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Optimizing Sampling, Sample Processing and Analysis Methods for Radon (<SUP>222</SUP>Rn) in Water by Liquid Scintillation Counting
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... The various methods of sample processing make it difficult to compare results from different laboratories for water samples even when they are from the same source and analyzed by the recommended LSC method. Original research by Saha et al. (8) compared different methodological variances in sample collection, sample processing, and LSC analysis of radon-in-water using several household well water samples, and made the following recommendations for optimized sampling and analysis conditions. ...
... After sample injection in the vials, the vials were immediately capped airtight and shaken vigorously to mix and expedite transfer of radon into the scintillation fluid. Further details and pictorial illustrations of 'Separate Drawing' and 'Simultaneous Drawing' are available elsewhere (8). ...
... The most remarkable observation was that the Optifluor preparations gave mean radon concentration very close to the known or theoretical concentration of 139 Bq/L, whereas Mineral-oil preparations gave mean radon concentration significantly higher than known or theoretical concentrations (Fig. 5). The aforementioned results are in good agreement with the findings reported by Saha et al. (8) from a study with household well water samples; however, a possible explanation of such observations is not currently available in literature, which needs further research. ...
A proficiency test is an integral part of any analytical procedure; however, there is no known proficiency test in place for radon-in-water analysis. This led us to conduct a long-term study. Successful preparation of a reusable radon (222Rn)-in-water standard containing a ‘radium (226Ra)-loaded filter paper (the source)’ sandwiched between polyethylene sheeting has been reported. As the source ‘226Ra-loaded filter paper’ is sandwiched between polyethylene sheets, the surrounding water (which is sampled and analyzed) in the bottle remains free of 226Ra. With this type of standards, a previous study reported that at full ingrowth (>30 days), 86% of the 222Rn produced by the source was emanated into the water and remained stable thereafter, and the remaining 14% was retarded by the polyethylene sheeting. We periodically measured radon-in-water in two such standard samples allowing a 40- to 50-day ingrowth interval for more than 6 years (2016–2022). In each measurement, we prepared in duplicate the cocktails in four different ways (in Mineral-oil vs. Optifluor in combination with two different ways of ‘pipetting or sample drawing’ and dispensing into the scintillation vials) and measured the radon-in-water using two different Liquid Scintillation Counting (LSC) assays: full-spectrum (0–2,000 keV) versus Region of Interest (ROI) for radon (ROI, 130–700 keV). A substantial number of repeated results unequivocally show that the reusable standards maintained its characteristics satisfactorily for a 6-year long period. Duplicate measurements were precise in almost all cases. We consistently observed significant differences in measured radon concentration between the two different LSC assays and between the two different scintillation fluids, but not between the two sample drawing methods. With full-spectrum assay (0–2,000 keV), both Mineral-oil and Optifluor grossly underestimated the actual radon concentration, and with ROI assay (130–700 keV), Mineral-oil overestimated the radon concentration; therefore, these should be avoided. Preparing the cocktails with Optifluor and measuring by ROI assay (130–700 keV) was the only method that consistently produced results within the acceptance window (±25% of the known), suggesting that a certain way of preparing and measuring the water samples could yield more accurate results for radon. Thus, our findings demonstrate that a proficiency test for radon-in-water using these reusable 226Ra-free radon-in-water standards is a valid and valuable option, and it should be a part of radon-in-water analysis by the laboratories.
... Liquid scintillation counting (LSC) method, gamma spectrometry method and emanometric method are recommended by ISO (ISO 13164-1, 2013) and commonly used today. For LSC method, water sample is transferred to scintillation cocktail and then radon atoms are counted in liquid scintillation spectrometry (ISO 13164-4, 2013;Freyer et al., 1997;Salonen, 2010;Schubert et al., 2014;Saha et al., 2018). For gamma spectroscopy method, gamma-ray emitted by radon progeny 214 Bi and 214 Pb, which are in equilibrium with 222 Rn, is measured (ISO 13164-2, 2013;Sanchez et al., 1995). ...
