Transport and Partitioning
DDT and its metabolites may be transported from one medium to another by the processes of
solubilization, adsorption, remobilization, bioaccumulation, and volatilization. In addition, DDT can be
transported within a medium by currents, wind, and diffusion. These processes will be discussed in the
following paragraphs.
Organic carbon partition coefficients (Koc) of 1.5x105 (Swann et al. 1981), 5.0x104 (Sablejic 1984), and
1.5x105 (Meylan et al. 1992) reported for p,p’-DDT, p,p’-DDE, and p,p’-DDD, respectively, suggest that
these compounds adsorb strongly to soil. These chemicals are only slightly soluble in water, with
solubilities of 0.025, 0.12, and 0.090 mg/L for p,p’-DDT, p,p’-DDE, and p,p’-DDD, respectively
(Howard and Meylan 1997). Therefore, loss of these compounds in runoff is primarily due to transport of
particulate matter to which these compounds are bound. For example, DDT and its metabolites have been
found to fractionate and concentrate on the organic material that is transported with the clay fraction of
the washload in runoff (Masters and Inman 2000). The amount of DDT transported into streams as runoff
is dependent on the methods of irrigation used (USGS 1999). In the Western United States, DDT
concentrations in streambed sediment increased as the percentage of furrow irrigation, as opposed to
sprinkler or drip irrigation, increased. In the San Joaquin River Basin, more DDT was transported during
winter runoff than during the irrigation season (Kratzer 1999). Since the compounds are bound strongly
to soil, DDT would remain in the surface layers of soil and not leach into groundwater. However, DDT
can adsorb to free-moving dissolved organic carbon, a soluble humic material that may occur in the soil
solution. This material behaves as a carrier and facilitates transport of DDT into subsurface soil (Ding
and Wu 1997). DDT released into water adsorbs to particulate matter in the water column and sediment.
Sediment is the sink for DDT released into water. There it is available for ingestion by organisms, such
as bottom feeders. Reich et al. (1986) reported that DDT, DDE, and DDD were still bioavailable to
aquatic biota in a northern Alabama river 14 years after 432,000–8,000,000 kg of DDT was discharged
into the river. DDT in the water column above the outfall of Los Angeles County’s Joint Water Pollution
Control Plant’s outfall was present both in the dissolved phase and the particulate phase (defined as
particles size >0.7 µm) (Zeng et al. 1999). It is interesting to note that more of the DDT was present in
the dissolved phase than in the particulate phase despite its high hydrophobicity.
There is evidence that DDT, as well as other molecules, undergoes an aging process in soil whereby the
DDT is sequestered in the soil so as to decrease its bioavailability to microorganisms, extractability with
solvents, and toxicity to some organisms (Alexander 1995, 1997; Peterson et al. 1971; Robertson and
Alexander 1998). At the same time, analytical methods using vigorous extractions do not show
significant decreases in the DDT concentration in soil. In one such study, DDT was added to sterile soil
at various concentrations and allowed to age (Robertson and Alexander 1998). At intervals, the toxicity
of the soil was tested using the house fly, fruit fly, and German cockroach. After 180 days, 84.7% of the
insecticide remained in the soil, although more than half of the toxicity had disappeared when the fruit fly
was the test species, and 90% had disappeared when the house fly was the test species. The effect with
the German cockroach was not as marked. Recently, a study was conducted to determine the
bioavailability of DDT, DDE, and DDD to earthworms (Morrison et al. 1999). It was shown that the
concentrations of DDT, DDE, DDD, and ΣDDT were consistently lower in earthworms exposed to these
compounds that had persisted in soil for 49 years than in earthworms exposed to soil containing freshly
added insecticides at the same concentration. The uptake percentages of DDT and its metabolites by
earthworms were in the range of 1.30–1.75% for the 49-year-aged soil, but were 4.00–15.2% for the fresh
soil (Morrison et al. 1999). Long term monitoring data have also indicated that aged and sequestered
DDT are not subject to significant volatilization, leaching, or degradation (Boul et al. 1994). The
concentrations of DDT, DDE, and DDD monitored at two sites in a silt loam in New Zealand declined
from 1960 to 1980, but very little loss was evident from 1980 to 1989 (Boul et al. 1994). The lack of
appreciable biodegradation as DDT ages in soil suggests that the compound is not bioavailable to
microorganisms. Aging is thought to be associated with the continuous diffusion of a chemical into
micropores within soil particles where it is sequestered or trapped, and is therefore unavailable to
microorganisms, plants, and animals (Alexander 1995). In the case of biodegradation, the aging process
results in the gradual unavailability of substrate that makes the reaction kinetics appear to be nonlinear.
