5 10 15 20 25 30 



SALINITY IN PARTS PER THOUSAND 



35 



Figure 1. — Sorption of gold 199 by montmorillonite clay 

 from sea water with increasing salinity. 



nomenon: (1) An increase in salinity caused the 

 clay to clump, and radioactive gold was trapped 

 within the clumps; and (2) The increase in salinity 

 caused the gold particles to coagulate and to sorb 

 more readily onto the clay. If the latter ex- 

 planation is accepted as correct, it would appear 

 that radioactive gold was colloidal in this sample 

 of sea water. 



DISTRIBUTION OF RADIOACTIVE GOLD IN BLUE 

 CRABS 



Edible portions of an organism such as a blue 

 crab can be relatively free from radioactivity even 

 though the total radioactivity content of the 

 organism is high. This is possible when the 

 activity is isolated in the stomach or associated 

 with the highly sorptive carapace and other 

 external sites. That this does occur was shown by 

 determining the distribution of ingested radio- 

 active gold in the blue crab. Twelve crabs with 

 an average weight of 152 g. were made radioactive 

 by pipetting 75.7 jic. (50 microliters) of gold 199 

 directly into the cardiac stomach of each crab. 

 They were then placed in flowing sea water. At 

 intervals of 3, 4, and 5 days after dosing, three 

 crabs were killed, dissected, and measured for 

 contained activity. 



Radioactivity content of tissues at 4 days in- 

 dicated that only a small portion of the gold 199 

 was assimilated from the stomach (table 1). In 

 view of the short half-life of the isotope, more than 



tracer amounts of radioactive gold would need to 

 be ingested rapidly in order to build up concen- 

 trations in edible tissues. 



DISTRIBUTION OF RADIOACTIVE GOLD IN 

 TOADFISH 



Bottom feeders, such as the oyster toadfish, 

 could become radioactive by taking in sediments 

 with loosely bound sorbed activity. If the 

 radioactivity were tightly bound to the sediment 

 particles, however, the sediment-sorption phe- 

 nomenon would reduce the possibility of animal 

 contamination by retaining and confining the 

 radioactivity. 



Table 1. — Radioactivity content of crab tissue 4 days after 

 an oral dose of 75.7 pc. of gold 199 



To test the capacity of fish to "strip" radio- 

 active material from sediments, five male toadfish, 

 average weight 325 g., were each force-fed 75.7 

 nc. of radioactive gold dispersed in 2 ml. of sea 

 water. Five other males of similar size were fed 

 the same amount of radioactivity sorbed onto 25 

 mg. of montmorillonite clay suspended in 2 ml. of 

 sea water. The sea water used in both instances 

 had a salinity of 30%o and a pH of 8.1. After 

 the fish had been fed the isotope, they were placed 

 in flowing sea water. Forty-eight hours later, 

 the fish were killed and dissected, and the amount 

 of radioactive gold in various tissues was measured. 



A comparison of the activity of tissues from 

 both groups of fish shows that most of the gold 

 remained sorbed onto the clay as it passed through 

 the digestive system of the fish (table 2). The 

 fish fed the isotope in sea water retained more 

 activity than those fed the isotope sorbed onto 

 clay. 



DISTRIBUTION OF RADIOACTIVE GOLD IN 

 CROAKERS 



The gastro-intestinal absorption and distribu- 

 tion of gold 199 in the tissues of the croaker were 

 determined after 75.7 pc. of the isotope were 



RADIOACTIVE GOLD USED AS A SEDIMENT TRACER 



429 



