Hexafluoropropene, oxidized, oligomers, reduced, fluorinated

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

OECD Guideline-conform study conducted under GLP. The conclusions of the study are cosidered reliable, although due to the substance properties, it was not possible to perform a correct measurement of the partition coefficient.

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

yes

Remarks:

Minor deviations, planned by the study director in order to optimize the study conditions.

Qualifier:

according to guideline

Guideline:

EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

Room temperature

Analytical monitoring:

yes

Details on sampling:

The test was conducted on EUROSOIL 1 with three different soil to solution ratios, control sample and blank samples
- Initial test item concentration in water of 50 ng/mL.
- Sampling interval: 4, 8, 24 and 48 hours of mixing. At each sampling point the soil and water phases were immediately separated by centrifugation and either the soil and the water phases were analysed.

Details on matrix:

COLLECTION AND STORAGE
The soils used in this study were purchased by the Test Facility from the Joint Research Centre and were chosen among the set of six European Reference Soils. The soil samples were stored at room temperature in the dark.
Since these soils were sampled and treated expressly for adsorption/desorption testing, they already met the homogeneity and particle size that the OECD Test Guideline 106 requires, therefore no pre-treatments such as homogenisation or sieving were needed.

The test was preliminarly performed on EUROSOIL No.1 only. Since the test item behaviour prevented the accurate measure of the partition coefficient value, it was decided to stop the study before testing other soil types.

PROPERTIES of EUROSOIL 1
- Soil texture: Clay
- % sand: 3.31
- % silt: 21.9
- % clay: 75.0
- pH: 5.56 (in 0.01 M CaCl2)
- Organic carbon (%): 1.30
- Nitrogen content (%): 0.17
- CEC (mval/100 g): 29.9
- C/N ratio: 7.65

Details on test conditions:

TEST SYSTEM
The test was conducted on EUROSOIL 1 with three different soil to solution ratios (1/5, 1/25, 1/100), control sample and blank samples, testing an initial test item concentration in water of 50 ng/mL. The analysis were carried out after 4, 8, 24 and 48 hours of mixing.

1/5 ratio test (test conducted in duplicate):
About 10 g of soil were mixed with 50 mL of 0.01 M solution of calcium chloride (CaCl2) in deionised water and 50 µL of a 50 µg/mL test item solution in methanol was added. Eight test tube were prepared, two per each sampling point.
1/5 ratio blank:
About 10 g of soil were mixed 50 mL of 0.01 M solution of calcium chloride (CaCl2) in deionised water. Four test tube were prepared, one per each sampling point.

1/25 ratio (test conducted in duplicate)
About 2 g of soil were mixed with 50 mL of 0.01 M solution of calcium chloride (CaCl2) in deionised water and 50 µL of a 50 µg/mL test item solution in methanol was added. Eight test tube were prepared, two per each sampling point
1/25 ratio blank
About 2 g of soil were mixed with 50 mL of 0.01 M solution of calcium chloride (CaCl2) in deionised water. Four test tube were prepared, one per each sampling point.

1/100 ratio (test conducted in duplicate)
About 1 g of soil was mixed with 100 mL of 0.01 M solution of calcium chloride (CaCl2) in deionised water and 100 µL of a 50 µg/mL test item solution in methanol was added. Eight test tube were prepared, two per each sampling point
1/100 ratio blank
About 1 g of soil was mixed with 100 mL of 0.01 M solution of calcium chloride (CaCl2) in deionised water. Four test tube were prepared, one per each sampling point.

Control sample
Consisting in 50 mL of 0.01 M solution without soil fortified with 50 µL of a 50 µg/mL test item solution in methanol. Four test tube were prepared, one per each sampling point.

The soil samples were equilibrated overnight with the 0.01 M calcium chloride (CaCl2) solution in deionised water before testing.
Afterwards the fortification diluted standard solution was added.
The pH of the aqueous phase was measured before and after contact with the soil.

The test item was known to be highly volatile, therefore the test was conducted minimizing the dead volume inside the test tube.
Nevertheless in order to obtain a correct mixing between the soil and the solution, the dead volume could not be totally removed (a dead volume of about 10 % of the total volume was kept).
For the 1/5 and 1/25 ratio tested the test was conducted directly inside the centrifuge test tube to prevent test item loss during mixture transfer.
This was not possible for the 1/100 ratio test that was instead conducted in 100 mL glass vial.
In each case the vials were sealed using Parafilm to prevent test item loss.