There is abundant evidence that DDT gets into the atmosphere as a result of emissions or volatilization.
The process of volatilization from soil and water may be repeated many times and, consequently, DDT
may be transported long distances in the atmosphere by what has been referred to as a ‘global distillation’
from warm source areas to cold polar regions (Bard 1999; Bidleman et al. 1992; Goldberg 1975; Ottar
1981; Wania and MacKay 1993). As a result, DDT and its metabolites are found in arctic air, sediment,
and snow with substantial accumulations in animals, marine mammals, and humans residing in these
regions (Anthony et al. 1999; Harner 1997). An analysis of sediment cores from eight remote lakes in
Canada indicated that ΣDDT concentrations in surface sediments (0–1.3 cm depth) declined significantly
with latitude (Muir et al. 1995). The maximum ΣDDT concentrations in core slices in midcontinent lakes
date from the late 1970s to 1980s, which is about 5–10 years later than the maximum for Lake Ontario.
Volatilization of DDT, DDE, and DDD is known to account for considerable losses of these compounds
from soil surfaces and water. Their tendency to volatilize from water can be predicted by their respective
Henry's law constants, which for the respective p,p’- and o,p’- isomers are 8.3x10-6, 2.1x10-5, 4.0x10-6,
5.9x10-7, 1.8x10-5, and 8.2x10-6 atm-m3/mol (Howard and Meylan 1997). The predicted volatilization
half-lives from a model river 1 m deep, flowing at 1 m/sec, with a wind of 3 m/sec are 8.2, 3.3, 10.5, 6.3,
3.7, and 8.2 days, respectively. Laboratory studies of the air/water partition coefficient of DDE indicate
that it will volatilize from seawater 10–20 times faster than from freshwater (Atlas et al. 1982). The
authors suggest that this process may be related to interaction at the bubble-water surface.
Volatilization from moist soil surfaces can be estimated from the Henry’s law constant divided by the
adsorptivity to soil (Dow Method) (Thomas 1990). The predicted half-life for DDT volatilizing from soil
with a K
oc of 240,000 is 23 days, compared to an experimental half-life of 42 days. Sleicher and Hopcraft
(1984) estimated a volatilization half-life of 110 days for DDT from soil in Kenya based on mass transfer
through the boundary layers, and claimed that volatilization of DDT was sufficient to account for its rapid
disappearance from soil. However, laboratory experiments in which 14C-p,p’-DDT was incubated in an
acidic (pH 4.5–4.8), sandy loam soil maintained at 45 EC for 6 hours/day for 6 weeks resulted in neither
volatilization of DDT or its metabolites nor mineralization (Andrea et al. 1994). Other studies using a
latosol soil (pH 5.7) found that 5.9% of the radioactivity was lost through volatilization during a 6 week
incubation at 45 EC (Sjoeib et al. 1994). The volatilization rate of DDT from soil is significantly
enhanced by temperature, sunlight, and flooding of the soil (Samuel and Pillai 1990).
