Fatty acids, C12-18 and C18-unsatd., 2-sulfoethyl esters, sodium salts

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

7 May - 21 July 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study has been performed according to OECD 106 and US EPA OPPTS835.1110 guidelines and according to GLP.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2009

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Test guideline 2

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OPPTS 835.1110 (Activated Sludge Sorption Isotherm)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

sewage sludge

Test material

Reference

Name:

Unnamed

Type:

Constituent

Details on test material:

Unlabelled test substance (NOTOX substance 196758/A)
- Name of test material: Sodium Lauroyl Isethionate (Batch 9276B)
- Physical state: Solid
- Purity: Pure sample
- Lot/batch No.: S2966001
- Test substance storage: At room temperature in the dark
- Stability under storage conditions: Stable
- Expiration date of the lot/batch: 29 April 2010

14C-labelled test substance (NOTOX substance 196722/A)
- Name of test material: Sodium Lauryl [14C]Isethionate
- Physical state: Solid
- Radiochemical purity: 95.2%
- Chemical purity: Not indicated
- Lot/batch No.: S2963601
- Specific activity: 28.6 mCi/mmol
- Test substance storage: In freezer (≤ -75°C) in the dark
- Stability under storage conditions: Not indicated
- Expiration date of the lot/batch: 22 October 2009

Radiolabelling:

yes

Study design

Test temperature:

20 +/- 2°C

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

Determination of adsorption equilibrium (kinetics experiments):
- Concentration: 0.8 mg/L
- Sampling intervals: 2, 4, 6 and 24 hours (adsorption), 2, 4, 24 hours (desorption)
Determination of isotherms:
- Concentrations: 0.07 - 0.38 - 1.47 - 3.64 - 7.31 mg/L
- Sampling intervals: 3 hours (adsorption) and 3 hours (desorption)

Details on matrix:

TILBURG SLUDGE COLLECTION AND STORAGE
- Type of sludge: Mix of domestic and industrial waste water.
- Geographic location: RWZI Tilburg-Noord, Tilburg, The Netherlands (Sewage treatment plant)
- Oxygen status: aerobic
- Details on preparation: The sludge was allowed to settle at ambient temperature. The water layer was separated as much as possible from the precipitated sludge and discarded. The sludge was centrifuged (700 g, 5 min) and the supernatant was decanted. The sludge was frozen at -80°C and subjected to freeze-drying. After freeze-drying, the sludge was sieved over a 2 mm sieve and dried overnight in an oven at 103°C.
- Storage conditions: ambient temperature

PROPERTIES
- Soil texture
- % sand: 2
- % silt: 32
- % clay: 66
- Soil classification: Clay
- pH: 6.2
- Organic carbon (%): 41.0
- CEC (meq/100 g): 134

MAASKANT SLUDGE COLLECTION AND STORAGE
- Type of sludge: Mix of domestic and industrial waste water.
- Geographic location: Waterschap de Maaskant, 's-Hertogenbosch, The Netherlands
- Oxygen status: aerobic
- Details on preparation: The sludge was allowed to settle at ambient temperature. The water layer was separated as much as possible from the precipitated sludge and discarded. The sludge was centrifuged (700 g, 5 min) and the supernatant was decanted. The sludge was frozen at -80°C and subjected to freeze-drying. After freeze-drying, the sludge was sieved over a 2 mm sieve and dried overnight in an oven at 103°C.
- Storage conditions: ambient temperature

PROPERTIES
- Soil texture
- % sand: 3
- % silt: 21
- % clay: 76
- Soil classification: Clay
- pH: 5.2
- Organic carbon (%): 43.0
- CEC (meq/100 g): 131

Details on test conditions:

TEST SYSTEM
- Type, size and further details on reaction vessel: 50 mL polypropylene tubes (pretest) and 50 mL glass containers (whole study)
- Solution: 0.01 M CaCl2 solution (1.47 g calcium chloride dihydrate/L Milli-Q water)
- Amount of sludge and water per treatment: 0.18 g sludge and 45 mL 0.01 M CaCl2 solution
- Sludge-water ratio: 1:250 (main study)
- Number of reaction vessels/concentration: 2
- Measuring equipment: LSC
- Are the residues from the adsorption phase used for desorption: yes

Computational methods:

The Freundlich adsorption and desorption isotherm parameters were calculated by fitting the Freundlich isotherm to the data. Optimisations were performed using the program ModelMaker (AP Benson, Wallingford, Oxfordshire, UK).

Results and discussion

Adsorption coefficient

Adsorption coefficient 1

Type:

Koc

Value:

ca. 1 451

Adsorption coefficient 2

Type:

log Koc

Value:

ca. 3.2

Results: Batch equilibrium or other method

Adsorption and desorption constants:

See tables below

Concentration of test substance at end of adsorption equilibration period:

Adsorption equilibrium was reached after 2-4 hours. The amount of Sodium Lauroyl Isethionate adsorbed to sludge was ca. 70%.

Concentration of test substance at end of desorption equilibration period:

Desorption equilibrium was reached after 2-4 hours. The amount of Sodium Lauroyl Isethionate desorbed was ca. 25%.

Details on results (Batch equilibrium method):

1.1. Moisture content

The moisture content of the sludges was 3.36% (Tilburg) and 4.01% (Maaskant).

1.2. Stability of the test substance/adsorption to container material

This experiment was performed to test the adsorption of the test substance to container material, as well as its stability in 0.01 M CaCI2 solution. The radiochemical purity of the test substance in the test solution was 97.2% at the start of the test. The amount of radioactivity recovered in the solutions after 24 hours in contact with the container material in the absence of sludge was 88-91% of the nominal applied activity in polypropylene containers and 94-98% for glass containers. These results indicate that the test substance slightly adsorbs on polypropylene, while the adsorption of the test substance to glass is negligible.

