Assessing soil quality in areas affected by sulphide mining. Application to soils in the Iberian pyrite belt (Sw Spain)

Mine als 2011, 1, 73-108; doi:10.3390/min1010073 mine als ISSN 2075-163X www.mdpi.com/jou nal/mine als/ A icle Assessing Soil Quali y in A eas A ec ed by Sul ide Mining. Applica ion o Soils in he Ibe ian Py i e Bel (SW Spain) Isabel González *, Emilio Galán and An onio Rome o Depa men o C ys allog aphy, Mine alogy and Ag icul u al Chemis y, Uni e si y o Se ille, Apdo. 553, Se ille 41071, Spain; E-Mails: [email protected] (E.G.); [email p o ec ed] (A.R.) * Au ho o whom co espondence should be add essed; E-Mail: [email p o ec ed]; Tel.: +34-954-556-318; Fax: +34-954-557-140. Recei ed: 1 Sep embe 2011; in e ised o m: 21 Oc obe 2011 / Accep ed: 25 Oc obe 2011 / Published: 7 No embe 2011 Abs ac : The cha ac e iza ion, e alua ion and emedia ion o pollu ed soils is one o he p esen en i onmen al challenges o be add essed in he coming yea s. The o igin o ace elemen s in soils can be ei he geogenic o an h opogenic, bu only he la e is in e es ing om a legal poin o iew. The haza d o he pollu an s in he soils no only depends on hei o al concen a ion, bu pa icula ly on hei a ailabili y. The mobili y o he ace elemen s depends on hei specia ion, and i is also a ec ed by se e al soil pa ame e s. Mining ac i i y is one o he mos impo an an h opogenic causes o soil pollu ion. As a case s udy, his wo k is ocused in he Rio in o mining a ea (Ibe ian Py i e Bel , IPB, SW Spain). The IPB is one o he mos impo an me allogenic p o inces in he wo ld and i has been exploi ed o housands o yea s. The disposal o mining esidues has p oduced impo an sou ces o con amina ion by ace elemen s and acidic wa e s a ec ing soils and i e s. In addi ion o hese p oblems, he closu e o mines in he Py i e Bel a he end o he 20 h Cen u y has led o a g ea loss o employmen , which has caused he de elopmen o an in ensi e ag icul u e o ci us ui s as a new sou ce o income. The in ensi e g owing o ci us ui s and he adi ional subsis ence ag icul u e ha e been de eloped su ounding he mining a eas and on loodplains nea o mining si es. The le el o soil pollu ion has no been aken in o accoun in hese cases, no has i s impac on he heal h o he inhabi an s o hese a eas. The e o e, i is o g ea in e es o s udy he cu en s a e o he cul i a ed soils and he sou ces and ypes o con aminan s de i ed om mining ac i i y in o de o p og am i s decon amina ion, whe e app op ia e, acco ding o legisla ion. In o de o know he p esen and u u e haza d posed by he soils chemical and mine alogical specia ion has been ca ied ou , gi en ha he a ailabili y o a me al depends on he phase OPEN ACCESS Mine als 2011, 1 74 in which i is ound. The esul s showed ha mining ac i i y has caused high le els o As, Cu, Pb and Zn in se e al cul i a ed soils. Mo eo e , Cu, Pb and Zn showed a high bioa ailabili y. This sugges s ha a leas o he s udies a e necessa y o p ese e heal h in he inhabi an s o his a ea. The me hodology ca ied ou in his wo k allowed o selec po en ially pollu ed a eas whe e ag icul u al ac i i ies a e no ecommended. Keywo ds: soil con amina ion; ace elemen s; sul ide mining; Ibe ian Py i e Bel 1. In oduc ion 1.1. Con amina ion and Con aminan s The p esence o ha m ul concen a ions o some chemical elemen s and compounds in soil is a special ype o deg ada ion known as con amina ion. Con aminan s a e always ound in anomalous (highe han usual) concen a ions and gene ally ha e a ha m ul impac on some o ganisms. The o igin o con aminan s is ei he geogenic i hey come om soil pa en ocks, olcanic ac i i y o mine al leaching, o an h opogenic i hey come om haza dous indus ial was e, ag icul u al o mining ac i i ies, o u ban solid was e om households. Howe e , an h opogenic con aminan s a e he only ones legally conside ed as ue con aminan s. The oxici y o a chemical elemen o compound is i s abili y o ad e sely a ec biological unc ions. Wi h he only excep ion o oxins (which a e biogenic), oxic compounds and ma e ials ha e a non-biological o igin. Con aminan s a e mobilized by physical, chemical and biological ec o s. They can lea e soil by ola iliza ion, dissolu ion, leaching o e osion and en e o ganisms when hey a e in a bioa ailable ( ela i ely soluble) o m. Thus, he po en ial o an elemen ––whe he a con aminan o o he wise––passing om soil in o i s solu ion is known as “a ailabili y”. The mo e speci ic e m bioa ailabili y is he deg ee o which a con aminan in a po en ial sou ce is ee o up ake (mo emen in o o on o an o ganism) [1]. Usually, only a small ac ion o each po en ially con amina ing subs ance in a medium is bioa ailable. Al hough con aminan s a e gene ally noxious, some may be ha mless o speci ic o ganisms. Bioa ailabili y is a unc ion o (a) he speci ic physical and chemical o m in which an elemen o subs ance occu s, and (b) he abili y o o ganisms o abso b o inges i . Bioa ailable elemen s can be accumula ed in an o ganism (i.e., bioaccumula ion) a concen a ions up o 3–5 o de s o magni ude highe han hose in hei medium. 