On-line continuous monitoring of radon concentration in water is of great significance for its environmental application as a radioactive tracer, for example, as a potential precursor for earthquake forecast and volcanic eruption. To realize on-line continuous measurement on radon in complex water body, a compact measurement system mainly consisted of a simple degassing device and an electrostatic radon monitor is newly developed. The sensitivity of the measurement system is 73 ± 5 cph/(Bq/L), and the detection limit is 0.04 Bq/L with a 60-min cycle at 25 °C water temperature. Intercomparison measurements with RAD H2O were performed both in laboratory condition and in field, and consistent results within the error range were achieved. To test the developed measurement system, a continuous monitoring of radon concentration in water in the drainage tunnel of Mount Jinping was performed for 3 months. The arithmetic mean of radon concentration in water is 0.34 ± 0.09 Bq/L, varying in the range of 0.04-0.60 Bq/L during the period. Several rapid decreases of radon concentration in water were observed, which might be attributed to the increase of rainwater mixing in the drainage tunnel caused by heavy rainfall. The stability of long-term operation of the system enables it to be widely used in the field of radon in water as a tracer.
Radon-in-water is an important tracer in hydrology, oceanography and geology, where a demand for fast response and long-term continuous measurement of radon-in-water concentration on-site is necessary. In this paper, an on-site radon-in-water measurement system based on a degassing membrane, an electrostatic radon monitor and a water temperature sensor is presented, and calibration experiment is carried out. The relative degassing efficiency of the degassing membrane was studied using self-made radon-in-water standard, which gives the result of (97.1 ± 7.3) %. The sensitivity of the measurement system is (3730 ± 190) cph/(Bq/L), and the lower limit of detection is 0.005 Bq/L, with 10 min cycle at 25 °C water temperature. The response time of the measurement system is about 26 min, which is independent of the water flowrate within the range of 0.5–2.5 L/min. Using this measurement system, field measurements were carried out on tap water and deep well water. And the measurement system has been successfully used in the continuous monitoring of radon-in-water concentration at a seismic station in Beijing.
Following more than a decade of scientific debate about the setting of a standard for 222Rn in drinking water, Congress established a timetable for the promulgation of a standard in the 1996 Amendments to the Safe Drinking Water Act. As a result of those Amendments, the EPA contracted with the National Academy of Sciences to undertake a risk assessment for exposure to radon in drinking water. In addition, the resulting committee was asked to address several other scientific issues including the national average ambient 222Rn concentration and the increment of 222Rn to the indoor-air concentration arising from the use of drinking water in a home. A new dosimetric analysis of the cancer risk to the stomach from ingestion was performed. The recently reported risk estimates developed by the BEIR VI Committee for inhalation of radon decay products were adopted. Because the 1996 Amendments permit states to develop programs in which mitigation of air-producing health-rsik reductions equivalent to that which would be achieved by treating the drinking water, the scientific issues involved in such “multimedia mitigation programs” were explored.
Radium-free standards are not readily available for proficiency testing of laboratories that conduct radon (222Rn) analyses of water. For this study, 33 identical, reusable, radon-in-water standards were prepared using a 226Ra-loaded filter sandwiched in polyethylene sheeting. The 222Rn concentrations in the 226Ra-free standards were measured by liquid scintillation counting and compared to 10 reference solutions containing 226Ra. The 222Rn concentrations measured in the standards were consistent (standard deviation of <2%), but averaged substantially less than concentrations determined in the 226Ra reference standards. At full ingrowth, 86% of the 222Rn produced by the sandwiched 226Ra sources emanated into the water. An intercomparison of radon-in-water standards, performed to examine the accuracy of analyses by commercial, government, and private companies, showed that 18 of the 21 participants reported concentrations within 25% of the known (693 Bq l−1).
The authors conducted a study of an aboriginal community to determine if kidney func-tion had been affected by the chronic ingestion of uranium in drinking water from the community's drilled wells. Uranium concentrations in drinking water varied from < 1 to 845 ppb. This nonin-vasive study relied on the measurement of a combination of urinary indicators of kidney function and markers for cell toxicity. In all, 54 individuals (12-73 years old) participated in the study. Correlation of uranium excreted in urine with bio-indicators at p <or=.05 indicated interference with the kidney's reabsorptive function. Because of the community's concerns regarding cancer incidence, the authors also calculated cumulative radiation doses using uranium intake in drinking water over the preceding 15-year period. The highest total uranium intake over this period was 1,761 mg. The risk of cancer from the highest dose, 2.1 mSv, is 13 in 100,000, which would be difficult to detect in the community studied (population size = 1,480). This study indicates that at the observed levels of uranium intake, chemical toxicity would be a greater health concern than would radiation dose.
