Potassium propionate

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This read-across hypothesis is based on transformation of the target and source substances to common compounds (scenario1 of the RAAF). The target substance Potassium propionate is a salt of the free acid Propionic acid. The target substance Potassium propionate dissociates in aqueous solutions thereby forming Propionic acid and potassium ions. Based on the pKa value of propionic acid (pKa= 4.85) propionic acid is expected to be present predominantly in the ionized form at physiological pH, i.e. as propionate. Both constituents are ubiquitously occurring molecules. Based on the available data for Propionic acid and potassium ions it can be deduced that Propionic acid is the toxicity determining constituent. Potassium ions are considered to be less toxic due to their role in cell metabolism and the well established mechanisms to maintain the cellular ion equilibrium.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Propionic acid
CAS: 79-09-4

3. ANALOGUE APPROACH JUSTIFICATION
The read-across hypothesis is based on the assumption that the potential toxicity of the target substance Potassium propionate , which is the salt of one of the source substances (Propionic acid) does not exceed the toxicity of the respective anion by changing or adding the cation. Propionic acid occurs in foods as a naturally occurring short chain fatty acid. It is rapidly absorbed through the gastrointestinaltract in both rats and humans. It metabolises by interaction with co-enzyme A and is carboxylated to form methylmalonyl-coenzyme A. Finally, it is trans-carboxylated to succinyl-CoA, which then enters the Krebs cycle to be metabolised to carbondioxide and water. Approximately 80 % of the propionate is oxidised to carbon dioxide after extensive metabolism and is excreted by exhalation. A similar toxicokinetic behaviour can be assumed for the salt Potassium Propionate. Once dissolved in aqueous solutions it dissociates to propionate and potassium ions which are metabolised and/or excreted on the same way. This hypothesis is also substantiated by a similar toxicological and biodegradation profile.
4. DATA MATRIX
Please refer to the attached justification. The attached document describes the different lines of evidence for a Weight of Evidence approach and includes detailed information about the data used.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Key result

Parameter:

% degradation (O2 consumption)

Value:

74

Sampling time:

20 d

Remarks on result:

other: Data provided for propionic acid from Dias and Alexander_1971

Key result

Parameter:

% degradation (O2 consumption)

Value:

73

Sampling time:

10 d

Remarks on result:

other: Data provided for propionic acid from Dias and Alexander_1971

Key result

Parameter:

% degradation (O2 consumption)

Value:

71

Sampling time:

5 d

Remarks on result:

other: Data provided for propionic acid from Dias and Alexander_1971

Key result

Parameter:

% degradation (O2 consumption)

Value:

60

Sampling time:

2 d

Remarks on result:

other: Data provided for propionic acid from Dias and Alexander_1971

Key result

Parameter:

other: % CO2 and CH4

Value:

100

Sampling time:

20 d

Remarks on result:

other: data provided for propionic acid by Chou 1978

Key result

Parameter:

% degradation (O2 consumption)

Value:

40.4

Sampling time:

24 h

Remarks on result:

other: Data provided for propioni acid by publication of Malaney et al. 1969

Key result

Parameter:

% degradation (O2 consumption)

Value:

30.8

Sampling time:

12 h

Remarks on result:

other: Data provided for propionic acid by publication of Malaney et al. 1969

Key result

Parameter:

% degradation (O2 consumption)

Value:

18.6

Sampling time:

6 h

Remarks on result:

other: Data provided for propionic acid by publication of Malaney et al. 1969

Key result

Parameter:

probability of ready biodegradability (QSAR/QSPR)

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

Remarks:

Data provided by QSAR prediction

Validity criteria fulfilled:

not applicable

Interpretation of results:

readily biodegradable

Conclusions:

Based on the data provided from a QSAR estimation performed with potassium propionate (CAS 327-62-8) and the results obtained from several publications investigating the biodegradability of propionic acid as well as based on the applied read-across approach due to the structural similarity of the both substances , potassium propionate is considered readily biodegradable.

