Hexanoic acid

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:

30 Apr - 04 Jun 1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: ISO 10708

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

Principles of method if other than guideline:

28 days BOD/COD test: Inoculated mineral salt medium was filled in glass flasks of known volume. After a one-week preincubation at 20 °C, the medium was saturated with oxygen and the test substance was added. The closed flasks were incubated on a shaker at 20 ± 1 °C and biodegradation was monitored through regular oxygen measurements. An inoculum blank (inoculated medium without test substance) and a positive control (sodium acetate as reference substance) accompanied the experiments.

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Activated sludge was obtained from the sewage treatment plant Ohligs, Germany

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

COD

Initial conc.:

49 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS:
Glass flasks were filled with 200 mL mineral salt medium and inoculated with activated sludge (30 mg dry matter/L). After a one-week preincubation at 20 °C, the medium was saturated with oxygen and the test substance was added (approx. 20 mg COD/flask). The closed flasks were incubated on a shaker at 20 ± 1 °C and biodegradation was monitored through regular oxygen measurements.

SAMPLING
- Sampling frequency: Measurement of oxygen after 7, 14, 21, 28 days

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes

Reference substance:

acetic acid, sodium salt

Parameter:

% degradation (O2 consumption)

Value:

84

Sampling time:

28 d

Parameter:

COD

Value:

2.128 g O2/g test mat.

Table: Biodegradation of the test substance in the BODIS test

Test substance	Test Concentr. (mg COD/L)	% Degradation (BOD/COD) after x days
		7	14	21	28
Hexanoic acid	100	57	70	79	84
Sodium acetate	100	62	73	79	79

Interpretation of results:

readily biodegradable

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

12 Sep - 10 Oct 1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Sewage was obtained from the municipal sewage treatment plant Hochdahl, Germany.

Duration of test (contact time):

28 d

Initial conc.:

2 mg/L

Based on:

act. ingr.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS:
Glass flasks were filled with mineral salt medium and inoculated with one drop of sewage/L. The closed flasks were incubated on a shaker at 20 ± 1 °C and biodegradation was monitored through regular oxygen measurements using the method of iodometric oxygen determination.

SAMPLING
- Sampling frequency: Measurement of oxygen after 7, 14, 22, 28 days

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (O2 consumption)

Value:

86

Sampling time:

28 d

Details on results:

The result of 86% degradation of the test substance after 28 d is based on the initial concentration of 2 mg/L.
The initial concentration of 5 mg/L was also tested but led to a depletion of oxygen in the closed bottles due to the good biodegradability of the test substance.

Parameter:

COD

Value:

2.128 g O2/g test mat.

Results with reference substance:

The reference substance sodium benzoate attained 85% degradation after 28 days.

Table: Biodegradation of the test substance in the closed bottle test

Test substance	Test Concentr. (mg COD/L)	% Degradation (BOD/COD) after x days
		7	14	22	28
Hexanoic acid	2	78	85	91	86
	5	68	82	79	81 (a)
Sodium benzoate	2	77	77	85	85

 (a) The lower degradation values for the 5 mg/L test concentration can be explained by oxygen depletion due to the good biodegradability, i.e. the given values are minimum values.

Description of key information

Readily biodegradable (84 % after 28 d based on O2-consumption, performed similar to OECD 301 D)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

For hexanoic acid (CAS 142 -62 -1) two GLP-studies on the ready biodegradability are available.

In the first study (Richterich, 1991), which is used as key study, a BODIS-test, similar to OECD 301 D was performed. The substance (100 mg/L) was directly weighend in a glass flask by using a glass plate as carrier. Resulting from the test, the biodegradability of hexanoic acid was determined to be 84% based on O2 -consumption after 28 days.

In the second test performed by Richterich (1992), hexanoic acid was pre-solved in an emulsifier (NP 9,5 EO + 5 PO). The study was conducted according to OECD 301D. After 28 days a degradation of 86% of the test substance was reported based on O2 -consumption.

Concluding from the results of both tests, hexanoic acid (CAS 142 -62 -1) is regarded as readily biodegradable.