Overcoming ICP-QMS instrumental limitations for Tc-99 determination in environmental solid samples using radiochemistry

Applied Radia ion and Iso opes 64 (2006) 502–507 O e coming ICP-QMS ins umen al limi a ions o 99 Tc de e mina ion in en i onmen al solid samples using adiochemis y Jose ´Luis Mas a, , M. Ga cı´a-Leo ´n b , J.P. Bolı´ a c a Depa amen o de Fı ´sica Aplicada I, Uni e sidad de Se illa, Escuela Uni e si a ia Poli e ´cnica, C/Vi gen de A ica, 7, 41012 Se ille, Spain b Depa amen o de Fı ´sica A o ´mica, Molecula y Nuclea , Uni e si y o Se illa , Apdo. 1065, 41080 Se illa, Spain c Depa amen o de Fisica Aplicada, Uni e sidad de Huel a, Facul ad de Ciencias, Campus del Ca men, 21071-Huel a, Spain Recei ed 21 Sep embe 2005; accep ed 13 No embe 2005 Abs ac Besides i s capabili ies, quad upole-based ICP-MS coun ing es ablishes se e al limi a ions on 99 Tc analysis in en i onmen al samples. O e coming hese limi a ions equi es he use o adiochemical me hods. We ha e de eloped a new me hod o he de ec ion o 99 Tc by ICP-QMS in solid en i onmen al samples. In o de o imp o e he limi o de ec ion o he echnique, high amoun s o solid samples (X100 g) a e used. Hence, g ea amoun s o he in e e ing elemen s a e in ol ed in he p ocess, and he e o e special emphasis is pu on achie ing a good commi men be ween adequa e ma ix elemen s emo al and a minimiza ion o he limi o de ec ion. The pe o mances o he me hod a e analyzed in e ms o con enien ly defined figu es o me i . The de eloped me hod is applied o se e al allou le el samples. In his way, he eal pe o mances and especially he eal limi a ions o his me hod a e shown. Keywo ds: Techne ium; ICP-MS; Concen a ion ac o ; Decon amina ion ac o 1. In oduc ion 99 Tc (T 1/2 ¼2.11 10 5 yea s) is a low ene gy b-emi e a ising om he fission o 235 Uo 239 Pu a a ela i ely high a e (6%). I s en i onmen al ele ance is well es ablished. Howe e , i s de e mina ion in non-pe u bed si es is di ficul due o he sub-pp le el concen a ions in en i onmen al samples (Eh ha d and A ep, 1978; Ga cı´a-Leo ´n e al., 1984). ICP-MS is becoming a powe ul ool o he analysis o 99 Tc (Mo i a e al., 1991;Tagami and Uchida, 1993; Nicholson e al., 1993). No sys ema ic di e ences we e ound in a ecen in e labo a o y s udy, when he esul s achie ed by ICP-MS we e compa ed o hose o he s p oduced by adiome ic coun ing (McCa ney e al., 1999a). A wide a ie y o adiochemical me hods ha e been de eloped o he measu emen s o 99 Tc in all so o en i onmen samples (E oglu e al., 1998;Kei h-Roach e al., 2002;Go ´mez e al., 2001;McCa ney e al., 1999b). Some o hem a e designed as ou ine me hods: he limi s o de ec ion o he de eloped echniques a e in ag eemen wi h he law egula ions. The adiochemical wo k is minimized as much as possible dealing wi h small amoun o samples (Nicholson e al., 1993;E oglu e al., 1998; Go ´mez e al., 2001;Rameba ¨ck e al., 1998). Howe e , we a e in e es ed in epea ing ou p e ious 99 Tc de ec ion capabili ies achie ed using gas flow coun ing (Ga cı´a-Leo ´n e al., 1984;Sa ´nchez-Angulo and Ga cı´a- Leo ´n, 1988;Ga cia-Leon e al., 1993). To do ha , he ICP-MS echnique is p oposed. Tha should imply a p econcen a ion o 99 Tc. Un o una ely, his echnique is qui e mo e sensi i e o he