Pentapotassium bis(peroxymonosulphate) bis(sulphate)

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2018-07-17 to 2018-08-17

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

no guideline followed

Principles of method if other than guideline:

The test was conducted in the course of the Biocidal Products registration process of the substance.

GLP compliance:

no

Remarks:

This study was conducted in non-compliance with Good Laboratory Practice Standards. Verification of the test substances stability under the storage conditions in accordance with Good Laboratory Practice standards.

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: in the dark in a cupboard at ambient temperature, approximately 18 - 25 °C
- Stability under test conditions: stable

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing:
For preparing a stock solution, 0.500 g (±0.001 g) of the test item was weighed into a borosilicate glass weighing boat. 75 - 80 g of deionized water was added to a 250 mL iodine flask with standard ground joint neck. Approximately 1 g of 20% sulfuric acid was added to the flask, followed by the pre-weighed test item. The weighing boat was rinsed with deionized water and additional deionized water was added to produce a 5000 ppm test item - solution. The total weight was in the region of 100 g, appropriate to the initial test item weight for a 5000 ppm solution. The flask was stoppered and the solution was inverted several times to mix. The 5000 ppm solution was used within 1-2 hours of preparation.
For preparing blanks and samples, 60 g of 5000 ppm test-item solution was weighed into a plastic beaker and added to 940.0 g deionized water in a 2 L beaker with stirring.
- Final dilution: The 5000 ppm solution was used as stock solution and the following concentrations were prepared as blanks nd samples by adding deionized water: 500 ppm, 300 ppm, 250 ppm, 30 ppm. Additonally, a 0 ppm concentration was tested (deionized water only).

Radiolabelling:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of activated sludge: Activated sludge was sourced from Scottish Water waste water treatment works at Denny and Drumnadrochit in Scotland. See Appendix 2. Water at these sites is treated according to the Urban Waste Water Treatment Directive 91/271/EEC. The sites use different coagulants during water treatment; ferric chloride coagulant is used at the Denny site, whereas an organic tertiary amine coagulant combined with polyaluminium chloride is used at the Drumnadrochit site. Coagulants are used to destabilize colloidal suspensions and aid removal of solid particles. The coagulants used at Denny and Drumnadrochit are common chemicals used in water treatment.
The activated sludge samples, which were municipal waste in origin, were sampled from the aeration outlets on August 2nd 2018. The samples were packed with ice during transport and stored in the dark. On receipt, the samples were stored refrigerated at 3-5 °C and kept in the dark when not in use.
- Storage conditions:
Whilst in use, activated sludge samples were maintained on the benchtop at ambient temperature and were either covered with Parafilm™ or closed with a lid between sampling points. Room temperature was set to 19 °C.
When not in use, the activated sludge samples were stored in the dark, refrigerated between 3 and 5 °C. For the Denny sample, the degradation study was performed within 7 days of sample collection; the final sludge measurements were made 11 days after collection. For the Drumnadrochit sample, the degradation study was performed 14 days after sample collection; the final sludge measurements were made 15 days after collection.
- Pretreatment:
Activated sludge from Denny and Drumnadrochit waste water treatment works were removed from refrigerated storage (3-5 °C). The bottles were inverted several times to produce a homogenous mixture and 940.00 g (±0.02 g) was weighed into a 2 L glass beaker. The mixtures were purged with nitrogen for 1 hour. Once the purge was complete, the beakers were covered with Parafil. The experiments were initiated within 35 minutes of the end of purging.

Duration of test (contact time):

240 min

Initial conc.:

0 mg/L

Based on:

test mat.

Initial conc.:

300 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

other: reaction with Ferrous Ammonium Sulfate

Details on study design:

TEST CONDITIONS
- Tests were conducted under ambient conditions of temperature and pressure. Test item - deionized water samples were tested at 19 °C (±1°C). Activated sludge solutions were tested at 16 °C (initial solution temperature was cooled by the nitrogen purge).

