heptan-2-yl [(5-chloroquinolin-8-yl)oxy]acetate

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:

30 May 1989 to 24 July 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20°C

Analytical monitoring:

yes

Details on sampling:

100 mL of 0.01M calcium chloride with 0.05 to 0.4 ppm CGA 185072 were mixed with 1 to 5 g of oven dried soil. The suspensions were then shaken for 6 hours prior to separation by centrifugation (ca 5000 g). Sub-samples of the supernatant were analysed by LSC and TLC.

Details on matrix:

Collombey (CH) - Loamy sand - pH 7.2, organic carbon 0.96
Lakeland (USA) - Sand - pH 6.7, organic carbon 0.70
Les Evouettes (CH) - Silty loam - pH 6.5, organic carbon 1.40
Vetroz (CH) - Silty loam - pH 7.1, organic carbon 4.20
Illarsaz (CH) - Loam - pH 6.7, organic carbon 19.60

Duration:

6 h

Initial conc. measured:

> 0.05 - < 0.4 mg/kg soil d.w.

Temp.:

20

Duration:

24 h

Temp.:

20

Type:

Koc

Value:

>= 6 521 - <= 19 314

Adsorption and desorption constants:

Adsorption Constants
Collombey (CH) - 1/n = 0.809
Lakeland (USA) - 1/n = 0.918
Les Evouettes (CH) - 1/n = 0.854
Vetroz (CH) - 1/n = 0.885
Illarsaz (CH) - 1/n = 0.973

Desorption Constants
Collombey (CH) - 1/n = 0.834
Lakeland (USA) - 1/n = 0.829
Les Evouettes (CH) - 1/n = 0.830
Vetroz (CH) - 1/n = 0.858
Illarsaz (CH) - 1/n = 0.992

Recovery of test material:

The recovery in all soils was between 90.0 and 115.1% of the applied radioactivity. Radioactivity extracted from the soil with acetone was found to be intact parent compound. Non-extractable radioactivity was low, between 2.4 and 4.7% of applied radioactivity.

Soil types, Origin	Org. C	Org. Matter	pH	Clay	CEC	Adsorption			Desorption		Ref.
						KF	1/n	KOC	KF	KOC
	[%]	[%]		[%]	meq/100g	[ml/g]		[ml/g]	[ml/g]	[ml/g]
Cloquintocet-Mexyl
Loamy sand, Collombey, CH	0.96	1.67	7.2	2.6	4.80	62.6	0.809	6521	82.1	8563	Keller, 1990
Sand, Lakeland, USA	0.70	1.2	6.7	1.3	2.37	135.2	0.918	19314	144.7	20671
Silty loam, Evouettes, CH	1.4	2.40	6.5	11.1	8.52	189.6	0.854	13640	290.5	20899
Silty loam, Vetroz, CH	4.2	7.2	7.1	19.4	30.58	641.9	0.885	15283	622.7	14826
Loam, Illarsaz, CH	19.6	33.8	6.7	n.d.	48.16	1855	0.973	9494	3987	20345
Average ± Standard dev.								12850 ± 4991		17061 ± 5380

Validity criteria fulfilled:

yes

Conclusions:

The adsorption/desorption of cloquintocet-mexyl was investigated in five soils having different properties. The study included sand, loamy sand, silty loam and loam soils with organic carbon contents between 0.7% and 19.6%. The Freundlich adsorption constants KFranged from 62.6 to 1855 ml/g, the KOC-values were between 6521 and 19314, the average being 12850 ± 4991 ml/g. These data indicate a strong adsorption to soil. The desorption constants showed that the adsorption was reversible, but that adsorption increased with time.

Executive summary:

The adsorption/desorption of cloquintocet-mexyl was investigated in five soils having different properties. The study included sand, loamy sand, silty loam and loam soils with organic carbon contents between 0.7% and 19.6%. The Freundlich adsorption constants KFranged from 62.6 to 1855 mL/g, the KOC-values were between 6521 and 19314, the average being 12850 ± 4991 mL/g. The corresponding KOM-values were 3782 to 11203 mL/g, the average being 7439 ± 2896 mL/g. These data indicate a strong adsorption to soil. The desorption constants showed that the adsorption was reversible, but that adsorption increased with time.

Description of key information

The adsorption behaviour of cloquintocet-mexyl was investigated in a reliable study performed to OECD 106 guideline. Keller (1990) reported Koc values for five soils with a mean value of 12850, which indicates strong adsorption to soil. In addition, Hill (1994) investigated the adsorption behaviour of the main environmental metabolite of cloquintocet-mexyl in three soils and reported a mean Koc of 1772.

Key value for chemical safety assessment

Koc at 20 °C:

12 850

Additional information

A reliable GLP-compliant study (Keller 1990) investigated adsorption behaviour of cloquintocet-mexyl for five soils. This study was conducted to OECD 106 guideline and is considered to be reliable without restrictions. The Freundlich adsorption constants ranged from 62.6 to 1855 mL/g, the Koc values were between 6521 and 19314 and the mean Koc was 12850 ± 4991 mL/g. Results indicate strong adsorption of cloquintocet-mexyl to soil.

The adsorption behaviour of the main metabolite, Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-, was studied by Hill (1994) in a reliable GLP-compliant study conducted to OECD 106 guideline. Results for three soils show that the metabolite is a slightly mobile to immobile compound, with a Koc ranging from 1186 to 2870 µg/g (mean Koc 1772).

The corresponding constants for the desorption cycles were somewhat higher revealing that sorption was only partially reversible and become stronger with time. Both compounds were stable within the equilibrium period of the adsorption and desorption tests.

The low mobility of cloquintocet-mexyl and its metabolite is confirmed by the finding of aged residue column leaching studies (Ellgehausen 2001, Keller 1991 (three reports)). These studies are not included in the IUCLID dossier, as they are going beyond the data requirements of REACH and do not provide relevant additional information. The studies indicate that the total radioactivity which is found in the percolation water amounts to ≤0.08% of the applied dose (200 mm precipitation within 4 days). Even under worst-case conditions of 508 mm of artificial rainfall within 40 days, no radiocarbon exceeding 0.7% can be detected in the leachate. On the other side, 85 - 108% are retained in the soil columns, mostly in the top 4 cm layers (79 - 92%).

A field leaching study performed under realistic worst-case conditions at two sites in England (Fogg and Carter, 1998) confirms these results. A formulation containing cloquintocet-mexyl was applied at a field rate of 15 g/ha cloquintocet-mexyl on a sandy and a clay soil on 6 December 1996. Both sites were located in Warwickshire, England, on land typically used for growing winter cereals; Sandy soil (0-26 cm): 11.28% clay, 26.49% silt, 62.22% sand, 2.3% organic carbon, pH 7.0, CEC 11.40 meq/100g; Clay soil (0-22 cm): 30.77% clay, 42.16% silt, 27.07% sand, 1.7% organic carbon, pH 7.3, CEC 17.6 meq/100g; Average annual rainfall: 620 mm; winter rainfall: 200-210 mm. No residues of cloquintocet-mexyl or its metabolite could be detected in the soil water samples (<0.05 mg/L) collected at soil depths between 25 cm and 120 cm. Drain water collected at 80 cm and run-off water both collected from the clay field did not contain any residues.

Based on these results, the potential of cloquintocet-mexyl and its metabolites to contaminate the shallow groundwater is negligible. Even under the worst-case conditions of application in winter, no risk can be perceived.