sorptive it is. Flexible tubings such as those used
al. 1985, Devlin 1987, Ranney and Parker, in prep.)
to pump water samples to the surface have been
and thus decontamination (desorption) takes
shown to be very highly sorptive (Barcelona et al.
longer.
1985, Reynolds and Gillham 1985, Gillham and
Understanding the kinetics of desorption of
O'Hannesin 1990, Ranney and Parker, in prep.).
organic contaminants from permeable materials
For example, Barcelona et al. (1985) found flexi-
is critical to determining the potential for effec-
ble polyvinyl chloride (PVC) and silicone rub-
tive decontamination. Unfortunately, only a few
ber tubing sorbed 80% of the chloroform in an
studies (Miller 1982, Barcelona et al. 1985, Parker
aqueous solution (100 ppb) in 1 hour. Gillham and
et al. 1990) have examined desorption of organic
O'Hannesin (1990) compared sorption of low (~1)
contaminants from polymeric materials. Specifi-
ppm levels of six aromatic hydrocarbons (benzene,
cally, Miller (1982) looked for desorption of sever-
toluene, ethylbenzene, and o-, m- and p-xylene)
al volatile organic analytes from polyethylene,
by rigid and flexible PVC. After 10 minutes, loss-
polypropylene, and (rigid) PVC. Parker et al.
es of these analytes ranged from 0 to 2% for solu-
(1990) looked for desorption of a suite of organic
tions exposed to rigid PVC vs. 35 to 50% for those
contaminants (VOCs, nitroaromatics, and a nitra-
exposed to flexible PVC tubing.
mine) from (rigid) PVC and PTFE. Although nei-
Leggett and Parker (1994) were able to success-
ther of these studies followed the kinetics of this
fully model (predict) equilibrium sorption of or-
process, they both found that the amount desorbed
ganic solutes by polytetrafluoroethylene (PTFE,
did not always parallel the amount sorbed; e.g.,
one type of Teflon) and rigid PVC based upon
Parker et al. (1990) found that although p- and m-
meaningful physical/chemical interaction param-
dichlorobenzene were sorbed the most rapidly
eters of the organic contaminants. They used
and to the greatest extent by PTFE, trichloroet-
multiparameter linear solvation energy relation-
hylene (TCE) and trans-1,2-dichloroethylene
ships (LSERs) to describe the equilibrium par-
appeared to be desorbed the most rapidly (since
titioning. Partitioning was related to the com-
they were desorbed to the greatest extent after
pound's basicity, acidity, polarity/polarizability,
3 days). (A biocide was added to prevent any loss-
and molecular volume. These models proved to
es due to biological activity in this study.) For
be more accurate than octanolwater partition
PVC, the amount desorbed tended to correlate
coefficients in correlating the experimental
with the amount sorbed. However for PTFE, it
partitioning data. This approach may also prove
appeared that smaller molecules were more easi-
useful for predicting how readily a surface can be
ly or rapidly desorbed than larger molecules, per-
decontaminated or if desorption of analytes that
haps because diffusion is more rapid for smaller
have been absorbed within the polymer matrix
molecules.
could be rapid and extensive enough to affect an-
Barcelona et al. (1985) compared desorption of
alyte concentrations.
chloroform from five flexible tubing materials
Thus, for permeable materials, decontamina-
(polypropylene, polyethylene, PVC, silicone rub-
tion may involve more than removing surface con-
ber, and PTFE). They found that with all the poly-
taminants, depending upon the kinetics of sorp-
mers, 80 to 90% of the desorption they observed
tion and desorption, contact times, and contact
occurred almost immediately (i.e., within the first
volumes. An example of this can be seen when
5 to 10 minutes) although, the amount desorbed
Devlin (1987) tried to decontaminate tubings made
constituted less than 10% of the total chloroform
of polyethylene and an unspecified fluoropoly-
sorbed. After 5 minutes, polypropylene and poly-
mer (Teflon) that had been exposed to ppb levels
ethylene desorbed more of the total chloroform
of a suite of VOCs. Devlin found it was harder to
sorbed (on a percentage basis) even though the
decontaminate polyethylene tubing than the flu-
silicone rubber and PVC tubings had sorbed more
oropolymer tubing. At least 5 L of deionized wa-
chloroform more rapidly.
ter was required to reduce the concentrations of
According to several researchers (Brusseau and
these analytes in the leachates from the fluoro-
Rao 1989, Di Cesare and Smith 1994), soil organic
polymer tubing to below 1 ppb, and the leachates
matter can be envisioned as a three-dimensional
from the polyethylene tubing still contained con-
matrix of randomly oriented polymer chains with
centrations greater than 1 ppb of several analytes
a relatively open, flexible structure. An apparent-
after 8 L flush. One explanation for these results
ly similar pattern of desorption of nonionic or-
may be that polyethylene is more sorptive of
ganic compounds from natural soils has also
organic solutes than Teflon tubing (Barcelona et
been reported in kinetic studies (Pavlostathis and
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