back into the aqueous solution. Because it has
rigid fluoropolymers and four polyethylene tub-
ings, and detected only one constituent that had
been shown that sorption of organic solutes by
leached from the polypropylene tubing. Among
tubings can be substantial, desorption of sorbed
the flexible tubings, we found several constitu-
organic contaminants has the potential to bias
ents leached from the PVC, thermoplastic elas-
samples if tubing is used for more than one sam-
tomer, and polyurethane tubings (Table 2). The
pling event, especially if it is moved from a well
two fluoropolymer tubings and one of the plasti-
containing high analyte concentrations to one
cized polypropylene tubings (PP1) each leached
with low analyte concentrations. Only a few
one constituent; we were unable to detect that
studies have addressed this issue.
any constituents leached from the other plasti-
Barcelona et al. (1985) studied the release of
organics from five flexible tubings: PP, PE, PTFE,
for the polypropylene (PP) and PE tubings are in
flexible PVC, and silicone rubber. These tubings
general agreement with those of Junk et al. (1974)
had been previously exposed to two test solu-
and Curran and Tomson (1983).
tions, one containing ppb levels of chloroform
Two of the previous studies (Junk et al. 1974,
and one containing ppb levels of four chlorinat-
Curran and Tomson 1983) were conducted under
ed organic solvents. Conditions for these tests
dynamic conditions (with flow rates of 60 and 30
were static, and desorption was followed for
mL/min, respectively). However, only one study
only 1 hr. They reported that most (8090%) of
has examined the effect flow rate (or linear veloc-
the desorption occurred during the first 5 min,
ity) has on leaching. Junk et al. (1974) observed
but by the end of the hour, most (> 50%) of the
that increasing the linear flow rate of water
sorbed organic solutes had not been recovered.
through flexible PVC tubing increased leaching.
They also found that while the rate and extent of
They attributed this to erosion of the polymer
sorption was greatest for the PVC and silicone
matrix. Curran and Tomson (1983) noted that the
rubber tubings, the percent desorbed relative to
total amount of contaminants they observed
the amount sorbed was greatest for PP and PE
leaching from the PE and PP tubings was less
tubings, intermediate for PTFE, and lowest for
than what Junk et al. (1974) had observed. They
the PVC and silicone rubber tubings.
attributed this to differences in flow rate, tubing
Devlin (1987) also found that the PE tubing re-
conditioning, or manufacturing. However, there
leased contaminants over a longer period than
can also be several different formulations of the
Teflon tubing. A test solution containing fifteen
same polymer, and some constituents (additives)
VOCs (ppb levels) was pumped through both
are more readily leached than others.
tubings, and PE was the more sorptive. Devlin
It is not clear what effect continued pumping
found that pumping 5 L of deionized (DI) water
has on leaching. Several leaching studies (Pack-
through the fluoropolymer tubing reduced con-
ham 1971a and 1971b, Gross et al. 1974, Boettner
centrations of the analytes in the rinse water to
et al. 1981) have shown that leaching of organic
less than 1 ppb, but did not do so for the PE tub-
constituents from PVC pipe decreases with time.
ing. No information was provided relative to
This may also be true for some polymeric tub-
which tubing desorbed the analytes most rela-
ings. On the other hand, leaching may remain
tive to the amount sorbed, or what flow rate was
the same or increase with time, as Junk et al.
used in the study. Devlin concluded that carry-
(1974) observed with flexible PVC tubing. They
over of organic contaminants may be a problem
reported that extensive rinsing of flexible PVC
unless a fluoropolymer tubing is used.
served no useful purpose and attributed this to
Thus, very little is known about the kinetics of
the fact that flexible PVC tubing contained "an
desorption, especially when water is pumped
almost inexhaustible source of plasticizers."
through the tubings. Furthermore, the effect that
Thus, relatively little is known about the effect of
flow rate has on this process is unclear.
flow rate and continued pumping on leaching of
organic constituents.
OBJECTIVE
The purpose of these studies was to determine
Desorption of sorbed organic contaminants
Desorption of sorbed organic compounds by
whether, under dynamic conditions, polymeric
polymers proceeds in the opposite order of sorp-
tubings sorbed TCE from contaminated well wa-
tion, i.e., diffusion through the polymer matrix to
ter, leached organic constituents, or desorbed
the surface followed by partitioning/dissolution
sorbed TCE. In our sorption/leaching studies,
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