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Case Study: Heavy metal Bioavailability in a soil affected by mineral sulphides contamination following the mine spillage at Case Study: Heavy metal bioavailability in a soil affected by mineral sulphides contamination following the mine spillage at Aznalcóllars (Spain) Clemente et al., Biodegradation, 2003 Aryani Sumoondur Environmental Geosciences, Spring 2005 * background of the study, the methods used, and processes behind the results that were found Los Frailes tailings dam failure, Aznalcóllar, Spain (April, 1998) * Tailings Tailings are waste material from the mining industry. As ore bodies are extracted the valuable mineral is surrounded by gangue (uneconomic material) that needs to be separated in a concentrating process. Crushing and grinding methods are used to reduce the mined ore to sand and silt sizes, and then the concentrating process can begin. Overview Table 1: Composition of Sludge Minerals% Pyrite(FeS2)83.1 Sphalerite (Zn,Fe)S 5.4 Galena( PbS ) 2.1 Chalcopyrite(CuFeS2) 1.4 Arsenopyrite(FeAsS ) 0.9 Several trace metalsN/A * Effect on Soil * Aim of Study * How to study bioavailabilty? * Methods and Sampling * Analytical Methods Total metal conc. in plant material and soil were determined following HNO3/HClO4 digestion Bioavailable metals were analysed after extraction with DTPA-CaCl2-triethanolamine Analysis: Atomic Absorption Spectrometry (AAS) Soil pH was measured in a saturated soil paste EC was determined in a 1:5 aqueous soil extract SO42- content was determined by turbidimetry with BaCl2 Plant growth(fresh and dry weight) were also determined * Results * pH levels during experiment * SO42- , EC and pH * * B. juncea survival and biomass production Type1st harvest2nd harvest Cow manure2869 ± 507 kg ha−1518 ± 135 kg ha−1 Compost977 ± 195 kg ha−12186±563 kg ha−1 Control1354 ± 470 kg ha−11631±946 kg ha−1 * DTPA-extracted heavy metals May 2000 April 2001 * Behaviour of different heavy metals * Behaviour of different heavy metals Conclusions * Effect of OM and lime on soil * Heavy metal bioavailability in a soil affected by mineral sulphides contamination following the mine spillage at Aznalcóllar (Spain) Biodegradation 14: 199–205, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. 199 Heavy metal bioavailability in a soil affected by mineral sulphides contamination following the mine spillage at Aznalcóllar (Spain) Rafael Clemente∗, David J. Walker, Asunción Roig & M. Pilar Bernal Department of Soil and Water Conservation and Organic Waste Management. Centro de Edafologı́a y Bio- logı́a Aplicada del Segura, CSIC. Apartado 4195, 30080 Murcia, Spain (∗author for Correspondence: e-mail:
[email protected]) Accepted 4 November 2002 Key words: bioremediation, heavy metals, metal availability, organic matter, pyrite, sulphide oxidation Abstract A field experiment, lasting 14 months, was carried out in order to assess the effect of organic amendment and lime addition on the bioavailability of heavy metals in contaminated soils. The experiment took place in a soil affected by acid, highly toxic pyritic waste from the Aznalcóllar mine (Seville, Spain) in April 1998. The following treatments were applied (3 plots per treatment): cow manure, a mature compost, lime (to plots having pH < 4),="" and="" control="" without="" amendment.="" during="" the="" study="" two="" crops="" of="" brassica="" juncea="" were="" grown,="" with="" two="" additions="" of="" each="" organic="" amendment.="" throughout="" the="" study,="" the="" evolution="" of="" soil="" ph,="" total="" and="" available="" (dtpa-extractable)="" heavy="" metals="" content="" (zn,="" cu,="" mn,="" fe,="" pb="" and="" cd),="" electrical="" conductivity="" (ec),="" soluble="" sulphates="" and="" plant="" growth="" and="" heavy="" metal="" uptake="" were="" followed.