222Rn In Water Research Articles

Optimization of time resolution and detection limit for online measurements of 222Rn in water

The online measurements of radon in flowing water with high temporal resolution and a lower limit of detection of some Bq/l is of growing interest in environmental research and earth sciences. Promising new fields of application in hydrogeology are the study of exchange and mixing processes and the monitoring of pumping procedures before and during groundwater sampling. A suitable, simple method has been proposed by Surbeck based on the separation of air and water by a diffusion membrane. Process parameters influencing the temporal resolution as well as the radon detection efficiency have been studied. Considering these results a new instrument has been developed enabling online radon-in-water measurement with time resolution of about one minute.

Radon in groundwaters from Guarany aquifer, South America: environmental and exploration implications

Groundwater and sandstone samples were analyzed for radon in Guarany aquifer, Paraná sedimentary basin, South America. The dissolved radon ranged between 3 and 3303 pCi/l, being lognormally distributed, with a modal value of 1315 pCi/l, and a median value of 330 pCi/l. 222Rn leakage experiments for sandstones yielded a theoretical value of 1390 pCi/l for 222Rn in water, showing that theoretical modeling can reliably be used to interpret laboratory and field data.

Preliminary Report on Radon Concentration in Drinking Water and Indoor Air in Kenya

A screening survey has been carried out to determine activity concentrations of radon (222Rn) in drinking water and indoor air in various locations in Kenya. The concentration of 222Rn in water was measured using a liquid scintillation counter (LSC). Three different passive integrating devices were used in the measurements of 222Rn in air. In the short-term measurements, radon is absorbed in activated charcoal and the analyses were carried out using either LSC or gamma ray spectrometry. The long-term measurements were carried out using solid-state nuclear track detectors (SSNTD). The mean and maximum values of 222Rn concentrations in water are 37 and 410 Bq L−1 and 100 and 1160 Bq m−3, respectively, in air. The highest values were obtained from groundwater sources and in the basements of buildings. When these values are compared with the internationally recommended reference levels, there are indications of existence of radon problems in some of the water sources and the dwellings tested in this survey.

A compact automatic low-level liquid scintillation system for radon-in water measurement by pulse pair counting

A novel compact liquid scintillation counting system with automatic changing of seven samples, dedicated to the assay of low levels of 222Rn in water, is described. Its has a single phototube, and its operating mode is 222Rn series selective, as only the close pulse pairs given by 214Bi and its short lived decay product 214Po (half life 0.16 ms), are counted. Its 214Bi/214Po counting efficiency is 90.4% and the background, with an unshielded detector, is 3 pulse pairs per hour. 75% of the radon in 200 ml water samples is transferred to the scintillator (15 ml toluene) by circulating air, which is bubbled through the two liquids for 4 min. With a counting time of 3 h, the minimum detection level is 8 mBq l−1. The method is also suitable for various environmental and geophysical studies of 222Rn and 226Ra.

A Portable Liquid Scintillation Counter for General LSC and High Sensitivity Alpha-Counting Applications

Applicability of a new portable, single tube liquid scintillation (LS) spectrometer was demonstrated for general LS applications, such as wipe tests and low level alpha counting, especially radon (222Rn) measurements in water. Wipe tests were performed with wad sticks. They were counted conventionally in a small volume in Eppendorf tubes with less than 200µl of LS cocktail, thus minimizing costs and waste. Small volume is specially recommended because low background can be achieved without heavy lead shielding, thus maintaining portability. Typical NRC recommended LLD's were reached for 3H and other typical LS isotopes. For 222Rn in water a biphasic extraction system was adopted where radon is extracted from water into a water-immiscible LS cocktail. The method is sensitive because radon can be extracted from a large water volume. It was observed that common non-evaporating "safe" cocktails with di-isopropyl naphtalene solvent are convenient to use and quite suitable for extraction. Also the isotope 226Ra can be reliably measured via production of its daughter 222Rn. The instrument includes pulse shape electronics to perform alpha/beta separation. This is based on the fact that in LS cocktails alphas generate pulses with longer duration than betas. The alpha/beta separation can be visualized with a two dimensional graph where the x-axis represents pulse amplitude (MCA channels) and the y-axis its length. The graphical operations are all done in standard Excel/Windows environment. Due to their longer pulses, alphas have greater y-coordinates than betas with the same x-coordinate (amplitude). With this graph, one can select a region occupied only by alphas and exclude betas. The above mentioned "safe" cocktails posses good alpha/beta separation properties. Because natural background (cosmic-rays and environmental gammas) produces beta-like pulses, they can be stripped away giving low background for alpha counting, typically a few counts per hour for the extraction samples. The LLD for 222Rn was 0.1 Bq/I.

