Low-level radioactivity studies in the marine environment of the South of Spain

virlnment Low-level radioactivity studies in the marine en of the South of Spain * G. Manjón, A. Martínez-Aguirre and M. García-León Facultad de Física, UniL·ersidad de Sel'illa, 41080 Sel'illa, Spain In this paper preliminary levels of natural and man-made radionuclides in the South Spanish marine environment are presented. Local man-made sources are found to be the main contributors to the natural environmental radioactivity in such areas while fallout is mainly responsible for the occurrence of artificial radioactivity in our zone. t. Introduction So far, the presence of environmental radioactivity in Andalucía (South of Spah) had not been studied. Thus, since 1988 a largc project for thc determination of natural and man-made radionuclidcs in this region was started. *Work partially supported by the contract PB89-0621 of the Spanish CICYT and the AMA of the Junta de Andalucía. Andalucía (sec fig. 1) occupies the whole South of Spain and the majority of the South of the lberian peninsula. The research programme consists of the measuremcnt of 9<JTc, 137Cs. U-. Raand Th-isotopes and 210Po in a large group of samples, such as seaweed, riverwaters, rainwaters, sediments, etc. (see fig. 1 ). Wc present herc sorne results obtained for the marine sidc of thc environment studied. We will de scribe in the next sections, levels of 99Tc and 137Cs in scawecd samples. U-isotopes and 2Hl Po in rivcrwater and sediment samples will also be givcn. MEOITERRANEAN SEA Q k: '.'Ei' -,.ATI.R SAMPLES D S�.A�"El:.'.J SAMPLES & üNDERGROUND WATERS • RAINWATER SAMPLES • MAIS TCXJNS Fig. l. Map of Andalucía (South of Spain) showing the type of samples and s:::11p!ing stations included in the research project. Thc mcthods for dctcrmination of thc abovc-mcn tioncd isotopcs and thc results obtaincd are outlincd in thc following scctions. 2. Experimental Low-background GM gas-tlow �-counting. -yand a-spcctrometry have been used for ('9Tc, 137 Cs and a-emitter measurcments, respectively. A brief account of the individual methods is given in thc following paragraphs. 2.1. 99Tc A solvent extraction tcchniquc is uscd for 99Tc determination. First, sorne 15-30 g of dried and pow dercd seaweed are spiked with a known 99mTc activity. The sample is then calcinated at 600 º C. The ashes are dissolved with 2% HCI, and technctium is extractcd with tributylphosphate (TBP). Subsequently, Te is back-extracted from the organic phase with 2M NaOH. This solution is electroplated at 0.35 A for 2 h and technetium is deposited onto a stainless steel planchet (1,2]. Due to the relatively soft 99Tc �-spectrum (Emax = 292.3 ke V) an electrodeposition technique for thc preparation of the final source is more adequate than a simple evaporation of the 2M NaOH solution, since in this way self-absorption effects are minimized. The radiochemical yicld Y of thc process is calcu lated by measuring the 99mTc activity rccovcred. This is accomplished with a 76 mm X 76 mm Nal(TI) -y-spec tromctcr, taking advantage of the 140-kcV photon emitted by this radionuclidc. After five or six days, when ali the 99mTc (T112 = 6.02 h) has dccayed, the 99Tc (3-activity from th · samplc is measured. Due to the very Iow 99Tc concentration in nature, a low-level counting technique has to be apTable 1 plicd. Thus, a low-background (0.2 cpm) gas-tlow GM countcr is uscd for (J9Tc mcasurcmcnts. The cfficiency of the detector rcachcs a valuc of 37%. It was calcu latcd with 99Tc standard samplcs of wcll-known activi tics. 2.2. 