late the time a pump might remain in a well. Ide-
for each well to reduce the possibility of cross con-
ally, 10 minutes would best simulate the contact
tamination, especially for the more hydrophobic
time of a sample with a bailer. However, since the
contaminants and when concentrations exceed
shortest time interval for which there was data
more than a few ppb.
was 1 hour, we used these data.) These data were
then used to estimate the amount desorbed if the
LOW-TEMPERATURE
concentration of the analytes in the test solution
had been much lower, e.g., 50 g/L. It is clear
CONSIDERATIONS
from this table that potential problems with cross
While the primary focus of this literature re-
contamination due to desorption of analytes is
view has been on determining the efficacy of var-
greater for the more sorptive material, PTFE, and
ious decontamination methods, the effect of cold
decreases substantially for relatively short con-
temperatures on this process should also be men-
tact times (24 hr or less).
tioned. As might be expected, subfreezing tem-
These values are only estimated, and there are
peratures limit the usefulness of aqueous and sol-
a number of factors that could affect the ability of
vent-based decontamination methods. Richter
a material to desorb contaminants. For example,
and Collentine (1983) reported that decontamina-
the potential for cross contamination would be
tion of field equipment in remote areas of Wyo-
less if the time for desorption were more realistic
ming was frustrating and that subfreezing tem-
of a sampling event and less than the three days
peratures of 40F rendered conventional methods
used in this study. On the other hand, more hy-
with soap and water impossible. They recom-
drophobic contaminants would be expected to be
mended taking additional clean equipment in
more readily sorbed; the most hydrophobic con-
the field so that decontamination can be conduct-
taminants used in our study (Parker et al. 1990)
ed later in a specially constructed (i.e., heated)
were p- and m-dichlorobenzene, which have log
wash area.
Kow values of 3.39 and 3.38, respectively (Hansch
and Leo 1979). For flexible tubings, sorption is
considerably more extensive. For example, Gill-
CONCLUSIONS
ham and O'Hannesin (1990) found that after only
10 minutes contact time, flexible PVC sorbed 50%
From these studies the following conclusions
of low (~1) ppm levels of m- and p-xylene, and
can be made:
rigid PVC sorbed little or nothing (losses were 2%
1) Although there are a number of published
or less). Thus, for a pump that remains in the well
methods for decontaminating sampling de-
for several hours, a large amount of some ana-
vices, there is a lot of disparity between the
lytes could be sorbed by the tubing. These con-
methods.
taminants would be available for desorption and
2) There has been very little systematic study
could cause problems with cross contamination.
of the effectiveness of various decontami-
A recent study by our laboratory shows that all of
nation protocols and apparently little docu-
the 20 types of tubing we tested (including sev-
mented basis for the existing guidance.
eral fluoropolymers) were highly sorptive of
3) The type of contaminants, level of contami-
some organics (Parker and Ranney, in press).
nation, and materials being decontaminat-
Given the previous example (Table 6), it is un-
ed clearly affect desorption and decontami-
derstandable how rigid materials subjected to
nation effectiveness.
low ppb concentrations of relatively water-solu-
4) To clean sampling pumps with flexible tub-
ble contaminants for short periods of time may be
ings (even Teflon tubings), neither a clean
easily decontaminated with a single aqueous rinse.
water wash nor a wash with warm deter-
It is also understandable how higher concentra-
gent followed with a clean water rinse is
tions of these contaminants or similar concentra-
generally effective if the pump was exposed
tions of more hydrophobic contaminants may re-
to ppm levels of VOCs. Steam cleaning with
quire several rinses or more stringent cleaning
a detergent solution may be more effective,
(e.g., detergent cleaning). For flexible materials,
although this remains untested.
such as pump tubing where contact times would
5) Cleaning bailers that have very short con-
be much longer than with a bailer, it is clear that
tact times with the samples appears to be
either more extensive cleaning will be necessary
much less problematic.
or that new or dedicated tubing may be required
13
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