Undecanal

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:

Test performed from 10 May 2010 to 09 June 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

adopted July 1992

Deviations:

yes

Remarks:

The temperature was a slightly higher than stated in the guideline. As all validity criteria were met, this deviation can be stated as uncritical.

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): The sludge was taken from the activation basin of the sewage treatment plant D-67480 Edenkoben. Date of collection: 07. May 2010, batch no: 20100507.
- Pretreatment: The sludge was filtrated, washed with tap water twice, then washed with and re-suspended in test medium. It was then aerated for >= 12 hours.
- Concentration of sludge: 4040 mg suspended solids dw/litre.
- Initial cell/biomass concentration: 25.0 mg/L
- Water filtered: no
- Type and size of filter used, if any: not stated

Duration of test (contact time):

28 d

Initial conc.:

26.2 - 27.3 mg/L

Based on:

test mat.

Initial conc.:

20 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: according to guideline
- Additional substrate: no
- Solubilising agent (type and concentration if used): no
- Test temperature: 19.4 – 22.6 °C
- pH: 6.99 to 7.58 (day 28, all vessels)
- pH adjusted: no
- CEC (meq/100 g):
- Aeration of dilution water: yes
- Suspended solids concentration: 25 mg/L
- Continuous darkness: yes/no
- Other:

TEST SYSTEM
- Culturing apparatus: 2000 mL-SCHOTT-flasks (flask volume: 1500 mL)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: flasks were aerated for 72 hours with purified, CO2-free, moistened air to purge the system of CO2.
- Method used to create anaerobic conditions: not applicable
- Measuring equipment: carbon analyser TOC multi N/C 2100S, Analytik Jena
- Test performed in closed vessels due to significant volatility of test substance:
- Test performed in open system: no
- Details of trap for CO2 and volatile organics if used: 100 mL scrubber flasks containing 1.5-molar NaOH; the initial IC value of the 0.25 m-NaOH was separately determined in each flask.
- Other:

SAMPLING
- Sampling frequency: samples taken on days: 0, 2, 4, 7, 9, 11, 15, 18, 29
- Sampling method: samples (1 mL) taken from first scrubber flask
- Sample storage before analysis: not applicable
- Other: On day 28, 5 mL HCl 2 molar. were added to each test flask in order to drive off dissolved CO2. On day 29, samples from both scrubber flasks were taken.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2
- Abiotic sterile control: 1
- Toxicity control: 1
- Other: 2 positive controls (positive control, mineral medium and inoculum)

Reference substance:

aniline

Parameter:

% degradation (CO2 evolution)

Value:

9

Sampling time:

2 d

Parameter:

% degradation (CO2 evolution)

Value:

24

Sampling time:

4 d

Parameter:

% degradation (CO2 evolution)

Value:

46

Sampling time:

11 d

Parameter:

% degradation (CO2 evolution)

Value:

61

Sampling time:

15 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

65

Sampling time:

29 d

Details on results:

See IUCLID section "Any other information on results incl. tables" below.

Results with reference substance:

Degradation of the positive control aniline was 63 % after nine days.

pH values in test flasks on day 28

Day	Control 1	Control 2	Positive Control 1	Positive Control 2	Test 1	Test 2	Abiotic Control	Toxicity Control
28	7.47	7.58	7.35	7.43	7.58	7.60	6.99	7.41

Details on measured inorganic carbon values is given in tables 8.1.a through 8.1e within the illustration attached to this robust study summary. Details on evaluation of measured inorganic carbon values is given in sections 8.1.2 and 8.2.1 with intermediate results given in tables 8.1.e, 8.1.f, and 8.3.a, all contained in the afore mentioned illustration.  From emitted carbon values (mg/L; table 8.3.a), % degradation values were calculated based on the ThCO2 calculated from the molecular formula:

Degradation (% CO2 of ThCO2)

