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Understanding the Radioactive Ingrowth and Decay of Naturally Occurring Radioactive Materials in the Environment: An Analysis of Produced Fluids from the Marcellus Shale.

Nelson AW, Eitrheim ES, Knight AW, May D, Mehrhoff MA, Shannon R, Litman R, Burnett WC, Forbes TZ, Schultz MK - Environ. Health Perspect. (2015)

Bottom Line: However, natural radioactivity found in the large volumes of "produced fluids" generated by these technologies is emerging as an international environmental health concern.Specifically, we examined the use of high-purity germanium gamma spectrometry and isotope dilution alpha spectrometry to quantitate NORM.Accurate predictions of radioactivity concentrations are critical for estimating doses to potentially exposed individuals and the surrounding environment.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary Human Toxicology Program, University of Iowa, Iowa City, Iowa, USA.

ABSTRACT

Background: The economic value of unconventional natural gas resources has stimulated rapid globalization of horizontal drilling and hydraulic fracturing. However, natural radioactivity found in the large volumes of "produced fluids" generated by these technologies is emerging as an international environmental health concern. Current assessments of the radioactivity concentration in liquid wastes focus on a single element-radium. However, the use of radium alone to predict radioactivity concentrations can greatly underestimate total levels.

Objective: We investigated the contribution to radioactivity concentrations from naturally occurring radioactive materials (NORM), including uranium, thorium, actinium, radium, lead, bismuth, and polonium isotopes, to the total radioactivity of hydraulic fracturing wastes.

Methods: For this study we used established methods and developed new methods designed to quantitate NORM of public health concern that may be enriched in complex brines from hydraulic fracturing wastes. Specifically, we examined the use of high-purity germanium gamma spectrometry and isotope dilution alpha spectrometry to quantitate NORM.

Results: We observed that radium decay products were initially absent from produced fluids due to differences in solubility. However, in systems closed to the release of gaseous radon, our model predicted that decay products will begin to ingrow immediately and (under these closed-system conditions) can contribute to an increase in the total radioactivity for more than 100 years.

Conclusions: Accurate predictions of radioactivity concentrations are critical for estimating doses to potentially exposed individuals and the surrounding environment. These predictions must include an understanding of the geochemistry, decay properties, and ingrowth kinetics of radium and its decay product radionuclides.

No MeSH data available.


Related in: MedlinePlus

Theoretical Bateman model of Ra decay product ingrowth and decay (system closed to release of gaseous radon) (A) 15 days after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (B) 70 years after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (C) 70 years after extraction for 226Ra (purple), 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (D) 15 days after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); (E) 70 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); and (F) 5,000 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue).
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f4: Theoretical Bateman model of Ra decay product ingrowth and decay (system closed to release of gaseous radon) (A) 15 days after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (B) 70 years after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (C) 70 years after extraction for 226Ra (purple), 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (D) 15 days after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); (E) 70 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); and (F) 5,000 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue).

Mentions: 232Th Series partitioning. The parent and supporting isotope in the natural Th decay series, 232Th (t1/2 = 1.4 × 1010 years), is not expected to undergo oxidation/reduction reactions under natural conditions at depth in the formation, but is nonetheless particle reactive and insoluble in environmental waters and brines (Melson et al. 2012). Accordingly, we observed exceedingly low concentrations of 232Th in unfiltered Marcellus Shale produced fluids. However, the decay of 232Th produces highly soluble divalent alkaline earth 228Ra (t1/2 = 5.75 years), which has likely been in radioactive secular equilibrium (steady-state) with 232Th for many millions of years (Gonneea et al. 2008). As a result, produced fluids are enriched in 228Ra (relative to 232Th), which is highly soluble in the high-salt-content brines that describe produced fluids. 228Ra decays by beta emission to short-lived 228Ac (actinium-228; t1/2 = 6.15 hr), which likely forms insoluble complexes and quickly adsorbs to mineral surfaces at depth—and decays rapidly to form highly insoluble alpha-particle–emitting radionuclide 228Th (t1/2 = 1.91 years) (Hammond et al. 1988). Similar to other Th isotopes, 228Th is insoluble in interstitial fluids of shale formations, and its concentration is also low in produced fluids as they emerge from depth. Notably, the large difference in solubility between 228Ra and 228Th gives rise to a chronometer that has the potential to determine the time when fluids were extracted from the Marcellus Shale (for more information, see Supplemental Material, “Expanded methods, Thorium-228 ingrowth”). As 228Th ingrows at a rate related to its half-life, its decay product 224Ra (t1/2 = 3.63 days), rapidly ingrows to steady-state radioactive equilibrium. Rapid ingrowth of 224Ra is followed by a series of short-lived radioactive decay products that ultimately decay to stable 208Pb (Figure 1). Within this series of relatively short-lived decay products, gaseous 220Rn (t1/2 = 55.6 sec) presents a potential challenge to modeling expected increases in total radioactivity resulting from radioactive ingrowth processes. In contrast, because the half-life of 220Rn is so short, migration beyond the immediate vicinity of nuclear formation is likely minimal and disequilibrium is not expected. Thus, in this decay series, the modeled total 228Ra-supported radioactivity concentration in produced fluids has the potential to increase to a maximum within 5 years of extraction from the shale formation, followed by a decrease determined by the half-life of 228Ra (t1/2 = 5.75 years) (Figure 4A,B). This suggests that inclusion of the ingrowth and decay of 228Ra decay products (particularly 228Th) is important for development of appropriate liquid waste management.


Understanding the Radioactive Ingrowth and Decay of Naturally Occurring Radioactive Materials in the Environment: An Analysis of Produced Fluids from the Marcellus Shale.