Transport of DDT in the atmosphere of central and eastern North America is facilitated by a circulation
pattern that brings moisture from the Gulf of Mexico into the Midwest and the airflow patterns across the
Transport and Partitioning
DDT and its metabolites may be transported from one medium to another by the processes of
solubilization, adsorption, remobilization, bioaccumulation, and volatilization. In addition, DDT can be
transported within a medium by currents, wind, and diffusion. These processes will be discussed in the
following paragraphs.
Organic carbon partition coefficients (Koc) of 1.5x105 (Swann et al. 1981), 5.0x104 (Sablejic 1984), and
1.5x105 (Meylan et al. 1992) reported for p,p’-DDT, p,p’-DDE, and p,p’-DDD, respectively, suggest that
these compounds adsorb strongly to soil. These chemicals are only slightly soluble in water, with
solubilities of 0.025, 0.12, and 0.090 mg/L for p,p’-DDT, p,p’-DDE, and p,p’-DDD, respectively
(Howard and Meylan 1997). Therefore, loss of these compounds in runoff is primarily due to transport of
particulate matter to which these compounds are bound. For example, DDT and its metabolites have been
found to fractionate and concentrate on the organic material that is transported with the clay fraction of
the washload in runoff (Masters and Inman 2000). The amount of DDT transported into streams as runoff
is dependent on the methods of irrigation used (USGS 1999). In the Western United States, DDT
concentrations in streambed sediment increased as the percentage of furrow irrigation, as opposed to
sprinkler or drip irrigation, increased. In the San Joaquin River Basin, more DDT was transported during
winter runoff than during the irrigation season (Kratzer 1999). Since the compounds are bound strongly
to soil, DDT would remain in the surface layers of soil and not leach into groundwater. However, DDT
can adsorb to free-moving dissolved organic carbon, a soluble humic material that may occur in the soil
solution. This material behaves as a carrier and facilitates transport of DDT into subsurface soil (Ding
and Wu 1997). DDT released into water adsorbs to particulate matter in the water column and sediment.
Sediment is the sink for DDT released into water. There it is available for ingestion by organisms, such
as bottom feeders. Reich et al. (1986) reported that DDT, DDE, and DDD were still bioavailable to
aquatic biota in a northern Alabama river 14 years after 432,000–8,000,000 kg of DDT was discharged
into the river. DDT in the water column above the outfall of Los Angeles County’s Joint Water Pollution
Control Plant’s outfall was present both in the dissolved phase and the particulate phase (defined as
particles size >0.7 µm) (Zeng et al. 1999). It is interesting to note that more of the DDT was present in
the dissolved phase than in the particulate phase despite its high hydrophobicity.
There is evidence that DDT, as well as other molecules, undergoes an aging process in soil whereby the
DDT is sequestered in the soil so as to decrease its bioavailability to microorganisms, extractability with
solvents, and toxicity to some organisms (Alexander 1995, 1997; Peterson et al. 1971; Robertson and
Alexander 1998). At the same time, analytical methods using vigorous extractions do not show
significant decreases in the DDT concentration in soil. In one such study, DDT was added to sterile soil
at various concentrations and allowed to age (Robertson and Alexander 1998). At intervals, the toxicity
of the soil was tested using the house fly, fruit fly, and German cockroach. After 180 days, 84.7% of the
insecticide remained in the soil, although more than half of the toxicity had disappeared when the fruit fly
was the test species, and 90% had disappeared when the house fly was the test species. The effect with
the German cockroach was not as marked. Recently, a study was conducted to determine the
bioavailability of DDT, DDE, and DDD to earthworms (Morrison et al. 1999). It was shown that the
concentrations of DDT, DDE, DDD, and ΣDDT were consistently lower in earthworms exposed to these
compounds that had persisted in soil for 49 years than in earthworms exposed to soil containing freshly
added insecticides at the same concentration. The uptake percentages of DDT and its metabolites by
earthworms were in the range of 1.30–1.75% for the 49-year-aged soil, but were 4.00–15.2% for the fresh
soil (Morrison et al. 1999). Long term monitoring data have also indicated that aged and sequestered
DDT are not subject to significant volatilization, leaching, or degradation (Boul et al. 1994). The
concentrations of DDT, DDE, and DDD monitored at two sites in a silt loam in New Zealand declined
from 1960 to 1980, but very little loss was evident from 1980 to 1989 (Boul et al. 1994). The lack of
appreciable biodegradation as DDT ages in soil suggests that the compound is not bioavailable to
microorganisms. Aging is thought to be associated with the continuous diffusion of a chemical into
micropores within soil particles where it is sequestered or trapped, and is therefore unavailable to
microorganisms, plants, and animals (Alexander 1995). In the case of biodegradation, the aging process
results in the gradual unavailability of substrate that makes the reaction kinetics appear to be nonlinear.
