Propargite

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:

22nd September 2008 to 6th January 2009

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

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 ± 2 ºC

Analytical monitoring:

yes

Details on matrix:

COLLECTION AND STORAGE
- Soil preparation: 2 mm sieved, air-dried

PROPERTIES
See Table 1 in field "Any other information on materials and methods incl. tables"

Details on test conditions:

PREPARATION OF DOSING SOLUTIONS
Dosing solutions for the 0.003, 0.015, 0.03, 0.15 and 0.3 µg/mL (ppm) samples were prepared by dilution of the concentrated stock solution. Final concentration was determined by LSC.

PRELIMINARY TESTS
To determine the tube type giving the best propargite recoveries, preliminary tests were performed with glass, silylated glass and Teflon tubes. Silanised glass surfaces showed the least adsorption of propargite to walls and were used for the test. Three soil to solution ratios (1:25, 1:45 and 1:90) were tested. Greater than 70 % adsorption of propargite onto five soils was observed at the ratio of 1:25. However, the 1:25 ratio showed the least amount of 14Cpropargite sticking to vessel surfaces (<5 %). As the aqueous volumes were increased, the test material plating increased on silanised glass surfaces. The equilibrium was reached after approximately 2 hours of shaking.

DEFINITIVE TESTS
One g of soil was added to 25 mL 14C-propargite dissolved in 0.01 M CaCl2 solution. Following equilibration, 20 µL of application solutions prepared in acetonitrile were added to each tube to obtain five concentrations (see above) covering two orders of magnitude. The tubes were shaken at a speed sufficient to keep the soils suspended in solution in the dark at 20 ºC for two hours. After centrifugation, the aqueous phase was decanted off and the radioactivity present in the solution within determined by LSC. The soils were used for desorption experiments for which 25 mL 0.01M CaCl2 was added to the soil and the shaking process repeated. The desorption experiment was repeated a second time using the same procedure. Representative solutions were analysed by HPLC and desorbed soils were subjected to combustion analysis.

Computational methods:

ADSORPTION COEFFICIENT
Kd(ads) = Cs/Cw

Kom(ads) = (Kd(ads) / om) x 100

Koc(ads) = (Kd(ads) / oc) x 100

Where:
Kd(ads) = adsorption coefficient (mL/g)
Cs = concentration of test material in the soil phase at adsorption equilibrium (µg/g)
Cw = concentration of test material in aqueous phase at adsorption equilibrium as determined by LSC and HPLC (µg/mL)
om = organic matter = oc x 1.72 (%)
oc = organic carbon (%)
Kom(ads) = adsorption coefficient corrected for the organic matter (om) (mL/g)
Koc(ads) = adsorption coefficient corrected for the organic carbon (oc) (mL/g)

DESORPTION COEFFICIENT
Kd(des) = Cs.D / Cw,D

Kom(des) = (Kd(des) / om) x 100

Koc(des) = (Kd(des) / oc) x 100

Where:
Kd(des) = desorption coefficient (mL/g)
Cs,D = concentration of the test material in the soil phase at desorption equilibrium (µg/g)
Cw,D = concentration of test substance in aqueous phase at desorption equilibrium as determined by LSC and HPLC (µg/mL)
om = organic matter = oc x 1.72 (%)
oc = organic carbon (%)
Kom(des) = desorption coefficient corrected for the organic matter (om) (mL/g)
Koc(des) = desorption coefficient corrected for the organic carbon (oc) (mL/g)

ADSORPTION ISOTHERMS
The Freundlich adsorption isotherm, KF(ads), and the exponential constant, 1/n(ads), were determined by linear regression analysis of the Freundlich equation.

Cs(ads) = KF (ads) x Cw(ads)1/n(ads)

The linear form of this equation is shown below.

log(Cs(ads)) = log (KF (ads)) + 1/n(ads) x log(Cw(ads))

Plotting the linear form of the Freundlich equation with log(Cs(ads)) on the y-axis and log(Cw(ads)) on the x-axis will yield a line with a slope of 1/n(ads) and a y-intercept of log(KF(ads)). The KF(ads) value will be used to calculate KFom(ads) and KFoc(ads) values.

KFom(ads) = KF(ads) / (om / 100)

KFoc(ads) = KF(ads) / (oc / 100)

DESORPTION ISOTHERMS
The Freundlich desorption isotherm, KF(des), and the exponential constant, 1/n(des), will be determined by linear regression analysis of the Freundlich equation.

Cs(des) = KF(des) x Cw(des)1/n(des)

The linear form of this equation is shown below.

log(Cs(des)) = log(KF (des)) + 1/n(des) x log(Cw(des))

Plotting the linear form of the Freundlich equation with log(Cs (des)) on the y-axis and log(Cw(des)) on the x-axis will yield a line with a slope of 1/n(des) and a y-intercept of log(KF(des)).

The KF(des) value will be used to calculate KFom(des) and KFoc(des) values.

