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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
(Q)SAR
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
1. SOFTWARE
EPISuite

2. MODEL (incl. version number)
Biowin v4.10 groups 7 different models:
- Biowin1 = linear probability model
- Biowin2 = nonlinear probability model
- Biowin3 = expert survey ultimate biodegradation model*
- Biowin4 = expert survey primary biodegradation model
- Biowin5 = MITI linear model*
- Biowin6 = MITI nonlinear model
- Biowin7 = anaerobic biodegradation model
*: Model used for final conclusion, all others are indicative.

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
The chemical name was captured. It was recognized by the built-in database, which retrieved the CAS number and structure. These were checked and indeed correspond to the chemical being modelled.

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL

• Defined endpoint:
BIOWIN estimates the probability of rapid aerobic and anaerobic biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. More information is available in Biowin help file.

• Unambiguous algorithm:
The estimation methodology is detailed in Biowin help file, including bibliographic references and several appendices. In summary: biodegradability estimates are based on fragment constants that were developed using multiple linear or non-linear regression analyses, depending on the model.
In accordance with ECHA Guidance and the Biowin help file, the criteria for an overall YES or NO prediction are as follows:
- If Biowin3 (ultimate survey model) result is “weeks” or faster (e.g. days or days to weeks) = 2.75 and Biowin5 (MITI linear model) = 0.5, then the prediction is YES (readily biodegradable).
- If this condition is not satisfied, the prediction is NO (not readily biodegradable).

• Defined domain of applicability:
The fragment domains are provided in Biowin help file for each specific model. They will be discussed in chapter IV below.

• Appropriate measures of goodness-of-fit and robustness and predictivity:
The regression performance and the classification performance are detailed in Biowin help file for each specific model.
Biowin 3: % correct predictions of degradation classification:
- 83.5% overall
- 93.5% for conclusion “fast” (value >2.5)
- 71.7% for conclusion “slow” (value =2.5)
Biowin 5: % correct predictions of degradation classification:
- 82.3% (training set) and 81.3% (validation set) overall
- 79.1% (training set) and 80.2% (validation set) for conclusion ”Readily degradable”
- 84.8% (training set) and 82.3% (validation set) for conclusion “Not readily degradable”

• Mechanistic interpretation:
Biodegradability assessment is based on molecular fragments with different biodegradation potentials, derived from the experimental training set.

5. APPLICABILITY DOMAIN
The below discussion is based on Biowin help file and aims to check that the substance falls within the model’s applicability domain. This discussion is limited to models Biowin 3 and 5, since the latter drive the overall “readily biodegradability prediction”.

• Descriptor, structural and mechanistic domains:
Biowin 3 and 5:
Biowin help file’s Appendix D which applies to both models, lists number of occurrences of each molecular fragment in the training set. The following fragments present in Gallic acid (GA) are all within fragment domains of training set molecules (TSM):
- Aromatic alcohol 3 in GA =3 per TSM present in 46 TSM
- Aromatic acid 1 in GA =2 per TSM present in 24 TSM

• Similarity with analogues in the training set:

Biowin 3:
Biowin help file’s Appendix F lists 200 training set chemicals. The 5 substances listed below are structurally related to Gallic acid and have been predicted as “fast” (value >2.5):
PRIM PRIM ULT ULT
OBS PRED OBS PRED
000078-59-1 Isophorone 3.71 3.4727 2.8 2.6591
000123-30-8 p-Aminophenol 3.9 3.6216 3.17 2.8794
000060-12-8 2-Phenylethanol 4.09 3.7373 3.52 3.0363
000492-38-6 Atropic acid 3.91 4.0244 3.2 3.2584
000104-15-4 p-Toluenesulfonic acid 3.52 3.5524 2.96 2.886
-------------------------------------------------------------------------------------
PRIM OBS: survey average of primary biodegradation by 17 experts
PRIM PRED: Primary biodegradation prediction by model
ULT OBS: survey average of ultimate biodegradation by 17 experts
ULT PRED: Ultimate biodegradation prediction by model

Biowin 5:
Biowin help file’s Appendix G lists 884 training set chemicals. The 3 substances listed below are structurally closely related to Gallic acid, have been assessed by experts as “biodegrades fast” (column “Bio”) based on experimental data and have been predicted as “readily biodegradable” (value >0.5) by linear and non-linear models (Biowin 5 and 6, resp.).
LINEAR NON-LIN
CAS BIO PRED PRED NAME
----------- --- ------- ------ ---------------------------------------
000069-72-7 1 0.7753 0.8757 Benzoic acid, 2-hydroxy-
000099-06-9 1 0.7753 0.8757 Benzoic acid, 3-hydroxy-
000099-96-7 1 0.7753 0.8757 Benzoic acid, 4-hydroxy-
--------------------------------------------------------------------------
BIO: Biodegradability evaluation; 0 = does not biodegrade fast, 1 = biodegrades fast
LINEAR PRED: Linear biodegradability value predicted by Biowin v4.00
NON-LIN PRED: Non-Linear biodegradability value predicted by Biowin v4.00