Relation between "terra rossa" from the Apulia aquifer of Italy and the radon content of groundwater: Experimental results and their applicability to radon occurrence in the aquifer

The radon-222 (222Rn) activity in groundwater of the Apulian karstic aquifer in southern Italy is as great as 500 Becquerel per liter (Bq/L) locally. Normal radium-226 (226Ra) activity in the limestone and calcareous dolomites of the aquifer is not enough to explain such a high level. Laboratory investigations identified high 226Ra activity in the "terra rossa," the residuum occupying fissures and cavities in the bedrock, and also the relation between (1) 226Ra-bearing bedrock and "terra rossa" and (2) 222Rn in water. The "terra rossa" is the primary source of the radon in the groundwater. The experimental results show the need to characterize the "terra rossa" of Apulia on the basis of 226Ra activity and also to study the distribution and variations in 222Rn activity over time in the aquifer.

The effects of water content and Mn-fiber surface conditions on measurement by emanation

Abstract 224 Ra (half-life, t1/2=3.64 days) has been used widely as a tracer. Its activity in natural waters can be measured by the 220 Rn emanation method [Rama, Todd, J.F., Butts J.L., and Moore, W.S., 1987. A new method for the rapid measurements of 224 Ra in natural waters. Mar. Chem., 22, 43–54.]. The measurement efficiency of 220 Rn is affected by Mn-fiber surface conditions and water content. We studied the effects of precipitated NaCl and water content on the emanation characteristics of 220 Rn from the 224 Ra adsorbed on Mn-coated fiber. The best emanation efficiency can be achieved when the Mn-fiber is covered by a water film with a thickness comparable to the recoil range of 220 Rn in water. By controlling the water content of the Mn-fiber, the measurement efficiency may be increased 2–3× compared to the very wet or very dry condition.

Iowa survey of waterborne 222Rn concentrations in private wells.

The major objective of the survey was to describe the distribution of waterborne 222Rn concentrations in Iowa's private well-water supplies. Well-water samples were obtained and analyzed for 222Rn from a random sample of 352 Iowa wells. The well-water 222Rn concentrations for the well sites were lognormally distributed and ranged from background concentrations to 87 Bq L-1, with a median value of 12 Bq L-1. The arithmetic mean 222Rn concentration for the sites was 16 Bq L-1 +/- 13 Bq L-1. The geometric mean 222Rn concentration was 12 Bq L-1 with a geometric standard deviation of 2.2. Over half of the samples (52%) exceeded 11 Bq L-1. Both well depth and indoor air 222Rn screening levels correlated with waterborne 222Rn concentrations; however, these correlations had very little predictive value. Glacial drift aquifers tended to have the highest 222Rn concentrations, although there was significant variance of 222Rn concentrations within all the aquifer classifications. In light of the estimate that 370 Bq L-1 of 222Rn in water may lead to 37 mBq L-1 in indoor air, the contribution of well-water derived indoor air 222Rn is minimal compared to ground sources in Iowa.

Application of 222Rn and CH4 for assessment of groundwater discharge to the coastal ocean

Groundwater discharge is a neglected source of freshwater and dissolved constituents to the ocean. It can occur via diffuse seepage and point source spring discharge. Two naturally occurring trace gases, 222Rn and CH4, are present in groundwater at concentrations that are elevated by several orders of magnitude relative to seawater, and they may be useful in tracing groundwater inputs to surface waters. Water samples collected near a submarine spring in the northeastern Gulf of Mexico displayed radon and methane concentrations inversely related to salinity and considerably greater than those found in surrounding waters. Coastal water 222Rn and CH4 inventories varied directly with groundwater seepage rates. The integrated quantities of 222Rn and CH4 in the nearshore waters overlying a seepage meter transect showed a significant positive relationship (95% C.L.) to direct measurements of seepage. Diffusive fluxes (178±56 dpm m‒2 d‒1), obtained by three different approaches at the same site, showed that these waters receive only a small contribution of 222Rn by diffusion. In contrast, benthic flux chamber measurements revealed a total advective‐diffusive contribution of 5,200±1,800 dpm m‒2 d‒1 (n = 14). Radon inventories in these shallow nearshore marine waters are consistent with the input of radon‐bearing groundwaters.

Optimization of LS counting parameters for measurement of low levels of 222Rn in water

Potential health hazards are associated with continued use of 222Rn rich water for drinking. Since high concentrations of 222Rn frequently occur in some well waters, it becomes important to analyze well waters that may be used for drinking, for its 222Rn concentrations. In view of the large number of water samples that may need to be analyzed and because of the relatively short half life of 222Rn, a rapid and sensitive counting method for measuring 222Rn in well waters should be useful. Such a method was achieved by optimization of some of the scintillation counting parameters including, type of fluor used, water/fluor ratio and width of the counting window used.