SAMPLING
- Sampling frequency: 8 time points from 0 to 240 minutes

Key result

Compartment:

activated sludge

DT50:

>= 4 - <= 62 min

Type:

(pseudo-)first order (= half-life)

Temp.:

16 °C

Other kinetic parameters:

other: correlation coefficients R = 0.9983 for experiments in Denny activated sludge, and R = 0.9145 for experiments in Drumnadrochit activated sludge

Transformation products:

not measured

The Limit of Detection of the titration methodology was determined as 53.6 ppm test item. For the test item - activated sludge samples from the Denny treatment works, the results were above the limit of detection for time points 0 to 140 minutes and below the final time point around 240 minutes, at 23 ppm test item. For the Drumnadrochit samples, the results fell below the limit of detection after 5 minutes. The results indicate that the test item - concentration tends towards zero over time.

Partial method validation has been assessed and confirmed using solutions of 500, 250 and 0 ppm test item. Excellent linearity was demonstrated (R= 0.9998) and acceptable repeatability was derived (% RSD < %RSDr).

Validity criteria fulfilled:

not applicable

Conclusions:

The half-life of the test item in activated sludge was found to be between 4 and 62 minutes.

Executive summary:

In this study, the methodology describes the degradation and half-life of Oxone™in activated sludge sampled from municipal sewage treatment plants.Oxone™ concentrations were determined by reaction with a known concentration offerrous ammonium sulfate (FAS) and the subsequent titration of FAS with standardized potassiumdichromate solution. The concentration of reductant is determined by the analogous titration of blank solutions.The initial concentration of around 300 ppm Oxone™ in activated sludge was confirmed by analysis of an identically prepared Oxone™-deionized water sample.Validation of the method in the activated sludge matrix was not possible due to degradation of Oxone™ in the sludge matrix. Therefore, the method was part validated instead, using deionized water as a stablematrix for the Oxone™ analyte. The linear correlation coefficient was determined as R = 0.9998, with acceptable repeatability.Based on fivefold measurements of a low concentration of Oxone™ in a deionized water matrix, an estimation of thedetection limit of the FAS titration can calculated. Using this titration method in activated sludge with the chosen experimental set-up, the detection limit can be calculated to 53.6 ppm.The degradation of Oxone in activated sludge follows first order kinetics. The half-life is between 4 and 62 minutes.

Reference 2

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2011

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:

The purpose of the study was to provide a robust analytical method for measurement of residual KHSO5 in activated sludge. Additionally, a kinetic analysis of the rate of KHSO5 degradation in an STP media was performed in order to show that potassium peroxymonosulfat will degrade rapidly in activated sludge.
Titration with ferrous ammonium sulfate was used to quench the remaining KHSO5 that has not been reacting with the activated sludge.

GLP compliance:

no

Remarks:

The study was conducted to provide a robust analytical method for measurement of residual KHSO5 in activated sludge. No GLP certificate has been prepared for this study.

Radiolabelling:

no

Oxygen conditions:

anaerobic

Inoculum or test system:

activated sludge (adaptation not specified)

Details on inoculum:

At the beginning, the active sludge (AS) was stirred creating a slight vortex, and slowly bubbling air through it. The AS was stirred for about 1 hour with air supply before using. During the experiment the AS was stirred and bioactivity maintained with the air supply. The AS plus Oxone mixture was only stirred and no air supply was added. The temperature of both solutions was cooled to approx 12 ºC by using ice baths, adding ice when needed.

Duration of test (contact time):

>= 0 - <= 240 min

Initial conc.:

300 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

other: measuring of remaining KHSO5 by titration with ferrous ammonium sulfate

Details on study design:

TEST CONDITIONS
At the beginning, the active sludge (AS) was stirred creating a slight vortex, and slowly bubbling air through it. The AS was stirred for about 1 hour with air supply before using. The activated sludge plus Oxone mixture
was prepared by starting with 994.01 grams of the AS, began stirring with a stir bar to create slight vortex, and then added 6.04 grams of the 50000 ppm Oxone solution. This mixture produces a solution of AS with about 300 ppm of Oxone added. During the experiment the AS was stirred and bioactivity maintained with the air supply. The AS plus 300 ppm Oxone mixture was only stirred and no air supply was added. The temperature of both solutions was cooled to approx 12 ºC by using ice baths, adding ice when needed.
After the 20 mL samples were taken, they were kept covered until enough time was available for analysis. Each sample was filtered through the filter aid and paper. The samples were poured into the filter, and then the solids were washed with small amount of fresh DI H2O. Afterwards the top layer was pressed with a stainless spatula and washed again with a small amount of fresh DI H2O. The filter was removed and its contents were discarded. A stir bar was placed into the filtrate in the vacuum flask and place on a stir plate with a speed which creates a deep vortex. Then 5 mL of the H2SO4 and two to three drops of the ferroin indicator solution was added. The hot solution was titrated with the potassium dichromate until reaching the end point. The endpoint was reached when the reddish solution turned into a blue to blue grey solution. This was achieved by stopping the titration when the color of the solution began to change and small increments more were added until the proper color end point was reached.

SAMPLING
- Sampling frequency: 8 times during the study (time points 0, 5, 10, 20, 40, 80, 160 and 240 min)
- Sampling method used: A 25 mL Sarstedt Serological Pipette was used for sample extraction, one for each of the solutions as the experiment went on. The samples were drawn from the 300 ppm and AS mixture at as close to the time required as possible and all times were recorded as to when the samples were first added to the beakers containing FAS. The beakers were covered with Parafilm to prevent loss, until they could be analyzed and given a quick swirl.

Test performance:

By using ferrous ammonium sulfate to quench the remaining KHSO5 (Oxone) that has not reacted with the activated sewage a robust method is provided. The blank values are very stable and do not show any reaction versus time with the ferrous ammonium sulfate.

% Degr.:

81

Parameter:

other: amount of KHSO4

Sampling time:

1 h

% Degr.:

89

Parameter:

other: amount of KHSO4

Sampling time:

2 h

Key result

% Degr.:

97

Parameter:

other: amount of KHSO4

Sampling time:

3 h

Key result

Compartment:

activated sludge

DT50:

11.23 min

Type:

second order

Temp.:

12 °C

Transformation products:

not specified

The purity of Oxone used in this experiment was determined to be 88.70 % by sodium thiosulfate titration.

Validity criteria fulfilled:

not applicable

Conclusions:

At the test temperature of 12 ° C, the half life of the test item was determined to be 11.23 minutes.

Executive summary:

By using ferrous ammonium sulfate to quench the remaining KHSO5 that has not reacted with the activated sewage a robust method is provided. The blank values are very stable and do not show any reaction versus time with the ferrous ammonium sulfate. The method confirms a rapid degradation rate of the test item in sewage. Kinetic analysis using a ln/ln method shows a second order reaction. This method is valid if there is no rate dependence on the sewage concentration, based on the assumption that the rate is only dependent on the test item-concentration. If there is a rate dependence on the active sludge, rate = k[test item][Sludge] a pseudo order method is required.

The degradation of the test item in activated sludge showed 81 % reduction in 1 hr, 89 % in 2 hrs, and 97 % in 3 hrs. At the test temperature of 12 ° C, the half-life of the test item was determined to be 11.23 minutes.

Reference 3

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2011

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study was performed at the request of the authorities of the Biocidal Directive approval process.

Principles of method if other than guideline:

At the request of the authorities of the Biocidal Directive approval process, a study was performed to determine how quickly the test substance will degrade when combined with activated sludge.

GLP compliance:

yes

Oxygen conditions:

not specified

Inoculum or test system:

activated sludge (adaptation not specified)

Duration of test (contact time):

>= 5 - <= 240 min

Parameter followed for biodegradation estimation:

test mat. analysis

Details on study design:

Refer to "Any other information on materials and methods."

Test performance:

Good results were obtained with the test substance in deionised water standards to give a limit of detection of 1 ppm. However, when using activated sludge for the blank measurements more variability was found and the limit of detection was increased up to 30 ppm. It is hypothesized that the organic matter in activated sludge can vary from sample to sample during pipetting causing more variance in the data than anticipated. Regardless, measurements obtained for test substance degradation in activated sludge are within the limit of detection and useful data was obtained.

