Assessing Radon-in-air from streamflow, comparing ...

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Assessing Radon-in-air from streamflow, comparing two study cases: Labso-Laura and Capodifiume springs (Campania region, southern Italy) DOMENICO GUIDA1, MICHELE GUIDA2, MARIA LETTIERI3*,VINCENZA TIRRI3, BIAGIO CAPACCHIONE3 1

Department of Civil Engineering, University of Salerno, via Giovanni Paolo II, 132, 84084 Fisciano (SA), ITALY [email protected] 2 Laboratory for Environmental Radioactivity (AmbRA), Department of Physics and National Institute for Nuclear Physics (INFN), University of Salerno via Giovanni Paolo II, 132, 84084 Fisciano (SA), ITALY [email protected] 3 Laboratory for Environmental Radioactivity (AmbRA), University of Salerno via Giovanni Paolo II, 132, 84084 Fisciano (SA), ITALY [email protected], [email protected] * Corresponding Author: [email protected]

Abstract: This paper deals with a particular kind of radon-in-air Springs: the degassing from spring and related channels in a rural and urban landscape. The two study areas are located, the first, at the Cilento Geopark Geosite of Capodifiume spring group and, the second, in the Montoro alluvial plain (southern Italy). Based on previous hydro-geological studies, field measurements campaigns have been carried out during the 2013 spring-autumn time on monitoring stations located along springs and downstream irrigation channels. Laboratory analysis and environmental calculations have yet provided insight on space-time radon distribution in spring and stream flow, confirming radon as effective tracer in hydro-geomorphological analysis. Beside this, field experiments on radon-in-air concentration and diffusion by radon degassing from the surface flowing water have been performed in order to define influenced areas by radon diffusion. Results give effective insights in radon risk assessment for urban planning and radon mitigation actions. Key-Words: radon, radon degassing, radon assessment, Cilento Geopark, Campania Region, southern Italy

1 Introduction

Agency for Research on Cancer (IARC), since 1988 has classified radon in Group 1, which lists the 85 substances classified as carcinogenic to humans. Radon is an inert gas and electrically neutral, so it does not react with other substances. Consequently, as it is inhaled, it is exhaled. However, since it is radioactive, it is transformed into other substances called Radon decay products.Previous studies, based on indoor surveys, at national scale, have found high level of radon in the houses of the Campania region

Radon is one of most widespread naturally occurred radioactive material (NORM) in the all environments. It is highly dangerous for human health, if it is present in high concentration. Radon is a carcinogen and in particular the risk posed by radon is to contract lung cancer and evidence comes from studies in humans and studies carried out in the laboratory. In fact, the World Health Organization (WHO), through the International

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(southern Italy). Indoor radon data non allow to define origin, exchange and indoor concentration mechanisms from outdoor Springs. The studies are focused on the use of Rn222 in territorial planning, water defence and mitigation and protecting the public from environmental risks. Starting from the knowledge on the subject on an international level, the research themes, operating at a local level, have been set for their implementation in the field of the range of institutional sphere of action of the local authorities responsible for monitoring and environmental protection in Campania Region, in accordance with the national regulatory framework and regional legislation in the matter of risk from Radon. These are electrically charged and attach to particulate matter in the air that can be inhaled and stick to the surfaces of the lung tissues. The atoms, deposited in this manner (especially two isotopes of polonium, Po-128 and Po-214) are still radioactive and emit alpha radiation that can cause physical and chemical damage to the DNA of lung epithelial cells. The decay of radon (the uranium decay series 238) then form a series of solid radioactive particles that accumulate in the lungs in the form of heav elements that continue to emit radioactivity and to damage the pulmonary epithelium and the accumulation of damage can actually determine the occurence of cancer. In fact, radon is the second leading cause of lung cancer after smoking and until today no other different effects have been proven. Moreover, fundamental importance is the combination of tobacco smoke and radon exposure, in fact for smokers the risk of lung cancer caused by radon is considered to be 15-20 times higher than the risk for non-smokers.

Fig. 1 Flow chart of the Rad-Campania Program

This Program involves interdisciplinary skills, such as Physics, Geology and Environmental Engineering and develops research on the study of natural radioactive isotopes in the environmental field. Within the “Water” Project in the framework of the RAD_Campania Program, since 2006, several monitoring campaigns were carried out on river and spring radon activity concentrations in the Campania region. Fig. 2 depict the distribution of the monitored river reach and spring stations, highlighting the location of the study areas considered in this paper: the Capodifiume spring groups, near Paestum archaeological site and Laura-Labso, in the right side of the Montoro valley.

