DDT UPTAKE IN EMERITA ANALOGA AND LEVELS OF
DDT RESIDUES OF POPULATIONS FROM ASILOMAR BEACH
AND NEAR THE MOUTH OF THE SALINAS RIVER
Richard E. King
Hopkins Marine Station
Stanford University
Pacific Grove, California
"Permanent address:
16
INTRODUCTION
While most of the DDT residues found in the oceans were probably
transported there by wind and subsequent chemical fallout, DDT residue levels
in marine organisms in Monterey Bay, California (Risebrough et al., 1968) are
high enough to suggest that pesticides are also being carried directly into the
bay by drainage from adjacent farmlands. This suggestion is supported by
studies of Emerita analoga described in this paper.
The 100 mile long Salinas Valley is a rich agricultural region producing
annually large amounts of lettuce, broccoli, celery, dried beans, carrots.
sugar beets, and artichokes. Accompanying this large production is the
widespread use of DDT. For the past ten years over 125,000 pounds of DDT
each year has been sprayed on crops in the valley (Scott, 1969). The valley
is drained by the Salinas River which originates in the northern part of the
Los Padres National Forest and winds for 150 miles in a northwesterly direction
through the Salinas Valley and reaches Monterey Bay about 5 miles south of
Moss Landing. A sandbar across the mouth of the river prevents the shallow
river from directly emptying into Monterey Bay for a large part of the vear.
However, the river drains approximately 1000 square miles and during the
rainy season (December to April), the Salinas River rises and empties directly
into the bay. It is highly likely that DDT present in the top surface layer
of soil in the fields is carried into the river with some of the soil in
agricultural run-off. In addition, even larger amounts of DDT may be added
directly to the river during heavy rains in January and February when the
farmlands bordering the river are flooded. At one critical flood period in
February 1969, the river became a mile wide in some spots, while flooding
thousands of acres of farmland and emptying 110,000 cubic feet of water per
second into Monterey Bay (Monterey Peninsula Herald, February 25, 1969).
After the rainy season, the water level of the river gradually decreases and
167
a sandbar usually forms and closes the river mouth.
A population of Emerita analoga, the sand crab, which inhabits the
stretch of beach approximately 100 to 600 yards from the mouth of the river
was chosen for a study of the influence of the Salinas River in the marine
environment.
Emerita burrow in the wash zones of sandy beaches and migrate with the
tides (Cubit, 1968). When the tide rises, Emerita ride incoming waves to
higher positions on the beach. At a falling tide, they are carried by the
back wash waves to lower beach positions. Emerita are exposed directly to
DDT in the water not only during their tidal migrations up and down the beach.
but also when they are burrowed in the sand and circulating water through
the gill chambers.
Emerita are filter feeders and feed on plankton and detritus between
bu and 2mm long (Efford, 1966). Because DDT is readily adsorbed to particles
(Odum et al., 1969) and the Salinas River contains a large amount of organic
material and silt, DDT may be entering the Emerita in the food chain, as
well as possibly by direct uptake.
Mature female Emerita are from 12 to 18 months old (Barnes and Wenner
1968) and would be indirectly exposed to outflow from the Salinas River for
4 to 6 months of the year when the river mouth is open to the sea.
Sand crabs are very abundant in the sandy beaches along the California
coast and constitute a large portion of the diet of several marine organisms.
Over 90% of the food by volume of the Barred Surfperch consists of sand crabs
(Carlisle et al., 1960). Emerita also forms as much as 75% of the diets of
the Western Sandpiper, Semipalmated Plover, Snowy Plover, and Sanderling
(Reeder, 1951). Emerita is thus in a position to concentrate DDT residues from
water, plankton, and detritus, and pass them on to fishes and birds through
the food chain.
160
WATER SALINITY AND SAND CRAB DISTRIBUTION
All sand crabs used were non-egg carrying females ranging in wet
weight from 2.5 to 7 grams. They were collected in two areas separated
by about 11 airline miles. One area was  Spanish Bay, just south of Asilomar
State Park, on the open coast. The other area was 100 to 600 yards north of
the mouth of the Salinas River on the shore of Monterey Bay. Collecting
stations are shown in Fig. 1.
Salinity was measured in the field with a refractometer. In the river
channel and mouth water samples were taken from the top 3 inches of water
where total water depth was about 2 feet at the time of sampling. Samples
were gathered at different times at the Salinas beach and river to study the
effects of incoming and outgoing tides on the river flow into the ocean.
At Asilomar Beach (Figs. 1, 2) sand crabs were collected only between
stations L and 5, although sand crabs were found at all stations. Fresh
water seepage is slight and most of it disappears into the sand before reaching
the water. The water washing the beach shows normal sea water salinity.
and sand crabs here are probably well beyond the influence of the Salinas
River.
At the mouth of the Salinas River (Figs. 1, 2) sand crabs were only found
at stations 13 through 18. Emerita used in experiments were collected between
stations 14 and 17. Results obtained (Fig. 2) show that the salinity of
the water washing the beach is affected by the tides. During a rising tide,
the water outside the river channel maintains salinities of 93% to 1002.
At a falling tide, beach salinities are lowered, though the salinity of
the shore water decreases gradually with increasing distance from the mouth
of the river. The population of Emerita living 100 to 600 yards away from the
river mouth is exposed to 25% to 10% river water for six hours every other
six hours or during each falling tide. DDT in the river, either dissolved in
16
the water or adsorbed to particulate matter is diluted before reaching the
sand crab population.
UPTAKE OF C14-DDT
In order to determine the ability of Emerita to take up DDT directly
from solution in the surrounding water, experiments were carried out using
DDT labled with C+. A 100 ppm (parts per million) solution of CHDDT
dissolved in ethanol, with a specific activity of 19 curies/mole was used
to make up the C+DDT-sea water solutions. All sea water used was filtered
once through an 8u millipore filter and a 3u millipore filter to remove
particles. The filtered sea water was aerated for 5 to 10 minutes before
addition of C+DDT in ethanol. Where different concentrations of C+DDT were
used, additional ethanol was added to insure that each jar contained equal
amounts.
Two types of C-DDT uptake experiments were conducted, both on sand crabs
obtained from Asilomar Beach. (1) Three Emerita were placed in a sealed one
gallon glass jar containing only 2.5 liters of a C-DDT sea water solution.
Sand crabs in these experiments lacked a substratum in which to burrow. They
were not observed continuously for 12 hours, but on every occasion when they
were seen they were either swimming or actively scrambling along the bottom
of the jar. (2) Three Emerita were placed in a sealed one gallon glass jar
with 2.5 liters of a C+DDT sea water solution and in addition a lcm layer
of sand on the bottom which allowed the animals to bury themselves completely,
On all occasions when these sand crabs were observed they were completely
buried with only the antennules protruding above the sand. Sand crabs were
circulating water down the antennular funnel and ejecting it from the branchial
chamber below the sand. The sand crabs were incubated overnight for 12
hours. Both types of experiments were conducted at concentrations of DDT of
O.1, 0.2, O.4, 0.6, 0.8, and 1.0 ppb (parts per billion).
After the 12 hour incubation, the Emerita were taken out of the jars,
rinsed in a beaker of sea water for 30 seconds, and placed on paper towels
to dry off for 5 minutes. The wet weight of each sand crab was determined
to an accuracy of one milligram on a Mettler scale. Each Emerita was then
cut into small pieces with scissors and ground up with a hand homogenizer
in 10 mls of dioxan for 20 to 30 minutes to extract the CLDDT. The liquid
homogenate was poured into a test tube leaving the large granular material at
the bottom of the homogenizing tube. A 1.0 ml aliquot of the liquid homogenate
was placed into each of two scintillation vials containing 10 mls of Bray's
solution and counted for 1 minute in a Unilux II Scintillation Counter.
The quenching of radioactivity was corrected for and the actual disentegrations
per minute were calculated using an average of the counts per minute from
the two vials. The wet weight of each crab was used to determine the CDDT
content in ppb.
The results of the uptake experiments (Fig. 3a and b) show that Emerita
can concentrate large amounts of DDT (55x increase over initial concentration)
over a short period of time while freely swimming in water at ambient
DDT levels of 0.2 to 1.0 ppb. A similar increase in the rate of DDT uptake
with increasing initial DDT concentration was not observed in the Emerita
buried in the sand. This may be explained by one or more of the following
reasons. (1) Much of the C+DDT may have been adsorbed to the sand and unavailable
to the sand crabs. Samples of the water after incubation were counted in the
scintillation counter and although too close to background level to calculate
actual C-DDT concentrations, the counts in the jars with sand were always
less than the counts in the jars without sand. (2) The increased activity
of the Emerita swimming in the jar without sand may have placed them in more
continuous contact with C+4DDT in the water, increasing the opportunity for uptake.
(3) The higher rate of activity in the swimming sand crabs was doubtless
accompanied by increased metabolic activity, which may in turn have been
related to increased CDDT uptake.
IEVELS OF DDT RESIDUES IN NATURAL POPULATIONS
If DDT is entering Monterey Bay by way of the Salinas River, it can be
expected that the population of sand crabs located near the mouth of the
Salinas River would contain more DDT residues than a population of sand crabs
located at an ocean exposed beach several miles away. In order to test
this hypothesis, the DDT and DDE levels of sand crabs from the Asilomar
Beach and the mouth of the Salinas River were measured and compared.