Determination of waterborne 222Rn concentrations using AC canisters.

A method for measuring 222Rn concentration in water using charcoal canisters is presented. 222Rn is transferred within a few minutes from water contained in a 0.720 L bottle to a charcoal canister using a portable degassing unit. In the laboratory, gamma counting is performed at least 10 h after sampling to determine waterborne 222Rn concentration. The results obtained with charcoal canisters are compared to measurements made with Marinelli beakers calibrated in a comparison with liquid scintillation counting. The efficiency of transferring dissolved 222Rn in water to activated charcoal is 99%, based on measurements made using Marinelli beakers. The lower limit of detection at the 95% confidence level is approximately 1 kBq m-3 for a 15 min gamma count. The system was used to measure radon concentration in mineral groundwater near Rome.

222Rn in Water

The U.S. Environmental Protection Agency has proposed a drinking water standard for 222Rn in public water supplies. When promulgated, operators of public water supplies will be required to determine water 222Rn concentrations. Most likely, water samples will be collected and mailed to laboratories for analyses. Additionally, it is probable that homeowners will test private well water in a similar manner by collecting water samples and mailing them to a laboratory for 222Rn analyses. In anticipation of these actions, this study was conducted to evaluate two methods of water sample collection and to evaluate the potential losses of 222Rn from water samples mailed to a laboratory. Thirdly, temporal variations in 222Rn concentrations in several groundwater supplies in North Carolina were examined. Water supplies at four sites in eastern North Carolina and five sites in western North Carolina were sampled over a 7-mo period beginning in the fall of 1993 and continuing through the spring of 1994. Samples were analyzed using a liquid scintillation method. This study showed that a "slow-flow" method is not only suitable for sample collection, but may be the preferable method for water sample collection since slow-flow collection resulted in less 222Rn loss than was observed during syringe collection, i.e., the water 222Rn concentrations in samples collected by the slow-flow method were generally higher. Further, based on this study, mailing water samples to a laboratory for analysis should not have a substantial effect on the measured 222Rn concentrations. Consequently, water samples can be collected by the slow-flow method by water supply operators, as well as homeowners, and mailed to laboratories for 222Rn analyses with reasonable assurance that the samples have not suffered significant 222Rn loss. Temporal variations in water 222Rn concentrations were observed in this study. One factor complicating the study of temporal variations in 222Rn concentrations was the striking influence that inconstant water usage and inadequate well purging prior to sample collection had on 222Rn loss from the water.

Quantitative measurement of 222Rn in water by the activated charcoal passive collector method: 1. The effect of water in a collector

The activated charcoal passive collector method can be applied to measure the concentration of 222Rn in river water. The 222Rn collector is composed of dry activated charcoal sealed in a polyethylene bag. However, we found it very difficult to keep activated charcoal in a collector dry during the period the collector was left in a river. The degree of dampness and the time lapsed when activated charcoal became wet were thought to affect the quantity of 222Rn collected. First, we studied the effect of some parameters in the activated charcoal passive collector method qualitatively in three experiments. We found that the quantity of 222Rn collected in a collector was not so sensitive to the quantity of activated charcoal in the collector or the thickness of polyethylene film under the condition of wet activated charcoal, and that wet activated charcoal accumulated less 222Rn than dry activated charcoal. We present some equations which could explain how much 222Rn was collected in a collector when activated charcoal was submerged directly in water and when activated charcoal was packed in a polyethylene bag but completely wet. These equations were proved effective by being compared with the results of the other experiments. Finally, we recommended some conditions which proved useful when measuring at an actual river.

A biokinetic model for 222Rn gas distribution and alpha dose in humans following ingestion

A biokinetic model for absorption and distribution of 222Rn in the body following ingestion in drinking water was developed. The rate parameters for the model are derived from historical human data reported in experiments of Harley et al. (1958) and Hursh et al. (1965). The biokinetic model fits the human data of Hursh et al. well for whole body retention following ingestion of 222Rn in water on an empty stomach. The equivalent dose to stem cells for stomach and colon cancer is estimated to be 1.6 × 10 −9 Sv Bq −1. The model calculations yield 4 and 3 calculated stomach and colon cancers from continuous intake of water at the estimated U.S. average of 5.5 Bq L −1.

