1,4-Dioxane Chemistry, Uses, and Occurrence - Environmental Investigation and Remediation - page 96

(USEPA, 1989a). Trace amounts of 1,4-dioxane are often found in pesticides because of the inclusion
of ethoxylated surfactants, which include 1,4-dioxane as an impurity (see Section 2.4.1 ). For exam-
ple, a solid mosquito larvicide designed to l oat atop ponds and release its active biocidal ingredient,
Bacillus thuringiensis , lists 1,4-dioxane as present at less than 20 ppm. Other formulations list
1,4-dioxane present at less than 10 ppm as a by-product with ethoxylated alcohols (Cognis Corporation,
2001). Some agency risk assessments and other reviews that list 1,4-dioxane use as a pesticide may
confuse 1,4-dioxane derivatives for 1,4-dioxane. For example, dioxathion [CASRN 78-34-2, is
O , O , O -(1,4-dioxane-2,3-diyl) diphosphorodithioate], a pesticide for deciduous

fruit, is a derivative of 1,4-dioxane that could be mistaken for 1,4-dioxane used as a pesticide.
1,4-Dioxane was used together with benzene to extract and distill the pesticide hexachlorocyclo-
hexane (also called benzene hexachloride, BHC, Lindane), which was widely used as a contact
pesticide for head lice, as a wood preservative, and for other purposes. The solvent mixture was
recovered and reused; however, losses to the waste by-products and product were routinely replaced
with new solvent. Waste solvents were thermally destroyed in well-controlled production opera-
tions; however, there have been examples of extraordinary volumes of waste BHC isomers littering
production sites in Europe (Vijgen, 2006). Disposal of BHC wastes could also be a source of
1,4-dioxane releases to soil and groundwater.

′ , O ′ -tetraethyl S , S ′

2.4.2 T EREPHTHALATE E STERS (P OLYESTER ) AND R ESINS
Polyethylene terephthalate (PET) polyester was i rst introduced in 1952 (USEPA, 1997b). Polyester
i bers are produced from the polycondensation reaction of a dicarboxylic acid, such as terephthalic
acid, and a dihydroxy alcohol, such as ethylene glycol. 1,4-Dioxane forms as a by-product during
esterii cation (Ellis and Thomas, 1998). To manufacture polyester i ber, terephthalic acid and ethyl-
ene glycol are i rst passed through primary and secondary esterii ers to form the monomer. The melt
is then passed to a polymerizer equipped with a high vacuum to allow excess ethylene glycol to
escape. Wastes generated during polymerization may include emissions of volatile organic com-
pounds (VOCs) from leaks, spills, and vents, solid wastes from off-specii cation polymers, and
spent solvent from incomplete polymerization (USEPA, 1997b).
Polymers of PET always contain a certain amount of incorporated diethylene glycol (DEG).
DEG is formed in a side reaction during the ester interchange of dimethyl terephthalate (DMT) with
ethylene glycol. Alternatively, during direct esterii cation of terephthalic acid with ethylene glycol,
DEG is formed via an unusual type of reaction: ester

+ alcohol ether + acid = DEG + 1,4-

methyl carbitol (Hovenkamp and Munting, 1970).
Factories producing PET are generally equipped with wastewater-treatment plants to remove
waste chemicals; however, 1,4-dioxane has proved difi cult to remove. Treated efl uent from an
industrial wastewater-treatment plant at a PET manufacturing facility contained 100 mg/L of
1,4-dioxane in 1995 (European Chemicals Bureau, 2002). Nearly 50% of efl uent samples from a
PET resin plant in Spain had 1,4-dioxane concentrations exceeding 1000

dioxane + methyl cellosolve +

μ g/L; the remainder

showed 1,4-dioxane present from 100 to 1000 μ g/L. The mean concentration of 35 samples was

6400 g/L (Romero et al., 1998). Waste streams from polyester

production plants in the eastern United States routinely contained as much as 2000 mg of 1,4-dioxane
per liter (Grady et al., 1997). Air emissions created during polyester production are estimated to
include 1 mg of 1,4-dioxane per kilogram of polyester i ber produced (Laursen et al., 1997).
The equipment used to produce polyester must be cleaned periodically. The cleaning process
consists of dipping parts in triethylene glycol (TEG) to remove accumulated polyester and by-
products. Spent TEG is recovered and transported off-site for recycling. Parts are then rinsed with
water to remove residual TEG and polyester ingredients. This rinse water represents the primary
wastewater stream at a typical polyester production facility and may total as much as 2 million
gallons annually. Rinse-water constituents typically include TEG, 1,4-dioxane as a by-product
of heating TEG, and polyester by-products such as methanol. Rinse waters may be processed in

μ g/L; the range was 100 to 31,400 μ