Deposition patterns of atmospheric 7Be, 210Pb, 40K in cost of west Mediterranean sea, Málaga (Spain)

DEPOSITION PATTERNS OF ATMOSPHERIC 7BE,210PB AND 40K IN COST OF WEST MEDITERRANEAN SEA, MALAGA (SPAIN) 1C. DUEÑAS, 1E. GORDO, 1S. CAÑETE 2E. LIGER, and 3M. PÉREZ and 1M. Cabello 1Department of Applied Physics I, Faculty of Sciences. 2Department of Applied Physics II, Faculty of Computer Engineering. 3Deparment of Radiology , Faculty of Medicine. University of Málaga (SPAIN) INTRODUCTION. The deposition of radionuclides on the ground is an essential process to understand atmospheric transportation, sedimentation and geological process, being the major removal pathway for airborne particulates. To predict the long-term radiological consequences of an accidental deposition of the radionuclides , it is a prerequisite to know the environmental long-term behaviour of these radionuclides an a relatively large number of values are required for statistically meaningful conclusions. 7Be and 210Pb are radionuclides which have been measured routinely in many places in order to study the description of environmental processes such as aerosol transit and residence times in the troposphere, aerosol deposition velocities and others . 40Kis also a natural radionuclide and has been associated with the arrival of coarse re-suspended material from the Africa continent. The bulk atmospheric deposition of 7Be ,210Pb and 40K has been measured at Málaga, south-eastern Spain from January 2005 to December 2015,on monthly basis. MATERIAL AND METHODS The sampling site is one of the environmental radioactivity monitoring network stations operate by the Spanish Nuclear Security Council (CSN). The sampling point is located above the ground, on the roof of the Faculty of Sciences (24 m.a.s.l.), University of Málaga (4°28′80“W; 36°43´40´´ N). Monthly precipitation and dry fallout samples were routinely collected on a monthly basis using a steel tray 1m2in area as a collecting system and polyethylene vessels of 25L capacity for rainwater samples reservoirs. Measurements by gamma spectrometry were performed to determine the 7Be ,210Pb and 40K activities of the samples using an intrinsic REGe detector. Table 1.- Summary statistics of the activity concentrations of the radionuclides Taking into account the local orography and meteorological features in Málaga, with strong rain events followed by long dry periods, different parameters have been considered to study their influence on the concentrations of these radionuclides: number of African dust outbreaks (days), rainfall amount (mm), rainfall duration, number of dry days and number of wet days. Best significant correlations found are shown in Fig. 2. N AM GM SD MAX MIN CV (%) GI 7Be 132 2.60 2.09 1.60 8.30 0.29 62.3 4.9 210Pb 132 0.40 0.33 0.22 1.32 0.05 57.7 6.5 40K69 0.20 0.16 0.14 0.84 0.02 70.9 6.5 Fig. 1.-Seasonal variation of specific activities of 7Be , 210Pb and 40K Fig. 2.- Scatter plots of radionuclides concentrations and some factors . RESULTS AND DISCUSSION The results from specific activities (in Bq/L) of 7Be, 210Pb and 40K were analyzed to derive the statistical estimates. Table 1 provides the summary of the descriptive statistics such as number of samples (N), arithmetic mean (AM), geometric mean (GM), standard deviation (SD), maximum and minimum values, the coefficient of variation (CV) and Skewness(GI). Figure 3 shows the average of the monthly variations in the deposition fluxes (in Bq/m2month) of 7Be, 210Pb and 40K, as well as the monthly rainfall (in mm). The lowest values were observed from June to September and the highest values from October to April. 7Be, 210Pb and 40K fluxes show respectively the correlation coefficients of 0.88, 0.89 and 0.66 with the rainfall. Table 2.- Results from factor analysis applied on 7Be, 210Pb and 40K depositional fluxes and some parameters. Fig.3.- Depositional fluxes of the three radionuclides during the eleven years study period. ACKNOWLEDGMENT The authors wish to thank to Spanish Nuclear Safety Council (CSN) for financial support and to the Spanish Meteorological Agency (AEMET), for the provision of data used in this study. The specific activity of 7Be exhibit its maximum values in spring (Fig. 1). The higher values of 7Be can be due to the rapid exchange of aerosols between stratosphere and troposphere by contraction of tropopause in the spring season. The specific activities of 210Pb and 40K show minimum values in winter and autumn and maximum values in summer and spring. Winter Spring Summer Autumn 0 2 4 6 8 10 7Be Winter Spring Summer Autumn 0 0,3 0,6 0,9 1,2 1,5 210Pb Winter Spring Summer Autumn 0 0,2 0,4 0,6 0,8 1 40K African dust outbreaks (days) 0 5 10 15 20 25 30 0 2 4 6 8 10 r = 0.26 (p<0.05) y = 2.01+0.06 x 7Be (Bq L-1) Rainfall (mm) 050 100 150 200 250 0 0,3 0,6 0,9 1,2 1,5 y = 0.43-0.001 x r= -0.26 (p<0.05) 210Pb (Bq L-1) African dust outbreaks (days) 0 5 10 15 20 25 30 0 0,2 0,4 0,6 0,8 1 40K (Bq L-1) r=0.42 (p<0.05) y = 0.11+0.009 x 210Pb 40K 7Be (101±14) Bq m-2 month-1 (12.0±1.4) Bq m-2 month-1 (5.6±1.4) Bq m-2 month-1 PC 1 (55%) PC 2 (21%) 7Be 0.885 -0.078 210Pb 0.941 -0.048 40K0.749 0.250 PM10 0.197 0.785 Air temperature -0.407 0.779 Relative humidity 0.724 -0.291 Number of intrusions -0.166 0.796 Rainfall amount 0.930 -0.146 Rainfall duration 0.894 -0.309 The first principal component (PC1) explained 55%of the total variance of the data set. Values listed in Table 2 for PC1 illustrate a positive correlation with fluxes of 210Pb, 7Be, 40K rainfall amount, rainfall duration and relative humidity. The second one (PC2) explained 21%of the total variance. The number of African outbreaks is correlated with PM10 and air temperature due to most of the African outbreaks occurs during the summertime. The 7Be, 210Pb and 40K depositions are significantly correlated with the rainfall amount and rainfall duration. Such relations explained that rainfall constitutes the major depositional pathway of these radionuclides. Radioecol, Sevilla 6 –9 November 2016