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insecticides to livestock. Because available data on the toxicology of the newer materials are limited largely to small laboratory animals, the Bureau of Entomology and Plant Quarantine has undertaken certain investigations in cooperation with the Bureau of Animal Industry, the Bureau of Dairy Industry, and certain state agricultural experiment stat,ions to determine the toxicological effects of some of the newer insecticides when applied t o livestock. These effects should be studied on small laboratory animals and livestock before extensive and costly research is carried out. In order that certain aspects of the toxicological investigations with tBhenew insecticides may proceed satisfactorily, met,hods must be developed for analyzing animal tissues, secretions, and excretions for the quantitative determination of all the new insecticides. Further research on the chemistry of new insecticides is,urgently needed. Much additional chemical research on the newer materials is also needed in efforts to improve formulations, such as wettable powders, eniulsions, and dusts. The trend is to employ wettable powders because they are generally considered safer. However, marked improvement of this type of product is needed, especially when i t is employed with existing equipment. The numerous effective insecticides t,hat have come t o light in
Vol. 40, No. 4
the past few years encourage the belief that many other chemical compounds possess distinct insecticidal value, and should stimulate synthesis and testing of many new compounds. LITERATURE CITED (1) Anon., U. S. Bur. Entomol. Plant Quarantine, E-623 (1944). ( 2 ) Barrett, W. L., Jr., and Wells, R. W'., J . Econ. Entomol., 39, 816 (1946). (3) Bishopp, F. C., Am. J . Pub. Health, 36, 601 (1946). (4) Bishopp, F. C., and Henderson, L: S., U. S. Dept. Agr., L e a f . 182, 4 (1946). (5) Bruce, W. G., and Blakeslee, E. B., J . Econ. Entornol., 39, 36774 (1946). (6) Dove, W. E., U. S. Bur. Entomol. Plant Quarantine, E-673, 2 (1945). (7) Knipling, E. F., S o a p Sanit. Chemicals, 23 (7), 127 (1947), (8) Laake, E. W., J . Econ. Entomol., 39, 65 (1946). (9) Parish, H. E., and Rude, C. S., I b i d . , 39, 92 (1946). (10 Rude, C. S..U. S.Bur. Entomol. Plant Quarantine, E-686 (1946). (11) Smith, C. N., and Gouck, H. K., J . Econ. Entomol., 38, 553 (1945). (12) Teleford, H. S., and Gnthrie, J. G., A g r . Chemicals. 1 (3), 31 (1946). (13) Twinn, C. R., C a n . J . Comp..lIed. V e t . Sci., 10,301 (1946). (14) U. S.Dept. Agr., Yearbook, 1942. .(15) Wachs, H., Science, 105, 530 (1947). RECEIVED November 22, 1947.
DDT Residues in Agricu R. H. Carter Bureau of Entomology and Plant Quarantine, Beltseille, Md. Residues of DDT that may result from insecticidal applications of this material to fruits, vegetables, and forage crops are discussed. The results of experiments on the absorption and translocation of this compound when applied as sprays and dusts to the aerial parts of vegetables are described. The absorption and storage of D D T in the tissues of farm animals and its elimination in milk are discussed.
T
HE widespread use of D D T for the control of insects has
stimulated interest in the amounts of D D T residue in and on field crops and farm animals that have been treated with this insecticide. The amounts of residue are of interest from the standpoint' not only of insect control but also of their presence in products intended for human and animal consumption. Investigations have included studies on: Deterniination oi D D T residues on fruits, vegetables, and forage crops. Absorption of D D T residues by plants and its translocation into the edible portions' from applications to the aerial parts. Absorption and storage of DDT in the organs and tissues of farm animals that received small amounts ingested with the food. D D T content of milk from cows fed silage containing D D T residues. Effect of cooking mect from animals that had stored appreciable amounts of D D T in their tissues as a result of having been fed rations containing this compound. D D T content of eggs froni hens receiving this compound in the diet. METHODS OF ANALYSIS
Most of the chemical results reported in this paper were obtained by determinations of organic chlorine (8, 4 ) , or by the Schechter-Haller colorimetric procedure for D D T ( 7 , 8). In many cases determinations were made by both methods with good agreement.
