Nickel bis(2-ethylhexanoate)

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:

January-February 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO DIS 9439 (Ultimate Aerobic Biodegradability - Method by Analysis of Released Carbon Dioxide)

Deviations:

no

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): activated sludge freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch

The freshly obtained sludge was kept under continuous aeration until further treatment. The concentration of suspended solids was 3.2 g/l in the concentrated sludge. Before use, the sludge was allowed to settle (50 minutes) and the liquid was decanted for use as inoculum at the amount of 10 ml/l of mineral medium.

Duration of test (contact time):

28 d

Initial conc.:

18 mg/L

Based on:

test mat.

Initial conc.:

10 mg/L

Based on:

other: TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS:

measurements
- pH: At the start of the test and on the 28th day.
- Temperature of medium: Continuously in a vessel with Milli-RO water in the same room.
- Test vessels: 2 litre all-glass brown coloured bottles
- Milli-RO / Milli-Q water: Tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q).

Stock solutions of mineral components:
A)  8.50 g KH2PO4; 21.75 g K2HPO4; 67.20 g Na2HPO4.12H2O ; 0.50 g NH4Cl : dissolved in Milli-Q water and made up to 1 litre, pH 7.4 ± 0.2
B)  22.50 g MgSO4.7H2O dissolved in Milli-Q water and made up to 1 litre.
C)  36.40 g CaCl2.2H2O dissolved in Milli-Q water and made up to 1 litre.
D)  0.25 g FeCl3.6H2O dissolved in Milli-Q water and made up to 1 litre.
Mineral medium: 1 litre mineral medium contains: 10 ml of solution (A), 1 ml of solutions (B) to (D) and Milli-RO water.

TEST SYSTEM and SAMPLING :

preparation of bottles
- Pre-incubation medium: Mineral components, Milli-RO water (ca. 80% total volume) and inoculum (1% final volume) were added to each bottle.
This mixture was aerated with synthetic air overnight to purge the system of CO2.

- Type and number of bottles:
Test suspension: containing test substance and inoculum (2 bottles).
Inoculum blank: containing only inoculum (2 bottles)
Positive control: containing reference substance and inoculum (1 bottle).
Toxicity control: containing test substance, reference substance and inoculum (1 bottle).

- Preparation:
The test substance and positive control were added to the bottles containing the microbial organisms and mineral components (ca. 80% of total volume).
The volumes of suspensions were made up to 2 litres with Milli-RO water, resulting in the mineral medium described before.
Three CO2-absorbers (bottles filled with 100 ml 0.0125 M Ba(OH)2) were connected in series to the exit air line of each test bottle.

DETERMINATION OF THE RESULT:
- Determination of CO2
The CO2 produced in each test bottle reacted with the barium hydroxide in the gas scrubbing bottle and precipitated out as barium carbonate. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl.

Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until the 28th day, for the inoculum blank and test suspension.
Titrations for the positive and toxicity control were made at least 14 days.
Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers was moved one position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series.
Phenolphthalein was used as pH-indicator.
On the 28th day, the pH of all test suspensions was measured and 1 ml of concentrated HCl (37%) was added to the bottles of the inoculum blank and test suspension. The bottles were aerated overnight to drive off CO2 present in the test suspension.
The final titration was made on day 29.

DATA EVALUATION:
Relative biodegradation values were calculated from the cumulative CO2 production relative to the total expected CO2 production based on the totalcarbon content of the amount of test substance present in the test bottles.

Reference substance:

acetic acid, sodium salt

Preliminary study:

Theoretical CO₂ production:
The ThCO₂ of Nickel 2-ethylhexanoate was calculated to be 2.04 mg CO₂/mg.
The ThCO₂ of sodium acetate was calculated to be 1.07 mg CO₂/mg.

Test performance:

The relative biodegradation values calculated from the measurements performed during the test period revealed 84 and 68% biodegradation of Nickel 2-ethylhexanoate for A and B, respectively. Furthermore, in test bottle A biodegradation of Nickel 2-ethylhexanoate of at least 60% was reached within a 10-day window. Thus, the criterion for ready biodegradability was met (See tables).

In the toxicity control more than 25% biodegradation occurred within 14 days (38%, based on ThCO2).
Therefore, the test substance was assumed not to inhibit microbial activity.

Parameter:

% degradation (CO2 evolution)

Value:

>= 60

Sampling time:

15 d

Remarks on result:

other: Bottle A: 60% degradation within a 10-day window.

Parameter:

% degradation (CO2 evolution)

Value:

84

Sampling time:

29 d

Remarks on result:

other: Bottle A

Parameter:

% degradation (CO2 evolution)

Value:

68

Sampling time:

29 d

Remarks on result:

other: Bottle B

Results with reference substance:

The reference substance acetic acid was biodegraded by at least 60% (74%) within 14 days.

CO₂ production and percentage biodegradation of the test substance (bottle A):

Day	Hcl (0.05 N) titrated (mL)		Produced CO₂ (mL Hcl)	Produced   CO₂ (mg)	Cumulative   CO₂ (mg)	Biodegradation (%) (1)
	Blank (mean)	Bottle A
2	45.69	45.63	0.06	0.1	0.1	0
5	45.17	39.89	5.28	5.8	5.9	8
7	44.98	32.85	12.13	13.3	19.2	26
9	46.01	36.00	10.01	11.0	30.2	41
14	45.53	35.35	10.18	11.2	41.4	57
19	43.68	36.32	7.36	8.1	49.5	68
23	43.51	38.40	5.11	5.6	55.1	75
27	43.05	37.18	5.87	6.5	61.6	84
29	44.20	44.88	0.00	0.0	61.6	84
29	47.10	48.19	0.00	0.0	61.6	84
29	48.01	48.95	0.00	0.0	61.6	84

(1): Calculated as the ratio between CO₂ produced (cumulative) and the ThCO₂ of the test substance: 73.0 mg CO₂ /2l. Note: 10% biodegradation was reached on day 5 and 60% on day 15.

CO₂production and percentage biodegradation of the test substance (bottle B):

Day	Hcl (0.05 N) titrated (mL)		Produced   CO₂ (mL Hcl)	Produced   CO₂ (mg)	Cumulative   CO₂ (mg)	Biodegradation (%) (1)
	Blank (mean)	Bottle B
2	45.69	44.26	1.43	1.6	1.6	2
5	45.17	37.60	7.57	8.3	9.9	13
7	44.98	34.71	10.27	11.3	21.2	29
9	46.01	38.95	7.05	7.8	29.0	39
14	45.53	37.30	8.23	9.1	38.0	51
19	43.68	38.08	5.60	6.2	44.2	60
23	43.51	40.68	2.83	3.1	47.3	64
27	43.05	40.17	2.88	3.2	50.4	68
29	44.20	44.86	0.00	0.0	50.4	68
29	47.10	47.95	0.00	0.0	50.4	68
29	48.01	49.30	0.00	0.0	50.4	68

(1): Calculated as the ratio between  CO₂ produced (cumulative) and the ThCO₂ of the test substance: 74.1 mgCO₂ /2l. Note: 10% biodegradation was reached on day 5 and 60% on day 19.

Validity criteria fulfilled:

yes

Remarks:

- Reference substance was biodegraded > 60% within 14 days. - Difference in degradation between test substance duplicates was < 20. - Total CO₂ release in the blank did not exceed 40 mg/l. - Inorganic Carbon content of the test substance was < 5%.

Interpretation of results:

readily biodegradable

Conclusions:

Nickel 2-ethylhexanoate was readily biodegradable under the conditions of the modified Sturm test presently performed.

Executive summary:

Determination of ready biodegradability: carbon dioxide (CO2) evolution test (modified Sturm test) with Nickel 2-ethylhexanoate.

 

The study procedures described in this report were based on the OECD guideline No. 301 B, 1992. In addition, the procedures were designed to meet the test methods of the Commission Regulation (EC) No. 440/2008 of 30 May 2008, Publication No. L142, Part C.4-C, ISO 9439, 1999 and ISO 10634, 1995.

 

Nickel 2-ethylhexanoate was a green paste with a purity around 94% and contained around 6% of Nickel acetate. TOC = 0.556 g/g substance.

The test substance was tested in duplicate at 18 mg/l, corresponding to 10 mg TOC/l. The Theoretical CO2 production (ThCO2) of Nickel 2-ethylhexanoate was calculated to be 2.04 mg CO2/mg.

 

The study consisted of six bottles:

- 2 inoculum blanks (no test substance),

- 2 test bottles (Nickel 2-ethylhexanoate),

- 1 positive control (sodium acetate) and

- 1 toxicity control (Nickel 2-ethylhexanoate plus sodium acetate).

 

Since Nickel 2-ethylhexanoate was not sufficiently soluble to allow preparation of an aqueous solution at a concentration of 1 g/l, weighed amounts were added to the 2-litres test bottles containing medium with microbial organisms and mineral components. To this end, 10 ml of Milli-RO water was added to each weighing bottle containing the test substance. After vigorous shaking the resulting suspension was added quantitatively to the test medium. The test solutions were continuously stirred during the test, to ensure optimal contact between the test substance and the test organisms. Test duration was 28 days (last CO2-measurement on the 29th day).

 

The relative biodegradation values calculated from the measurements performed during the test period revealed 84 and 68% biodegradation of Nickel 2-ethylhexanoate for A and B, respectively.

Furthermore, in test bottle A biodegradation of Nickel 2-ethylhexanoate of at least 60% was reached within a 10-day window. Thus, the criterion for ready biodegradability was met.

In the toxicity control, Nickel 2-ethylhexanoate was found not to inhibit microbial activity.

 

Since all criteria for acceptability of the test were met, this study was considered to be valid.

 

In conclusion, Nickel 2-ethylhexanoate is designated as readily biodegradable

 

Description of key information

Upon dissolution of nickel bis(2-ethylhexanoate) in water, a complete dissociation resulting in nickel ions and 2-ethylhexanoate ions may be assumed under environmental conditions. The concept of biodegradation is not applicable to nickel ions. However, 2-ethylhexanoate is readily biodegradable (99% biodegradation in 28 d) based on results according to standard OECD test guideline 301E and supporting studies. The predicted ready biodegradability of the organic part in nickel bis(2-ethylhexanoate) is also experimentally confirmed.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable