INSECTICIDES AND REPELLENTS 85 



of the chlorinated hydrocarbon insecticides. The median lethal oral 

 dose for laboratory animals is about 6 grams per kilogram of body 

 weight. Unlike DDT, it is not readily stored in animal fat or excreted 

 in milk when applied to or consumed by animals. Because of its low 

 toxicity it is considered safe as normally used for insect control, 

 including applications inside dairy barns and milk rooms for fly 

 control and on dairy pastures that may require treatment for mosquito 

 control. 



The toxicity of methoxychlor to fish and other aquatic life is not 

 well known. For mosquito control it should be used with the same 

 precautions outlined for DDT (see p. 84). 



TDE 



TDE is also related chemically to DDT. Its acute oral toxicity 

 to animals is lower than that of DDT but higher than that of methox}^- 

 chlor. The median lethal oral dose to laboratory animals is about 

 3.4 grams per kilogram of body weight. It is low in toxicity to live- 

 stock; concentrations up to 8 percent in emulsion sprays caused no 

 harm to calves. 



The chronic toxicity is lower than that of DDT but higher than that 

 of methoxychlor. TDE is stored in animal fat in about the same degree 

 as DDT when taken orally or absorbed through the skin. It is also 

 excreted in milk to about the same extent as DDT. 



Although generally less toxic to animals than DDT, TDE should 

 be used with the same precautions (see p. 84). 



BHC (BENZENE HEXACHLORIDE) 



The several isomers of BHC vary in their toxicity to animals as 

 well as to insects. The gamma isomer is the most toxic to insects. 

 Most technical BHC contains about 12 percent of this isomer, but 

 some preparations are available in which the gamma concentration 

 ranges almost to that of lindane (99 percent) . 



The acute oral toxicity of BHC to rats is lower than that of DDT. 

 Some of the isomers are readily stored in the fat of animals when 

 consumed in the diet or absorbed through the skin. The residues 

 stored in fat are not quickly eliminated. 



BHC is volatile, and the vapors may prove harmful on excessive 

 exposure. 



The musty odor of BHC is a serious objection to its use inside living 

 establishments. It may also lead to tainting of foods if they are 

 accidentally contaminated or if the material is applied to soils in which 

 certain crops are grown. 



BHC is regarded as one of the least toxic of the chlorinated hydro- 

 carbon insecticides to fish. 



Special Precautions in Using BHC 



Do not apply to edible food crops or to soils where vegetables and other 

 crops are grown. 



Do not use inside homes. 



Do not apply inside dairy barns or milk rooms. 



Do not use on man. 



Avoid excessive exposure to mists and sprays, especially oil solutions. 