Nelson AW, Eitrheim ES, Knight AW, May D, Mehrhoff MA, Shannon R, Litman R, Burnett WC, Forbes TZ, Schultz MK - Environ. Health Perspect. (2015)

Theoretical Bateman model of Ra decay product ingrowth and decay (system closed to release of gaseous radon) (A) 15 days after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (B) 70 years after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (C) 70 years after extraction for 226Ra (purple), 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (D) 15 days after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); (E) 70 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); and (F) 5,000 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue).
© Copyright Policy - public-domain
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4492269&req=5

f4: Theoretical Bateman model of Ra decay product ingrowth and decay (system closed to release of gaseous radon) (A) 15 days after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (B) 70 years after extraction for 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (C) 70 years after extraction for 226Ra (purple), 228Ra (green dots), associated alpha (red dashes), and total activity (blue); (D) 15 days after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); (E) 70 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue); and (F) 5,000 years after extraction for 226Ra (purple), associated alpha (red dashes), and total activity (blue).
Mentions: 232Th Series partitioning. The parent and supporting isotope in the natural Th decay series, 232Th (t1/2 = 1.4 × 1010 years), is not expected to undergo oxidation/reduction reactions under natural conditions at depth in the formation, but is nonetheless particle reactive and insoluble in environmental waters and brines (Melson et al. 2012). Accordingly, we observed exceedingly low concentrations of 232Th in unfiltered Marcellus Shale produced fluids. However, the decay of 232Th produces highly soluble divalent alkaline earth 228Ra (t1/2 = 5.75 years), which has likely been in radioactive secular equilibrium (steady-state) with 232Th for many millions of years (Gonneea et al. 2008). As a result, produced fluids are enriched in 228Ra (relative to 232Th), which is highly soluble in the high-salt-content brines that describe produced fluids. 228Ra decays by beta emission to short-lived 228Ac (actinium-228; t1/2 = 6.15 hr), which likely forms insoluble complexes and quickly adsorbs to mineral surfaces at depth—and decays rapidly to form highly insoluble alpha-particle–emitting radionuclide 228Th (t1/2 = 1.91 years) (Hammond et al. 1988). Similar to other Th isotopes, 228Th is insoluble in interstitial fluids of shale formations, and its concentration is also low in produced fluids as they emerge from depth. Notably, the large difference in solubility between 228Ra and 228Th gives rise to a chronometer that has the potential to determine the time when fluids were extracted from the Marcellus Shale (for more information, see Supplemental Material, “Expanded methods, Thorium-228 ingrowth”). As 228Th ingrows at a rate related to its half-life, its decay product 224Ra (t1/2 = 3.63 days), rapidly ingrows to steady-state radioactive equilibrium. Rapid ingrowth of 224Ra is followed by a series of short-lived radioactive decay products that ultimately decay to stable 208Pb (Figure 1). Within this series of relatively short-lived decay products, gaseous 220Rn (t1/2 = 55.6 sec) presents a potential challenge to modeling expected increases in total radioactivity resulting from radioactive ingrowth processes. In contrast, because the half-life of 220Rn is so short, migration beyond the immediate vicinity of nuclear formation is likely minimal and disequilibrium is not expected. Thus, in this decay series, the modeled total 228Ra-supported radioactivity concentration in produced fluids has the potential to increase to a maximum within 5 years of extraction from the shale formation, followed by a decrease determined by the half-life of 228Ra (t1/2 = 5.75 years) (Figure 4A,B). This suggests that inclusion of the ingrowth and decay of 228Ra decay products (particularly 228Th) is important for development of appropriate liquid waste management.

Bottom Line: However, natural radioactivity found in the large volumes of "produced fluids" generated by these technologies is emerging as an international environmental health concern.Specifically, we examined the use of high-purity germanium gamma spectrometry and isotope dilution alpha spectrometry to quantitate NORM.Accurate predictions of radioactivity concentrations are critical for estimating doses to potentially exposed individuals and the surrounding environment.

View Article: PubMed Central - PubMed

Affiliation: Interdisciplinary Human Toxicology Program, University of Iowa, Iowa City, Iowa, USA.

ABSTRACT

Background: The economic value of unconventional natural gas resources has stimulated rapid globalization of horizontal drilling and hydraulic fracturing. However, natural radioactivity found in the large volumes of "produced fluids" generated by these technologies is emerging as an international environmental health concern. Current assessments of the radioactivity concentration in liquid wastes focus on a single element-radium. However, the use of radium alone to predict radioactivity concentrations can greatly underestimate total levels.

Objective: We investigated the contribution to radioactivity concentrations from naturally occurring radioactive materials (NORM), including uranium, thorium, actinium, radium, lead, bismuth, and polonium isotopes, to the total radioactivity of hydraulic fracturing wastes.

Methods: For this study we used established methods and developed new methods designed to quantitate NORM of public health concern that may be enriched in complex brines from hydraulic fracturing wastes. Specifically, we examined the use of high-purity germanium gamma spectrometry and isotope dilution alpha spectrometry to quantitate NORM.

Results: We observed that radium decay products were initially absent from produced fluids due to differences in solubility. However, in systems closed to the release of gaseous radon, our model predicted that decay products will begin to ingrow immediately and (under these closed-system conditions) can contribute to an increase in the total radioactivity for more than 100 years.

Conclusions: Accurate predictions of radioactivity concentrations are critical for estimating doses to potentially exposed individuals and the surrounding environment. These predictions must include an understanding of the geochemistry, decay properties, and ingrowth kinetics of radium and its decay product radionuclides.

No MeSH data available.


Related in: MedlinePlus