1.2. Hea y Me als and T ace Elemen s The pe iodic able includes abou 70 me als, 59 o which a e hea y me als (i.e., me als wi h an a omic weigh exceeding he weigh o i on, which is 55.85 g/mol). This de ini ion excludes me als wi h a lowe a omic weigh , which howe e can also include con aminan s. Such is he case o V, Mn and C , which ha e an a omic weigh o 50.95, 54.44 and 52.01 g/mol, espec i ely. I also happens wi h o he non-me al elemen s such as As, F and P. The e o e i is mo e accu a e o e e o hem as Mine als 2011, 1 75 ace elemen s, e en hough mos ino ganic con aminan s a e in ac hea y me als. Occasionally, soil is con amina ed wi h high concen a ions o majo elemen s such as Na, Fe o Al. T ace elemen s a e p esen a low concen a ions (mg⋅kg−1) in he ea h c us , soils and plan s. Many o hem (Table 1 [2]) a e essen ial o plan , animal and human g ow h, bu can be oxic abo e ce ain concen a ion le els. As a ule, ace elemen s a e oxic i inhaled o inges ed in la ge quan i ies and o e a long pe iod o ime. Fo example, he de iciency and oxici y h esholds o Se, F and Mo di e om one ano he only by a ew pa s-pe -million (ppm) [3]. Table 1. Mic onu ien s and mac onu ien s o op imum wo king o li e o ganisms (collec ed om di e en sou ces by Siegel [2]). T ace elemen s ha a e essen ial mic onu ien s (a ew mg o µg/day) As, Co, C , Cu, Fe, Mn, Mo, Se, V, Zn O he essen ial mic onu ien s F, I, Si Mac onu ien s (100 mg o mo e pe day) Ca, Cl, Mg, P, K, Na, S Non-essen ial ace elemen s * Be, Cd, Hg, (Ni), Pb, Sb, (Sn), Ti * Me als in b acke s can be essen ial. Mos o ace elemen s in soil can be classi ied in i e g oups acco ding o hei chemical o m in soil solu ion, namely: ca ions (Ag+, Cd2+, Co2+, C 3+, Cu2+, Hg2+, Ni2+, Pb2+, Zn2+), na i e me als (Hg, V), oxianions (AsO43−, C O42−, HSeO3−, SeO42−), halides (F−, B −, I−) and o ganome als (Ag, As, Hg, Se, Te, Tl). These g oups a e no mu ually exclusi e and, in ac , some ace elemen s can all in o mo e han one. Typically, he concen a ions o C , Ni, Pb and Zn in soil ange om 1 o 1500 mg⋅kg−1; hose o Co, Cu and As om 0.1 o 250 mg⋅kg−1; and hose o Cd and Hg om 0.01 o 2 mg⋅kg−1 [4]. Table 2 lis s o he usual and anomalous geochemical concen a ions o a a ie y o elemen s [5]. Table 2. No mal and anomalous geochemical concen a ions o se e al ace elemen s in soils [5]. Elemen No mal ange (mg/kg) Anomalous concen a ions (mg/kg) As <5–40 Up o 2,500 Cd <1–2 Up o 30 Cu 2–60 Up o 2,000 Mo <1–5 10–100 Ni 2–100 Up o 8,000 Pb 10–150 10000 o mo e Se <1–2 Up o 500 Zn 25–200 10,000 o mo e F om all o he ace elemen s ound in soil, he ollowing 17 a e especially oxic and a ailable a concen a ions exceeding oxic le els: Ag, As, Bi, Cd, Co, Cu, Hg, Ni, Pb, Pd, P , Sb, Se, Sn, Te, Tl and Zn. Ten o hem (Ag, As, Cd, Cu, Hg, Ni, Pb, Sb, Sn and Tl) a e eadily mobilized in concen a ions exceeding conside ably hei geological le els due o human ac i i ies [6]. The la es US En i onmen al P o ec ion Agency (EPA) lis o p io i y pollu an s includes he ollowing 13 ace Mine als 2011, 1 76 elemen s: Sb, As, Cd, C , Cu, Hg, Ni, Ag, Pb, Se, Tl, Zn and Be, which was no included in p e ious lis s. 1.3. Pu i ying Powe o Soil Soil usually ac s as a p o ec i e ba ie o mo e sensi i e media such as wa e and o ganisms by il e ing, decomposing, neu alizing o s o ing con aminan s. Hence i subs an ially educes hei bioa ailabili y. The pu i ying abili y o soil depends on i s con en s in o ganic ma e , ca bona es, and Fe and Mn oxyhyd oxides, as well as on i s clay con en and mine alogical composi ion, ca ion exchange capaci y, pH, Eh, ex u e, pe meabili y and mic obial ac i i y. The e o e, he pu i ying powe o soil has a limi o each subs ance. I his limi is exceeded, he soil becomes con amina ed and is a sou ce o con amina ion. The load capaci y o soil shows i s abili y o con ol he ad e se impac s o con aminan s and ende hem inac i e o ha mless. Cheng e al. [7] p oposed he Load Capaci y o Ag icul u al Soils o Hea y Me als (LCASHM), which depends on soil p ope ies, he ype and con amina ion his o y, he p esence o oxici y indica o s and a ious en i onmen al pa ame e s. 1.4. The O igin o T ace Elemen s in Soil T ace elemen s p esen in soil can be geogenic o an h opogenic. The p esence o he o me is la gely de e mined by hei geoa ailabili y, which is ha po ion o he o al con en o a chemical elemen o a compound in an ea h ma e ial ha can be libe a ed o he su icial o nea -su ace en i onmen (o biosphe e) h ough mechanical, chemical, o biological p ocesses [8]. Geoa ailable ace elemen s ypically each he soil when hey a e eleased om hei pa en ock because o wea he ing. Toge he wi h me als om olcanic emissions and mine al leacha es, hey cons i u e he so-called “geogenic me als”. The ease wi h which ace elemen s can be eleased om hei pa en ock depends on he s uc u e and he he modynamic s abili y o he ock o ming mine als. Thus, highly polyme ized s uc u es a e especially s able and esis an o des uc ion, and hei s abili y dec eases acco ding o he ollowing sequence o a omic bonds: Si–O > Al–O > X–O. The amoun o geoa ailable elemen s eleased om ocks in o soil is negligible compa ed o hose o an h opogenic o igin. Wea he ing causes ace elemen s o concen a e in soil, bu usually a le els below hei oxic h esholds. E en i hese le els a e exceeded, he e will be almos no isk o oxici y due o high s abili y and he low a ailabili y o hese me als in soil. Ul abasic ocks can con ain la ge amoun s o some ace elemen s such as C , Ni, Cu o Mn. On he o he hand, acid igneous ocks and sedimen a y ocks (sands one and limes one) con ain e y small amoun s o hem. The highes le els o ace me als in soils––inhe i ed om he pa en ock––a e ypically hose o C , Mn and Ni, ollowed by Co, Cu, Zn and Pb, and, a beyond As, Cd and Hg, which a e usually p esen a e y low concen a ions. Anomalous high concen a ions o ace elemen s in soil usually come om me al o es (sul ides, oxides). Me al mining and ex ac ion p oduce ons o was e each yea ; mos o i con ains py i e and o he sul ides whose oxida ion eleases a la ge amoun o ace elemen s in o he en i onmen , especially in o soils. The uppe laye s o soil a ound mining and ex ac ion a eas can con ain high concen a ions o Cu, Ni, As, Se, Cd o Fe among o he elemen s, depending on he pa icula o e. Mine als 2011, 1 77 T ace elemen s in soil can come om a ious o he an h opogenic ac i i ies in addi ion o mining, namely: • Fa ming (i iga ion, ino ganic e ilize s, pes icides, manu e, liming amendmen s and, especially, sewage sludge). • Elec ical powe p oduc ion. Coal bu ning is one o he p ima y sou ces o me al deposi ion in soil. Fo example, he mal powe plan s ypically elease Pb, Ni and V con ained