Study of environmental radioactivity in Las Canteras beach

STUDY OF ENVIRONMENTAL RADIOACTIVITY IN LAS CANTERAS BEACH Ana del Carmen Arriola Velásquez Curso 2015/2016 Dra. Alicia M. Tejera Cruz Dr. Pablo Martel Escobar Trabajo Fin de Título para la obtención del título: Grado en Ciencias el Mar Study of environmental radioactivity in Las Canteras beach 1 STUDY OF ENVIRONMENTAL RADIOACTIVITY IN LAS CANTERAS BEACH Datos personales del estudiante: Datos de los tutores: Dra. Alicia M. Tejera Cruz Universidad de Las Palmas de Gran Canaria Facultad de Ciencias del Mar Departamento de Física e-mail: [email protected] Dr. Pablo Martel Escobar Universidad de Las Palmas de Gran Canaria Facultad de Ciencias del Mar Departamento de Física e-mail: [email protected] En Las Palmas de Gran Canaria a 11 de Julio de 2016 Ana del Carmen Arriola Velásquez Grado en Ciencias del Mar Curso 2015/2016 Universidad de Las Palmas de Gran Canaria Facultad de Ciencias del Mar e-mail: [email protected]c.es Estudiante: Ana del C. Arriola Velásquez Estudiante: Ana del C. Arriola Velásquez Tutora: Dra. Alicia M. Tejera Cruz Co-tutor: Dr. Pablo Martel Escobar Study of environmental radioactivity in Las Canteras beach 2 INDEX Abstract……………………………………………………………...…………………...3 Introduction……………………………………………………..………………….........4 Study region………………………………………………..……………………………8 Material and methods………………………………………….……………………….11 Results and discussion…………………………………………….……………………16 Conclusions…………………………………………………………………………….21 References...…………………………………………………………………………....22 Annex……………………….…………………….………………………………….....26 Personal Assessments………….……………………………………………………….28 Study of environmental radioactivity in Las Canteras beach 3 ABSTRACT In this final degree work an assessment of the impact of environmental radioactivity, mainly on bathers of the most important beach in Las Palmas de Gran Canaria (Las Canteras), has been done. For this purpose, the main radionuclides contained in intertidal superficial sand samples have been measured by using gamma spectrometry analysis. Also alpha activity of the beach water was determinated by means of ZnS(Ag) scintillation detector. The radioactivity detected was due to the natural occurring radionuclides 226Ra (238Useries), 232Th and 40K in sand samples with an average activity concentrations of 14.6±1.0, 17.4±1.0 and 528±24 Bq/kg, respectively. From these values, the outdoor annual effective dose was of 0.047 mSv/y, which is below to the world’s average value (0.07 mSv/y). The average gross alpha value for Las Canteras water samples obtained was 0.101±0.003 Bq/L, a similar magnitude to the mean in seawater. Finally, the activity concentrations of 40K in the sand and the gross alpha of the beach water have been suggested as possible tracer of the sedimentary dynamic of the beach and the presence of submarine groundwater discharges, respectively. Study of environmental radioactivity in Las Canteras beach 4 1. INTRODUCTION Radioactivity is around us. It is a process that happens due to the interactions that occurs in the nucleus of the atom between protons and neutrons. Protons push each other away (repulsive electrical force) while nucleons try to hold them together (nuclear force). If these two forces are not in balance the nucleus become unstable or radioactive and decay to another nucleus, stable or also radioactive, emitting the extra energy they have in form of electromagnetic energy and particles (to which we will refer as radiation). There are more than 3000 nucleuses known (nuclides) and only around 100 are stable. This means that most of them are radioactive so they are known as radionuclide (Karam, P.A. and Stein, B.P., 2009). As described in Pope, J.A., (1989) when an element decay on another (fathers decay on daughters), different kinds of nuclear radiation emissions are produced. These emissions are able to produce ionisation, which is the ability to remove orbital electrons from target atoms, producing a number of ion pairs along its path. Also these emissions have different characteristic of velocity, penetration of matter and mass, depending on the type of particle that is emitted. These would be: α-emission. If during the decay the particle emitted is a helium nucleus (a particle formed by two protons and two neutrons). This emission is more likely to happen among nucleus of elements with atomic number greater than the lead (Z=82). It reduce in 2 the atomic number (Z) of the radionuclide and the mass number (A) is reduced in 4, as it is shown on the next equation: 𝑋→ 𝑌 𝑍−2 𝐴−4 +𝐻𝑒 (=𝛼) 4 2 𝑍 𝐴 (1) Father → Daughter + Radiation These α-particles have a high positive charge and a large mass with a small penetration of matter. They have the ability of tear electrons easily from target atoms, leaving behind a dense track of ionisation. β-emission. In this case we can differentiate two different β-particle emissions. One would be the β--emission, in which a neutron is converted in a proton and an electron is released from the nucleus during decay. Normally this decay occurs in radioisotopes with an excess of neutrons. In in this case the mass number (A) stays the same while the atomic number (Z) is increased by 1. Also an antineutrino (𝑣) is released: 𝑋 𝑍 𝐴→ 𝑌 𝑍+1 𝐴+𝑒−+𝑣 (2) The other one would be the β+- emission. In this case a proton is converted in a neutron and a positron (the same as an electron but with positive charge) is released. Normally this occur in neutron-deficient radioisotopes. In such decay A stays the same but Z decrease by 1. In addition a neutrino (𝑣) is released: 𝑋 𝑍 𝐴→ 𝑌 𝑍−1 𝐴+𝑒++𝑣 (3) The neutrino (𝑣) and the antineutrino (𝑣) are particles that carry away certain amount of energy and momentum from the decay process but have zero charge and Study of environmental radioactivity in Las Canteras beach 5 approximately zero mass. These β-particles have higher penetration of matter than αparticles. γ-ray emission. Normally these emissions are produced as a photon emitted after another decay process like αor β-emission that has left the daughter of the initial element in an excited state. This is due to the fact that γ-rays are emitted during transitions from an excited nuclear state to a lower-energy nuclear state in the form of a photon: 𝑋 𝑍 𝐴∗→ 𝑋 𝑍 𝐴+𝛾 (4) Talking about penetration of matter, γ-rays do not have a precise range because they follow very tortuous path, even though they are very penetrating. Also they suffer an exponential drop in intensity as they break through matter. There are three major mechanisms that can produce ionisation by γ-radiation. These would be photoelectric effect (for low photon energy), Compton Effect (for medium photon energy) and pair production (for high photon energy). Radioactivity is not a man-made phenomenon, contrary to what some might think, although it has both, natural and artificial origins. Some of the natural radionuclides exist since the formation of the earth. The most abundant elements between the former ones are the 40K and the radioisotopes from the natural radioactive series of 238U, 235U and 232Th. Also 237 Np and its decay products were formed alongside the Earth but, due to its half-life, it was extinct. Nevertheless a small amount of it has been found in small amounts on nature. This 237Np is supposed to have been created during the nuclear tests of the XX century. Other elements are produced continuously from the interaction of the cosmic rays with the atmosphere. These rays come from the sun, the stars and the interstellar space and are formed by protons, alfa particles and heavier nucleuses. These particle interact with the nucleuses from the upper atmosphere producing new radioactive species. The production rate of these elements changes with time because the cosmic radiation flux is not uniform. This depends on different factors as the solar activity, human influence on the atmosphere or the changes on the Earth’s magnetic fields (Ortega Aramburu, X. and Jorba Bisbal, J., 1996; Azouazi, M., et al., 2000). The artificial radionuclides are produced mostly by the bombardment of a nucleus with light particles such as protons, neutrons or α-particles. This creates some nuclear reactions that lead to different artificial radioisotopes (Pope 1989). This artificial elements can be released to the environment by different means and