Dicarbonyl(pentane-2,4-dionato-O,O')rhodium

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:

27 Sept 2019-21 Jan 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

17 July 1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

40% Rhodium (Rh) (= 100% purity based on chemical formula)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Fresh samples of activated sludge were withdrawn on October 31th, 2019 from the sewage treatment plant Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany, which is mainly fed with municipal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 4.4 g/L and verified by dry mass measurement. The concentration used in the test was 29.6 mg dry mass/litre (7.40 mg dry mass/250 mL).

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

ThOD

Remarks:

The test item concentration in the test assays were 100 mg per litre mineral test medium (25 mg / 250 mL). 100 mg test item correspond to 187 mg ThOD.

Parameter followed for biodegradation estimation:

O2 consumption

Remarks:

measurement of oxygen demand

Details on study design:

test suspension treatment plus 4 control treatments tested:
-Blank control (Inoculum blank): The blank control consisted of inoculated mineral medium only.
-Abiotic control: An abiotic control containing test item at 100 mg per litre mineral test medium (25 mg / 250 mL) and a sterilizing agent (10 mL NaN3 (100 g/L) per liter) was applied.
-Procedural control: A procedural control containing inoculum and sodium benzoate as reference item at 100 mg per litre mineral test medium (25 mg / 250 mL) was applied.
-Toxicity control: A toxicity control containing inoculum and test item at 100 mg per litre and reference item at 100 mg per litre mineral test medium (25 mg / 250 mL) was applied.

2 vessels per treatment

Reference substance:

benzoic acid, sodium salt

Remarks:

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

Preliminary study:

The ThOD values for Na-benzoate, the test item and the toxicity control were determined as follows:
ThODCARAC: 0.84 mg O2/mg test item
ThODNa-Benzoate: 1.67 mg O2/mg reference item
ThODtoxicity control: 1.25 mg O2/mg substance mixture

Parameter:

% degradation (O2 consumption)

Value:

-7.8

St. dev.:

2.5

Sampling time:

14 d

Remarks on result:

not readily biodegradable based on QSAR/QSPR prediction

Key result

Parameter:

% degradation (O2 consumption)

Value:

-11.9

St. dev.:

3.4

Sampling time:

28 d

Remarks on result:

not readily biodegradable based on QSAR/QSPR prediction

Details on results:

-oxygen consumption (14d, mg O2/L, 2 vessels):
Inoculum blank: 20-22
Test suspension: 13-16
Abiotic control: 0-13
Procedural control: 163-166
Toxicity control: 15-18
-oxygen consumption (28d, mg O2/L, 2 vessels):
Inoculum blank: 26
Test suspension: 14-18
Abiotic control: 0-16
Procedural control: 180-189
Toxicity control: 56-21

Key result

Parameter:

ThOD

Value:

0 g O2/g test mat.

Results with reference substance:

The reference item sodium benzoate was degraded by 87% within the first 14 days.

-pH values at test end (2 vessels):

Inoculum blank: 7.3

Test suspension: 7.3

Abiotic control: 9.4 -9.6

Procedural control: 7.6 -7.7

Toxicity control: 7.3 -7.4

- The biodegradation of the item mixture in the toxicity control was found to be 0% after 14 days of incubation. Thus, the demanded threshold value of 25% was not exceeded and the test item Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (CARAC) must be identified as toxic under this test conditions.

Validity criteria fulfilled:

yes

Remarks:

difference of extremes of replicate values of the removal of the test item at test end=5%,percentage degradation of reference item > 60% by day 14, oxygen uptake of inoculum blank < 60 mg/L in 28 days and pH of test assays was 6.0 - 8.5

Interpretation of results:

not readily biodegradable

Conclusions:

No significant abiotic degradation of Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (CARAC) was noticeable after 28 days of incubation.

Executive summary:

A study was performed to investigate the biodegradation of Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (‘CARAC’) over a 28-day period in a Manometric Respirometry Test according to OECD guideline 301 F (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 100 mg/L (ThOD = 84 mg), respectively, 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 Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (‘CARAC’) and 100 mg/L sodium benzoate.

The biodegradation of Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (‘CARAC’) in the static test was found to be 0% with a standard deviation of 3.4% for a concentration of 100 mg test item per liter after 28 days. The degradation rate within the 10-day-window was 0%.

The degradation of the reference substance sodium benzoate had reached 87% within the first 14 days. The difference of extremes of replicate values of the removal of the test item at the end of the 10-day window and the end of the test is less than 20%. Therefore, the test can be considered as valid.

Less than 25% degradation occurred within 14 days in the toxicity control. Therefore, according to the guideline [5] an inhibitory effect of the test item on the microorganisms of the inoculum occurred and the test item must be considered to be toxic under the chosen test conditions.

Due to the results in this study, Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (‘CARAC’) must be considered as not readily biodegradable under the chosen test conditions.

Description of key information

No significant abiotic degradation of Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (CARAC) was noticeable after 28 days of incubation.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

A study was performed to investigate the biodegradation of Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium (‘CARAC’) over a 28-day period in a Manometric Respirometry Test according to OECD guideline 301 F (1992) and EC method C.4-D (440/2008/EEC). No significant abiotic degradation of Dicarbonyl(pentane-2,4-dionato-O,O’)rhodium was noticeable after 28 days of incubation.