KFom(des) = KF(des) / (om / 100)

KFoc(des) = KF(des) / (oc /100)

Key result

Type:

Koc

Value:

15 608.6

Temp.:

20 °C

% Org. carbon:

> 0.81 - < 4.03

Remarks on result:

other: adsorption (mean value)

Key result

Type:

Kd

Value:

324.1

Temp.:

20 °C

% Org. carbon:

> 0.81 - < 4.03

Remarks on result:

other: adsorption (mean value)

Key result

Type:

Koc

Value:

9 260

Temp.:

20 °C

% Org. carbon:

> 0.81 - < 4.03

Remarks on result:

other: desorption (mean value)

Key result

Type:

Kd

Value:

193.3

Temp.:

20 °C

% Org. carbon:

> 0.81 - < 4.03

Remarks on result:

other: desorption (mean value)

Recovery of test material:

90.8-107.8 %

Transformation products:

yes

Table1: Adsorption and desorption coefficients

	Adsorption			Desorption
Soil type	Kd(ads) (mL/g)	Kom(ads) (mL/g)	Koc(ads) (mL/g)	Kd(des) (mL/g)	Kom(des) (mL/g)	Koc(des (mL/g)
02-A (silt loam)	242.1	10248	17668	132.2	5596	9648
03-G (clay loam)	610.8	8792	15157	383.4	5519	9514
06-A (clay loam)	391.1	8249	14221	220.8	4657	8029
Speyer 2.1 (sand)	143.0	10240	17653	89.8	6434	11091
Speyer 6S (clay)	233.5	7758	13344	140.3	4661	8018
Mean	324.1	9057.4	15608.6	193.3	5373.4	9260

Table 2: Freundlich isotherm parameters

		Adsorption				Desorption
Soil type	OC%	KF	KFOC	1/n	r^2	KF,des	KFOC, des	1/n	r^2
02-A (silt loam)	1.37	478.08	34896	1.1251	0.9880	305.21	22278	1.1742	0.9608
03-G (clay loam)	4.03	2326.48	57729	1.2134	0.9817	12.27*	304*	1.0030	0.9968
06-A (clay loam)	2.75	1192.89	43378	1.1906	0.9817	989.69	35989	1.2489	0.9574
Speyer 2.1 (sand)	0.81	169.98	20985	1.0348	0.9943	187.97	23207	1.1563	0.9860
Speyer 6S (clay)	1.75	337.13	19265	1.0676	0.9920	560.27	32016	1.2811	0.9692
Mean*		900.91	35251	1.13		510.79	28373	1.22

*The Kd(des) and Koc(des) were determined to be 383.4 and 9514, respectively, in the preliminary test. Therefore the value from the mean test soil 03-G were not used for the mean.

Validity criteria fulfilled:

not specified

Conclusions:

Under the conditions of the test, the average Kd(ads) values ranged from 143.0 to 610.8 mL/g. The average Kom(ads) values ranged from 7758 to 10248 mL/g while the average Koc(ads) values ranged from 13344 to 17668 mL/g. The average Kd(des) values ranged from 89.8 to 383.4 mL/g. The average Kom(des) values ranged from 4657 to 6434 mL/g while the average Koc(des) values ranged from 8018 to 11091 mL/g. The mean Freundlich adsorption coefficients values KF(ads), KFom(ads) and KFoc(ads) of propargite in soils amounted to 901, 20452 and 35251 (1/n = 1.13), respectively. The mean values for the desorption coefficients KF(des), KFom(des) and KFoc(des) amounted to 409, 13174 and 22698 (1/n = 0.98) respectively. The carbon content of the soil seems to have an effect on the extent of sorption. Propargite is non-mobile in soils and is poorly desorbed.

Executive summary:

The adsorption/desorption of ¹⁴C-propargite was examined in five soils. The average K_d(ads) values ranged from 143.0 to 610.8 mL/g. The adsorption coefficients were corrected for organic matter and organic carbon content to calculate the K_om(ads) and K_oc(ads) values. The average K_om(ads) values ranged from 7758 to 10248 mL/g while the average K_oc(ads) values ranged from 13344 to 17668 mL/g. The average K_d(des) values ranged from 89.8 to 383.4 mL/g. The desorption coefficients were corrected for organic matter and organic carbon contents to calculate K_om(des) and K_oc(des) values. The average K_om(des) values ranged from 4657 to 6434 mL/g while the average K_oc(des) values ranged from 8018 to 11091 mL/g. The mean Freundlich adsorption coefficients values K_F(ads), K_Fom(ads) and K_Foc(ads) of propargite in soils amounted to 901, 20452 and 35251 (1/n = 1.13), respectively. The mean values for the desorption coefficients K_F(des), K_Fom(des) and K_Foc(des) amounted to 409, 13174 and 22698 (1/n = 0.98) respectively. The carbon content of the soil seems to have an effect on the extent of sorption. Propargite is non-mobile in soils and is poorly desorbed.

Description of key information

Mean Koc was determined to be 35251; study conducted in accordance with OECD 106; Walsh (2009).  Key value for chemical safety assessment was based on all available data.

Key value for chemical safety assessment

Koc at 20 °C:

30 538

Additional information

See 'Environmental fate and pathways'.