A report on methods for the determination of D D T in insecticide tesidues and in animal products has been published recently (3); several methods are now being subjected t o collaborative testing by federal and state chemists. DDT RESIDUES ON CROPS
The amount of residue found on agricultural crops depends on the weight of the crop per unit area, the amount of insecticide applied per unit area, the interval between treatment and collection of the sample, the gron-th since the last treatment, weathering, and various other factors. For this reason no prediction can be made as to the amount of residue that may be found on any particular sample. The author has made residue determinations of thousands of samples of fruits, vegetables, forage crops, and forest vegetation. On apples, for instance, he has found D D T residues ranging from 1 to 12.5 p.p.m., and on peaches from 6 to 23 p.p.m. On pea-vine samples he has found amounts ranging from practically nothing to 40 and 50 p.p.m. on the dry weight basis. On forage crops such as alfalfa and clover he has found residues as high as 48 p.p.m. An application of 1 pound of insecticide per acre to forage crops yielding 1 ton of hay per acre should result in a reqidue of 500 p.p.m. if all the insecticide n.ere retained on the vegetation. The residues obtained from various crops following treatment Kith D D T , according to the usual commercial practice, are given in Table I. ABSORPTION AND TRANSLOCATION O F DDT BY PLAUTS
h cooperative investigation with the Bureau of Plant Industry, Soils, and Agricultural Engineering was carried out over two seasons to determine whether vegetable plants would absorb D D T from insecticidal applications and translocate the compound into the edible portions.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
p.p.m., indicating that t)he DDT was not completely lost or decomposed during the cooking.
ON CROPS TABLE I. DDT RESIDUES
Crop Apples Peaches Unbrushed Brushed Pes, vines
DDT Treatmenta S p a y s , 1 lb. per 100 gal.
Sprays’ 1 lb per 100 gal. Sprays’ 1 Ib. per 100 gal. Aerosois, 0.3-0.5 Ib. per acre Dusts, 0.5-1 Ib. per acre Shelled peas Dusts, 0.5-1 lb. per acre Alfalfa Dusts, 1-2 lb. per acre a 4 cover sprays for apples, 2 for peaches.
Time of Sampling Harvest Harvest Harvest Maturjty Maturity Maturity Hay cutting
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DDT Residue, P.P.M. 1-12.5 6-23 3-14 15-50 2-10 None 2-48
Beans, beets, cabbage, cantaloups, cucumbers, onions, peas, potatoes, squash, tomatoes, and turnips grown in field plots were treated with dusts or sprays containing 3 t o 10 % ’ of D D T in amounts ranging from sufficient t o a n excess over that required t o give practical control of the insects affecting these crops in Maryland. Samples of the crops were collected during the growing season and a t maturity and analyzed for the presence of DDT. Samples of whole green beans were stripped by washing with benzene, and duplicate samples were dried, ground, and then extracted with benzene; the benzene solution was analyzed in both cases. Samples of pods containing peas were stripped of their residue in a similar manner, and the peas, shelled by hand from duplicate samples, were dried, ground, and then extracted t o remove the residue for analysis. Samples of beets, cantaloups, cucumbers onions, potatoes, squash, tomatoes, and turnips were washed t o remove soil and any adhering residues, and then peeled, and only the fleshy parts sliced, dried, and extracted, and the extracts were analyzed. Some cabbage samples showed the presence of D D T up to 6 p.p.m. on the four wrapper leaves, but on the stripped heads less than-0.5 p.p.m. was found. The presence of even this small residue was probably due to the short interval between the last application and harvest. The amounts found absorbed in the other vegetables. were not significant, and the results indicate t h a t DDT is not absorbed by vegetables and translocated into the edible portions following application to the aerial parts of the plants. Gunther and Elliott (6) in their investigations of the penetration of field-applied DDT into citrus fruits, avocados, olives, apples, and pears, found that in oil solutions D D T penetrates into and through the flavedo and permeates the albedo of the rind of navel and Valencia oranges, but as a dust appears to penetrate only the flavedo. DDT CONTENT OF MEAT AND FAT
