3,5,5-trimethylhexanoic acid

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:

experimental phase: 15 Mar 2010 to 06 Apr 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 A (Ready Biodegradability: DOC Die Away Test)

Qualifier:

according to guideline

Guideline:

EU Method C.4-A (Determination of the "Ready" Biodegradability - Dissolved Organic Carbon (DOC) Die-Away Test)

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): wastewater treatment plant (ARA Ergolz II, Füllinsdorf / Switzerland) treating predominantly domestic wastewater
- Storage conditions: room temperature
- Storage length: 1 d
- Preparation of inoculum for exposure:sludge was washed twice with tap water by centrifugation; supernatant liquid was decanted
- Pretreatment: The sludge was aerated at room temperature during holding period of one day prior to use
- Concentration of sludge: 30 mg dry material/L
- Initial cell/biomass concentration: 4 g (±10%) dry material/L
- Water filtered: yes
- Type and size of filter used, if any: no data

Duration of test (contact time):

21 d

Initial conc.:

ca. 30 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

TEST CONDITIONS
- Composition of medium: according to guideline
- Additional substrate: no
- Solubilising agent (type and concentration if used): none used
- Test temperature: 22-24 °C
- pH: 7.8
- pH adjusted: yes
- Aeration of dilution water:
- Suspended solids concentration: 30 mg dry material/L
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: 2000-mL Erlenmeyer flask (final volume: 1000 mL; loosely covered with aluminum foil)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: sludge aerated for one day prior to use
- Test performed in closed vessels due to significant volatility of test substance: no
- Test performed in open system: yes

SAMPLING
- Sampling frequency: Exposure Day 0, 3, 7, 10, 14 and 21
- Sampling method: One sample of about 10 mL was taken from each test flask per sampling date.
- Sample storage before analysis: analysed for DOC on day of sampling

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2
- Toxicity control: 1
- Other: Procedure control: 2

Reference substance:

benzoic acid, sodium salt

Remarks:

(ca. 30 mg/L DOC)

Test performance:

In accordance with the testing guidelines, the test was ended ahead of schedule since the biodegradation curves of the test and reference item had reached a plateau for at least three determinations.

Parameter:

% degradation (DOC removal)

Value:

96

Sampling time:

21 d

Parameter:

% degradation (DOC removal)

Value:

96

Sampling time:

14 d

Parameter:

% degradation (DOC removal)

Value:

92

Sampling time:

10 d

Parameter:

% degradation (DOC removal)

Value:

79

Sampling time:

7 d

Parameter:

% degradation (DOC removal)

Value:

1

Sampling time:

3 d

Results with reference substance:

In the procedure controls, containing the reference item sodium benzoate and activated sludge (inoculum), sodium benzoate was completely biodegraded (>90%) within seven days of exposure, thus confirming suitability of the activated sludge.

Dissolved Organic Carbon Concentration (DOC) in the Test Flasks

	DOC(mg/L)^1,3
	Test item			Procedure control			Inoculum control			Toxicity control
Time	ReplicateNo.			ReplicateNo.			ReplicateNo.			ReplicateNo.
(days)	1	2	mean^2	1	2	mean^2	1	2	mean	1^2
0	30.9	33.6	29.7	31.8	30.9	28.8	3.2	2.0	2.6	57.4
3	30.3	32.2	29.4	2.3	2.4	0.5	1.8	1.9	1.9	n.d.
7	6.2	9.9	6.3	2.1	2.1	0.3	1.8	1.8	1.8	14.7
10	3.8	4.9	2.4	n.d.	n.d.	n.d.	2.0	2.0	2.0	n.d.
14	4.1	3.5	1.2	2.5	2.1	-0.4	2.0	3.3	2.7	3.0
21	4.3	2.7	1.0	3.8	2.1	0.5	2.5	2.5	2.5	0.7

