Forensic Applications for 1,4-Dioxane and Solvent Stabilizers - Environmental Investigation and Remediation - page 420

A broad estimate of the rate and concentration of 1,4-dioxane accumulation in solvent waste can
be inferred from solvent-waste recovery studies. The vapor degreasing operations using methyl
chloroform at the southeastern air force bases listed in Table 1.8 are proi led more extensively in
Table 9.1 for their potential to accumulate 1,4-dioxane in liquid solvent waste.
Estimates of the total mass of 1,4-dioxane at release sites are not widely available. Approximately
16,000 gallons of methyl chloroform from the Rocky Flats Closure Project were buried at the Idaho
National Engineering Laboratory (INEL). Engineers at INEL estimated the 1,4-dioxane content of
the methyl chloroform from the industrial literature because the methyl chloroform in question was
not used for vapor degreasing where 1,4-dioxane would become progressively concentrated; rather,
the methyl chloroform was used in uranium processing (Shuckrow et al., 1982). On the basis of an
average 1,4-dioxane content in methyl chloroform of 2.75 vol% (2.1 wt%) and a maximum
1,4-dioxane content of 3.5 vol% (2.67 wt%), the corresponding average and maximum 1,4-dioxane
masses in the buried methyl chloroform were 1720 kg and 5900 kg, respectively. The only docu-
mented value for 1,4-dioxane in methyl chloroform at the site of origin was 1.9% (INEL, 2006).
A major Midwest manufacturer studied the stabilizer content of solvents to improve the quality
of solvents recovered by distillation for reuse. The i rm's industrial engineers sought to identify the
solvent stabilizers in methyl chloroform, TCE, and PCE to restore the original composition follow-
ing on-site distillation. The stabilizers in TCE were identii ed as 1,2-butylene oxide, cyclohexene
oxide, p - tert -butyl phenol, and 1-propanol. Stabilizers in new methyl chloroform supplied by two
solvent producers were identii ed. The i rst, presumably supplied by Dow Chemical, contained the
familiar formula of 1,4-dioxane (3.17 wt%), nitromethane (0.35%), and 1,2-butylene oxide (0.45%),
whereas the second, presumably supplied by Vulcan Chemical, contained 1,3-dioxolane (2.45%),
nitromethane (0.3%), and 1,2-butylene oxide (1.45%) (Bohnert and Carey, 1991). * The concentration
of stabilizers in the solvent that was removed from vapor degreasers and stored in drums was not
measured, as the study objective concerned rei ning distillation techniques. Following a i ltering,
desiccation, and distillation process, the distilled methyl chloroform solvent waste had a lower
weight percent of 1,4-dioxane, as shown in Table 9.2 .
This i nding of less 1,4-dioxane in the distilled solvent waste is consistent with the expectation
of increased 1,4-dioxane concentrations in vapor degreasing waste due to boiling-point differences.
Distillation retains only the vapor fraction of 1,4-dioxane (~27%). The Tarrer et al. study of south-
eastern air force base vapor degreasers also observed a decrease in 1,4-dioxane concentration fol-
lowing distillation of methyl chloroform solvent waste. The waste had 2.9% 1,4-dioxane initially
and 1.96% after distillation, a decrease of 32% (Tarrer et al., 1989). A second study by the same
Midwest manufacturer analyzed the amount of 1,4-dioxane in distilled methyl chloroform and
found a 65% decrease in 1,4-dioxane concentration (Holt, 1990) (see Table 9.7 ).
The solvent distillation process proi led in the Bohnert and Carey report used a preparatory dry-
ing step to return the solvent to required moisture conditions (less than 100 ppm water in methyl
chloroform and TCE). Drying was achieved with a recirculating pump and a 3 Å (angstrom) (0.3 nm)
molecular sieve desiccant bed. Solvent waste was recirculated through the sieve for 24-48 h or as
needed to decrease the moisture level to the target of 100 ppm water (Bohnert and Carey, 1991).
While removing the water that accumulated in the solvent, water-soluble stabilizers are also
likely to be removed, particularly 1,4-dioxane. The fate of the removed water then becomes impor-
tant to the forensic investigation. If the desiccant was regenerated by using a centrifuge or gravimet-
ric technique, then the handling of the wastewater should be investigated to coni rm whether it was
discharged on site or hauled away as hazardous waste. If the desiccant was regenerated through an
evaporation step, then it is likely that the 1,4-dioxane was emitted to the atmosphere, where it is
* The report did not identify the solvent producers; Dow held the i rst patent for use of 1,4-dioxane in methyl chloroform,
and Vulcan held an early patent for use of 1,3-dioxolane to stabilize methyl chloroform (Bursack et al., 1963). Both Dow
and Vulcan produced methyl chloroform stabilized by 1,4-dioxane or 1,3-dioxolane. The third major solvent producer,
PPG, often used dimethoxymethane and tert -butyl alcohol instead of either 1,4-dioxane or 1,3-dioxolane (PPG, 1998).