There is abundant evidence that DDT gets into the atmosphere as a result of emissions or volatilization.
The process of volatilization from soil and water may be repeated many times and, consequently, DDT
may be transported long distances in the atmosphere by what has been referred to as a ‘global distillation’
from warm source areas to cold polar regions (Bard 1999; Bidleman et al. 1992; Goldberg 1975; Ottar
1981; Wania and MacKay 1993). As a result, DDT and its metabolites are found in arctic air, sediment,
and snow with substantial accumulations in animals, marine mammals, and humans residing in these
regions (Anthony et al. 1999; Harner 1997). An analysis of sediment cores from eight remote lakes in
Canada indicated that ΣDDT concentrations in surface sediments (0–1.3 cm depth) declined significantly
with latitude (Muir et al. 1995). The maximum ΣDDT concentrations in core slices in midcontinent lakes
date from the late 1970s to 1980s, which is about 5–10 years later than the maximum for Lake Ontario.
Volatilization of DDT, DDE, and DDD is known to account for considerable losses of these compounds
from soil surfaces and water. Their tendency to volatilize from water can be predicted by their respective
Henry's law constants, which for the respective p,p’- and o,p’- isomers are 8.3x10-6, 2.1x10-5, 4.0x10-6,
5.9x10-7, 1.8x10-5, and 8.2x10-6 atm-m3/mol (Howard and Meylan 1997). The predicted volatilization
half-lives from a model river 1 m deep, flowing at 1 m/sec, with a wind of 3 m/sec are 8.2, 3.3, 10.5, 6.3,
3.7, and 8.2 days, respectively. Laboratory studies of the air/water partition coefficient of DDE indicate
that it will volatilize from seawater 10–20 times faster than from freshwater (Atlas et al. 1982). The
authors suggest that this process may be related to interaction at the bubble-water surface.
Volatilization from moist soil surfaces can be estimated from the Henry’s law constant divided by the
adsorptivity to soil (Dow Method) (Thomas 1990). The predicted half-life for DDT volatilizing from soil
with a K
oc of 240,000 is 23 days, compared to an experimental half-life of 42 days. Sleicher and Hopcraft
(1984) estimated a volatilization half-life of 110 days for DDT from soil in Kenya based on mass transfer
through the boundary layers, and claimed that volatilization of DDT was sufficient to account for its rapid
disappearance from soil. However, laboratory experiments in which 14C-p,p’-DDT was incubated in an
acidic (pH 4.5–4.8), sandy loam soil maintained at 45 EC for 6 hours/day for 6 weeks resulted in neither
volatilization of DDT or its metabolites nor mineralization (Andrea et al. 1994). Other studies using a
latosol soil (pH 5.7) found that 5.9% of the radioactivity was lost through volatilization during a 6 week
incubation at 45 EC (Sjoeib et al. 1994). The volatilization rate of DDT from soil is significantly
enhanced by temperature, sunlight, and flooding of the soil (Samuel and Pillai 1990).
Transport of DDT in the atmosphere of central and eastern North America is facilitated by a circulation
pattern that brings moisture from the Gulf of Mexico into the Midwest and the airflow patterns across the
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