2. Radon water-gas assessment in the river and spring at regional scale

Radon in-water gas classes, Bq/m3

As previously defined, the distribution of radon in water is one of the main project included in the RAD-CAMPANIA Program, promoted by researchers of the Salerno University (Fig. 1).

>105

q >

104-105 103-104 102-103

Fig. 2 - Location of the monitoring stations and study areas and related radon in-water activity concentration classes in Campania region

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Considering the radon in-water spatial distribution at regional scale, this paper deals with the problem: what is the influence of the radon concentration inair by degassing from river and spring stream flow on surrounding rural and urban areas?

suitable for sampling in river stretches, which have a lower concentration of Radon. When proceeding to the sampling, the operator has to fill and close the vial keeping it below the water level to avoid even a minimal degassing of radon in the air. Once samples are taken, the vial must be labelled indicating the initials of the monitoring station, in addition to the date of the measurement campaign, then also the date and time of sampling and the name of the operator. Finally, the vials were placed in a specific case and measured in the Laboratory of Environmental Radioactivity of the Department of Physics “CAIANIELLO” at the Salerno University (QMS Quality Management System: ISO 9001 2008) by using the RAD7 monitor by Durridge Inc. (USA).

In fact, radon is a radioactive element, but unlike others, it is gaseous, therefore, subject to the phenomenon of degassing according to which its atoms can be easily released from water, spreading into the surrounding area. In fact, its danger lies in the fact that it can also spread to areas distant from the area of production and here accumulate until it reaches a quantity that can be extremely harmful. Specifically, in the cases under analysis, measurements of radon in air were carried out, in order to identify a possible buffer zone, within which the population and/or workers were exposed to a real risk to their health, even in function of exposure time.

3. The study area of Capodifiume The Capodifiume springs, located downhill the Capaccio village (SA), are one of the most important geosite of European Geopark of Cilento, Vallo di Diano and Alburni. The water of these springs, have a relevant discharge (annual average: 3 m3/s) originating the homonymous river. They are unusable both for irrigation and drinking water because of high mineralization. In Holocene times, the high salt content deposited the travertine plastron (several km2 wide and several tens of meters thick), where was founded the greek-roman town of Poseidonia-Paestum.

Following the methods, procedures and protocols proposed within the “Water” Project of the RAD_Campania Program, the monitoring program carried out in the two cited study areas was addressed to collect hydro-chemical spring and stream flow data during the discharge period of the aquifer feeding the above springs. In the spring and channel stations several monitoring campaigns were carried out and data on water flow (Q), average velocity (Vmean), specific electric conductivity (EC), temperature (T) were recorded. At same time, water samples were taken for the evaluation of activity concentration in Radon water-gas in the laboratory. The discharge measurements were carried out using the current meter Swoffer 3000 by Swoffer inc. USA and adopting the DISCH Protocol. The Electrical Conductivity measurements were carried out using the multi-parametric probes HI 9828 and HI99300 by Hanna Inc. For the measurement of radon water-gas, a specific protocol was used, in which the whole experimental procedure is outlined, that goes from the earlier phases of sampling to the mode of execution of the final measurement. A first stage concerns the detection and identification of a monitoring station, which may be a point along a stretch of river or a spring or a structure of uptake. A second stage of the procedure concerns the operations of sample collection. The containers used are glass vials W40 (with a capacity of 40ml) and W250 (with a capacity of 250ml) of the American company Durridge: the former are more suitable for sampling in wellspring locations, which have a high concentration of radon, while the latter are more

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Fig. 3 - Hydrogeological sketch: 1) Fluvial sediments; 2) Travertines; 3) Clays, sandstones, marls, calcareous marls; 4) Limestones; 5) Springs.

The springs of Capodifiume show higher values both of 222Rn concentrations (average of 230 Bq/l) and salinity compared to other karst springs in the

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Cilento, Vallo di Diano and Alburni European Geopark and Campania region. Following the previous hydrogeological studies and based on monthly monitoring radon activity measurements, an experiment was programmed in order to define the influence of the Radon degassing on in-air Radon concentration and diffusion. Assuming that the volatilization of the gas from the water surface is the main contribution to the degassing, in 06/08/2013 a preliminary test measurement was performed at the Lateral Spring LS01. Based on the results of this test, in 28/09/2013, a complete experiment was carried out, performing three set of measurements and positioning for each three RAD7 instruments along a transect at a distance of 0 m, 5 m and 10 meters from the spring stations to find a trend of the 222Rn activity concentration in the air once were identified the wind constant direction. Velocity and direction of the wind were also monitored using a Ventus weather station, detecting an average wind speed of 4,9 km/h in a constant NW wind direction. three sets of measures were performed according to that direction at 14:00, 15:10 and 16:30, respectively (Fig. 4).