Day	Positive Control 1	Positive Control 2	Positive Control Mean	Test 1	Test 2	Test Mean	Abiotic Control	Toxicity Control
2	0.7	-0.8	0.0	5.4	13.0	9.2	2.1	4.0
4	20.0	14.8	17.4	22.8	24.9	23.8	2.6	33.0
7	42.0	49.9	46.0	30.2	31.8	31.0	3.4	46.9
9	57.2	69.0	63.1	37.3	43.5	40.4	5.0	51.4
11	68.2	74.9	71.6	44.1	48.2	46.2	4.1	51.4
15	81.3	91.5	86.4	57.5	64.4	61.0	5.9	62.3
18	86.9	94.8	90.8	51.9	68.5	60.2	6.5	62.8
29	83.1	91.0	87.0	59.5	70.1	64.8	5.5	57.7

A plot of the course of biodegradation over time is given within the illustration attached to this robust study summary.

Validity

All validity parameters and values are presented in the following table:

Validity

Parameter	Criterion	Found	Assessment
IC content of test item solution in medium	<=5% of TC	<1 %	valid
CO2emitted by the controls	< 70 mg/L	10.3 mg/L	valid
Difference within replicates	<=20%	10.6 %	valid
Degradation of positive control > 60%	< 14 days	9 days	valid
Degradation in the toxicity flask on day 14	> 25%	60 %	valid

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable, but failing 10-day window

Conclusions:

n-Undecanal is readily biodegradable, but failing 10-day window (OECD 301B, 65% after 28 d).

Executive summary:

The ready biodegradability of n-undecanal was tested in a valid and reliable study performed compliant with GLP according to OECD 301B (CO2 evolution test). The inoculum was activated sludge from a wwtp treating predominantely domestic sewage. CO2 was followed to determine the degree of biodegradation. The degree of biodegradation reached 65 % after 28 days. Therefore, the test item is biodegradable. The 10-day-window began on day 3, at its end, 58% were reached, missing the pass level of 60 % given in the OECD guideline only barely. The abiotic degradation reached 5.5 %. As degradation in the toxicity flask was 60% after 14 days, the test item can be stated as “not toxic towards the inoculum in a concentration of 25.9 mg/L”.

In conclusion, n-undecanal is readily biodegradable.

Description of key information

n-Undecanal is readily biodegradable, but failing 10-day window (OECD 301B, 65% after 28 d).

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable but failing 10-day window

Type of water:

freshwater

Additional information

In the available key study, the ready biodegradability of n-undecanal was tested in a valid and reliable study according to OECD 301B performed compliant with GLP. The inoculum was activated sludge from a waste water treatment plant treating predominantly domestic sewage. The test item was tested at a concentration of 26.8 mg/L in duplicate; corresponding to a carbon content of 20.8 mg C/L. CO2 was followed to determine the degree of biodegradation. Any relevant inoculum toxicity could be ruled out by the results from the toxicity control included in the test. Under the conditions of this test, the degree of biodegradation of n-undecanal reached 65% after 28 days. Therefore, the test item is biodegradable. The 10-day-window began on day 3, at its end at day 13 degradation extent reached 58%, missing the pass level of 60% given in the OECD guideline only barely. The result must be regarded as conservative: due to the volatile nature of the test item (Henry's law constant: 64.3 Pa*m^3/mol) and the design of the Modified Sturm Test (test flasks are continuously aerated by the passage of carbon dioxide-free air) a continuous loss of test item to the air must be assumed, being accelerated by the permanent air stream passing the flask and leading to a high concentration gradient from liquid to air. Accordingly, there was a competition between volatilisation and biodegradation, with both pathways contributing to the decline of test item in the flask. However, removal by volatilisation is not accounted for in the experimental set-up, as only CO2 is being trapped in the sodium hydroxide solution. Rather, biodegradation extent is expressed by the ratio of CO2 evolved versus the full initially available test item concentration. The actually reduced test item concentration available for biodegradation as a result of partial volatilisation is not accounted for, leading to an underestimation of biodegradation extent. Based on the results of this test, n-undecanal is readily biodegradable, but failing the 10-day window.

