WITHOUT CLAY 



-\ 1 1 1 ' 1 ' I ' I 



5 10 20 30 40 50 



TIME (HOURS) 



Effect of clay on toxicity of DDT (50 p.p. b. ) 

 on pinfish, Lagodon rhomboides. Four grams 

 of clay were added to 40 liters of medium. 



Technical grade compounds tested on postlarval brown shrimp rang- 

 ing from 13 to 16 millimeters in total length and on blue crabs (Callinectes 

 sapidus) ranging from 2 to 7 millimeters in carapace width, yielded the follow- 

 ing 24- hour median tolerance limits: 



Compound 



End r in 



Heptachlor 



Dieldrin 



Toxaphene 



DDT 



Brown shrimp 

 0. 5 p.p.b. 

 6 



These results were obtained using glass containers and no diluent 

 so they are not strictly comparable to the results shown earlier. They do 

 show, however, that the postlarvae are extrem^ely sensitive to very low con- 

 centrations of insecticides. 



A change in bio- as say methods was instituted early in March of 

 this year because of evidence that polyethylene containers reduce the strength 

 of pesticide compounds. Tests using fish and crustacesins are now being con- 

 ducted in glass vessels. 



53 