Executive summary:

No data regarding biodegradability is available for potassium propionate. However, based on the read-across hypothesis that potassium propionate and Propionic acid are transformed to the same common compounds the biodegradability of potassium propionate was assessed by using non-experimental data, i.e. ECOSAR-QSAR prediction and published results for propionic acid.

The target substance Potassium propionate dissociates in aqueous solutions thereby forming Propionic acid and potassium ions. Based on the pKa value of propionic acid (pKa= 4.85) propionic acid is expected to be present predominantly in the ionized form at physiological pH, i.e. as propionate. Both constituents are ubiquitously occurring molecules. Based on the available data for Propionic acid and potassium ions it can be deduced that Propionic acid is the toxicity determining constituent.

The biodegradation potential of Potassium propionate was estimated using the EPISuite QSAR program of the US EPA and the BIOWIN model. BIOWIN estimates the probability of rapid aerobic and anaerobic biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. BIOWIN contains seven separate models. Biodegradability estimates are based upon fragment constants that were developed using multiple linear or non-linear regression analyses, depending on the model. The substance falls in the applicability domain of these models because it contains common moieties/structures that are present in the training data sets. Thus, the prediction is considered reliable for propionic acid. Based on the read-across approach potassium propionate is structurally very similar to propionic acid, i.e. it is the ionic form of the free acid, hence, potassium propionate is also considered to be readily biodegradable.

In the publication of Malaney (1969) the degradation of several saturated mono-carboxylic acids was determined using the Warburg test. The degradation of either 500 mg/L test item was observed for 24 h. Activated sludges from three municipal waste treatment plants were used. The degradation of propionic acid was 18.6% of TOD after 6 h, 30.8% of TOD after 12 h, and 40.4% of TOD after 24 h. The substance was thus considered to be readily biodegradable.

In the publication of Chou (1978) the biodegradation of propionic acid under anaerobic conditions was determined according to the Hungate Serum bottle technique. An acetate-enriched culture originated from domestic sewage sludge was incubated for 20 days with 500-1000 mg/L test substance. The biodegradation was determined measuring the percent CO2 and CH4 generation during that time. As 100% CO2 and CH4 were produced in 20 days propionic acid is considered to be readily biodegradable even under anaerobic conditions. Based on the read-across approach that potassium propionate and propionic acid share a high structural similarity, potassium propionate is also considered to be readliy biodegradable.

In the publication of Dias and Alexander (1971) the degradation of propionic acid under aerobic conditions was determined using the Warburg respirometer test. 3 µmol/L of the test substance were incubated with non-adapted domestic sewage for 30 days. The O2 consumption was measured at day 2, 5 10, and 30. The percent O2 consumption was 60, 71, 73, and 74, respectively, thus propionic acid is considered to be readily biodegradable. Based on the read-across approach the structurally similar potassium propionate is also considered to be readily biodegradable.

All information was assessed within a Weight of Evidence approach. All lines of Evidence were evaluated independently and revealed consistently that propionic acid is readily biodegradable under aerobic conditions.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

Method: Warburg respirometer test

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

sewage, domestic, non-adapted

Details on inoculum:

- Preparation of inoculum for exposure: Before use, the raw sewage was stored at 25°C for 24 to 48 hr; it was then filtered through cotton, and 5.0 mL was added per liter of dilution water.
- Concentration of sludge: To prepare resting cells, cultures were grown in 250 or 500 mLof medium contained in 1.0- or 2.0-liter flasks maintained on a rotary shaker at 25 C for 48 hr. The cells were collected by centrifugation, washed once with 0.10 M phosphate buffer (pH 7.1), and then resuspended in the same buffer. Oxygen uptake was measured at 30 C by standard manometric techniques. The Warburg flasks contained 1.0 mL of cell suspension,100 µmoles of phosphate buffer (pH 7.1), and 3.0 µmoles of substrate.

Duration of test (contact time):

30 d

Initial conc.:

3 µmol/L

Based on:

test mat.

