Sampling Trace-Level Organics with Polymeric Tubings
LOUISE V. PARKER AND THOMAS A. RANNEY
1988, Kjeldsen 1993). In this paper we will focus on
INTRODUCTION
the biases caused by sorption of organic analytes
It is important that the reported concentrations
by polymeric tubings and leaching of organic con-
of contaminants in samples taken from ground-
stituents from these tubings.
water monitoring wells accurately reflect in-situ
values. Recent studies suggest that, among cur-
rently used sampling methods, low-flow-rate
LITERATURE REVIEW
(~100 mL/min) purging and sampling may cause
When assessing these studies it is important to
the least disturbance to the well during the sam-
differentiate between flexible and rigid formula-
pling process. Samples taken using this method
tions of the same polymer, and to note whether the
have lower turbidity (Kearl et al. 1992, Puls et al.
material that was tested was actually sampling
1992, Puls and Powell 1992, Backhus et al. 1993)
tubing. This is because the formulations can vary
and yield perhaps the most accurate values for
between different products made of the same
inorganic contaminants (Puls and Powell 1992,
polymer and between flexible and rigid formula-
Puls et al. 1992). There is some evidence that indi-
tions of the same polymer, especially polyvinyl
cates that low-flow-rate purging and sampling
chloride (PVC). It is also useful to note whether a
may also produce samples that reflect the true in-
biocide was used. This is especially true for sorp-
situ values of at least some organic contaminants,
tion studies that last several days or longer, be-
such as polycyclic aromatic hydrocarbons (Back-
cause losses of analytes could be due to biodegra-
hus et al. 1993).
dation rather than by sorption by the polymer.
One concern about the slow-rate pumping
For the purpose of clarity in this review, we will
methods for sampling groundwater is that there
discuss separately those studies that were con-
may be interactions between the sampling tubing
ducted using polymeric products other than tub-
(which can be several hundred feet in length) and
ings.
the sample as it is pumped to the surface. The
tubing could either leach inorganic or organic
Leaching of organic constituents
contaminants, thereby giving inaccurate high
With respect to leaching, the importance of dis-
values, or sorb these contaminants from the sam-
cerning between rigid and flexible formulations is
ple, thus giving inaccurate low values. Also, if
most clearly shown with PVC. Several studies (Jae-
pump tubing is not dedicated to a particular well,
ger and Rubin 1970 and 1972, Junk et al. 1974,
it is possible that tubing that was used previously
Christensen et al. 1976, Fayz et al. 1977, Barcelona
to sample a well with high concentrations of con-
et al. 1985) have shown that flexible PVC (FPVC)
taminants would release sorbed contaminants
products leach considerable quantities of phthal-
into the next sample, thereby giving inaccurate
ate ester plasticizers into a variety of fluids (blood,
high values. The diffusion of gases, especially
plasma, saline, water). However, this has not been
oxygen, through the tubing may also affect the
observed with rigid PVC (RPVC) (Miller 1982,
sample as it is pumped to the surface (Holm et al.
Curran and Tomson 1983, Ranney and Parker
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