sample ma ix e ec s han gas flow de ec ion (see below) o Liquid Scin illa ion Coun ing and, u he mo e, dealing wi h a high amoun o sample usually causes he lowe ing o chemical eco e ies (e.g., Nicholson e al., 1993, limi ed he analyzed sample mass o 50 g when sedimen samples we e ea ed). Special a en ion has been paid in he li e a u e o he decon amina ion om Ru a oms due o he isoba ic o e lap om 99 Ru (12.6% na u al abundance). Howe e , o many au ho s i seems ha he p oblem associa ed o he 0969-8043/$ - see on ma e doi:10.1016/j.ap adiso.2005.11.005  Co esponding au ho . Tel.: +34 959019782; ax: +34 954554341. E-mail add ess: [email p o ec ed] (J.L. Mas). p esence o Mo in he analyzed solu ion is no so se ious. On he con a y, we ound unde ou wo king condi ions ha aspi a ing solu ions wi h Mo concen a ions in he ange o 10 ng g 1 (o highe ) would in oduce se e e inc eases in he ins umen al esponse o mass 99. This ac is due o he abundance sensi i i y (50 10 6 ) calcula ed o he middle ange o masses. On he con a y, he in e e ences om 98 Mo hyd ides seem o be less impo an unde ou wo king condi ions. The e ec o o he in e e ences has been p e iously s udied (E oglu e al., 1998;Mas e al., 2002). The e, hei negligible e ec on he mass spec um has been shown. In his pape , we p esen a obus adiochemical me hod designed o he de ec ion o 99 Tc by ICP-MS. This me hod is es ed wi h eal soil samples in o de o show hei pe o mances and limi a ions acco ding o se e al figu es o me i . Fi s , he concen a ion ac o (CF) o Tc is defined as CF ¼M0 M RQ, whe e M 0 is he sample mass submi ed o chemical analysis, M he mass o he final 2–5% HNO 3 acid solu ion, which is aspi a ed by he ICP-MS, and R Q is he chemical eco e y o Tc. Hence, his coe ficien ep esen s he a io o he Tc concen a ion in he solu ion aspi a ed by he ICP-MS o ha concen a ion in he s a ing sample, be o e any chemical analysis. The desi ed me hod should ha e a CF as high as possible. The in e se o he CF, when e e ed o he in e e ing elemen s, has been used in his wo k as decon amina ion ac o (DF); hence, i should be also as high as possible. Finally, he minimum de ec able mass concen a ion (MDMC) o ICP-MS was also used o e alua e he p oposed me hods when hey we e applied o eal samples. I is defined as MDMC ¼ LOD bCF , whe e b(coun s pp 1 ) is he slope o he calib a ion cu e o ou sys em a he ypical wo king condi ions, while LOD is he Limi o De ec ion exp essed in e ms o he achie ed coun ing a e. A comple e discussion on he dependence o MDMC on he di e en a iables o he expe imen (including he p esence o in e e ing iso opes) was published elsewhe e (Mas e al., 2000). 2. Expe imen al 2.1. Ins umen a ion and samples The quad upole ICP-MS Agilen 4500 wi h a Babing on ype nebulize was used o he p esen ed expe imen s. The ope a ing condi ions a e summa ized in Table 1. The yield ace , 99m Tc, was ob ained om medical gene a o s. I s con ibu ion o MDMC a ising om he 99m Tc decay o 99 Tc is negligible, once p o ided ha some gi en condi ions a e ollowed du ing he elu ion p ocess (Mas e al., 2000). The ace was de e mined by measu ing he in ensi y o i s 140.5 keV g-emission using a NaI(Tl) scin illa ion coun e . Mo and Ru concen a ions we e analyzed using he co