Radium-224 and Its Relation to Gross-Alpha-Particle, Radium-226, and Radium-228 Activities in Ground Water from Rocks of the Piedmont Physiographic Province, Southeastern Pennsylvania
L.A. Senior and R.A. Sloto
U.S. Geological Survey
Radium-224 is a potential health risk in drinking water but little is known about the activity of this short-lived, alpha-emitting radium isotope in ground water from rocks of the Piedmont. Thirteen wells sampled in 1986-88 for analysis of radium-226, radium-228, and gross-alpha- and gross-beta-particle activities were resampled in 1999 for the same constituents and radium-224. The wells were completed in lower Paleozoic quartzites, schists, and carbonate rocks and Mesozoic shales. Radium-226 and radium-228 had been detected in the thirteen wells at activities ranging from 0.5 and 1 picoCurie/liter (pCi/L) up to 12 and 160 pCi/L, respectively. Activities of radium-226 and radium-228 in the 1999 samples were similar to those in the 1986-88 samples for most wells. Radium-224 activities ranging from 0.4 to 265 pCi/L were measured in water from wells sampled in 1999. The highest radium-224 activities were measured in samples from wells in the Chickies Quartzite and the Harpers Phyllite-Antietam Quartzite. Gross-alpha- and gross-beta-particle activities counted within 48 hours of sample collection were as high as 1,300 and 700 pCi/L, respectively, and were up to ten times greater than those activities counted several weeks later, indicating the presence and decay of short-lived radionuclides, such as radium-224, in the sample. Therefore, delayed counts of gross-alpha-particle activities may not be adequate to detect activities above the maximum contaminant level of 15 pCi/L in water samples from some wells used for drinking water. Radium-224 activities were apparently correlated with radium-228 activities, as inferred from gross-beta-particle activities. Radium-224 is decay product of radium-228. Elevated radium-224 activities were measured in samples with elevated radium-226 and radium-228 activities partly because the chemical behavior of isotopes is similar.
Senior, L.A., and Sloto, R.A., 2000, Radium-224 and its relation to gross-alpha-particle, radium-226, and radium-228 activities in ground water from rocks of the Piedmont Physiographic Province, southeastern Pennsylvania [abstract]: Geological Society of America Abstracts with Programs, Northeastern Section, v. 32, no. 1, p. A-73.