Environmental Engineering Reference
In-Depth Information
ingredient in technical DDT but is a contaminant (Metcalf 1995). Although the use of
DDT in the U.S. was discontinued in 1973, DDT and its metabolites are frequently
encountered in soil, with
p
,
p
'-DDE being a major component (Aigner et al. 1998;
ATSDR 2002; Boul et al. 1994; Thiele et al. 1997). Although DDE can come from tech-
nical-grade DDT as a contaminant, the production of DDE from DDT may result from
aerobic biotic degradation, abiotic dehydrochlorination, and even from photochemical
decomposition (Thiele et al. 1997). DDE, however, has been reported to be more persist-
ent than DDT and can be found in soil decades after the last DDT treatment (Boul et al.
1994; Spencer at al. 1996). The U.S. Geological Survey (USGS 1999) has reported that
in the U.S. the frequency of detection was
p
,
p
'-DDE (in 60% of urban sites and 48% of
rural areas surveyed), followed by
p
,
p
'-DDD,
p
,
p
'-DDT,
o
,
p
'-DDD,
o
,
p
'-DDT, and
o
,
p
'-
DDE, with the latter two being in less than 5% of the samples.
DDE toxicity and recalcitrance to degradation are regarded by many as a serious
environmental problem. To be able to model and predict the fate and transport of DDE,
it is necessary to have accurate partitioning data. However, the reported values of the
physicochemical properties often vary by several orders of magnitude for
p
,
p
'-DDE;
hence, the values reported in Table 1 represent the means (Shen and Wania 2005). Data
for
o
,
p
'-DDE were scarce, with the most recent values given in ATSDR (2002).
The formula log
K
oc
= 0.989 log (
K
ow
) − 0.346 uses the octanol-water partition coef-
ficient to give a semiempirical measurement of the sorption of hydrophobic chemicals
to soil and sediment (Karickhoff 1981). For
p
,
p
'-DDE and
o
,
p
'-DDE, the log
K
oc
values
are 3.1 and 2.6, respectively. A value greater than 3 indicates a strongly sorbed chemical
with little potential for leaching from the soil surface. However, the chemical may be
bound to soluble humic acid material that occurs as free-moving organic carbon and can
Table 1
Data available for
p
,
p
'-DDE (Shen and Wania 2005) and
o,p
'-DDE (ATSDR 2002)
Common name
p
,
p
'-DDE
o
,
p
'-DDE
IUPAC name
1-Chloro-4-[2,2-dichloro-1-
1-Chloro-2-[2,2-dichloro-1-
(4-chlorophenyl)ethenyl]
(4-chlorophenyl)ethenyl]
benzene
benzene
Structure
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
CAS registry number
72-55-9
3424-82-6
Molecular weight (g/mole)
318.03
318.03
Melting point
88.6°C
No data
Aqueous solubility
(mg/L at 25°C)
0.26
0.14
Vapor pressure (torr at 25°C)
4.3 × 10
−6
6.2 × 10
−6
Henry's law constant
(atm-m
3
/mol at 25°C)
4.1 × 10
−5
1.8 × 10
−5
Log (octanol-water
partition coefficient)
6.96
6.00
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