Key result

Parameter:

% degradation (O2 consumption)

Value:

74

Sampling time:

30 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

73

Sampling time:

10 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

71

Sampling time:

5 d

Key result

Parameter:

% degradation (O2 consumption)

Value:

60

Sampling time:

2 d

Validity criteria fulfilled:

not applicable

Interpretation of results:

readily biodegradable

Conclusions:

According to the results presented by Dias and Alexander (1971) the O2 consumption of propionic acid was 71% at 10 days of incubation and 74 % at 30 days incubation, thus, the substance is considered readily biodegradable under the conditions of the test.

Executive summary:

In the publication of Dias and Alexander (1971) the degradation of propionic acid under aerobic conditions was determined using the Warburg respirometer test. 3 µmol/L of the test substance were incubated with non-adapted domestic sewage for 30 days. The O2 consumption was measured at day 2, 5 10, and 30. The percent O2 consumption was 60, 71, 73, and 74, respectively, thus propionic acid is considered to be readily biodegradable. Based on the read-across approach the structurally similar potassium propionate is also considered to be readily biodegradable.

Reference 3

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

Method: Hungate Serum Bottle Technique

GLP compliance:

no

Oxygen conditions:

anaerobic

Inoculum or test system:

other: enriched methane cultures

Details on inoculum:

Acetate-enriched culture originated from domestic sewage sludge.

Duration of test (contact time):

20 d

Initial conc.:

500 - <= 1 000 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CH4 evolution

Parameter followed for biodegradation estimation:

CO2 evolution

Key result

Parameter:

other: % Co2 and CH4

Value:

100

Sampling time:

20 d

Details on results:

Kinetic: lag time, 2 days
Removal rate: 100 mg/L/day

Validity criteria fulfilled:

not applicable

Interpretation of results:

readily biodegradable

Conclusions:

Under the conditions of the test presented by Chou et al (1978) the substance is readily biodegradable under anerobic conditions.

Executive summary:

In the publication of Chou (1978) the biodegradation of propionic acid under anaerobic conditions was determined according to the Hungate Serum bottle technique. An acetate-enriched culture originated from domestic sewage sludge was incubated for 20 days with 500-1000 mg/L test substance. The biodegradation was determined measuring the percent CO2 and CH4 generation during that time. As 100% CO2 and CH4 were produced in 20 days propionic acid is considered to be readily biodegradable even under anaerobic conditions. Based on the read-across approach that potassium propionate and propionic acid share a high structural similarity, potassium propionate is also considered to be readliy biodegradable.

Reference 4

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: Study to observe the ability of activated sludges from three municipal waste treatment plants in the Columbus, Ohio, area to oxidize aliphatic organic compounds. Chemical compounds at a concentration of 500 mg/L were exposed to activated sludge solids at 2,500 mg/L in the Warburg respirometer with oxygen uptake as the measure of oxidation of the compound. The theoretical oxygen demand (TOD) is defined as the concentration of oxygen in mg/Lrequired to oxidize 500 mg/L of substrate completely, i.e., to CO2, water, nitrate, sulfate, and chlorate.
- Parameters analysed / observed: BOD of TOD

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, industrial (adaptation not specified)

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): activated sludges from three municipal waste treatment plants in the Columbus, Ohio, area, Hilliard, Columbus, Brookside
- Concentration of sludge: 2500 mg/L

Duration of test (contact time):

24 h

Initial conc.:

500 mg/L

Parameter followed for biodegradation estimation:

O2 consumption

Key result

Parameter:

% degradation (O2 consumption)

Value:

40.4

Sampling time:

24 h

Key result

Parameter:

% degradation (O2 consumption)

Value:

30.8

Sampling time:

12 h

Key result

Parameter:

% degradation (O2 consumption)

Value:

18.6

Sampling time:

6 h

Validity criteria fulfilled:

not applicable

Interpretation of results:

readily biodegradable

Conclusions:

Based on the O2 consumption of propionic acid after 24 h (40.4%) the substance is considered readily biodegradable.

Executive summary:

In the publication of Malaney (1969) the degradation of several saturated mono-carboxylic acids was determined using the Warburg test. The degradation of either 500 mg/L test item was observed for 24 h. Activated sludges from three municipal waste treatment plants were used. The degradation of propionic acid was 18.6% of TOD after 6 h, 30.8% of TOD after 12 h, and 40.4% of TOD after 24 h. The substance was thus considered to be readily biodegradable.

