2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018-11-14to 2020-04-21

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)

Version / remarks:

April 2002

Principles of method if other than guideline:

Some modifications to accommodate the volatility of the test substance were made, such as the selection of a spiking solvent and method to ensure distribution to the test material mainly to the sediment phase at test initiation.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Oxygen conditions:

aerobic

Inoculum or test system:

natural water / sediment: freshwater

Details on source and properties of sediment:

- Details on collection (e.g. location, sampling depth, contamination history, procedure):
Sediments were collected according to the ISO/DIS guidance on sampling of bottom sediment. Samples were taken from the entire 5 cm upper layer of the sediment. The associated waters were collected from the same site at the same time. Temperature, pH
value and O2 concentration of the water were measured at field sampling.
The sampling sites were selected with respect to the regional biological and chemical water
quality maps (interactive online version) of the Lower Saxony Water Management , Coastal
Defence and Nature Conservation Agency (German: NLWKN). The sampling sites were classified as unpolluted. The sampling site Alte Leine is located in a water protection area.
Alte Leine:
Sampling site location:Redener Strasse, 30982 Pattensen (Koldingen), Germany
Sampling date:2018-10-30
Weather conditions: Dry, cloudy
Depth of collection:Water from the surface (0 – 20cm). Sediment: 0 – 5 cm upper layer

Altwarmbuchen:
Sampling site location: Moorwaldweg, 30659 Hannover, Germany
Sampling date: 2018-11-02
Weather conditions: dry sunny
Depth of collection: Water from the surface (0 – 20cm); Sediment: 0 – 5 cm upper layer

Sieved sediment samples and associated water were stored together, water-logged (6-10 cm water-layer), in the dark, at 4 ± 2°C, with free access of air for seven days (Alteleine) and five days (Altwarmbuchen).

- Textural classification (i.e. %sand/silt/clay):
Alte Leine: 31.9% / 52.9% / 15.2% (sand/silt/clay)
Altwarmbuchen: 96.2% / 2.5% / 1.3%

- pH at time of collection:
Alte Leine: 7.28 (water) [7.39 at start of acclimation phase]; 6.97 (sediment)
Altwarmbuchen: 6.84 (water) [6.79 at start of acclimation phase]; 5.82 (sediment)

- pH at test start (day 0)
Alte Leine: 7.70 (water); 6.61 (sediment)
Altwarmbuchen: 6.66 (water); 6.04 (sediment)

- Organic carbon (%):
Alte Leine: 3.32%
Altwarmbuchen: 0.994

- Redox potential (mv) initial/final:
Alte Leine: Acclimation day -28: 218 mV (water), -144 mV (sediment)
Acclimation day -18: 195 mV (water), -125 mV (sediment)
Altwarmbuchen: Acclimation day -13: 194 mV (water), -324 mV (sediment)
Acclimation day -4 : 192 mV (water), -175 mV (sediment)


- Biomass (e.g. in mg microbial C/100 mg, CFU or other):
Alte Leine: >2E+05
Altwarmbuchen: 5.7E+04

- Sediment samples sieved: yes

Duration of test (contact time):

100 d

Initial conc.:

50 µg/L

Based on:

test mat.

Remarks:

nominal

Parameter followed for biodegradation estimation:

test mat. analysis

Details on study design:

TEST CONDITIONS
- Volume of test solution/treatment:
Alte Leine: 37 μL of 378.5 mg/L stock solution in DGBE.
Altwarmbuchen: 28 μL of 427.8 mg/L stock solution in DGBE.

- Solvent for application: Diethylene glycol butyl ether. Appropriate volumes of the stock solution of 500 mg test item /L diethylene glycol butyl ether were applied directly with a positive displacement pipette centered in the water phase for each replicate. Due to the high specific gravity of the used solvent, the
drift of the applied volume on the sediment surface was promoted. No mixing or aeration was done after application to avoid volatilisation from the water phase.

- Test temperature: 11.8 – 13.0°C

- pH: 6-8

- pH adjusted: no

- Aeration of dilution water: No. Aerobic conditions were maintained by diffusion of oxygen from the headspace to the surface water.

