Forensic Applications for 1,4-Dioxane and Solvent Stabilizers - Environmental Investigation and Remediation - page 446

scrubbing and distillation, and was stabilized with n -methyl pyrrole and pentaphen ( p - tert -amyl
phenol).
Some transformers require a dielectric l uid that will vaporize at higher temperatures. PCE will
react with oxygen at high temperatures, particularly in the vapor phase; therefore, the stabilizers
added to PCE must be equally effective in the liquid and vapor phases. N -methyl pyrrole boils at
112°C (compared with 121°C for PCE) and will be carried into the vapor phase, whereas pentaphen
boils at 266°C but has sufi ciently high vapor pressure in the system to be partially carried into the
vapor phase at the boiling point of PCE (Borror and Rowe, 1981).
N -methyl pyrrole is not unique to the stabilization of PCE in transformers; it is also used to sta-
bilize methyl chloroform and TCE, as described in Chapter 1. Similarly, pentaphen is also used to
stabilize TCE against oxidation. Neither stabilizer provides a unique marker if TCE was among the
solvents released at a site that also had a PCE release from a transformer. However, if the task is to
differentiate PCE from a transformer versus PCE from a dry cleaner, then there may be some poten-
tial to use these stabilizers as marker chemicals. Dry-cleaning grades of PCE apparently did not use
n -methyl pyrrole or pentaphen. The patent literature includes citations of commercial PCE contain-
ing 0.022-0.028% n -methyl pyrrole as an antioxidant (Copelin, 1959); however, citations referring
to pyrrole as a stabilizer of PCE are presented in the vapor degreasing/metal-cleaning context and
not in the dry-cleaning context.
Dow Chemical's dry-cleaning grade of PCE, DowPer, used 4-methyl morpholine, Vulcan's
PerSec used diallylamine and tripropylene compounds, and PPG's dry-cleaning grade used cyclo-
hexene oxide and -ethoxypropionitrile. A stabilizer concentrate for PPG's dry-cleaning grade of

PCE adds cyclohexene oxide,

β

β -ethoxypropionitrile, n -methyl morpholine, and 4-methoxyphenol

(see Table 1.21).
The comparative fate of these stabilizers is fundamental to establishing their utility as marker
chemicals. Table 9.11 contrasts the fate and transport properties of stabilizers of dry-cleaning versus
transformer grades of PCE. The fate and transport properties rule out some stabilizers as marker
chemicals; for example, cyclohexene oxide has low solubility and hydrolyzes easily, and both dial-
lylamine and 4-methyl morpholine are susceptible to sorption in the ionized form they assume once
dissociated in water. In the BIOWIN GCM, all of the PCE stabilizers are estimated to be easily
biodegradable in a matter of weeks. As discussed in Chapter 3, BIOWIN estimates are less reliable
than some of the other estimation tools in the EPIWIN suite, and i eld evidence suggests that at least
one of the compounds in Table 9.11 is resistant to biodegradation because it has been detected years
after the probable date of release.
Butoxymethyl oxirane, also called n -butyl glycidyl ether or n -BGE, was found in soils at a PCE
release in Mountain View, California. The n -BGE was detected in soils adjacent to a chemical pack-
aging facility that packaged paint thinners and related products, but never handled PCE. A PCE
plume of unknown origin was identii ed adjacent to the property, and in soil samples retrieved
beneath a stormwater drainage ditch, where it occurs together with n -BGE. The adjacent property
housed a printing operation, which may have used PCE to clean printing presses and could be a
source of PCE; the stormwater drainage ditch drains from the printing facility toward the chemical
packaging facility. Sewer lines also traverse the area and collect wastewater from an area that
included several former dry-cleaning operations. A complicating factor for interpreting the presence
of n -BGE collocated with PCE is its possible presence in printing inks. Butoxymethyl oxirane is
used as an epoxy resin diluent in some ink formulations (NIEHS, 2004). The detection of butoxym-
ethyl oxirane did not factor into the determination of responsibility for the PCE plume.
For the hypothetical situation in which PCE was released from both a dry cleaner and an electri-
cal transformer, the fate and transport properties suggest that it may be possible to track the move-
ment of the transformer solvent with n -methyl pyrrole and the dry-cleaner solvent with n -butyl
glycidyl ether. The scenario used for this example would be uncommon if it has occurred at all, so
of course no i eld data are available to test the viability of leveraging these stabilizers to differentiate
commingled PCE plumes. Nevertheless, there is a reasonably good potential that some combinations