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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:
2018
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:
River water used as inoculum in place of effluent
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Polynt Lot No. 3606217355
- Manufacturing date: 21 Dec 2017
- Expiration date of the lot/batch: The test material, due to its nature, does not have expiry date.

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Keep container tightly closed. Keep in a dry, cool and well ventilated place.
- Storage at testing facility: 5 years.
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): River water sampled from the Rhine near Heveadorp, The Netherlands on 15-02-2018. The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream
- Storage conditions: The river water was aerated for 7 days before use to reduce the endogenous respiration
- Storage length: 7 days
- Preparation of inoculum for exposure: River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating. The inoculum was not pre-exposed to the test substance. The river water was used undiluted

Duration of test (contact time):
> 28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: As described in OECD but excluding ammonium chloride to prevent nitrification
- Solubilising agent (type and concentration if used): Tween 80, 2 mg/L
- Test temperature: 22 .6 - 22.9 deg C
- pH: 8.0 on Days 0 and 28
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 300 mL BOD bottles
- Number of culture flasks/concentration: 10 x test, 10 x solvent control, 10 x inoculum blank, 6 x toxicity control
- Measuring equipment: Oxygen electrode
- Test performed in closed vessels due to significant volatility of test substance: Not applicable
- Test performed in open system: No
- Details of trap for CO2 and volatile organics if used: Not applicable


SAMPLING
- Sampling frequency: On Days 0, 7, 14, 21 and 28
- Sampling method: Direct measurement

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Toxicity control: Yes

Reference substance:
acetic acid, sodium salt
Remarks:
6.7 mg/L
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
0 d
Parameter:
% degradation (O2 consumption)
Value:
2
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
37
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
50
Sampling time:
21 d
Parameter:
% degradation (O2 consumption)
Value:
65
Sampling time:
28 d
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable, but failing 10-day window
Conclusions:
The tested substance should be regarded as being readily biodegradable because >60% biodegradation was reached within 28 days (OECD 301D).
Executive summary:

The tested substance was biodegraded by 65% at Day 28 in the Closed Bottle test. The time-day window concept assumes that biodegradation of a single organic compound in a ready biodegradability test is a growth-linked process which follows an S-shaped growth curve. The tested substance may be regarded as consisting of two chemicals linked together by ester bonds. Upon hydrolysis the diester, then the monoester, and finally two compounds are formed i.e. octanol and 1,2,4-benzenetricarboxylic acid which may then be further degraded. The biodegradation kinetics (lag period, growth rate, and yield) of the individual hydrolysis products are not necessarily the same. The time window applied as a validity criterion to Closed Bottle tests is therefore considered not applicable (OECD 2006). The substance should therefore be classified as readily biodegradable because >60% biodegradation was reached within 28 days (OECD 301D).

Description of key information

Biodegradation in water: biodegradable

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window
Type of water:
freshwater

Additional information

Significant (65%) degradation was observed in a Closed Bottle test utilising a test concentration of 2 mg/L. A modified MITI test using a high test concentration of 100 mg/L resulted in low biodegradability.

The higher degree of biodegradation observed in tests with a lower initial test substance concentration indicates limited bioavailability. It is possible that the rate of biodegradation may be limited by the rate of hydrolysis of the test substance and/or the rate with which the substance dissolves. Modelling of possible biodegradation pathways indicate that aerobic degradation is likely, the first steps in this being hydrolysis to trimellitic acid and octanol, both of which have been shown to be readily biodegradable.

Tests with a structural analogue of the substance, a trimellitate ester with mixed C8 -C10 side chains, showed significant biodegradation and, while not readily biodegradable, this analogue can be considered to be inherently biodegradable. The differences observed in tests on the two substances may be a result of methodology, particularly important when testing “difficult” substances – in this case, substances with low water solubility.