- Continuous darkness: yes

- Any indication of the test material adsorbing to the walls of the test apparatus: no

TEST SYSTEM
- Culturing apparatus: 500 mL glass bottles (height 181 mm, diameter: 78 mm) closed with screw cap and septum.
Water/sediment ratio 3:1 (based on height): Alte Leine: 370 mL water and 150 g wet sediment per replicate. [height of water column:sediment 7.5:2.5 cm]
Altwarmbuchen: 280 mL water and 170 g wet sediment per replicate. [height of water column:sediment 6.0:2.0 cm]

- Number of culture flasks/concentration: Duplicates per water/sediment system and per sampling time for the determination of the transformation rate were prepared. 20 replicates were prepared for Alte Leine and Altwarmbuchen. 9 additional replicates were prepared for the water/sediment system Alte Leine. Two replicates per water/sediment system of the control were prepared. Two replicates per water/sediment system of the solvent control were prepared. Ten abiotic control replicates per water sediment system were prepared.

- Method used to create aerobic conditions: Aerobic conditions were maintained by diffusion of oxygen from the headspace to the surface water.

- Method used to create anaerobic conditions: Not applicable.

- Method used to control oxygen conditions: Not applicable.

- Test performed in closed vessels due to significant volatility of test substance: Yes

- Details of trap for CO2 and volatile organics if used: Plungers from disposable polypropylene syringes were replaced by polyurethane foams. The volatile traps were connected to syringe needles and placed in the headspace of the test vessels. Test item present in the headspace was purged with nitrogen and
trapped on the volatile trap.


SAMPLING
- Sampling frequency: Sampling for determination of the transformation rate (dissipation) was carried out directly after application and at least at 5 additional
sampling points. For the definite sampling points, refer to the table in Additional Information.

- Sampling method used per analysis type: Two test item replicates were harvested at each sampling time. Headspace (volatiles), water and sediment phases were sampled.

- Sterility check if applicable: Abiotic controls were sampled at three timepoints.

- Sample storage before analysis: samples were extracted and analysed without further storage.


DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION
CONTROL AND BLANK SYSTEM

- Inoculum blank: Yes

- Abiotic sterile control: Yes

- Toxicity control: No

- Other: Solvent control

STATISTICAL METHODS:The kinetic evaluations were done based on the FOCUS guidance document on estimating persistence and degradation kinetics with the software package GMKIN 0.6.8.

Compartment:

natural water / sediment: freshwater

DT50:

0.04 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Alte Leine sediment

Compartment:

natural water: freshwater

DT50:

0.03 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Alte Leine sediment

Compartment:

natural sediment: freshwater

DT50:

1.35 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Alte Leine sediment

Compartment:

natural water / sediment: freshwater

DT50:

0.06 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Altwarmbuchen sediment

Compartment:

natural water: freshwater

DT50:

0.05 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Altwarmbuchen sediment

Compartment:

natural sediment: freshwater

DT50:

8.5 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Altwarmbuchen sediment

Transformation products:

not measured

Details on transformation products:

The detection and identification of metabolites was technically not feasible in this study due to the low test concentration. A GC-MS/MS method was developed to analyse the test item at this low concentration. No analytes other than the test item were detectable by using this method. A statement detailing the efforts to identify the degradation products is attached to the EPSR. Comparison of the biotic and abiotic replicates in this study indicates that abiotic transformation comprises the main pathway of degradation. The transformation products are therefore considered to be the hydrolysis products of the test substance, as reported in IUCLID Section 5.1.2.

Evaporation of parent compound:

not measured

Remarks:

Losses from the test system were observed in the Alte Leine system directly after test item application (mean recover 70.2%). It is not possible to conclude whether this is due to volatilisation from the test system, or due to other dissipation processes.

Volatile metabolites:

not measured

Remarks:

It was not feasible to identify metabolites in this study. See attached statement for details.

Residues:

not measured

No full mass balances were determined due to the use of non-labelled test item.

Dissipation of the test item from the water into the sediment and transformation of the test item 2,4,6-Trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (CAS 2374-14-3) was rapid and started directly after application of the test item into the water phase. Transformation (dissipation) of the test item was fastest in the water/sediment system Alte Leine.

At test start the total amount of test item in the water/sediment system was 70.2 % of applied test item for Alte Leine consisting of 67.8 % of applied test item in the water phase and 2.4 % in the sediment. For Altwarmbuchen, 80.1 % of applied test item were measured in the water phase and 26.9 % in the sediment at test start, corresponding to 106.9 % of applied test item in the total water/sediment system.

