Anthropogenic emissions of Po-210, Pb-210 and Ra-226 in an estuarine environment

. .. 1ANTHROPOGENIC EMISSIONS OF 21oPo, 21oPb ANO 226Ra IN AN ESTUARINE ENVIRONMENT A. MARTÍNEZ-AGUIRRE,* M. GARdA-LEÓN,* C. GASCÓ,** A. TRAVESI** *Facultad de Física, Universidad de Sevilla, 41080 Sevilla (Spain) **! nstituto de Medio Ambiente, Ciemat, 28040 Madrid (Spain) An extensive study on the distribution of natural radionuclides in an estuarine ecosystem located in Southwestem Spain is presented. This environment is highly affected by the wastes released by a phosphoric acid industry which uses phosphate rocks as raw material for fertilizer production. This rock has generally high concentrations of U and its daughters. The estuary is formed by two rivers, Odiel and Tinto, which have a common mouth into the Atlanic Ocean and a salt marsh (Odiel marsh) affected by the in come of Odiel riverwaters. This river receives directly the liquid and part of the solid (gypsum) wastes released from the industries. Besides that, most of the phosphogypsum wastes are stored in uncovered piles at the right margin of the Tinto river. The study has concluded that the wastes from such industries are the cause of the enhanced concentrations found at the bed of both river channels as well as the enhancement found in surface soils in certain zones of the Odiel wet marshland. lndeed, the Northem marsh and the Mojarrera channel at the Odiel marsh seem to be the main sinks of the contaminant released by the phosphoric acid industry. On a historical time scale, sediments may be regarded as, at least, a temporary sink for much of the material which passes through the various chemical and biological cycles operating on the earth's surface. At present, the material which is released and takes part in these cycles can have its composition markedly affeéted by anthropogenic emissions. Sediments became an environmental host for many of the waste products discharged by society. Toe effects of these man-made emissions, in sorne situations, can be sufficiently strong to affect highly the composition of the deposited sediment. In the marine environment, near-shore sediments retain the strongest memory of the impact of the released material on the earth 's surface. This is because these sediments accumulate at rates which can be as much as several orders of magitude higher than those in deep sea and because they are being formed in areas in which many anthropogenic substances initially reach the sea. Most industrial complexes are located in estuarine areas close to the sea. Thus, they behave as sinks of much of the anthropogenic emissions, which with time will probably be transported to their close sea environment. Thus. the study of natural environmental radioactivity in estuarine systems is of great importance and interest in health physics and many other purposes. J:;S. Pile• ol pho1phogypsum O 3 km Fig. l. Map of the Estuarine area of Huelva. Bottom sediments from the Odiel and Tinto rivers are denoted by "O" and "T', respectively, followed by a number which indicates the location of the sample. Soil samples from the Odiel marsh are denoted by "M" followed by the number of the station In Spain a large industrial complex is located near the city of Huelva, along the estuary formed by the Odiel and Tinto rivers. A phosphoric acid industry for fertilizer production is located at the left margin of the Odiel river (see Fig. 1 ). Phosphate ores used for phosphoric acid production contain important amounts of natural radioactive elements, specially 238U and daughters, in concentrations that depend on their geographical and geological origin, but which can reach up to 300 ppm for U. Toe radioactive impact of the industrial complex over the Odiel and Tinto rivers has been widely studied for the case of U and Th isotopes.1•2 A dose estimation due to the 222Rn inhalation emitted by the phosphogypsum piles has been also published. 3 Toe movements of these waters due to the flow of the water during change in tide, produce the logical distribution of the contaminant upwards and downwards of the point of release. Next to the rivers, there is a large saline wet marshland. This area is a natural reservation with high biological activity. It is located at the right side of the Odiel river in front of the fertilizer industry and is highly affected by the income of the Odiel river waters. Toe radiological significance of 210Po, 210Pb and 226Ra in the future <lose received by the population motivated the extention of previous works. Toe present paper discusses the results obtained in the study in the presence of these radionuclides in bottom sediments from the Odiel and Tinto rivers as well as in surface soil samples from the wet Marshland. The general aim was to study the reach and influence that the fertilizer production has over all the estuarine area. Experimental Two sampling campaigns were performed in February and November 1993, respectively. In each campaign bottom sediments from the Odiel and Tinto rivers and surface soil sampes from the Odiel Marsh were collected. Bottom sediments were collected at the center of the rivers, whereas soil samples were collected during the low tide in areas covered with water during the high tide. Toe samples were dried, powdered and homogenized before the analysis. Sorne 1 g of sample was spiked with well known 208Po activities. After digestion of the sample with HN03 and aqua regia, Po is extracted by solvent extraction and the final solution is self-deposited onto silver planchets.4 210Po activity is determined by a-spectrometry with surface barrier or ion-implanted detectors. 210Pb and 226Ra are measured by y-spectrometry with Reverse Coated Germanium detectors. 210Pb duplicate analysis were performed in sediment aliquots,5•6 being significantly concordant with those obtained by y-spectrometry. Results and discussion To simplify the discussion, the data obtained on bottom sediments from the Odiel and Tinto rivers for both sampling campaigns will be first discussed. For the sake of clarity, we will denote by "O" those samples collected at the Odiel river and by "T" those from the Tinto river. Samples collected in the confluence of both river will be denoted by "OT". The number following these data will denote the location of the sampling station (see Fig. 1 ). Latelly, data obtained for the same sampling campaigns in surface soils from the Odiel wet marshland will be presented and discussed. Toe location of the soils collected at this area is shown in the same Figure. Code 210p0 01 518 ± 26 02 726± 21 03 4919± 126 04 1300± 100 05 884± 33 TI 76± 10 T2 221 ± 16 T3 1498± 75 OTl 474± 13 OT2 1062± 47 OT3 56± 5 OT4 54± 8 Bottom sediments In Tables 1 and 2 the 210J>o, 210Pb and 226Ra activity concentrations in mBq/g together with sorne activity ratios, for February and November campaigns are presented, respectively. From the results for ali radionuclides in both sampling campaigns,7 it can be concluded that all bottom sediments from the Odiel river present activity concentrations Table 1 Radioactive concentrations in mBq/g in bottom sediments from the Odiel and Tinto rivers collected in Februay 1993 210pb226Ra 506± 31 406± 96 922 ± 38 584± 88 2743 ± 64 3395 ± 198 1176 ± 41 1140 ± 129 763 ± 35 723 ± 65 31 ± 16 70± 20 82±20 �203 914 ± 40 618 ± 110 445 ± 27 211 ± 68 629 ±31 364± 77 20± 15 �67 <26 <62 Table 2 210p0¡210pb 1.02 ±0.08 0.79±0.04 1.79± 0.06 1.16 ± 0.07 2.45 ± 1.30 2.70±0.69 1.64 ± 0.11 1.07 ±0.07 1.69 ± 0.11 2.80±2.11 21 ºPbt226Ra 1.24± 0.30 1.57 ± 0.25 0.81 ±0.05 1.03± 0.12 1.05± 0.11 0.44± 0.26 1.47 ± 0.27 2.11 ± 0.69 1.73 ± 0.37 Radioactive concentrations in mBq/g in bottom sediments from the Odiel and Tinto rivers collected Code 210p0 01 567 ± 38 02 500± 30 03 2080± 140 04 1330± 80 05 1660± 140 T1 T2 233± 16 T3 788± 50 OTI 600± 24 OT2 618± 39 OT3 21 ± 2 OT4 19 ± 2 in November 1993 210pb226R_a 511 ± 86 405 ± 55 419 ± 66 363 ± 75 925 ± 134 972 ± 109 1160 ± 189 831 ± 83 1450±213 1273 ± 112 98± 22 94± 22 73 ± 14 87± 20 733±116 718± 62 408 ± 70 407± 45 529 ± 81 416± 29 �35 �32 15± 10 19± 10 210p0¡210pb 1.11 ± 0.20 1.19 ± 0.20 2.25 ± 0.36 1.15 ± 0.20 1.15 ± 0.19 3.19 ± 0.65 1.08 ± 0.18 1.47 ± 0.26 1.17 ± 0.19 1.27 ± 0.86 21 ºPbt226Ra 1.26± 0.27 1.15 ± 0.30 0.95 ± 0.17 1.40± 0.27 1.14 ± 0.19 1.04 ± 0.34 0.84± 0.25 1.02 ± 0.18 1.00± 0.21 1.27 ± 0.21 0.79± 0.67 ... above background levels. 8 Thus, radioactive concentrations above 470, 445 and 211 mBq/g for 210Po, 210pb and 226Ra, respectively, are found along the estuary of the Odiel river in February. Radioactive concentrations in November are similar to thos� found in February. The highest activity concentration is found, as it was expected, at thc, point of release of the phosphoric acid industry (03), being the radioactivt concentration in February much higher than that in November for ali radionuclides. Tui\ activity concentration decreases downstream the river channel but still high radioactivd concentrations were found at the common confluence with the Tinto river (OTl and OT2). Pattem distributions of 210po and 210Pb along the Odiel river for samples collected in November are shown in Fig. 2. These pattem distributions are similar to that for 226Ra, and reflects ali said above. Samples OT3 and OT4 were collected at the Atlantic Ocean coast close to the mouth of the river. From the data in Tables 1 and 2 for stations OT3 and OT4 is easy to conclude that the contamination in the Odiel river does not yet reach the coast. In fact, radioactive concentrations are similar to typical background levels ( - 25 mBq/g).9 In the case of the Tinto river channel, three samples were collected. The radioactive concentration in both sampling campaigns are similar and excepting station T3, they are 10l 5 CT 'b 4 x 3 2 _210Po ----- 210Pb Fig. 2. Comparison of 210Po and 210Pb activity concentration in mBq/g in bottom sediments from the Odiel river collected in February 1993 lower than those found in the Odiel river channel. Therefore, the exception of station T3, has an activity concentration even higher than in most Jocation of the Odiel rive�. This station is located at the confluence of a small natural rivulet (Estero del Rincón) with the Tinto river. This rivulet crosses the phosphogypsum storage area and probably, it can redissolve part of the radioactivity concentration contained in these wastes. Station T2 also seems to be contaminated. This sample was collected close to an artifical stream which crosses the phosphogypsum storage area. Upstream this stations, the activity concentrations are similar to background. From the results it is clear that the wastes from the phosphoric acid production enhance the radioactive concentrations in bottom sediments from the Odiel and Tinto rivers. However, this contamination seems to be restricted to the estuarine area of the rivers, thus being the radioactive concentrations at the coastal area similar to background levels. It is also interesting to discusse the 21°I>o/210Pb and 210Pb/226Ra activity ratios which are also given in Tables 1 and 2 for February and November campaigns, respectively. The 21 0Po/21°I>b activity ratio reveals the existence of secular equilibrium in those stations less contaminated whereas those highly enhanced show an excess of 21°I>o compared to 21°I>b. The excess is confirmed by the values of this activity ratio in stations 03, T2 and T3. This excess should reflect either a higher presence of 210Po in the wastes from the industries or a different environmental behaviour after the release. Toe excess disappears downstream the river channel. The excess of 210Po found at station STl, located upstream from the phosphogypsum piles in the Tinto river, which seems to be unenhanced by the industries, must be related with the higher 21°I>o association with solid particles. In the case of the 21°I>b/226Ra activity ratio, most stations present values which indicate the existence of secular equilibrium between both radionuclides or a little excess of 210Pb compared to 226Ra. However, station 03 from the Odiel river and T1 from the Tinto river, present a clear excess of 226Ra related to 210Pb (mainly in samples collected in February) given 210Pb/226Ra activity ratios clearly below unity. This