Computational methods:

Adsorption percentage Ati = 100 x mass of the test item adsorbed on the soil at time point ti (µg) / mass of the test item initially added to the test system (µg)

Adsorption and desorption coefficients (Kd) = content of the test item adsorbed on the soil at time point ti (µg g-1) / content of the test item in the aqueous phase at time point ti (μg cm-3)

Content of the test item adsorbed on the soil at time point ti (µg g-1) = (analytically obtained values of test item’s concentration in soil) x (analysed soil dry mass) / (tested soil mass, corrected with dry residue)

The organic carbon normalized adsorption coefficient was also calculated as:
Koc=Kdx100/%of organic carbon in the soil sample

Type:

Koc

Value:

> 1 000 - < 10 000

Remarks on result:

other: Estimated. Due to volatility of the substance, the recovered test item in both soil and water at the different time points was less than 1 %. The concentration in water was always < LOD.

Adsorption and desorption constants:

Kd and Koc were calculated for each time points and soil/water ratio.
The test item concentration in the water phases was always below the limit of detection of the analytical method, nevertheless an estimation of the Kd value at each sampling point was calculated setting the water concentration of the test item equal to the limit of detection of the analytical method.
Being the water concentration of the test item below the value used for calculation the obtained values are surely underestimated.
See tables for details.

Recovery of test material:

The sum of the recovered test item in both the two phases at the different time points was less than 1 % of the test item added to the test system.
The test item concentration in the water phase was always below the limit of detection of the analytical method.
An analysis of the test item present in the test tube’s dead volume was also carried out. This analysis should be considered only indicative since the analytical methodology was not tested for reproducibility and recovery however, the quantity of test item found in the dead volume is of the same order of magnitude of the added test item while the test item found in water and soil is two to three order of magnitude below.
Therefore this analysis is useful to state that a large part of test item can be found in the air phase.

Details on results (Batch equilibrium method):

The test item showed a great volatility that prevented a correct measurement of the partition coefficient, despite the precaution taken to prevent sample loss (sealing with Parafilm, minimization of the dead volume, minimal sample treatment before analysis).
Moreover it was not possible to observe the achievement of an equilibrium because the most part of the test item was dispersed in the test tube dead volume and the variability of test item concentration in soil is probably due to the variation of the dead volume from test to test.
Nevertheless the experimental data obtained according to the guideline “OECD 106: Adsorption / desorption using a batch equilibrium method” evidences a test item higher affinity for soil than for water, since the calculated koc values are in the range 10E3 – 10E4. (see tables 1,2,3 and 4 for details).
The calculated Kd and koc values are underestimated since it was not possible to analytically determine the test item’s water concentration, whichever the soil / solution ratio used, even if the limit of detection of the analytical method was 1 order of magnitude below the OECD 106 requirements.
Since the test item behaviour prevented the accurate measure of the koc value, it was decided to stop the study before testing other soil types.

Table 1: Adsorption results after 4 hours, calculations.

Time 4 h	caq^ads(ti)* (ng/mL)	cs^ads(ti) (ng/g)	Corrected soil weight (g)	kd	koc	Ati (%)
Test item control 4h	<0.025	-	-	-	-	0.0
Soil 1 1/5 A 4h	<0.025	1.13	9.4	>45	>3482	0.4
Soil 1 1/5 B 4h	<0.025	1.67	9.4	>67	>5143	0.6
Soil 1 1/25 A 4h	<0.025	9.45	2.0	>378	>29075	0.7
Soil 1 1/25 B 4h	<0.025	6.15	2.0	>246	>18937	0.5
Soil 1 1/100 A 4h	<0.025	4.77	0.9	>191	>14673	0.1
Soil 1 1/100 B 4h	<0.025	7.10	1.0	>284	>21859	0.1

Table 2: Adsorption results after 8 hours, calculations.

Time 8 h	caq^ads(ti)* (ng/mL)	cs^ads(ti) (ng/g)	Corrected soil weight (g)	kd	koc	Ati (%)
Test item control 8h	<0.025	-	-	-	-	0.0
Soil 1 1/5 A 8h	<0.025	0.32	9.4	>13	>970	0.1
Soil 1 1/5 B 8h	<0.025	1.83	9.4	>73	>5630	0.7
Soil 1 1/25 A 8h	<0.025	6.55	2.0	>262	>20163	0.5
Soil 1 1/25 B 8h	<0.025	8.79	1.9	>351	>27036	0.7
Soil 1 1/100 A 8h	<0.025	1.99	1.0	>80	>6130	0.0
Soil 1 1/100 B 8h	<0.025	2.59	0.9	>104	>7978	0.0

Table 3: Adsorption results after 24 hours, calculations.