in oil. • Indus ial ac i i ies (pa icula ly i on and s eel making ac o ies, which elease me als con ained in Fe and Ni o es). Hea y indus ial a eas a e ypical sou ces o As, Cd, C , Hg, Fe, Ni, Pb and Zn. • Household ac i i ies. Roughly 10% o all household was e consis s o me als. The e o e, i s bu ial can lead o he con amina ion o g oundwa e and i s ashing o a mosphe ic con amina ion wi h ola ile me als and hei subsequen inco po a ion in o soil. 2. Soil Con amina ion by T ace Elemen s 2.1. Physical S a e and Rela i e A ailabili y o Soil Con aminan s Con aminan s in soil and sedimen s can be p esen in six di e en o ms, namely [9]: pa icles (pa icula e con aminan s), liquid ilms, adso bed, abso bed, and solids o dissol ed ma e in po e wa e . The beha io o a con aminan in soil depends on i s pa icula o m. As a esul , o al concen a ion o ace elemen s in soil may ep esen hei po en ial oxici y in ela ion o ag eed h esholds, bu no an ac ual isk. The e o e, he accu a e assessmen o hei oxici y equi es de e mining no only hei concen a ions, bu also hei physical and chemical o ms, as well as hei a ailabili y, which p o ides a di ec measu e o hei ac ual haza dousness. Las ly oxici y o ace elemen concen a ion in he soil should also be es ed agains some speci ic o ganisms. Ne e heless he ease wi h which a po en ially oxic subs ance can en e he ood chain om soil depends on whe he he me al is in ee o m in he in e s i ial solu ion o in solid o m, and also on he way he me al is bound o soil pa icles and on i s speci ic chemical o m (i.e., i s specia ion). Acco ding o Kaba a-Pendias [10], how s ongly a me al is e ained by soil condi ions dic a es i s ela i e a ailabili y o plan s and hence he isk o i s eaching o ganisms (Table 3). Table 3. Rela i e mobili y and phy oa ailabili y o me als species in soils. Me al species and associa ion A ailabili y-mobili y Simple o complex ca ions in solu ion phase Easy Exchangeable ca ions Medium Chela ed ca ions Sligh Me als adso bed by soil pa icles Sligh Me al compounds p ecipi a ed on soil pa icles A ailable a e dissolu ion Me al bound o ixed inside o ganic subs ances A ailable a e decomposi ion Me al bound o ixed inside mine al pa icles A ailable a e wea he ing and/o decomposi ion Mine als 2011, 1 78 2.2. Con aminan Mobili y in Rela ion o Soil Pa ame e s The mobili y o a me al depends no only on i s chemical specia ion, bu also on a ious soil- ela ed pa ame e s such as pH, o ganic ma e , ca bona es and clay mine als. Thus, no all he exchange ca ions a e equally a ailable; a he , hei a ailabili y depends on he pa icula mine als con aining hem in he exchange complex. Fo example, me als ound in smec i e o illi e do no necessa ily beha e iden ically. Also, i he me al is ound in i s p ecipi a ed o m, he e is no eason why i has o beha e iden ically, whe he i is in a ca bona e, sul a e o phospha e. Likewise, me als in sul ides—which a e ela i ely easily oxidized and dissol ed––will usually beha e di e en ly om me als in silica es, which a e i ually s able in any medium. Usually ace elemen s show a e y low mobili y and accumula e wi hin he op ew cen ime e s o soil as a esul . The e o e hey a e leached in e y small amoun s o he lowe ho izons. Hence an an h opogenic me al p esen a high concen a ions in he uppe soil ho izon will usually be a much lowe le els in deepe laye s. Howe e , his beha io is addi ionally dependen on he p ope ies o he pa icula soil. The ollowing soil a iables a e c ucial wi h a iew o assessing he sensi i i y o soil o con aminan agg essions: • pH. Mos me als end o be mo e eadily a ailable in acid media, whe e hey a e less s ongly adso bed. As an excep ion, As, Mo, Se and C a e mo e mobile in alkaline media. • Tex u e. Clayey soils a e highly e ec i e in e aining me als by adso p ion (o in hei exchange complex o clay mine als). On he o he hand, sandy soils a e unable o ix me als, which can hus easily each he wa e able. • Clay mine als. Clay mine als di e in speci ic su ace a ea and elec ical cha ge. Thus, he highe he speci ic su ace a ea o a silica e is, he highe i s abili y o adso b me als [11]. Howe e , abso p ion by clay mine als is negligible in soils con aining la ge amoun s o o ganic ma e and/o i on oxyhyd oxides which a e mo e e ec i e in his espec [12]. • O ganic ma e eac s wi h me als o o m exchange complexes o chela es. Me als can be adso bed o he ex en o being s abilized as a esul (Cu) o o m highly s able chela es wi h o ganic ma e (Pb, Zn). • Ca ion exchange capaci y. The ca ion exchange capaci y o soil depends on he clay mine als, o ganic ma e , and alence and hyd a ed ionic adius o he me al. The g ea e he adius and lowe he alence a e, he less s ongly he me al will be e ained. • Redox po en ial. The edox po en ial dic a es whe he he me al is p esen in oxidized o educed o m. Eh–pH plo s p o ide in o ma ion abou he s abili y o me al compounds and i is a con enien me hod o p edic ing he esponse o ace elemen s o a change in en i onmen al condi ions. • Ca bona es. The p esence o ca bona es acili a es p ese a ion o a highly alkaline medium and hence p ecipi a ion o ace elemen s. Also, Cd and o he me als end o be abso bed by ca bona es. • I on and manganese oxides and hyd oxides. They a e inely sp ead ac oss soil and hence hey a e highly ac i e. Thei low c ys allini y and small pa icle size make hem highly so p i e o di alen me als especially Cu and Pb, and, o a lesse ex en , Zn, Co, C , Mo, Ni and As. Mine als 2011, 1 79 • Salini y. An inc eased salini y can esul in he mobiliza ion and e en ion o ace elemen s ia wo di e en mechanisms. Fi s , Na and K can eplace me als a ca ion exchange si es, and hen chlo ide and sul a e ions can o m mo e s able compounds wi h p e iously eleased me als such as Pb, Zn, Cu and Hg. The sal s usually make soil alkaline. 