76 MISCELLANEOUS PUBLICATION NO. 10 65, U.S. DEPARTMENT OF AGRICULTURE 



for the control of plant species, such as ragweed Rachel Carson's book, "Silent Spring," shocked 



and bermudagrass, that produce allergenic pollen. the general public. People began to wonder if Mul- 



Much has been learned about problem species, ler's discovery had not created many more ominous 



however, through observations incidental to other problems than it solved. Objective evaluation {64, 



research projects. 133) has made a strong case that development of 



Information is available for the control of rag- DDT was indeed a tremendous contribution to 



weed, for example, but that knowledge has not man's welfare. 



been put to use in a widescale control operation. Retention in the Environment. — The U.S. De- 



Since the seed is disseminated by wind and can partment of Agriculture began laboratory studies 



remain viable in soil for long periods of time, on the persistence of DDT in soils in 1943 {38) . 



areawide treatments would be necessary for ade- Soil samples were collected from 85 different lo- 



quate control. cations infested with the Japanese beetle and 



The prevention of pollen production by trouble- treated with 25 pounds of DDT per 3 acre-inches, 



some weed species would alleviate much suffering The average results for all soils, based on bioassay, 



and save many thousands of dollars in medical were as follows : 



expenses. Persistence after years indicated : Percent ddt 



Agricultural Chemicals remaining 



2 90 



insecticides 3 79 



Paul Miiller of Basel, Switzerland, was 4 64 



awarded the 1948 Nobel Prize in Physiology and 6 56 



Medicine in recognition of his outstanding work 



in development of DDT as an insecticide. Midler's Persistence tended to be greater in sandy than in 



product first showed its dramatic power when used fine-textured soils, and to be inversely related to 



to control an infestation of Colorado potato beetles organic matter content of soil. In soil containing 



in Switzerland in 1939. During the war years, 29 percent organic matter, the persistence after 3 



researchers in the U.S. Department of Agriculture years was 24 percent, whereas in soil containing 0.7 



determined the value of DDT for controlling a percent, the persistence was 94 percent, 



number of disease vectors, and the insecticide was The high degree of persistence of DDT in soil 



used extensively by the Armed Forces to control found in this laboratory study has been confirmed 



arthropodborne diseases. Millions of illnesses were many times. 



prevented; thousands of lives were saved {71). No Comparable studies {39) showed that chlordane 



adverse effects on humans were recorded. was somewhat persistent in soil but not nearly so 



Following the war DDT and a number of persistent as DDT. A number of problems related 



similar insecticides were developed for agricul- to the persistence of chlorinated hydrocarbon in- 



tural pests. Extensive use of DDT to control insect secedes were discussed in the 1952 Yearbook of 



pests of field crops and forests sometimes has re- gucu ure ( ). 



suited in the direct kill of small numbers of fish Research toward characterizing the resistance to 



and storage of DDT in the tissues of survivors; degradation of such insecticides as the chlorinated 



sprays used to kill bark beetles that transmit hydrocarbons still is under intensive study at the 



t-., 1?v j. 1 iix . Wisconsin and other State agricultural experiment 



Dutch elm disease fungus have led to contamma- ... „, _„. . , M ° M „ s . , , 



„ ,. . ,. ., .^ T-.-T.™ -, stations. 1 he Wisconsin {72,73) work has shown 



tion of earthworms in the soil with DDI and , , , ,, 1A , . , , » / ,, , . „ 



, . . ,. •, . that the 10 most important factors that influence 



robins feeding on the worms were sometimes the persistence of insecticides in soils are the chemi- 



killecl; eagles and other predatory birds were C al specificity of the insecticide itself , the soil type, 



found with DDT in their tissues. Wildlife con- soil mo i sture , soil temperature, wind or air move- 



servationists became concerned, not only over ment, cover crops, soil cultivation, mode of appli- 



possible adverse effects of DDT but also over other cation of the insecticide to the soil, the insecticidal 



broad spectrum pesticides, including endrin, formulation, and soil micro-organisms. Studies 



aldrin, dieldrin, heptachlor and toxaphene. show that the most important factor among these 