¹Mean values of at least triplicate measurements per sample

²Values corrected for the inoculum controls

³Sampling was ended before 28 days because the biodegradation curves reached a plateau for at least three determinations

n.d. not determined

Percentage Biodegradation in the Test Flasks

	Percentage Biodegradation^1,2
	Test item			Procedure control^2			Toxicity control
Time	Replicate No.			Replicate No.			Replicate No.
(days)	1	2	mean	1	2	mean	1
0	0	0	0	0	0	0	0
3	-1	2	1	98	98	98	n.d.
7	84	74	79	99	99	99	74
10	94	91	92	n.d.	n.d.	n.d.	n.d.
14	95	97	96	101	102	101	95
21	94	99	96	95	101	98	99

¹Corrected for the inoculum controls

²Sampling was ended before 28 days because the biodegradation curves reached a plateau for at least three determinations

n.d. not determined

pH Values at the Start and at the End of the Test

Replicate No.	Identification	pH
		Start	End
1	Test Item	7.2 / 7.4*	7.6
2	Test Item	7.2 / 7.4*	7.5
1	Procedure control	7.3 / 7.4*	7.5
2	Procedure control	7.3 / 7.4*	7.5
1	Inoculum control	7.3 / 7.4*	7.4
2	Inoculum control	7.3 / 7.4*	7.4
1	Toxicity control	7.2 / 7.4*	7.6

* before/after adjustment

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

3,5,5-Trimethylhexanoic acid is readily biodegradable according to OECD 301A (Harlan, 2010).

Executive summary:

The ready biodegradability of 3,5,5 -trimethylhexanoic acid was tested according to OECD 301A (DOC Die-Away Test). Non-adapted activated sludge from a wastewater treatment plant receiving predominantely domestic sewage was used as inoculum. Biodegradation was monitored as DOC removal. After 21 d, the mean biodegradation of the test item 3,5,5 Trimethylhexanoic acid based on DOC decrease amounted to 96 %. In conclusion,the test item 3,5,5 -trimethylhexanoic acid can be classified as readily biodegradable under the test conditions.

Description of key information

 3,5,5-trimethylhexanoic acid is readily biodegradable (OECD 301A; Harlan, 2010)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The ready biodegradability of 3,5,5 -trimethylhexanoic acid was studied in a DOC Die-Away Test according to OECD 301A (Harlan, 2010). The biodegradation reached 96% after 21 d based on DOC removal. The 10 -d window was passed. From the value determined after 3 days (1% biodegradation on average) potential DOC losses due to sludge adsorption can be ruled out. In conclusion, 3,5,5 -trimethylhexanoic acid is readily biodegradable.

Further studies are available (see table below), however with the exception of one study (Zahn & Wellens, 1980) the reliability of these studies is not assignable due to poor documentation. This latter spporting study (RL 2) on inherent biodegradability comfirms the ready biodegradability of the submission substance determined in the reliable key study, in that 80% of the chemical oxygen demand (COD) was degraded within 14 days.

Test method	Inoculum	Result	Evaluation	Reliability	Source
OECD 301 A	activated sludge, domestic, non-adapted	96% in 21 d	readily biodegradable	1	Harlan (2010)
OECD 301 B	no data	73 % ThCO2/DOC removal in 25 d (10-d window met)	readily biodegradable	4	Wellens (1986a)
OECD 301 B	no data	63 % ThCO2/DOC removal in 25 d (10-d window failed)	(not) readily biodegradable and failing 10-d window	4	Wellens (1986b)
OECD 302 B	activated sludge	100 % DOC removal in 20 d	inherently biodegradable	4	Wellens (1986c)
Batch method (similar to OECD 302 B)	activated sludge, not adapted	80 % BOD of COD in 14 d	inherently biodegradable	2	Zahn & Wellens (1980)
Batch method (similar to OECD 302 B)	activated sludge, not specified	95 % of COD removal in 15 d	inherently biodegradable	4	Wellens (1975a)