Table 1 - Capodifiume Radon Experiment dataset

The reduction of the measured concentrations was quite gradual (about 8-9% every 5 m), so that at a distance of 10 m from the spring LS01 (Lateral Spring 01), the 222Rn in-air activity concentration remained still about 363 Bq/m³. The particular emission of this spring due to a weakly turbulence suggests a greater volatilization of radon in the air compared to the slower diffuse emissions of the Seepage Springs 10 and 13.

Fig. 5 - Decrease of 222Rn concentrations in air as a function of distance (campaign 28/09/2013).

Assuming that the springs are point Spring, we calculated the transfer coefficient of radon from the water body to the air with the following equation: ncrement of air orne added y water activity in water Fig. 4 - Location of the RAD7 instruments and weather station during the campaign of 28/09/2013.

The Table 2 contains the average concentration inwater versus the corresponding average concentration Radon in-air at the selected stations.

The resulting concentrations shown evaluable decreasing trend, as reported in Table 1.

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Table 2 Radon in-water and in in-air concentration

Fig. 6 Calculated Transfer Coefficient CT

222

Comparing the average values of Rn activity concentration in water with the corresponding values measured in air at 0 m distance from the springs, the resulting CT values are listed in Table 3.

Compared to the value proposed in the scientific literature, about the transfer of radon into homes from domestic services (Ct=10-4, from Hess et al., 1982, 1990 and Nazaroff et al., 1987), the transfer coefficient estimated was approximately higher of an order of magnitude (1.3-1.7*10-3).

4 The Montoro study area The Labso and Lauro springs, located in Montoro valley closed to the Borgo and Preturo villages, are part of a geological and hydro-geomorphological district characterized by the hydrogeological features recognized and depicted in the Fig. 7 [ 1, thesis of three-year degree ].

Table 3 Transfer Coefficient CT with its error ∆CT

∆CT was calculated in the following way: ∆

*(

∆

+

∆

)

where: -

A = 222Rn activity concentration in air; ∆A = 222Rn activity concentration in air measurement error; B = 222Rn activity concentration in water; ∆B = 222Rn activity concentration in water measurement error.

The results obtained are comparable to each other in order of magnitude, and for the two diffuse Springs SS10 and SS13, taking into account the measurement errors, the transfer coefficient CT is very similar (Fig. 6).

Fig. 7 - Location of the Laura-Labso springs and reinterpretation of the hydro-geological setting of the Montoro study area. Legend: 1) Stratified limestone sequence; 2) Pyroclastic deposits and soils; 3) Piedmont loose debris,4) Floodplain deposits-

According to the hydrological setting and the aims of the research, a monitoring activity was programmed on an appropriate monitoring system was build-up by locating and characterizing the

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stations to be monitored (Fig.s 8, 9), as fully described in [1, thesis of three-year degree ].

evident. Concerning the interaction between the underground waters of the Spring and the surface waters of the canal, reference is made to the data obtained during the various campaigns, particularly comparing the various concentrations of Radon activity representing them in a single plot in which there is an immediate perception of its spatial and temporal variation.

Fig. 8 - Location of the Labso reach stations

Fig. 9 - Location of the Laura reach stations Fig. 12 - Space-time variation of the 222Rn activity concentration

The field and laboratory data obtained from monitoring activities were validated and properly recorded in comparative datasets. Fig.s 10 and 11 show plots referred to the 30/10/2013 campaign on both springs and related downstream reaches.

Based on the above and further data and elaboration, an up-to-date hydro-geomorphological model was obtained for the two springs, highlighting a different recharging mechanism: autogenic for Laura and autogenic.allogenic for Labso spring, respectively. Further analysis was made about the Radon concentration in stream flow, revealing a downstream decreasing trend in space and time at the different stations (Fig. 13). Clearly, this trend is due to Radon degassing from streamflow to atmosphere.