2.3. Assessing he Haza dousness o Me als in Soil The haza dousness (mobili y and a ailabili y) o a con aminan can be assessed by using a ious chemical and mine alogical p ocedu es. Whe he a gi en elemen o compound is p esen in a wa e -soluble phase––and hence eadily a ailable o be ans e ed o a plan o li ing o ganism––can be checked by assessing i s mobili y ia i s wa e solubili y. This p ocess equi es he ex ac ion o happen wi h neu al o sligh ly acidic wa e . Ano he way o assessing he ans e abili y o me als (pa icula ly di alen ca ions) o plan s is ex ac ing soil wi h DTPA o 0.05 M EDTA a pH 7 [13]. The e is a wide consensus abou he ac ha his p ocess p o ides qui e an accu a e measu e o he amoun o me al ha plan s can abso b om soil unde egula condi ions [14]. These simple me hods can only be used o disc imina e be ween esidual me al and me al ex ac ed by wa e o a mild o ganic sol en . Howe e he e a e mo e elabo a ed me hods in ol ing sequen ial chemical ex ac ions o ca y ou specia ion o elemen s in soil (i.e., ope a ional specia ion). Also chemical specia ion is used o disc imina e be ween oxida ion s a es o an elemen , and unc ional specia ion, which dis inguishes be ween molecula o ms. The plan a ailable ac ion o an elemen in soil depends on i s chemical and unc ional specia ion (i.e., o i s dis ibu ion among i s di e en species and chemical o ms). Ope a ional specia ion, which is o en e e ed o as simply “specia ion”, is he mos equen choice o soils because i is he simples analy ically and can be i ually implemen ed in any labo a o y wi h usual a ailable means. Howe e , p ope specia ion equi es de e mining he o al concen a ion o each me al and i s di e en chemical species. The selec i i y o each me hod used o his pu pose depends la gely on how as he o ma ion and dissocia ion eac ions o he a ge species occu . Roughly, classical p ocedu es used in his con ex ha isola e and examine each cons i uen sepa a ely, a e subjec o wo majo sho comings, namely: (a) comple e isola ion is e y di icul o e en impossible; and (b) he p ope ies o a componen in a complex mix u e a e no addi i e owing o he many in e ac ions i can ha e wi h o he componen s. Sequen ial ex ac ions do no allow us o comple e ull specia ion p ocesses bu hey can be use ul o cha ac e ize he beha io o a con amina ing elemen as hey allow i s con en in he ac ion associa ed o each soil componen ela ed o i s mobili y and ans e abili y o li ing o ganisms. In summa y, sequen ial ex ac ion p ocedu es can p o ide ough es ima es o he dis ibu ion o ace elemen s in di e en soil phases and hei ela i e mobili y. Sequen ial ex ac ion p ocedu es ha e been a ound o a leas ou decades. Du ing ha ime hey ha e been con inuously modi ied and upda ed, o e en eplaced wi h o he s p ocedu es p o iding us wi h imp o ed esul s abou speci ic elemen s and soil phases. Hall e al. [15] e iewed he mos widely used specia ion sequences o me als in soils and sedimen s. The p ocedu e essen ially in ol es ob aining a ious consecu i e ac ions by ex ac ing p ocedu es wi h di e en sol en s o de e mine Mine als 2011, 1 80 he dis ibu ion o ace elemen s in a solid sample be ween i s cons i uen phases. Such a dis ibu ion is usually called pa i ioning. López Julián and Mandado [16] c i ically e iewed a ailable specia ion me hods o his kind and hei ope a ional p o ocols. One o he mos popula p o ocols was ini ially p oposed by Tessie e al. [17]. I has been he subjec o a numbe o a ia ions [18-21]. B ie ly, he p ocedu e is as ollows: ac ions 1 o 3 (F1–F3) a e he esul s o ex ac ion wi h ammonium ace a e, a educ i e solu ion made o hyd oxylamine hyd ochlo ide in ace ic acid, and hyd ogen pe oxide in a ni ic medium, espec i ely, whe eas ac ion 4 (F4) is he insoluble esidue emaining a e he h ee ex ac ions (Table 4). Table 4. Sequen ial ex ac ion scheme o assessmen o pa i ioning o me als in sedimen s gi en by Tessie e al. [17] and modi ied by Galán e al. [21]. F ac ion P ocedu e Acid (F1) NH4Ac 1 M (35 mL), pH 5, 1 h, 20 °C, con inuous shaking (40 pm) Reducing (F2) NH2OH.HCl 0.4 M in ace ic acid 25% (20 mL), 6 h, 96 °C, manual shaking e e y 30 min. Oxidan (F3) HNO3 0.2 M (3 mL) + H2O2 30% (5 mL), pH 2 wi h HNO3, 2 h, 85 °C, manual shaking e e y 30 min.; add H2O2 30% (3mL), pH 2 wi h HNO3, 3 h, 85 °C, NH4OAc 3.2 M (5mL) / in HNO3 dilu ed in 20 ml wi h H2O2, 30 min., 20 °C, con inuous shaking (40 pm) Residue (F4) HF/HNO3/HCl 10/3/2.5 (20 mL), 2 h o d y F1 con ains me als in he exchange complex and hose o ming o being abso bed in ca bona es. The ea men used o ob ain his ac ion in ol es wo s eps: ex ac ion wi h 1 M MgCl2 o 1 h o sepa a e exchangeable ca ions (i.e., hose which can be eplaced wi h o he mo e compe i i e ca ions in clay mine als, amo phous ma e ials, e c.) and ex ac ion wi h sodium ace a e-ace ic acid a pH 5 o 5 h o a ack ca bona es. F2 con ains me als in educible compounds (Mn oxides, and amo phous o low-c ys alline Fe- and, occasionally, also Al-hyd oxides). F3 is he oxidizable phase and con ains o ganically bound (complexed, adso bed and chela ed) ca ions in addi ion o some sul ides. Finally, he esidual ac ion (F4) con ains me als in he mine al s uc u e o each ex ac ion- esis an mine al. O e all, he pe o mance o sequen ial ex ac ion p ocedu es is limi ed by ac o s such as (a) he selec i i y o he eagen s, (b) po en ial edis ibu ion (o e-adso p ion) o elemen s, (c) he expe imen al condi ions used and (d) a sca ci y o e e ence ma e ials, which o en p e en s alida ion and p ecision assessmen . A numbe o ex ac an s a e no ully selec i e o some me als p esen in speci ic geochemical phases. Such is he case o soil con aining la ge amoun s o i on hyd ous oxides, which equi e epea ing hei ex ac ion wi h hyd oxylamine hyd ochlo ide se e al imes. Al e ing he pH o ensu e ha all me als associa ed o he a ge phases will be comple ely eleased [20,21] is also needed. In summa y, sequen ial ex ac ion p o ocols should be