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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
4th May 2017 to 1st June 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
The test material is a UVCB
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
An inoculum containing an active microbial population was prepared as follows. Six days prior to test initiation, a sample of secondary effluent was collected from the Guelph Wastewater Treatment Plant (Guelph, Ontario). The secondary effluent was continuously aerated during transport to, and storage at AquaTox, and then pre-conditioned for testing. During preconditioning, the secondary effluent was maintained at test temperature (22 ± 2 °C) prior to test initiation. The secondary effluent was settled for 40 minutes prior to the clear supernatant being decanted for use as the inoculum.
Duration of test (contact time):
28 d
Initial conc.:
2.23 mg/L
Based on:
test mat.
Initial conc.:
4 mg/L
Based on:
COD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The test involved exposure of an active microbial population (secondary effluent from a wastewater treatment plant) to the test item for 28 days under constant temperature in the dark. Initial oxygen demand for the test item was determined from the Chemical Oxygen Demand (COD) The test item was evaluated at approximately 4.0 mg COD test item/L in a series of test chambers. During the test, the bacteria utilize a nutrient solution (devoid of carbon) and the test item (the carbon source), consuming dissolved oxygen in the process. The dissolved oxygen from each biodegradation test vessel was measured with an oxygen electrode on a frequency adequate to track the degradation of the test item (i.e., on Days 0, 4, 7, 14, 21 and 28). The test was terminated on the 28th day.

The amount of oxygen consumed within the test system was compared to the COD of the test substance and the percent (%) degradation was calculated. The 28-day biodegradation curve for the test item was prepared using calculations prescribed in the test method and by graphical representation. The degradation rates of the test item and degradation values for any point in time were calculated and reported to the nearest 0.1%.

Since the test item did not contain nitrogen, there was no requirement to collect samples for analysis of nitrate and nitrite.
Reference substance:
other: Potassium Hydrogen Phthalate (KHP)
Remarks:
KHP, which does not degrade in the absence of an inoculum within the duration of the test, was selected over the reference substances recommended by OECD (1992) which will degrade in water in the absence of an inoculum
Test performance:
The reference substance achieved >60% degradation within 14 days of test initiation.

• The difference of extremes of replicate values of the removal of the test item at the plateau, at the end of the test or at the end of the 10- day window, as appropriate, was less than 20%.
• Inoculated control (nutrient blank) did not exhibit more than 1.5 mg/L reduction in dissolved oxygen concentration.
• The residual dissolved oxygen concentration in the test vessels did not fall below 0.5 mg/L.
• The toxicity control achieved > 25% degradation in 14 days
Key result
Parameter:
% degradation (O2 consumption)
Value:
6.2
Sampling time:
28 d
Remarks on result:
other:
Details on results:
Reference Series (Procedural Control)
Percent Biodegradation of the Reference Substance After 14 and 28 Days
Duration (Days) Percent Degradation
14 85.0
28 91.2

Inhibition Series (Toxicity Control)

Percent Biodegradation in the Inhibition Test After 14 and 28 Days
Duration (Days) Percent Degradation
14 41.9
28 45.0


Test Item Series (Test Suspension)
Estimate of the Ready Biodegradability of the Test Item After 28 Days
Test Item Degradation (%) after 28 days
X-19933 6.2


Comment;
* The percentage degradation is the average of two replicates. The accuracy of the dissolved oxygen meter is +/-2%
* Since the test item did not contain nitrogen, there was no requirement to collect samples for analysis of nitrate and nitrite.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The pecentage degradation obtained by the test item in the first 28 days was 6.2%. Therefore, the test item is not considered to be readily biodegradable according to OECD Guideline 301D (i.e., did not achieve 60% degradation within the 28-day test period).
Executive summary:

The study was conducted in accordance with the OECD 301 D Biodegradability Closed Bottle Test guideline to investigate the ready biodegradability of the test item. The test exposes microorganisms to the test items, which they utilise as carbon source. The test involved exposure of an active microbial population (secondary effluent from a

wastewater treatment plant) to the test item for 28 days under constant temperature in the dark. Initial oxygen demand for the test item was determined from the Chemical Oxygen Demand (COD). The test item was evaluated at approximately 4.0 mg COD test item/L in a series of test chambers. During the test, the bacteria utilize a nutrient solution (devoid of carbon) and the test item (the carbon source), consuming dissolved oxygen in the process. The dissolved oxygen from each biodegradation test vessel was measured with an oxygen electrode on a frequency adequate to track the degradation of the test item (i.e., on Days 0, 4, 7, 14, 21 and 28). The test was terminated on the 28th day. The amount of oxygen consumed within the test system was compared to the COD of the test substance and the percent (%) degradation was calculated. The 28-day biodegradation curve for the test item was prepared using calculations prescribed in the test method and by graphical representation. The degradation rates of the test item and degradation values for any point in time were calculated and reported to the nearest 0.1%.

The percentage degradation obtained by the test item in the first 28 days was 6.2%. Therefore, the test item is considered to be non rapidly biodegradable according to the CLP crietria for classification and labelling.

Description of key information

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information