Abstract
The Safe Drinking Water Act (SDWA) mandates that the drinking water should be monitored for 226Ra and 228Ra isotopes and establishes the Maximum Contaminant Level of 185 mBq/L (5 pCi·L-1) for the sum. In addition, SDWA regulates the Detection Limit (DL) of 37.0 mBq/L (1 pCi/L) for each isotope. The purpose of this work is to develop a working method for the determination of radium isotopes in drinking water satisfying the regulatory requirements of U.S. Environmental Protection Agency by utilizing our extensive experience in low-background gamma spectrometry at this laboratory. Two versions of the method were studied: destructive and non-destructive. Destructive method used the BaSO4 coprecipitation as well as 133Ba tracer for chemical recovery. We have used three gamma spectrometers: low-background 102% and 134% efficient with top muon guards, as well as an ultralow-background 140% efficient with full muon guard. We obtained a range of DLs from 5.3 to 22.6 mBq/L for 226Ra and from 7.4 to 30.4 mBq/L for 228Ra using the destructive method. For non-destructive method, the DL range was 26.0 to 26.9 mBq/L for 226Ra and 27.6 to 28.6 mBq/L for 228Ra using the 140% detector. To verify the methods, 7 to 10 laboratory control samples were spiked with both 226Ra and 228Ra at two different activities of 37.0 and 185 mBq/L. The results were evaluated by performing a combined location/variance chi-square test at a right-tail significance of 0.01 (99% Confidence Level), as stipulated by EPA. The verification results passed the chi-square tests at both activity levels. The destructive method can be accomplished using low-background gamma spectrometry, whereas non-destructive method requires ultralow-background gamma spectrometry.
Highlights
Radium is present naturally in soil, minerals, groundwater, and can incorporate in foodstuffs, and several common materials, including many used in construction
The purpose of this work is to develop a working method for the determination of radium isotopes in drinking water satisfying the regulatory requirements of U.S Environmental Protection Agency by utilizing our extensive experience in low-background gamma spectrometry at this laboratory
From the regulatory health perspective, 226Ra (T1/2 = 1600 y) from the uranium series and 228Ra (T1/2 = 5.75 y) from the thorium series are the most significant radionuclides. 224Ra is already included in the thorium series as a progeny of 228Ra; it has been studied separately as it can deviate from the series equilibrium [5] [6]
Summary
Radium is present naturally in soil, minerals, groundwater, and can incorporate in foodstuffs, and several common materials, including many used in construction. Exposure to radium isotopes by ingestion can lead to significant committed radiation dose considering their affinity to bone structures as well as rapid series equilibrium of the progeny resulting in several alpha-emitting radionuclides [1]. This radiation dose is known to cause bone cancer [2]. For these reasons, we investigate 226Ra and 228Ra only in this work
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