SOLUBILITY AND SORPTION OF 8:2 FLUOROTELOMER ALCOHOL BY SURFACE SOILS
Jinxia Liu and Linda S. Lee, Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA
Results and Discussion
Abstract
Solubility in Binary Solvents
ƒ Elucidating sorption by soils of fluorotelomer alcohols is important
towards predicting their fate and related polymers particularly in
landfills where products such as polymer-coated carpets and paper
utensils are disposed.
Aqueous soloubility
1.5
0.5
y = 7.04 x - 0.65
R2 = 0.98
-0.5
-1.5
0
0.1
0.2
0.3
Select the cosolvent with most linear behavior
Measure sorption coefficients in
cosolvent/water solutions
Estimate water solubility
by extrapolation
ƒ Reliable aqueous data is difficult to obtain due to the unique
properties of FTOHs including high vapor pressure, low aqueous
solubility, and a strong affinity for glass and fluoropolymeric materials.
Estimate aqueous-based sorption
coefficients by extrapolation
Directly measure water
solubility
ƒ The use of cosolvents can minimize volatilization losses,
degradation, sorption to glassware, and mass-transfer limitations.
Directly measure aqueous-based
sorption coefficients
0.4
ƒ Kd,mix increased with
increasing fc.
10% acetone
24% acetone
15.0
9.0
6.0
ƒ
2
log S mix = log S w + σ ⋅ f c
0
log K d , mix = log K d , w − α ⋅ σ ⋅ f c
ƒ
-1
ƒ Dissolved organic carbon (DOC) of aqueous supernatants
analyzed using a Shimadzu TOC-VCSH Analyzer.
4
3
2
1
0
Reduction of Matrix Effects
-1
4
Soil Properties
Unbuffered
mobile
phase
Soil
Texture
pH
(Isotherm)
Sand
(% )
Clay
(% )
OC
(% )
CEC
(cmolc/kg)
EPA14
Drummer 6
Oakville 24
7CB
SK961098
Clay
Clay loam
Sandy
Silt loam
Clay loam
3.6
5.8
4.4
5.3
7.5
2
21
92
32
38
64
36
4
18
34
0.48
2.5
0.52
8.18
4.6
18.9
23.3
3.8
10.9
38.2
0
Buffered
mobile
phase
After
cleanup
Before
cleanup
0.4
0.6
0.8
1.0
Cosolvent-extrapolated Kd,w values
are consistently higher than those
measured directly from water with
relative differences being soildependent.
Lower Kd,w values measured directly
was hypothesized to be due to DOC.
DOC was measured in FTOH-free
soil slurries and cosolventextrapolated Kd,w were assumed to
be the true values (Ktrue):
Resulting in an overall average log
KDOC of 5.30 ± 0.29.
2
1
empirical constant reflecting solvent-sorbent interactions.
0.2
K d* , w = K true (1 + K DOC [DOC ])
3
where S is solubility, Kd is the sorption coefficient (L kg-1), subscripts
mix and w refer to the cosolvent/water mix and water, respectively, fc is
the volume fraction of cosolvent, and σ is the cosolvency power, α is an
0.010
0.020
Cw (ug/mL)
Evaluation of Cosolvency Method
log Kd,mix (log Kd,w )
ƒ Log-linear cosolvency models for solubility (Yalkowsky, 1972) and
sorption (Rao et al., 1985) are:
-1
0.0
0.1
0.2
127 (13.3)
452.2 (32.6)
124 (15.5)
453.1 (82.1)
ƒ Reversible sorption equilibrium was
established within 24 h; Kd values
constant ≥ 24 h.
ƒ Irreversible sorption increased with
time; increasing contact times from 3
h to 72 h decreased soil extraction
efficiency from 85% to 45%.
ƒ 8:2 FTOH sorption is
exothermic; Kd,w increased
with increasing temperature.
Temp. Soil: water ratio
4 °C
22 °C
Kd, L/Kg
1:40
1:40
318.4
196.1
Note: Soil SK961089 and equilibration time = 3 h
0.0
4
ƒ Deuterated 8:2 (1D,1D,2D,2D, 313C-perfluorodecanol) was used
as the internal standard.
24 h
72 h
Effects of Temperature
4
3.0
1
Log-linear Cosolvency Models
Measured Soil 7CB Kd (L/kg)*
Equil.
Water
Time 10% Acetone
230.8 (25.5)
83.1 (4.7)
3h
Serie
Liquid Phase Conc. Cw (ug/mL)
Sample Analysis
Irreversible Sorption
* Single applied conc. in triplicate
6
0
0.000
0.0
Compare
ƒ Average log Koc = 4.13 ± 0.16 and 3.84 ± 0.16 estimated by extrapolation
from cosolvents and measured directly, respectively.
