2-(2-butoxyethoxy)ethyl 6-propylpiperonyl ether

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Remarks:

adsorption/desorption

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Principles of method if other than guideline:

EPA Guideline, Subdivision N, Section 163-1

GLP compliance:

yes

Type of method:

HPLC estimation method

Media:

soil

Radiolabelling:

yes

Test temperature:

room temperature

Details on study design: HPLC method:

Extraction of soil samples:
Extract 1: Sonicated with acetonitrile (20 mL) for 15 min at room temperature, shaken for 15 min at room temperature and centrifuged for 20 min at 2000 rpm.
Extract 2: as extract 1
Extract 3: as extract 1, using acetonitrile/water (1:3 by volume)
Extract 4: as extract 3.
Adsorption:
Aliquots (100 µL) of adsorption supernatants from the additional vessel prepared at a concentration of 4.0 mg 14C-Piperonyl Butoxide/L for all soil types removed after the adsorption phase were analysed by HPLC. Possible degradation of the test substance was investigated. The actual concentration of Piperonyl Butoxide was calculated from the solution data and the equilibrium concentration of Piperonyl Butoxide adsorbed to soil was obtained from soil extract data. The remainder of the soil samples at different concentrations was used to generate the Freundlich
adsorption isotherm.
Desorption:
Representative pools (10 % by volume) of supernatants removed after the second desorption from the two vessels remaining for each soil type at a concentration of 4.0 mg/L of the test substance were made. Aliquots (100 µL) of these pools were also analysed by HPLC.
After the second desorption phase had been carried out on duplicate samples of the 4 soils at a concentration of 4.0 mg/L of the test substance each soil was solvent extracted.
High Performance Liquid Chromatography:
Injector: Waters model U6K, Pump: Spectra Physics SP8800 or Waters 600E Multisolvent delivery system, Column oven/heater: RD30-99 Kariba or Waters 680, Radiodetector: Ramona-5 or B-RAM-2A fitted with 400 µL CaF2 (x-cell) detector cell
Method A (reverse phase) Method B (normal phase)
Column Zorbax ODS (ZODS-250A) 250 x 4.6 mm Exsil 100-5 (EX-S-250A) 250 x 4.6 mm
Temperature 40°C ambient
Mobile phase A: 0.1M ammonium formate (pH 4)
B: acetonitrile A: ethylene acetate B: hexane
Flow rate 1.5 mL/min 1.5 mL/min
Gradient Time %A %B Time %A %B
0 98 2 0 5 95
35 0 100 15 10 90
45 0 100 30 50 50
50 98 2 45 100 0

Key result

Type:

Koc

Value:

>= 687 - <= 8 103 L/kg

Temp.:

25 °C

Key result

Type:

Koc

Value:

2 506.5 L/kg

Temp.:

25 °C

Remarks on result:

other: arithmetic mean

4.4              Calculations
4.4.1         Ka , Kd	Soil Ka Kd1 Kd2 Sand 0.98 - - Clay loam 12.04 16.81 94.72 Sandy loam 8.37 8.20 6.32 Silt loam 29.87 41.48 58.15 - not determined due to a low adsorption
4.4.2         Kaoc, Kdoc	Soil Kaoc Kdoc1 Kdoc2 Organic matter (%)   Sand 490 - - 0.2   Clay loam 708 989 5572 1.7   Sandy loam 399 390 301 2.1   Silt loam 830 1152 1615 3.6   - not determined due to a low adsorption

The preliminary test showed that a 24-h equilibrium time was optimum for Piperonyl Butoxide sorption. Desorption time also lasted 24 h. Pilot experimentation with different soil : solution ratios showed that Piperonyl Butoxide was moderately well absorbed to soil. A low ratio of 10:1 corresponding to 2 g soil was therefore chosen.

Furthermore the data showed that a small amount of the test substance was degraded during the equilibrium phases. The results of the no soil control experiment indicated there was some adsorption of radioactivity to glass at the higher concentrations of the test substance.

The mean recovery of radioactivity from all soils after adsorption and    two desorption equilibrations was 104.2 ± 9.5 % sd of that applied. Piperonyl Butoxide was not significantly degraded in the presence of all soil types after the equilibration periods. Due to the exhaustive extraction procedure it was assumed that radioactivity not extracted from the soil was not Piperonyl Butoxide.

The Freundlich adsorption constants K_aranged from 0.98 to 29.87, showing that Piperonyl Butoxide was moderately adsorbed to the range of soils tested. Adsorption constants for sandy loam, clay loam and silt loam appear to correlate reasonably well with soil organic content. With the low organic carbon sand, the extent of adsorption was greater than would have been expected from consideration of soil organic carbon content alone, showing that other mechanisms are contributing to the adsorption.

HPLC analysis of soil extracts and aqueous solutions after desorption showed that Piperonyl Butoxide was only partially degraded. The proportion of Piperonyl Butoxide in soil extracts ranged from 70.9 % - 95.2 % of sample radioactivity. The proportion of Piperonyl Butoxide in aqueous solution ranged from 52.2 % - 76.2 % of sample radioactivity.

For each soil type the K_dvalue for the first desorption was greater than the K_avalue for adsorption except of sand and sandy loam. No desorption isotherms were calculated for sand due to the low adsorption of Piperonyl Butoxide on sand. The K_dvalue for the second desorption was greater than the K_dvalue for the first desorption soil except for sandy loam. For these three other soils this indicated that Piperonyl Butoxide was only weakly desorbed.

Validity criteria fulfilled:

yes

Conclusions:

The Koc values in six soils varied between 687 to 8103 mL/g. The arithmetic mean of 2506.5 L/kg (n=6) is proposed to be used for risk assessment purposes.

Key value for chemical safety assessment

Koc at 20 °C:

2 506.5

Additional information

Piperonyl Butoxide was moderately well adsorbed to the sandy loam, silt loam, clay loam soils and only weakly to sand. Based on the results, Piperonyl Butoxide can be classified as having a low to moderate potential for mobility in sandy loam, clay loam and silt loam and a high mobility in sand.