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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:
October to November 2021
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
There was one deviation to the study plan during this test but there was no impact on the validity or integrity of this test.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
There was one deviation to the study plan during this test: the timepoints scheduled were at 0, 7, 14, 21 and 28 days, however the actual timepoints tested were at 0, 7, 14, 23 and 28 days. There is no impact on the validity or integrity of this test due
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Batch number: CT20201015
Re-test date: 10th September 2022
Storage conditions: store in a cool dry place
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on inoculum:
Mineral media was strongly aerated for at least 20 minutes and allowed to stand for a minimum 20 hours at test temperature. The solution of the test substance in mineral medium, usually at 2-5 mg/L of test material, was inoculated with a relatively small number of micro-organisms from the Loch of Harray, Orkney and kept in completely full, closed bottles in the dark at constant temperature of 22 ±2 °C.
Duration of test (contact time):
28 d
Initial conc.:
4.53 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS

Mineral media was strongly aerated for at least 20 minutes and allowed to stand for a minimum 20 hours
at test temperature. The solution of the test substance in mineral medium, usually at 2-5 mg/L of test
material, was inoculated with a relatively small number of micro-organisms from the Loch of Harray,
Orkney and kept in completely full, closed bottles in the dark at constant temperature of 22 +/-2 °C.
Degradation was followed by analysis of dissolved oxygen over a 28-day period. The amount of oxygen
taken up by the microbial population during biodegradation of the test substance, corrected for uptake
by the blank inoculum run in parallel, was expressed as a percentage of ThOD

TEST SYSTEM

The concentration of active test material added to the test vessels was in the range of 2-10 mg of test
substance per litre of test medium.

The size of glass BOD bottles used were 260 to 280 mL. Three replicate bottles per time-point for each
sample/reference type were set up. A minimum of two replicates per time-point were used for data
processing. At 22 °C, the minimum dissolved oxygen saturation value upon test initiation at normal
atmospheric pressure was 8.7 mg/L. Luminescent dissolved oxygen was measured at ca 7 day intervals
using a Luminescent dissolved oxygen meter (Hach HQ40d) and probe (Hach LDO10101). A minimum
of four determinations were measured.

CONTROL AND BLANK SYSTEM

An inert support medium was used to provide a large and controlled surface area, and support medium
blank vessels were also prepared. A weighed amount of test material was added to, and homogenised
with, a volume of silica powder. A small quantity of the primary homogenate was then added to a larger
mass of powder and re-homogenised. The ‘dilution’ of the test material was controlled by the amount of
powder added to the final homogenate. The addition rate of the test substance to the test vessels was
determined by the quantity of final homogenate per vessel and the final homogenate was added to the
vessel before the addition of the test medium.

A readily degradable soluble reference material, sodium benzoate, was used to provide confirmation of
the viability of the inoculum bacterial population. To enable an assessment of potential inhibitory effects
of the test material (or its primary degradation products), an inhibition control was used, in which a
mixture of the soluble reference compound and the test material was tested. Inhibition is inferred if there
is less than 25 % biodegradation within 14 days. Only two data points are required so replicate dissolved
oxygen readings out with approximately +/- 0.4 mg/L can be excluded in analysis of the data set while the
raw replicate readings are still within 20 %.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
5
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
5
Sampling time:
23 d
Parameter:
% degradation (O2 consumption)
Value:
4
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
-1
Sampling time:
7 d
Results with reference substance:
Control test data
Material Sodium benzoate 100% BOD = 3.32 (mg/L ThOD)
Percentage biodegradation Day 7 = 72%
Day 14 = 73%
Day 23 = 71%
Day 28= 74%
Validity criteria fulfilled:
yes
Remarks:
Sodium benzoate: guideline criterion >60 % biodegradation in 14 days. Observed values 73 % Oxygen consumption of freshwater blank: guideline criterion ≤1.5 mg/L dissolved oxygen depletion in 28 days. Observed values 1.23 mg/L
Interpretation of results:
not readily biodegradable
Conclusions:
According to the biodegradation data with nitrification taken into account 4,4’-[2,2,2-trifluoro-1-
(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) biodegraded by 5 % over 28 days and achieved a maximum biodegradation of 5 % on day 28 of the 28 day study. Therefore, 6FDA is not considered readily biodegradable.
Executive summary:

The aerobic degradability of 4,4’-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) in freshwater was determined using the “closed bottle” procedure according to the OECD guidelines 301D. 


The oxygen blank and n-Octanol biodegradation were within formal and informal limits of acceptability respectively. The soluble reference material, sodium benzoate, degraded by more than 60 % in the first 14 days, indicating that the inoculum used in the test contained a satisfactory population of viable bacteria.


According to the biodegradation data with nitrification taken into account 4,4’-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) biodegraded by 5 % over 28 days and achieved a maximum biodegradation of 5 % on day 28 of the 28 day study.  It should be noted that concentration of the test item was above the water solubility level (4.53 mg/L).  However, the ion present in the mineral media will increase the solubility of the test item.


The OECD 301D guideline states the test material can be considered to be inhibitory to bacteria (at the concentration used) if the percentage degradation of the mixture of reference and test materials is less than 25 % within 14 days. 4,4’-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) achieved a percentage degradation of 28 % at 14 days and therefore is not considered inhibitory.

Description of key information

The aerobic degradability of 4,4’-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) in freshwater was determined using the “closed bottle” procedure according to the OECD guidelines 301D. 


The oxygen blank and n-Octanol biodegradation were within formal and informal limits of acceptability respectively. The soluble reference material, sodium benzoate, degraded by more than 60 % in the first 14 days, indicating that the inoculum used in the test contained a satisfactory population of viable bacteria.


According to the biodegradation data with nitrification taken into account 4,4’-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) biodegraded by 5 % over 28 days and achieved a maximum biodegradation of 5 % on day 28 of the 28 day study.  It should be noted that concentration of the test item was above the water solubility level (4.53 mg/L).  However, the ion present in the mineral media will increase the solubility of the test item.


The OECD 301D guideline states the test material can be considered to be inhibitory to bacteria (at the concentration used) if the percentage degradation of the mixture of reference and test materials is less than 25 % within 14 days. 4,4’-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]diphthalic anhydride (6FDA) achieved a percentage degradation of 28 % at 14 days and therefore is not considered inhibitory.

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information