Reference 5

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 v4.11
2. MODEL (incl. version number)
BIOWIN v4.10
3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
SMILES: OC(=O)CC
CAS: 327-62-8
NAME: Propionic acid
4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
[[Explain how the model fulfils the OECD principles for (Q)SAR model validation. Consider attaching the QMRF and/or QPRF or providing a link]
- Defined endpoint: Aerobic and anaerobic biodegradation
- Unambiguous algorithm: BIOWIN estimates the probability of rapid aerobic and anaerobic biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. The abstract from Boethling et al. (1994) briefly summarizes the methodology.
- Defined domain of applicability: Based on the methodology which is built on structure fragments, every substance that exhibits or lacks a fragment that is contained in the 5 training data sets will be taken into account. However, currently there is no universally accepted definition of model domain. Users may wish to consider the possibility that biodegradability estimates are less accurate for compounds outside the MW range of the training set compounds, and/or that have more instances of a given fragment than the maximum for all training set compounds. It is also possible that a compound may have a functional group(s) or other structural features not represented in the training set, and for which no fragment coefficient was developed; and that a compound has none of the 36 or 37 (Biowin 7) fragments in the model’s fragment library. In the latter case, predictions are based on molecular weight alone. These points should be taken into consideration when interpreting model results.
- Appropriate measures of goodness-of-fit and robustness and predictivity: The goodness of fit and robustness of the models used are described in detail in the attached QMRF.
- Mechanistic interpretation: BIOWIN estimates the probability of rapid aerobic and anaerobic biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. BIOWIN contains seven separate models. This version (v4.10) designates the models as follows (see also Boethling et al. 2003). Biodegradability estimates are based upon fragment constants that were developed using multiple linear or non-linear regression analyses, depending on the model. A discussion of the methodology used to derived the linear and non-linear fragment constants in the first two models is presented in a journal article by Howard et al. (1992). The same basic methodology was used for all the other models, and abbreviated descriptions may be found in the corresponding publications (Boethling et al. 1994, Tunkel et al. 2000, Aronson et al. 2007).

5. APPLICABILITY DOMAIN
Currently there is no universally accepted definition of model domain. However, users may wish to consider the possibility that biodegradability estimates are less accurate for compounds outside the MW range of the training set compounds, and/or that have more instances of a given fragment than the maximum for all training set compounds. It is also possible that a compound may have a functional group(s) or other structural features not represented in the training set, and for which no fragment coefficient was developed; and that a compound has none of the 36 or 37 (Biowin 7) fragments in the model’s fragment library. In the latter case, predictions are based on molecular weight alone. These points should be taken into consideration when interpreting model results. For more detailed information please refer to the attached QMRF.

6. ADEQUACY OF THE RESULT
For detailed information please refer to the attached QMRF.

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Software tool(s) used including version: EPISuite v4.11
- Model(s) used: BIOWIN v4.10
- Model description: see field 'Attached justification'
- Justification of QSAR prediction:see field 'Attached justification'

GLP compliance:

no

Key result

Parameter:

probability of ready biodegradability (QSAR/QSPR)

Remarks on result:

readily biodegradable based on QSAR/QSPR prediction

SMILES : OC(=O)CC
CHEM :
MOL FOR: C3 H6 O2
MOL WT : 74.08
--------------------------- BIOWIN v4.10 Results ----------------------------

Biowin1 (Linear Model Prediction) : Biodegrades Fast
Biowin2 (Non-Linear Model Prediction): Biodegrades Fast
Biowin3 (Ultimate Biodegradation Timeframe): Days-Weeks
Biowin4 (Primary Biodegradation Timeframe): Days
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

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin1 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 0.0727 | 0.0727
MolWt| * | Molecular Weight Parameter | | -0.0353
Const| * | Equation Constant | | 0.7475
============+============================================+=========+=========
RESULT | Biowin1 (Linear Biodeg Probability) | | 0.7850
============+============================================+=========+=========

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin2 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 0.6431 | 0.6431
MolWt| * | Molecular Weight Parameter | | -1.0519
============+============================================+=========+=========
RESULT | Biowin2 (Non-Linear Biodeg Probability) | | 0.9309
============+============================================+=========+=========