Key result

Remarks on result:

other: The test substance is degraded down to below 100 ppm very rapidly. The initial half life of the test substance is less than 1 minute at room temperature and the concentration reaches below 100 ppm in just over 5 minutes at 20°C.

Transformation products:

not measured

Details on results:

It is clear that the test substance is degraded down to below 100 ppm very rapidly. The initial half life of the test substance is less than 1 minute at room temperature and the concentration reaches below 100 ppm in just over 5 minutes at 20°C. When the test substance is released to the sewer system it is reasonable to predict a rapid decrease in concentration to below 100 ppm given the large excess of organic matter in such an environment.

The PNEC value outline in the REACH Chemical Safety Report is 108 ppm for toxicity to aquatic micro-organisms in sewage treatment systems. Based on this value it is reasonable to predict that the test substance would be completely broken down to inert potassium sulfate without any harm to the microorganisms in the STP through reaction with organics, inorganics, and by hydrolysis.

Validity criteria fulfilled:

yes

Conclusions:

It is reasonable to predict that the test substance will be completely broken down to inert potassium sulfate without any harm to the microorganisms in the STP through reaction with organics, inorganics, and by hydrolysis.

Executive summary:

A study was performed to determine how quickly the test substance will degrade when combined with activated sludge at 20°C. Good results were obtained with the test substance in deionised water standards to give a limit of detection of 1 ppm. However, when using activated sludge for the blank measurements more variability was found and the limit of detection was increased up to 30 ppm. It is hypothesized that the organic matter in activated sludge can vary from sample to sample during pipetting causing more variance in the data than anticipated. Regardless, measurements obtained for the test substance degradation in activated sludge are within the limit of detection and useful data was obtained.

It is clear that the test substance is degraded down to below 100 ppm very rapidly. The initial half life of the test substance is less than 1 minute at room temperature and the concentration reaches below 100 ppm in just over 5 minutes at 20°C. When the test substance is released to the sewer system it is reasonable to predict a rapid decrease in concentration to below 100 ppm given the large excess of organic matter in such an environment.

The PNEC value outline in the REACH Chemical Safety Report is 108 ppm for toxicity to aquatic micro-organisms in sewage treatment systems. Based on this value it is reasonable to predict that the test substance would be completely broken down to inert potassium sulfate without any harm the microorganisms in the STP through reaction with organics, inorganics, and by hydrolysis.

Description of key information

The following half-life values were revealed by degradation studies in activated sludge:

-      Analysis of KMPS degradation in activated sludge at 12 °C (DuPont Chemicals & Fluoroproducts 2011), DT50 (12 °C)=11.23 min (Doc. No. 713-002)

-      Decomposition of Oxone® in Activated Sludge from STP (DuPont Chemicals & Fluoroproducts, 2011): DT50 (12 °C)=0.149 (Doc. No. 713-001)

-      Degradation of Oxone™ in Activated Sludge (Antec International Limited, 2018; Doc. No. 713 -003):

DT50(sludge 1, 16 °C) = 61.9 min, corrresponding to a Dt50 (12 °C) = 85.24 min

DT50(sludge 2, 16 °C) = 3.5 min, corresponding to a Dt50 (12 °C) = 4.82 min

The geometric mean value of those four values was calculated to be 5.12 min at 12 °C. This value was used as key-value for chemical safety assessment.

Key value for chemical safety assessment

Half-life in freshwater:

5.12 min

at the temperature of:

12 °C

Half-life in marine water:

5.12 min

at the temperature of:

12 °C

Additional information

Oxidation reactions upon contact with oxidizable substances

 

1.

In the study on the “Depletion of Potassium Monopersulfate in Synthetic Pool Water”, Doc. No. 711-002, A7.1.1.1.1/02, it was shown that the decomposition of KMPS in water is very dependent on the presence of oxidizable contaminants. The addition of a ‘body fluid analog’ to the synthetic pool water used in this laboratory test reduced the half-life for decomposition of KMPS from ca. 120 hours (synthetic pool water without ‘body fluid analog’) to ca. 3 hours. This is explained by the consumption of KHSO5in many different oxidation reactions with reduced amine substrate components of the added ‘body fluid analog’, according to the general reaction:

 

KHSO5+ X®KHSO4+ X=O.

