NUMBER OF MOUH^ AFTER SPR4V 



Figure 2. --Numbers of aquatic insects per 

 drift sample from Swan Creek after DDT 

 spray, by taxonomic order . 



DDT found in fish were the same, i . e . , 0.1 ppm . 

 Fish with full stomachs were analyzed separate- 

 ly from those with empty stomachs and there 

 appeared to be no difference in DDT content be- 

 tween the two groups. This suggests that the 

 accumulation of DDT in fish was not necessarily 

 related to feeding on exposed insects . 



In addidion, 20 rainbow trout previously 

 placed in a polyethylene container were offered 

 insects that had been collected from Swan Creek 

 3 to 6 hours after the spray was applied. TTie 

 fish had an opportunity to feed on affected in- 

 sects for 20 hours. Then the fish were removed 

 from the container and frozen for chemical anal- 

 ysis . They contained . 1 ppm of DDT, the same 

 as the measurable amounts found in the fish ex- 

 posed in Swan Creek, indicating that ingested 

 dead or morbid insects alone may provide the 

 DDT accumulated in fish tissues . 



SUMMARY 



Portions of Swan Creek received at 

 least 0.01 ppm of DDT, although the plane did 

 not spray within one -quarter mile of the 

 creek. 



Measurable amounts of DDT were not 

 present in Swan Creek after 1 hour , 



There were no apparent acute effects 

 on fish. 



Rainbow trout accumulated up to . 1 ppm 

 of DDT after short exposure to low concentra- 

 tions of the toxicant in water, whether or not 

 their stomachs contained stream insects at the 

 time of sampling. 



Rainbow trout acquired a tissue concen- 

 tration of . 1 ppm of DDT by feeding on insects 

 that had been exposed to low concentrations of 

 DDT for 3 to 6 hours. 



Large numbers of aquatic insects were 

 adversely affected by the relatively low concen- 

 tration of DDT found in the water. 



Aquatic insects apparently concentrate 

 DDT very rapidly. Insects exposed to low con- 

 centrations for 3 hours averaged 11.0 ppm of 

 DDT and 14.2 ppm of DDE. 



Table 2.--DDT residues in fish exposed 

 in Swan Creek 