Samples consisting of 5 sand crabs were allowed to dry on paper towels
for 5 minutes and then weighed to the nearest milligram. The sand crabs were
digested in a glacial acetic acid- perchloric acid mixture for 24 hours, followed
by lipid extraction with nanograde hexane, and lipid removal by passage
through a column of celite and sulfuric acid. The cleaned-up sample was
concentrated if necessary. For details of this procedure see Stanley and
LeFavoure (1965).
The Beckmann GC h chromatograph with a electron capture detector was
used for all experiments. The DDE values were determined using a 3% OF-1
column, and the DDT values were determined using a 10% DC 200 column, both of
which were on DMCS treated Chromosorb 1, 80 to 100 mesh. Conditions during
runs were as follows. Temperatures: inlet 220°0, column 200°C, detector 280°c.
Helium pressure: input 40 psig. Flow rate of helium: 10 ml/min for OF-l and
200 ml/min for DC 200. Column injections were made with Hamilton 10-ul
syringes.
The DDE and DDT content of female Emerita from Asilomar Beach and near
the mouth of the Salinas River are summarized in Fig. 4. There is no
statistically significant difference between the DDE content of the two
Emerita populations. The probability of exceeding the t value of 1.008 is
between.3 and.l.
However, there is a very clear difference in the DDT content in the two
populations. The DDT content of sand crabs from near the mouth of the
Salinas River was approximately 110 ppb, while the DDT content of the sand
crabs at Asilomar Beach was too low to be measured with the gas chromatograph.
The DDT content of the two populations of sand crabs suggests that the
Emerita from the mouth of the Salinas River are exposed to DDT which is not
present in the sea water at Asilomar Beach. The DDE content of the two
populations are identical and suggests that the DDE concentration in the
water washing the beach is the same.
A possible hypothesis to explain the similarity in DDE level and the
difference in DDT levels of the two populations is as follows. DDT is broken
down by ultraviolet light, and consequently most of the DDT residue present
in the ocean is DDE. However, during the rainy season, DDT reaches the fast
flowing Salinas River and is transported rapidly to the mouth of the river
and into Monterey Bay. The small amount of DDE that has been formed during
the short trip down the river does not effectively alter the concentration of
DIE present in the ocean. However, because the DDT concentration of the ocean
is extremely low, the amount of DDT emptied into Monterey Bay from agricultural
run-off and the flooding of farmland significantly raises the DDT concentration
of the water surrounding the mouth of the river. During low tide, the
population of Emerita near the mouth of the Salinas River are exposed to
both DDT from the river and DDE already present in the ocean. Eventually
all of the DDT reaching the bay is broken down into DDE but this amount is
too small to change the DDE concentration of the ocean. Consequently, the
DDE concentration is the same in the sea water washing the Emerita population
at Asilomar Beach and near the mouth of the Salinas River.
The levels of DDT and DDE found in either of the populations of sand crabs
12
do not appear to be high enough to produce any harmful effects to the sand
crabs themselves. However, as already noted the Barred Surfperch, Sanderling.
Snowy Plover, Semipalmated Plover, and Sandpiper regularly feed on large
numbers of sand crabs. DDT residues taken in with the sand crabs may be stored
and accumulated in the tissues of these birds and fishes, and studies should
be made to determine whether thse animals are approaching harmful levels
of DDT residues or even already suffering from the effects of high concentrations
of the pesticide.
SUMMARY
The filter feeding sand crab, Emerita analoga, is abundant in sandy
beaches on California shores. It is an important food source for the
Barred Surfperch and several shore birds including the Snowy Plover, Sanderling.
and Sandpiper. Several California birds and fished contain high levels of
DDT and its derivitives. Emerita is in a position to concentrate DDT residues
from water, plankton, and detritus, and pass them on to fishes and birds
through the food chain.
To measure the rate of uptake of DDT from sea water, sand crabs were
exposed to solutions of C+DDT at concentrations of 0.1, 0.2, 0.4. 0.6. 0.8.
and 1.0 ppb for 12 hours. Sand crabs burrowed in sand took up a constant
amount of DDT in concentrations of 0.l to 1.0 ppb (increases from lOx to 25x).
Sand crabs free in sea water took up amounts of DDT proportional to the DDT
concentration in the sea water (an increase of 55x).