Considering the volatile nature of the test item and bearing in mind the draw-back of the key study (anticipated loss of test item from the test system during the course of the test due to volatility, and associated underestimation of degradation extent), a new study (supporting study) was performed according to OECD TG 310 (Headspace test). The headspace test was chosen because of its appropriateness for the volatile test item. Non-adapted activated sludge served as inoculum, total duration of the test was 28 days. The test item was tested at a concentration of 13.66 mg/L in triplicate (test end: 5 replicates), corresponding to a carbon content of 10.4 mg C/L. The biodegradation of the test item was followed by TIC analyses of the quantity of CO2 produced by the respiration of bacteria. The activity of the test system was confirmed via two different reference items, sodium benzoate (60% within 7 days; 97% on day 28) and the moderately volatile 1-Octanol (60% within 7 days; 100% on day 28). Any relevant inoculum toxicity could be ruled out by the results from the toxicity control included in the test. However, the test item n-undecanal unexpectedly failed the pass-level for ready biodegradability (≥ 60% mineralisation) under the conditions of this test, based on a maximum mineralisation extent of 44% (day 21) and a mineralisation of 43% after 28 days (95% CI day 28: 38 – 46%). A possible reason for this may be deduced from the shape of the biodegradation curve:

The biodegradation curve of the test item in the OECD 310 test is characterised by a fast on-set of mineralisation and the formation of a plateau already between 14 and 16 days, such that between sampling days 21 and 28 there was no further increase of mineralisation extent of n-undecanal at all (maximum day 21: 44% mineralisation). Accordingly, already at the first day of sampling (day 4), 20% mineralisation was observed, corresponding to 45% of the maximum mineralisation extent achieved after 21 days. At the second sampling day (day 7), 24% mineralisation was observed, corresponding to 55% of the maximum achieved mineralisation extent (day 21). A biodegradation curve like this normally indicates the decrease of biodegradation rate due to a rapid decline in substrate, with the plateau indicating the ceasing of biodegradation at all due to the insufficient concentration of organic carbon remaining. Due to the closed flasks and the limited headspace in the OECD 310 test, the possible loss due to volatilisation is very limited and cannot be the reason for this observation. Rather, a relevant fixation of the oxidation product of n-undecanal, the fatty acid undecanoic acid, is likely: because n-undecanal is quickly and abiotically transformed to the fatty acid undecanoic acid (as could analytically be demonstrated in preliminary testing for ecotoxicity tests on Algae and Daphnia), which then is obviously rapidly bio-transformed to CO2 by 44%, microbial degradation (shortening) of the hydrocarbon chain obviously presents no obstacle to microorganisms as might be expected from the linear structure (hydrocarbon chain); accordingly, accumulation of 56% (100% - 44% mineralized) recalcitrant metabolites is highly improbable. Rather, the readily utilisable fatty acid is transformed into microbial biomass, such that only a limited extent of the initially added organic carbon is left for mineralisation to CO2. This explains the steep incline of the biodegradation curve and the observed plateau forming already after ca. 14 days (fast mineralisation) but at a mineralization extent of only ca. 44% (limitation of substrate for mineralization due to fixation into biomass).

With regard to the higher degradation extent of 65% after 28 days observed in the valid key study, it is important to note that fairly accurate twice the initial test item concentration was applied in this study compared to the OECD 310 test (20.8 mg C/L versus 10.4 mg C/L) at approximately the same initial concentration of microorganisms. At comparable absolute fixation of test item into biomass (due to comparable biomass concentration) a higher relative carbon fraction may have been available for respiration into CO2 at the higher test item concentration applied in the OECD 301B test, leading to the higher mineralisation extent within 28 days compared to the OECD 310 test.

Concluding, while failing the pass level of 60%, study results of OECD 310 demonstrate the very fast biodegradability of the test item and thus corroborate the results of the key study. According to the conservative nature of the key study (not accounting for volatilisation losses), n-undecanal is demonstrated to be (at least) readily biodegradable failing the 10-day window criterion.