To confirm these findings, we (Parker and Ran-
those of the controls. These samples were also
ney 1994) repeated the final set of samples from
rubbery and could be bent easily. We concluded
the previous experiment with a few modifications
that there was evidence of a cumulative or inter-
to improve the sensitivity of the test, including
active effect for solutions containing multiple
more replicates and a longer contact time (77 days).
organic solutes that are PVC solvents or good
However, this time there was no significant dif-
swelling agents when the activity of each organic
ference in the hardness readings of the samples
solute is 0.3 or more. We recommended that fu-
exposed to the 0.6-activity solutions and the con-
ture studies should look at mixtures containing
trols. We did note that this time the samples ex-
more solutes, each at lower activities.
posed to the 1.0-activity solutions were pliable.
One other issue that had not been addressed
Generally the TCE results agree well with what
previously in the literature was whether an organic
would be predicted using Berens's isotherms, i.e.,
solvent that is a good solvent or swelling agent
PVC should be softened by TCE at activities of
of PVC and that is also totally miscible in water
0.8 and greater and should become rubbery at an
can soften PVC when mixed with water. For sol-
activity of 0.95 (at 30C). We are not certain why
vents that are totally miscible in water, it is im-
the results for the samples exposed to the 0.6-ac-
possible to estimate the activity of these solutions
tivity solutions from this study did not agree with
using the method described above since this would
those from the previous study. We thought that
involve dividing the analyte's concentration by
if these samples had been given more time, then
an infinite number. To answer this question, we
softening might have occurred, or it may be that
conducted a study using acetone (Parker and
since PVC is known to be very heterogeneous,
Ranney 1994). Acetone is a good swelling agent
of PVC [χ = 0.61 (Berens 1985)] and is totally mis-
then these different results were due to differences
between the test pieces. These studies were rela-
cible in water. In this study, pieces of PVC were
tively short term, and equilibrium was not reached
subjected to a range of concentrations (75, 50, 25,
at the lower activities. We concluded that a longer-
5.0, 0.5, 0.05, 0.0% w/v) for seven days. Because
term study would help resolve whether TCE can
there were no replicates in this study, statistical
soften PVC at an activity of 0.6, and we are cur-
analyses could not be conducted on these data.
rently conducting such a study.
However, after three days we found a very large
Another issue that we addressed in our most
change in the Barcol readings for the samples
recent study (Parker and Ranney 1994) is what
exposed to the 50 and 75% solutions. These sam-
effect an aqueous solution that contains a mix-
ples were rubbery and could be bent easily by
ture of several different organic solvents would
hand. In contrast, by the end of the study (seven
have on PVC. Since groundwater is much more
days) the Barcol readings for the samples exposed
likely to contain a mixture of organic contami-
to the 5, 0.5 and 0.05% solutions did not appear
nants, this is an important question for the ground-
to be different from those of the control samples.
water monitoring industry. Neither Berens nor
There may have been some change in the samples
Vonk has addressed this issue. For 21 days, pieces
exposed to the 25% solution, as the Barcol read-
of PVC were exposed to an aqueous solution that
ings were slightly lower. We concluded that a 50%
contained three organic solvents that were either
solution of acetone rapidly softens PVC and that
good swelling agents or solvents of PVC [meth-
a longer-term study would better define the ef-
ylene chloride, 1,1,2-trichloroethane and 1,2-
fects of lower concentrations.
dichloroethane (χ < 0.6 for all three compounds)],
The purpose of the current study was to an-
each at an activity of 0.3. At this activity level,
swer the following questions:
none of these organic solutes should be able to
What concentrations of acetone are able to
soften PVC by themselves, at least in the time frame
soften PVC when exposure is longer than
of this study. [In fact, previously in this study we
one week?
found that it took eight weeks before there was a
Are there other organic solvents (besides
significant change in the hardness readings of
acetone) that are totally miscible in water
samples exposed to a solution containing one of
and are either good swelling agents or sol-
these solvents (methylene chloride) at a nearly
vents of PVC that can soften PVC when
equivalent activity (0.4).] Statistical analyses of
dissolved in water?
these data revealed that after two days, the Barcol
Is a mixture of several PVC solvents in aque-
readings of the samples exposed to the mixed-
ous solution, each at an activity of 0.05, able
organic solution were significantly lower than
to soften PVC?
4
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