Preliminary Investigation of Radon Concentration In

Radiation Protection Dosimetry Advance Access published April 22, 2015

Radiation Protection Dosimetry (2015), pp. 1–6 doi:10.1093/rpd/ncv207

PRELIMINARY INVESTIGATION OF RADON CONCENTRATION IN SURFACE WATER AND DRINKING WATER IN SHENZHEN CITY, SOUTH CHINA Ting Li1,2, Nanping Wang1,2,* and Shijun Li1,2 1Key Laboratory of Geo-detection, China University of Geosciences, Ministry of Education, Beijing 100083, China 2School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China

*Corresponding author: [email protected] Downloaded from A radon survey in surface water and drinking water was conducted using a portable degassing system associated with an ionisation chamber AlphaGUARD (PQ2000) for understanding levels of dissolved radon (222Rn) concentration in different types of water sources and risk assessment of radon in drinking water in Shenzhen City (SC) with a population of 10 628 900 in 2013, Guangdong Province of China. The measurements show that arithmetic means +++++ standard deviations of radon (222Rn) concentration are 52.05 +++++ 6.64, 0.29 +++++ 0.26, 0.15 +++++ 0.23 and 0.37 +++++ 0.42 kBq m23 in spring water, surface water, large and small

public water supplies, respectively. Only radon concentrations of two water samples collected in mountainous areas are more http://rpd.oxfordjournals.org/ than 11.10 kBq m23, exceeding the limit of radon concentration in drinking water stipulated by the national standard of China (GB5749-2006). The annual effective doses due to radon in drinking water were also calculated. The investigation suggests that there are no risks caused by radon in the drinking water in SC.

INTRODUCTION water in China. Based on radon measurements in drinking water in 49 cities in China, the radon activity Radon can be ingested by people through drinking concentrations varied from 0.23 to 42.70 kBq m23(8). water, which will result in the exposure of human The radon concentrations in the public water supplies organs, primarily stomach. The radon isotope of inter- 23 (9) ranged from 0.65 to 29.0 kBq m in Beijing City . at Universite Laval on November 13, 2015 est in this article is 222Rn with the physical half-life of In Baoji City, the mean values of tap water and well 3.825 d. The kinetic energy of 24.5 MeV emitted by water were found to be 12 kBq m23 with a maximum alpha particles of 222Rn daughters accounts for 89 % of 18 kBq m23 and 41 kBq m23 with a maximum of of the total emitted energy (27.6 MeV). Therefore, the 127 kBq m23, respectively(10). The surface water (in problem of radon hazards has aroused concern of river, lake, reservoir) had radon concentrations from the public, the government and many organisations 0.02 to 1.55 kBq m23(11, 12). around the world. However, in the radon in drinking water investiga- The concentration levels of radon dissolved in tion from 1986 to 1991, only one or two water water show a wide range. Many researchers have been samples were collected from each city of the 49 cities working on the investigation and dose estimation of in China, and samples were not obtained from high- radon in water. In surface water such as in lake, river radiation-background areas. This article introduces a and sea, the radon concentration levels generally have preliminary investigation of radon concentration in very low values in the range of several hundred surface water and drinking water and a risk assess- Bqm23(1 –5), but high radon activities exist in Nordic ment of radon in drinking water in Shenzhen City countries such as Finland and Norway. It was (SC), a city with high radiation background. reported that radon activity concentrations more than 1000 kBq m23 in 10 % of the drilled wells, more than 100 kBq m23 in 59 % of the drilled wells and in SURVEYEDAREA 11 % of the wells dug in the ground were detected(6). Radon concentration in groundwater as high as There are three types of geomorphology in SC: moun- 57 000 kBq m23 has been measured in U-rich granitic tain, tableland and coastal area. The Quaternary terrains in Sweden(7). In the United States, the strata are composed of gravel, sand, clay, silt and New England state overall had the highest radon con- peat. Magmatic activity was very intense during the centrations in water from all sources; state geometric Yanshanian period in this area. The outcrop areas of means ranged from 18.5 kBq m–3 in Massachusetts to the Yanshanian granitoids and volcanic rocks cover 88.8 kBq m–3 in Rhode Island(1). up to about 56 % of the entire area. Volcanic rocks Compared with American and European countries, are mainly composed of the Mid-Jurassic and the fewer researchers have worked on the radon levels in Late Jurassic rocks. The intrusive rocks are composed

# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected] T. LI ETAL. of the Middle and the Late Jurassic and the until the bottles were filled with fresh water. At every Cretaceous biotitic granite and granodiorite(13). sampling site, two samples of water were collected There are abundant water resources in SC with 310 using two plastic bottles with a volume of 550 ml. rivers and 173 reservoirs such as the Shenzhen Then, the sampling time, date, location, depth, code Reservoir, Xili Reservoir and Sanzhoutian Reservoir. and description of source were recorded. Drinking water is supplied mainly by surface water The samples of surface water were collected at the such as lake and reservoir. Surface water accounts for depth of about 0.3 m below the water level near the 68.7 % of the total water supply and underground shore. water only 3.2 %(14). The samples were measured in situ or indoors while A radon in water survey was carried out in SC in keeping a track of the delayed time. The dissolved October 2013, when the means of temperature, pres- radon concentrations in water from 15 different sure and relative humidity in the air were 24.538C, sample locations across SC were mostly measured 1007.87 mbar and 52.02 %, respectively. A total of 15 within 5 h. water samples were collected, and the sampling codes Radon concentration in water was measured using Downloaded from and locations are shown in Figure 1. the professional radon monitor AlphaGUARD Of the 15 water samples, 3 samples were taken from PQ2000 PRO (GENITRON, Frankfurt, Germany), surface water, 3 from tap water of large public water which has a measurement range of 2–2 000 000 supplies and 6 from small public water supplies. Bq m23. For radon measurements in water, the Another 3 samples were taken from spring water in special equipment was used that contains one degas- the mountain areas. sing vessel (for water) and two security vessels. The http://rpd.oxfordjournals.org/ The locations of surface water samples SW1, SW2 effective detection volume was 0.68 l. In ‘flow’ mode, and SW3 were at Xili Lake, Xichong Village and radon without progeny was pumped through the side Tianxi Village, respectively. The spring water samples air filter intakes directly into the ionisation chamber MW1, MW2 and MW3 were taken from Zhutou by the AlphaPUMP. Radon concentration was Mountain covered with sandstone, Maluan Mountain recorded every minute. Figure 2 shows the set-up for composed of granite and Wutong Mountain com- radon measurement in water. posed of rhyolite, tuff and tuff lava, respectively The operation procedures for radon measurement (Figure 1). are briefly described in the following: at Universite Laval on November 13, 2015 (1) Measure the system background after connecting SAMPLING AND MEASUREMENT METHODS the empty degassing vessel, security vessels, The water samples were collected following the AlphaGUARD and AlphaPUMP for 15 min methods described in the ‘Radon in Water Sampling with 1 l min21 flow rate of the pump; Program’(15). The sampling bottles were cleaned twice (2) Pour the water sample into the degassing vessel to using the water in lake or reservoir and then filled avoid any turbulence, and then close the system as with water. When collecting the public supply water soon as possible; in the pipe (tap water), the valve was slowly turned on (3) Degas radon in water with 0.3 l flow rate for and the water stream was allowed to flow for 2 min 10 min, and then switch off the pump;

Figure 1. Map of SC with the locations of water sampling.

Page 2 of 6 RADON CONCENTRATION IN SURFACE WATER AND DRINKING WATER Downloaded from http://rpd.oxfordjournals.org/

Figure 2. Scheme of measurement set-up.

