ABSTRACT
A broad spectrum of radionuclides was produced following the creation of the cosmos and those whose radioactive half-lives are long compared to the age of the earth remain as ubiquitous components of today’s environment. These primeval radionuclides include those of the uranium and thorium series, and their daughter products, and 40K (1). Another radioelement, plutonium, was formed in large quantities in early supernova explosions, but because of the relatively short radioactive half-lives of its principal isotopes, it is virtually extinct today; however, some natural 239Pu is present in the earth’s crust due to continuous production by spontaneous neutron capture in 238U (2, 3). In addition, largely as a result of the development of nuclear weapons and nuclear technology, a number of artificial radionuclides, especially 134,137Cs, 90Sr, and 239Pu, have been released to become part of the human environment. This chapter discusses the concentrations of the primeval radionuclides, especially those of the actinide elements and their radioactive daughter products, and the nature of the radioactive environment in which life developed on earth. The present distribution and concentrations of both natural and manmade radionuclides in the earth’s crust and the processes underlying their transfer to plants animals and human beings are considered. The concentrations of radionuclides that occur in human tissues are considered and discussed in terms of their possible long-term effects on human health. Although the emphasis is on radionuclides of heavy metals, it is also necessary to consider other radioelements, metallic and nonmetallic, particularly those that are members of the uranium and thorium decay chains, or are components of the fallout from nuclear weapon testing.
