302 



STRONTIUM 



Intake Levels. Strontium occurs in traces in most biological material 

 but is not considered an essential element for plants and animals. It is 

 similar to calcium in chemical and physiological behavior. On account 

 of the low naturally occurring levels and the difficulties of analysis, there 

 are no comprehensive survey values available. Early workers reported 

 0.01 to 0.1 Mg/g of Sr in fresh animal tissue, 0.1 to 0.3 ppm in human livers, 

 and about 10 ppm in sea water. In a recent study (Sr-1) the Sr content 

 of human bones was found to average 0.016 per cent of the ash for fetal 

 specimens and 0.024 for adult. The metabolism of the radioisotopes of 

 strontium has been widely investigated because these activities are per- 

 haps the most hazardous of the fission products. This is due to the fact 

 that radiostrontium is usually well absorbed by the biological system, 

 is deposited in the bones of animals by the growth and/or exchange 

 processes, is transmitted in relatively large amounts to milk and to the 

 developing fetus, and is known to cause bone tumors. The LD50 in I'ats 

 for intravenously injected strontium acetate was about 260 mg/kg. 



Since strontium and calcium have similar biological behavior, it is of 

 interest to gain information on their relative utilization from the Sr/Ca 

 ratio in various materials. In terms of number of strontium atoms per 

 1,000 calcium atoms, a value of 9.23 has been reported for sea water 

 (Sr-la) and 2.7 to 3 for fossils (Sr-2). Also, evidence is now available 

 from tracer studies that plants and animals selectively utilize calcium by 

 about a factor of 3 over strontium (Sr-9; see also Ba-5). The above 



