Abstract
Preliminary investigations of several aspects of DDT
residue flow through the food chain were carried out using
DDT tracer. These consisted of measurement
GLC analysis and(
of field concentration levels, uptake from water, uptake through
feeding, and determination of accumulation sites. Results
indicate that more DDT is available to the organism over time
than is accumulated, suggesting an equilibrium of DDT residue
concentration between animal and environment. A thorough
description of DDT flow in the food chain will require more
detailed information on the kinetics at each level. The study
will continue with investigation of DDT kinetics in Hermissenda.
340
DDT residues are concentrated when transferred into higher
trophic levels. Although several studies deal with the kinetics
of DDT assimilation in a single organism, there is little research
that elucidates the details of DDT transfer through several steps
in a marine invertebrate food chain. 2 This study represents
some preliminary investigations of the transfer of DDT residues
in a 3-level epibenthic food chain comprised of Campanularian
hydroids, the eolid nudibranch Hermissenda crassicornis, and the
tectibranch Navanax interminis. There are three aspects to this
study: 1) measurements of field concentrations of DDT residues in
the organisms; 2) a determination of the kinetics of DDT uptake
from solution; 3) a determination of the efficiency of removal of
DDT from food and its storage sites in the organism.
Navanax were collected intertidally from White's Point on
the Palos Verdes Peninsula near Los Angeles, and from a depth of
10 feet in Los Angeles Harbor. Hermissenda were collected from
Los Angeles Harbor, from floating piers in the marina of Monterey,
California, and primarily the pilings of Pier #2 at Monterey from
depths of 2 to 25 feet. Sufficient quantities of the hydroid on
which Hermissenda were observed to feed could not be collected
for feeding and uptake studies. DDT residue concentrations were
determined in Obelia from the floating piers. Uptake studies
were with Bowerbankia gracilis, a bryozoan very abundant on pilings,
and on which the nudibranchs were generally found grazing on the
small hydroids interspersed among the stolons. Although Bowerbankia
probably constitutes a minimal portion of Hermissenda's diet, its
393
surface to volume ratio, general structure, and feeding habits
are similar to those of hydroids, and DDT uptake is comparable
in the two.
FIELD CONCENTRATIONS
Samples, digested in 1:1 perchloric and glacial acetic acid,
were extracted with hexane. Extracts were cleaned-up using a
silica gel microcolumn to which 1% Nuchar Attaclay was added to
insure removal of pigments. Samples were injected into a Beckmann
GC-4 gas-liquid chromatograph equipped with an electron capture
detector.
The results are summarized in Table 1. The high value for
Hermissenda from Los Angeles Harbor is probably due to large inputs
of DDT into the nearby White's Point sewage outfall by the
Montrose Chemical Corp. of California, sole producers of DDT
in the U.S.% The value for Hermissenda from floating piers at
Monterey is a factor of 2.3 above the mean value for those obtained
from submerged pilings nearby. This suggests that these nudibranchs,
always near the surface, are exposed to more DDT, perhaps from
input into the surface layer from aerial fallout. The concentration
factors are expressed as the ratio between the concentration of
DDT residues in an organism and that of its food supply in its
particular location. The decreasing factor with high trophic
level may be a reflection of differing feeding habits, and additional
autecological information is needed to interpret this trend.
In order to determine a relationship between weight and DDT
concentration, weight classes of .2gram intervals from o to 1.8 gram
349
of Hermissenda were analyzed separately; each class containing
enough animals to provide an optimal analytical sample weight
of 3 grams.
Concentrations vs. weight are shown in Figure 1. There is
a clear increase in the concentration of DDT residues with greater
weight. Though weight is presumably a rough indication of age,
it would not appear that this merely represents à oonstantly
increasing accumulation over the animal's life span. Since
Hermissenda have higher concentrations in areas with higher
environmental levels of DDT, the population sampled in this
experiment cannot have reached a saturation point. It seems
likely that a Hermissenda of any size will have consumed more
than five times its weight in hydroids, roughly the amount needed
to account for its level of DDT residues. It would then be retain¬
ing less than 100% of its intake and presumably be in an equilib-
rium condition. The increase must then be due to some other factor.
Experiments discussed later showed the cerata as the principal
site of at least short-term accumulation of DDT, and casual obser-
vations indicate that larger Hermissenda have relatively more
cerata. This may account for a greater lipid fraction in larger
animals, and thus a greater concentration, since values are based
on the weight of the entire animal. Even among Hermissenda of the
same approximate weight the number of cerata varies, and could
account for some of the scatter in the data. Further experiments
will be done to test these possibilities.
296
DDT UPTAKE FROM SOLUTION
Colonies of Bowerbankia, divided into 50 approximately
1 gram clumps, were placed in a glass container with 16 liters of
sea water. Ring-labelled C DDT dissolved in ethanol was added
to bring the initial concentration in the water to 100 parts per
trillion (PPT). Samples of Bowerbankia were removed at various
times and prepared as in the GLC analysis procedure, except for
the clean-up. Pigments were removed instead by shaking with
Nuchar Attaclay which was then removed by centrifugation. 10 ml
aliquots of the water were also taken at various times and extracted
by shaking with redistilled petroleum ether. Extracts, evaporated
to .5 ml and combined with 10 ml of scintilation fluid, were
counted in a Nuclear Chicago Unilux II scintilation counter.
In a similar experiment, 40 Hermissenda were placed in 40 liters
of sea water with an initial concentration of 50 PPT of C DDT,
and samples were removed and analyzed in the same manner over a
38 hour period.
