Sodium bis[4-hydroxy-3-[(2-hydroxy-1-naphthyl)azo]benzenesulphonamidato(2-)]cobaltate(1-)

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:

2014/2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: OECD guideline study, GLP

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Municipal activated sludge from the wastewater treatment plant of Mannheim, Germany. The inoculum was collected on 03 November 2014 from the aeration tank of the plant. A suitable aliquot of the activated sludge suspension was sieved by a finely woven mesh with a mesh size about 1 mm. To reduce the content of inorganic carbon in the blank controls the activated sludge was aerated with carbon dioxide free air for about 48 hours at 20 ± 2° C.

At the day of exposure the suspension was washed one time with drinking water. Subsequently the aeration was stopped and the sludge was allowed to settle. After settling the supernatant was discarded and the remaining sludge suspension was filled up with drinking water and the concentration oft the sludge was adjusted to 6.0 g/L dry weight.

Aliquots of 7.5 mL were added to the test vessels to obtain an activated sludge concentration of 30 mg/L dry weight.

Duration of test (contact time):

28 d

Initial conc.:

20 mg/L

Based on:

DOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

The Carbon Dioxide Evolution Test was performed in 2 L incubation bottles filled up to a volume of 1.5 L. The bottles were connected to two serial scrubbing bottles (total volume 250 mL) filled with 100 mL 0.05 mol sodium hydroxide solution for the adsorption of carbon dioxide from biodegradation processes. Usually twice a week the Total Inorganic Carbon (TIC) values of the adsorption solutions of the first trap were determined and used for the calculation of the produced carbon dioxide. After each sampling the second trap was moved forward and the new trap with fresh sodium hydroxide solution was placed into the second position. Each trap was analyzed separately. The TIC-value of the freshly prepared sodium hydroxide solution was determined and considered by the calculation of biogenic produced carbon dioxide amount. The incubation bottles were stirred on magnetic stirrers; the aeration was performed with carbon dioxide free air at a flow of approximately 800 mL per hour.

The test assays were prepared at the day of exposure. First, the required volumes of deionized water and the solutions of mineral salts were dosed to all test vessels. For preparation of the test vessels with test substance, the required amounts of the test substance aliquots for a test concentration of 20 mg/L TOC were weighed onto small plastic cups and completely added with the plastic cups to the vessels of the test substance assays and to the vessel of the inhibition control. These test assays were treated for few minutes in an ultrasonic bath to dissolve test substance in test medium. Finally enough reference substance stock solution was added to reach 20 mg TOC/L in the reference substance assay and 20 mg TOC/L in the inhibition control.

The pH-values in the test vessels were measured and adjusted to 7.4 ± 0.2, if necessary. Aliquots of activated sludge suspension were added to all test vessels, to adjust the concentration of activated sludge to 30 mg/L dry weight. Samples for DICmeasurement (validity criterion) from the blank control assays were taken. For determination of the decrease of dissolved organic carbon (DOC) samples were taken from the test vessels of the blank control and from the test vessel of the reference substance control and the DOC content was determined after centrifugation (approx. 15 minutes at 4000 rpm). At begin of the exposure phase the test vessels were connected with an aeration unit and the bubble aeration with carbon dioxide free air was started after connecting the several test vessels with the absorption units. The test assays were stirred using magnetic stirrers.

At the end of exposure, the pH values were measured in each test vessel. For stripping of carbon dioxide, dissolved in the test medium, each test vessel was acidified by adding 2 mL of concentrated hydrochloric acid. The concentration of dissolved organic carbon in the blank controls and reference substance assays were determined. Since the test substance was insufficiently soluble in water, no DOC-measurements could be performed from the test assay of the inhibition control and from the test substance test assays.

The aeration was continued for about 24 hours and the released carbon dioxide amounts in both traps of each test vessel were determined and added to the calculated amount of the previous day.

The TIC- and DOC-analyses were performed as repeat determination, using a TOCanalyzer equipped with an auto sampler (Shimadzu TOC-5000A and/or TOC-L CSH/CSN). The system works with a combustion/non-disperse infrared gas analysis method. For calibration of the TOC-Analyzer, standard samples were measured before start of measurements to prove the conformity with the calibration curve. The samples for TICanalysis (absorption solution) were measured without further treatment.

The samples for the DOC-analysis were centrifuged for about 15 minutes at 4000 rpm. The samples were analyzed on the day of sampling.

Reference substance:

aniline

Parameter:

% degradation (CO2 evolution)

Value:

< 10

Sampling time:

28 d

Validity criteria fulfilled:

yes

Conclusions:

The degree of biodegradation after an exposure period of 28 days was <10 % CO2/ThCO2 in this test.

Based on the rate of biodegradation of <10 % CO2/ThCO2 at the end of exposure the test substance can be evaluated as poorly biodegradable in this test.

The results in this study are consistent with all validity criteria and the test is valid according to the test guideline of this study. No deviations from the test guidelines or other incidents occurred during the course of the reported test, which may have influenced the results.

Description of key information

Not readily biodegradable (by OECD criteria).

Additional information

The biodegradablility of the test compound was assessed in an experimental study conducted according to OECD guideline 301 B under consideration of GLP. The initial test substance concentration was 20 mg/L based on TOC. After an incubation time of 28 d < 10% of the test compound was degraded. The substance is not readily biodegradable (by OECD criteria) and regarded as poorly biodegradable.