from different origins. Some of them have been released from the nuclear weapon testing during the middle of XX century, from nuclear weapons production or from nuclear accidents on the industry. Others are released from the general used of radioactive materials on medicine, non-nuclear industries producing Naturally-Occurring Radioactive Materials (NORM industry), research and space exploration (Livingston, H.D., 2004). Natural radioisotopes have different distribution in earth crust and in the oceans. In table 1 the worldwide activity concentration value of radioisotopes 226Ra (a representative isotope of the 238U decay series), 232Th and 40 K is shown. This values Study of environmental radioactivity in Las Canteras beach 6 correspond to the mean value concentration of natural radioisotopes on the earth crust and are given on Bq/kg (1Bq= 1 radioactive decay per second). Location 226Ra 40K 232Th Worldwide 32 420 45 Table 1. Mean activity concentration of natural radionuclides on earth crust in Bq/kg (UNSCEAR 2000). In addition to the difference with the earth crust, radionuclide concentration in the ocean varies from one nuclide to another. In table 2 it is shown the main different radionuclides that can be found on seawater. Also appears their concentration and activity in mBq/L for seawater. Radionuclide Concentration (g/L) (mBq/L) 3H 3.2x10-18 1.11 14C 3.1x10-14 22.2 40K 4.5x10-5 11840 87Rb 3.4x10-5 107.3 226Ra 8.0x10-14 2.96 U(238U & 234U & 235U) 3.3x10-6 81.4 232Th 2.0x10-8 0.074 Table 2. Concentrations and activities of radionuclides in seawater. Modified from Garzón Ruiperez, L., (1979). In general, it is worth noting that the concentrations of 238U, 232Th and its daughters are smaller in seawater than in earth’s crust. Depending on the environmental conditions U can be found in different forms, so that sometimes uranium ores can be insoluble and they are deposited on sediments. Also the relation Th/U is 6*10-4, while in continents it has a value of 2-3. This shows that seawater is impoverished on Th in contrast to continents. This relation can give an idea of the high stability that Th ores present against U ones, since all of them are contributed by continental water discharges. Another radionuclide that can vary depending on the conditions is the 226Ra. Being a daughter from 238U, the concentration of 226Ra could be calculated but the result would be higher than the one indicated on table 2. This means that part of the 226Ra is deposited on sediments. Also some marine organism are able to concentrate this radionuclide. As a result, the presence or absence of this organisms can change noticeably the presence of 226Ra in seawater. In addition this element also has a smaller presence in seawater than in continents. Finally the nuclide that contributes more, by far, to the total activity of seawater is the 40K. This radionuclide represent the 98% of the total activity (Garzón Ruiperez, L., 1979). Different activity concentrations in marine sediments from different parts of the world are shown in table 3. As it can be observed, the average concentration for natural radionuclides is different from one place to another. These variations give and idea that the presence of radionuclides varies depending on the composition of the sample that is analysed. Study of environmental radioactivity in Las Canteras beach 7 Table 3. Activity concentrations (Bq/kg) of natural radionuclides in different parts of the world. According to Pope, J.A., (1989), for measuring all this radioactivity and its effect on the matter different parameters are proposed. One would be the absorbed dose: E Dm  (5) where E is the mean energy imparted by ionising radiation to a volume of mass m. In other words, this parameter gives information about the radiation absorbed by any kind of matter. Its unit is J/kg, also known as Grey (Gy). But the biological effects on matter not only depend on absorbed dose. Depending on the type of ionizing particle the biological damage will be important, even if the energy absorbed is the same in one case and another. To measure the effectiveness of a concrete ionizing particle in producing