After 3 hours the concentration of the test item in the water phase was 6.6 % for Alte Leine and 17.5 % in the system Altwarmbuchen. Simultaneously, the test item concentration in the sediment phase was 6.5 % for Alte Leine and 13.9 % in the system Altwarmbuchen. After one day of application, the test item amount was between 1.6 and 3.8 % (≤ LOQ) in the water phase of both water/sediment systems.

In parallel, dissipation of the test item 2,4,6-Trimethyl-2,4,6-tris(3,3,3- trifluoropropyl)cyclotrisiloxane (CAS 2374-14-3) in the sediment phase was detected.

In the sediment of Alte Leine a maximum concentration of 10 % was measured at day 2, followed by rapid decrease to 1.5 % (≤ LOQ) at day 6. In the sediment of Altwarmbuchen, a maximum concentration was detected at day 1 (22.7 %).

By day 2 the test item concentration decreased and remained in a range 13.1–15.2 % (day 3–day 6), followed by almost complete dissipation by day 22 to 3.0 % (≤ LOQ).

In the abiotic controls of both water/sediment systems the course of transformation (dissipation) was comparable as in the biotic replicates. This indicates that abiotic processes comprise the major pathway of dissipation.

During the respective test period formation of volatile test item was negligible as amounts were mostly ≤ LOQ. For Alte Leine 1.7 % and 0.3 % were determined in the headspace of the individual replicates after 3 hours. For Altwarmbuchen mean values of 0.2 % and 0.3 % were determined in the headspace after 3 hours and 24 hours, respectively. Thereafter the detected amount was <LOQ in both systems. In the sterile replicates 1.8% (Altwarmbuchen) and 0.6% (Alte Leine) were determined in the headspace after 1 day, thereafter the amounts were < LOQ in both systems.

See attached data tables for distribution of test item in the system.

Kinetic Analysis

The kinetic evaluations were done based on the FOCUS guidance document on estimating persistence and degradation kinetics with the software package GMKIN 0.6.8.

The kinetic models were chosen based on the following criteria:

·      Visual assessment of the fitted and observed data versus time

·      Visual assessment of the residuals

·      Estimation of the error percentage at which the χ2-test was passed

The single first order kinetic model (SFO) was used to describe the dissipation of 2,4,6-Trimethyl- 2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (CAS 2374-14-3).

Data of Kinetic Fit (Single First Order) and DTxValues of 2,4,6-Trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (CAS 2374-14-3) for Alte Leine

Endpoint / statistic	Compartment
	Total system	Water	Sediment
C0(%Applied Test Item)	70.15 ± 5.163	67.85 ± 1.01	27.70 ± 19.670
First order rate constant	16.82	23.30	0.513
χ2	27.1	5.3	2.1
DTxValues (days)
DT50	0.04	0.03	1.35
DT90	0.14	0.10	4.49

 

Data of Kinetic Fit (Single First Order) and DTxValues of 2,4,6-Trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (CAS 2374-14-3) for Altwarmbuchen

Endpoint / statistic	Compartment
	Total system	Water	Sediment
C0(%Applied Test Item)	106.90 ± 11.48	80.1 ± 2.34	20.49 ±2.40
First order rate constant	12.27	15.2	0.082
χ2	37.2	8.9	21.7
DTxValues (days)
DT50	0.06	0.05	8.5
DT90	0.19	0.15	28.1

Validity criteria fulfilled:

yes

Conclusions:

Sediment degradation half-lives of 8.5 d and 1.35 d at 12°C were obtained in a reliable study conducted according to a relevant test method and in accordance with GLP.

Reference 2

Endpoint:

biodegradation in water: simulation testing on ultimate degradation in surface water

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance is highly insoluble in water

Transformation products:

yes

No.:

#1

Details on transformation products:

The registration substance hydrolyses rapidly. The final hydrolysis product is expected to be the ultimate degradation product in water.

Description of key information

Sediment degradation half-life : 8.5 d at 12 °C (OECD 308)

Key value for chemical safety assessment

Half-life in freshwater sediment:

8.5 d

at the temperature of:

12 °C

Additional information

Sediment degradation rates were determined in a reliable study conducted according to an appropriate test method. Preliminary testing identified the potential for volatile losses from the test system, and therefore adaptation of the test guideline and customisation of the test system was required. Further modifications to the OECD TG 308 include the selection of a spiking solvent (diethylene glycol butyl ether) and method to ensure distribution of the test material mainly to the sediment phase initially.

