Environmental plutonium in humans.

Although the current world inventory of plutonium is overwhelmingly man-made, it is important to recognize that 244Pu was a primeval radioelement and that 239Pu is formed continuously by spontaneous fission of 238U; the atom ratio U:Pu being about 10(11):1. It has been calculated that the human body has always carried a base load of, perhaps 10(3)-10(5) atoms (< 0.2 amol) of natural plutonium. Since 1945, the release of 239Pu into the environment from atmospheric nuclear weapons testing has added to this base load a civilization-related load which, at approximately 300 fmol, is at least 5 orders of magnitude greater. Within the human body plutonium is deposited mainly in the liver and skeleton where it appears to be retained tenaciously with half-times of many years. Based on 1970-1980 levels, environmental plutonium may give rise to alpha-particle radiation doses of approximately 3-7 microSv/a in human bone and approximately 10-20 microSv/a in liver, doses which from our present understanding of the radio-and chemical toxicity of plutonium are far too small to cause any recognizable health effects.