esponding MERCK VI Ce i-P ep mul i-elemen s anda d solu ion and an ALPHA APS- 100046-2 Ru s anda d solu ion, espec i ely. 99 Tc calib a- ions we e pe o med using successi e dilu ions o an 99 Tc DAMRI s anda d solu ion (Gi -su -Y e e, Cedex, F ance). Di e en es s we e pe o med o op imise and de elop he me hod he e p oposed by using unspiked eal soil samples, which we e p e iously analyzed o o he adio- nuclides (Mas e al., 2001). We conside ha his app oach could be much mo e ealis ic han using s anda d solu ions. The samples we e aken in he Sou hwes o Spain. This a ea is only a ec ed by a mosphe ic allou , a a e y low le el bea ing in mind he e y low la i ude. The samples ha e a e y low o ganic ma e con en and he le els o 137 Cs a e also e y low (o0.7 Bq kg 1 ). The e o e, we can es ima e 99 Tc concen a ions in he ange o 0.07 mBq kg 1 . Ou aim o limi o de ec ion is no so ambi ious. The e o e, his should be a good sample ma ix o he ealiza ion o ou expe imen s, once p o ided ha hei concen a ions o Mo (in he ange o 1–2 ppm) and Ru (up o 1 ppb) assu e he possibili y o using hem o check he DF. The me hod was alida ed analyzing he seaweed samples used in he p e iously men ioned in e compa ison exe cise o 99 Tc (McCa ney e al., 1999a). D . Vale ie Oli e (Sco ish Uni e si ies Resea ch and Reac o Cen e) kindly p o ided us wi h he samples. Finally, se e al samples om he SW o Spain we e analyzed in o de o es he me hod. The so-called DFS sample co esponds o d y allou . I was aken a he oo o he Facul y o Physics o he Uni e si y o Se ille and co esponds o a d y pe iod om Ap il o June 2001. Samples ZM1 and 2 co espond o ma ine sea-g ass Zos e a Ma ina, which we e aken om he coas o Huel a (Sou h–Wes o Spain) in Ma ch 2001. Finally, samples 1SD1 and 1SD4, and 2S1 and 2S2 co espond o o es soil samples collec ed om a Eucalyp us plan a ion also in he p o ince o Huel a in 1997 (Vaca e al., 2001). ARTICLE IN PRESS Table 1 Ope a ing condi ions o he ICP-MS ins umen Radio equency powe (W) 1240 Sampling dep h (mm) 6.3 Ca ie gas (l min 1 ) 1.17 Ex ac ion lens 1 (V) 150 Einzel lens No 2 (V) 5.5 Bias Omega lens (V) 41 Omega minus lens (V) 3 Quad upole ocus (V) 6 J.L. Mas e al. / Applied Radia ion and Iso opes 64 (2006) 502–507 503 2.2. Radiochemical me hod 2.2.1. P e ea men To a po celain beake , 100–125 g pe sample eplica e a e ans e ed and 150 ml o a 5% NH 4 OH solu ion a e pou ed inside. The ace is added and mechanically homogenized while his mix is so ly wa med un il he e apo a ion o ha solu ion. The ea e he sample is educed o ashes a 450 1C o 90 min. Techne ium is dissol ed om he ashes using 8 M HNO 3 in he p esence o 30% H 2 O 2 while wa ming on a ho pla e a 90 1C unde eflux. In his way, we expec ha Tc appea s in he TcO 4  ion o m. The solu ion is fil e ed h ough a Wha man CF/G glass fib e fil e . The p ecipi a e is leached again, and hen he supe na an s a e mixed in o a 1 l p ecipi a e glass. Hence, Tc emains dissol ed in a olume o app oxima ely 100–250 ml 8 M HNO 3 . 