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Environmental fate & pathways

Biodegradation in water: screening tests

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3 Biodegradability in Seawater (OECD 306) studies have been conducted on the read-across substance. The percentage test substance degraded after 28 days ranged from 35 to 45%.
A marine BODIS test was also conducted. After 28 days 42-82% biodegradation was observed (depending on addition rate of test substance) and after 42 days 56-95% degradation was observed (depending on addition rate of test substance).

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

3 Biodegradability in Seawater (OECD 306) studies and a marine BODIS test have been conducted on the read-across substance (Fatty acids, C18 unsaturated, reaction products with diethylenetriamine), the results are discussed below.

Study Reference: Kuc W J (2011)

The primary objective of the study was to determine the ready biodegradability in seawater of BL5177. This was achieved by measuring dissolved oxygen consumption of a dilute solution of the designate organic material in natural seawater. The test solution contained an indigenous population of heterogeneous microorganisms and was not inoculated with any further test seed. Test bottles were incubated in the dark at a temperature of 20±1°C. Biological oxygen demand (BOD) of the test system was monitored over a specified incubation period of 28 days. Percent biodegradability was calculated as the ratio of the BOD to the chemical oxygen demand (COD) or the theoretical oxygen demand (ThOD) multiplied by a factor of 100.

The chemical oxygen demand (COD) for BL5177 was determined to be 2.24 mg O2per mg substance. The maximum percent biodegradation for BL5177 of 45% was observed on day 28. The sodium acetate 2 mg/L reference control achieved greater than 60% biodegradation within the 28 day test period, 96percent degradation was observed by day 28. Dissolved oxygen depletion in the seawater controls remained within the test guideline of 30%; on day 28 a maximum dissolved oxygen depletion of 9.2% occurred (oxygen levels had decreased from 7.6 to 6.9 mg/L)

The test substance attained 45% degradation after 28 days but cannot be considered to be readily biodegradable in the marine environment under the terms and conditions of OECD Guideline No 306.

Study Reference: Kuc W J (2011a)

The primary objective of the study was to determine the ready biodegradability in seawater of BL5176. This was achieved by measuring dissolved oxygen consumption of a dilute solution of the designate organic material in natural seawater. The test solution contained an indigenous population of heterogeneous microorganisms and was not inoculated with any further test seed. Test bottles were incubated in the dark at a temperature of 20±1°C. Biological oxygen demand (BOD) of the test system was monitored over a specified incubation period of 28 days. Percent biodegradability was calculated as the ratio of the BOD to the chemical oxygen demand (COD) or the theoretical oxygen demand (ThOD) multiplied by a factor of 100.

The chemical oxygen demand (COD) for BL5176 was determined to be 2.56 mg O2 per mg substance.

The maximum percent biodegradation for BL5176 of 43% was observed on day 28.

The sodium acetate 2 mg/L reference control achieved greater than 60% biodegradation within the 28 day test period i.e. 96

percent degradation was observed by day 28.

Dissolved oxygen depletion in the seawater controls remained within the test guideline of 30%; on day 28 a maximum dissolved oxygen depletion of 9.2% occurred (oxygen levels had decreased from 7.6 to 6.9 mg/L).

The test substance (BL5176) attained 43% degradation after 28 days but cannot be considered to be readily biodegradable in the marine environment under the terms and conditions of OECD Guideline No 306.

Study Reference: Backe-Hansen, P (2004)

Biodegradation testing has been performed on the test substance BL5316 based on OECD Guideline 306 for testing of chemicals: "Biodegradability in Seawater - Closed Bottle Test".

The test substance was degraded by 35% after 28 days based on COD calculations and measurements to account for O2 consumption. The results were also corrected for oxygen consumption due to nitrification.

Results indicated that the test substance can be considered to be inhibitory to bacteria at the concentration used in the study.

A test substance has a potential for biodegradation in the marine environment if it has been degraded 60% with 28 days. The test substance cannot be characterised as readily biodegradable in the marine environment according to the OECD Guideline 306.

Study reference: Hudson B (2007)

A study (Marine BODIS test) was conducted to determine the aerobic degradability in seawater of AO1C2 -Acetate at three different concentration rates.

A01C2-Actetate (a) had an addition rate of 8.333 mg/l.

A01C2-Actetate (b) had an addition rate of 4.165 mg/l.

A01C2-Actetate (c) had an addition rate of 2.083 mg/l.

The test vessels were closed glass bottles with a known volume of aqueous test mixture (66.6%) and air (33.3%). They were shaken continuously to assure steady state oxygen partitioning between the aqueous and gaseous phase. The degradation was followed by weekly measurements of the BOD in the aqueous phase for a minimum 28 day period. The test vessels were re-aerated and resealed after measurement. The total oxygen uptake in the test flasks was calculated from the measured dissolved oxygen concentration divided by the saturation value at normal conditions and multiplied with the total oxygen content originally present in the aqueous and gaseous phases.

A summary of all testing conducted is given below:

Test material

A01C2-Acetate (a)

A01C2-Acetate (b)

A01C2-Acetate (c)

COD (mgO2/mg)

2.40

2.40

2.40

Addition rate (mg/l)

8.333

4.165

2.083

% Inhibition (Day 28)

-21%

-44%

-53%

28 day biodegradation

42%

64%

82%

Final 42 day biodegradation

56%

75%

95%

Discussion:

Based on the results obtained from the OECD 306 studies, the read-across substance cannot be considered to be readily biodegradable in the marine environment under the terms and conditions of OECD Guideline No 306, as 60% degradation was not obtained within 28 days.

However, as 35 - 45% degradation after 28 days was obtained, it can be considered that Fatty acids, C18 unsaturated, reaction products with diethylenetriamine, acetate salts does have some potential to biodegrade in the marine environment.

The results of a marine BODIS study supports this. The test was run using three different concentration (addition) rates. After 28 days 42 - 82% degradation was obtained. The test was extended for an additional 14 days to establish whether degradation was continuous after the test period. After 42 days 56 -95% degradation was obtained.

These results support the conclusion that the substance can be considered to have inherent biodegradability potential and is expected to ultimately biodegrade in the marine environment.

Though studies only exist for the biodegradability of the read-across substance in marine water, this is considered appropriate for Fatty acids, C18 unsaturated reaction products with pentaethylenehexamine, acetate salts, as the main release of the substance will be to the marine environment from offshore industry uses.

A further biodegradation study conducted in freshwater is considered unnecessary, as the substance is not anticipated to behave substantially differently in freshwater than sea water. It is therefore considered that the substance is also not readily biodegradable in freshwater, but will ultimately degrade. A further biodegradation study is not required for the purposes of classification and labeling of the substance.