6. ADEQUACY OF THE RESULT
Biodegradation potential is used as follows in hazard and exposure assessments:
- It drives Aquatic chronic classification. For Gallic acid, no adequate chronic toxicity data are available, but this substance is of moderate Aquatic acute toxicity and is naturally present in tannins so aquatic chronic toxicity seems unlikely whatever the biodegradation potential.
- It drives PBT and vPvB assessments. For Gallic acid, the low octanol-water partition coefficient (0.7) is in itself sufficient to exclude any PBT or vPvB properties, so biodegradation potential is not critical.
- It impacts aquatic and soil exposure (PECs) when effluents are treated by a sewage treatment plant. However, no exposure and risk assessment is required below 10 tpa. In addition, the moderate aquatic toxicity, the low tonnage values and the identified uses would overall lead to no environmental risks whatever the biodegradation potential.
Therefore the prediction fits the purpose of classification and labelling as well as PBT/vPvB, exposure and risk assessments.
Qualifier:
according to guideline
Guideline:
other: ECHA’s Practical guide : How to use and report (Q)SARs Version 3.1 – July 2016
Principles of method if other than guideline:
(Q)SAR prediction. For all details, see "Justification for type of information"
GLP compliance:
no
Remarks:
not applicable to (Q)SAR
Oxygen conditions:
aerobic/anaerobic
Remarks:
depends on model
Key result
Parameter:
probability of ready biodegradability (QSAR/QSPR)
Remarks on result:
readily biodegradable based on QSAR/QSPR prediction
Details on results:
Biowin1 (Linear Model Prediction) : Biodegrades Fast
Biowin2 (Non-Linear Model Prediction): Biodegrades Fast
Biowin3 (Ultimate Biodegradation Timeframe): Weeks
Biowin4 (Primary Biodegradation Timeframe): Days-Weeks
Biowin5 (MITI Linear Model Prediction) : Readily Degradable
Biowin6 (MITI Non-Linear Model Prediction): Readily Degradable
Biowin7 (Anaerobic Model Prediction): Biodegrades Fast
Ready Biodegradability Prediction: YES
Validity criteria fulfilled:
not applicable
Remarks:
not applicable to (Q)SAR. For applicability domain discussion, see "Justification for type of information"
Interpretation of results:
readily biodegradable
Conclusions:
Biowin v4.10 models 1 to 7 all predict Gallic acid to be readily biodegradable. Key models Biowin 3 and 5 lead to the overall conclusion “readily biodegradable”.
Gallic acid falls within Biowin 3 and 5 applicability domains as training sets include several related substances. The ready biodegradability prediction can therefore be considered as reliable with a high level of confidence. In addition, Gallic acid is a natural constituent of tannins so biodegradability is expectable.
Last, this prediction fits the purpose of classification and labelling as well as PBT/vPvB, exposure and risk assessments.
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
abstract
Qualifier:
no guideline followed
Principles of method if other than guideline:
3 methods: TOC removal, O2 consumption, HPLC analysis. 4-week exposure.
GLP compliance:
not specified
Remarks:
No information on GLP status in the summary
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
Concentration of activated sludge : 30 mg/L
Duration of test (contact time):
4 wk
Initial conc.:
100 mg/L
Parameter followed for biodegradation estimation:
O2 consumption
Parameter followed for biodegradation estimation:
TOC removal
Parameter followed for biodegradation estimation:
test mat. analysis
Remarks:
HPLC
Reference substance:
not specified
Parameter:
% degradation (O2 consumption)
Value:
>= 58 - <= 73
Remarks on result:
other: test with pH adjustment; unknown sampling time
Parameter:
% degradation (test mat. analysis)
Value:
100
Remarks on result:
other: test with pH adjustment; HPLC; unknown sampling time
Parameter:
% degradation (O2 consumption)
Value:
95
Sampling time:
2 wk
Remarks on result:
other: test without pH adjustment
Parameter:
% degradation (TOC removal)
Value:
97
Sampling time:
2 wk
Remarks on result:
other: test without pH adjustment
Parameter:
% degradation (test mat. analysis)
Value:
100
Sampling time:
2 wk
Remarks on result:
other: test without pH adjustment; HPLC
Results with reference substance:
not specified
Validity criteria fulfilled:
not specified
Interpretation of results:
readily biodegradable
Conclusions:
The test item %biodegradation over 2 weeks ranged 58-100% when using 3 different follow-up methods (O2 consulptiopn, TOC removal, HPLC), with or without pH adjustment.
As 4 of the 5 results were >60% (the worst-case cut-off for all these follow-up methods), the test item is considered as readily biodegradable.

Description of key information

Based on QSAR and experimental study, gallic acid is considered as readily biodegradable:

  • Biowin v4.10 models 1 to 7 all predict Gallic acid to be readily biodegradable. Key models Biowin 3 and 5 lead to the overall conclusion “readily biodegradable”. Gallic acid falls within Biowin 3 and 5 applicability domains as training sets include several related substances. The ready biodegradability prediction can therefore be considered as reliable with a high level of confidence. In addition, Gallic acid is a natural constituent of tannins so biodegradability is expectable. Last, this prediction fits the purpose of classification and labelling as well as PBT/vPvB, exposure and risk assessments.
  • The test item %biodegradation over 2 weeks ranged 58-100% when using 3 different follow-up methods (O2 consulptiopn, TOC removal, HPLC), with or without pH adjustment. As 4 of the 5 results were >60% (the worst-case cut-off for all these follow-up methods), the test item is considered as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information