立川断層地帯の地下水中｀２２２´Ｒｎの起源

東京都の西部に位置する立川断層では, 断層を境界にして南西側の地帯で地下水中の222Rn濃度が特徴的に高かった。 (1) この地帯では, 井戸深度が深いほど222Rn濃度が高くなるという傾向はみられないこと, および帯水層から基盤岩までの堆積層が200m以上と厚いことから, 222Rnは基盤岩を供給源, 断層を経路とした上昇物ではないと考えた。この南西側の地帯と周辺を比較して, 以下のことがわかった。 (2) トリチウム濃度の分布から, この地帯では地下水の年代が新しく, 水が地下浸透しやすい構造であることを支持する結果が得られた。 (3) この地帯は多摩川寄りに位置していて, 扇状地の扇頂に近いことから, 河川水が作用しやすい地形であった。以上のことから, この南西側地帯における高濃度222Rnの供給源は帯水層土壌中の226Raと考えられた。帯水層土壌中の226Raの濃集は多摩川の河川水の浸透によって起きたものと推定した。

Analysis of 222Rn concentration in North Carolina household water supplies derived from private wells.

The objectives of this study were to characterize the concentrations of 222Rn in North Carolina household groundwater supplies and to investigate the relationship between indoor air and groundwater 222Rn concentrations. Measurements of 222Rn in groundwater supplies were performed in 400 North Carolina homes in which a state/Environmental Protection Agency survey had made measurements of indoor airborne 222Rn. The arithmetic mean 222Rn concentration measured in groundwater supplies statewide was 67 Bq L-1 (1,800 pCi L-1), and the geometric mean was 24 Bq L-1 (660 pCi L-1). Sixty-seven percent of the state's homes with wells had 222Rn water concentrations in excess of the Environmental Protection Agency's proposed limit for public drinking water supplies of 11 Bq L-1 (300 pCi L-1). The percentage of homes with water concentrations in excess of the proposed limit was 30% in the eastern region of the state, 75% in the central region, and 83% in the western region. No significant correlation was observed between measurements of indoor air and water 222Rn concentrations in these homes.

Electret Ion Chamber Radon Monitors Measure Dissolved 222Rn in Water

This paper describes a simple and relatively inexpensive method of determining the concentration of dissolved 222Rn in water. The method involves a recently developed electret-passive environmental radon monitor, which uses an electret ion chamber. The procedure consists of sealing a known volume of a carefully collected water sample with one of these monitors in an exposure container and determining the average equilibrium 222Rn gas concentration in the air phase during the exposure time period. This average concentration can then be used to calculate the 222Rn concentration in the original water sample. Identical samples were analyzed both by this new method and by a standard liquid scintillation method, and the results were compared over a wide range of 222Rn concentrations. There was good agreement except that the electret ion chamber method gave results that were consistently lower by about 15%. This bias in the results was attributed to both 222Rn losses during sample handling and possibly to some errors in the assumptions made in the theoretical model. A correction factor is recommended to bring the results of this technique into agreement with the standard method. The procedures are simple and economical and can be easily employed by many primary 222Rn-measuring laboratories currently using these monitors for measuring indoor 222Rn.

Improved Calculation for Measurement of 222Rn in Water.

The measurement of 222Rn in water, ‘liquid scintillation counting of radon extracted with toluene’, was improved. It was found in the previous calculation method that radon concentration had been determined low about 2%. The equation in the previous calculation was derived by the underestimation of radon solubility in toluene. The applicable calculation of radon concentration was proposed using mole fraction form and thermodynamic solubility equations.

東京およびその周辺の地下水中ラドン濃度分布

東京を中心とした半径約50km圏内で地下水中222Rnの濃度分布調査を行った。調査点数は1114, 濃度範囲は0-45Bq/l, 平均濃度は8±11Bq/lで堆積地質レベルであった。分布における濃度の代表的な値は沖積低地では3Bq/l, 陸成砂礫層地域では6Bq/l, 武蔵野台地の扇状地砂礫層地域では12Bq/l, 立川断層地帯では21Bq/l, 荒川断層地帯では16Bq/lであった。

Measurement of 226Ra in Water and 222Rn in Water and Air by Liquid Scintillation Counting

In the Austrian province of Lower Austria a comprehensive programme for measurement of 222Rn and 226Ra in drinking water was conducted. A simple LSC method was used which gives a LLD of 30 mBq per litre for 226Ra without any chemical separation. Results are presented and the health significance is discussed. For 222Rn in air a commercially available simple charcoal system with LSC was used. The system was tested in a house with elevated radon concentration under normal living conditions. During relatively short 2 day periods a maximum deviation of ±30% from the monthly mean value was found. The disadvantages of LSC are that the procedures are very simple and cheap.