used wi h g ea cau ion, bo h when selec ing he speci ic scheme o be applied and when in e p e ing he esul s. Some o he mos impo an c i e ia o alida ing an analy ical me hod (e.g., i s heo e ical backg ound, c oss- alida ion wi h o he echniques and sample-independence o he esul s) canno be applied o hese p ocedu es, which p ecludes alida ion o hei ope a ional esul s. Howe e , hey a e bound o con inue in use, cons an ly being imp o ed and upda ed, un il a uni e sally accep ed s anda d p o ocol is de eloped. Mine als 2011, 1 81 I will happen his way because he in o ma ion hey p o ide abou dis ibu ions bea s a di ec ela ionship o he geochemical beha io and he bioa ailabili y o chemical elemen s in na u e [22]. Cu en ly, analyses o en include a mine alogical s udy o he ac ions ob ained om each ex ac ion. This no only shows us he pa icula elemen s eleased, bu also he speci ic mine als dissol ed by each ex ac an , o be known, i.e., chemical-mine alogical specia ion. Dold and Fon bo é and Dold [23,24], de eloped a specia ion scheme adap ed o sul ide mining esidues which in ol es six s eps and mine alogical analysis o each ex ac in ela ion o he mine alogical composi ion o he sample. Indi ec and semi-di ec me hods o cha ac e izing solid phases by in a ed, X- ay luo escence spec ome y o ene gy dispe si e spec ome y a e being supe seded by di ec specia ion me hods based on mo e sophis ica ed echniques such as X- ay pho oelec on spec oscopy (XPS), ex ended X- ay abso p ion ine s uc u e spec oscopy (XANES), X- ay abso p ion nea -edge s uc u e spec oscopy (XAF) o X- ay abso p ion spec oscopy (XAS), all o which a o d comple e chemical specia ion [25,26]. These echniques p o ide a mo e p ecise desc ip ion o p ocesses abou solid su aces, whe he c ys alline o no , and chemical species a a omic le el. Howe e , some analyses equi e using a synch o on, which is usually inaccessible o many labo a o ies. Also, he ou ine wo k needed o p ocess hund eds o samples makes hese al e na i e p ocedu es a he slow and expensi e unless hey a e used o de e mine a single elemen . Ano he classical way o assessing he mobili y o ace elemen s is by leaching, whe he on si e o a he labo a o y. By using es columns o ba ch es s, one can un iso he ms o adso p ion-deso p ion cu es and model he esul s as a unc ion o pH o he amoun o each con aminan and i s na u e wi h a iew o p edic ing he beha io o a soil. This me hodology can be used in combina ion wi h one o he p e ious al e na i es. Fo example, adso p ion-deso p ion iso he ms can be used join ly wi h specia ion esul s ob ained om sequen ial ex ac ions and me al solubili y modeling condi ions o p edic he geochemical mechanisms go e ning me al leaching and mobili y in soil. The so wa e PHREEQC-2 [27] is among he mos widely used o modeling in his con ex . Al hough all specia ion me hods (ope a ional, unc ional, chemical, chemical-mine alogical, di ec ) and modeling o hei esul s p o ide us wi h a b oad pic u e o he po en ial “a ailabili y” o elemen s in soil and hei ease o abso p ion by plan s, each ype o plan abso bs elemen s in a speci ic way. Thus, some elemen s a e mo e eadily abso bed, and some plan s a e mo e selec i e abso be s, han o he s. Chojnacka e al. [28] de ined he so-called “ ans e coe icien ” o a me al as i s concen a ion in plan issue in ela ion o soil. This coe icien is maximal o Cd, Tl, Zn, Sn and Cu; in e media e o Ni; and minimal o Co, C , Pb, As and Sn. As a ule, he mo e pe sis en a gi en ace con aminan in soil is, he mo e s able i is and he lowe i s bioa ailabili y and oxici y a e. 3. Claim o Soils Con amina ed by T ace Elemen s Whe eas o claim a soil is con amina ed is pu ely an adminis a i e ac ion, o ac ually demons a e i is no an easy ask. Wi hin he con ex o his cu en wo k, con amina ion could be de ined as he p esence o an anomalous high le el o a gi en elemen in he soil. Howe e since no soil in he wo ld is p is ine and comple ely uncon amina ed, i is qui e di icul o de e mine i i has been con amina ed o no . In ac , e e y soil has been unde some kind o human p essu e leading o a g ea e o lesse Mine als 2011, 1 88 Figu e 2. Me hodological app oach ollowed in his s udy. Majo elemen s we e de e mined by induc i ely coupled plasma op ical emission spec ome y (ICP-OES) and mino elemen s by bo h ICP-OES and ins umen al neu on ac i a ion analysis (INAA). Chemical specia ion was done in 11 samples o ag icul u al soils, ollowing he scheme o iginally p oposed by Tessie e al. [17] as subsequen ly modi ied by Galán e al. [21]. The ace elemen s ex ac ed by each sol en we e de e mined spec opho ome ically. Mine alogical specia ion was pe o med on 7 samples selec ed in e ms o hei ace me als con en , i on oxides, and phyllosilica es. Tha was done using XRD o iden i y he mine al phases p esen in he solid esidues le by he di e en ex ac an s in Tessie ’s p o ocol. Fo subsequen cha ac e iza ion, scanning elec on mic oscopy (SEM-EDS) and mic opa icle induced X- ay emission (mic oPIXE) spec oscopy we e also used. Soil sampling a andom. G inding, sie ing, homogenizing S a is ical ea men Discussion CONCLUSIONS pH Chemical analysis Majo (ICP-OES) and ace (ICP-OES, INAA) Mine alogical analysis Global sample (DRX, Powde Me hod) <2µm acción (AO, EG, 550 °C) Semiquan i a i e analysis Chemical Specia ion (Tessie ) Bioa ailabili y. Acid wa e and EDTA ex ac ions Cha ac e iza ion SEM-EDS and P ó on Mic obeam (mic oPIXE) XRD o solids esidues al e each ex ac ion Mine alogical Specia ion <2 mm ac ion Mine als 2011, 1 89 Bioa ailabili y was assessed ex ac ing he samples wi h a 0.05 M solu ion o EDTA in sodium o m a pH 7 unde con inuous s i ing o 1 h. Acid-ex ac able me als we e ob ained ea ing he samples wi h wa e acidi ied wi h HNO3 o pH 1 unde con inuous s i ing o 1 h. Bo h ex ac s we e spec opho ome ically analyzed. In o de o con i m some ela ionships be ween elemen s wi h a simila geochemical beha iou in he soils, he esul s we e subjec ed o co ela ion analysis and p incipal componen analysis. Mo eo e , in o de o acili a e spa ial analysis o he da a and mapping po en ially dange ous zones o ag icul u al use, each sample was ela ed o i sel and o all o he s by using a Geog aphic In o ma ion Sys em (GIS). Speci ically, alphanume ic alues we e in oduced as inpu in o a da abase and geo e e enced o ob ain geog aphic loca ion mapping ou pu s and de elop in e ac i e maps o display speci ic da a o he sample conce ned. Tha was done using he so wa e A cGIS . 