102 EADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



mine to a large extent the difficulty of the problem. If the half-life is 

 short, the waste can be stored until it has decayed to an acceptable level. 

 It is convenient to consider the specific details of waste disposal in terms 

 of isotopes classified as follows: 



Isotopes with a Half-life Not Greater Than 2 Weeks {Such as K^'~, Na-\ 

 jui^ p32 Guidance for isotopes in this category may be obtained from 

 the official recommendations for P^- and P^^ (6). Disposal into the 

 sewage system is usually most convenient, and greatest consideration has 

 been given to this route. The value for maximum short-period contam- 

 ination of P^- or P" in sewage has been set at 0.1 mc/liter. Dilutions are 

 estimated for the discharge point from the institution into the sewage 

 system into which the radioactive wastes are discharged (i.e., for the insti- 

 tutional treatment plant or the main sewer outfall). No account is taken 

 of hazards that may develop in private drainpipes owing to the concentra- 

 tion of radioactive wastes or to the use of certain pipes exclusively for the 

 discharge of these materials. This depends on local conditions, which are 

 best controlled by monitoring the plumbing. The single-batch disposal 

 has been limited to 10 mc when the expected water flow through the sew- 

 age plant is 1,000,000 gal/day. Under such conditions, as much as 

 100 mc/day maj^ be disposed of if the waste is discharged uniformly 

 during a 6-hr period. 



Solid combustible wastes and small animal carcasses containing tracer 

 levels of these isotopes may be incinerated without special precautions. 



An interesting study of the behavior of radioisotopes in the typical 

 institutional incinerator has been reported by Kruse et al. (49). The 

 recovery distribution was found to be as follows: 



Recovery, % of charge incinerated 



This demonstrates the difference in behavior of the various elements. 

 The recommended maximum charge, in microcuries per pound of refuse 

 per hour, was 4 for P^- and 2 for P^^ Large animal carcasses present a 

 difficult problem due to the bulk of material, and discussion is deferred 

 until the next classification. 



It is apparent that there will be no appreciable difficulties in the dis- 

 posal of these short-lived isotopes, certainly not at tracer levels ( < 1 mc) 

 or even at levels of about 100 mc which are useful mainly for producing 

 irradiation effects. 



Isotopes of Intermediate Half-life Used in Small Quantities {Such as Ca*^, 

 ;^g55.59^ ^35) _ ^Q recommendations have been formulated for radioiso- 



