50 



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



magnification. Robins feeding on earthworms liv- 

 ing in DDT-contaminated soil have been killed. 

 Wildlife conservationists and others are concerned 

 over this problem. 



An adequate explanation is lacking of how and 

 why certain insecticides such as DDT become so 

 widely distributed in organisms throughout the 

 environment. Conservationists are concerned over 

 the direct kill of animals that occasionally occurs 

 because of accumulation of residues, but they are 

 even more concerned over the possible adverse 

 effects on reproduction in animals because of a low 

 level of residues in tissues. The chief culprits in 

 this problem are the persistent chlorinated hydro- 

 carbon insecticides that accumulate in animal 

 tissues. 



These persistent insecticides are being replaced 

 by insecticides that degrade more rapidly in the 

 environment and that do not accumulate in animal 

 tissues. However, use of the more persistent types 

 is still substantial in agricultural and public health 

 programs. 



Pesticide monitoring programs conducted by 

 Federal and State agencies show that residues of 

 certain insecticides, particularly DDT, are wide- 

 spread, not only in soils, but also in the tissues of 

 fish, wild animals, birds, and man himself. The 

 significance of these residue levels has not been 

 established. 



DDT residues were detected in the soils of In- 

 diana orchards at levels exceeding 100 pounds per 

 acre when 50 to 75 pounds per acre per year were 

 applied to the trees for 8 to 10 years. Residues of 

 endrin or dieldrin have been found in grass, soy- 

 beans, peanuts, carrots, and other crops. These 

 residues are generally associated with correspond- 

 ing residues found in the soil. 



The average human in the United States carries 

 approximately 270 milligrams of DDT or 900 mil- 

 ligrams of DDT-derived materials, expressed as 

 DDT, in body fat (52). The human body burden 

 of these pesticides appears to have remained fairly 

 constant for several years. Most toxicologists con- 

 sider these levels to be of no health significance. 



The significance of residue levels of DDT and 

 other insecticides found in fish and wildlife is not 

 known. In some instances the levels are substan- 

 tially higher in game animals than the maximum 

 tolerance set for meat of livestock. 



Because of its potential effect on fish and wild- 



life, the U.S. Forest Service is restricting the use 

 of DDT for the control of spruce budworm, pine 

 tip moth, tussock moth, and other destructive for- 

 est pests, and substitute materials are used wher- 

 ever possible. 



Some conservationists believe that certain ma- 

 rine fisheries' resources, such as shrimp, salmon, 

 and oysters, may be adversely affected in river 

 estuaries. 



Entomologists are deeply concerned over the 

 adverse effects of insecticides on insect parasites 

 and predators. Beekeepers sometimes take heavy 

 losses in destroyed or Aveakened colonies because 

 of insecticide exposure. 



The upset in balance of insect parasites and de- 

 structive insects gives rise to new problems. For ex- 

 ample, it is generally conceded that mites in apple 

 orchards now constitute an important pest prob- 

 lem because the mite predators have been destroyed. 

 Bollworms have become major pests of cotton. 

 Their growing importance is due, at least in part, 

 to the destruction of their natural enemies when 

 insecticides are applied to control boll weevils and 

 fleahoppers. 



Fungicides 



Air, soil, water, and plant contamination by all 

 types of fungicides does not appear to be significant 

 even though they are used in large quantities on 

 certain crops. 



The organic mercury fungicides are generally 



the most hazardous to man. These compounds are 



widely used as seed treatments, but the amounts 



per acre are relatively small compared with those 



of most other fungicides. 



Trace amounts of tetrachloro nitrobenzene 

 (TCNB) and several of the dithiocarbamate 

 fungicides have been detected in the total diet 

 studies conducted by the Food and Drug Adminis- 

 tration. The levels detected did not appear to 

 present a problem. 



Tolerances set for most currently used fungicides 

 allow applications at rates needed to control or pre- 

 vent diseases. However, for the antibiotic, strep- 

 tomycin sulfate, which is used to control fire blight 

 of apples and pears, the Food and Drug Adminis- 

 tration permits no fruit residue. Thus, application 

 of this antibiotic is restricted to the bloom season, 

 but this does not allow effective control of this 

 disease and copper-bearing summer sprays are 

 necessary. 