I n a cooperative experiment with the Bureau of Animal Industry, two lots of six pigs each were fed for 36 days on a ration containing 75% of corn meal and 25% of ground beef that contained DDT absorbed from insecticide residues. The feed of the pigs in one lot contained 5 p.p.m. of DDT and 3 p.p.m. in the other, based on the weight of the total ration, This percentage of meat is abnormal in rations for pigs. The pigs were butchered and the carcasscs separated into three portions-lean meat, leaf fat, and external plus intramusculai fat. The amounts of DDT from the two lots were 2 and 1.7 p.p.m. in the lean meat 15.6 and 11.4 p.p.m. in the external and intramuscular fat, an& 17.6 and 11.4 p.p.m. in the leaf fat. The D D T accounted for in the fat and meat portions of tKe animals was 49 t o 57% of the total intake. Effect of Cooking on DDT Content of Meat. I n a cooperative experiment with the Bureau of Home Economics and Human Nutrition, five samples of meat from a beef animal containing D D T stored in the body as a result of eating hay containing this compound were selected for cooking by roasting, broiling, pressure cooking, braisin , and frying. Each sample was divided into two portions, one of which was analyzed raw, and the oiher was cooked before being analyzed. The DDT content of the raw meat ranged from 15 t o 27 p.p.m. and of the cooked meat from 7 t o 21
DDTCONTENTOFMILK
In a cooperative experiment with the University of Maryland, cows were fed pea-vine silage at the rate of 3 pounds per 100 pounds of animal for 2 months. The silage contained 2.7 to 5.4 p.p.m. of DDT. Weekly milk samples from these cows did not show appreciable amounts of DDT. Allen et al. ( 1 ) reported that no DDT was found in the milk from cows fed silage from field-dusted pea vines containing 1 p.p.m. of DDT. The milk from cows that had been fed on silage made from pea vines to which D D T had been added a t the rate of 1 pound per ton was found to contain 15.6 p.p.m. of D D T near the end of the feeding experiment. Carter (2) and Schechter et al. (7‘) reported a DDT content as high as 25 p.p.m. in milk from cows t h a t had grazed on DDTsprayed pastures or fed on hay containing 184 p.p.m. of D D T residue. The insecticide applications on these forage crops were heavier than would be necessary for control of insects. DDT CONTENT OF EGGS
I n a cooperative experiment conducted with the Bureau of Animal Industry (e), chickens were fed on diets containing various percentages of DDT, and the eggs from these chickens were analyzed for the DDT content. The diets contained 0, 0.031, 0.062, 0.125, and 0.250% of DDT, and the amounts found in the eggs were 0, 180, 240, 360, and 320 p.p.m., respectively. These amounts were based on organic chlorine determinations corrected for similar determinations on eggs from the hens on the DDT-free diet. Colorimetric determinations for DDT were strongly positive on the eggs containing 360 p.p.m. and were negative on the eggs from the check lot. The amounts of DDT in the diets were much more than would be present as a result of insecticide applications. CONCLUSIONS
Insecticide, formulations containing D D T applied to field crops during the growing season generally result in residues which persist until the crop is harvested. When forage crops containing large amounts of DDT residue are fed to farm animals, D D T may be stored in the tissues and eliminated in the milk. It appears that DDT present as residues on vegetation is chemically unchanged when stored in animal fat and tissues and eliminated in milk, since extracted residues of these materials subjected to colorimetric tests gave the characteristic blue color obtained by treatment of D D T . The organic chlorine content of aliquot portions of these extracted residues was in good agreement with the amounts calculated from the DDT content obtained by the colorimetric method. LITERATURE CITED (1) Allen, N. N., Lardy, H. A . , and Wilson, H. F., J . Dairu Sci., 29 ( 8 ) , 530-31 (1946). ( 2 ) Carter, R. H., ANAL.CHEM.,19,54 (1947). (3) Carter, R. H., J. Assoc. Oficial Agr. Chem., 30, 456-63 (1947). (4) Carter, R. H., and Hubanks, P. E., Ibid., 29, 112, 114 (1946). (5) Gunther and Elliott, Pacific Slope Branch, Am. Assoc. Economic Entomologists, Berkeley, Calif., June 1947.
(6) Rubin, Max, Bird, H. R., Green, Nathan, and Carter, R. H., , Poultry S C ~ 26, . , 410-13 (1947). (7) Schechter, M. S., Pogorelskin, M. A., and Haller, H. L.. ANAL.
CHEM.,19,51-3 (1947).
(8) Sohechter, M. S., Soloway, S. B., Hayes, Robert A., and Haller,
H.L.,Ibid., 17,704-9 (1945). RECEIVED November 29, 1947.
END OF SYMPOSIUM ON INSECTICIDES IN FOOD PRODUCTION