137Cs mes is dircctly detcrmined by HPGc -y-spectromc try. For that, a givcn mass of dricd and powdcred scaweed is placed in a standard geomctry and counted with the spectromctcr [3]. The detector background is reduced by using a passive lead shielding 1 O cm thick, intcrnally covered with a few mm of copper. The counting efficiency was obtained by counting algae material, in thc standard geomctry. homoge ncously spiked with known mes and 152 Eu activities. 2.3. U-isotopes and 210 Po Thc a-activity from 238 U. 234U, 235 U and 210Po was measured by Si surfacc barricr or ion implanted a spectrometry [4,5]. For that, sorne few grams of dried and powdered sediment are spikcd with known 232 U and 208Po activities. Then the sample is digested with HN03 and aqua regia. The residuc is dissolved in 8M HN03 and the solution filtered into a decantation funnel which contains TBP. After shaking, U and Th pass to the organic phasc while Po and Ra remain in the aqueous phasc. Both phases are scparated. The aqueous phasc is evaporated to near dryness and the rcsidue dissolved with concentrated HCI. After that, Po is self-deposited onto Ni planchets at 60 º C. according to the method of Flynn et al. [6]. lt is important to note that sorne mg of ascorbic acid are added to the electrolyte to avoid the deposition of Fe. The organic phasc is dissolved with xylenc and Th is back-extractcd from it with 1.5M HCI. Thc rcmaining organic phase is mixed with distilled H :!O to back-cx137Cs levels in seaweed samples collected along the coasts of Andalucía region (South of Spain) during 1988 and 1989 Type of Species Number of Activity (dry weight) [mBq/g] alga data mínimum maximum average Brown halopteris scoparia 10 0.7±0.2 2.9±0.3 l.4±0.7 Green ulva rígida 7 0.6±0.5 2.3 ± 0.3 l.4±0.6 Green codium 7 0.7 ±0.3 3.8± 1.7 2.2± 1.1 Brown fucus ó 0.6±0.2 1.5 ±0.3 1.2±0.3 Green sargassum vulgare 6 0.7 ±0.4 2.8±0.6 l.3±0.8 Brown dyctiota dichotoma 2 0.6±0.4 1.4±0.6 l.0±0.6 Brown cystoseira ericoides 2 0.3±0.7 0.8±0.3 0.6±0.3 Brown corallina mediteranea l.6±0.6 Brown cimodocea modosa l.2±0.4 Red holopitis incunous 0.8±0.3 tract U. Thc final solution is dricd and U is clcctro platcd onto stainless steel planchets by the rnethod of reís. [7] and [8]. As for water sarnples, sorne 1 to 5 1 are spiked with a known m U activity and cvaporatcd. Thc rcsiduc is trcated as a scdimcnt samplc for U cxtrac tion. 3. Results 3.1. Levels in seaweed mes and 99 Tc activities havc becn studicd in a widc nurnber of scawccd specics. In table 1 thc mes rnini murn, rnaxirnum and average activity values for sorne of such species are prescnted. Very similar, and low, B7Cs spccific activities, roughly 1.3 rnBq/ g dry weight, are obtained eithcr for the red, brown or green alga species. Such low values do not allow to determine thc best bioindicator for our zonc. On the other hand, sincc there is no local source of radioactivity for our region, the levels obtained seem to be rcprescntative of thc worldwide fallout background in the South of Spain. This idea can be confirmed when our results and the very scarce previous data existing in thc current litera ture are compared. Table 2 n7Cs and ""'Te lcvcls found in fucu!ii spiralis and VC!iiiculo!iius samples collcctc,• along thc South Spanish coa!-ih during 19kK and 19H9. Thc silc numhcr corrcsponds to thc !-iampling sitc shown in thc map of fig. 1. Mean valucs for thc Mcditcr rancan and Atlantic coasts are also givcn. Sampling Activity (dry wcight) (mBq/g} site (date) 1'7Cs l,ltlTc activity activity Palomares (1988) [1] 0,6±0.2 0.25±0.04 Palomares (1989) (1) 1.3±0.5 0.31 ±0.03 Cabo de Gata (1988) [2] 1.6±0.3 O.IS ±0.04 Punta Palomas (1988)(3) 1.1 ±0.4 0.43±0.06 Rota ( 1989) (4) n.m.ª 0.1 ±0.2 Isla Cristina (1989) [5] 1.2±0.5 0.30 ± (l.03 Ayamonte (1988) (6) 1.5 ±0.4 0.14±0.oJ Mediterranean coasts 1.1 ±0.4 0.25±0.13 Atlantic coasts 1.3 ±0.2 0.22+0.11 ª n.m. = not measured Thus, leve Is of 0.8 rnBq/ g wcrc found in Galicia, North-West of Spain, during 1984 [9] and of about 0.9 rnBq/g in the coasts of Portugal during 1985 [10], both for Fucus spccics. They wcrc attributcd essentially to fallout, which supports our previous comment. O Water Samples 6 Sediment 5afflPleS Fig. 2. Map corresponding to the sampling stations of Tinto and Odiel rivers around the town of Huelva (see also fig. 1 ). Table 3 U-isotopes activity concentration. together with the 234U ¡ 2Jsu activity ratio for riverwater samples taken at the Odiel (O) and Tinto (T) rivers. Samples OT were taken at the contluence of both rivers. The pH of the waters are also givcn. See fig. 2. for an easier comprehension of the table. Sample pH Activity concentration [mBq/1) T1 T2 T3 T4 OTl OT2 07 06 05 04 03 02 01 2.0 5.0 5.0 5.5 5.5 6.0 5.5 4.5 4.5 4.5 5.5 5.5 3.0 23NU 170.0± 11.0 37.0± 3.8 24.8± 3.0 26.0± 2.0 31.0± 5.1 31.1± 1.7 30.0± 4.0 '60.0± 8.1 778.0±50.0 206.5± 18.8 13.9± 2.6 20.0± 2.7 66.0± 8.0 350.0±20.2 41.0± 4.1 30.3± 3.4 23.0± 2.0 46.0± 6.4 38.0± 2.0 36.0± 4.6 SO.O± 7.0 777.0±50.0 206.5± 18.9 20.3± 3.11 22.0± 2.8 121.0± 13.0 Activity ratio 2.02±0.06 1.09±0.11 1.22±0.20 0.88±0.10 1.40±0.09 l.22±0.08 1.20±0.18 0.83±0.12 l.00±0.02 1.00±0.07 1.47±0.35 1.10±0.17 1.83±0.30 In table 2, wc present sorne few additional 137es results together with the q9Tc activities in Fucus sam ples. Therc is no differencc, both for mes and 99Tc, betwecn thc activitics obtaincd in thc mcditcrranean and thc atlantic sidcs of the Andalusian coast. eon ccrning thc 99Tc rcsults, vcry similar comments to those given in table 1 for 137es can be made. Thus, an average valuc of 0.2 mBq/g dry weight can be ob scrvcd. which is in modcratc agrccment with valucs found in Galicia [21 and Portugal [10) coasts, of about 0.4 and 0.6 mBq/g dry weight, rcspcctivcly, both dur ing 1985. Table 4 3.2. Lel'el.,· in sedimcnt and ril'envater U-isotopes and 2111Po have been dctcrminated in scdiment and rivcrwater samplcs collectcd at the Odiel and Tinto rivcrs (South-West of Spain). Such rivcrs (scc fig. l and 2) surround a largc indus trial complcx, which includes several phosphate f eriliz ers factories near their mouths at the Atlantic Ocean. It is well known that such facilities produce a clcar radiological impact in their immcdiatc environment [11]. Our rcsults, using U and 210Po as indicators, confirm such obscrvations. In table 3 the U-isotopc activitics found in watcrs of thc Odicl and Tinto rivers are presentcd (sec fig. 2 for an casier comprehension of table 3). In general, thc activities in thc Odicl river are highcr than in the Tinto rivcr. Thus, in thc Odiel waters, a clcar peak of activity can be seen. This corresponds to samples taken ncar the place whcre the phosphatc fertilizer complex is located. It seems, thereforc, that such industries are directly relcasing thcir wastes to thc Odiel rivcr. It does not occur so, for thc case of