The results of the two experiments are presented in Figure 2
and Figure 3. In both cases the rate of uptake decreases with
decreasing concentration in the water. Although the curves tend
to level off, it is difficult to tell at what point the systems
would have reached an equilibrium condition since the ratio between
concentration in the animals and concentration in the water
increased linearly with time in both cases over the periods
measured. Since various factors including an inconstant volume
of water per animal and competition for the available label
were not taken into account in this experiment, the data is not
34
sufficient for further interpretation. Additional experiments
will be carried out in order to determine the mechanisms of DDT
uptake in Hermissenda.
DDT UPTAKE FROM FEEDING
A group of 14 Hermissenda were fed portions of C'' DDT
labelled Hermissenda and were the placed in 2 liters of clean
sea water. An additional 3 labelled Hermissenda were fed to a
single Navanax which was also placed in clean sea water. Feces
were removed from the container and analyzed, and water samples
were removed and analyzed periodically. At the end of 48 hours,
the Hermissenda were dissected into samples of total cerata,
viscera, and muscle tissue (foot and head). The Navanax was
likewise dissected and the tissues divided into separate samples.
The results of liquid scintilation counting of the samples
is presented in Table 2. Percentages are based on the total
'DDT recovered. Two results are evident: 1) the major fraction
of DDT in both cases was accumulated in the digestive glands;
2) the efficiency of DDT assimilation from food is high: 96% in
Hermissenda and 97% in Navanax. It is assumed that the label
recovered from the feces represents all that was lost from the
animals, since the water samples did not vary from background
over the entire period.
DISCUSSION
The results of this study suggest that more DDT residues
are available to these organisms over time than are actually
accumulated, and that an equilibrium condition is reached
39
between the concentration level in the organism and the level
of DDT residues in its environment. The concentration in the
animal is dependent upon a number of variables determining rates
of uptake, retention and loss. A complete description of the
flow of DDT residues through this food chain will require eluci-
dation of the nature of the equilibrium in each trophic level.
This study will continue with the investigation of this problem
in Hermissenda.
39
REFERENCES AND NOTES
1. Only p.p' DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane),
p.p' DDD (1,1-dichloro-2,2-bis (p-chlorophenyl) ethane) and
p.p' DDE (1,1-dichloro-2,2-bis (chlorophenyl) ethylene) were
measured. DDT residues refers to all three compounds.
2. J.L. Cox, Ph.D. thesis, Stanford University (1970).
3. D.J. Reish, K.E. Maxwell, J.R. Austin, Western Society of
Naturalists, Abstracts of Contributed Papers to the 49th
Annual Meeting, (1968).
4. A.M. Kadoum, Bull. Environ. Contam. Toxicol. 3, 65 (1968);
ibid., p. 354.
5. All GLC parameters were those suggested in Pesticide Analysis
Manual (U.S. Dept. of Health, Education and Welfare, Food
and Drug Administration, revised 1968), vol. 2.
6. County Sanitation District of Los Angeles County, Pesticides
and Heavy Metals, Progress Report, prepared by C.W. Carry.
J.A. Redner, (1970).
O
Acknowledgements
I wish to thank Mr. Robin Burnett for his patient assistance.
35
FIGURE LEGENDS
Figure 1. Concentrations of DDT residues vs. weight of
Hermissenda. Each point is the value measured for a
sample composed of from 4 to 30 animals with weights
ranging over the.2 gram interval. Points are plotted
at the mean weight/animal in each sample.
Figure 2. Removal of C DDT from sea water by Bowerbankia.
The curves indicate increase of concentration of label in
the Bowerbankia (solid line) vs. decrease of the concen-
tration in the water.
Figure 3. Removal of C DDT from sea water by Hermissenda.
The curves indicate increase of concentration in Hermissenda
vs. decrease of concentration in water from an initial
calculated value of 50 PPT. The fluctuation was probably
due to varying temperature.
TABLE LEGENDS
Table 1. Field concentrations of DDT residues in the food chain.
The number of animals measured (colonies in the case of the
bryozoan and hydroid) is noted along with the location.
All walues are based on wet weight.
No measurement was made of the water from Monterey Harbor.
Value here is very rough estimate based on values for
open ocean water.
** Condition of the GLC column did not allow quantification
of the DDT peak.
O
Table 2. CDDT measu.
and various tissues of
iinf
Hermissenda and Navanax 48 hours after feeding on labelled
Hermissenda.
TABLE I
PARTS PER BILLION
DDE
DDD
DDT
WATER, INCLUDING SMALL
approx..Ol"
PARTICULATE MATTER
BOWERBANKIA (4)
3.04
(WHARF PILINGS)
5.55
2.58
OBELIA (10)
. .
(FLOATING PIERS)
15.5
9.4

HER
PTSSENDA
(PILINGS) (62)
29.6
18.2
9.1
* .
(FLOATING PIERS)
65.5
(7)
45.7
. .
(L.A. HARBOR) (14)
416
194
NAVANAX (1)
. .
(L.A. HARBOR)
756
162
CONCENTRATION
FACTOR
approx. 102
approx. 2.5x10
1.5
3
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CERATA
VISCERA
FOOT and HEAD
FECES
NAVANAX
DIGESTIVE GLAND
FOOT and HEAD
TENIDIUM
BUCCAL MASS
STOMACH
FLUIDSS
CES
TABLE 2
nu gm C DDT
RECOVERED
9580
995
650
450
70240
10025
3210
775
690
365
2295
PPB
3.68
.79
93
26.22
1.10
8.88
.60
.82
—
% OF TOTAL
82.1
8.5
5.5
3.9
80.0
11.7
3.6
.9
8
4
2.6
351