Biomedical Engineering Reference
In-Depth Information
Table 2.1. (continued)
Common Acronyms
or Trade Names
Solvent
Main Uses
Comments
1,2-Dichloroethane
Ethane dichloride,
ethylene dichloride,
EDC, 1,2-DCA
Chemical intermediate Major use is for the production
of VC, the precursor to
manufacture polyvinyl chloride
(PVC) resins. The uses of 1,2-
DCA as lead scavenger and soil
fumigant were discontinued.
Annual worldwide production
exceeds 1,000,000 tons.
1,2-Dichloropropane Propylene dichloride,
1,2-D
Solvent, chemical
intermediate, soil
fumigant
Generated as undesirable
by-product of the chlorohydrin
process. Use as fumigant to
control root parasitic nematodes
has been discontinued in the
United States and the EU.
Resources: (ATSDR,
1997
; Doherty,
2000a
,
b
; Rossberg et al.,
2006
)
Halogenated Solvents Industry Alliance, Inc. (
http://www.hsia.org/
)
increased recycling of spent PCE solutions) rather than a true reduction of PCE use. Dry
cleaning is a multibillion dollar industry and PCE remains the solvent of choice for the majority
of the 27,000-30,000 United States dry-cleaners and launderers. Recently, some United States
states have introduced legislation to phase out PCE in dry cleaner operations over the next
decade, and a gradual decline in PCE usage can be expected (Chemical Week,
2007
).
Chlorinated solvents are colorless, highly volatile liquids at room temperature, with limited
solubility in water, low viscosity and low interfacial tension relative to water. Another unifying
feature of chlorinated solvents is their high density relative to water, with densities ranging
from 1.1 to 1.7 grams/milliliter (g/mL). The characteristic physical-chemical properties govern
chlorinated solvent behavior following release into the environment and profoundly impact
their environmental distribution and longevity. Table
2.2
lists some relevant properties of CAHs
commonly encountered as groundwater pollutants.
Without clear regulatory guidance in place in the United States until the 92nd United States
Congress enacted the Clean Water Act in 1972 (CWA,
1972
) chlorinated solvent wastes were
commonly disposed by pouring them onto the ground or down a drain. These disposal practices
assumed that the solvents would readily volatilize to the atmosphere where photochemical
degradation would occur. Unfortunately, the solvents often infiltrated through the subsurface,
causing extensive subsurface contamination. Upon release, the poorly water-soluble and
denser-than-water chlorinated solvents migrated downward and penetrated the water table, a
characteristic that coined the term dense nonaqueous phase liquids (DNAPL).
In aquifer formations, capillary forces retain discontinuous liquid ganglia or droplets of
chlorinated solvent within the porous media. Furthermore, low permeability layers (e.g., clay)
cause DNAPL to accumulate and spread laterally resulting in the formation of high-saturation
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