2
Compare
ƒ LC/MS/MS (Shimadzu LC; Applied Biosystem 3000 MS) in the
negative ionization mode (see Szostek et al., 2004).
17% acetone
30% acetone
8
12.0
3
Materials and Methods
0.5
Cosolvent Volume Fraction, fc
ƒ Sorption isotherms
were well fitted by the
linear sorption model (R2
≥ 0.94). Isotherms
exemplified for soil 7CB
(figure to right).
ƒ Aqueous sorption coefficients are best correlated with soil OC
ƒ Sw = 0.226 mg/L (22°C)
estimated by extrapolation
from acetone/water data in
good agreement with
aqueous data of 0.194 ±
0.032 mg/L & slightly higher
than 0.137 ± 0.053 mg/L
(Kaiser et al., 2004).
Cs (ug/g)
Measure solubility in binary solvents
Correlation with OC content
ƒ Acetone cosolvency power
(σ) for 8:2 FTOH is 7.04.
Methanol/water
2.5
Solid Phase Conc. Cs (ug/g)
Introduction
ƒ Deviations greater in
methanol/water mix
Acetone/water
Sorption Isotherms
Experimental Scheme
ƒ Fluorotelomer alcohols (FTOHs) are raw intermediates in the
synthesis of fluorinated polymers and surfactants, which are suspected
to contain or degrade into FTOHs, and subsequently into
perfluorinated acids.
3.5
Log Solubility, Smix (mg/L)
The 8:2 fluorotelomer alcohol (CF3-(CF2)7-(CH2)2-OH) (8:2 FTOH), one of the confirmed precursors of perfluorooctanoic acid was
selected as the probe compound to elucidate the sorption mechanisms of FTOHs in soils. Solubility and sorption by five soils of 8:2 FTOH were
measured from water and cosolvent/water solutions. Aqueous solubility and soil-water distribution coefficients (Kd,w, L kg-1) were extrapolated
from cosolvent data using a log-linear cosolvency model and compared to direct aqueous measurements. Liquid chromatography tandem mass
spectrometry with electrospray ionization was employed to analyze the 8:2 FTOH in solutions and soil extracts. The cosolvent-extrapolated
water solubility is 0.224 mg L-1 in good agreement with the measured value of 0.194 mg L-1. All sorption isotherms were generally linear
regardless of cosolvent composition or soil organic carbon (OC) content. Kd,w values extrapolated from cosolvent data were similar, but
consistently higher than those measured in aqueous solutions. The latter was hypothesized to be due to dissolved OC (DOC) in the aqueous
slurries. An average log KDOC of 5.30 was estimated and supported by DOC and Kd,w measurements at two soil-water ratios. Sorption appeared
to be driven by hydrophobic partitioning with a log Koc of 4.13 ± 0.16. Irreversible sorption was also observed and appeared related to OC
content with extraction efficiency reduced from 85% to 45% with increasing contact time from 3 h to 72 h for the highest OC soil.
0.3
Volume Fraction Acetone, f c
ƒ Likewise, SK961089 equilibrated at
soil:water ratio of 1:1 yielded higher
DOC and lower Kd,w than measured
for a 1:40 soil:water ratio and gave a
similar log KDOC (see table below).
Summary of log Koc values and estimated log KDOC Values
Conclusions
ƒ 8:2 FTOH solubility of 0.224 mg/L from log-linear extrapolation from
acetone/water data is in good agreement with measured aqueous values.
ƒ Aqueous sorption coefficients from log-linear extrapolation from
acetone/water data are consistently higher than measured aqueous
values. Aqueous DOC was speculated to cause the lower sorption from
water with an estimated log KDOC = 5.30 ± 0.29.
ƒ Sorption appears to be primarily driven by hydrophobic partitioning with
a log Koc = 4.13 ± 0.16.
ƒ Sorption of 8:2 FTOH to soils is an exothermic process.
ƒ Irreversible sorption of 8:2 FTOH increased with increasing contact time.
ƒ Irreversible sorption and large Koc values in the absence of DOC
suggests that mobility of telomer alcohols may be limited.
ƒ If DOC levels are high (e.g., landfill scenario), facilitated transport may
be a concern.
Acknowledgements
Funded in part by DuPont’s Center for Collaborative Research and Education in
Wilmington, DE & a Purdue University Lynn Fellowship. Special thanks to Stephen
Sassman for assisting in methods development & Matt Ruark for DOC analysis.
References
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10-fold increase in response by
adding 5 mM ethanolamine to
mobile phase.
(b) soil extracts:
> 2 fold increase in response after
cleanup with SupelCleanTM ENVICarb bulk packing.
Szostek, B.; Capka, V. et al. Application of LC-MS/MS methodology to determination of
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