Fatty acids, C12-18 (even numbered)-methyl esters, sulfonated, sodium salts

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

28 March 1994 to 06 June 1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Analytical monitoring:

no

Details on test conditions:

SOIL PREPARATION AND STORAGE
- Samples of three soil types were air dried, passed through a 2 mm sieve and stored in the dark at ambient temperature until required for testing.
- Soil type 1: strongly acidic (pH 4.5-5.5)
- Soil type 2: moderately to slightly acidic (pH 5.5-6.5)
- Soil type 3: slightly alkaline (pH 7.1-8.0)
- Each soil was characterised with respect to pH, organic carbon content, particle sixze distribution, cation exchange capacity and exchangeable cations (see Appendix 1, attached).
- Prior to initiation of the test, the soils were sterilised by autoclaving aqueous suspensions of soil samples (1:2) for 15 minutes at approximately 121 °C.
- Moisture content of each soil was determined by drying samples at 105 °C for a minimum of 12 hours.
- Equilibration of each soil sample with approximately twice its weight equivalent of water was performed by gently tumbling the soil and water together for a period of 24 hours prior to the start of the test.

PRELIMINARY TEST
- A preliminary test was performed on each soil type to confirm the validity of the analytical method.

SCREENING TEST - ADSORPTION
- An aliquot of test item (0.0836 g) was diluted to 100 mL using 0.017 M calcium chloride (CaCl2) solution.
- The resulting solution was further diluted by a factor of 100 using 0.017 M CaCl2 solution.
- Duplicate wet soil/test solution mixtures and a wet soil/0.017 M CaCl2 solution (blank) were prepared for each soil type.
- A control consisting of test solution with no soil was also prepared.
- Each sample was protected from light in order to minimise photodegradation.
- Quantities of soil and test solution/0.017 M CaCl2 solution taken for each sample are shown in the table below.
- Samples were shaken continuously at ambient temperature for 16 hours to allow adsorption equilibrium to be reached.
- Agitation was sufficient to maintain the soil in suspension but not so vigorous as to cause breakdown of the soil structure.
- After the period of equilibration, the samples were centrifuged to separate the phases and a known volume (20 mL) was removed for analysis by spectrophotometry.

SCREENING TEST - DESORPTION
- The desorption step of the procedure was only performed on those samples which had adsorped significantly (> 25 %).
- The supernatant removed during the adsorption step was replaced with the equivalent volume (20 mL) of 0.01 M CaCl2 solution.
- Samples were protected from light then equilibrated by shaking continuously for a period of time equivalent to the adsorption step.
- After the period of equilibration, the samples were centrifuged to separate the phases and a known volume (20 mL) was removed for analysis by spectrophotometry.
- The desorption step was then repeated using a further volume (20 mL) of 0.01 M CaCl2 solution.

ANALYSIS
- An aliquot (20 mL) of supernatant from each sample, control and sample blank was derivatised then analysed spectrophotometrically.

STANDARDS
- Standard solutions were prepared in 0.01 M CaCl2 solution at concentrations of 5 mg/L (adsorption step); 5 mg/L (desorption step, first dilution); 0.5 mg/L (desorption step, second dilution).
- An aliquot (20 mL) of each standard solution was derivatised and analysed spectrophotometrically.

BLANK
- An aliquot (20 mL) of 0.01 M CaCl2 solution was derivatised and analysed spectrophotometrically.

DERIVATISATION
- Phenolphthalein 1 % solution (2 drops) was added to each aliquot (20 mL) together with enough 1 M sodium hydroxide to render the sample alkaline.
- Methylene blue (0.2015 g) was diluted to 200 mL with water. To 60 mL of this solution was added sodium dihydrogen orthophosphate monohydrate (102.03 g) and 3 M sulphuric acid (84 mL). The solution was then diluted to 2000 mL with water to give methylene blue reagent.
- After neutralising each sample with 0.5 M sulphuric acid, methylene blue reagent (50 mL) was added and the samples were shaken to mix.
- The samples were then extracted with three aliquots (15 mL) of chlorofom and the combined extracts were diluted to 50 mL with chlorofom.

ANALYSIS
- The absorbances of the standard, sample, control and blank solutions were measured at 653 nm in cells of 10 mm path length using chloroform as the reference medium.

Sample No.:

#1

Type:

Koc

Value:

433 dimensionless

pH:

4.8

Temp.:

20 °C

% Org. carbon:

0.6

Remarks on result:

other:

Remarks:

pH measured using soil:water ratio of 1:2.5; ambient temperature

Key result

Sample No.:

#2

Type:

Koc

Value:

256 dimensionless

pH:

5.5

Temp.:

20 °C

% Org. carbon:

1.8

Remarks on result:

other:

Remarks:

pH measured using soil:water ratio of 1:2.5; ambient temperature

Sample No.:

#3

Type:

Koc

Value:

209 dimensionless

pH:

7.3

Temp.:

20 °C

% Org. carbon:

0.6

Remarks on result:

other:

Remarks:

pH measured using soil:water ratio of 1:2.5; ambient temperature

Sample no.:

#1

Duration:

16 h

% Adsorption:

34.1

Remarks on result:

other: Soil type 1

Remarks:

pH 4.8

Sample no.:

#2

Duration:

16 h

% Adsorption:

45.4

Remarks on result:

other: Soil type 2

Remarks:

pH 5.5

Sample no.:

#3

Duration:

16 h

% Adsorption:

19.8

Remarks on result:

other: Soil type 3

Remarks:

pH 7.3

Sample no.:

#1

Duration:

32 h

% Desorption:

26.5

Remarks on result:

other: Soil type 1

Remarks:

pH 4.8 (two euilibration periods of 16 hours)

Sample no.:

#2

Duration:

32 h

% Desorption:

47.6

Remarks on result:

other: Soil type 2

Remarks:

pH 5.5 (two equilibration periods of 16 hours)

Sample no.:

#3

Remarks on result:

other:

Remarks:

Investigation of desorprtion not necessary

Transformation products:

no

Details on results (Batch equilibrium method):

MOISTURE CONTENT
- The moisture content of the soil types was determined to be 2.31 % w/w (soil type 1); 3.86 % w/w (soil type 2); 1.88 % w/w (soil type 3).

PRELIMINARY TEST
- Preliminary testing showed the analytical procedure to be suitable for use with each soil type and adsorption of test material by the apparatus was shown to be negligible.

SCREENING TEST
- Mean absorbance values relating to standard, sample, control and blank solutions are attached.
- Details of test material adsorbed, adsorption coefficient and Koc for each sample are attached together with mean values for each sample.
- Details of desorption for each sample are attached.
- Details of calculation methods are attached.

Adsorption

Sample ID	Dry mass of soil (g)	Total volume of aqueous phase	Concentration in aqueous phase corrected for blank (mg/L)
1a 1b	5.069 4.965	2.51 x 10^-2 2.48 x 10^-2	2.69 3.02
2a 2b	4.808 4.882	2.47 x 10^-2 2.48 x 10^-2	1.93 2.83
3a 3b	5.013 5.020	2.48 x 10^-2 2.62 x 10^-2	3.48 3.32
Control	-	2.48 x 10^-2	4.34

Dry mass of soil = weight of soil taken corrected for moisture content

Quantity of test material recovered from control = 0.108 mg

Validity criteria fulfilled:

yes

Conclusions:

Mean adsorption coefficients as a function of organic carbon content (Koc) were reported as 433 (soil type 1; strongly acidic; pH 4.8), 256 (soil type 2; moderately to slightly acidic; pH 5.5) and 209 (soil type 3; slightly alkaline; pH 7.3). Mean test material desorbed was reported as 26.5 % w/w (soil type 1; strongly acidic; pH 4.8) and 47.6 % w/w (soil type 2; moderately to slightly acidic; pH 5.5). It was not necessary to undertake the desorption step on soil type 3 (slightly alkaline; pH 7.3)because there was no significant adsorption of the test material (< 25 %).

Executive summary:

The adsorption/desorption characteristics of the test material were investigated in three different soil types in accordance with the batch equilibrium method of OECD 106. Mean adsorption coefficients as a function of organic carbon content (Koc) were reported as 433 (soil type 1; strongly acidic; pH 4.8), 256 (soil type 2; moderately to slightly acidic; pH 5.5) and 209 (soil type 3; slightly alkaline; pH 7.3). Mean test material desorbed was reported as 26.5 % w/w (soil type 1; strongly acidic; pH 4.8) and 47.6 % w/w (soil type 2; moderately to slightly acidic; pH 5.5). It was not necessary to undertake the desorption step on soil type 3 (slightly alkaline; pH 7.3) because there was no significant adsorption of the test material (< 25 %).

Description of key information

Koc = 433 (soil type 1; strongly acidic; pH 4.8); Koc = 256 (soil type 2; moderately to slightly acidic; pH 5.5); Koc = 209 (soil type 3; slightly alkaline; pH 7.3) (OECD 106). Mean test material desorbed = 26.5 % w/w (soil type 1; strongly acidic; pH 4.8); 47.6 % w/w (soil type 2; moderately to slightly acidic; pH 5.5). Desorption is not relevant to soil type 3 (slightly alkaline; pH 7.3) because adsorption of < 25 % of the test material takes place (OECD 106).

Key value for chemical safety assessment

Koc at 20 °C:

256

Additional information

The adsorption/desorption characteristics of the test material were investigated in three different soil types in accordance with the batch equilibrium method of OECD 106. Mean adsorption coefficients as a function of organic carbon content (Koc) were reported as 433 (soil type 1; strongly acidic; pH 4.8), 256 (soil type 2; moderately to slightly acidic; pH 5.5) and 209 (soil type 3; slightly alkaline; pH 7.3). Mean test material desorbed was reported as 26.5 % w/w (soil type 1; strongly acidic; pH 4.8) and 47.6 % w/w (soil type 2; moderately to slightly acidic; pH 5.5). It was not necessary to undertake the desorption step on soil type 3 (slightly alkaline; pH 7.3) because there was no significant adsorption of the test material (< 25 %).