9.2. All in o ma ion collec ed was eco ded on a e e ence sys em used by he Spanish Geog aphic Ins i u e (IGN) and Spain’s A my Mapping Se ice (SCE) o zone 30 in he 1950 Eu opean Da um (ED-50), which was made compulso y in ou coun y by Dec ee 2303/1970. 5.3. Resul s and Discussion 5.3.1. Cha ac e iza ion o Ag icul u al Soils The soil samples s udied we e ound o con ain high p opo ions o g a el occasionally exceeding 50%. The e o e he soils we e classi ied as sandy g a el. Because o hei sandy na u e, hese soils ha e a low abili y o abso b ace elemen s. In ac only hose in Ne a zones, which we e sligh ly mo e clayey, we e able o e ain g ea e amoun s o he elemen s s udied. Soil pH anged om 4.6 o 7.6, he mos acid samples being hose collec ed e y nea he Peña del Hie o mine, Mon e So ome o and Tha sis (wi h pH < 5.5). These esul s a e simila o hose o con amina ed soils in Mexico [58] and Mendips, England [86]. pH is a e y impo an pa ame e since he concen a ion o hyd ogen ions in soil in luences he bioa ailabili y o ace elemen s and nu ien s. Also, i can be unde s ood as a measu e o soil de iciencies o al e a ion [87,88]. Mos o he me als s udied end o be mo e eadily a ailable a an acid pH. As a ule, he con en s in di alen me als such as Cu, Zn, Ni, Co, Cd and Mn dec eased when inc easing he pH [67,89]. The mine als ound in he samples consis ed mainly o qua z, phyllosilica es and eldspa s. The la e a e calcium plagioclases which explains he high Ca con en s o some samples despi e he absence o ca bona es. The e we e also subs an ial amoun s o hema i e and goe hi e in some samples om Tha sis, Rio in o and Las Delgadas. The high con en in i on oxides o some samples (5–13% Fe2O3)––pa icula ly he ones o m nea he Tha sis and So iel mines, and om some si es in Rio in o ––whe e no hema i e o goeh i e was de ec ed, sugges he p esence o i on gels. This is an in e es ing inding since he high speci ic su ace a ea and chemical eac i i y o hese ma e ials play a majo ole in he so p ion o ace elemen s (pa icula ly me als such as Cu, Pb, and As) [90]. The <2 μm ac ion consis ed o illi e, kaolini e and chlo i e as majo mine als, in addi ion o smec i e in some samples om zones wi h al e ed olcanic ocks (Be ocal, Ma igen a, Zalamea). Some lep osols (soils wi h shales as pa en ocks) we e ound o con ain chlo i e- e miculi e mixed laye s (Peña del Hie o, Rio in o) and illi e-smec i e mixed laye s (Las Delgadas). Unlike o he Mine als 2011, 1 90 con amina ed soils [79], no ja osi e was de ec ed in any sample since hei pH, abo e 3, p ecluded i s o ma ion. The soils we e poo in alkaline and alkaline-ea h me als. Thei con en s in CaO, K2O, MgO and Na2O ne e exceeding 5%. These esul s a e consis en wi h hose epo ed by Chopin e al. [76] o Tha sis soils, and hose epo ed by Fe nández Caliani e al. [77], Ba ba e al. [83] and López e al. [80] o o he simila ly con amina ed soils in he Ibe ian Py i e Bel . The spa ial dis ibu ion o majo elemen s in soils explains he exis ence o a zone wi h an inc eased abundance o i on and manganese associa ed o olcanic ocks (Figu e 3), which is iden i ied in he sou h o he s udy a ea [91]. Figu e 3. Spa ial dis ibu ion o Fe and Mn oxides o samples s udied a Rio in o Mining Dis ic . The ace elemen s s udied included As, Cd, Co, Ni, Cu, Pb and Zn, which a e especially abundan in soils a ec ed by sulphide mining [4]. All o hem can be ound in he US EPA p io i y pollu an lis . The con en s in As anged om 19 o 994 ppm and peaked in he samples ex ac ed om Tha sis (994 ppm) and So iel (882 ppm), which clea ly exceeded he a e age alue (227 ppm). This is logical i we conside hese samples we e unde he di ec in luence o dumps and we e hus mine soils. The con en s in Pb anged om 40 o 4,900 ppm. The highes alues belong o he samples ex ac ed om Tha sis (2,650 ppm) and So iel (4,890 ppm). Those o Zn anged om 95 o 900 ppm and hose o Cu om 27 o 1,160 ppm; he la e , howe e , we e high in mos samples and clea ly exceeded he egional backg ound le el o his elemen [85]. The Co, C and Ni con en , which we e no oo high, exceeded hei espec i e egional backg ound le els o Las Delgadas, Ma igen a and Zalamea zones. The anomalous high le els hey show we e possibly geogenic and associa ed o he pa en ock [84]. Mine als 2011, 1 91 Excep o Cd, all he elemen s exceeded he le els o he 95 pe cen ile in Andalusian soils and he 90 pe cen ile o he geological domain o he Sub-Po uguese Zone [85]. In he ag icul u e soils, which we e no di ec ly unde he in luence o acid mining d ainage, he ace elemen s con en s exceeded he c i ical eco oxic concen a ion es ablished by Kaba a-Pendias [10], excep o Cd and Zn (Table 7). Also, he mean alues o all elemen s we e simila o hose p e iously ound in Tha sis (Ibe ian Py i e Bel ) by Chopin and Alloway [79]. Table 7. Minimum and maximum alues (mean) o some soils close o mining exploi a ions and e e ence alues. Da a in mg/kg. Soils a ec ed by mining exploi a ion As Cd Cu Pb Zn C Sou h Ko ea [56] 23.3–75.9 (47.7) 2.6–6.1 (4.3) 40–99 (59) 289–948 (477) 275–568 (384) ----- Ko ea [47] 64.8–131 (99.6) ----- 49.6–50.3 (50) 2–11.3 (6.7) 153–322 (237) ----- China [48] ---- 4–24 (8) 11–100 (15) 11–380 (15) 33–1,600 (52) 48 Some se , England [86] ----- 0.5–127 (2.1) 2.8–145 (12) 8–1,000 (52) 14–8,344 (132) Mexico [58] 7–1738 (569) ----- ----- 30–3,450 (312) ----- ----- “La Unión”, Spain [69] ----- 2–322 (41) 36–2,255 (332) 0–19,000 (8) 1,200–53,100 (12.5) “San Quin ín”, Spain [94] ---- (3.76) (57.01) (393) (596) ---- “Tha sis” Spain [79] 2–1519 (94) ---- 20–3,090 (216) 18–6,350 (172) 45–870 (118) ------ “Rio in o” Spain [80] 12–204 (68) 0.3–3.2 (0.53) 47–586 (181) 34–605 (177) 72–795 (197) 48–776 (149) Wo ld no mal alues [4] 6 0.35 70 30 35 ------ Allowable alues [10] 20 3 100 100 300 54 The ac o analysis be ween ace elemen s sugges s an associa ion be ween Cu, Pb, Zn and As on he one hand, and C , Ni, Co and Fe on he o he (Table 8). This is a logical esul because o he p esence o massi e sul ides––and also, occasionally, eins o hese elemen s––associa ed o he olcano sedimen a y complex in he Sub-Po uguese Zone [91]. The p incipal componen analysis con i med hese wo associa ions, which we e ela ed o he po en ial o igin o he elemen s. Thus, C , Ni and Co we e essen ially geogenic, whe eas Pb, Zn, As and Cu we e ma kedly an h opogenic. I should be no ed ha , unlike less con amina ed soils [92-94], none o he ace elemen s we e ela ed o he phyllosilica e con en ound in he soil es ed. Mine als 2011, 1 92 Table 8. Eigen ec o s F1 and F2 a e a imax o a ion. Elemen Fac o 1 Fac o 2 Cu 0.840748 −0.09327 Cd 0.647392 −0.12501 Pb 0.916278 0.067878 Ni −0.16902 0.870814 Zn 0.882436 0.078646 As 0.910778 0.081364 Co 0.130555 0.892078 C −0.26457 0.883246 Fe 0.34058 0.843938 SiO2 −0.15414 −0.72585 Phillosilica es −0.35041 0.568918 Expl.Va 3.951898 3.938739 P p.To l 0.359263 0.358067 5.3.2. Chemical Specia ion O e all, he sum o ace elemen con en s in each sequen ial ex ac ion was compa able o hose in he o al sample acco ding o he INAA and he ICP-OES (Table 9). Al hough some samples exhibi ed e y di e en alues, hey would be accep ed i he combined me al con en s o hei di e en ac ions we e wi hin a ange o ± 10% in ela ion o hose in he o al sample [95,96]. Table 9. Chemical analyses o sequen ial ex ac ions (mg/kg). Samples di ec ly a ec ed by was e ock piles o acid leacha es a e in bold. F ac ion Loca ion Sample As Fe Pb Zn Cd Cu Co Ni To al sample Peña Hie o RT-4-1 77 37,400 145 186 1 212 24 38 Peña Hie o RT-5-1 54 47,500 66 91 0 97 11 39 Peña Hie o RT-6-1 103 46,900 108 215 1 586 12 40 Las Delgadas RT-8-1 18 10,900 39 127 0 80 88 424 Las Delgadas RT-8-2 120 51,500 126 114 0 245 12 43 Ne a RT-20-1 77 51,800 598 795 3 495 15 47 Ne a RT-21-1 204 52,300 563 374 3 482 18 38 Ne a RT-21-2 197 48,400 603 388 1 526 16 41 Tha sis R -28 444 65,600 1,270 667 1 198 41 51 Tha sis R -29 994 88,100 2,650 897 1 443 70 54 So iel R -30 882 70,900 4,890 585 1 1160 19 48 In e changeable Peña Hie o RT-4-1 2 0 2 109 0 6 0 1 Peña Hie o RT-5-1 1 1 5 9 0 4 0 0 Peña Hie o RT-6-1 1 0 1 0 0 20 0 0 Las Delgadas RT-8-1 1 0 1 0 0 2 0 5 Las Delgadas RT-8-2 1 0 14 20 0 9 0 0 Ne a RT-20-1 1 0 1 22 0 4 0 0 Ne a RT-21-1 1 0 1 14 0 8 0 0 Ne a RT-21-2 1 0 1 11 0 7 0 0 Tha sis R -28 5 0 35 211 1 0 N.D. 7 Tha sis R -29 8 0 114 337 1 10 N.D. 18 So iel R -30 20 0 83 15 1 33 N.D. 0 Mine als 2011, 1 93 Table 9. Con . F ac ion Loca ion Sample As Fe Pb Zn Cd Cu Co Ni Labil/ca bona es Peña Hie o RT-4-1 2 180 10 336 0 132 4 1 Peña Hie o RT-5-1 2 126 25 0 0 43 0 1 Peña Hie o RT-6-1 2 39 41 659 0 390 9 8 Las Delgadas RT-8-1 2 248 2 0 0 9 6 47 Las Delgadas RT-8-2 2 89 49 24 0 191 1 3 Ne a RT-20-1 2 28 94 1713 2 268 2 4 Ne a RT-21-1 2 27 48 428 0 96 2 1 Ne a RT-21-2 2 25 54 404 0 98 0 1 Tha sis R -28 20 180 162 26 1 17 N.D. 2 Tha sis R -29 26 2,747 457 202 1 92 N.D. 7 So iel R -30 42 1,371 1,574 342 1 455 N.D. 7 Fe-Mn Oxides Peña Hie o RT-4-1 1 15,174 22 24 2 72 5 2 Peña Hie o RT-5-1 1 20,484 11 8 3 36 1 2 Peña Hie o RT-6-1 1 24,779 19 32 4 276 2 3 Las Delgadas RT-8-1 1 30,348 9 9 5 26 17 39 Las Delgadas RT-8-2 1 20,861 18 7 3 68 1 2 Ne a RT-20-1 1 15,322 60 118 3 177 2 4 Ne a RT-21-1 1 14,106 70 58 2 174 3 2 Ne a RT-21-2 1 14,261 62 50 2 167 2 2 Tha sis R -28 194 47,984 1,259 3,414 0 214 N.D. 31 Tha sis R -29 513 70,834 2,781 5,713 1 390 N.D. 30 So iel R -30 246 42,384 3,877 2,740 1 1,380 N.D. 23 O ganic ma e Peña Hie o RT-4-1 1 1,789 1 13 0 3 1 2 Peña Hie o RT-5-1 1 1,774 1 7 1 1 7 3 Peña Hie o RT-6-1 1 1,384 1 6 0 5 0 2 Las Delgadas RT-8-1 1 2,803 1 5 1 1 3 16 Las Delgadas RT-8-2 1 1,137 1 4 0 2 0 2 Ne a RT-20-1 1 1,306 2 14 0 13 0 2 Ne a RT-21-1 1 1,730 3 9 0 6 0 2 Ne a RT-21-2 1 1,487 3 7 0 4 0 2 Tha sis R -28 15 2,892 99 79 0 57 N.D. 6 Tha sis R -29 39 2,947 158 66 0 126 N.D. 4 So iel R -30 24 2,861 292 180 0 17 N.D. 5 Residue Peña Hie o RT-4-1 71 20,257 110 0 0 0 14 32 Peña Hie o RT-5-1 50 25,114 25 67 0 12 2 33 Peña Hie o RT-6-1 99 20,698 47 0 0 0 1 27 Las Delgadas RT-8-1 13 75,601 26 113 0 43 62 317 Las Delgadas RT-8-2 116 29,413 44 59 0 0 9 36 Ne a RT-20-1 73 35,144 441 0 0 32 11 36 Ne a RT-21-1 200 36,437 442 0 0 198 12 33 Ne a RT-21-2 193 32,627 486 0 0 249 13 36 Tha sis R -28 98 28,157 1,210 861 0 24 N.D. 14 Tha sis R -29 366 14,135 644 961 0 61 N.D. 17 So iel R -30 245 17,395 1,291 112 0 110 N.D. 13 N.D.: no de ec ed. Mine als 2011, 1 94 I should be no ed ha only Cd was p esen in high p opo ions in he exchangeable ac ion. Howe e i s p esence was no haza dous because o hei low o al con en . All o he ace elemen s we e la gely associa ed o i on oxyhyd oxides and he esidual ac ion. These esul s con i m he p esence o amo phous oxyhyd oxides capable o inco po a ing la ge amoun s o me al ca ions [24]. Figu e 4. Sequen ial ex ac ion o se e al ace elemen s in selec ed samples. Samples di ec ly a ec ed by mining was es o leacha es a e highligh ed. A senic and Ni we e associa ed o he i on and manganese oxides ac ion in he samples di ec ly a ec ed by mining was es and o he esidual ac ion in all o he s. Hence i was sca cely p esen in he mos mobile ac ions (Figu e 4). Coppe was p esen in all ac ions, bu la