The radiochemical purity of the test substance in the test solution after 24 hours was 57-65% in the glass containers and 88-90% in the polypropylene containers based on HPLC analysis. Therefore, Sodium Lauroyl isethionate (Batch 9276B) was considered unstable in 0.01 M CaCI2 solution over 24 hours. Further experiments were carried out in sterile conditions.

1.3. Determination of an appropriate sludge:solutlon ratio

The results of the experiment to determine a suitable sludge:solution ratio seem to suggest that the test substance does not adsorb to sludge at all at the tested ratios. However, the HPLC chromatograms show that the test substance is unstable in the experimental conditions. The test substance metabolizes completely after 24 hours. Therefore, it was decided to perform a short kinetics experiment with a sludge:solution ratio of 1:100.

1.4. Determination of equilibrium time (adsorption and desorption kinetics)

A short experiment was carried out in glass vials at a sludge:solution ratio of 1:100 and an initial test concentration of 0.7 mg/L. After 4 hours almost all activity was recovered in the supernatant and less than 10% was adsorbed to sludge. HPLC analysis showed that the test substance was fully degraded. In control samples (absence of sludge) the test substance was stable over the test period. Additionally, abiotic controls (sterilised sludge slurries) were spiked and sampled after 4 hours. Based on the activity measured in the supernatant, adsorption was determined to be 83% for Tilburg sludge and 87% for Maaskant sludge. In Maaskant supernatant no degradation product was detected; in Tilburg supernatant the degradation product was responsible for approximately 15% of the recovered activity.

Based on the results obtained in this short experiment, it was decided to perform the kinetics experiment in glass vials on sterile conditions at a sludge:solution ratio of 1:250.

The initial test substance concentration in the solution was approximately 0.8 mg/L. 100% was recovered in the control samples. The results are based upon LSC analysis of the water layer. Supernatants were also analysed by HPLC.

HPLC analysis showed that the test substance was stable for the duration of the experiment in contact with Maaskant sludge. One additional peak with a retention time of 2.70 minutes was observed in Tilburg supernatant. This peak represented a minor proportion of the total applied test substance at the timelines of equilibrium.

Mass balances were determined for two samples of each sludge after the adsorption and one sample after the desorption stage of the short kinetics experiment, and they were calculated again for one sample of each sludge after the adsorption and the desorption stage of the second kinetics experiment. The mass balances were in the range of 90-110% as specified by the OECD guideline, with three exceptions that were between 83.8 and 89.2%. These lower values could be justified for technical reasons due to the very low amounts of sludge used for this experiments and the possible loss of small amounts of sludge during the transference steps.

The pH of the remaining supernatants obtained after the adsorption and desorption kinetics experiments were respectively 6.3 and 5.9 for Tilburg sludge and 5.4 and 5.8 for Maaskant
sludge.

1.5 Determination of adsorption/desorption isotherms

HPLC chromatograms of the supernatants of the sludge samples after the isotherms experiments show only one peak, which corresponds to the test substance. The test substance was therefore stable in the presence of sludge during the timeframe of the experiment.

At the end of the adsorption and desorption stage of the isotherm measurements, the pH of the supernatant was measured for each sludge at the lowest and highest test substance concentration. The pH ranged from 5.4 to 6.1 after adsorption and from 6.2 to 6.6 after desorption.

Any other information on results incl. tables

Sodium Lauroyl Isethionate adsorption and desorption isotherms could be described by the Freundlich equation. Freundlich isotherm parameters are summarised in the tables below.

Freundlich adsorption isotherm parameters for Sodium Lauroyl Isethionate

Sludge	KF^ads (L/g)	KF,oc^ads (L/g)	1/n	r^2	data points
Tilburg	579	1412	1.03	0.9988	10
Maaskant	641	1490	0.981	0.9997	10

Freundlich desorption isotherm parameters for Sodium Lauroyl Isethionate

Sludge	KF^des (L/g)	KF,oc^des (L/g)	1/n	r^2	data points
Tilburg	730	1780	0.996	0.9996	10
Maaskant	792	1842	0.994	0.9999	10

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

Sodium Lauroyl Isethionate (Batch 9276B) adsorption and desorption isotherms could be described by the Freundlich equation. KfOC ads values were 1412 L/kg (Tilburg sludge) and 1490 L/kg (Maaskant sludge).

Executive summary:

The adsorption behaviour of Sodium lauroyl Isethionate (Batch 9276B) was studied in two sludges. The sludges were taken from waste water treatment plants treating predominantly domestic waste water (RWZI Tilburg-Noord, Tilburg, The Netherlands and Waterschap de Maaskant, 's-Hertogenbosch, The Netherlands).

Adsorption and desorption kinetics were determined at a nominal initial concentration of approximately 0.7 mg/l. Adsorption and desorption isotherms were determined over a concentration range from approximately 0.007to 0.7 mg/l. The adsorption-desorption

experiments were carried out under sterile conditions at 20°C±2°C in the dark on a roller mixer at a sludge:0.01 MCaCI2 solution ratio of 1:250.

Adsorption equilibrium in sludge was reached after 3 hours. Desorption equilibrium was also reached after3 hours. Sodium lauroyl Isethionate (Batch 9276B) was shown to be stable under sterile conditions.

Sodium lauroyl isethionate adsorption and desorption isotherms couldbe described by the Freundlich equation. Freundlich adsorption and desorption coefficients are summarised in the table below.

Test System	%OC	KF,oc^ads(cm3/g)	KF,oc^des(cm3/g)
Sludge	41.0	1412	1780
Maaskant Sludge	43.0	1490	1842