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MISCELLANEOUS PUBLICATION NO. 1065, U.S. DEPARTMENT OF AGRICULTURE 



This involves 1 square mile in which there is a 

 slough. This slough retains water draining from 

 300 acres of surrounding cultivated land. The 

 rotation followed on this cropland involves soy- 

 beans, corn, and cotton. Insecticides are used on 

 these crops whenever necessary for pest control. 

 Although other chemicals were found in trace 

 amounts, endrin residues have shown an interest- 

 ing sequence of analytical peaks which have some 

 significance. 



The treatment history of this study area shows 

 that an average of 7.5 applications of endrin at 

 0.3 pound per acre had been applied to cotton 

 fields since 1956. During 1965, when the follow- 

 ing data were obtained, the 37-acre cotton field in 

 the 300 acres being studied received weekly appli- 

 cations of endrin from July 14 to September 3. 

 Endrin residues in the soil of the watershed area 

 under study averaged 0.30 p.p.m, in the spring of 

 1965 and 0.32 p.p.m. in the fall following the 

 treatment period. 



One part per million equals approximately one 

 pound per acre in the surface 3 inches of soil. In 

 the 9 years endrin has been used on this acreage, 

 a total of approximately 22.5 pounds per acre 

 had been applied and residues remaining in the 

 soil amounted to approximately 0.3 pound per 3 

 acre-inches, or approximately the amount applied 

 in a single application. 



Development of Improved Insecticides. — The 

 public concern regarding certain insecticides that 

 may impair the quality of our environment is be- 

 ing met through research on the development of 

 improved insecticides with a higher degree of de- 

 gradability, and with minimum toxic effects to 

 humans, farm animals, fish, wildlife, and benefi- 

 cial insects. Most every State agricultural experi- 

 ment station, as well as the U.S. Department of 

 Agriculture, has research underway on use of less 

 persistent organic phosphorus and the carbamate 

 insecticides in place of the chlorinated hydrocar- 

 bon insecticides. 



Following availability of the chlorinated hydro- 

 carbon insecticides in the forties, research and use 

 experience soon began to show that these insect 

 killers were highly persistent in soils and in water. 

 Of even greater concern, it was found that in- 

 secticides such as DDT, dieldrin, and heptachlor 

 would accumulate in animal tissues. Meat and 

 milk showed high residues when the livestock con- 

 sumed feeds containing substantial residues of 

 these materials. When animals were sprayed with 

 chlorinated hydrocarbons to control flies, ticks, 

 lice, and other livestock pests, the insecticides were 

 absorbed through the hide, and residues appeared 



in meat and milk. Once present in animals the 

 residues persisted in the tissues for some time, 

 slowly decreasing for weeks or months. They were 

 not readily degraded in animal tissues. Wildlife 

 biologists found that the residues would magnify 

 in animal tissues through food chain organisms 

 and even result in death of animals at the top of 

 the food chain. 



Research showed that organophosphorus com- 

 pounds and carbamates degrade more rapidly in 

 soils and water and on plants. Even more impor- 

 tant, these types of insecticides were found to de- 

 grade rapidly in animal systems, thus the prob- 

 lem of residues in meat and milk was largely 

 avoided, and the problem of biological magnifica- 

 tion in wildlife was prevented. Unfor(unately, the 

 organic phosphorus compounds as a class are gen- 

 erally more toxic than the chlorinated hydrocar- 

 bons to man and animals that have had acute ex- 

 posure. Both classes include materials that are 

 highly toxic to beneficial insects. 



Zectran and stabilized pyrethrins appear, from 

 current research, as possible substitutes for DDT 

 in the control of forest defoliators such as the 

 spruce budworm. 



Research on aerial spraying of forest insecti- 

 cides indicates that the addition of fluorescent 

 particles to the spray provides an excellent means 

 to track deposits. 



Many changes and adjustments in recommenda- 

 tions and registrations have been made as the re- 

 sult of research on the biodegradable properties 

 of insecticides in soils, water, plant tissues, and 

 especially in livestock. As a result of these find- 

 ings, the use of DDT and certain other persistent 

 insecticides on dairy animals and on crops grown 

 for dairy foods was discontinued by the late for- 

 ties. Their use on beef animals and on forage for 

 beef animals was greatly restricted. 



To protect forage crops as well as livestock from 

 insect attack, such insecticides as methoxychlor, 

 malathion, and carbaryl, have almost completely 

 replaced the persistent tissue-accumulating chlori- 

 nated hydrocarbon insecticides. This has greatly 

 alleviated the problem of residues in meat, milk, 

 and poultry products. 



Scientists in industry, as well as in public- 

 supported research institutions, recognize that bio- 

 degradable insecticides must eventually replace 

 the nondegradable types in situations v here wild 



