as accumulation by the biota. In the present 

 experiment, an increase in sediment activity up to 

 the 250th hour occurred (figs. 2 and 3). From 

 this time until the experiment ended, the activity 

 was maintained with no significant increase or loss ; 

 it appears that the sediments were saturated with 

 gold at 250 hours (curve A, fig. 3). The actual 

 activity of the sediments, uncorrected for decay, 

 is shown in curve B of figure 3. The latter values 

 would be of more importance to the health 

 physicists, as they show the actual amount of 

 activity present in the sediments. If the gold 

 were released into sea water in a restricted area 

 where dispersion was minimal, these results in- 

 dicate that natural decay would exceed uptake 

 after about 1 50 hours with a resulting decrease in 

 sediment activity. 



Live clams accumulated more radioactivity than 

 did the separated clam shells. Since clams feed by 

 filtering suspended matter from large volumes of 

 water passing over their gills, they are susceptible 

 to contamination from particulate radioactive 

 materials released into the estuarine environ- 

 ment. As bottom dwellers, restricted in their 

 movements, they are in contact with sediments 

 and associated radionuclides. A comparison of 

 the mean radioactivity content of 10 clams to 10 

 separated clam shells on a unit weight basis by a 

 standard t test at the .05 level showed that live 

 clams were significantly more radioactive. The 

 higher concentration of the isotope in the live 

 animals was attributed to the movement of water 

 through the animals. This movement would ex- 

 pose internal tissues as well as shell surfaces to 

 contaminated water. 



The clams placed on top of the sediment at the 

 beginning of the experiment accumulated much 

 less radioactive gold than those placed in areas 

 without sediment. As the experiment progressed, 

 the clams burrowed into the sediments, leaving 

 only a portion of their shells exposed. The bur- 

 rowing clams contained 38 percent less activity 

 than those that remained on the bottom surface 

 of the tank — an indication that a large portion of 

 the gold accumulated by clams was due to sorption 

 of the shell. 



Fish accumulate radioactive materials by ad- 

 sorption, absorption, or by ingestion. In nature, 

 these three modes of uptake can occur simulta- 

 neously, singly, or in various combinations, 

 depending upon the physical state of the isotope 



432 



in the water, the food habits of the fish, and the 

 length of time the fish remains in a polluted area. 

 In this experiment, the sheepshead minnow accumu- 

 lated the least amount of radioactive gold of any 

 test organisms (fig. 2). The activity of the fish 

 decreased during the latter stages of the experi- 

 ment. A sloughing off of the epidermal mucous 

 layer containing sorbed activity could account for 

 the loss, or the physiological condition of the fish 

 could have deteriorated and their rate of metab- 

 olism changed. 



FIELD INVESTIGATIONS 



The accumulation of radioactive gold released 

 into the Cape Fear River was observed in both 

 indigenous organisms and in caged organisms 

 collected in Beaufort and maintained in the river. 

 The investigations were coordinated with the 

 release of radioactive gold which had been sorbed 

 onto sediment particles. 



The specific problem under investigation by the 

 U.S. Army Corps of Engineers was to determine 

 if sediment being deposited in the channels of the 

 Cape Fear River, N.C., near the Sunny Point 

 Army Piers near Southport, N.C., had been 

 transported by currents from a spoil area on the 

 opposite side of the river (U.S. Army Corps of 

 Engineers, 1964). The answer was sought by 

 tagging a small quantity of the sediment with 

 gold 198, releasing this sediment in the spoil area, 

 and tracing its distribution with an underwater 

 scintillation probe mounted on a sled. The 

 sediment was tagged by first forming a slurry into 

 which 5 c. of gold 198 chloride were thoroughly 

 mixed to allow maximum sorption. This was 

 done in a special conical-bottomed container 

 which served also as the release mechanism for 

 the tagged sediment. The container floated in 

 the water and was towed by boat "over a prede- 

 termined course while the tagged sediment was 

 being released. The entire procedure has been 

 described in greater detail by Krone (1960). 



Gold-tagged sediments were released at two 

 different sites. The first 5 c. "drop" was made on 

 October 24, 1962, at 6 p.m., at high tide, along an 

 east-west line on the southern end of the Spoil 

 area (fig. 4). A second 5 c. drop was made on 

 the northern end of the spoil area on October 25 

 at 4 p.m., also at high tide. A water sample 

 collected in the drop zone at this time had a 



U.S. FISH AND WILDLIFE SERVICE 