biological damage, the dimensionless quality factor (Q) is used (1-2 for X, γand βradiation, 5 for low neutron, 10 for fast neutrons, protons and α-particles and 5 for heavy recoil nuclei). Also it depends on the distribution of absorbed dose in space and time. This factor would be grouped on the N parameter. For external sources N is taken as 1 but for ingested radiation material can change. With the absorbed dose, Q and N factor dose equivalent (H) can be calculated: H D Q N   (6) Dose equivalent thus explains the relative radiation risk of a particular radiation. Its units would be J/kg, as the absorbed dose. To distinguish one from another, Sievert unit (Sv) is assigned to dose equivalent. In figure 1 the main sources of annual doses absorbed by a person are shown. It appears an element called Radon. This is a radioactive gas that comes mainly from the radioactive series of 238U, in form of 222Rn and on smaller magnitude from the 232Th series, in form of 220Rn (Bonotto, D.M., 2014). As it can be appreciated radon radiation represents almost half of the natural radiation received. Location 226Ra 40K 232Th Reference Range Mean Range Mean Range Mea n Rizhao beaches (China) 8-17 12 883-1314 1079 8-25 15 Lu,X. & Zhang, X., 2008 Beaches of Aegean sea (Turkey) 79-1885 290 687-1421 1160 97-4360 532 Örgün, Y., et al., 2007 Sediments of Cadiz Bay (Spain) 3-41 13 105-1342 451 3-73 19 Casas-Ruiz, M., et al., 2012 Montenegrin coast (Yugoslavia) 2-16 8 16-263 150 1-12 7 Vukotic, P., et al., 1998 Rio de Janeiro coast (Brazil) 5-286 33 32-888 253 7-963 95 Veiga, R., et al., 2006 Study of environmental radioactivity in Las Canteras beach 8 The aim of this work is to give a radiological characterization of the most important beaches of Gran Canaria, Las Canteras. For this purpose γ-emissions and αemissions will be measured in order to stablish a baseline of natural an artificial radioactivity present on the area of study, as well as to evaluate the possible radiological hazards related to it. This assessment of the impact of environmental radioactivity, mainly on the bathers, will be obtained by analysing of intertidal superficial sand and water beach samples. After describing the study region, the methodology development in this work is presented. Main results and conclusions of this final degree work are exposed in sections 4 and 5, where, in addition to the radiological impact assessment, we point the possibility of the use of certain measures obtained in this work as tracers of different environmental processes in the beach. In the last section the references used in present study are listed. Finally, an annex, including the method followed to determine an important quantity for alpha radioactivity analysis of the water samples, which was carried out during the traineeship, is added. 2. STUDY REGION The Canary Island are located in the NE of the central Atlantic Ocean, between 27º 37’ - 29º 25’ N and 13º 20’ - 18º 10’ W. The island of Gran Canaria is situated in a relatively central position and its surface is of 1532 km2. It is a volcanic island, originated by a “hot spot” inside the oceanic crust associated to the passive continental margin of the African plate (Figure 2). The volcanic materials emitted during its creation were stacked during different eruptive phases and inactivity periods that happened during the last 14.5 million years. The current morphology of the island was created after three important magmatic cycles and erosive and sedimentary processes inbetween the magmatic cycles. These periods of magmatic activity are known as “Ciclo I or Ciclo Antiguo” during the Miocene. The second one is the “Ciclo II or Ciclo del Roque Nublo” starting at the Early Pliocene. The last one is the “Ciclo III or Ciclo Reciente” that has not finished yet (Pérez-Torrado, F.J., 1992). Figure 1. Annual Dose received by a person and its different sources. Modified from CSN, (2004). Study of environmental radioactivity in Las Canteras beach 15 The activity concentration measurement for the radionuclides of interest where realized with the following methodology:  Radium (226Ra): This was taken as a representative of the 238U decay series. An indirect measurement was made based on the activity concentration value of 214Pb found by analysing the gamma-ray photopeak with energy 351.9 keV.  