Answer to Question #724 Submitted to "Ask the Experts"

• local concentrations of uranium in regional geology
• geographic location with respect to fallout plumes from atmospheric nuclear weapons testing
• local geochemistry and groundwater chemistry (in particular, pH and dissolved oxygen)

According to Eisenbud and Gesell (Environmental Radioactivity, Academic Press, 1987), ²³⁹Pu occurs naturally in minerals in the ratio of about 10^-11 to 10^-13 to ²³⁸U concentrations. Concentrations in water, however, will vary because uranium and plutonium have different chemistries. In addition, plutonium was released by atmospheric nuclear weapons testing. According to Eisenbud and Gesell again, ^{239, 240}Pu account for about 3.5% of the total radioactivity released. The 2000 UNSCEAR report notes that about 153 PBq (about 4.1 million Ci) of plutonium isotopes were released during weapons testing (they do not note the production of ²³⁸Pu, only ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Pu). These received global distribution, but were concentrated in the northern hemisphere and, particularly, near the test sites. Other major releases were primarily local in nature because they were in liquid or solid form and did not spread far. The bottom line is that, with sufficiently sensitive measurements, you can find trace amounts of plutonium in water, but the concentrations are likely to be very low and to vary widely. Andy Karam, CHP University of Rochester