A Probability Greater Than or Equal to 0.5 indicates --> Biodegrades Fast
A Probability Less Than 0.5 indicates --> Does NOT Biodegrade Fast

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin3 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 0.3646 | 0.3646
MolWt| * | Molecular Weight Parameter | | -0.1637
Const| * | Equation Constant | | 3.1992
============+============================================+=========+=========
RESULT | Biowin3 (Survey Model - Ultimate Biodeg) | | 3.4001
============+============================================+=========+=========

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin4 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 0.3856 | 0.3856
MolWt| * | Molecular Weight Parameter | | -0.1069
Const| * | Equation Constant | | 3.8477
============+============================================+=========+=========
RESULT | Biowin4 (Survey Model - Primary Biodeg) | | 4.1264
============+============================================+=========+=========

Result Classification: 5.00 -> hours 4.00 -> days 3.00 -> weeks
(Primary & Ultimate) 2.00 -> months 1.00 -> longer

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin5 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 0.1812 | 0.1812
Frag | 1 | Methyl [-CH3] | 0.0004 | 0.0004
Frag | 1 | -CH2- [linear] | 0.0494 | 0.0494
MolWt| * | Molecular Weight Parameter | | -0.2204
Const| * | Equation Constant | | 0.7121
============+============================================+=========+=========
RESULT | Biowin5 (MITI Linear Biodeg Probability) | | 0.7227
============+============================================+=========+=========

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin6 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 1.1346 | 1.1346
Frag | 1 | Methyl [-CH3] | 0.0194 | 0.0194
Frag | 1 | -CH2- [linear] | 0.4295 | 0.4295
MolWt| * | Molecular Weight Parameter | | -2.1386
============+============================================+=========+=========
RESULT |Biowin6 (MITI Non-Linear Biodeg Probability)| | 0.8777
============+============================================+=========+=========

A Probability Greater Than or Equal to 0.5 indicates --> Readily Degradable
A Probability Less Than 0.5 indicates --> NOT Readily Degradable

------+-----+--------------------------------------------+---------+---------
TYPE | NUM | Biowin7 FRAGMENT DESCRIPTION | COEFF | VALUE
------+-----+--------------------------------------------+---------+---------
Frag | 1 | Aliphatic acid [-C(=O)-OH] | 0.1868 | 0.1868
Frag | 1 | Methyl [-CH3] | -0.0796 | -0.0796
Frag | 1 | -CH2- [linear] | 0.0260 | 0.0260
Const| * | Equation Constant | | 0.8361
============+============================================+=========+=========
RESULT | Biowin7 (Anaerobic Linear Biodeg Prob) | | 0.9693
============+============================================+=========+=========

A Probability Greater Than or Equal to 0.5 indicates --> Biodegrades Fast
A Probability Less Than 0.5 indicates --> Does NOT Biodegrade Fast

Ready Biodegradability Prediction: (YES or NO)
----------------------------------------------
Criteria for the YES or NO prediction: If the Biowin3 (ultimate survey
model) result is "weeks" or faster (i.e. "days", "days to weeks", or
"weeks" AND the Biowin5 (MITI linear model) probability is >= 0.5, then
the prediction is YES (readily biodegradable). If this condition is not
satisfied, the prediction is NO (not readily biodegradable). This method
is based on application of Bayesian analysis to ready biodegradation data
(see Help). Biowin5 and 6 also predict ready biodegradability, but for
degradation in the OECD301C test only; using data from the Chemicals
Evaluation and Research Institute Japan (CERIJ) database.

 

Validity criteria fulfilled:

not applicable

Interpretation of results:

readily biodegradable

Conclusions:

In the present report biodegradability was estimated by QSAR prediction: Using EPISUITE software and the BIOWIN models propionic acid was considered to be readily biodegradable.

