COMMU N ICATl ON
Accumulation of DDT by Daphnia magna Donald G. Crosby and Richard K. Tucker' Dept. of Environmental Toxicology, University of California, Davis, Calif. 95616
of the technical product from ethanol until a constant melting point of 108"C was obtained. Solvents were carefully distilled immediately prior to use. A laboratory strain on D. magna Straus was cultured as previously described (Crosby et al., 1966). Groups of 24 first-instar organisms were starved for two and one-half hr and then transferred to 100-ml beakers containing 25 ml of deepwell water of the composition employed previously. An acetone solution (50 pl) containing the desired quantity of DDT was injected below the surface of the water, and the beakers were maintained at 21.1" f 0.05"C for 26 hr. At the end of this period, those daphnids unable to swim more than 1 cm vertically toward light were considered to be immobile; those which showed no movement of appendages, eye, or heart under repeated microscopic (40 X) observation were counted as dead. The organisms and deposited carapaces were removed by centrifugation, washed carefully with water, and separated by hand. The water was extracted with several consecutive portions of petroleum ether, and a separate extraction of all test glassware was made with petroleum ether. Daphnids, carapaces, and extracts were analyzed separately by the gas chromatographic procedure of Crosby and Archer (1966). Groups of 10 first-instar Daphnia were removed from their culture medium after starving, dried briefly by careful application of filter paper, and weighed immediately on a Cahn microbalance. From a series of measurements, the average weight of an individual was determined to be 9 i 1 pg, although the weight declined rapidly on exposure of the animals to air.
u Daphnia magna, an important link in the aquatic food chain, accumulates the insecticide DDT in 16,000 to 23,000fold quantities from dilute suspension in water within 24 hr. Uptake is principally through the carapace and initially is rapid. Final body levels may reach several thousand milligrams per kilogram.
ith the increasing use of synthetic pesticides in agriculture, public health, forestry, and wildlife management, continuing concern has been expressed over the possibility of biological magnification of chemical residues in members of food chains (Hunt, 1966). Aquatic food chains have received particular attention, and there is no doubt that mollusks, fish, and other aquatic animals accumulate considerable quantities of certain compounds (Bridges et al., 1963,1964; Newsom, 1967). The planktonic Entomostraca generally are considered to be among the first animal links in the aquatic food chain, and Daphnia have been shown to represent an important part of this group (Gerking, 1962). Although there is field evidence for the concentration of chlorinated hydrocarbon insecticides by the genus (Keith, 1965), exact laboratory methods for the study and measurement of this phenomenon have not been reported previously. The insecticide DDT [1,1 ,l-trichloro-2,2-bis(4'-chlorophenyl) ethane] has been found widely distributed in surface water. The present communication describes the laboratory measurement of DDT uptake by D. magna and the distribution of the compound during the experiments.
Results and Discussion It is apparent that D. magna accumulates DDT from its environment. For example, exposure to an insecticide level of about 8 ppb in water for a 24-hr period resulted in a 16,000fold concentration, while exposure to water containing 50 ppb resulted in a 23,000-fold concentration (Table I). At the latter level, 25 first-instar, 9-microgram organisms
Materials and Methods
Pure
~ , ~ ' - D D was T
prepared by repeated recrystallization
Present address: U.S. Dept. of the Interior, Fish and Wildlife Service, Denver, Colo.
Table I. Uptake of DDT by Daphnia magna DDT in whole Daphnia
level in water, ng/mP DDT
a
b c
714
Total added DDT, ng
0.0
0
8.0 16.0 50.0 100 200 1100
400 800 2,500 5,000 10,000 55,000
7 Of initial dose
0
...
...
28.8 60 260 285 530 990
7 2 7.5 10.4 5.0 5.3 1.8
128 266 1150 1260 2364 4280
Nanograms per milliliter is equivalent to parts per billion in water. Calculated for Daphnia weight of 9 pg. Milligrams per kilogram is equivalent to parts per million in Daphnia. Environmental Science & Technology
Y Effect
Ng
Mg/kgb+
Dead
0