gely associa ed o labile ac ions and i on and manganese oxides i ually in all samples. Lead and zinc we e associa ed o i on and manganese oxides and in he insoluble esidue, bu also o labile ac ions. The ac ha Zn, Pb and Cu we e pa ially associa ed o he exchangeable ac ion ha consis ed o phyllosilica es and ca bona es, sugges s ha hei p esence was a esul o ion exchange in clay mine als o p ecipi a ion as oxides on hei su ace. As 0% 20% 40% 60% 80% 100% RT-4 RT-5 RT-6 RT-8 RT-20 RT-21 R -28 R -29 R -30 Samples Ex ac ed % F1 F2 F3 F4 F5 Fe 0% 20% 40% 60% 80% 100% RT-4 RT-5 RT-6 RT-8 RT-20 RT-21 R -28 R -29 R -30 Samples Ex ac ed % F1 F2 F3 F4 F5 Pb 0% 20% 40% 60% 80% 100% RT-4 RT-5 RT-6 RT-8 RT-20 RT-21 R -28 R -29 R -30 Samples Ex ac ed % F1 F2 F3 F4 F5 Zn 0% 20% 40% 60% 80% 100% RT-4 RT-5 RT-6 RT-8 RT-20 RT-21 R -28 R -29 R -30 Samples Ex ac ed % F1 F2 F3 F4 F5 Cu 0% 20% 40% 60% 80% 100% RT-4 RT-5 RT-6 RT-8 RT-20 RT-21 R -28 R -29 R -30 Samples Ex ac ed % F1 F2 F3 F4 F5 Ni 0% 20% 40% 60% 80% 100% RT-4 RT-5 RT-6 RT-8 RT-20 RT-21 R -28 R -29 R -30 Samples Ex ac ed % F1 F2 F3 F4 F5 Mine als 2011, 1 95 Simila esul s we e p e iously epo ed o soils unde he in luence o mining was e in China and Ko ea [52,97], and he Pb-Zn mine in San Quin ín (Spain) [94]. In conclusion, mos o he elemen s s udied we e adso bed in (o as s uc u al componen o ) i on oxyhyd oxides, o p esen in he esidual ac ion. The e o e, he p esen physical–chemical condi ions o he soils acili a e he immobiliza ion o he oxic elemen s s udied, bu hei cu en le els pose a po en ial haza d ha wa an s assessmen . 5.3.3. A ailabili y and Bioa ailabili y Tes s The ac ion ex ac ed wi h acid wa e con ained all elemen s s udied, some a i ually negligible concen a ions and o he s, including Fe, Mn, Zn, Cu and Pb, a e y high le els (close o he 40% in some samples). As i can be no iced in Figu e 5, As and Ni exhibi ed a high a ailabili y in all samples unde he di ec in luence o a mine dump, maybe because bo h elemen s we e associa ed o i on oxides. Figu e 5. Acid wa e and EDTA ex ac ions in selec ed samples wi hou esul s o Fe, Mn, Pb, Zn and Cu. Samples di ec ly a ec ed by mining was es o leacha es a e highligh ed. The ac ion ex ac ed wi h EDTA also con ained all elemen s. As Figu e 5 shows, As was highly a ailable, especially in soils nea he mines in Tha sis (R 28-29) and So iel (R -30), which con ained EDTA 0 20 40 60 80 100 RT-4-1 RT-5-1 RT-6-1 RT-8-1 RT-8-2 RT-20-1 RT-21-1 RT-21-2 R -28 R -29 R -30 Samples Concen a ion (mg/kg) Ni Co Cd As Acid Wa e 0 20 40 60 80 100 RT-4-1 RT-5-1 RT-6-1 RT-8-1 RT-8-2 RT-20-1 RT-21-1 RT-21-2 R -28 R -29 R -30 Samples Concen a ion (mg/kg) Ni Co Cd As Mine als 2011, 1 96 high le els o ace elemen s. Simila esul s we e p e iously ob ained in ag icul u al soils and ice ields in Ko ea, whe e As, Cu and Zn we e highly bioa ailable and posed se ious heal h haza ds [47]. 5.3.4. Mine alogical Specia ion The XRD esul s ob ained om he di e en ac ions did no allow us o assign he di e en ace elemen s o speci ic mine al phases because he ac ions we e e y simila in mine alogical e ms, and he de ec ion o mino mine al phases was no possible wi h his me hod. The SEM s udy con i med he p esence o he majo mine als de ec ed by XRD (qua z, phyllosilica es, eldspa s and i on oxides) in addi ion o accesso y mine als such as py i e, ba i e, zi con, u ile, monazi e and ilmeni e (Table 10). No associa ion o any ace elemen o clay mine als was de ec ed hough. Mic og aphs e ealed he p esence o i on oxide agg ega es con aining subs an ial concen a ions o Pb and smalle amoun s o As and Sb (Figu e 6). The e we e also isola ed py i e c ys als ans o med in o i on oxides (hema i e) associa ed o no ace elemen . Some samples addi ionally con ained galena. Table 10. Mine alogical composi ion o o al and <2 µm ac ion by XRD and SEM-EDS. Samples di ec ly a ec ed by was e ock piles o acid leacha es a e in bold Loca ion Sample Q Phy Fd Hem V K Ch I O he s Peña Hie o RT-4–1 55 34 6 - T 15 - 83 Ilmeni e, zi con, ba i e, u ile, monazi e and ce iani e Peña Hie o RT-5–1 45 44 6 - 5 35 - 60 Ilmeni e, zi con, u ile and monazi e Peña Hie o RT-6–1 57 38 T - 5 5 - 90 Ru ile, monazi e and ilmeni e Delgadas RT-8–1 7 61 27 T Non quan i iable Py i e Delgadas RT-8–2 52 43 T X Monazi e, ba i e and u ile Ne a RT-20–1 55 40 T X 5 - 5 90 Ba i e, monazi e, u ile, ilmeni e Ne a RT-21–1 53 35 7 - 5 - 5 90 Zi con, ba i e, u ile, monazi e Ne a RT-21–2 59 31 5 - 5 - 5 90 Pb an imonide, cassi e i e, py i e, Pb associa ed o sulphides. Tha sis R -28 56 34 5 T - 21 - 79 Fe oxy-hyd oxides wi h Pb Tha sis R -29 76 24 5 - - 30 - 70 Fe oxy-hyd oxides wi h Pb So iel R -30 80 16 4 - - 15 - 85 Fe oxy-hyd oxides wi h Pb Q: qua z; Phy: Phyllosilica es; Fd: Feldspa ; Hem: Hema i e; V: Ve miculi e: K: Kaolini e; Chl: Chlo i e; I: Illi a; T : <5%. Mine als 2011, 1 97 Figu e 6. SEM image showing a polyc ys alline agg ega e composed o i on oxides, micas, qua z and apa i e. The spec um show Pb, Sb and As peaks. Figu e 7. Composi ional mapping o majo and ace elemen s by means o mic oPIXE (sample 21). Selec ed samples we e subjec ed o a mic op o on p obe (PIXE) s udy in hei <63 μm ac ion. The esul s we e used o p oduce dis ibu ion maps o majo and ace elemen s. Some o hese elemen s such as Al, we e uni o mly dis ibu ed ac oss he s udy a ea (Figu e 7), whe eas o he s (Si, Mn, As, Cu, Pb and Zn) appea ed accumula ed in small g anules. The esul s we e exp essed in quan i a i e o m using he da a acquisi ion so wa e OMDAQ o ans o m he s udy a ea in o a ma ix o 256 × 256 elemen s con aining a PIXE spec um each. Tha p o ided he o e all PIXE spec um o he a ea and he indi idual spec a o each zone o po en ial in e es . This allowed us o Mine als 2011, 1 104 34. Sie a, M.; Díez, M.; Ma inez, J.; Fe nández, J.; Aguila , J. 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