Abstract
Preliminary investigations using radioactively labelled
DDT indicate that 50-90% of the DDT at a low concentration
in water is codistilled with as little as 5-20% loss of water
by evaporation over a 48 hour period. Under a constant air
flow as much as 15of this loss is recovered by water and
particulate material of a second solution placed in series.
Particulate matter in the second solution concentrates DDT
1.000 to 50,000 times the level in the ambient water, depend¬
ing both on the surface area and nature of the particles.
Experiments with the bay mussel Mytilus edulis suggest that
filter feeders can readily incorporate DDT from water and
particulate matter. These results indicate that codistilla-
tion and air currents may be important in transporting
significant quantities of DDT to the marine environment where
it may enter the food chain. The variation of levels of DDT
on glassware, suspended particles and in the sea water suggests
that an equilibrium exists between the DDT adsorbed on various
materials and that found in the surrounding water.
Introduction
Earlier studies have indicated a high codistillation
rate of DDT with water (Acree 1963). In addition, signifi-
cant levels of DDT residues have been found in the atmosphere
(Risebrough et al. 1968; Abbott et al. 1965). These results
suggest that evaporation and subsequent transport by air
currents may be important processes in the transfer of DDT
from the site of application to distant areas. Of special
interest is the possible role of these mechanisms in the
contamination of the marine environment. Further, Odem.
Woodwell, and Wurster (1969) reported high levels of DDT
on particles of organic detritus, and suggested that this
might be an important mode for the entrance of DDT into
marine animals. The preliminary studies presented here
support the hypothesis that codistillation and air currents
are important in transporting DDT to the marine environment
where it can be concentrated on particles and enter the food
chain through filter feeders.
Materials and Methods
The experimental apparatus was composed of three one-
gallon jars as shown in Figure 1. Jar 1 was sealed and
served as a control for the system. Two one-gallon jars
and two oil traps were connected in series by glass tubing
as pictured in Fig. 1. An air stream of 2-3 liters/minute
entered the otherwise sealed system from a pressurized line
and blew across the water surface in jars 2 and 3.
After washing all jars and glass tubing with ethanol
and rinsing clean with filtered sea water, one liter of sea
water was successively filtered through O.8u, O.45u, and 0.22u
Millipore filters and added to each jar. Particles of known
weight were placed in jar 3 and kept circulated by means of
a magnetic stirer. In order to compare the affinity of DDT
for natural particles, three materials were used. Celite,
a diatomaceous earth (Johns Mansfield Co.), approximated
inorganic detritus. Organic detritus was simulated by taking
material from a phytoplakton tow, freezing it in an acetone
dry-ice bath, and drying to a powder in a 52°C oven. Fine
sand ranging from 0.2-0.4mm was collected in the Monterey
Marina, frozen, and dried to permit direct comparison with
the "detritus" discussed earlier. Celite and the "detritus"
were of comparable size and weight, while the inorganic
nature of both celite and sand allowed comparisons between
these materials. 20mg of particles were used in all runs
except one. In that case O.2gm sand, with a volume equal to
that of 20mg dry detritus, was used to provide a comparison
for approximately equal surface areas of the two materials.
O.lml of 14 parts per million C1+ DDT in ethanol (phenyl
ring C14 (U) 54uC/mg, Aldrich Chemical Co., Milwaukee, Wis.)
was added to jars 1 and 2 making the concentrations in the
sea water of these jars equal to 1,4 parts per billion,
194
slightly above the upper range of the solubil ity of DDT in
water (Bowman, Acree, Corbett 1960). Jar 3 contained no
C14 DDT.
After 48 hours the level of DDT was determined for the
system. DDT in the water of jars 1 and 2 was removed in
three extractions of 50ml reagent grade hexane. For each
extraction the separatory funnel was shaken vigorously for
one minute then left standing for ten minutes. A lml aliquot
of each hexane extract was placed in 1Oml Toluene scintillation
fluid (4gm PPO, O.lgm POPOP in toluene to make 1 liter solution)
and counted in a liquid scintillation counter (Nuclear-Chicago
Unilux II) for 10 minutes. Counts from each extraction were
summed and the activity of the total water sample was calcu-
lated. This procedure had earlier been demonstrated to remove
greater than 99% of the DDT from the water. To check adsorption
on the glass, the jars were washed with 25ml hexane and a lml
aliquot was counted.
The particles in jar 3 were separated from the water by
centrifugation (about 4000x g for 10-15 minutes) and the DDT
content of both was determined. The supernatent from the
centrifugation was pipeted off and extracted with hexane
according to the same procedure used for the water in jars I
and 2. The particles were resuspended in ethanol, put in
scintillation fluid and counted. Filtration was not used to
isolate particles since C+ DDT was found to be absorbed
readily by Millipore filters.
3
Results and Discussion
The table of Fig. 1 lists the levels of the DDT in the
system after 48 hours. DDT concentrations for the water do
not include the amount adsorbed on the glassware. This
adsorption accounts for the drop from the initial concen¬
tration in the control (jar 1). Although there was much
variability in the adsorption of DDT on the glass jars, most
of the Yalues range from 10-35% of the total amount present
in the jar. This percentage remained fairly constant in
spite of changes in the actual concentrations of DDT in the
jars, indicating that an equilibrium might exist between the
DDT in the water and that adsorbed on the glass. Further
investigations are necessary to confirm the presence of
this equilibrium.
