480 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



L_[ 



Fig. 2 Pathways of plutonium transport to man via beef cattle and dairy cattle. 



assumes that all inhaled plutonium is transferred to the gastrointestinal tract or the blood 

 within 24 hr. 



If we assume that the parameter values given in Fig. 2 are reasonably close to the true 

 values, the only parameters remaining to be determined are the plutonium ingestion and 

 inhalation rates and the rate at which plutonium enters the blood (rb). 



Plutonium Ingestion Rates. Kleiber (1961) shows that the basal metabolic rate of 

 mammals (heat production by a fasting animal) is proportional to the three-fourths power 

 of body weight and that the feeding capacity (maximum energy intake) of domestic 

 animals, such as the cow, is about five times the food intake required for basal 

 metabolism. Data given in The Merck Veterinary Manual (Siegmund, 1967) for the 

 digestible energy (DE) requirements for maintenance of mature cows are based on 



DE= 163.5 W°''3 



(19) 



where DE is the digestible energy required for maintenance (kcal/day) and W is the body 

 weight (kg). 



The additional DE requirement for milk production in the range from 20 to 35 kg 

 milk/day at 5% butterfat is 1850 kcal (DE)/kg milk. The additional DE requirement for 

 growth ranges from about 8600 to about 19,800 kcal/kg gained, depending also on body 

 weight. According to McKell (1975), the average digestibility of desert vegetation is about 

 36% compared with 52% for good alfalfa hay and up to 80% for some concentrates 

 (Siegmund, 1967). The average energy content of most plant materials is about 4.5 kcal/g 

 (dry weight) (Golley, 1961), and the digestible energy content of desert vegetation is 