Natural levels of DDT residues were determined by gas liquid chromatography
in populations of sand crabs from the mouth of the Salinas River, which
drains an agricultural valley where DDT use is widespread, and from Asilomar
Beach, an exposed ocean beach several miles away. Approximately 80 ppb of
DDE were found in both populations. Only trace amounts of DDT were present
in sand crabs from Asilomar Beach, while approximately 110 ppb were found in
sand crabs from the mouth of the Salinas River.
174
C
ACKNOVLEDGEMENTS
This work was supported in part by the Undergraduate Research
Participation Program of the National Science Foundation Grant GY-5878.
I would like to thank the faculty and staff at the Hopkins Marine Station
for their help and encouragement throughout this course with special thanks
to Dr. Donald P. Abbott, John Miller, Philip Murphy, Larry Eickstaedt, and
Sam Johnson.
LITERATURE CIEED
Barnes, N. B. and Wenner, A. M. (1968). Seasonal variation in the sand
crab, Emerita analoga (Decapoda, Hippidae) in the Santa Barbara
area of California. Limnology and Oceanography. 13 (3), 164-475.
Carlisle, J. G., Schott, J. W., Agramson, N. J. (1960). The Barred Surfperch
(Amphistichus argenteus Agassiz) in Southern California. State of
California Department of Fish and Game Marine Resources Operation.
Fish Bulletin No. 109, 18-52.
Cubit, J.
(1968). Behavior and physical factors causing migration and
aggregation of the sand crab Emerita analoga (Stimpson). Ecology.
50 (1), 118-123.
Efford, I. E. (1965). Feeding in the sand crab, Emerita analoga (Stimpson)
(Decapoda, Anomura). Crustaceana. 10 (2), 167-182.
Monterey Peninsula Herald, February 25, 1969. Monterey County again disaster
area. IXXXX (18).
Odum, W. E., Woodwell, G. M., Wurster, C. F. (1969). DDT residues absorbed from
organic detritus by fiddler crabs. Science. 164, 575-577.
Reeder, W. G. (1951). Stomach analysis of a group of shorebirds. The Condor.
53, 43-45.
Risebrough, R. W., Reiche, P., Peakall, D. B., Herman, S. G., Kirven, M. N.
(1968). Polychlorinated biphenyls in the global ecosystem. Nature.
220 (5172), 1098-1102.
Scott, D. (1969). Speech to students and faculty of Hopkins Marine Station in
May 1969.
Stanley, R.,and LeFavoure, H. (1965). Rapid digestion and cleanup of animal
tissues for pesticide residue analysis. Journal of the Association
of Official Agricultural Chemists. 18, 666-667.
176
FIGURE CAPTIONS
Fig. 1: Map of Asilomar Beach and the mouth of the Salinas River.
Numbered collecting stations are 50 yards apart. Sand crabs were found only
at dotted stations. The large dot on the graphs of tide movement represent the
period of salinity testing. The vertical axis is height and the horizontal
axis is time. Underlined times indicate A.M.
Fig. 2: Percentages of normal sea water found at collecting stations
at Asilomar Beach and the mouth of the Salinas River. Salinity was
measured at both the surface (T) and belows the surface (B) in the river
channel. Sample number refers to the graphs in Fig. 1 showing the period
of sampling in relation to tidal position.
Fig. 3a,b: DDT uptake by Emerita analoga at various DDT concentrations,
Fig. 3a shows uptake of CDDT by sand crabs burrowed in sand while Fig. 3b
shows CDDT uptake by sand crabs swimming freely in sea water. Each dot
represents one sand crab. The circles in Fig. 3a indicate that CH4ppT
uptake was to close to background levels to calculate. Uptake is expressed
in wet weight of whole Emerita per 12 hours.
Fig. I: DDE and DDT levels expressed in ppb of wet weight of whole
Emerita found in samples consisting of 5 sand crabs from Asilomar Beach and
near the mouth of the Salinas River. The DDT levels of the Asilomer Beach
sand crabs were too low to be measured and the standard deviation could not
be calculated.
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ANIMALS BELOW SAND
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02 0 05 03
DOLIN SEAWATER (PPB)
F16. 32
AMIMALSTER
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IMWATER

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5
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FIG. 35 LDOT IN SEA WATER (PP
1
BEACH
ASILOMAR
Sample
DDE
Wet
(ppb)
Weight (9)
Number
95
29.705
28.032
85
2
32.514
3
4
30.157
80
84
5
24.533
Standard
6.0
Deviation
SALINAS
RIVER
Sample
Wet
DDE
Number
Weight (g)
(ppb)
33.024
65
35.65
71
27.630
3
87
4
28.375
97
Standard
14.2
Deviation
FIG. 4
(ppb)
TRACE
TRACE
TRACE
TRACE
TRACE
DDT
(pph)
140
122
154
155
15.4
g