application (fig. 5). However, this occurred 5 

 hours before the second application. 



Background samples of biota and water collected 

 in the drop zone area 1 week prior to the release of 

 the labeled sediments did not contain measurable 

 gamma activity in the energy range between 100 

 and 400 kiloelectron volts (Kev), the setting which 

 includes the photopeak of radioactive gold. How- 

 ever, sediment samples contained gamma activity 

 ranging from 367 to 729 counts per minute per 

 kg. wet weight at this setting. Biota, water, and 

 sediments collected from the same area 41 hours 

 after the release did not show an increase in 

 radioactive content over the background samples. 



Table 5. — Radioactive gold content of field samples ' 

 [Activity m./ic/kg.] 



1 NS indicates activity not significantly greater than background; dash 

 indicates no sample was taken. 



DISCUSSION 



The potential hazards accompanying the release 

 of radioactive material into the marine environ- 

 ment should be investigated so that the most 

 dangerous situation possible is evaluated. The 

 accumulation of radioactive gold from sea water 

 by the animal community contained in the large 

 tank was a simulation of this extreme situation: 

 The closed system offered no opportunity for the 

 animals to escape the contaminated area, and 

 there was neither inflow of nonactive sea water nor 

 outflow of contaminated water. Under these 

 controlled conditions, organisms and sediments 



accumulated the isotope from sea water, with 

 crabs and filter-feeding organisms accumulating 

 the isotope to the greatest extent. 



Surface sorption of radioactive gold, no doubt, 

 is an important factor contributing to rapid accu- 

 mulation by marine organisms and sediments. 

 This is based on the observation that 50 percent 

 of the isotope added to the water in an experi- 

 mental environment moved very quickly to orga- 

 nisms and sediments within the tank. It is known 

 that biological accumulation of a radiosotope by 

 sorption occurs rapidly. Further, it has been 

 shown that gold occurs in sea water in a particu- 

 late state. Since particles have difficulty passing 

 through biological membranes, surface sorption is 

 most important in their accumulation by marine 

 organisms. The importance of surface sorption 

 in the accumulation of radioactive gold by orga- 

 nisms was demonstrated experimentally when the 

 radioactive content of clams buried in sediment 

 was shown to be less than that of clams resting on 

 the smooth bottom surface of the tank. Although 

 the buried clams had less area exposed, the same 

 average amount of water should have passed 

 through their siphons as through the siphons of 

 those resting on the bottom. If all the accumu- 

 lation of gold had been a result of metabolism, the 

 gold content of buried and exposed organisms 

 should have been the same. 



The literature contains several references per- 

 taining to the surface accumulation of material 

 from sea water. As early as 1937, Harvey demon- 

 strated that particulate matter such as ferric 

 hydroxide was associated with phytoplankton cells 

 by electrostatic attraction to external surfaces. 

 Also, Goldberg (1952) observed that particulate 

 and colloidal iron was utilized by Asterionella 

 japonica. Rice and Willis (1959) showed that 

 particulate cerium 144 became attached to Nitz- 

 schia cells as a result of particles and cells coming 

 in contact with each other and sticking. 



The distribution of this isotope within the 

 animals was observed by placing large quantities 

 of radioactive gold directly into the gut of several 

 estuarine animals. Those organs associated with 

 excretion retained more gold 199 than did others, 

 suggesting that the gold was simply being excreted 

 rather than hems' stored or utilized . The principal 

 route of gold administered as an oral dose to 

 mammals was reported by Spector (1956) to be 

 directly from the alimentary tract to the feces with 



RADIOACTIVE GOLD USED AS A SEDIMENT TRACER 



435 