Time 24 h	caq^ads(ti)* (ng/mL)	cs^ads(ti) (ng/g)	Corrected soil weight (g)	kd	koc	Ati (%)
Test item control 24h	<0.025	-	-	-	-	0.0
Soil 1 1/5 A 24h	<0.025	0.71	9.4	>29	>2194	0.3
Soil 1 1/5 B 24h	<0.025	1.93	9.4	>77	>5951	0.7
Soil 1 1/25 A 24h	<0.025	3.16	1.9	>126	>9727	0.2
Soil 1 1/25 B 24h	<0.025	5.61	2.0	>224	>17254	0.4
Soil 1 1/100 A 24h	-	-	1.0	-	-	0.0
Soil 1 1/100 B 24h	-	-	0.9	-	-	0.0

Table 4: Adsorption results after 48 hours, calculations.

Time 48 h	caq^ads(ti)* (ng/mL)	cs^ads(ti) (ng/g)	Corrected soil weight (g)	kd	koc	Ati (%)
Test item control 48h	<0.025	-	-	-	-	0.0
Soil 1 1/5 A 48h	<0.025	3.82	9.4	>153	>11763	1.4
Soil 1 1/5 B 48h	<0.025	1.07	9.4	>43	>3282	0.4
Soil 1 1/25 A 48h	<0.025	7.44	1.9	>298	>22902	0.6
Soil 1 1/25 B 48h	<0.025	5.46	2.0	>218	>16793	0.4
Soil 1 1/100 A 48h	-	-	0.9	-	-	0.0
Soil 1 1/100 B 48h	-	-	1.0	-	-	0.0

*these values are set, for K_dcalculation purposes, to the method’s limit of detection.

Since no test item was recovered in the water phases, A_ticorresponds also to the percentage of recovered test item with respect to the amount initially added.

Validity criteria fulfilled:

no

Conclusions:

Due to the great volatility of the test item, it was not possible to perform a correct measurement of the partition coefficient. Neverthenless, based on the experimental data it can be concluded that the test item has higher affinity for soil than for water, since the calculated koc values are in the range 10E3 – 10E4 and these value represent an undestimation of the actual Koc.

Executive summary:

The partition coefficient between soil and water of the test item was studied according to OECD Guideline for the Testing of Chemicals, No. 106, “Adsorption – desorption using a batch equilibrium method”.

 

A test item solution in aCaCl₂solution in water was put in contact with soil. The mixture was kept shaking and the test item’s concentration decrease in water and the contemporary concentration increase in soil was analytically measured after 4, 8, 24 and 48 hours.

 

The test was conducted using only one soil type, classifiable as soil type 1 following the OECD guidance for selection of soil sample for adsorption – desorption.

 

The study was carried out testing in duplicate three different soil to solution ratios.

 

The test item showed a great volatility that prevented a correct measurement of the partition coefficient.

Due to this reason it was not even possible to observe the achievement of an equilibrium in the test item partitioning between soil and water.

 

Based on the performance of the analytical methods used, an estimation of the partition coefficient was made.

 

The experimental data obtained evidenced a test item higher affinity for soil than for water, since the calculated partition coefficient values were in the range 10³– 10⁴.

This calculated values were underestimated since it was not possible to analytically determine the test item’s water concentration, whichever the soil to solution ratio used.

 

Since the test item behaviour prevented the accurate measure of the partition coefficient value, it was decided to stop the study before testing other soil types.

Description of key information

The partition coefficied Koc has been estimated basing on experimental measurements obtained under an OECD No.106 Study (Adsorption - Desorption Using a Batch Equilibrium Method). 
The partition coefficient Koc has been estimated to be in the range 1000 - 10000.  The average value Koc = 5500 has been taken as key value for risk assessment purpose.

Key value for chemical safety assessment

Koc at 20 °C:

5 500

Additional information

The partition coefficient between soil and water of the test item was tried to be studied according to OECD Guideline No. 106. Under experimental conditions, the test item showed a great volatility that prevented a correct measurement of the partition coefficient and therefore the study was concluded before ending.

Based on the experimental measurements in soil and the performance of the analytical methods, an estimation of the partition coefficient Koc in the range of 10E3 – 10E4 was made. These calculated values were underestimated since it was not possible to analytically determine the test item’s water concentration, whichever the soil to solution ratio used.

The data evidenced the test item has higher affinity for soil than for water.

The following average values have been set as key values for risk assessment purpose:

Koc = 5500

Log Koc = 3.74