Fig.10 - Radon-Discharge-EC plot from Labso reach; data from 30/10/2013 measurement campaign

Fig. 13 - Variation of the Radon activity concentration along the Laura-Viara reach

Based on the results of the Capodifiume experiment, the same activity was repeated at the Labso and Laura spring, where previous radon in-water dataset was available.

Fig. 11 Measurement Campaign of 30/10/2013-RadonDischarge-EC-Laura

Once collected the data and defined the mean values of the basic parameters, the data from Labso and Laura spring have been compared and interpreted. In spite of the space proximity, about 1000 m, and short monitoring time, some significant differences described in [1, thesis of three-year degree ] are

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Consequently, in date 30/10/2013 two Radon in-air experiments were carried out at and surrounding the Labso and Laura springs. The Fig.s 14 and 15

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5 Radon in-air assessment from spring water Radon degassing

depicts the location of measurement transects and Table lists 4 the resulting dataset.

In consideration of the lacking in legislation regulating the threshold values of exposure to Radon in outdoor areas, in this paper is considered the regulations provided by the Legislative Decree April 9, 2008, n ° 81 regarding workers and by the Recommendation of the EURATOM n.143/90 February 21, 1990, regarding the population, both designed for confined spaces (indoor). The above LD April 9, 2008 provides that the following levels of action must not be exceeded: - 500 Bq/m³ annual average (corresponding to 3 mSv/year for 2,000 working hours) for workers while in underground sites or on the surface in those identified areas; - 1 mSv/year effective dose for workers in the workplace involving the use or storage of materials containing natural radionuclides and in spas; - 0.3 mSv/year for people involved in flying activities. Once rated an average annual exposure time in the workplace according to which the solar year is 2000 hours (about 170 hours per month), it is possible to calculate the dose to which workers are exposed in the surveyed areas, assuming that the measured concentration corresponds to the annual average value. An example of calculation referred to the Labso and Laura springs is listed in Tables 5, 6.

Fig. 14 - Location of the measurement transect

Fig. 15 Location of the measurement transect Table 4 - Data resulting from Labso-Lauro Radon in-air experiments.

Table 5 - LBS_S01 dose values estimated for workers at a distance 0, 5, 10 m from the edge spring at the station Station LBS_S01 Dose

222

Distance (m) 0 5 10

Comparing the Radon data recorded at the two above spring, despite Laura spring has a higher concentration of 222Rn activity in the water, no concentration of Radon is present in the air at a 5mdistance; differently for Labso spring, although its lower water radon value, there is a concentration of radon at a distance of 10 m from the channel bank. This difference is due to the fact that during the measurement in the air, near the two Springs, there were different weather conditions. In fact, in the case of Laura there was wind with a speed of about 6 km/h, while in the case of Labso spring it was approximately equal to 0 km/h.

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Rn Activity

Concentrazion (Bq/m3) 37,3 36,8 39,8

mSv/anno

µSv/h

0,224 + 0,1122 0,221 + 0,1104 0,239 + 0,138

0,1119 + 0,0561 0,1104 + 0,0552 0,1194 + 0,069

Table 6 - LAR_S01 dose values estimated for workers at a distance 0, 5, 10 m from the edge spring at the station Station LAR_S01 Dose

222

Distance (m) 0 5 10

Rn Activity

Concentrazion (Bq/m3) 37,3 0 0

mSv/anno

µSv/h

0,224 + 0,124 0,00 + 0,00 0,00 + 0,00

0,1119 + 0,0618 0,00 + 0,00 0,00 + 0,00

Referring to the case study of Capodifiume, in the following is examined the case of a part-time worker with a work schedule of no more than 20 hours per week (4 hours per day for 5 days), trying to verify the compliance with the limits prescribed y the regulations (1 μSv / year).

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Table 7 - Dose values (mSv / h) estimated, in the case of workers, at distance 0, 5 and 10 m from shore of the lake at stations LS01, SS10 and SS13.

ionizing radiations above those to which people are normally exposed. In this case, in fact, the greatest contribution to ionizing radiation, in fact, entirely attributable to radon that evaporates from water and disperses into the surrounding area. The recommendation of the EURATOM n.143/90 February 21, 1990 on the protection of the public against exposure to radon in indoor provides for the establishment of an adequate system for reducing any exposure to indoor radon concentrations: 1) With respect to existing buildings, the reference level must not exceed an effective dose equivalent to 20 mSv per year, which, for practical purposes, can be considered equivalent to an annual average concentration of radon of 400 Bq/m³; 2) As for the buildings to be constructed, the reference level must not exceed an effective dose equivalent to 10 mSv per year, which, for practical purposes, can be considered equivalent to an annual average concentration of radon gas of 200 Bq/m³ . Bearing this recommendation, it is therefore possible to calculate, through a simple proportion, the exposure values corresponding to the results obtained from the measurements (Tables 3.5, 3.6 and 3.7), considering the limit of 200 Bq/m³, corresponding to an effective dose equivalent to 10 mSv per year.