The study was conducted under aerobic conditions with two aquatic freshwater sediment systems which meet the requirements of the OECD TG 308. The first sediment system “Alte Leine” is a fine texture (31.9% w/w sand / 52.9% w/w silt / 15.2% w/w clay) with an organic carbon content of 3.32 %. The pH of the sediment was recorded as 6.97, and the pH of the overlying water as 7.39 at the start of the acclimation phase. The second sediment system “Altwarmbüchen” is a coarse texture sediment (96.2% w/w sand / 2.5% w/w silt / 1.3% w/w clay) with an organic carbon content of 0.994 %. The pH of the sediment was recorded as 5.82, and the pH of the overlying water as 6.79 at the start of the acclimation phase. 

In the Alte Leine sediment system, at the start of the test the total recovery of test item was 70.2% (mean recovery of total test item from the water phase, sediment phase, and headspace trap, based on percentage of applied test item), consisting of 67.8% of applied test item in the water phase and 2.4% in the sediment. The test substance dissipated rapidly from the test system. The measured total recovery of test item after 3 hours was 13.0 % (6.6% in the water phase, 6.5% in the sediment) and continued to decline to only 2.3% of the applied test item after 6 days (0.8% in the water phase, 1.5% in the sediment. The formation of volatile test substance was negligible based on amount extracted from the volatile traps (<1.7% and mostly≤LOQ). Similar dissipation is observed in the sterile abiotic controls.

 

In the Altwarmbüchen sediment system, the total recovery of test item was 106.9% of the applied test item, with 80.1% of applied test item measured in the water phase, and 26.9% in the sediment at test start. Dissipation from the test system was slower, with a total recovery of the test item approximately 31.3% after 3 hours (17.5% in the water phase, 13.9% in the sediment) and continued to decline to 3% after 22 days (at day 22, test item in the water phase was not detectable, the remaining 3% of the applied test item was in the sediment phase). The formation of volatile test substance was negligible. Mean values of 0.2 % and 0.3 % were determined in the headspace after 3 hours and 24 hours, respectively, but the headspace measurements were <LOQ at all timepoints thereafter.

Dissipation of the test item from the water into the sediment and transformation of the test item was rapid and started directly after application of the test item into the water phase. The DT50 values for the water phase were 0.03 days for Alte Leine and 0.05 days for Altwarmbuchen (based on SFO kinetic analysis). This is consistent both with the hydrolytic instability of the test substance, and the potential for removal from the aqueous phase by adsorption to the sediment (based on the high adsorption coefficient (Log Koc) of the test item). The DT50 values for the sediment phase were 1.35 days for Alte Leine and 8.5 days for Altwarmbuchen. The decline in measured test item in the sediment phase is expected to principally be due to abiotic degradation, however irreversible adsorption (formation of non-extractable residues) may also have contributed to the observed decline. The DT50 values for the total system were 0.04 days for Alte Leine and 0.06 days for Altwarmbuchen.

In the abiotic controls of both water/sediment systems the course of transformation (dissipation) was comparable to the biotic replicates, indicating that abiotic processes comprise the major pathway of dissipation. The dissipation of the test substance from the total system may be attributed to formation of the degradation products. The recovery of the total applied test item therefore appears to be lower, and dissipation from the system faster, in a sediment system with a higher pH. This is consistent with the hydrolysis study, which indicates that the degradation rate increases with pH.

Formation of non-extractable residues (NERs) is not anticipated, due to the physico-chemical properties of the parent substance. However, since radiolabelled material was not obtained for the study, it is not possible to determine the extent of non-extractable residue formation. Identification and quantification of metabolites/transformation products was also not possible in this study, due to the analytical methodology required for adequate monitoring of the test substance itself. A GC-MS/MS method was developed to allow optimal analysis of the test substance (target compound), and was considered to be the best available approach for this study. A statement from the CRO regarding the chemical analysis and identification of degradation products is attached to the EPSR of the key study.

The simulation test on ultimate degradation in surface water is waived because the substance is highly insoluble in water (and testing is not technically feasible) and furthermore exposure of the aquatic (or sediment) compartments is unlikely or negligible. The registration substance is not manufactured or used as such in the EU and is registered in accordance with the REACH Regulation (Article 6) in order to support import of polymers. Residual unbound monomer in polymer is <0.1% by weight and the substance is of extremely low water solubility, such that unintentional release to the aquatic environment from end use of the polymers is negligible.