Thorium (232Th): This was calculated from the activity concentration values of 212Pb and 228Ac obtained following the ISO 11929.  Potassium 40K: This was obtained directly from the analysis of gamma-ray photopeak with energy 1460.8 keV. For water samples the gross alpha activity index was calculated following the equation (Llauradó, M., et al., 2006): 60 alfa alfa i cpm cpmb AE F V     (9) where cpmalfa is the alpha counting rate of the sample in counts per minute, cpmbalfa is the alpha counting rate of the reference sample also in counts per minute. E is the efficiency of the used detector and Fi is the self-absorption factor. This parameter is calculated from an absorption curve that is created with standard of 241Am as it is described in Annex. V corresponds to the volume of the sample, in this case 0.5 L. There is an error associated to this activity that is known as count uncertainty in the determination of gross alpha activity index. For calculate this uncertainty the following equation is used:   2 60 ( ) ( ) alfa alfa i cpm cpmb uA E F V t m t b     (10) In this case cpmalfa, cpmbalfa, E, Fi and V are the same parameters as in the calculation of gross alpha activity. The measurement time is represented by t(m) and t(b), being the measurement time of the sample and the blank respectively. The minimum detectable activity for gross alpha activity index, for a confidence level of 95%, was also calculated with the expression:     11 3.29 2.7 ( ) ( ) 60 alfa alfa i cpm cpmb t m t b t m t b AMD E F V           (11) where cpmalfa is the alpha counting rate of the sample in counts per minute. The alpha counting rate of the reference sample is represented by cpmbalfa and its unit are counts per minute. E is the efficiency of the detector used unit, Fi is the self-absorption factor and V is the volume of the sample in L. The measurement time is represented by t(m) and t(b), being the measurement time of the sample and the blank respectively. Study of environmental radioactivity in Las Canteras beach 16 4.- RESULTS AND DISCUSSION 4.1.- Activity concentration distribution of 226Ra, 232Th and 40K The activity concentration 226Ra, 232Th and 40K for each sample is represented in figure 8. Table 5 shows the average activity concentration of these radioisotopes on each part of the beach is shown. The mean value of points 1, 2, 3 and 4 corresponds to the southern arch, points 5 and 6 to the central arch and points 7, 8, 9 and 10 are used for the northern arch. For each location three different values are presented corresponding to the three different campaigns that were carried out. Activity concentration of 226Ra ranges from 8.4 to 18.5 Bq/kg (mean value 15.4±1.0 Bq/kg), from 8.8 to 19.0 Bq/kg (mean value 14.2±1.0 Bq/kg) and from 6.1 to 20.68 Bq/kg (mean value 14.1±0.9 Bq/kg) in the first, second and third campaign, respectively. Activity concentration of 232Th ranges from 9.8 to 23.4 Bq/kg (mean value 17.2±0.9 Bq/kg), from 11.3 to 23.1 Bq/kg (mean value 16.9±0.9 Bq/kg) and from 8.6 to 27.9 Bq/kg (mean value 18.1±1.3 Bq/kg) in the first, second and third campaign, respectively. Figure 8. Comparison of activity concentration (Bq/kg) of 226Ra (a), 232Th (b) and 40K (c) on each sample in each campaign. (a) (b) (c) Study of environmental radioactivity in Las Canteras beach 17 Campaign Area 226Ra 232Th 40K PLC15 Southern arch 13.2±0.9 13.1±0.7 313± 14 PLC15 Central arch 16.8±1.2 20.9±1.0 632± 28 PLC15 Northern arch 16.8±1.1 19.7±1.0 591± 26 PLC16 Southern arch 12.0±0.9 12.9±0.7 643± 28 PLC16 Central arch 13.9±1.0 15.6±0.8 592± 26 PLC16 Northern arch 16.5±1.1 21.5±1.0 631± 28 PLC16_2 Southern arch 10.6±0.8 12.2±0.8 237± 12 PLC16_2 Central arch 16.5±1.0 21.8±1.1 579± 26 PLC16_2 Northern arch 16.4±1.1 22.1±2.0 646± 29 Table 5. Average activity concentration of 226Ra, 232Th and 40K in Bq/kg in the different zone of Las Canteras beach. Finally the activity concentration of 40K ranges from 124 to 683 Bq/kg (mean value 486±22 Bq/kg), from 407 to 776 Bq/kg (mean value 628±27 Bq/kg), and from 90 to 762 Bq/kg (mean value 470±21 Bq/kg), in the first, second and third campaign, respectively. In all three cases the third campaign is the one with the largest range of activity concentration. The activity concentrations of 226Ra in La Cícer (southern arch) are slightly lower than those found in areas of Playa Chica (central arch) and La Puntilla (northern arch). This behaviour also presents the 232Th. Furthermore, the three campaigns show no significant variations in the mean values of activity concentration for both 226Ra and 232Th along the beach. The 232Th/238U ratio represented by the 232Th/226Ra was calculated and they are maintained throughout the beach with a coverage factor of 2. The 235U has not been detected in any sample. Instead, the average value of activity concentration of 40K show remarkable variations along the beach and on the different time periods. In 2015 the southern arch had almost half the activity of the rest of the beach while in January 2016 there is an significant increase of activity, reaching in the southern arch the values of the central and northern arch. In May 2016 the data show that the values of the southern arch have significant decreasing reaching lower values than on the first campaign. This changes in the activity concentration of 40K might indicate some change on sand composition of the area of the southern arch in the second campaign that made it similar to the rest of the beach. Anthropogenic radioactivity (artificial radionuclides) has not been detected; more specifically 137Cs. Global fallout is associated with the testing of nuclear weapons, and also as a result of the accident of the nuclear power plant in Chernobyl (Aarkrog, A., et al., 1999; Livingston, H.D., 2004). 4.2.- Analysis of 210Pbexcess 210Pb is a radioisotope that comes from the 238U decay series. It is originated after the decay of 226Ra that produces 222Rn, a short-lived gas that then end up producing 210Pb that is in equilibrium with the parent226Ra. As 222Rn is a gas, part of it diffuses upward into the atmosphere and once it arrives there it rapidly decays into 210Pb that is deposited as fallout. Atmospheric fallout, like rain snow and dry deposition, also help to deposit 210Pb on the ground. This 210Pb deposited is known as unsupported or Study of environmental radioactivity in Las Canteras beach 18 excess 210Pb (Mabit, L., et al, 2008; Hülse, P. and Bentley Sr, S.J., 2012). This 210Pbex is obtained by the difference between the activity concentration of 210Pb and the activity concentration of 226Ra, which is assumed in secular equilibrium, measured on the detector (Sanchez-Cabeza, J.A., et al, 2012; Szmytkiewicz, A. and Zalewska, T., 2014). The unsupported lead activity is represented in figure 9 for each sample and for each campaign. The average values for each part of the beach and campaign are shown in table 6. Activity concentration of 210Pbex ranges from 18.5 to 51.2 Bq/kg (mean value 34.4±5.8), from 12.6 to 36.8 Bq/kg (mean value 27.1±6.2) and from 16.2 to 46.4 Bq/kg (mean value 29.4±6.8) for the first, second and third campaign, respectively. While the ranges vary slightly from one campaign to another, the average values of the different parts of the beach show that there is no variation or along the beach or on the different campaigns. These similar values along the beach on the three different campaigns could indicate the idea that the fallout is the factor which determines the constant deposition of 210Pbex through time (Mabit, L., et al, 2008) but, since there are not previous works on this subject in the study area and the samples are only superficial sand, a further study should be done. Campaign Area 210Pbex PLC15 Southern arch 30.3±5.5 PLC15 Central arch 33.4±5.5 PLC15 Northern arch 36.7±6.5 PLC16 Southern arch 25.2±5.8 PLC16 Central arch 24.7±6.5 PLC16 Northern arch 30.2±6.4 PLC16_2 Southern arch 29.0±6.3 PLC16_2 Central arch 31.3±6.9 PLC16_2 Northern arch 28.9±7.2 Table 6. Average activity concentration of 210Pbex (Bq/kg) in the different parts of Las Canteras Beach. 4.3.