ABSTRACT
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The radionuclides present in the environment are classi ed as being either of natural or of anthropogenic origin1:
Naturally occurring radionuclides a. Radionuclides of terrestrial origin (e.g., 40K and 87Rb) b. Cosmogenic radionuclides (e.g., 3H, 14C, 32Si, and 36Cl) c. Primary radionuclides: these long-lived radionuclides have been ubiquitous on the Earth
ever since its formation, that is, approximately 4.5 × 109 years ago. The radionuclides 238U, 232Th, and 235U are the respective parent members of the uranium, thorium, and actinouranium radioactive decay series
Anthropogenic radionuclides a. Neutron activation products (e.g., 22Na, 54Mn, 55Fe, 60Co, 63Ni, 64Cu, 65Zn, 110mAg, 124Sb,
and 125Sb) b. 235U and 239Pu ssion radionuclides (e.g., 90Sr, 95Zr, 131I, 132I, 132Te, 137Cs, and 144Ce) c. Transuranic elements (e.g., 237Np, 238Pu, 239Pu, 240Pu, 241Pu, 241Am, and 243Am)
Because of their long half-life, type of decay, and strong radiotoxicity, the most important radionuclides in the aquatic environment are 40K (primordial radionuclide), 55Fe and 63Ni (neutron activation products), 90Sr and 137Cs ( ssion products), 210Po, 210Pb, 234U, 235U, and 238U (naturally occurring alpha and beta emitters), and 238Pu, 239Pu, 240Pu, and 241Pu (arti cial plutonium radionuclides).1
