EFFECTS OF DDT AND OTHER INSECTICIDES 



13 



surface film of the DDT in oil used 

 in 1947. The reduction of bot- 

 tom fauna in 1947, as in 1946, was 

 very heavy and amounted to 90 

 percent at two of the lower sta- 

 tions. The bottom species affected 

 by the oil spray were about the 



same as those hardest hit by the 

 suspension. The kill of fish, also, 

 was somewhat heavier with the 

 oil formulation, and in contrast to 

 the results with the DDT in sus- 

 pension, a number of adult fish 

 were among those killed. 



LABORATORY TESTS 



TOXICITY TO FISHES OF NEW 

 INSECTICIDES 



Tests were made at the experi- 

 ment station of the Fish and Wild- 

 life Service at Leetown, W. Va., 

 to determine the toxicity to fishes 

 of some of the new insecticides. 

 Although these studies have not 

 as yet been completed, pond and 

 aquarium tests have shown the 

 relative toxicities of several com- 

 pounds to be about as follows : 



Chlorinated camphene is con- 

 siderably more toxic to fishes than 

 is DDT and is lethal to silverling 

 minnows, spotfin shiners, creek 

 chubs, fallfish, and black-nosed 

 dace in concentrations of less than 

 0.04 p. p. m. (parts per million). 

 In outdoor ponds an application of 

 0.125 pound to an acre (0.02 

 p. p. m.) killed all these species, 

 but goldfish survived. 



Repeated tests on bluegill sun- 

 fish and young rainbow and brown 

 trout indicated that bluegills were 

 less sensitive than trout, which 

 were killed even at concentrations 

 of 0.005 p. p. m. (one part in 200,- 



000,000) . The threshold limit for 

 bluegills was 0.01 p. p. m. 



Benzene hexachloride is less 

 toxic to fishes than is DDT. Ap- 

 plication of 1 pound to an acre 

 (0.18 p. p. m.) in a field formula- 

 tion ^ on daphnia ponds did not kill 

 bluegill sunfish, goldfish, creek 

 chubs, black-nosed dace, common 

 shiners, fallfish, blunt-nosed min- 

 nows, sculpins, golden shiners, 

 and darters. In aquaria, inch- 

 long bluegills tolerated concentra- 

 tions of 0.45 p. p. m. 



A comparison of the beta, delta, 

 and gamma isomers and their ef- 

 fects on rainbow and brown trout 

 at 0.05, 0.2, and 0.5 p. p. m. in ace- 

 tone solutions of the pure chemi- 

 cals showed a marked difference 

 in toxicity to the fish. Gamma 

 isomer killed all fish exposed at 

 these rates; beta isomer showed no 

 effect ; and delta at the two higher 

 levels produced symptoms of tox- 

 icity (pectoral fins forward, loco- 

 motion affected), but the fish re- 

 covered. Rainbow trout were 

 more susceptible to the gamma 

 isomer than were brown trout. 



* Field formulation: 



1 lb. tech. benzene hexachloride (12 per- 

 cent gamma isomer) 

 2,846 ml. aux. solvent (PD-544-B) 

 Fuel oil No. 2 to make 1 gallon. 



