104 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



following precautions are directed: (a) Insoluble particles containing C* 

 should not be discharged into the air, since there may be considerable 

 lung retention of particle sizes of the order of microns. (6) The contam- 

 ination of wounds with insoluble C^* particles should be avoided. 

 The general disposal recommendations for carbon 14 are as follows: 



1. Isotopic dilution. Carbon 14 may be disposed of in any manner 

 provided it is intimately mixed with stable carbon, in the same chemical 

 form, in a ratio that never exceeds 1 /zc C^* for every 10 g of stable carbon. 



2. Sewers. Carbon 14 may be discharged to sewers in amounts that 

 do not exceed 1 mc/100 gal of sewage based on the sewage flow available 

 to the disposer within his own institution. 



3. Incineration. Combustible material containing C*'* may be incin- 

 erated if the maximum concentration does not exceed 5 fxc/g of carbon. 

 (In animal carcasses, this requirement would usually be met by an average 

 concentration not exceeding 0.2 ;uc/g of tissue.) Sufficient fuel should be 

 employed to make sure that there is not more than 5 fxc C^"* per pound of 

 total combustible material. 



4. Atmospheric dilution. C^^02 from carbonates may be discharged in 

 the exhaust system of a standard chemical-laboratory hood that has a 

 lineal air flow of at least 50 ft/min, at a rate not to exceed 100 ^ic/hr/ft^ 

 of air-intake area in the face of the hood as operated. 



5. Garbage. Carbon 14 may be disposed of with garbage in amounts 

 that do not exceed 1 Mc/lb of garbage available to the disposer within his 

 own institution. Approximate equivalents of this requirement are stated 

 here for convenience: 



1 jLtc/lb of garbage = 20 nc per 10-gal garbage can (allowing for 



50 per cent voids) 

 = 800 /ic/yd' of garbage 

 = 0.5 Mc/day per person contributing garbage 



6. Burial. Carbon-14-containing material may be buried provided it 

 is covered with at least 4 ft of well-compacted earth and does not exceed 

 the following limits: 



a. The maximum permissible concentration of C^^ in biological mate- 

 rial (plant or animal) for burial shall not exceed 5 nc/g. 



b. The maximum permissible amount of C^^ in chemical compounds 

 mixed with 1 ft^ of soil shall not exceed 10 mc. 



In summary, it may again be stated that the disposal of radioisotopes 

 used in metabolism studies will not be a serious problem. The Isotopes 

 Division of the Atomic Energy Commission is cognizant of the amounts 

 of radioactivity allocated to each community and will be in a position to 

 advise when the burden may become significant. The present outlook 

 indicates that the use of radioisotopes will not approach these levels for 