2.2.2. Concen a ion A e ha , Tc is educed and p ecipi a ed ollowing a p ocess widely used o wa e samples (Ga cı´a-Leo ´n e al., 1984, 1993;Sa ´nchez-Angulo and Ga cı´a-Leo ´n, 1988). In his case, we p opose his echnique o solid samples. The solu ion pH is u ned o 3–4 by using 5% NH 4 OH. A sui able mass o FeSO 4 7H 2 O (see Sec ion 3 o de ails) is added in o de o educe he Tc o he +IV alence s a e. A ce ain mass o FeCl 3 is also added as a p ecipi a ion ca ie . The ea e , he solu ion is adjus ed o pH 9 using NH 4 OH, and he cop ecipi a ion o Tc occu s. This p ecipi a e is dissol ed wi h 3 M H 2 SO 4 (Nicholson e al., 1993;Sa ´nchez-Angulo and Ga cı´a-Leo ´n, 1988; Ga cia-Leon e al., 1993). Then Tc is ex ac ed in o 40–70 ml o TBP, which was p e iously condi ioned wi h he same olume o 3 M H 2 SO 4 . Finally, he echne ium is back-ex ac ed in o 25–30 ml o 25% NH 4 OH, in he p esence o Xylene. In his way, he Tc is concen a ed as he final olume dec eases, and a ce ain ac ion o Ru is emo ed om he sample. This solu ion is no sui able o be di ec ly analyzed by ICP-MS. Thus, ha basic solu ion is gen ly e apo a ed o almos d yness. We ha e no ound losses o Tc du ing he e apo a ion om such a basic solu ion. Then he esidue is dissol ed wi h 0.5 M HNO 3 and he solu ion is adjus ed o 2–5% HNO 3 . This solu ion would be eady o ou ICP-MS sys em. Howe e , many Mo a oms would be p esen in his solu ion acco ding o ou expe imen s. Hence, u he sample pu ifica ion is pe emp o y. 2.2.3. Pu i ica ion An Eich om’s TEVA Spec TM ch oma og aphic esin mic o-column is used ollowing he sol en ex ac ion s ep. Ve y high capaci y ac o s o Tc and Re ha e been al eady epo ed (Tagami and Uchida, 2000). As we will show below, hei pe o mances a e also qui e help ul o emo ing he Mo a oms. The 0.5 M HNO 3 p e iously p oduced is di ec ly loaded on o such a mic o-column, which was p e iously condi- ioned using fi s 5 ml o 8 M HNO 3 and hen 5 ml o a 0.5 M HNO 3 blank solu ion. The mic o-column is washed using abou 40 ml o 2 M HNO 3 o emo e a ac ion o he in e e ing elemen s (Mo and Ru). Finally, he Tc is s ipped using a small olume (app oxima ely 10 ml) o 8 M HNO 3 . Ru is almos o ally emo ed om he solu ion wi h a single p ocess o loading, washing and s ipping wi h his mic o-column (Mas e al., 2004). Howe e , he p ocess mus o be epea ed in o de o imp o e he Mo decon amina ion. This can be done using he same mic o- column, wi hou ema kable losses on Tc e en ion. This app oach has he ad an age o educing ea men cos s wi hou a ec ing he adiochemical quali y o he analysis. The e-loading p ocess has o be ca ied ou as ollows: once he s ipping is done, he d ain is e apo a ed a low empe a u e and he esidue is eco e ed wi h 0.5 M HNO 3 . This app oach is less ime-consuming han dilu ing he fi s s ipping solu ion, as he flow a e h ough he column is small. This scheme could be epea ed wo o h ee imes depending on he ini ial sample mass. Then he las elu ed solu ion is e apo a ed again o nea d yness and eco e ed wi h 2% HNO 3 . Finally, eco e y calcula ion and a om coun ing a e ca ied ou . 