The DDT remaining in the water of jar 2 varied from
2.1 to 0.5 ppb. At the same time the volume of water re¬
maining in the jar also varied. These variations are believed
to be a result of small fluctuations in velocity and humidity
of the air flow, acting over the 48 hour period. A direct
correlation exists between evaporation of water and loss of
DDT. However, while the decrease of water was 5-207, the
DDT showed a 50-90% loss. The rate of codistillation as
defined by Acree et al. (1963) was calculated for jar 2.
The rates varied from 0.006 to 0.014 ugm/ml water and are
virtually identical to the range of rates reported by Acrée
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for similar concentrations of DDT over a 24 hour period.
After 48 hours jar 3 contained up to 15% of the DDT
removed from jar 2. This percentage representing 2-117
of the total DDT in the control, is the sum of the amounts
recovered from particles, water, and glassware of jar 3.
Late in the investigation it was discovered that the
centrifugation procedure removed a substantial amount of the
C DDT from the water. DDT thus adsorbed to the plastic
centrifuge tubes was then partially removed with the part-
icles. Consequently, DDT levels for the particles appeared
higher and levels for the water appeared lower than was
actually the case. The last run of the experiment was
designed to estimate this effect. Sand was used because
it settled without centrifugation. The water was decanted
and the particles were removed from the jar with a spatula,
placed in a scintillation vial with ethanol, and counted
directly. Although this method of collecting particles
was not entirely effective, it is believed that at least
90% of the material was recovered. After thorough mixing
the decanted water was divided into two equal portions.
One sample was extracted directly with hexane, while the
other was centrifuged before the extraction procedure, as
in previous experiments. Aliquots of both extracts were
then counted in the scintillation counter and compared.
The centrifuge tubes were then rinsed with ethanol as if
particles were being collected, to provide a correction
factor to adjust the previous data. Radioactivity in these
rinses gave an estimation of the extent to which earlier
particle counts were biased by C DDT from the water.
Table 1 shows the corrected values for the levels of
C DDT in the water and particles. In all cases the cor-
rected figures represent minimum values for DDT concentrations.
Although the values presented here represent only
approximations, some preliminary conclusions may be drawn.
Celite and sand, both composed primarily of inorganic silichus
material, concentrate DDT to about the same degree -- greater
than 1000 times the concentration in the surrounding water.
The detritus, containing more organic material,cocentrates
DDT to an even greater extent, at least 50,000 times above
the level in the ambient water. On a volume basis also the
detritus concentrated DDT to a higher level. In this case
the detritus contained three times as much DDT as the sand.
These results indicate that the nature of the material as
well as the available surface area may be important in
determining how much DDT is eventually concentrated.
Since it had been demonstrated that particulate matter
picked up DDT to a significant extent, experiments were
designed to show that this could serve as a pathway for
the incorporation of DDT into filter feeding marine organisms.
labelled DDT was fed to the bay mussel Mytilus edulis.
Results showed that in 12 hours, the mussels had taken up a
large amount of the radioactivity that was available to them
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from the particles (20-50%). However, an experiment in which
C DDT detritus was incubated in unlabelled sea water
indicated a large percentage of the radioactivity from the
particles was leached into the water. Thus it cannot be
concluded definitely at this time that the uptake in Mytilus
was from the particles only. These results suggest the exist-
ence of an equilibrium between the particles and the water,
both of these serving as potential donors of DDT to the
organisms.
Implications
The experiments discussed here demonstrate the signifi-
cnace of DDT adsorption on glassware even at concentrations
below the limits of solubility. Clearly the removal of large
percentages of the added DDT from the water affects the
reliability of sample aliquots and alters the concentration
that experimental animals are actually exposed to. This is
a factor that cannot be overlooked in experiments dealing
quantitatively with DDT.
More directly, the results presented here illustrate the
extreme mobility of DDT. Although the experimental conditions
did not attempt to duplicate exactly those accuring in nature,
they demonstrate clearly that codistillation and air currents
can remove high percentages of DDT from one location and
transfer it to water and particulate matter in another. Pro-
20
jecting these conclusions to the agricultural use of DDT
would suggest that the insecticide may readily leave the
area of application, be carried by the wind systems, and enter
the marine environment. This mechanism of transfer and
contamination has, in fact, been suspected for some time.
Finally, DDT entering sea water from the air is concentrated
in suspended organic and inorganic particulate matter. In
this way translocated DDT is made available to filter feeding
organisms and thus can enter the marine food chains, both
from being on particulate matter and from direct uptake from
the water. In conclusion, it appears that the marine ecosystem
may be serving as a receptocle for large amounts of DDT and
its residues.
s
References
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Bowman, M. C., F. Acree Jr., M. K. Corbett. 1960. Solubility
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Bowman M. C., F. Acree Jr., C. H. Schmidt, M. Beroza. 1959.
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52
Odum,
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