- Radiological risks assessment For measure the radiological risk assessment the external dose rate, the outdoor annual effective dose (H), the external hazard index (Hex) and the radium equivalent (Raeq) were calculated. These were determinated for each part of the beach. The results are shown in table 7. Figure 9. Comparison of activity concentration (Bq/kg) of 210Pbex on each sampling point in each campaign. Study of environmental radioactivity in Las Canteras beach 19 The external gamma dose rate (D) due to natural radioisotopes at 1 m above the ground level was calculated following the equation (Arnedo, M.A., et al., 2013): 𝐷=0.462𝐴𝑅𝑎+0.0417𝐴𝐾+0.604𝐴𝑇ℎ (12) where ARa, AK and ATh are the activity concentrations of 226Ra, 40K and 262Th in Bq/kg. The units of the external dose rate are nGy/h. The highest values of external dose rates were found on the central and northern arch with a value of 43.4±2.2 and 46.8±2.5 nG/h respectively. These values are lower than the Spain mean which is 76 nGy/h but still are in the range of Spain gamma dose rate that goes from 40 to 120 nGy/h (UNSCEAR 2000). The value of the southern arch is smaller than the Spain mean with a value of 29.8±1.6 nGy/h. Even though these values are smaller than the values found on Spain, comparing with the work of Arnedo, M.A., et al, (2013) the values are near to the Gran Canaria mean value (43.9±2.8 nGy/h). In the case of the southern arch the value also is similar to the value found in that work on Las Canteras beach (31.5±2.4 nGy/h). The outdoor annual effective dose is another type of absorbed dose that is calculated following the equation (Arnedo, M.A., et al., 2013): 6 10  OTFDH (13) where D is the external dose rate given in nGy/h, F is the absorbed to the effective dose conversion factor (0.7 Sv per Gy), T is h per y-1 (8760), O is the occupancy factor (0.2) and 10-6 is the nano to milli conversion factor. The outdoor annual effective dose is given in mSv/y. Again the values of the central and the northern arch (0.053±0.003 and 0.057±0.003 mSv/y respectively) are higher than the value of the southern arch (0.037±0.002 mSv/y). All values on Las Canteras beach are smaller than the world’s average which is 0.07 mSv/y (UNSCEAR 2000). The value found in the southern arch is similar to the value of 0.038±0.003 mSv/y found for Las Canteras beach in Arnedo, M.A., et al, (2013). Another parameter that is useful to measure the radiological risks of an area is the external hazard index (Hex) that is calculated with the equation (Elisha, J.J., et al., 2013): 𝐻𝑒𝑥=𝐴𝑅𝑎 370+𝐴𝑇ℎ 259+𝐴𝐾 4810 (14) where ARa, AK and ATh are the activity concentrations of 226Ra, 40K and 262Th in Bq/kg. In this case the value of Hex for each part of the beach must be less than 1 in order to keep the radiation risks insignificant. In all the three areas of the beach the value was under the unit with a maximum value of 0.26±0.01 on the northern arch and a minimum Table 7. The external gamma dose rate, outdoor annual effective dose rate, the radium equivalent and the external hazard index for the different parts of Las Canteras beach. Area D (nGy/h) H (mSv/y) Hex Raeq (Bq/kg) Southern arch 29.8±1.6 0.037±0.002 0.17±0.01 60.7±3.3 Central arch 43.4±2.2 0.053±0.003 0.24±0.01 88.6±4.5 Northern arch 46.8±2.5 0.057±0.003 0.26±0.01 95.4±5.1 Study of environmental radioactivity in Las Canteras beach 20 value on the southern arch of 0.17±0.01. The value of the southern arch is also similar to the value of 0.18±0.01 found in Arnedo, M. A., et al, (2013) for Las Canteras beach. If the sand were to be used as building material the last parameter that should be calculated is the Radium equivalent activity (Raeq). This allows the comparison of the activity concentration of samples with different amounts of 226Ra, 232Th and 40K. It is calculated with the equation (Elisha, J.J., et al., 2013): 𝑅𝑎𝑒𝑞=𝐴𝑅𝑎+1.43𝐴𝑇ℎ+0.077𝐴𝐾 (15) where ARa, AK and ATh are the activity concentrations of 226Ra, 40K and 262Th in Bq/kg. The highest value was found on the northern arch, with a value of 95.4±5.1 Bq/kg, and the smallest value was found on the southern arch, 60.7±3.3 Bq/kg. The average value found in Las Canteras beach (81.6±4.3) is similar to the overall