Experiments with Peas and Sweet Corn Treated with DDT Insecticides H. A. Lardy University of Wisconsin, Madison, Wis. Possible hazards arising from the use of DDT on crops of peas and sweet corn and from their by-products when used as livestock feed are discussed.
D
URING the past two years at the Wisconsin Agricultural Experiment Station, a study has been made of the possible hazards arising from the use of D D T in the control of insects on peas and sweet corn grown as canning crops, and from their by-products which are commonly used as livestock feed. The object of this study was to determine the amount of D D T retained by these feeds and the amounts of D D T to be found in various tissues of the farm animals consuming them. The investigation was carried out cooperatively by the Departments of Entomology, Animal Husbandry, Dairy Husbandry, Agricultural Engineering, and Biochemistry. I n all this work the highly specific quantitative method of Schechter and Haller ( 1 ) was used for the determination of DDT. The data is divided into two sections: those dealing with pea crops treated under the supervision of H. F. Wilson (a)and those dealing with sweet corn whose treatment was supervised by John Lilly. PEAS
The canning peas were given one treatment of either 3 or 5y0 DDT dust at a rate of 35 to 50 pounds per acre for the control of aphids. Samples of the vines collected immediately after dusting a t the heaviest rate contained from 9 to 13 parts per million of DDT. Dusts containing 3y0 of D D T and applied at 35 to 40 pounds per acre left residues of about 5 p.p.m. on the vines. New growth and loss of D D T from the plant decreased the content of DDT to about one half this value at the time of harvesting. Of greatest importance, as far as human food production is concerned, is the fact that no D D T was found in any sample of shelled peas or canned peas obtained from sprayed plots. Eight samples of peas shelled by hand in the field or taken from the viner, and thirteen samples of canned peas from sprayed fields were analyzed and all were negative. Likewise, a sample of pods was found to be free of DDT. This indicated that no absorption and translocation of D D T to the edible portions of the plant had occurred. Relatively low concentrations of DDT were found in the silages prepared from the vine residues, and appreciable losses of DDT occurred from the silage during storage. Data from one silage stack are shown in Table I. There was a steady rate of loss during the first 6 months of storage, and it is doubtful if any DDT remained after 6 months.
A group of five dairy cows was fed this silage from December 1, 1946, until May 1, 1947. The silage was fed to the cattle a t a daily rate of 3% of the body weight; an average of 37 pounds of silage per cow per day. The D D T content of milk samples collected a t various intervals from these cows is shown in Table 11. KO sample was found to contain more than 0.4 p.p.m. D D T and several samples had less than detectable amounts.
TABLE 11. D D T
IN
MILK OF Cows FEDON DUSTED PEAVINE SILAGE P.P.M. D D T in Milk From cow 500 From others
Days on'Expt. 75 82
0.0
0.3
...
120 135 a Colostrum sample.
...
0.1a
0.2
TABLE 111. D D T Days After Ensiling
Fodder (4 dusts)
40 100
19 9 3
140
...
0.3 0.0 0.4
116
IN
CORNSILAGE
P.P.M. D D T in Fodder (2 dusts) 9 8 6
Husk and cob 4 1 0.2
One of these cows was slaughtered on the 135th day of experiment and samples of the body fat and muscle tissues weke analyzed. The fat was found to contain about 1 p.p.m. of D D T ; none was found in the muscle. Similar results were obtained with two cows that were fed pea vine silage from dusted fields of the 1945 crop season. In other experiments conducted during 1945 one pound of pure DDT was uniformly distributed over each ton of pea vines as they were ensiled. Between the time of ensiling (early July) and the middle of November approximately 8070 of the D D T added had disappeared from the silage, for it contained only about 100 p.p.m. of DDT. When this silage was fed at the above rate to a herd of dairy cows no ill effects were observed. Milk from these cows contained as much as 15 p,p.m. DDT. This milk was fed as the sole source of food to growing rats who thrived on it. They grew as well as did rats fed milk from control cows (a). This artificially treated pea vine silage was also fed to a group of ewes throughout their gestation period. They delivered normal, vigorous lambs fully the equal of those born to control ewes. SWEET CORN
I n the experiments with sweet corn, DDT was applied a t the TABLE I. Loss OF DDT ON PEAVINESAND SILAGE IN STORAGE rate of 20 to 35 pounds of 5% dust per acre for the control of Date* Tested 6/22/46 9/5/46 10/10/46 11/10/46 12/1/46 1/16/47 2/16/47
Sample Pea vines (50 lb. 5 % dust/acre) Silage (60 day) Silaee Silage Silane Silage Silage
corn borer. Two dustings were applied to part of the fields and four to the rbmainder. The husk and cob refuse from both types of the dusted fields were combined. Data on the DDT content of these silages are shown in Table 111. Again a loss of DDT from the silage during storage was observed. Each of these silages was fed as the sole roughage to a separate pen of five fattening steers for a period of 108 days. The steers
P.P.M. DDT 9 t o 13 5
3
2
1
Trace 0
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INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1948
TABLE IV. D D T Steer No. 1 2 3 4 . 5 Average
IN
7
...
