mine the behavior of gold in sea water, and the 

 translocation of this element in several animals; 

 (2) observing the transfer of radioactive gold from 

 sea water to a community maintained in a large 

 salt-water tank; and (3) measuring the accumula- 

 tion of the isotope in animals and sediments in the 

 natural environment. 



PRELIMINARY LABORATORY 

 EXPERIMENTS 



The behavior of radioactive gold in sea water, 

 its affinity for sediments, and its assimilation 

 by individual organisms were studied prior to 

 following the movement of radioactive gold 

 through a community of organisms. Character- 

 istics of radioactive gold in sea water and the 

 effect of salinity on the sediment-sorption of this 

 isotope were observed. Bentonite clay composed 

 of montmorillonite clay minerals was used in the 

 sediment-sorption experiments because of the 

 natural occurrence of these minerals in marine 

 sediments and because of their reported sorptive 

 properties (Grim, 1953). Experiments on the 

 assimilation of radioactive gold by individual 

 animals were conducted in sea water ranging in 

 salinity from 28 to 32 %o and having a tempera- 

 ture range of 27.0° to 30.2° C. These animals 

 included blue crabs, Callinectes sapidus; oyster 

 toadfish, Opsanus tau; and Atlantic croakers, 

 Micropogon undulatus; all collected near Beaufort, 

 N.C. 



Gold 199 was selected in preference to gold 198 

 because of its longer half-life (3.1 days compared 

 with 2.7 days) and its availability in the carrier- 

 free form (2.09 X10 6 curies (c.)/gram). The gold 

 199, in the form of auric chloride was supplied 

 from Oak Ridge, Tenn. 



The radioactivity content of sediment, water, 

 and animals in these preliminary experiments was 

 measured with a scintillation detector large enough 

 to contain live animals (4J{ inches diameter by 

 9 inches long) and a single-channel gamma spec- 

 trometer. Measurements were corrected for de- 

 cay, geometry, and background. 



BEHAVIOR OF RADIOACTIVE GOLD IN SEA WATER 



The behavior of tracer amounts of radioactive 

 gold in aqueous solutions was investigated by 

 Schweitzer and Bishop (19.53). These investiga- 

 tors have shown by filtration and cent rif ligation 

 that gold (in concentrations less than 10" 8 M) 



appears to behave as a radiocolloid in certain 

 aqueous solutions ranging in pH from 2 to 12. 

 Schweitzer and Jackson (1952) also discussed the 

 use of cation exchangers in the identification of 

 radiocolloids. The uptake of a cationic tracer by 

 an exchanger should decrease with an increase in 

 the cationic concentration of the solution. If tbe 

 tracer is a radiocolloid, however, the uptake 

 increases as the cationic concentration increases. 

 This is attributed to the effects of the cations 

 acting as a coagulant and the exchanger acting as 

 an absorbent. 



Several experiments were conducted in this 

 study to determine, qualitatively, the behavior of 

 radioactive gold in sea water. A water sample 

 was prepared by adding 200 microcuries (/xc) of 

 gold 199 (4.9X10" 11 M) to 1 liter of Millipore- 

 filtered sea water of 30 %o salinity and a pH of 

 8.2. The temperature of the water was main- 

 tained at 25° ±2° C. during the experiment. 

 Centrifugation of 500 ml. of this sample at 3,000 

 r.p.m. for 15 minutes forced 58 percent of the 

 radioactivity to the bottom of the tube indicating 

 that gold particles had been formed. When 500 

 ml. of the initial sample were passed through a 

 Mfilipore filter of 45 millimicrons (m/x) pore 

 diameter, 100 percent of the radioactivity was 

 removed. Even though some of the gold could 

 have been retained as a result of pores being 

 clogged by large molecules, the gold in sea water 

 appeared to be particulate, rather than ionic. 



Further indications of the properties of radio- 

 active gold in sea water were obtained by observing 

 the sorption of gold onto clay. Equal amounts 

 (200 /iC.) of gold 199 were placed in four tanks, 

 each containing 1 liter of millipore-filtered water 

 and 1 g. of clay. The first tank contained distilled 

 water; the second, water having a salinity of 

 8°/ 00 ; the third, 24°/ 00 ; and the fourth, 34% . 

 The waters having salinities of 8°/ 00 and 24°/ 00 

 were prepared by adding appropriate amounts of 

 distilled water to sea water having a salinity of 

 34%o- The water in the tanks was agitated for 

 15 minutes and allowed to stand for 24 hours. 

 The clay slurry was withdrawn from each tank, 

 centrifuged, and the water decanted. The clay 

 was then dried and the amount of radioactive 

 gold measured. 



The uptake of gold 199 on clay increased as the 

 salinity increased (fig. 1). There are at least two 

 possible explanations for this sorption phe- 



•IL'S 



U.S. FISH AND WILDLIFE SERVICE 