average value of Gran Canaria (91.3±5.9) given in the work of Arnedo, M.A., et al., (2013), and is also less the safe limit value of 370 Bq/kg. Instead, the value for Las Canteras beach found in that work (64.9±5.1) was smaller than the mean value found in this work but similar to the value of the southern arch. 4.4Gross alpha activity concentration on seawater Gross alpha activity concentration for each sample and for each campaign is given in table 8. The activity concentration and the minimum detection limit is given in Bq/L. Sample Area Gross-α MDA APLC16_1 Southern arch 0.120±0.003 0.0007 APLC16_2 Peña la vieja 0.099±0.004 0.0011 APLC16_3 Northern arch 0.084±0.004 0.0011 APLC16_2.1 Southern arch 0.114±0.005 0.0012 APLC16_2.2 Peña la vieja 0.089±0.003 0.0009 APLC16_2.3 Northern arch 0.098±0.003 0.0007 Table 8. Gross alpha activity and the minimum detection limit in Bq/L for each sample on each part of the beach. As it can be observed on the southern arch gross alpha activity values are higher than on the rest of the beach with values of 0.12±0003 Bq/L for the first campaign and 0.114±0.005 Bq/L on the second campaign. On the rest of the beach the values are not higher than of 0.1 Bq/L. Since the gross alpha activity presence is mainly due to uranium, specifically 234U and 238U, and 226Ra (Degerlier, M. and Karahan, G., 2010; Otansev, P., et al., 2016) the higher value found on the southern arch could be an indicator of the presence of this element on that part of the beach and this could be due to some input of continental waters in the area of the southern arch. However, since there is not any study that gives information about this discharges water another study should be made in order to support this hypothesis. In table 9 the average value of gross alpha activity in Las Canteras beach is compared with the activities found in sea water in other parts of the world. Study of environmental radioactivity in Las Canteras beach 21 Table 9. Average gross alpha activity values in Bq/L for sea water samples in different parts of the world. It can be observed that the gross alpha from Chonburi in Thailand and the value of Las Canteras beach are very small. Within the rest of the values, the Marmara sea is the only place where a value smaller than the one in Las Canteras beach is found. 5.- CONCLUSIONS 1.- An assessment of the radiological environmental impacts was performed in Las Canteras beach. For this purpose the radionuclides present in samples of intertidal sand and water were evaluated. The main conclusions obtained for this analysis have been: For sand samples: a) Mean activity concentrations of the natural radionuclides were 14.6±1.0 Bq/kg for 226Ra, 17.4±1.0 Bq/kg for 232Th, 528±24 Bq/kg for 40K and 235U was not detected. b) These obtained values in Las Canteras beach are within the normal values. c) Artificial radionuclides, specific 137Cs, were not found. d) The outdoor annual effective dose in Las Canteras beach had a mean value of 0.048±0.003 mSv/y. This is below the world’s average value (0.07 mSv/y). e) This study provides a useful current baseline for the detection of any future radiological alteration in Las Canteras. For water samples: a) The mean value of gross alpha activity is 0.101±0.003 Bq/L. This value is similar to the value found in other parts of the world. b) The mean value of gross alpha activity is also similar to the mean value of uranium on seawater (0.0814 Bq/L). 2.- The activity concentration of 40K on the southern arch show a significant variation between the campaign of June 2016 and the other two. This might suggest the use of 40K as a tracer for the sedimentary dynamic of the beach. 3.- With respect to 210Pbex, the mean activity concentration are similar along the beach and in the different campaigns. It could indicate that the fallout is the main factor which determines the deposition of 210Pbex along the beach. 4.- The gross alpha activities are slightly higher on the southern arch than on the other zone of the beach. This could be an indicator of the submarine ground water discharges in the southern arch. 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