0. ..8.
... ...
8
16 12
0.6
Fodder (2 Dusts) P.P.M. D D T In fat I n muscle
1.8 1.3 2.8 0.7 4.3 2.2
...
... 0.0
... ...
...
consumed, on an average, 32 pounds of silage per head daily. When slaughtered on the 108th day, samples of shoulder muscle and kidney fat were removed for analysis. The results, shown in Table IV, indicate that significant amounts of D D T do accumulate in the fat of steers fed silages which contain less than 10 p.p.m. of DDT. Extremely small concentrations of D D T were found in the lean meat from these steers. It was also found that the steers fed on the husk and cob silage retained the greatest amount of D D T in spite of the fact that the silage, when fed, contained only about 1 p.p.m. of DDT, or roughly 0.1 as much D D T as fed to the steers in the first lot of silage. When canning corn is cut from the cob much of the germ remains on the cob. It seems likely that the high oil content of the germ aids the absorption and retention of the small amount of D D T present in the silage.
TABLEV.
Based on these experiments, feeding corn silage from dusted fields to beef Husk and Cob animals creates no appreciable hazard to P.P.M. D D T human beings who later eat the meat I n fat I n muscle 24 ... from such animals. The small amounts 12 ... of D D T that are absorbed are largely 17 0.5 4 0.1 deposited in inedible portions of the 27 0.7 body fat and only negligible amounts are 17 ... found in the muscle tissue. The high-DDT sweet corn silage from plots dusted four times was also fed to a group of dairy cows a t the rate of about 32 pounds per cow daily for a period of 100 days. Composite samples of the milk were analyzed a t intervals with the results shown in Table V. Again extremely small quantities of D D T were secreted in the milk.
TISSUES OF STEERSFEDON CORNSILAGE
Fodder (4 Dusts) P.P.M. D D T I n fat I n muscle
17 11
D D T IN MILK FROM Cows FED CORN SILAGE CONTAININQ 5 TO 10 P.P.M. D D T Days on Expt.
711
SUMMARY
The results of this work indicate that DDT insecticides can be used under practical conditions for the control of pea aphids and corn borers without detrimental effects to livestock fed on the treated crop residues. Extremely small amounts of D D T find their way to the meat and milk of these animals; this indicates a negligible hazard to human health. However, as yet federal and state agencies have not set official tolerance levels for D D T in foods for human consumption, except for apples and pears. This fact should be considered when suggestions regarding the use of D D T on feed crops are made to farmers. LITERATURE CITED
D D T in Milk, P.P.M
Schechter, M. S., Soloway, S. B., Hayes, R. A,, and Haller. H. L., IND.ENG.CHEM.,17,704-9 (1946). (2) Wilson, H. F., Allen, N. N., Bohstedt, G., Betheil, J., and Lardy, H. A,, J. Econ. Entomol., 39,801 (1947). (1)
31 42 65 85 100
RECEIVED November 22, 1947.
Metabolism of Chlorinated HydrocarbonInsecticides Geoffrey Woodard, Bernard Davidow, and Arnold J. Lehman Food and Drug Administration, Federal Security Agency, Washington 25, D . C .
A summary of the present knowledge concerning the metabolism, fate, and excretion in mammals of the six newer chlorinated hydrocarbon insecticides is given. These six are diohlorodiphenyltrichloroethane, dichlorodiphenyldichloroethane, methoxychlor, benzene hexachloride, chlordan, and chlorinated camphene. An understanding of the mammalian metabolism and fate of these compounds necessary for evaluation of the possible hazards involved in their use in insecticidal applications, when exposure to man and animals will result, is far from complete.
A
INTEGRAL part of the determination of the toxicity of any compound is a study of the fate of that compound in the body. An understanding of how the compound is absorbed, how it is metabolized, how it is excreted, and whether or not it is stored in any tissue is necessary for the evaluation of the possible hazard connected with the use of the compound. Such an understanding is especially needed in the case of insecticides to which man and animals will be exposed. With the introduction of D D T work was undertaken in several laboratories t o elucidate the
metabolic fate of this insecticide in mammals. As each new insecticide was made available, the inevitable question arose regarding its metabolic fate in mammals. Including DDT, there are now six chlorinated compounds generally available as insecticides. The over-all picture of our present knowledge concerning their absorption, accumulation, fate, and excretion may be summarized as follows:
Compound Absorbed DDT + Dlohlorodiphenyldichloroethane ( T D E D D D ) Methoxychlor (methoxy analog of D D T ) Benzene hexachloride (BHC) Chlordan Chlorinated camphene
+ + +
++
Accumulated
+
Excreted in Urine Unchanged Changed
-
-I-
+
-
?
?
+ + tI
6?
i i
1
That each of these insecticides is absorbed from the gastrointestinal tract follows directly from the fact that animals can be severely poisoned or killed following oral administration of the compounds in corn oil solutions. Accumulation of D D T in the fat of animals and its appearance in milk have been amply demon-