situation should be explained in different ways for each sample. Sample 03, was collected at the point of discharge from the phosphoric acid industry into the Odiel river. Thus, the excess of 226Ra should indicate the existence of a similar excess in the wastes. As it is well know, phosphogypsum (mainly CaS04) are enriched in 226Ra comparing with other radionuclides (rom the 238U decay series.10 The equilibrium is restored downstream the Odiel channel due to a higher association of Pb11 to solid phases as well as to the redissolution of 226Ra in saline waters.8,12 Toe case of station T1 located upstream from the industries must be related to a higher presence of 226Ra in solution. Thus, due to the solubility of this radionuclide in natural waters, releases of wastes with high concentration of 226Ra would produce a general increase of 226Ra in solution in compare with uncontamined rivers. This excess of Ra would produce a higher contain of 226Ra in bottom sediments in locations upwards, compared to 21 0Po whk.h has been already incorporated to the sediments. Swface soils In Tables 3 and 4 radioactive concentrations for the same radionuclides and same activity ratios as those for bottom sediments are presented here but for surface soil samples from the Odiel wet marshland. In each Table results for February and November campaigns are presented, respectively. Toe results reveal clearly that the Marsh is also enhanced by the phosphoric acid production.13 Toe activity concentrations are, in general, below the maxima fo�nd in bottom sediments from the Odiel river. However, activity concentrations up to 370, 660 and 500 mBq/g for 210Po, 210J>b and 226Ra, respectively, were found in February, being in November the levels up to 580, 670 and 600 mBq/1 for 210Po, 210Pb and 226Ra, respectively. Besides that, much higher radioactivity concentrations were found in samples collected in the Northern marsh (see Fig. 1) in the campaign of November. In the Odiel river margin of the marsh, eight stations were sampled for soils. These located in front of the fertilizer industries, present radioactive concentrations in the campaign of February only slightly above background concentrations, being those upstream and downstream more contaminated. In November, the station in front of the industries presents the lowest radioactive concentrations, below the concentrations found in February. Thus, it seems that contamination in the transversal direction is not as high as in the longitudinal direction. Of course, this fact must be related with the flow velocity of the river water. Toe differences in stations M20 and M21 between both Table 3 Radioactive concentrations in mB/g in surface soil samples collected at the Odiel wet marshland Code 2JOp0 M6 264 ± 412 M7 290± 31 MIO 341 ± 19 Mll 276± 14 M12 25.1 ± 1.7 M14 108±6 MIS 367 ± 34 M16 117±7 M20 288 ±25 M21 181 ± 14 M22 168±9 M23 124± 8 M24 44.9 ± 2.9 M18 29.0± 1.8 M17 40.5 ±2.3 in February 1993 210pb 226Ra 454 ±27 321 ± 40 424 ±29 280± 43 514±36 326± 56 435 ±30 304± 39 37.4 ± 9.1 26.4 ± 14.8 160±25 143 ± 35 658 ± 30 505 ± 44 137 ± 18 65.4 ± 25.4 125 ±20 �241 125 ± 21 � 148 236 ±25 136 ± 36 205 ±23 76.6± 35.9 34.8 ±6.8 33.2 ± 11.4 34.0± 8.4 34.8 ± 13.7 53.2 ± 6.5 43.3 ± 10.5 2H)po¡2JC>pb 0.581 ± 0.043 0.684 ± 0.087 0.663 ± 0.059 0.634 ± 0.054 0.671 ± 0.169 0.675 ± 0.112 0.558 ± 0.058 0.854 ± 0.123 2.30 ±0.42 1.45 ± 0.27 0.716 ± 0.085 0.605 ± 0.078 1.29 ± 0.26 0.853± 0.217 0.761 ± 0.102 21 Opb¡226Ra 1.41 ± 0.20 1.51± 0.25 1.58± 0.29 1.43 ± 0.21 1.42± 0.87 1.12 ± 0.32 1.30± 0.13 2.10±0.86 1.73± 0.50 2.68 ± 1.29 1.05 ± 0.41 0.98± 0.45 1.13 ± 0.33 Table4 Radioactive concentrations in mBq/g in surface soil samples collected at the Odiel wet marshland in November 1993 Code 210p0 210pb226R_a210p0¡210pb210pb¡226Ra Ml 199± 10 236± 16 166± 25 0.843 ± 0.071 1.42 ± 0.24 M2 778 ± 41 820±27 711 ± 45 0.949 ± 0.059 1.153 ± 0.082 M3 643 ±28 795 ±23 681 ± 36 0.811 ± 0.042 1.167 ± 0.070 M4 210± 11 233 ± 13 242 ± 23 0.901 ± 0.069 o. 963 ± 0.106 M5 222± 11 156 ± 14 161 ± 24 1.42 ± 0.15 0.97 ± 0.17 M6 580±26 673 ± 16 598 ±25 