="" the="" study="" indicates="" that:="" (1)="" soil="" acidification,="" due="" to="" the="" oxidation="" of="" metallic="" sulphides="" in="" the="" soil,="" increased="" heavy="" metal="" bioavailability;="" (2)="" liming="" succeeded="" in="" controlling="" the="" soil="" acidification;="" and="" (3)="" the="" organic="" materials="" generally="" promoted="" fixation="" of="" heavy="" metals="" in="" non-available="" soil="" fractions,="" with="" cu="" bioavailability="" being="" particularly="" affected="" by="" the="" organic="" treatments.="" abbreviations:="" dtpa="" –="" diethylenetriamine-pentaacetic="" acid;="" ec="" –="" electrical="" conductivity;="" om="" –="" organic="" matter="" introduction="" in="" april="" 1998="" a="" dam="" wall="" enclosing="" pyritic="" mine="" sludge="" at="" aznalcóllar="" (seville,="" spain)="" was="" broken="" and="" about="" 5="" million="" m3="" of="" a="" highly="" toxic="" pyrite="" waste="" spread="" along="" the="" guadiamar="" river,="" covering="" 45="" km2="" of="" the="" sur-="" rounding="" arable="" land.="" the="" solid="" phase="" (9="" ×="" 105="" m3="" of="" toxic="" tailings)="" spread="" 37="" km="" downstream.="" the="" mineral="" phases="" consisted="" of="" different="" sulphides,="" such="" as="" pyrite="" (83.1%),="" sphalerite="" (5.4%),="" galena="" (2.1%),="" chalcopyr-="" ite="" (1.4%)="" and="" arsenopyrite="" (0.9%)="" and="" numerous="" trace="" metals="" (almodovar="" et="" al.="" 1998).="" although="" most="" of="" the="" sludge,="" together="" with="" the="" surface="" soil,="" was="" removed,="" heavy="" metal="" levels="" (especially="" zn,="" cd="" and="" cu)="" of="" soils="" in="" some="" areas="" are="" still="" present="" in="" concentrations="" that="" are="" phytotoxic.="" the="" main="" source="" of="" these="" elements="" was="" the="" solution="" phase="" of="" the="" spill,="" which="" penetrated="" into="" the="" soil="" and="" the="" solid="" phase="" for="" the="" other="" elements="" (simón="" et="" al.="" 2001).="" the="" sulphides="" from="" the="" sludge="" remaining="" in="" the="" soil="" can,="" under="" adequate="" moisture="" and="" aeration="" con-="" ditions,="" be="" oxidised="" to="" sulphates="" with="" the="" formation="" of="" sulphuric="" acid,="" such="" that="" ph="" falls="" markedly="" (för-="" stner="" &="" wittmann="" 1983).="" soil="" ph="" is="" one="" of="" the="" main="" factors="" controlling="" the="" solubility="" and="" bioavailability="" of="" heavy="" metals,="" together="" with="" redox="" potential,="" soil="" tex-="" ture,="" cec,="" and="" organic="" matter="" (om)="" content="" (ross="" 1994).="" the="" concept="" of="" soil="" metal="" bioavailability="" refers="" to="" metal="" fractions="" in="" chemical="" forms="" which="" can="" be="" taken="" up="" by="" different="" soil="" organisms="" and="" by="" plants="" (mench="" et="" al.="" 2000).="" the="" most="" widely="" used="" approach="" to="" pre-="" dict="" the="" bioavailability="" of="" toxic="" metals="" in="" soils="" is="" to="" choose="" a="" chemical="" extractant,="" or="" a="" series="" of="" extract-="" ants,="" thought="" to="" remove="" particular="" chemical="" phases="" of="" 200="" metals="" in="" the="" soil,="" which="" correlate="" well="" with="" amounts="" of="" metals="" taken="" up="" by="" plants="" grown="" in="" the="" soil="" (turner="" 1994;="" bañuelos="" 2000).="" of="" the="" weak="" chelating="" agents,="" dtpa="" has="" been="" used="" successfully="" as="" an="" extractant="" for="" characterising="" bioavailability="" of="" soil="" metals="" (lindsay="" &="" norvell="" 1969;="" gough="" et="" al.="" 1980;="" lee="" et="" al.="" 1983;="" ross="" 1994).="" addition="" of="" humified="" om="" such="" as="" compost,="" to-="" gether="" with="" lime="" to="" raise="" soil="" ph="" (kuo="" et="" al.