3. Resul s and discussion 3.1. P e ea men pe o mances In o de o check he losses o Tc a e he educ ion o ashes, we de eloped a fi s es . A 150 g aliquo o e e y sample ( es soils A, B,y, G) was spiked wi h he ace and educed o ashes as desc ibed abo e. As we show in Fig. 1, his p e- ea men does no p oduce any loss o Tc, since he e en ion is always a ound 100%, being he mass loss in o he same ange al eady de e mined in p e ious wo ks (Mas e al., 2001). An expe imen was ca ied ou o find he adequa e mass o he educing agen . Se e al aliquo s o soil ashes, unspiked wi h he ace , we e fil e ed as desc ibed abo e, ollowing he p e ea men . Each fil a e was spiked wi h he ace in he 99m TcO 4  o m. Di e en amoun s o educing agen we e used and he p ecipi a ion s ep was ca ied ou . The supe na an was eco e ed by cen i uga- ion, and he p ecipi a ion deg ee was measu ed in each solu ion (Fig. 2). Tc ac ion emaining in he solu ion apidly alls down when he educing agen mass is g ea e han 0.05 g pe g am o solid sample. As a esul i was ound ha some 15 g o educing agen pe li e o acid solu ion was su ficien o ge a quan i a i e educ ion and an e ec i e p ecipi a ion o Tc. Tha is qui e di e en om he amoun o 7 g l 1 ound o ainwa e samples (Sa ´nchez-Angulo and Ga cı´a-Leo ´n, 1988). Bu his is no s ange, howe e , due o he di e ences o he s udied ma ix: he leaching solu ion con ains many mo e ma ix elemen s in compe i- ARTICLE IN PRESS J.L. Mas e al. / Applied Radia ion and Iso opes 64 (2006) 502–507504 ion wi h Tc o he educing compound han a ainwa e sample. 3.2. Pe o mances o he me hod Two es soils samples (125 g each) we e analyzed using his me hod, whose pe o mances a e summa ized in Table 2. Mo concen a ion in he solu ions a e a below ou uppe limi o 5–10 ppb; using his in o ma ion, i is possible o assu e ha 99 Tc coun ing could be done in se e al en i onmen al samples wi hou spec al in e e - ences associa ed o concomi an Mo iso opes. I is qui e in e es ing o see ha DF o Molybdenum inc eases almos an o de o magni ude a e epea ing he TEVA esin sepa a ion p ocedu e h ee imes (aliquo S32) ins ead o wo imes (aliquo S31). This ac is in ag eemen wi h ou p e ious s udies (Mas e al., 2004). The chemical yields o Tc a e e y low. This is a consequence o a combina ion o ci cums ances: (1) he used sample masses a e g ea e han 100 g, and in his way, possibly, he ex ac ion e ficiency du ing he acid leaching diminishes in a e y impo an p opo ion. (2) Using 0.5 M HNO 3 du ing he sepa a ion wi h he TEVA Spec esin ins ead o 0.1 M HNO 3 dec eased he esin’s selec i i y o Tc along he washing p ocess (Tagami and Uchida, 2000). I is easy o see ha hese MDMC alues a e smalle han hose achie ed in some o he p e iously men ioned ou ine me hods. Howe e , ou MDMC alues a e highe han he 99 Tc concen a ions epo ed a allou le el (e.g., Tagami and Uchida, 2002). They p e iously p oposed he Tc ola iliza ion om soil samples (Tagami and Uchida, 1993), ollowed by apping in aqueous solu ions. Using his app oach, he e ec i e concen a ion o up o 500–1000 g o soil has been done. Fu he mo e, e ec i e emo al o many ma ix elemen s was achie ed. Un o u- na ely we do no ha e ha kind o usion de ices a ou labo a o y. Howe e , ou limi s o de ec ion a e in a ange o 50–700 imes less han hose Tc concen a ions a ising om hea ily con amina ed places, such as o es soil samples nea o Che nobyl nuclea plan (Uchida e al., 1999). This ac ma ks he limi capabili ies o ou me hod: al hough we a e no ye able o de ec allou le el echne ium, we could easily de ec se e e con amina ion e en s, which could be di ficul o de ec using he ou ine me hods al eady men ioned. I is