cesium"' in marine fishes 



183 



The retention process may be expressed by the 



form ^_aie-V+a2«-V+ • • • fl»«-S,' 

 in which ai, as, . . . a„ and t,, . . . k„ are the 

 intercept and rate constants, respectively, of 

 the individual or fu'st-order components of the 

 retention or elimination process (Richmond, 

 1958). Values of k were calculated by multiph-ing 

 the slope of the hne by 2.3, the slope being (log 

 ^0— log *4)/< in which A represents the amount of 

 material at zero time and A the amount at time t. 

 Biological half-life was determined by the form 

 Ui=0M3lk (Comar, 1955). 

 Whole-body retention 



The retention of Cs''" by flounder which had 

 accumulated the radionuclide for 3 months was 

 followed over a period of 44 days. Water tem- 

 perature varied between 22° and 26° C, and the 

 average salinity was 32°/oo. Twenty-thi'ee 

 flounder were radioassayed individually, and the 

 values averaged for each determination. Mor- 

 tality reduced the number of fish to 13 by the 

 37th day and to 8 fish by the last day. 



The retention curve for postlarval flounder was 

 composed of two exponential rate functions (fig. 

 4). The first component (A) contained 34 per- 

 cent of the amount of Cs'^^ at zero time and had a 

 t^ of 5.3 daj's. The second component (J5) con- 

 tained 66 percent of the Cs"' at zero time and 

 had a t^ of 36.9 days. It is significant that the 

 larger portion of Cs''^ was represented by the 

 slower moving component. In view of the experi- 

 ments wnth croaker described earlier, this larger 

 portion probably represented the influence of 

 muscle. It should be remembered that these 

 fish had been exposed to Cs"" for 3 months so 

 there was ample time for a buildup of the radio- 

 nuchde in nmscle. Furthermore, muscle repre- 

 sents the largest mass of anj* single tissue. 



The same data also were plotted on a unit- 

 weight basis. As expected, the results were 

 different because of changes in rate of weight 

 increase (table 4). The fii-st component con- 

 tained 67 percent of the Cs'" at zero time and had 

 a fi^ of 6.8 da.ys. The second component contained 

 33 percent of the Cs''^ and had a L^ of 46.4 days. 

 It is interesting to note that the slow-moving 

 component represented the smaller portion. The 

 reason for this tlifference is that during the j)criod 

 from the 24tli to 44tli day no significant change in 

 weight occurred, but diu-ing the first 23 days 



Figure 4. — Retention of Cs"' by postlarval flounder, 

 showing separation of composite curve into two rate 

 functions. 



there was an increase. The weight increase in 

 effect produced an elimination rate largely in- 

 fluenced by "biological dilution" which was not 

 evident in the period from the 24th to the 44th 

 da}'. This resulted in a slower apparent eUmina- 

 tion rate for the second component which indi- 

 cated a small percentage when extrapolated back 

 to zero time. Undoubtedly, the fii-st curve based 

 on the amount of Cs'" per fish presents the more 

 reliable picture of whole-body retention by post- 

 larval flounder. 



Tissue retention 



Retention of Cs'" by selected tissues of 

 croaker following administration of an oral dose 

 was observed over a period of 219 days. The 

 experiment was begun in May and completed in 

 Januarj', so that water temperatures graduallj- 

 increased from 24° C. to a ma.ximuni of 32° C. 

 during August, then decreased to a mininmm of 

 10° C. at the end of the experiment. Sahnity 