(4) Continuously measure radon concentration for The detection limit of this system of radon mea- the next 20 min, and record the radon concentra- surement in water is 23.3 Bqm23 (a ¼ 0.05). tion per minute; (5) Remove radon in the system with fresh air until the initial background of the system is reached. RESULTS AND DISCUSSION The radon concentrations in water samples are calcu- The radon concentrations of the above 15 samples are at Universite Laval on November 13, 2015 lated by the following equation using a value indi- listed in Table 1. The following conclusions about cated by the AlphaGUARD(16): radon in water in SC can be obtained from these results: 1. Radon concentrations in the public water sup- Vsystem Vsample Cwater ¼ Cair þ k C0 ð1Þ plies and surface water are generally low. Three Vsample surface water samples were taken from a lake, a sea and a brook, and the average radon concentration 23 where Cwater is the radon concentration in water was 0.29 + 0.26 kBq m ; another three samples 23 sample (Bq m ), Cair is the radon concentration in were collected from large public water supplies such the system after expelling the radon from water as hotel and restaurant tap water, with the average 23 23 sample (indicated by AlphaGUARD in Bq m ), C0 radon concentration of 0.15 + 0.23 kBq m .In 23 is the background of the system (Bq m ), Vsystem is addition, six samples were collected from the tap the interior gas volume of the system (ml), Vsample is water of small public water supplies in the outskirts the volume of the water sample (ml; in the device used such as parks, villages and near reservoirs, and the in this study, the volume was 150 ml) and k is the average radon concentration of these samples is 0.37 23 radon distribution coefﬁcient. + 0.42 kBq m . The radon distribution coefﬁcient is the ratio of 2. The average radon concentration in spring water C to C , and it varies inversely with the tempera- collected from Wutong Mountain, Maluan Mountain water air 23 ture. The value of k can be calculated by the following and Zhutou Mountain is 52.05 + 6.64 kBq m , 23 equation(1, 17): and the maximum value is 82 + 8.9 kBq m .Of the 15 samples, only 2 spring water samples collected ð0:0502TÞ from the mountainous area have radon concentra- k ¼ 0:1057 þ 0:405 e ð2Þ tions above 11.10 kBq m23, which are higher than the reference value for the radon level in the Standard of During this radon survey in SC, the average temperature, Drinking Water Quality published by the Chinese pressure and relative humidity were 24.538C, 1007.87 government(18). mbar and 52.02 % in the air, respectively. So, the k value 3. A high radon concentration in spring water is was equal to 0.22 when the temperature was at 258C. related with the local lithology. The spring water

Page 3 of 6 T. LI ETAL. Table 1. 222Rn concentrations in water in SC. belonging to the Lotus Mountain volcano eruption zone, which belongs to the volcano activity belt of Sample Location Source Radon Zhejiang, Fujian, Guangdong and Hong Kong. The code concentration, ages of the Mesozoic volcanic rocks can be further mean + SD 23 divided into the Middle Jurassic and the Middle– (kBq m ) Late Jurassic volcanic rocks (156.9 + 2 and 165.8 + 2.9 Ma, respectively), the Late Jurassic volcanic SW1 Xili Lake Surface water 0.15 + 0.18 rocks (141.9–145.6 Ma) and the Late Jurassic (lake) to Early Cretaceous volcanic rocks (131 + 2to SW2 Xichong Surface water 0.22 + 0.21 146.2 + 2.9 Ma)(19). Intrusive rocks are widespread Village (sea) in the Shenzhen area with an exposed area of about SW3 Tianxi Surface 0.51 + 0.39 2 Village water(brook) 760 km , making up 37.6 % of the total area of (19) LPS1 JY Hotel LPWS 0.12 + 0.14 SC . Uranium and thorium concentrations are very LPS2 XC LPWS 0.16 + 0.25 high in granite in the Middle and Late Jurassic and Downloaded from Restaurant Cretaceous age in Guangdong Province, China. The LPS3 AS Hotel LPWS 0.18 + 0.29 uranium and thorium levels in granite in the SPS1 YS Park SPWS 0.09 + 0.20 Doumen District in Zhuhai City are 213.5 + 159.6 SPS2 LWS SPWS 0.23 + 0.32 and 146.7 + 7.1 Bq kg21, respectively(20).So,high Reservoir radium concentrations in soil in the Wutong SPS3 FML SPWS 0.35 + 0.31 Mountain area were observed. But, it needs to do Reservoir http://rpd.oxfordjournals.org/ SPS4 XT Village SPWS 0.42 + 0.42 more detailed surveys about radon and radium con- SPS5 XWD SPWS 0.42 + 0.49 centrations in soil and spring water in Wutong Reservoir Mountain because only one spring water sample was SPS6 ML Park SPWS 0.69 + 0.76 taken in this study. MW1 ZT Spring water 3.05 + 1.29 Mountain MW2 ML Spring water 71 + 10 Mountain DOSE ASSESSMENT MW3 WT Spring water 82 + 8.9 222 Mountain The annual effective dose caused by Rn in drinking water can be calculated by the following at Universite Laval on November 13, 2015 LPWS, large public water supplies; SPWS, small public formula: water supplies; SD, standard deviation. Deff ¼ K G C t ð3Þ