To determine the risk of lung cancer associated with exposure at home to the radioactive disintegration products of naturally occurring radon gas.
Collaborative analysis of individual data from 13 case-control studies of residential radon and lung cancer.
Nine European countries.
7148 cases of lung cancer and 14,208 controls.
Relative risks of lung cancer and radon gas concentrations in homes inhabited during the previous 5-34 years measured in becquerels (radon disintegrations per second) per cubic metre (Bq/m3) of household air.
The mean measured radon concentration in homes of people in the control group was 97 Bq/m3, with 11% measuring > 200 and 4% measuring > 400 Bq/m3. For cases of lung cancer the mean concentration was 104 Bq/m3. The risk of lung cancer increased by 8.4% (95% confidence interval 3.0% to 15.8%) per 100 Bq/m3 increase in measured radon (P = 0.0007). This corresponds to an increase of 16% (5% to 31%) per 100 Bq/m3 increase in usual radon--that is, after correction for the dilution caused by random uncertainties in measuring radon concentrations. The dose-response relation seemed to be linear with no threshold and remained significant (P = 0.04) in analyses limited to individuals from homes with measured radon < 200 Bq/m3. The proportionate excess risk did not differ significantly with study, age, sex, or smoking. In the absence of other causes of death, the absolute risks of lung cancer by age 75 years at usual radon concentrations of 0, 100, and 400 Bq/m3 would be about 0.4%, 0.5%, and 0.7%, respectively, for lifelong non-smokers, and about 25 times greater (10%, 12%, and 16%) for cigarette smokers.
Collectively, though not separately, these studies show appreciable hazards from residential radon, particularly for smokers and recent ex-smokers, and indicate that it is responsible for about 2% of all deaths from cancer in Europe.
The report is part of the National Network for Environmental Management Studies under the auspices of the Office of Cooperative Environmental Management of the US Environmental Protection Agency. In 1988 the US Environmental Protection Agency, Region IV, began a pilot study to investigate the natural occurrence and concentration of Uranium 238, Thorium 232, and Uranium 235 radionuclide series in the ground water for selected aquifers in Georgia. Specific rock types, somewhat geologically homogeneous, were selected as representative of one or more aquifers for each of the geologic provinces in Georgia (Piedmont, Blue Ridge, Valley Ridge, and Coastal Plain). Aquifers sampled within the Piedmont provinces included pre-Cambrian and Paleozoic granite/gneisses and granites from four Piedmont county areas (Gwinnett/Barrow, Greene, Elbert/Oglethorpe, and Spalding/Pike). Ground waters from private water supply wells developed in these aquifers were sampled and analyzed for their radioisotopic and chemical characteristics. Preliminary analysis of 90 ground-water and radioisotopic samples from the pilot study indicates that the geologic setting of the differing aquifers an provinces strongly influences the occurrence of natural radioisotopes in drinking water. Extremely high concentrations of uranium, radium, radon 222, lead 210, and polonium 210 in some aquifers indicate radioisotope enrichment within and near the well bore for some areas. Based on these findings, the present public water monitoring scheme, which is based on gross alpha particle activity, may require modification depending on differing isotopes, rock types, and geological provinces.
Two analytical methods for the determination of radon in water concentration were tested in a multilaboratory study with twenty-eight participating laboratories. Eighteen laboratories analyzed prepared samples by the liquid scintillation (LS) method, and twelve laboratories analyzed the same samples by the Lucas Cell (LC) method. A comparison of the grand averages for the three samples with the known values for those samples showed good accuracy for both methods. The accuracy index was not less than 94% for any of the three samples when analyzed by either method. Test results for the LS method showed better precision than test results for the LC method. The average repeatability (within-laboratory) precision for the LS method was 3.6 plus or minus 3.0% at 95% confidence and for the LC method it was 6.4 plus or minus 3.8% at 95% confidence. The average reproducibility (combined within-and between-laboratory) precision for the LS method was 10.2 plus or minus 4.2% at 95% confidence and for the LC method it was 17.6 plus or minus 4.2% at 95% confidence.