necessa y o bea in mind ha he capabili ies o his me hod o a g ea e sample mass amoun a e limi ed by he ac ha he only way o e ec i ely emo ing Mo a oms is ela ed o he capabili ies o he TEVA Spec esin (acco ding o ou p e ious esul s, i seems ha he combina ion o p ecipi a ion+LLX does no in oduce a e y e ec i e decon amina ion om Mo). Thus, i necessa y, an al e na i e scheme would conside a ba ch sepa a ion o Tc om Mo mixing he loading solu ion wi h a la ge amoun o esin in o a ba el, and hen epea ing he p e iously explained me hod using a home-made column, ins ead o he comme cially a ailable mic ocol- umns. I can be concluded ha his me hod o e s a good commi men be ween limi o de ec ion and in e e ing elemen DF, a e less han 20 h eal ime analysis. ARTICLE IN PRESS ABCDEFG 100 80 60 40 20 3 4 5 6 0 Soil sample code Pe cen age o 99mTc e ained in he soil (%) Mass losses a e igni ion (%) Fig. 1. 99m Tc e en ion (%) and mass losses (%) a e educing o ashes he soil samples used o check he p e ea men s ep o he me hod. Please, no e he double scaling. &: Pe cen age o ace e ained in he soil. K: Mass losses a e educ ion o ashes. 0.00 0.02 0.04 0.06 0.08 0.10 0.12 100 80 60 40 20 0 Mass o FeSO4⋅7H2O pe g am o solid sample (g g-1) Pe cen age o 99mTc e ained in he supe na an (%) Fig. 2. 99m Tc e en ion (%) in he supe na an as a unc ion o he educing compound (FeSO 4 7H 2 O) mass added o each es soil sample p io o he Techne ium p ecipi a ion s ep (See he ex o de ails). Table 2 Resul s ob ained o he di e en aliquo s o he es soil samples a e applying he di e en me hods explained in he ex Chemical yield (%) CF DF o Mo DF o Ru MDMC (Bq kg 1 ) 32.071.4 4.670.2 487 X9500 0.02 29.071.4 4.070.2 3500 X9500 0.01 J.L. Mas e al. / Applied Radia ion and Iso opes 64 (2006) 502–507 505 3.3. Valida ion o he echnique Due o he lack o e e ence ma e ials o Tc wi h ce ified concen a ions, alida ion o he me hod was ca ied ou using fi e b own algae samples (McCa ney e al., 1999a). Two eplica es we e analyzed o e e y sample (A–E in o de o inc easing adioac i e concen a- ion). Masses anging om 0.5 o 20 g we e used in each analysis, depending on he expec ed concen a ion. The a e age and unce ain y alues a e p esen ed in Table 3. Ou esul s a e in good ag eemen wi h he consensus alues o he in e -compa ison exe cise. Unde hese condi ions, we can assume his me hod as alida ed o a wide ange o echne ium concen a ions. 3.4. En i onmen al samples om he Sou h–Wes o Spain Di e en kinds o samples aken om he Sou h o Spain we e analyzed using his me hod. Ou hypo hesis is ha unde ec able 99 Tc concen a ions a e expec ed, as his iso ope would p oceed mainly om global allou . In his way, we expec o show he eal capabili ies (and, specially, he eal limi a ions) o his me hod. Resul s a e gi en in Table 4. I is easy o see ha almos all he adioac i i y concen a ions o soils a e unde he MDMC, al hough he CFs a e usually high. The mass ac i i y co esponding o he DFS is ac ually equal o he MDMC, in o he unce ain y in e als. This ac shows he ex ao dina ily low amoun s o 99 Tc p esen in samples om egions no di ec ly a ec ed by nuclea indus ies. The o igin o Tc in hese kinds o samples would be ela ed o he mili a y a mosphe ic nuclea es s du ing he second