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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:
2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to other study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
Lulu Island Domestic Wastewater Treatment Plant, Richmond BC, Canada
received January 12, 2005
Duration of test (contact time):
ca. 28 d
Initial conc.:
ca. 3.5 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Summary of Test Conditions

Test type Aerobic
Duration 28 days
Inoculum Secondary effluent
Inoculum source Lulu Island Domestic Wastewater Treatment Plant, Richmond, BC
Date of receipt of inoculum 12 January 2005
Inoculum volume received Approximately 3.5 L
Inoculum pre-test treatment Filtered through a 75 micron Nytex filter; aerated at test temperature for 2 days before use
Inoculum concentration in test vessels 6.2 x 104 CFU/L
Test solution temperature 19.3 to 21.1°C
Photoperiod In the dark
Test vessel 300 mL BOD bottles
Test volume 300 mL
Replicates Two (minimum)
Nominal test substance concentration 3.5 mg/L
Controls : Inoculum blank ; Toxicity control (reference and test substance)
Sampling days Day 0, 4, 7, 11, 14, 18, 21, 25, 28
Reference substance Sodium benzoate
Reference substance concentration 2 mg/L
Criterion for ready biodegradability ≥60% biodegradation in 10-day window within 28 day test period

Test vessels were 300 mL glass bottles and were the same as those used for biological oxygen demand (BOD) analysis. All test bottles were initially filled with mineral media to approximately one third to one half of the final volume using a bubble-free method. This bubble-free method consisted of slowly siphoning mineral media through plastic tubing with a terminal glass end into the bottles, while keeping the glass end slightly above the water surface. Appropriate volumes or amounts of test substance, reference substance, and inoculum, were then added, and mineral media was added to a final volume of 300 mL.
The bottles were tapped several times to remove bubbles, sealed with a stopper and cap, and then inverted several times to mix. They were randomly placed into cardboard boxes and left in the dark at an incubation temperature that ranged from 19 to 21°C with a mean and standard deviation of 20 ± 0.6°C.
All containers and apparatus were thoroughly cleaned in accordance with the Vizon SOP “Labware Cleaning” (EQP 8). The test bottles were also washed in an acid-bath containing an acidic potassium iodide solution. This particular acid wash was used because dissolved oxygen (DO) was measured with a DO electrode.

A series of four test solutions were used in the test :
- inoculum blank => to determine the biological oxygen demand in the absence of either the reference or the test substance
- test substance
- reference substance => is classified as ready biodegradable and was used as a positiv control to assess test validity
- and toxicity control => contained both test and reference substances and were used to determine if the test substance inhibited inoculum metabolism.
Reference substance:
other: sodium benzoate
Preliminary study:
none
Parameter:
% degradation (O2 consumption)
Value:
> 0 - < 1
Sampling time:
11 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
> 0 - < 1
Sampling time:
28 d
Details on results:
there was no biodegradation of the test substance.
Parameter:
BOD5
Value:
ca. 0 mg O2/g test mat.
Results with reference substance:
74.9% at 7 days
76% at 14 days
69.5% at 21 days
70.2% at 28 days

The percent biodegradation of the toxicity control treatment (containing test substance and reference substance) was significantly lower than in the reference substance treatment, especially after Day 14. However, the toxicity control treatment reached pass levels within the first seven days of the test, and the percent biodegradation at Day 14 was the same as in the reference substance treatment. Therefore, it is unlikely that the lack of the biodegradation observed in the test substance bottles was caused by toxicity of the test substance to the microbes.

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Based on the closed bottle test performed it has to be concluded that 4,4'-DDS is not biodegradable within 28 days.
Executive summary:

A sample of the test substance, 4,4"-DDs, was tested to assess its degree of ready
biodegradability, using the procedure outlined in the Vizon SciTec Inc. (Vizon) Standard
Operating Procedure (SOP), “Closed Bottle Test” (TOX 1706), which is based on the OECD
Guideline 301D for the “Closed Bottle Test” (OECD 1992). The biodegradability was assessed by measuring the uptake of oxygen by a microbial population (secondary effluent) exposed to a low concentration of test substance under controlled conditions, and by comparing that oxygen
uptake to the theoretical oxygen demand (ThOD) of the test substance.
The results of this study indicated that the test substance was not readily biodegradable.
Biodegradation did not reach >60% in a 10-day window within the 28-day test period. Percent biodegradation in the test bottles was 0% at every sampling event during the test. On Day 14, there was 76.0% biodegradation in the bottles containing reference substance alone and 75.9% in the bottles containing reference substance and test substance (toxicity control). Therefore, the low biodegradation observed for the test substance was probably not due to toxicity to the microbes. In conclusion, biodegradation did not reach >60% in a 10-day window within the 28-day test period, and therefore, the test substance was not readily biodegradable.

Description of key information

Based on the OECD 301D TG closed bottle test performed, it has to be concluded that 4,4-DDS is not readily biodegradable within 28 days.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The percent biodegradation of the toxicity control treatment (containing test substance and reference substance) was significantly lower than in the reference substance treatment, especially after Day 14. However, the toxicity control treatment reached pass levels within the first seven days of the test, and the percent biodegradation at Day 14 was the same as in the reference substance treatment. Therefore, it is unlikely that the lack of the biodegradation observed in the test substance bottles was caused by toxicity of the test substance to the microbes.