Executive summary:

The biodegradation potential of Potassium propionate was estimated using the EPISuite QSAR program of the US EPA and the BIOWIN model. BIOWIN estimates the probability of rapid aerobic and anaerobic biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. BIOWIN contains seven separate models. Biodegradability estimates are based upon fragment constants that were developed using multiple linear or non-linear regression analyses, depending on the model. The substance falls in the applicability domain of these models because it contains common moieties/structures that are present in the training data sets. Thus, the presition is considered reliable for propionic acid. Based on the read-across approach potassium propionate is strucurally very similar to propionic acid, i.e. it is the ionic form of the free acid, hence, potassium propionate is also considered to be readily biodegradable.

Description of key information

- QSAR estimation using EPISuite/BIOWIN, potassium propionate is considered readily biodegradable, RL2

- publication (Malaney 1969), determination of O2 consumption during the biodegradation (aerobic) from propionic acid over 24 h, readily biodegradable, RL2, read-across

- publication (Chou 1978), determination of %CO2 and CH4 consumption under anerobic conditions, degradation of propionic acid observed over 20 days, readily biodegradable, RL 2, read-across

- publication (Dias and Alexander 1971), determination of O2 consumption during the degradation of propionic acid, measurement over 30 days under aerobic conditions, readily biodegradable, RL 2, read-across

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

No data regarding biodegradability is available for potassium propionate. However, based on the read-across hypothesis that potassium propionate and Propionic acid are transformed to the same common compounds the biodegradability of potassium propionate was assessed by using non-experimental data, i.e. ECOSAR-QSAR prediction and published results for propionic acid.

The target substance Potassium propionate dissociates in aqueous solutions thereby forming Propionic acid and potassium ions. Based on the pKa value of propionic acid (pKa= 4.85) propionic acid is expected to be present predominantly in the ionized form at physiological pH, i.e. as propionate. Both constituents are ubiquitously occurring molecules. Based on the available data for Propionic acid and potassium ions it can be deduced that Propionic acid is the toxicity determining constituent.

The biodegradation potential of Potassium propionate was estimated using the EPISuite QSAR program of the US EPA and the BIOWIN model. BIOWIN estimates the probability of rapid aerobic and anaerobic biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. BIOWIN contains seven separate models. Biodegradability estimates are based upon fragment constants that were developed using multiple linear or non-linear regression analyses, depending on the model. The substance falls in the applicability domain of these models because it contains common moieties/structures that are present in the training data sets. Thus, the prediction is considered reliable for propionic acid. Based on the read-across approach potassium propionate is structurally very similar to propionic acid, i.e. it is the ionic form of the free acid, hence, potassium propionate is also considered to be readily biodegradable.

In the publication of Malaney (1969) the degradation of several saturated mono-carboxylic acids was determined using the Warburg test. The degradation of either 500 mg/L test item was observed for 24 h. Activated sludges from three municipal waste treatment plants were used. The degradation of propionic acid was 18.6% of TOD after 6 h, 30.8% of TOD after 12 h, and 40.4% of TOD after 24 h. The substance was thus considered to be readily biodegradable.

In the publication of Chou (1978) the biodegradation of propionic acid under anaerobic conditions was determined according to the Hungate Serum bottle technique. An acetate-enriched culture originated from domestic sewage sludge was incubated for 20 days with 500-1000 mg/L test substance. The biodegradation was determined measuring the percent CO2 and CH4 generation during that time. As 100% CO2 and CH4 were produced in 20 days propionic acid is considered to be readily biodegradable even under anaerobic conditions. Based on the read-across approach that potassium propionate and propionic acid share a high structural similarity, potassium propionate is also considered to be readliy biodegradable.

In the publication of Dias and Alexander (1971) the degradation of propionic acid under aerobic conditions was determined using the Warburg respirometer test. 3 µmol/L of the test substance were incubated with non-adapted domestic sewage for 30 days. The O2 consumption was measured at day 2, 5 10, and 30. The percent O2 consumption was 60, 71, 73, and 74, respectively, thus propionic acid is considered to be readily biodegradable. Based on the read-across approach the structurally similar potassium propionate is also considered to be readily biodegradable.

All information was assessed within a Weight of Evidence approach. All lines of Evidence were evaluated independently and revealed consistently that propionic acid is readily biodegradable under aerobic conditions.