusions:

According to this OECD 301 F study, Hexyl Butyrate should be regarded as readily biodegradable.

Hexyl Butyrate undergoes 74 % biodegradation after 28 days in the test conditions.
The 10-day window criterion is not fulfilled (13% biodegradation on day 1 and 59% on day 11). This should be attributed to the structure of the test substance : Esters are usually not viewed as a single substance by microorganisms. Both hydrolysis products are sequentially degraded , often by different microorganisms. The 10-day window criterion should therefore not be used as a pass fail criterion.
Thus , Hexyl Butyrate should be regarded as readily biodegradable according to this test.
Hexyl Butyrate 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 .

Executive summary:

Hexyl Butyrate undergoes 74 % biodegradation after 28 days in the test conditions.

 

The 10-day window criterion is not fulfilled (13% biodegradation on day 1 and 59% on day 11). This should be attributed to the structure of the test substance : Esters are usually not viewed as a single substance by microorganisms. Both hydrolysis products are sequentially degraded , often by different microorganisms. The 10-day window criterion should therefore not be used as a pass fail criterion.

Thus , Hexyl Butyrate should be regarded as readily biodegradable according to this test.

Hexyl Butyrate 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.