0.862 ± 0.044 1.125 ± 0.054 M7 213 ± 10 287 ± 12 213 ± 21 0.742 ± 0.047 1.347 ± 0.144 M8 130±7 212 ± 14 130± 21 0.613 ± 0.052 1.631 ± 0.285 M9 141 ±7 161 ± 12 149 ± 20 0.876 ± 0.078 1.081 ± 0.166 MIO 188 ± 10 161 ± 13 149 ± 22 1.168 ± 0.113 1.081± 0.182 Mll 64.6±4.0 76.2 ± 12.3 49.0± 18.6 0.848 ± 0.147 1.56 ± 0.64 M12 27.9 ± 2.0 24.8 ± 12.3 46.0± 22.3 1.13 ± 0.56 0.54 ± 0.37 M13 565 ±23 681 ± 23 673 ± 39 0.830 ± 0.044 1.012 ± 0.068 M14 41.0 ± 3.2 18.4 ± 10.1 30.4± 16.5 2.23 ± 1.24 0.605 ± 0.467 M15 441±20 589 ± 21 484± 32 0.749 ± 0.043 1.217±0.091 M16 131 ±7 162 ± 11 134 ± 16 0.809 ± 0.070 1.21 ±0.17 M19 233± 11 268 ± 15 245 ± 26 0.869 ± 0.064 1.094 ± 0.131 M20 16.2 ± 2.5 15.4± 10.1 21.3 ± 16.0 1.05 ±0.71 0.72 ±0.72 M21 37.2 ± 2.5 22.9 ± 10.9 20.3 ± 17.7 1.62 ±0.78 1.12 ± 1.12 M22 44.2±2.5 26.6 ± 11.1 31.7 ± 17.2 1.66 ±0.70 0.84 ±0.57 M23 194±9 121 ± 13 97.3 ± 20.7 1.61 ±0.19 1.24 ±0.30 M18 54.4± 3.7 51.9 ± 11.1 35.3 ± 17.6 0.830 ± 0.044 1.012 ± 0.068 M17 54.7 ± 3.7 51.9 ± 11.1 35.3 ± 17.6 0.68 ± 0.10 2.7 ± 1.7 campaigns must be related to the composition of the samples. Thus, samples collected in November had higher content of sand particles, which was reflected in the density (0.7 and 1.5 g/cm3 dry weight in February and November, respectively), and in the organic content (10% and 1.5%, respectively) of the samples. Concentrations at the east side of the Saltés island, which clearly reveals a contamination, are similar to those found in bottom sediments at the confluence of the Odiel and Tinto rivers (OTl and OT2). Toe differences found in stations at the east side of the Saltés island again must be partially related with the composition of the samples. Thus, values of density and organic content of stations M16 and M14 may reveal that they have a high amount of sandy particles, which produces a decrease in the specific activity of the samples. In general, the differences i11 radioactive concentrations in stations along the Odiel river margin could be due to differences in organic content. If we nonnalize the radioactive concentrations to the organic content of the soil samples, the differences ,,,, between stations are less significative. This effect can be clearly observed in Fig. 3, where the 210Po concentration in mBq/g are compared with the data normalized to the organic content for those soils along the Odiel river margin, which showed wider differences in composition. Only, station M14 does not seem to be contaminated in the same degree as those stations in the vicinity. 300 200 100 M21 M20 M19 M13 M14 M15 M16 Fig. 3. Comparison of 210Po activity concentration in mBq/g of dry soil sample (continuous line) with the 21 Üpo activity concentration nonnalized to the organic content of the soil samples (dashed line) collected along the Odiel river bank of the Odiel marsh in November 1993. Data of normalized concentrations (in mBq/g) have been divided by 10 Besides, that, a set of samples appears in which the influence of the wastes released from the industries is clearly reflected. Thus, soils along the Mojarrera channel have quite high radioactive concentrations. If we consider that the cause of the high activity concentrations found in sediments O 1 and 02 was the movement of the contaminants upstream the Odiel river during high tide, this should be also the cause of the contamination along the Mojarrera channel. Thus, during the high tide the Odiel riverwater flows upstream. Part of this contaminated water will flow to the Northem marsh and the other part will flood the Odiel marsh through the north of the Bacuta island. The same could occur through the south of this island. Of this most of the contaminated water flows into the Mojarrera channel and a small part would flow into the Chate channel. The activity concentration at the Northwest of the Enmedio island decreases downstream thc Chate channel and the Punta Umbría river, where background concentrations for 210Po. 210Pb and 226Ra were found. Thus, the pattem distribution of radioactivity concentrations in soils across the marsh has clearly identified the way of