little absorption along the way. In the present 

 study, little, if any, radioactive gold was found in 

 the organs of fish that were fed this isotope sorbed 

 onto clay. 



In field studies, animals and sediment main- 

 tained in cages in the drop zone sorbed little 

 activity. This could have been caused by the 

 tremendous dilution by river water and strong 

 currents, and to the short physical half-life of the 

 gold isotope. Since it was demonstrated experi- 

 mentally that the animals retained little activity 

 from ingested labeled sediment particles, the 

 initial accumulation of activity was perhaps from 

 unbound gold that was not sorbed onto sediments 

 in the mixing hopper but remained in the water 

 phase of the slurry. 



Since gold is not biologically essential and is not 

 concentrated significantly by estuarine animals, 

 the isotope gold 198, with its short physical half- 

 life of 2.7 days, appeared to be a safe and effective 

 tracer for following sediment movement. Even 

 though as much as 5 c. of gold 198 were released 

 in the Cape Fear River at one time, the maximum 

 concentration found in any of the animals tested 

 was 70.9 X10 -6 nc. per g. of oyster at station II 

 (table 5). This is slightly in excess of the maxi- 

 mum permissible concentration (MPC) for gold 

 198 in water effluent released in an unrestricted 

 area, i.e., 5X10 -6 /iC./ml. (Code of Federal Regula- 

 tions, 1960). However, station II was purposely 

 located in the drop zone so that the caged animals 

 would be subjected to the most extreme conditions 

 of contamination. There is no evidence now that 

 radiation from the low levels of gold 198 involved 

 in these investigations affected the biota. 



ACKNOWLEDGMENTS 



Thomas J. Price provided unpublished data 

 on mollusks and George H. Rees furnished data 

 on blue crabs. The U.S. Army Corps of Engineers 

 and its consultant, R. B. Krone, cooperated and 

 assisted. 



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436 



U.S. FISH AND WILDLIFE SERVICE 



