Table 4. — Composition of experimental environment 

 showing distribution of gold 199, 600 hours after intro- 

 duction of the isotope 



300 



HOURS 



Figure 2. 



-Movement of gold 199 in an experimental 

 marine environment. 



Components of the community rapidly accu- 

 mulated radioactive gold and reached an apparent 

 steady state after 225 hours (fig. 2). There was 

 not a direct relation between the accumulation of 

 the radioactive gold by the components and the 

 loss of the isotope from the water. Even though 

 the radioactive content of the organisms and 

 sediments did not increase after 225 hours, the 

 radioactivity content of the water continued to 

 decrease. This decrease was attributed to sorp- 

 tion of the radioactivity to exposed surfaces in the 

 tank (a total area of 29,784 cm. 2 ) and to accu- 

 mulation by patches of bacterial film that appeared 

 on the sides of the tank after the experiment had 

 been in progress about 120 hours. Although it 

 was not possible to measure the total amount of 

 film present, 1 g. of this material contained 57 

 mc. of radioactive gold after 600 hours. The 

 distribution of the radioactive gold in the 



community at the end of the experiment is shown 

 in table 4. 



Crabs accumulated more radioactive gold than 

 the other organisms in the experiment. As an 

 estuarine species, blue crabs are a part of a marine 

 community that appears most likely to be ex- 

 posed to radioactive material in any appreciable 

 concentration. As bottom-dwelling, omnivorous 

 predators and scavengers, blue crabs are, at one 

 time or another, in contact with almost all of the 

 abiotic components of their environment. The 

 carapace and gills offer many surface sites for 

 sorption of materials from the environment. Gill 

 area alone of a blue crab has been estimated to be 

 about 275,000 mm. 2 (Gray, 1957). 



Although sediments often are not included in 

 the food web of marine organisms, many organisms 

 can utilize materials sorbed onto sediments as a 

 source of nourishment. Thus, it is necessary to 

 observe accumulation of gold by sediments as well 



Figure 3. — Sorption of gold 199 by sediment in an 

 experimental environment. Curve A is activity cor- 

 rected for decay, curve B is observed activity. 



RADIOACTIVE GOLD USED AS A SEDIMENT TRACER 



431 