The literature on metabolism of U and Ra for man relevant to deriving drinking water standards has been reviewed and summarized. Radium is well understood, but significant gaps remain in our knowledge about U metabolism. Limits should be based on an equilibrium model where a constant relationship between intake and organ burden is established, using the best and most likely metabolic parameters. For the skeleton we conclude that the best estimate of skeletal burden expressed in days equivalent intake are 25 days for 226Ra, 10 days for 228Ra, and 0.3 days for 224Ra. For long-lived isotopes of U, we chose 11 days, with a range between 1 and 35 days. The committee believes that intake of natural U in water should be limited by considerations of toxicity to the kidney, and we believe that the metabolic model of Spoor and Hursh with a modified gastrointestinal (GI) absorption (1.4%) should be used to infer kidney content. Our review and analysis of the world literature leads us to believe the average human GI absorption of U is most likely 1-2% and is probably reasonably independent of age or the mass of U ingested. Using a safety factor of 50-150, the committee recommends a limit of U in water of 100 micrograms/l in order to limit toxic effects in the kidney. One hundred micrograms/liter is equivalent to 67 pCi/l of long-lived alpha-emitting natural U isotopes. Further research into the distribution of U in the human body is desirable, especially at natural levels in kidney and skeleton, the time-dependent pharmacokinetics of U in animals, the GI absorption of U in man from water and food, toxicological and U distribution studies in animals under conditions of chronic oral U intake, and metabolic model error propagation.
The first cycle of statewide radionuclide concentration measurements of public drinking water supplies was completed in accord with the Federal and Georgia Safe Drinking Water Acts. The recommended pattern of analysis is initial screening for gross alpha-particle activity, followed by measuring 226Ra if the gross alpha-particle activity is above 5 pCi/l. and then measuring 228Ra if the 226Ra concentration is above 3 pCi/l; and uranium analysis if the gross alpha-particle activity exceeds 15 pCi/l. Surface water supplies for more than 100,000 persons are analyzed for 3H and 90Sr and screened for gross beta-particle activity, with additional analytical requirements if the latter is above 50 pCi/l. Specified supplies downstream for nuclear facilities are analyzed for 3H, 90Sr and 131I, and further analyses are required if the gross beta-particle activity is above 15 pCi/l. More thorough screening was applied for 1400 public water supplies in Georgia, of which about 90% use groundwater. Radium concentrations exceeded the maximum contaminant level (MCL) of 5 pCi/l. in 24 groundwater supplies, mostly due to elevated 226Ra. The gross alpha-particle activity minus uranium concentrations exceeded the 15 pCi/l. MCL in 3 additional samples. No MCL was exceeded in surface water. The S.D.s of analytical results estimated from replicate analyses were approximately twice those based on counting statistics, suggesting that screening levels should be lowered to assure detection of 226Ra at MCL values.
The distribution of 222Rn has been measured in the sixteen counties of Maine, U.S.A. by liquid scintillation counting of water samples from more than two thousand public and private wells. Three hundred and fifty of these wells have been characterized for geology and hydrology. Airborne radon has been measured in seventy houses with grab samples and in eighteen houses for 5-7 days each with continuously recording diffusion-electrostatic radon detectors. Concentrations of radon in water ranged from 20 to 180,000 pCi/l. Granite areas yielded the highest average levels (mean = 22,100 pCi/l.; n = 136), with considerable intra-granite variation. Metasedimentary rocks yielded levels characteristic of the lithology for metamorphic grades ranging from chlorite to andalusite. Sillimanite and higher-grade rocks yielded higher 222Rn levels, probably due to the intrusion of uranium-bearing pegmatites in these terranes. Airborne 222Rn in homes ranged from 0.05 to 210 pCi/l. At the high end of this range, doses will exceed recommended industrial limits. In some homes only a small fraction of the airborne 222Rn was due to the water supply. Average 222Rn levels in domestic water supplies for each of the 16 counties, calculated by areally averaging rock types and their associated 222Rn levels, were found to be significantly correlated with rates for all cancers combined and rates for lung and reproductive cancers in the counties. Although numerous factors other than cancer induction by indoor daughter exposures may be responsible for the observed correlations, these have not been investigated in detail.