Forensic Applications for 1,4-Dioxane and Solvent Stabilizers - Environmental Investigation and Remediation - page 422

TABLE 9.2
Stabilizer Content in Distilled Methyl Chloroform Solvent Waste at a Major
Midwest Manufacturer

Amount in New Methyl
Chloroform (wt%)

Amount in Distilled Methyl
Chloroform Solvent Waste (wt%) Stabilizer Difference

1,4-Dioxane 3.17 0.92-2.79 −12% to −71%

1,2-Butylene oxide 0.45 0.26-1.59

−42% to +253%

Nitromethane 0.35 0.26-0.54

−26% to +54%

Source: Bohnert, G.W. and Carey D.A., 1991, Scale-up of recovery process for waste solvents. Technical
Communications. Kansas City, Missouri: Allied Signal Aerospace Company.

expected to photo-oxidize, disperse, or return to the surface through precipitation or condensation
at inconsequential concentrations (see Section 3.1.4).

9.1.2 I MPURITIES *
The impurities in chlorinated solvents mentioned in Section 1.2.7 can also be important to forensic
investigations and can be used together with stabilizers for determining whether iterative concen-
tration in vapor degreasing cycles due to boiling-point differences could produce enough impurity
mass to be used as a marker chemical to trace the plume. Studies of the occurrence and fate of
solvent impurities provide a model for the analysis of “high-boiler” stabilizers that boil at tempera-
tures higher than the solvent. The presence of impurities in solvents is difi cult to document as most
producers list their products in terms of their purity, attributing the fraction that is not the solvent to
unspecii ed proprietary stabilizers. Nevertheless, some documentation of impurities in solvents is
available, as tabulated in Table 9.3 .
Two published studies describe the potential for PCE to be present at TCE release sites where PCE
was never used, through the presence of PCE as an impurity of TCE production and the concentration of
PCE during vapor degreasing because of boiling-point differences. The key distinction between the two
proi les is the assumption of the starting PCE concentration that may be present as an impurity of TCE.
The i rst proi le of PCE as an impurity of TCE is provided in Environmental Forensics—
Contaminant Specii c Guide (Morrison and Murphy, 2006). Morrison, Murphy, and Doherty have
noted that these solvents are produced by the same process and then separated by fractional distil-
lation (Morrison et al., 2006), which is facilitated by the large boiling-point difference between
TCE and PCE, that is, 87.2°C and 121.2°C, respectively (Shepherd, 1962). Morrison et al. (2006)
cited a recent chemical supplier's specii cations website for impurity content in degreasing grade
TCE of up to 3-4% chlorinated compounds. † As described subsequently in this section, this esti-
mate is probably too high for most grades of TCE.
The second proi le of PCE as an impurity of TCE is provided by Lane and Smith (2006), ‡ who have
cited Dow Chemical's records showing that Dow's TCE had no detectable “perchloroethylene as a
manufacturing impurity” (“PCEMI”) of TCE since about 1990. The reporting limit for analyses per-
formed by Dow Chemical was 1 ppm PCE in TCE. Dow has been one of the leading providers of TCE
in the United States since the 1960s. PCEMI may have been present in TCE produced by Dow before
the 1990s, or in TCE from other solvent producers, as suggested by older MSDS and other citations.

* From Gauthier, T.D. and Murphy, B.L., 2003, Environmental Forensics 2003(4): 205-213. With permission.
† Unfortunately, the cited website is no longer operational.
‡ See Lane and Smith (2006).