="" 1985),="" is="" a="" common="" practice="" for="" immobilisation="" of="" heavy="" metals="" and="" improvement="" of="" soil="" conditions,="" to="" facil-="" itate="" re-vegetation="" of="" contaminated="" soils="" (williamson="" &="" johnson="" 1981).="" conversely,="" soluble="" om="" present="" in="" fresh="" manure="" can="" increase="" the="" short-term="" solubility="" of="" heavy="" metals="" (almås="" et="" al.="" 1999),="" through="" the="" forma-="" tion="" of="" soluble="" metal="" chelates.="" however,="" walker="" et="" al.="" (2003)="" indicated="" that="" the="" effect="" of="" om="" on="" heavy="" metal="" bioavailability="" in="" calcareous="" soils="" was="" often="" not="" related="" to="" the="" om="" composition="" or="" degree="" of="" humification.="" a="" remediation="" programme="" has="" been="" carried="" out="" in="" the="" area="" affected="" by="" the="" aznalcóllar="" spill="" to="" effect="" metal="" immobilisation="" in="" these="" strongly="" contaminated="" soils,="" to="" reduce="" phytotoxicity="" and="" thus="" to="" re-establish="" a="" vegetation="" cover.="" the="" aim="" of="" this="" field="" experiment="" was="" to="" assess="" the="" effect="" of="" soil="" amendments="" (om="" and="" lime)="" on="" the="" bioavailability="" of="" heavy="" metals="" in="" a="" zone="" close="" to="" aznalcóllar.="" special="" interest="" has="" been="" paid="" to="" the="" evolution="" of="" soil="" ph="" and="" sulphate="" form-="" ation,="" as="" these="" parameters="" can="" strongly="" affect="" heavy="" metal="" bioavailability="" and="" therefore="" the="" bioremediation="" programme.="" materials="" and="" methods="" experimental="" procedure="" the="" experimental="" site="" was="" located="" on="" the="" right="" mar-="" gin="" of="" the="" guadiamar="" river="" (longitude="" w="" 06="" ◦13′00′′,="" latitude="" n="" 37="" ◦26′21′′),="" 10="" km="" downstream="" from="" the="" aznalcóllar="" mine.="" the="" site="" (20="" ×="" 30="" m)="" was="" divided="" into="" 12="" plots="" (8="" ×="" 4="" m="" each,="" with="" a="" margin="" of="" 1="" m="" between="" plots).="" the="" soil="" was="" a="" non-calcareous="" loam="" with="" 19.7%="" clay,="" 34.3%="" silt="" and="" 46%="" sand,="" classi-="" fied="" as="" typic="" xerofluvent="" (american="" soil="" taxonomy),="" with="" about="" 1.1%="" om.="" the="" following="" treatments="" were="" applied="" (3="" plots="" per="" organic="" treatment):="" cow="" manure,="" which="" provided="" soluble="" and="" easily="" mineralisable="" om="" (om="" 188,="" water="" soluble-c="" 33.4,="" naoh="" extractable-c="" 30.1,="" total-n="" 6.8,="" all="" g="" kg−1);="" a="" mature="" compost="" with="" highly="" humified="" om="" (om="" 875,="" water="" soluble-c="" 26.4,="" naoh="" extractable-c="" 125,="" total-n="" 26.6,="" all="" g="" kg−1);="" control,="" without="" organic="" amendment="" (repeated="" 6="" times="" because="" of="" the="" great="" differences="" of="" soil="" ph="" and="" heavy="" metal="" content="" between="" plots);="" lime,="" applied="" to="" highly="" acidic="" plots.="" the="" organic="" amendments="" were="" added="" at="" annual="" rates="" of="" 13.6="" t="" ha−1="" of="" compost,="" and="" 36="" t="" ha−1="" of="" manure="" (on="" a="" dry="" matter="" basis)="" in="" order="" to="" increase="" the="" soil="" om="" content="" to="" about="" 1.6%.="" the="" initial="" liming="" procedure="" was="" carried="" out="" using="" 25="" kg="" per="" plot="" of="" a="" by-="" product="" from="" the="" industrial="" extraction="" of="" sugar="" from="" sugar="" beet,="" which="" contained="" 85%="" caco3="" (equivalent="" to="" 21="" kg="" caco3="" per="" plot).="" during="" the="" study,="" two="" crops="" of="" brassica="" juncea="" (l.)="" czern="" (cv.="" z1)="" were="" grown,="" with="" two="" organic="" amend-="" ment="" additions="" (one="" month="" before="" each="" sowing).