thc Tinto rivcr. In fact, thc U levels found in its waters are totally compatible with activitics obtained in the Guadalquivir river [12], which crosses our rcgion from East to West, and that havc bcen takcn as a background level for our study. Thc results of samplcs Tl and O 1 are specially intcrcsting. Such waters wcrc takcn near thc sources of the Tinto and Odiel rivers, rcspcctivcly. Thc natural Iow pH of such watcrs favours thc rcdissolution of U from thc bcd of the rivcrs to thc aqucous phasc, which would cxplain thc rclatively high lcvcls of activitics found. Furthcrmorc. this would account for thc high 234U cnrichment obscrved in thcse samplcs. It would be intcrcsting to study the form in which thc wastcs from the fertilizer factorics are rcleased U-isotopes and zwpo activity concentrations (in mBq/g) for sediment samples taken ,:t the Odiel (SO) and Tinto (ST) rivers. Sample SOT was taken at the confluence of both rivers. Sec fig. 2 for and easier comprehension of the table. Sample Activity concentration [mBq/1] :!JNU z35u z3..iu :iwpo ST2 100.0± 7.8 3.60± 0.72 110.0± 8.1 n.m:1 ST3 250.0 ± 1.7 11.0 ± 1.2 260.0 ± 1.7 252.0± 10.0 ST4 277.0± 13.0 l().3 ± 0.8 290.0± 14.0 341 ± 12.0 SOT 264.1 ± 29.6 n.d.h 275.7± 30.8 339.4 ± 13.3 S07 1060.0± 75.0 48.0 ± 4.9 1060.0± 75.0 1194.8 ± 112.2 SOó 42.0± 3.9 2.80± 0.66 45.0± 4.2 41.6± 2.7 sos 1100.0 ± 130.0 55.0 ± 1 o.o 1200.0 ± 130.0 820.9± 50.2 S04 160.0± 11.0 7.7 ± 1.0 170.0 � 12.0 615.2 ± 28.0 ª n.m. = not measured. h n.d. = not detcctcd. into thcir immcdiatc cnvironmcnt. This work is cur rcntly bcing car:-icd out in our group. Howcvcr, from thc data wc prcscnt in table 4. it seems that both river beds, those for Odiel and Tinto rivcrs, are accumulating U and 2111Po adivitics. lndccd, thc lcvels obscrvcd in scdimcnts are clearly highcr, both for U-isotopcs and for 2H>Po, than othcr levcls found in diffcrcnt rivcrs, including Spanish systems [13,14]. Thc case of samplc S06 is not surprising, sincc sorne othcr chemical matcrials, without radioactivity, are bcing rclcascd in such sampling point togcthcr with thc wastcs from thc fcrtilizcr industries. This would contributc to Iowcring the spccific activity. References [1] E. Holm, J. Rioseco and M. García-León, Nucl. lnstr. and Meth. 223 (1984) 204. [2] G. Manjón and M. García-León, An. Fís. 886 (1990) (in Spanish) 63. (3) C.I. Sánchez-Angulo and M. García-León, Nucl. Geo phys. 2 (1988) 69. (4) A. Martíncz-Aguirrc. M.C. Monín and M. Garda-Lcún. to he puhlishcd in J. Radionanal. Nucl. n.�m. (5) A. Martíncz-Aguirrc and M. García-Lc<,n. to he puhlishcd in J. Radioanal. Nucl. Chcm. Lctt. (6) W.W. Flynn, Anal. Chcm. Acta 43 (1968) 221. (7) L. Hallstadim,. Nucl. lnstr. and Mcth. 22J ( 1984) 266. lXJ R. García-Tenorio, M. García-León, G. Madurga and C. Piazza, An. Fís. 882 (1986) 238 (in Spanish). (9) P.I. Mitchell. A. Vidal-Quadras. J.L. Font and M. Oliva. J. Environ. Rad. 6 ( 1988) 77. [ 10) A. Aarkrog, S. Boelskifte, E. Buch. G.C. Christcnsen. H. Dahlgaard, L. Hallstadius. H. Hansen. E. Holm and J. Rioseco, Ris0 National Laboratory Report-R-510 (1987) 74. (11] R.J. Guimond and J.M. Hardin, Radiat. Phys. Chem. 2 (1989) 309. (12] A. Martínez-Aguirrc and M. García-León. in prcpara tion. (13) F. Vera-Tomé and A. Martín-Sánchez, J. Radioanal. Nucl. Chem. 1 ( 1989) 73. (14) M.C. Morón, A. Martínez-Aguirre and M. García-León. Proc. lnt. Conf. on Environmental Radioactivity in the Mediterranean Arca. Barcelona. 1988 (SNE-ENS. 1988) p. 111.