middle o 20 h cen u y. Assuming a mean esidence ime o abou 18 mon hs (Ga cia-Leon e al., 1993), he wo king hypo hesis would be an almos comple e e u n o Tc o he ea h su ace. Ou esul seems o suppo such a hypo hesis. Ou p e ious analysis o ainwa e samples aken a he same loca ion seems o suppo his conclusion (Mas e al., 2004). Fu he mo e, Tagami and Uchida (1996) ecen ly published some o hese da a calcula ed om samples aken a Hi achina a (Japan). They es ima ed Tc concen a ions in d y allou as less han 0.4–0.9 mBq m 2 mon h 1 .Ou esul s show an ac i i y deposi ion equal o (o lowe han) 0.06 mBq m 2 mon h 1 . And hen, e y high ag eemen be ween he e e ed conclusions is obse ed. Rega ding he sea g ass samples, no de ec ion o Tc was possible. This is he expec ed esul , as acco ding o Bohn e al. (1984), he echne ium CFs o hese species a e a leas h ee o de s o magni ude less han o b own seaweed. Bea ing in mind p e ious esul s o b own seaweed collec ed om he same egion, (Manjo ´n e al., 1995), he echne ium concen a ion in sea g ass would be o0.1 mBq kg 1 . Hence, once again, ou esul s below MDMC a e in ag eemen wi h ou hypo hesis, suppo ing he lack o any s ong Tc en ance o his a ea. 4. Summa y and conclusions Measu emen o 99 Tc by ICP-MS in en i onmen al samples equi es decon amina ion om Mo and Ru o a oid isoba ic o e lap and in e e ences due o ins u- men al abundance sensi i i y. A adiochemical me hod has been p oposed o he ea men o di e en kinds o solid samples, which sa is ac o ily decon amina es he sample om Mo and Ru. I couples high sample concen a ion using a cop ecipi a ion-LLX s ep wi h u he solu ion pu ifica ion achie ed by anion exchange ch oma og aphy. A e y in e es ing poin has been ound, as epea ing he sepa a ion wi h a TEVA Spec TM esin g ea ly imp o es he sepa a ion om Mo a oms p esen in he sample; hus, he sensi i i y o he me hod is imp o ed. This e ec is achie ed in a less ime consuming way han dilu ing (o e en e apo a ing o d yness) he leaching solu ion. The g ea e pa o Tc concen a ions ound seems o lie unde he limi s o de ec ion (which is in he ange o se e al en hs o mBq kg 1 ), as expec ed bea ing in mind ha all he samples we e aken om a egion a om any nuclea indus y. Acknowledgemen s The au ho s would like o exp ess hei deep acknowl- edgemen o he s a a Cen al Resea ch Se ices (Uni e si y o Huel a) and Radiological P o ec ion ARTICLE IN PRESS Table 3 Consensus alues ob ained o fi e b own algae samples in an in e compa ison exe cise, and he esul s we ound when applying he S3 me hod Sample Consensus alue (Bq kg 1 ) This wo k (Bq kg 1 ) A 5.971.1 4.670.3 B 58.374.6 48.871.0 C (3.9170.13) 10 3 (3.2970.14) 10 3 D (1.79170.078) 10 4 (1.61470.055) 10 4 E (1.3370.12) 10 5 (1.1870.03) 10 5 Table 4 Ob ained esul s o 99 Tc in a d y allou sample (DFS), wo Seag ass (Zos e a Ma ina) samples (ZM1 and ZM2) and ou Medi e anean o es soil samples (1SD1, 1SD4, 2S1 and 2S2) collec ed in he Sou h–Wes o Spain Sample Mass amoun (g) CF MDMC (mBq kg 1 ) 99 Tc (mBq kg 1 ) DFS 125 4.470.1 16 1975 ZM1 35 1.0470.03 70 66719 ZM2 35 0.8470.03 77 60728 1SD1 125 3.6570.06 21 — 1SD4 125 4.3570.04 36 — 2S1 75 3.3770.06 32 779 2S2 90 3.7670.16 30 15726 J.L. 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