where Deff is the effective dose from ingestion (Sv), K samples MW2 and MW3 were collected from is the ingesting dose conversion factor of 222Rn Maluan Mountain and Wutong Mountain. Wutong (Sv Bq21), G is the water consumption (l d21), C is Mountain, a national forest park, is located in the the concentration of 222Rn (Bq l21) and t is the dur- southeast of SC 15 km east of the city centre and ation of consumption, where t ¼ 365 days. Shenzhen Reservoir is on its west. Wutong Mountain The dose conversion factor, more commonly known is mainly covered with rhyolite, tuff and tuff lava. as the ‘equivalent dose to stomach per unit activity of Wutongshan Formation was happened in the Late 222Rn ingested’, has been calculated by several Jurassic–Early Cretaceous period. And, seven soil authors(21, 22). The average accepted value of the dose samples (rhyolite) collected in Wutong Mountain conversion factor for adults is 3.5` 1029 Sv Bq21(1), have high 226Ra content. The mean and standard de- which was used in the effective dose calculation. In viation of radium content of the seven samples are various studies, the average of water consumption daily 95.58 and 5.67 Bq kg21, respectively, measured by a per capita was usually found to be ,2 l, but there was high pure germanium gamma-ray spectrometer. considerable variation between individuals(23).The Maluan Mountain, which is composed of biotitic water consumption values of 1 and 2 l d21 are often granite, is located in the northeast of Wutong Mountain, used for calculating the annual effective dose due to so MW2 spring water sample has a higher radon concen- 222Rn in drinking water(24–26). An average drinking tration. MW1 sample was collected from Zhutou water consumption of 1 l d21 per person was assumed Mountain, which is covered with quartzitic conglomerate in annual effective dose calculation. and sandstone. There, the radium radioactivity concen- Theannualeffectivedosesduetoradoninwater tration in soil is 31.45 + 3.0 Bq kg21, so a lower radon in SC are listed in Table 2.Thistableindicatesthat concentration was observed in the spring water. only the annual effective dose of water sample Volcano activity in the Mesozoic in the Shenzhen MW3 collected from Wutong Mountain exceeds area is part of the whole Paciﬁc volcano-active belt, 0.1 mSv y21.

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Dosim. 121, 452–455 (2006). The radon concentration levels in SC show obvious 11. Zou, M. Investigation and analysis of radon concentra- differences among various water sources. In general, tion in water of Jiujiang City. Jiangxi Energy. 4,81–82 Downloaded from the spring water presents a higher radon concentra- (2012). (In Chinese.) tion value. The tap water in the outskirts shows a 12. Tian, Y. Correlation between radon, thoron in the surface middle-level value. The lower values are found in water and U-226Ra–Th concentration in Tianjin City. samples from the large water supplies and the surface Chin. J. Radio. Health. 21, 453–454 (2012). (In water. This investigation results suggest that the Chinese.) 13. Xiong, S., Wang, N., Fan, Z., Chu, X., Wu, Q., Pei, S., drinking water in SC is generally safe and it may not http://rpd.oxfordjournals.org/ be healthful to directly drink spring water collected Wan, J. and Zeng, L. 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