Octamethyltrisiloxane

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP.

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

- Temperature: 23.7±0.1°C

Analytical monitoring:

yes

Details on matrix:

Soil 164
- Geographic location: Farditch Farm, Chelmorton, Buxton, Derbyshire, UK. location: Royal Agricultural Society of England, Stoneleigh Park, Stoneleigh, Warwickshire. Soil 248 location Hill Barn Farm, Snowhill, Broadway, Hereford and Worcester

- Storage conditions: Air dried soils refrigerated 5±4°C in sealed opaque bags


PROPERTIES
- Soil texture: Silt loam
- % sand: 22
- % silt: 56
- % clay: 22

- pH: 6.6

- Organic carbon (%): 3.4

- CEC (meq/100 g): 18.0

- Bulk density (g/L): 890

- Water holding capacity (%): 41.1


Soil 248
- Geographic location: Royal Agricultural Society of England, Stoneleigh Park, Stoneleigh, Warwickshire, UK.

- Storage conditions: Air dried soils refrigerated 5±4°C in sealed opaque bags

PROPERTIES
- Soil texture: Sandy loam
- % sand: 72
- % silt: 13
- % clay: 15

- pH: 5.5

- Organic carbon (%): 2.0

- CEC (meq/100 g): 9.9

- Bulk density (g/L): 966

- Water holding capacity (%): 16.4

Soil 282
- Geographic location: Hill Barn Farm, Snowhill, Broadway, Hereford and Worcester, UK.

- Storage conditions: Air dried soils refrigerated 5±4°C in sealed opaque bags

PROPERTIES
- Soil texture: Sandy loam
- % sand: 61
- % silt: 19
- % clay: 20

- pH: 8.3

- Organic carbon (%): 5.5

- CEC (meq/100 g): 20.4

- Bulk density (g/L): 920

- Water holding capacity (%): 31.4

Details on test conditions:

TEST CONDITIONS
- pH: 5.5 to 8.3

TEST SYSTEM
- Type, size and further details on reaction vessel: 20 mm x 125 mm borosilicate glass tube

- Amount of soil/sediment/sludge and water per treatment (if simulation test): 0.25 g dry weight

- Soil/sediment/sludge-water ratio (if simulation test): 1:50

- Number of reaction vessels/concentration: For isotherm experiments: 10, 23, 63, 160, 400, 800 ng 13C-L3 per tube.

- Measuring equipment: Calibrated balance

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

- Method of preparation of test solution: moist test soil and 0.01 M CaCl2 solution added to test vessels and equilibrated overnight by mixing on a rotational mixer. At initiation of each experiment, the vessels were removed from the mixer, a 25 µL aliquot of spike solution (13C-L3 in DMF) was added and the vessel was immediately returned to the mixer in the incubator for the predetermined equilibrium time

Duration:

24 h

Duration:

24 h

Type:

log Koc

Value:

4.34

Temp.:

23.7 °C

Remarks on result:

other: Overall average over different soils

Type:

log Koc

Value:

4.28

Temp.:

23.7 °C

% Org. carbon:

3.4

Remarks on result:

other: Soil 164

Type:

log Koc

Value:

4.37

Temp.:

23.7 °C

% Org. carbon:

2

Remarks on result:

other: Soil 248

Type:

log Koc

Value:

4.38

Temp.:

23.7 °C

% Org. carbon:

5.5

Remarks on result:

other: Soil 282

Adsorption and desorption constants:

Desorption log Koc 4.35 (overall average over different soils)
Desorption log Koc: 4.27 (Soil 164); 4.35 (Soil 248); 4.42 (Soil 282).

Recovery of test material:

Average mass balance ranged from 66 ± 9% to 88 ±5 % for adsorption and 55 ± 5% to 76 ±3% for desorption. These results were noticeably low, and probably due to loss of L3 from the aqueous phase through volatilisation and degradation. However, the similarity in the Koc values for L3 when approaching equilibrium from opposite directions (i.e. adsorption vs. desorption) indicated that the losses were sufficiently slow so as to not affect the Koc measurement.

Table 1: Concentration of L3 in the solid and liquid phases at the end of adsorption equilibration period

Concentration (ng 13C-L3 per tube)	Soil 164 (OC 3.4%)				Soil 248 (OC 2.0%)				Soil 282 (OC 5.5%)
	on soil (ng/g)	in solution (ng/g)	Kd	Log Koc	on soil (ng/g)	in solution (ng/g)	Kd	Log Koc	on soil (ng/g)	in solution (ng/g)	Kd	Log Koc
10	7.523	0.01057	712	4.32	8.183	0.01314	623	4.49	8.161	0.005370	1520	4.44
	6.541	0.01108	590	4.24	5.860	0.01318	444	4.35	7.411	0.006294	1177	4.33
23	19.52	0.02919	669	4.29	17.74	0.03645	487	4.39	21.28	0.01541	1374	4.40
	20.64	0.02999	688	4.31	15.19	0.03546	428	4.33	20.01	0.01468	1363	4.39
63	48.50	0.07025	690	4.31	39.87	0.08469	471	4.37	51.32	0.03954	1298	4.37
	46.68	0.07052	662	4.29	35.90	0.7882	455	4.36	53.70	0.03820	1406	4.41
160	143.3	0.2234	642	4.28	87.78	0.1837	478	4.38	124.7	0.09203	1355	4.39
	127.3	0.1900	670	4.29	99.44	0.2137	465	4.37	132.9	0.1031	1289	4.37
400	289.8	0.4565	635	4.27	290.4	0.6437	451	4.35	369.4	0.2775	1331	4.38
	311.9	0.5027	620	4.26	267.8	0.5989	447	4.35	328.4	0.2741	1198	4.34
800	741.1	1.173	632	4.27	531.5	1.183	449	4.35	778.8	0.6289	1238	4.35
	712.7	1.210	589	4.24	537.7	1.267	424	4.33	764.0	0.6096	1253	4.36
Average			650	4.28			469	4.37			1317	4.38

Validity criteria fulfilled:

yes

Conclusions:

An adsorption log Koc value of 4.34 at 23.7 °C (overall average over three different soils) and desorption log Koc value of 4.35 at 23.7 °C (overall average over three different soils) were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Adsorption / desorption: adsorption log K_oc 4.34 at 23.7 °C (overall average over three different soils); desorption log K_oc 4.35 at 23.7 °C (overall average over three different soils)

Key value for chemical safety assessment

Koc at 20 °C:

21 877.616

Additional information

An adsorption log Koc value of 4.34 at 23.7 °C (overall average over three different soils) and a desorption log Koc value of 4.35 at 23.7 °C (overall average over three different soils) were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

[LogKoc: 4.34]