 

It can be assumed that KMPS is degraded at similar rates in natural waters, such as pond and river water. The higher the concentration of oxidizable organic substrate is in the water, the faster KMPS will be degraded. Such oxidizing reactions can also occur in soil due to the high content of oxidizable agents in soil.

 

2.

The degradation of KMPS by reactions upon contact with oxidizable substances was also determined in activated sludge, i.e. in a medium containing inorganic and organic oxidizable substances in abundance. In order to check the design firstly a pre-study was performed (Durante, R. (2011) Doc. No. 713-002). In the main study (Durante, R. (2012) Doc. No. 713-001) this design was mostly applied (pre-study: test temperature 12 °C; main study: test temperature 20 °C). The purity of the test substance Oxone (KMPS) was analyzed at the beginning of the test. From this analyzed substance the inoculum for the test substance/active sludge reaction mixture was prepared and added to the activated sludge so that the initial concentration in the reaction mixture was 300 ppm KMPS.

KMPS reacts immediately and extremely quickly upon contact with the diverse substances that can be oxidized and which are abundantly available in activated sludge. Therefore, it is absolutely impossible to measure the immediate initial concentration of 300 ppm KMPS in the reaction mixture. The three measurements from the first sampling time in the main study showed all very similar KMPS values. For this reason and since the test substance purity was determined directly before starting the test it can be concluded that no experimental mistake had occurred and that the initial concentration was equal to 300 ppm, according to the mass of KMPS which was added to the system. Such rapid degradation behaviour is very well known also from other peroxides like peracetic acid and hydrogen peroxide, for which degradation half lives in activated sludge of 2 – 3 minutes have been determined. These other peroxygen compounds have the same general spectrum of various different potential reaction partners for oxidation and decomposition as KMPS: organic material, inorganic material (such as halides and sulphides), transition and heavy metals (catalytic degradation), particle surfaces (heterogeneous catalytic decomposition). These diverse reaction partners and reaction pathways explain why the reaction kinetics for the peroxides are not constant over the whole degradation time, as the observed degradation is the overall result of various decomposition pathways. This could also be seen for KMPS. In order to obtain more profound information on degradation of KMPS in activated sludge, a further study was performed in 2018 (Board, K., 2018). The degradation of Oxone™ (KMPS) in activated sludge from two municipal STPs was determined via titration of ferrous ammonium sulphate (FAS). The initial Oxone concentration was 300 ppm, likewise to the pre-study (Durante, R., 2011-06-20) and main study (Durante, R., 2011-10-17). Degradation tests of Oxone™ were performed at 16 °C and revealed first order kinetics. Determined half-lives were 61.9 minutes (i.e. 85.24 min at 12 °C, Denny activated sludge) and 3.5 minutes (i.e. 4.82 min at 12 °C, Drumnadrochit activated sludge). The difference in half-lives can be attributed to the difference in organic loading of the sludge samples as evidenced by the measurement of the COD (chemical oxygen demand). The Drumnadrochit activated sludge sample exhibited with 239.8 mg/L a significantly higher COD value than the Denny activated sludge sample (COD: 27.2 mg/L). Since Oxone™ is consumed in the reaction with organic species, the Drumnadrochit activated sludge is expected to show faster degradation which is in agreement with obtained study results.

Since the half-lives determined in the different studies differ between 0.149 min (12 °C) and 85.24 min (12°C), a reliable DT50-value needs to be derived on the basis of the available experimental data.

Thus, the four experimentally derived DT50-values in activated sludge were used to calculate the geometric mean (geomean) value.

Pre-study (2011-06-20), Doc No. 713-002:         11.23 minutes at 12 °C

Main study (2011-10-17), Doc. No. 713-001:      0.149 minutes at 12 °C

Board, K. (2018):                      85.24 minutes at 12 °C (Denny activated sludge)

Board, K. (2018):         4.82 minutes at 12 °C (Drumnadrochit activated sludge)

Geometric mean DT50-value in activated sludge: 5.12 minutes at 12 °C

 

The calculated geomean DT50-value of 5.12 min (12 °C) is used for the environmental risk assessment.