shrimp, Penaeus setijerus, appeared in samples 

 taken after the release. Sediment samples from 

 the drop zone were composed mostly of sand. 

 Additional information on the sediments is given 

 by the U.S. Army Corps of Engineers (1964). 



Cages containing various estuarine organisms 

 were placed at six stations around the proposed 

 drop zone 24 hours before the scheduled release 

 (fig. 4). Test animals at each station included 

 25 blue crabs; 50 oysters, Crassostrea virginica; 

 and 50 mummichogs, Fundulus heteroclitus . Ten 

 croakers were included at stations IV, V, and VI. 

 The blue crabs were kept in separate cages to 

 prevent predation on the other test animals. 

 Also, at each station, plastic petri dishes filled 

 with montmorillonite clay were placed in minnow 

 traps to test for adsorption of gold 198. Five to 

 ten animals of each species were removed from the 

 cages for each sample. 



The radioactivity content of the field samples 

 was measured at the Bureau of Commercial 

 Fisheries Radiobiological Laboratory, Beaufort, 

 N.C., 110 miles from the sampling area. The 

 detector system consisted of a 3-inch Nal(Tl) 

 crystal coupled to a single-channel gamma spec- 

 trometer. Sediment and biological samples were 

 placed in individual plastic bags, packed in an ice 

 chest, and transported to the laboratory as soon 

 as possible after sampling. Water samples were 

 held in screw cap jars. If the water samples were 

 found to be radioactive, the water was Millipore- 

 filtered and counted again, along with the separated 

 material, to determine whether the radioactive 

 gold was associated with suspended material. 



The various samples were measured for radio- 

 activity in a manner that permitted the comparison 

 of ^organisms, sediments, and water. To make 

 these comparisons, it was necessary that the radio- 

 activity in all of the samples be measured under 

 similar conditions of geometry. Organisms con- 

 taining gold 198 were measured for radioactivity 

 before and after being dissolved in nitric acid and 

 diluted to 900 ml. A factor was thus obtained for 

 converting measurements made on the intact 

 organisms to measurements which would be ob- 

 tained after dissolving and diluting the organisms 

 to 900 ml. A factor was obtained for the sedi- 

 ments in a similar manner, except that no acid 

 was used and Calgon was added as a wetting agent. 

 NO preparation was necessary to measure gold 199 

 in the 900 nil. samples of water. Since radio- 



activity measurements in intact organisms and 

 sediments could be converted to measurements 

 based on their being contained in a 900-ml. 

 volume of water, and since all measurements of 

 water were for 900 ml., it was possible to compare 

 activity contained in these three types of samples. 



The radioactivity content of water, sediments, 

 and biota varied widely between stations. Bio- 

 logical samples from stations III and VI did not 

 contain measurable amounts of radioactivity at 

 any time (table 5). As one would expect, bio- 

 logical samples from station II, located directly 

 in the drop zone, contained higher concentrations 

 of radioactivity than those of other stations. 

 Lateral dispersion of radiogold was indicated by 

 the increase in activity in the crabs and oysters 

 from stations I and IV after 41 hours elapsed time. 



The second application of gold appeared to have 

 little or no effect on the levels of concentration in 

 the samples, except perhaps those in station IV. 

 Oysters and crabs accumulated radioactivity to 

 maximum level 17 hours after the first radiogold 



Figure 5. — Radioactivity content of biota and sediments 

 from Cape Fear River after release of gold tracer. 



434 



U.S. FISH AND WILDLIFE SERVICE 