="" all="" plots="" were="" fertilised="" with="" an="" 8="" :="" 15="" :="" 15="" n="" :="" p="" :="" k="" inor-="" ganic="" fertiliser="" at="" a="" rate="" equivalent="" to="" 750="" kg="" ha−1="" (2.4="" kg="" per="" plot).="" after="" the="" first="" crop,="" the="" plots="" were="" divided="" into="" two="" or="" three="" subplots="" due="" to="" the="" great="" variation="" of="" contamination="" and="" ph="" within="" plots,="" and="" plots="" showing="" excessive="" soil="" acidification="" were="" limed="" at="" an="" appropriate="" rate="" to="" increase="" ph="" values="" to="" about="" 6.0.="" soil="" samples="" were="" taken="" on="" four="" different="" dates:="" march,="" may="" and="" december="" 2000,="" and="" april="" 2001,="" corresponding="" to="" the="" first="" sowing="" and="" harvest="" and="" the="" second="" sowing="" and="" harvest,="" respectively.="" all="" samples="" were="" taken="" at="" 0–20="" cm="" in="" depth,="" and="" were="" air="" dried="" and="" sieved="" to=""><2 mm="" for="" analysis.="" the="" evolution="" of="" soil="" ph,="" total="" and="" plant-available="" heavy="" metals="" content="" (zn,="" cu,="" mn,="" fe,="" pb="" and="" cd),="" sulphate="" concentra-="" tion="" and="" electrical="" conductivity="" (ec)="" were="" followed="" throughout="" the="" study.="" sulphate="" concentration="" and="" ec="" were="" determined="" at="" the="" four="" samplings="" in="" 9="" of="" the="" 12="" plots,="" corresponding="" to="" three="" plots="" per="" treatment="" (con-="" trol,="" manure="" and="" compost).="" plant="" growth="" (fresh="" and="" dry="" weight)="" and="" heavy="" metal="" concentrations="" were="" also="" determined.="" analytical="" methods="" total="" metal="" concentrations="" in="" plant="" material="" and="" soil="" were="" determined="" following="" hno3/hclo4="" digestion.="" plant-available="" metals="" in="" soil="" were="" analysed="" after="" ex-="" traction="" with="" dtpa-cacl2-triethanolamine="" (lindsay="" &="" norvell="" 1969).="" extracted="" metals="" were="" analysed="" by="" atomic="" absorption="" spectrometry.="" soil="" ph="" was="" meas-="" ured="" in="" a="" saturated="" soil="" paste.="" ec="" was="" determined="" in="" a="" 1:5="" aqueous="" soil="" extract="" and="" sulphate="" content="" was="" determined="" by="" turbidimetry="" with="" bacl2="" (abrisqueta="" et="" al.="" 1962).="" all="" analyses="" were="" done="" at="" least="" in="" duplicate.="" 201="" statistical="" analysis="" using="" spss="" version="" 10.0="" software="" (spss="" inc.),="" the="" data="" were="" subjected="" to="" one="" way="" anova="" and="" differ-="" ences="" between="" means="" were="" determined="" using="" the="" least="" significant="" difference="" test="" (at="" p="">< 0.05). regression equations were calculated using sigmaplot version 5.0 software, by the least-square procedure where correlation coefficient (r) was calculated, and the non- linear least-square procedure (marquardt-levenberg algorithm), where residual mean square (rms) and f-value of the curve fit were calculated. results and discussion the soil at the experimental site was characterised by a wide variation in total metal concentrations between and within 0.05).="" regression="" equations="" were="" calculated="" using="" sigmaplot="" version="" 5.0="" software,="" by="" the="" least-square="" procedure="" where="" correlation="" coefficient="" (r)="" was="" calculated,="" and="" the="" non-="" linear="" least-square="" procedure="" (marquardt-levenberg="" algorithm),="" where="" residual="" mean="" square="" (rms)="" and="" f-value="" of="" the="" curve="" fit="" were="" calculated.="" results="" and="" discussion="" the="" soil="" at="" the="" experimental="" site="" was="" characterised="" by="" a="" wide="" variation="" in="" total="" metal="" concentrations="" between="" and="">