Table 8 - Values of dose (μSv / year) received from a part-time worker for 960 h/years

Table 9 - Dose values estimated, in the case of the population at a distance 0, 5, 10 m from the edge spring at the station LBS_S01 Station LBS_S01 222

Distance (m) 0 5 10

Dose

Rn Activity

Concentrazion (Bq/m3) 37,3 36,8 39,8

mSv/anno

µSv/h

1,865 + 0,935 1,84 + 0,92 1,99 + 1,15

0,213 + 0,107 0,21 + 0,11 0,227 + 0,131

Table 10 - Dose values estimated, in the case of the population at a distance 0, 5, 10 m from the edge spring at the station LAR_S01 Station LAR_S01 Distance (m) 0 5 10

As can be observed near the Lateral Spring 01 at a distance of 10 m from the shore the worker is exposed to an annual dose exceeding 1 mSv / year. Our study case does not fall into any of the three working conditions provided by law, but wanting to make a working assumption, the only more likely condition is the working activities involving the use or storage of materials containing natural radionuclides as, regardless of the distinction between indoor or outdoor work, it has to do with

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Dose

222

Fig. 16 Annual dose received by a part-time worker in proximity of the various stations at different distances

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Rn Activity

Concentrazion (Bq/m3) 37,3 0 0

mSv/anno

µSv/h

1,865 + 1,03 0,00 + 0,00 0,00 + 0,00

0,213 + 0,118 0,00 + 0,00 0,00 + 0,00


4 Conclusion

Table 11 - Dose values (mSv / h) estimated, in the case of population, at distance 0, 5 and 10 m from shore of the lake at stations LS01, SS10 and SS13.

The analysis represents one of the first attempt concerning the monitoring of radon in selected study areas: Labso and Laura Springs, situated in the plain of Montoro Inferiore and Capodifiume, springs. In particular, through the use of gas Radon222 as a natural tracer, an attempt was made to characterize and study the interactions between groundwater, surface water flows (rivergroundwater interactions) and degassing in the atmosphere. In addition to a purely scientific aspect, another factor took our attention, that is the protection of human health, certainly not negligible. During the last decade, many studies have demonstrated that inhalation of high concentrations of radon can significantly increase the risk of lung cancer. In this regard, a protocol of measurements in air have to be developed in order to understand how and in what quantity the gas present in the water can diffuse in the air. The results obtained from the analysis performed on the base of the measurements of radon concentration available for the two case study suggest a protocol and method to assess this scenario not considered in national and European legislation, providing an experimental procedure in the Radon risk planning.

The value of estimated dose received per hour associated with exposure to radon is, in all stations and at all distances examined, significantly higher (Fig. 5.2) than the dose associated with the natural ackground (from 0.10 to 0.12 μSv/h).

References: [1] M.Lettieri, V.Tirri, Analisi della distribuzione spazio temporale del radon connessa ai corpi idrici: i caso studio delle sorgenti Labso e Laura nella piana di Montoro (AV), thesis of three-year degree 2014. [2] Nazaroff, W.W., Doyle, S.M., Nero, A.V., Sextro, R.G., 1987. Potable water as a Spring of airborne 222Rn in US dwellings: a review and assessment. Health Phys. 32, 281–295. [3] Olle Selinus, Brian Alloway, Josè A.Centeno, Robert B.Finklman, Essentials of Medical Geology,Radon in Air and water,239-278. [4]Valentì Rodellas et al./Journal of Hydrology,2012. Quantifying groundwater discharge from different Springs into a Mediterranean wetland by using 222Rn and Ra isotopes.

Fig. 17 - Hourly dose received by population in proximity of the various sections at different distances.

Unlike the case of the springs of Labso and Laura, near the springs of Capodifiume at all stations and at the distances examined, the calculated values demonstrate that the dose received per hour associated with exposure to radon, is significantly higher than the natural ackground γ (approximately an order of magnitude). This condition could pose a serious risk to human health and therefore requires further study and, in the meanwhile, regulation and mitigation measures.

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