Palladium(II) acetate

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:

6 July - 16 Sept 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

version 17.07.92

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Palladium content: 48.13%
Palladium purity: 99.9%

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, domestic, non-adapted

Details on inoculum:

Fresh samples of activated sludge were withdrawn on July 13th, 2021 from the sewage treatment plant Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany, which is mainly fed with municipal wastewater.
The samples were sieved to a particle size of 2 mm and washed once with tap water after the arrival at the laboratory and kept aerobic until use. The sludge was left for settlement for ca. one hour. Subsequently the supernatant was discarded and the concentration of suspended solids was measured in the remaining sludge. The concentration was adjusted to 3.8 g/L and verified by dry mass measurement. The concentration used in the test was 29.6 mg dry mass/liter (7.41 mg dry mass/250 mL).

Initial conc.:

102 mg/L

Based on:

ThOD

Remarks:

102 mg test item/L (giving 51 mg ThOD/L) as the nominal sole source of organic carbon

Parameter followed for biodegradation estimation:

O2 consumption

Remarks:

The consumption of oxygen is determined by measuring the quantity of oxygen (produced electrolytically) required to maintain constant gas volume in the respirometer flask.

Details on study design:

A measured volume of inoculated mineral medium, containing a known concentration of test item (102 mg test item/L giving 51 mg ThOD/L) as the nominal sole source of organic carbon, is stirred in a closed flask at a constant temperature of 22 °C ± 1 °C over 28 days. The consumption of oxygen is determined by measuring the quantity of oxygen (produced electrolytically) required to maintain constant gas volume in the respirometer flask. Evolved carbon dioxide is adsorbed on a suitable adsorbent. The amount of oxygen taken up by the microbial population during biodegradation of the test item (corrected for uptake by blank inoculum, run in parallel) is expressed as a percentage of ThOD. The test was performed according to the guideline OECD 301F and EC method C.4-D.

Mineral medium
For the preparation of the stock solutions for mineral medium the following reagents (analytical grade) were used:
( a ) KH2PO4 8.51 g/L
K2HPO4 21.75 g/L
Na2HPO4 26.63 g/L
NH4Cl 0.50 g/L
The pH value of the solution was found to be 7.4 ± 0.2.
( b ) CaCl2 x 2 H2O 36.42 g/L
( c ) MgSO4 x 7 H2O 22.52 g/L
( d ) FeCl3 x 6 H2O 0.25 g/L.
The mineral medium applied in the test contained 10 mL/L and 1 mL/L of the mineral stock solution a and b–d, respectively.

Water
For the test deionized water, free from inhibitory concentrations of toxic substances (e.g. Cu2+ ions), was used. The organic carbon content was checked at regular intervals (monthly) by dissolved organic carbon (DOC) analysis. The maximum DOC content was verified in the last sampling before medium preparation and was 0.57 mg/L, corresponding with 1.4% of the organic carbon content introduced by the test material (41.50 mg C per liter). According to the OECD 301F guideline , a value of 10% should not be surpassed.

Controls
Blank control (Inoculum blank)
The blank control consisted of inoculated mineral medium only.
Procedural control
A procedural control containing inoculum and sodium benzoate as reference item at 100 mg per liter mineral test medium (25 mg/250 mL) was applied.
Toxicity control
A toxicity control containing inoculum and test item at 102 mg per liter (25.5 mg/250 mL) and reference item at 100 mg per liter mineral test medium (25 mg/250 mL) was applied.
Abiotic control
An abiotic control without inoculum but containing test item at 102 mg per liter mineral test medium (25.5 mg test item/250 mL) and 10 mL/L NaN3 (10%) as sterilising agent was applied.

pH value
Before test start the pH values of all solutions were determined and adjusted to 7.4 ± 0.2 with H2SO4 (50 g/L). At the end of the test the pH values of all solutions were determined again and varied between 6.7-6.9 for the test suspension and toxicity control to 7.5-7.7 for the procedural and abiotic controls. pH of the inoculum blanc was 7.3.

The test was run for 28 days, in darkness at 22 °C ± 1 °C in a water bath.

Test procedure
The solution of the reference substance in the mineral medium equivalent to a concentration of 100 mg/L was prepared using a stock solution (10 g/L). The required amount of test item to ensure a final concentration of 102 mg/L (25.5 mg/250 mL) was added directly on a weight basis via Teflon discs. Subsequently, the mineral medium was added to the vessels. Further flasks with mineral medium only were prepared for inoculum controls. A further solution containing both test and reference item at the same concentrations as in the individual solutions (100 mg/L) was prepared to determine the possible toxicity of the test item against the inoculum. Flasks with test item only (102 mg/L) and 10 mL/L NaN3 (10%) as sterilising agent were prepared to determine the possible abiotic oxygen demand of the test item.
Before test start the pH values of all solutions were determined and adjusted to 7.4 ± 0.2 with H2SO4 (50 g/L). The vessels were allowed to reach the desired temperature of 22 °C ± 1 °C and were inoculated with prepared activated sludge to give a concentration of suspended solids not greater than 30 mg/L (in fact 29.6 mg/L). The total volume of solution was 250 mL in 500 mL respirometer flasks. The solutions were stirred during the whole test duration. In this way, dispersion of the test item and the contact between inoculum and test item was maximized. Twice a week the correct incubation temperature of the water bath and an adequate stirring were checked.

Reference substance:

benzoic acid, sodium salt

Remarks:

Sodium benzoate was used as reference item. The concentration in the test vessels with reference item (procedural control, toxicity control) was 100 mg per liter mineral test medium (25 mg/250 mL).

Test performance:

The Manometric Respirometry Test fulfills the validity criteria of the guideline:

• With 2% the difference of extremes of replicate values of the removal of the test item after 28 days was less than 20%.

• The percentage degradation of the reference item has exceeded the pass level of 60% by day 14.

• The oxygen uptake of the inoculum blank is < 60 mg/L in 28 days and the pH value of the test assays was inside the range of 6.0 - 8.5.

Parameter:

% degradation (O2 consumption)

Value:

-28.4

St. dev.:

1.4

Sampling time:

14 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

-37.2

St. dev.:

1.3

Sampling time:

28 d

Remarks on result:

other: not readily biodegradable

Details on results:

There was no biodegradation of the test item Palladium(II) acetate within the 28-day test duration. Consequently, no degradation rate for a 10-day-window could be calculated.

No abiotic oxygen demand occurred.

There was no biodegradation of the test and reference item mixture in the toxicity control within the 28-day test duration. Thus, the demanded threshold value of 25% was not reached and the test item Palladium(II) acetate must be identified as toxic in this ready biodegradability test at a concentration of 102 mg/L.

The reference item sodium benzoate was degraded to 92% within the first 14 days. The degradation rate at test end was 98%.

A repetition of the test with lower test item concentrations is not possible, since the ThOD at 102 mg/L test item concentration already hits the lower level of the ThOD range required (50 – 100 mg ThOD/L).

Results with reference substance:

The percentage degradation of the reference item has exceeded the pass level of 60% by day 14 (i.e. 92.2% after 14d, 98.2% after 28d).

	Inoculum	Test	Procedural	Toxicity	Abiotic
	blank	suspension	control	control	control
oxygen consumption after 14d (mean (SD))	174 (1)	3(1)	171 (2)	2(2)	0 (0)
% degradation after 14d (mean (SD))	/	-28,4 (1,4)	92,2 (1,3)	-7,1 (1,0)	0 (0)
oxygen consumption after 28d (mean (SD))	25(2)	6(1)	188(3)	4(4)	0(0)
% degradation after 28d (mean (SD))	/	-37,2 (1,3)	98,2 (1,7)	-9,4 (2,0)	0 (0)

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test item Palladium(II) acetate is identified as being not readily biodegradable under the chosen test conditions (according to OECD301F).

Executive summary:

A study was performed to investigate the biodegradation of Palladium(II) acetate over a 28-day period in a Manometric Respirometry Test according to OECD guideline 301F (1992) and EC method C.4-D (440/2008/EEC). The test medium was inoculated with microorganisms from a digester of a sewage treatment plant mainly fed with municipal wastewater.

The test solutions were stirred in closed flasks at 22 °C ± 1 °C for 28 days. The rate of degradation was monitored by measuring the quantity of oxygen required to maintain a constant gas volume in the respirometer flasks over a 28-day period. The amount of oxygen taken up by the microbial population during biodegradation of the test item at a concentration of 102 mg/L (ThOD = 51 mg O₂/L), corrected for uptake by the blank inoculum run in parallel, was expressed as a percentage of the ThOD (theoretical oxygen demand). In order to check the procedure, sodium benzoate was used as a degradable reference item at a concentration of 100 mg/L, along with a toxicity control at 100 mg/L Palladium(II) acetate and 100 mg/L sodium benzoate.

No biodegradation of the test item Palladium(II) acetate within the 28-day test duration was observed. No abiotic oxygen demand occurred.

No biodegradation in the toxicity control within the 28-day test duration was observed. Since less than 25% degradation of the Palladium(II) acetate and sodium benzoate mix occurred within 14 days, the test item has to be considered bacteriotoxic at 102 mg/L test item concentration. According to the criteria of the guideline OECD 301F, the test can be considered as valid. 

Considering the results in this study, Palladium(II) acetate is considered as being not readily biodegradable under the chosen test conditions.

 

Description of key information

The biodegradation of Palladium(II) acetate over a 28-day period was determined in a Manometric Respirometry Test according to OECD guideline 301F and EC method C.4-D. Palladium(II) acetate is considered as being not readily biodegradable under the chosen test conditions.

 

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater