CHANGES IN METAL SPECIATIONFOLWWING ALTERATION OF SEDIMENT

REDOX STATUS

Joltn II. Pard", tllld William II. Patrick, Jr.WetlandB~$lf)'1ll$ti\UleCenter fO( CotiIaI. Energy and Environmenlal ResourcesLouisian.a S\.lte UniYa'Wt)'Bal()ll Rouge. LA 70803

L L'lITRODUCTION

Changes in oxidation-rcdllC1ion (redox) potential can result fromnatural (q;" flooding) andamh~k(e.g" dredging) altenuions ofsedi""'nt conditions. Changc$ in metal and metalloid speciationgenerally folio.... these changes in sediment Ell and pH conditions.Alleralion of sediment Ell and pH conditions are often driven bymicrobially-mediated reduclion of .hemal. electron aa:cptors indlldingnilJalc. sulfate and ""idiud fOl'lrul of iron and manganese. FoJlowin.the lkplction of nxygen, reduction ofl~ vuKluS alternate electrona.c:ceptcn OCCUR in a "'-ell-defined s.equence th::ll can affecl the solubilityand iipeCialion of U1lCe mews pruenl in the sediment. OJanges in~liWlIS can be lk..ribed in terrnt of both the illtelllit)' of reduction (Eh)and the OlpQCUy of sediment redox systerm that buffer changes in~intensity. Changes in metal speciation are affected by both redo.intensil)' and capacit)'. Srudiu "'ill be di$Cus~ th.at in,·e.tiJlltedehangc.s in speciation of~k, ",lenium and chromium under differentcootrolled Eh·pH ronditioni in s.edimenl. The use of specifIC: analyticaltcchniqP<::l for s.peciation of the m<:Qls and mc:t.llloids in ~iments "'illbe presented. Differeoocs in solubility. b~vail~biliry and toxic:iry forthese metals ..'ere obscr'o'Cd following changes in ~.l potential. Theu'" of the concepI or Mcritical~ redox poIentials to identify important"hanse. in $peCiation Qf the", metal$ will also be pl"C"'nted. TheKstudies demonstr:lle the importance ofredo.l changes 00 .peciatioo andIOlubilily of mc:taI. and metalloids in ~imc:nt systems.

OI99~ by Ann Arbor Pres•. Inc.

CHANGES IN METAL SPECIATIONFOLLOWING ALTERAnON OF SEDIMENT

REDOX STATUS

Jolt,. II. I'llfdur lind WiIIUrm Ii. Patrick, Jr.WnlllIId Biogeod>emisuy lMU\UleCenter for CoasIaI. Energy and En"ironmenw RC$OUrteS

Louisiana State Unh"CnityBalOll Route, LA 70803

I. L'Ir,TRODUCl10N

Changes in oxidation·rWlIC1ion (redox) potential can result fromnatura] (q:" nooding) and anlh~iI;(e.g., dmlging) alterations ofsediment conditions. Changes in metal and metalloid speciationgenerally folio..... these changes in sediment Ell and pH rondiliO<ls.Alleralion of sediment Ell and pH conditiQns are often driven bymicrobially-mediated reduction of 'hemal' electron aa:cpcors incllldiDgnitralt. sulfate and o:o;idizcd fomu of iron and maIlilUleSe. FoJlowinathe lkpleti<ln of MygCD, redoclion of lhe$e var1Qus aIlemltc electronaa:c:pton occun in a "-ell-<iefined s.equence th:ll can affect the liCllubiliryand speciation of tr.lCe mews presa11 in the llCdiment. Changes in~xWl(US can be lk!ICribed in term.' of both the intenlity of rWlICtion (Eh)and the ropucily of sediment redox s)'$l':JI1$ that buffer changes in redoxiDlensil)'. Changes in metal specialion are affected by both redoxinlensity and capac it)'. Studiu will be discussed th.at inveSliptedehangcs in ~iation of~ic, selenium and chromium under dirrel't'Mcootrollcd Eh·pH conditiOll5 in sediment. "The use 01 specifIC analyticaltcchniques for speciation of the me\.lls and me\.llloids in sediments willbe prescnlCd. Dirrel't'D<%S in solubility. bi~vail.bililyand toxicily fOt"these melals were obsoervcd following ch:lngcs in redox potential. Tbcusc of the concepI or Mcrilical~ rcOOX poIenti.ls to identify important"hange. in speciation Qf lhcse metals will also be presented. Tbcscstudies demonstr:lle the importance of redox changes 00 .peciatioo andsolubility of metal. and metalloids in sediment sys.lems.CI99~ by Ann Arbor Press. Inc.

CHANGES IN METAL SPECIATIONFOLLOWING ALTERAnON OF SEDIMENT

REDOX STATUS

Jolin II. l'/lrdur lind William fl. Patrick, Jr.Wetllllld Biogeochemistry [MU\UleCenter for Coa$Ial, Energy and En";ronmenlal RC$OUrteS

Louisiana State Unh-enityBalon Rouge. LA 70803

L L'Ir,TRODUCl10N

Changes in Qxidalion-rcdllC1ion (redox) potential can resull fromnatura] {q:" nooding} and anlhl'QjlOl('nil; (e.g., dmIging) al1Cnllions of$Cdi"",nt conditions. Chang's in metal and metalloid speciationgenerally folio.... these changes in sediment Ell and pH rondiliO<ls.Allt-ralion of sediment Ell and pH conditions are often driven bymicrobially-mediated reduction of lllemale electron acccpcon; incJlIdiognilrate. sulfate and o:o;idizcd fOl'lrul of iron and maIlilUleSe. FoJlowinathe lkpleti<ln of llJ.ygcn, ll:dOClion of lhe$e various aIlemltc electronaa:c:pton occun in a ""ell-defined s.equence th:ll can affecl the $OI.ubiliryand speciation of tr.lCe metals presa11 in the llCdiment. Changes in~liWUS can be lkllCribed in term.' ofbolh the int'fllity of reduction (Eh)and the copQdry of sediment redox systell1$ that buffer changes in redoxiDiensil)'. Changei in metal specialion are affected by both redoxintensily and capacity. Sludiu "'ill be discussed th.at in'"cs\iptedehangcs in speciation of~ic, 'iClcnium and ehromium under djffert'ntcontrolled Eh·pH rontIitioM in .sediment. The use 01 specifIC analyticaltcchniques for J.pCCiation of the me\.lls and me\.llloids in sediments ",mbe prescnlCd. Dirrert'DCeS in solubility. bio.vailability and toxicity f~these melals were ob'iCO'Cd following changes in redox potential TbcU'iC of the concepl or Mcrilical~ rcOOX poIentials to identify importantf;hMngf;S in speciation Ilf the.se metals will also be presented. Thes<:studies demonstr:llC the importance of redox changes 011 speciation andsolubility 01 metals and metalloids in sediment sys.lems.

CI99~ by Ann Arbor Press. Inc.

'''' Pudue and " •• rlck

Sedim<nll em ..,,'... -"Rh- Qr -"""""",- 0( """' """"Y .........I<> """rlym, "'Iler bodieL Tho~ 01 m<UI< "'..... 1lle ocdiment·..'oter intelfilU <kpeft<b <Xl. ",""pl<. in""",y of p/lYJical. rh<mi<caI,and IlioIoV=aI ,"' "'" lh.ao. <:on"'" 'f'<'Ci.Ilion. lIOlubilily. ond lbode""klpmom of ronceOlr=ioa padlen An i~ r.".,re i> lbecradicn, of meI.1 conoeIlltlU;"" bctwoen tho ..d ' p<><....... and...rf~ ..--.. th.. can~ tho <JICha.S. of """ 0'''''''''' "'" lo<4i_"'&In inlerfocc. C<Jnce:IuOli""" of mew. in ""dimon' """'....... inIum, on: """,rQllod by SQfplioo ;n;l pm:ip;l<l1ioo .."",ion< Ilopendml ""..di.....n' propcniet.....'.1 lpcci.,iDII. pof.....,.r compooition. on<!fulldamcnlal p/Iyskuc:bcmie'" 0001I";",,, ...,b u 1''' and ".idMiOll­rcdl><1io11 (n:<k).} poIen'ial or Eh. ChilnS" in .<edilllCc' Eb-pHo:ondili<>m eM ......, '''"''8<-' in melol .ped.l"", oDd soIubilily ...lU<:hcan J,Ubloequr:mJy ",,.,1, in. "u, from botI<>m ..-dimento lO ""••lyine"1leI' III.

Chanl'" in oedimu, Eh-pH e<>ndili"", hO'. bun s!l<>wn toP'Od_ ...id< <1if'Farn<u in lIX'IaI and m<Ulloid spcciatioll and iOloo;lily"flde. conlrolled .oodi,ioo. 12,3). [n<tt• .." in Wlublc "",,01concrmmiao>j; in ".idiK<l oedi"",,,, from ....1, mush i•• clonie.>;ample of tlli> """""" [41, Th<: _"" in rhi> ....icul..-I.al' mar'"oali.....m I. UIe o.""'~"" 0( "",,1.1 MlJ(uk,. '''''h.dinl p~,i~.....hich..,n a, • "'om'Oir of '"u< "",,&I. ,n u..~ »'~m.a_ S<~ andtemporal vlrialioo i. oedi,,,,., proper1J<S h .. Ell and pH __,rivi&l I;lOCUJO'OOC" i. tbe environ,,,.nt. Sedi !> ... r>eve, fully illequilihrillJl1 (SI ar.d. ",ide variel)' ol.llura! ('.1.• lid&l and "",,·lidolfloo<!inll and ..."""""-<nic ('_1_. d"""in,) !W'O«>.... CIllO< <!wi,..in ,be.. ponm<I<nI. etlaol'<' in Eh <>lOdi,ion§ may D<Jl &1""0)" n:suk inIn<liclabl< ct."""" In met&l SPOC'alio<l. '-'....r. O1i<!.ioI:I·~ioal"""".... ",ilh &I.... kinel",,- at'< ....nmon """ pr<dicriooo bao<d Oft an,"umprion 0( equiJihrium ",ill be in("O<Te<;'_ ...d,·....... '1""'Iationmodel. {~I,. GEOCllal Ihl:mel ML\1B) 1711 have '-n develclp<dbill tbe.. ",IJ "n ~u;lil>rium<""""pt. Ind ,hi. limjt>lioa "",., be""""S"iud in Il>eir ..... For rn:onJ n"""I. and ,,,,,,.II,.;d<. ,be", i. II<>

subslilule for rN-kiJl,l«u""e. di=c _ ..........n.. of 'Jl"<'U

Sedi_ Eh <lAW< i,. coo>pb.. diffocuh '" n><asun: ~'er_....'lIi.. Ell <IJ\ be <\ao.oicall)' defined i. len", of. ,jndo <bernie&l ')">tern( inl,be Nem" "'I",'ioo). .«<limen, porow.tc, ;, • romp .miuun of~n<kundrr,oln' ,edo. re.>ctiono in .-.rioI>o "agel ofnon-.eqttilibrium. Me"......",.!>- 01 redo. poIeoli~ in I"'''....ylilC:01O.'be",n-. "'p<nent-mi.ud- poIe"'ilb ...ith ,"""Iri~tiono rrom 0CWSlIIredo». e<lU1Jko lSI ...-lueh may or may nol be fuUy .."""",,,, 10 "'" Ehek<:1Z\kk. llka>w'<mt.1l of 0. i, e<omononlj' pul'-'"""<l .mOl p1:lli."mel«1f'OCie>,. Linul:ll><>na in ""n, p1aunum .I..,rode., ha," boon ",i<l<ly

'''' I'ndue and ""rlck

Sedimcu. em ..,,'. '" "'in~." Qf """"""",' ot ""'"' he_')' mctol,to O"Ulyin, w..... bodies. T1It uchan~ n( mrtaI.""..... 1lle ocdim<nt.,...1.. illtelf""" <ic:pell<b "". c""'plu I y of p/lyu"l. rh<mio:.:Il,IIId bioIoslcal p' "N th.ao. "",,1roI ~ oolubllity. ond "'"""",,lopmoIU of conccOlnolioo padienli. An i"'l"'fl"'" f..."", i> 1""gradient of meI,1 conceIllra,ion ""lwca> ,he ..d"'><II' po«"'aler MId,or1'.,., .....",. thal can dri.., Iho. <.uhansc of "",,>.I. """"'" "'" ><4i_"'...,,- ;nlafocc. Olnce<l",.l,"'" o( mc<al. '" ",dime"' po.."..' ...... i.'urn. on: """'rdlod by .....-po;"" ;on<! p...."J'Il>lioo ..1<'1..... 60pendml ""..d,men, prnpeniet. """.1 .peci.'i"". pofc"'"c, compositiofl, ondfundamcnlal p/Iysicochemical ""'"'"i",,. _b .. 1''' ODd o.;.J.MiOCl­rcd""lion (""I poIen/i.1 Or Eh. C'hionsc, in oedilllCOI Eb-pH,"""",lions eM......, chanB<" in m<lol 'lJ<'CiOl"",.1Id IiOIl>\lI.lily ...lU<:h.u "'~lII:Il1Jy .......1' in. nUl from bo<Iom ..-dime.1i 10 """lyin,"1leI' III.

Chan.... in oe<timul Eb-I'H rood;!'0tI1 h... b«n llI<>wn toptJduco wid<d.i~ "' "",La! >nil """-'110M! opec;..ioII >nd idubjlilyufl<k. c".'rolled .""dil;"'" 12,3). ["" ..,. in ""Iubl......\.atc"""",nlrati"",, in ".OdiKd ~iment rrom 1, mush i•• cll..iccUlIlf'lo or ,hi> """"'"" [41, Th<: _Ill in """ J>U1icu1... >all ....'">ed;mc:"l is lhe Olidatloa 0( "",,1.1 ",Wdc•. ,""hod"'J p~li~. which..,rw., _rewn'Oir of '"u< "",,01. ,n u..~ ,~~"". S<~_

'.mpara) _&rial"", i. oedi,nc.1 prop<l1iQ ....h .. Ell lind pH .... _,ri_i.&I 0«"Un'<""<' i. tho: «,.i",,"ncnl s.d''''''.'' ~ nc"., fully",equ.librium Ul and a wid< varic:!)' ol.lluro.l «.,.. lid.. oDd ."....idA!floodind _lid .."111_''';' {<.,.. dr<d.i.,)~. cau.. <1wlJain ,~.. ponrncc<n. 0Ia"B<' i. Eb <><lrIdi,iorI< ""'y _ oJ""')" n:suh ,nIn<li<labl< <"""'I"" i. me'ol $p«"alio<\. h<>w..",. Oo.idIli<>ll·~"'"

l'f'XC"'" wllb 01_· kin<'iu on: roI...... """ "",di<liofto ba><d Oft OIl.,,..ml"ion ol .quilibrium will b< ilX"O<T«1. Ad" ....<d ,,,,,,,;otionmodo" Ie-". GEOCIlal 161 and MJ~'1B) l7111la\'C """'" <it\'C1op<dbut ,b<.... ",Iy <). <'1u;lil>rium <D>I«pU and ,hi, li"'Jt>li<sn ",...1 bem><llniud In ,b<ir ""'. F... l1Uny m<1al. """ tn<1.lkIl<h. ,be", i. 110subst,tul< f<>r makiol >«"""<. din:<! ",",...."''''''.l> "'" ,p«:a.

S<di_ f.h.<laLu.> i, o"""'pkx. diff"",h '" m.oa.""" ~t.,.....'lIilc f.h <.. be~l)' d<r""", in "'111I.' 01_ >in"" , 01 ')">k'"(0.'.• u'ina ,be Nom" "'I",I;Oft). >«Ii.,.n, po«w.~, complumUlItlC of~rodoWldnIOllli ,<do. K.><1M)n< III \'2riow. ....,.. ofoon-<quilibnum. ~\c;u.ur.n",nl> 01 «<lo. pot<OIi.b in lhue: .y""'01I.,,,,,,,,r-. ..,""'_ -mia«!- po<ontialo ...illl <u.uribu,ionI from oew.noImlon """pi<> 1$1 luch .....y \If ttl>y nol be fUlly «SpIlftJi'''1O u.. J::h.....U\lok. 114 " of Eh i ........nonIy "",rurm<d lUi". p1.u.om<1«1rodos. UIN'."'o, i. 0"01 pl.uoum .Joc'rOOo., ha,-. been wi<l<ly

ChI-lDII'!.lil In. lall' lion,:" d!iml, R ,S hIS nl

driseu~ [S]. particulul, as die'}' peflain 10 mea un=mel'lt of Eb infill, 'r.: spite tbe limitatoolliS-, I'edo ffi!mSUt'Cmenl am ufoJl

III sMimems willi high ooncentl'tuiol'ls of I'Cdb .•acti'e, , ..allywllm l!he el«inlde n~~l!'1l'Me coupled wilh diJtli;t~o "rcdo~ ,olilplcs.

Tbe En profile in S;edi~[lu; deviJops iflrc:spon5t: lO Ilhe OJIYlc-nI!ll' 'ieDl ~l lbc; s~dirn~oL-wl1tc~ illl(rf~ce. OJl,ygc'tl! ,II ,llillibJikty Inscdim.e--nl.!i re uh5 fll;lm Ihr' bl)l;c of 0:1; gcnl "U , l)'!JM dem!md.S dimrntllfn re~dH -t.le~lcorgl;jrlit IlJIIilCf . nel'a!ly dri Oz,con5<umpHon. When OIil)!I;,tllJ Ii;. ,abl!ent. mkfQoQrgilJli~m~ ulHiz""._ qocnhotlly ..:!l.ernille dccltro~ :a(~p!O~ ~eh a!'. nitn\l:e. iwo.,man~ ulbt~ ;md COl ,ubsequcntly Itd~i I:l ' lhc:se ,0 mpoum'ls,in !:he 'process. Accumulatioo oflbcse reduced ,pee' in Iht~I !:'M,pe .ibl fnr the d ·e,c ing B! mule in ' i •. hsb!lIWD that \'Ii, criUrol, Ehl, 'isl r r Ill~ Iln1~ -" ofe3Cll of tbese :1lI''tm~

c.leaJ'OO ~ ,ptor~ It!')' :llf!.il;i'OO1l'gilllisms [9'). The " i ' occurstqucotialliy ,- on:I:in~ til 'rrnoo)'nami!: consider.ili'oos

Marl,,. of lbe '1\'31" \II I'r'.5e 'Clim ollio,g Ihe l,l.Ibility ,aniispc.cimion . iii III liiI ha\~ I· II r~vi,,"et! e\~iOQslyUOJ. . pape:

, II oi .- :' i>1iIldie. documenlillr& c'lI;mges in me poe ,i~rO!I fol.1owingclianges in m me:ot EIrI st [I,l -, ctUp iz-mg the· nee I of i'edoii.cLenSity andl ~ ily. ObvL iSIy, odw eootroJlilll!· '(e,g" pK}IlDd~. (,c.,g".·. llonld~-Wfp(ioll)1 play i~rtan.l roles ' .. pel'limion mil sol hility, This p'ape will focu on cal w:be-.reotidaIion·mdUl:lJl [j f 11~ 5 ·cil:s dirtdl . :affects wiD >lity.

A cmnmol'l],Y 0- erlooked eharacleri~!ic Qf redo, Il.tmlled:proces s' i.s, l t (hey h.ave ooth !JTir:'uU, ;md cl.pO.:Ji' specl.M . wemellr of redo:t p I'lU I with ,;1 plawlIIm electrode mea!iurc~. iL11 io":n, ily but ,ool l::<lplllcity, Ei'lBmpIc:5 of U!5t:ful 'inl~n. itym lISUrtmcol. includ( lbe '·,criticalft redo- :polenltMS' _( wWeb themorgani Nd.Q 'Y1;It1~ bc:c.lil1Pe I.IDslabl ("igilrrc: I). Aftboou Ibis, iviii UlIble' jflJgrm!ltioo, itSM\'l:, 00 indk _ '{In flf lhe; , ize gf In: . I meJeclF ,.;ml!e to be __ cep\.Qd Qr dooatcd !1M (h(:~ron;, IbI: _ _!.In! ofIJliC'robi :r¢P~J: iO!lllhil! c; _ ., sujl(lQl1W 'by Ih:ll'(d~ ~)I ~,

RedU\1l C.. ' 'ilV ,refer. (0 !.he iiIJ1l!)Wi1 or eleclron . Ithin musl be~d (-W:ida.th~ - . il)') or felllO.....w (reductive ca i[~O 10 il£hic:vc ill

h'c:nJ!b .kcdv~ c"p<JA: it)' is, iUl.iJ.logoos ~o Ikalll'ut)' .ilb respect Ito Ihc:

C n In lall .~ I lion: ~ d'iml Redo Stllltus n .1

d.l!!Q.l~ [El]. paftic:ulul as thc'}' pemin 10 me ur:emel'lt of Eb inground, l3.le. : . spilt tilcse IimLtaOOns. redo D~menl5 IIle gse,foJlill sedVmen1S wllb high coooentmiions o.C redo Idi:e. '. espedi1.lly""bm lib:eJ~fl~OI ;)If. ooupled wilb diltct IlftSlIieJl~Qf redox COlJples.

The: En profile:- in srdiml:rl1.!i deVl:lops ill re~n5t: Kl Ihe Wlyjt.ngriCD! :lil the st=di:qu::ol-wlltcr illierface. OJl,y~n.lIVlIila'bility insedirnenl;" ~~u 1'-" from tl:u: billlliru; oro:!; sen, "l,I . ')' aDd demlm.d.S dimrnt3tkm re~ I, -tl gm&Iblc (J'rgilflic 1P!Ii1~ f.~ly drives Oz.,con5Uffiption. Wilen Q~YI;,eo i, ,ame I],t. IIlIC rQOrgalli !iml\ uli1i~" quenliaJ Iy J~mle dt=ctrQIl l;Ci:pIOr5 .Ill::h .~!'i. nitrl!!-l:e. icon.mai1g~ • ulbte;md COlubsequently nd' i I:l . Ih!::se cOlllJlOlmds.in Ibe proce:ss. Acc:wnulatioo of Uwse reduced pee' ,in die pore:wm:ui re p4)DSibl for tbe deefe ;ing Ell fome in wi.i!rnt:Ill. ]1 bas. been

wn ihat ;j ailirn.l EI'l eoci t For the utili.l;·~ oreach ofe.lewoo oc ptOO •.Il11iCfOOfgamilifllS [9'), Th . tr; orm:t.li.' occurseqLiCOl:ial.ly , oo.fjn~ tl) tbJrmod)'namic c:ons,j~r.ID·OIl:!l

Many of 11 var~ II rpr!l!CCS ,emIt Q io,& Ihe l\!bilily ilDd!lpccialion if m la!I Im\~ II revie ed ~\'i('JO~ly UO]. ' . paper

,HI oi .' U !iUldie documenlinrg, cbanges in me.tal ' i.lIoon fo11owing:JJanges in liel1IinMn( Ell st LU • emphasizing the nee of tedo~

icLenSity and c "it)', Obviouly, ~eontroUIllg • . (e,g., pH)aod procc.ssc (,e~. S(!l.!pllonldCSQfPtioo)i play imponanJ role . mel2lspeciation Ddl so] bility. TkIi~ ltape will foeu, tlll cases whereoxidJllion-mdldi of IIMliU1.1 species directl atf~ts ~1Ibi.ljt}...

of Eh

A common] y o"'cr'looked eharacleri:>tic Qf fedo , ..11'lrnlledproce-s ~ is Illat Ibey have OO1.h /,ul1!1land Ct padr)' specl.M ' wemenr' af redo:t p nti:lll with ,Ol. platinum eJectrode measure

. LtJg ioh::n. ily bllot nol capacity. Eumplc: of lJi5t:ful inlt=n ilymeasure 01.' indud.!: lhe ",erilicalft redQ leJllialr> at wbkb tbeinorganic!'OOo ~y);Ii,;1l'L'; bc:c. qw;; unslahl ( igul1:!). Altooug,h l!Ii~, j

v~ILmble infllrJl\lllion. il ~l\'t:. nQ iodie 'on (Ir lhe :"i~ of ~hc: J ofelect' .:.m~ I.Q be: C;l;ptocl, Qr d~3.leclll!Jd UJtm::r(ln;, lbe anml:l!'!! ofmiccobi :co 1".1\ iog Ithlll can .,su~ by the m1Ql!; . Y:tern,

RedUx C' pae:ily rder~ Itl (he I;IIUI:Jllnl oJ elet.:lrons 'thilt mlJ"1 be~d (u 'idative . PiJ'"lt)') <irRfl'lO'l'«l (red\&."1i\'eeapacilY) 10 achic:"c ill

M\'cmEh Rediux c<lpilcClt}' is. i'UI.illogoo.s ~o a1blitlll)' willi ttespea 10 the

boni~ . ' the aulhors, many of lbese: "umbersthege:oer J uen c' h lie, en detennihCld

and ahdated cl obcre (c.g., • po i!.O et ai. (22).

2), ''''Trans!omrallan'' capacity of Tedo;r syJunu·bile tbe cmica! redo potc!!l1i aJ ; in_ an

iDdi~lIhon of 'Whether , ,me al ede-Ie Il forma.lionr i· po. L Ie. . cap" it errn i_IlJCCC loc, tim te, bow mny, oJe of lhelM11J will· lually be lr-ansformod b he ,redoproce . Since every 0 id lion mil l be 'lIpl:ed

ilh, 'u it b.le' reduc I ion. 'Qua n'l j licatioD ofredw..,an -cb c . parthpa ill the It: I.longive, c it)' m ucemenL I) tbe palelui 1peei . tra.n form tion. 'simple c.xampJc' tbe

o jdioo 0 Cr{In) to Cr(ViI) ;01 n !Utili wte~ oredlmenl . Pre iou ~ludies (23] ha"'e

,.4' ... ,- - -s'" 1r,I I" ~t ctotidi",:d .r. ~ , ,; '-Ul-:e-!'it'l,IClIWIl: ......... Yol. . •.... I' I,!I ~,._

ilb r( . I ing il~ lin el tron - pl0r

to COD\'ert Oro its 0 id~ cd fo • ' 'H- lberel,ative bilil)' - fLo' its :md :edimen15 1,0 normlhi' uansfontWion. dk:refore, ~an be estimated bymeasu,ring r ducible D, 'Inu, ,llybydroquill!OOC-cedu' Ie ,The, ,:red -isan e' a.mple r a c· p' 'ily llllr¢lJ l.m:~ment Ib'tquantifi .1be. b'Uty ohibe soil to o. idize C:r(1Il' .

owe...er; the intensit . of red eti on mti t . til] befa, or bJc for the Q)I;id(ldon .'0 ocellI'. Th~

~(c·, cI 'cal' e- l equation will preictc rtaio di tribubOD of Cr ~pecic:s (e.g ..rImr]). -ta partiClll:lf Ell. "ow Vef, thi.

equation u that pecies a' equilibriumand that 11 rcvcr.:ible, reaction-an occUr'. "t'l

diment' ~ it 10 co . nInuions of .uciblMn. for e ample, the oxid tiono; C 'lll) ~,~ very

fo t ....tn when. the .rtdo . jllteo.·ily is fa 0 ·le.S~O. i tic 0 Iran. formation are common forma.oy met MId Ihe ~. ernst quation rarely h

y. an.itali,. .'eli...e val. e after aber'ALic:lD: insedir!OC .t Eh. Other meml specie tran. orma 'onsare' re comple lfJan thi. r example. . 'Iu lipl~

red,01'i. . ; ,(em" may be ~ Ie l paltkip le in. lhetnm f ion and detl'nninin . lhe lrnn form.tl1ioo

pocil ' for Ik specie is difficult.

bonIloty the aurnors mIDIy of(~ numbersthe general ueru h lie· en determined

and vali.dated ej- where (e.g., SposilO f"t aL (22) ,

2). "Transformillion" capacity ,of redO;f sy.uenu·. tille the cnlkal redo potenlia] i\o'cs, an

i:odi~8tlon of whellu:r me'a]" ede'rnn (ormauon i· po,.j Ie, cap itle'ftrl i'ncce toe· titrulte how m ny moJe of lbelnell.! will lu. l1y be lram! fom'led by (he .redoproee·. ince e ery oxidation musl be C'Oup~

ilh suitable reduclion. 'Qu,ln'lificatioD ofredl.K.1an .' b c partj'ipal ill the: m tiungt . c pit)" m ucemenl of me poLe.ui Ipecic . tran form lion. simple e:-:;amplc :. dte

o id81ion 0 eron) to Cr(VJ) in nalu I ""nctll or~dime(ll . Pre iou sWdies, (23J ha"'e

dClDQIliitraled lhat o:tidil d forms of mangu' ..react wilt Cr(TIJ) " rving ll' n el tron· p!orto CO.D\'ert Cr to its (l)!idizcd fo • CVn. lDerelative ·bililY - f ojls, 3lld :ediIIlCI1l.S10 performlhis, trlUlM'OlTILlilion, therefore, -WI b: estimaled bymea l),riDg redudble ,no 'llSP aUy abydroq i.fI()rIC-teduc:ible n. ~~me':!Wrro '" I:l is3D e' ample of a, ..pacuy' (\eli luement lb t

. tm 1be biltty of~he soil toolcidl.,l.e Cr(LU).However. tile intenl;Lty of red cti' n musl ~liU be:fnorable for the Qxidatj{m 1,('1 OCcllr. Ttl.rbeorctic ' •cI Nemst equ31.1on will pre .ct IIc rlaio di tribul'on Off ~pccicll (c_g..

r(lU)I-- Vl) t a particllJ r Eh. ow \" r. . isequation 'SUOleS tIYlt pecies are equilibrium.and tbat It rever iblt' reaCt ion Can occur. In. -diments ilh low co- . nlrations of reducibJM.n. for e ample, the ox.id tioa of Cr(lU) is vel}'~1'0 • c veil Whell tbe redo iJltcn, 'if Y is fa orable.

10. ·iJI ti lran fOrIDalion are comm<m forlDIUly met-_s and the • em t equation ~ly b

Y utollillc redictiveal c . alteflllioll' insed!'!IlCllt Eh.Othet metal :pecie trans orma .ODS

are m re co pie !han lhi~ J' example. . lu(Jjplredo~ .ste'ms may be· Ie l' articip le in lbetra.nc f ._ iQD and detennining l.he unnsfon:ruJboocapocil ' fur IJhese specie IS dlffi ull.

l). ·B~ff.rUtJ·~Iry- A >CC<Itld ",law! capacity....~"I i. ,I>< obiliry ol all red<u .yJlemO to"buff..... ,I>< Ell I><Iow or .rove the critial Ell ((}l

a p&lticular >pt<'i.llion Ir.1It<fOfmllioa. Tho mIo•• leme... t<IOIlribllti"flto thiI capocily .....y line DO

dim;I.1f«1 '"' tile melal, tl><m...hu. bill ......, totMdify and dimiII~~ im Ell _ ~ atIi:>ctspecilllioa. AD e'""'I'le is the (eme_[""""" iroII.sy"""', ..hich in mllny ooil.:md >editllCfl" iI b)'fo, lhe mosl imporlallt ,edD. system i" terInI ofO'Yl\'n fIlui,'alentl Thil iI demunlilllled ilTable I ..'tIM: __"""""".. lor 0 Mi.....ippia11""ia1 soil _ preaetlled. Tho oxygen equiv&Ienlollbex _ 0"""""........ COD I>< c:Mculooed booed0fI lolOKhiometry ..,ith Ii........ os ." .Iecl",.dono.- [1$1. Cole"l.,i"", dem"""... tllei......,n.nc. of ttle !OIid redo. components (<.."Fe and Mn). In "';1, and iedimenll ..,ilhappreci.ble iron 'Olltenl, cbaD,.. in Ell ondiminiohrd or bufrcml b)' the .Iecl....... ocup:o:Ior ",Ie_ by microlli:tI mel_ism wsiot; the ironsyst.m. This i, p.Ricol.. ly impottonl inal...:Il;"", loch o. nOO<!ins/dryinl or <lredlilll..'he", redo••yoIttnO .... buf~, the Ell all"". thecritical Eh or a p->Riculor t......format;.,., (or •oeRaUI period d,in...

Thi, caJ""'lty term .... be me....red by ...imati •• the ai"", ofimpon..... n>iloJl S)'lIems illdividu&lly <It by 0~i(.. n>etbod "";11&... w.ldano or """"" flO). S<:>'<'r.Il~. or the capacity ('.1.•OJ. NO). on<! soh ·ooIublo ond lly meosurW, Howe_.oj""" ..,Iid iron and lIIInl ".ides "'1"" the bulk of tilt redo,cop.dty in .....y .y hod> ot ,,'imatin, ",idllli..., copac:L1Yr..,.. on estim>lio,l!Ie rraction oll_~ a.. is poIeIIliallyreC.ocib!e, Vori<l<n mc:thod> hu" h<aI dc:vclopod (tor. ",V".., _Stunwn ond Sul,.mjtf r241~ oltlnlgh lower ronoenrraliord of redIo:i....agtlllO ore DOCtiwy to oaunIel)' qlWl~fy~y in -.,.;rm [201.

OIhe, capacity "" "'menu I>Ol diroctly "'bt<d '" o~~ioa-mdu<;t;.,., on 01110 impot1 for .........peciolion, The """,,"pi of ..,io!-volotile ,.If••, for ",."",Ie, i••IOCI l<> qu.... ify a "''''''lve pool QfIUlf. ,hal Oan "''''' ..lib trlWI$i,;"" mel;1.,[s [ormin, ittOOluble meul,ulfioJe>,.

31. "BIl/f,rUtW· N11'''..rry. A occond ...10lCd capll<ilyme_me"l ilo lhe ability of oil mlo1 oyJlemO 10"buff.... lhe Ell below Of .hove lh> ~ritiaJ Ell fot• pan;r;...br >po<i>Ilon ~rOfmllioa. Tho rrdc>.,lemelll. toIItribulin£ 10 !hi< ~apocity moy~ DOdim:! dl«. "" lh> melol .•~ bill ....... 10mc>diry and dimi,,~~ ill Ell _ ....,. arr...,;:t.pteiOlioa. An .ump""!be f.rric·l......... in>n.y....... ",tOCb in mllny ""il. and >edimmll;" byrot lhe man Impottanl ,edo••ySltm i. ttrmo g{

ooyge. l'\Iui"alcnl~ Thi, il dtmun!ilrlled i.T>blc ] .'hen: It'd<.>x _1lpOII<"1< lOr I l>(i......ippioIl....ial soil _ p.......,!!'d. The oxYl!"" cquinlcnlof lbcK _ 0<01"""..... c:m he <:okul.oled '-'cdOft >IOKhiomcll)' ..~h .1......... la .ltctro.d<>na.- [lSI- Clkula.i"", ~moasrllt 'nl......,m"". of lbe.lOlid redo. compon<:nlo (C-I..Ft In<! !>In). La ""II, """ Stdlmenll .. llhoppteei'blt iron '0II1.n'. ~baD.., in Ell arcdirni"j!bod ot buffered by lhe .lox1rons ocuplCdot ",lcaocd by Itl>CIUllOoI mel_ism .,nl me iron.yll,m. TIIi. i. p&"icul•• ly imporlODI in'l'tmio<lS .""b "' no<><!ln&!dry;"1 Of dI.d,in•..'be... """'••y>ltrns .... buffer the Ell obcw. 'hecrilk'] Eb of. po.r1i<:ullr .......fotmllioa for ,ctRoift pcriocI .... ,iJI...

nIl••IJ"I""y Itrm <an be me by uri....ll., the lius ofimpotl..... rcdoJI .)'....... illldividually 1»' I __l,p"O>f,. n>c<bod "";11&In 0>.idlInl ot re<lud0lll [lO]. S<>'<'nlI .ot,,,,,,,.,I' .... the ..pcity (••1-.OJ. NO), and sol") .... wa«,·so!ublc and ,ully meMlftd, How<:\'tI".Ii""" ",lid iron and illlnlll'>C'C ",ideo lCp'<:>crl tbc bo&lk of Ibt redelonp"d.y In nu.ny .y.""". "',:tho<\>. .... ,,'imlll"1 ""id"'i.... caplOilYfoous on csUlll.Iltal tbe fraction of~~. lbll if, poIeIIliallyredu<:jb!<, Voriuln m<tht>d> b;o"", been dcYCl<>pod (for. "' ...,Sllllml and SIll'........... r241~ oIlhw'" klwtr..........ualions _in,.gcntI .. lICCCISIty to 'w'..d)· qlWltify COIpIIcil)' in ...,;rm 1201.

OIher oapo<:lIy .,.....1IU iIOt dlrc.:lIy ...1>iN 10 o~<Iolj",,·

re<ludioo. 11,.., Unpotu.nI rOt """al ,p:ci.>li<Jn, "., tuna:pl uf ..,id-vol.ilt ."If '. rot ua"'l'lt. i. u!OC<l to q".."lfy a .,,,,,,IV<' p<>OI of",lfi<k ,ba, "0<1 ..ilb trlRSl,ion ""'lol.lormin. ituOlob" mctaI,,,Irides.

176 .....d... "rid r.lrld

J. OlRmOUM,SF.I..F.NIUM AND ARSENIC

01100';1111\, .d<nill"' and ~'" n:p<~n1 • <I.., or me'oI. arM!melolloid. mol .~l'l in "'uhipl< ,.1< in ,he ..dimenlenvftonm<oll. Sludies .... dcKribcd 'hicll quallify $fl<l<ialioncllanp in "'S9"'!" W oIl<...ion in l<1Iime'" Eh. n.... m<tal. andmetalloid< panidpal' directly ;n redo~ ",..,ion/; arM! .an unde,1Oo~iclarionlnld ....ion .........", 'beir v"""", 'lienee .......~ "opedat"" or. illlptJlUnl bDc""", biol'O"b<mi••1 and 'o~irologicol

<bancl<rillk. of ,h<oc .I."",nli <bani. dr>malically bc'w=n m<talfQnltl. Rw uamplc••lIm<nium (VI) i. """"",imood, • l!>ouIaro;l,ime.,I-.: 'o.tic lban Crl:Ill). Sclenlll., ,he o~jdiU<l form or ....niwn, i.""","y I(IIbcd wben conlpil<'d. to ,hot ..leni,. rorm In].. I_poic.......... <_I. -..iu:(Ao(llI)).;'. 0II11p«1<d .""'........ 12'1 aIthoupun"n <qanic ....Ric.;, {•.I .. arwlloObelaine. tlIc primary form or AIin rioll arM! wllr""" ore ...I",;'·.I~ non·'o~ic 126). PrcdiclinllhcK.1wIi<" ill .potialioD. 'ben:rorc, Il<a:>mt:> cri.icol in -.-illl ri>J;. oM"",,",,'ia1 cffo::to.

e:tIarIF' in mcta.I and meI:sll<*l ....ulKIiIy in <apoo:t< 10 oIl<J11tioco1in ..dimMr. Eh :we _ -.-i<I<d so .Ie"""", ...-iIh .....hiP'< val<to<e IlMeI

{•.I .. Cr. All and Sc~ SoIubili,ie> or Olhc, "",laIs (•.J.. Zn) tan be"""rt>lkd by oorption '0 !T'do.>.·..ru.i'i'·. <urfaca "",h ... j"", _

manl...... o~;dcI [211. Chanl" in Eh. 'hc",roo:, <an "'00""""ubili" chan~ in 'hue d."""". -lin<. d'W).....iO<l of 'heK ~idescan. occur under ..,.,. """'~ condition<. Di......ion pcesenl<d below willf""II' 0<1 hi·vaIe""" .10""' Ilsor dir",-",I~ pmlcipor. in o.id.a1ios1-rcd""lion i<lni. Tbe OI i.. di",.,1<11 he", iJJII<It1I1e ..",,<ll1importlm poirll' O<JII«ming melll .potillO"" II""" !he innllCncc ormW. p""""1ai.

3.1 Chromium

Chromium ~ne..II, ...... in ''''0 VII........,"" (Cl(VI) _CrjDlll in tlIc ...virosomeal- CI(VI) is tho """i.. or """" """""'" due toitt_itil,. fJIlIlIC<'ftir:ity. -.kct inl<flrC'ion wilh panicles~ Jrut<I",I~l>tlily. III:n"",,,,,,...ud.;"; l\avc in_i• .,ed ,he ,ran.(onrwjonp<OCO:.... orCt in ,.-iou< ...ir"nm.nb 128.29). "Iaill. tho kinecicl ofl~ 'ransformalinsl prt>.."C>'C' Irt: or in'<n:" .in« «fIIilihri"'" "ID.Irt:ly be ....,rnc<l. "~.n' "ud, hy M...",hele~n ~, ~I_ [J) ""<hromlum redo~ <h<mll1'Y in I ......nllJy.noodcd boIlomlaad.hanhrrood fores......... '0 ill.""". -... or ,.....~ The<hem;II'}' of <l1I"",;ulII in ,he 5001 and 1'lonr:I-...:uu of lttis iysltnl 'Waidomi~.,<>1 by o.<i<Ialio....e<hl<lioIII lAd oorplion r<-IoCliosII. Cluwni.....

176 ""rd... and ralrlri;

J. <:1lRmOUM,SF.J.F.NIUM AN[)ARSE1\1C

OunoniulJ\, IICl<niuOl and ~'" ~pteli<nl ad.." "f ""'101,_meloll"Od, <hoI .~ill in <n"lIip~ ~01 in ,lot ..di nlenvitonrntoll. Sludies .... duaibcd lot ""I\iclo 'fI'II'Iify SflOC'ioI"",.hanp io ""9""'" Ul a1k"'''''' in lItdilDN\l Ell. n..... metal, _melollnidl paniotipal. diroctly in ",do>. ruciioniand. can ulldt'loo';daIioc>/m;lllO"ti<ln bet.....n ,lot;, v"""", v.1c1Ice Olllel..~ ill

'l"""01"'" OR: impotl.nl br>:,....,. bloFO"htrnlcal and. '''~icol<>ciotol

.Itoncltrilllc, of ,htoc .1.""'011 .banJc dr:unalicalty belwtal metalforntl, For "URlplc. ellm<nium (VI) i, lII'!I'tO'i.......y a trou-.l,ilDClI''''''' 'o.tic: lban Cl{Ill). StI•• lII•. lhe o~jdiud rorm or .. IeAi...... i.p<>Oriy I<IIbcd ...bon conlpllc<l Ul lbo ..leni ... form 122~ lQOtpniconenic. ,_(..~ (Ao(lJI». ;, a ...>pctocd (art",,-, fIjI aIthouchcen"o "'Ionic ....nicll. {•. I-. IIVtIObeIainc.lhe primary form or..ui. filh _ wll(u.hl .... reJ..iv.l~ """·'o~i. 1261. Prcdk.inllhtoc.too"iC' in .pcciMion. ,herd"",. bco...... criticol in __i., rist_"",".'iI! effect>.-

Chanp in nlClol and mmllo>icl ....ubiJil)' 1/1 ""f'JC'C 10 oIlCl111iouill~ Ell ..... _ -.iCIed 10 .10_ ..-M n·••lliplc valrto<e .......\•.1.. C•. A. and St~ SoIubili,ies or Olht, "",ws (•.1-. Zn).1II becomralkd. by ootption '0 mX».·..n.i"'·. sun..,.. "",h ,ron _maIll....... o~idc. 1271. Ch•.,.. in Eh. lhererore "'00....""ul>iiil)' .hanFS in Ihuo c1.n>tn15 """'. d' 1uolio<I of 'he>e lUidescan ....... oodct low re<lo.l tIlIO:lilions. Di ion F'ft'SC'IIlCd be illfncus"" mohi·VIlcn<e .Ie""'.... Iluo directl~ r-ticipor. io idal_.c<l""li"" ...ctioou. The 'hod;", di..u.1Itd he iHol!nte ..",no!impxllM poi".. CUI<.m;nl "",..l .pee....,"" u , !he ,,,n...nee or~. p:>U>IIi.II.

J.I Chromium

C!Iromjum ~......lIy ...... in '''''' v.I..... 01.1.. (Cl(VI) II><!CljDI)) i" the ...vitoon>r1ll. Cl(VI) is the """,i<' or....,.,-.. due '"i"l(l.<itit)'.lDlIlaitnicil~....ukct inlCfall:lion ...ith panicle:<_1feII<roolobllil)'. Nu",""",' 1I1>di.e< 100ft in_i.Ole<! the 'r.u"fonna<i<>ftptOCe...,. orCt in v.-iool ...ironmcnl. (2'.29). A...... !he tincticl orI...... Iran.'"""",",,, 1""'-"0'<' .re nr 'nl ' ,in.< cqniJihriOfll "lOll.on:ly he ....,rncd. A ~<nt IIlIdy by M hele~. I' ./. (J) "".h.omiom "",o~ .hc:m,1tr)' in a lJy.nooded bon""'-IandIootd...""" fotal ........ 10 tllu>lr.llc ..,.... nr lhtoc proca.ocI. ThechemiRry of cll"""io'" ,n ,lot soil and I'l<>nd~,of tIIis i)'$lC'" """donIiDl",d by <>.<idoli<>B·redlI<tioa llIId o«pli<>. n:actioIII.. Chromi.....

ChanlU In Motoll SpodulOll: SocIl.......1 R",o~ Stoll... In

'0''' "Filled ....mllllle o-<liphc:nylalrbWdo _hod [n] for Cr(Vl) ond1<:1' for '0101 C,. Tri ••k", C. "'... <ict<m>in<d hy diff..._. ... criricalEh of +300 mV~ ide",ifiod for ,he reductioII ofCr(Vl) LoCt(nn i.soih. Kinetic< of Cr(vl) 10 Cr<IlI) red....i<xI _'" ..pi<! (.. I mirwtojand~ ... hip C2J'8<"y for """"=6011 .................. '0'",,", so ""of Cr(VI)q: of ""I ......;""~y~_ The re>'eI'K ruction.I"" oxldaii"" of Cl{lll) 1<, Cr<Vlj. was not~ i. soil bul wuoboo.-d in ,"" llood".......... $lId_ fil:o """lainill. Fe and MIl w..promi... n' in ,"" wo<l.nd f\oOO"'alU duri". periodl or ,"" ye;>r.O>.ldal;"" '"Ct(1l1) has boorllM"" Lo be: dependoenl 0II1ho pi......... ofal'lOfpboln manganese O.idol In]. The JlItlCDCe ol1llesc: c:ompouod.in ,he ..ufoc.c: f,lm ~ .u,i"",'" •• ,"" c....... of C, oIidoIi"" i.f\oo<Iwal....

Tho off«1 of dang.. in C, .p«iation '0',' moIt ..,ide", inoorp.ion ..udi<.t.. SorpIioo is of,OlI mothomalically doocribod lI!.in.i""henu "'i"alien•. for Cr. IIowe'·.... ;""1Ientl pa<amelt;n; IIlInI' IKIIooly lOrpIion blot oIKI.tioo·reduc';"" and procipi'ali"" ..""Ii"'"",,"tho,. T'berof.......hal" ",fened 10 .. Cr ~MxJIlionM ioolbmPo IIld""",rrocienb.•c".oIl~ inclL>de multiple p""""-' 10 oorplion iIolhetmi""""""led undo. CQIllrollod E.I> condi,ioa. sorpli"" .... 'l/-ul: (uiodie.1ed by 10... sorpti"" C""fflC;'''tl. FmlodIic:h "K") above lbecritical Eh for Cl1"Yl) redUCt""'. IkIQw ,he criticol E.I>, when Cl(lIl)..... p.....,,'. MS<KJI'i",," """,rr",io"l> ,,,,,,,,.,,ed by Ikn>c-orden ofmagnilL>de (FillutC 2~

•. ,--=:;--;;:;-o;;:;--;;=-,~-_. -- ._. _.;: _ lb

~ t:IV n- ..'9 '",.

I

.,

on I'.rd~ and I'alrl••

Chromium """" ch<mi>lry ""....... to illlal"u" ..,'....1i~poifll' lboul cIIM#S '" $fl<ci>liod wiotl fA Fi >p«ialioa chanca..., 1>01 oIways ",V<niblc (Of lu~ nlUCh difT ti_ico). JlN:Mtl" ofIbi., ......JCS in bult lo<>dimalt Ell &'" 1>01 }'. accomp.anicd by.Il'.g•• 1n .......1 .p<d..iQft. St<:ondly. for Cr. ,<la/ive n'e. of~.formol;"" prGCCSX<. i .•.. o~idatio. <>f Cr{Ill) tond red.....ioo ofCl(VI), indkale ..·....00 llIi. cnvitunmtn, ~"." ....$i..... Of-_=''" Cr. Si""" ,he ~""Iio" of C"VI) i, rapid and oo<:or> in bolbflood...""" and ooil:! (11)qe pQ<)I <>f 0) and ,hi; ""idoIioa 0( Cl1m) is...... on<! IlC'<VB ""Iy in flood", (I ,mall 1"""1 or Ctl, lhi. wetlandbias • V"l" pole..,iaIlO .."" "'" ";1Ik for Ct.

J.2 Sdcnlum

StleIDllm can u;",;., fow dilf.....' ....""" lcniok (Sc(-II» ••1.."",,,,01 So:: (Sc{O))...Ie.i,. (XliV). and .. Ion (Se(VI»).$c:knium dl<m;<Uy i. romp.labk 10 ..."b<, Gtovp VIA c""""....>lJlfIIr. Api'" major r.,l<ln aIT«,;ollh< flU and """'PO" "'....niumin "dimont· ....'., ')"OIe'l" Ire it. o.i4:l,i'.....cduOli"" ud "'""",~n'eff«.. "" ,,"ent"'" proc.._ (e.•_. ""P'ionl. Nu"",,,,,,,,>ludles have oo:o_nI<:d Uf'<dS of ""len;nm bi<>v<'<h<","lr)' IlO.J I~S'udic. compkled by M."""b<kyn "oL 1111 On coo,.minalOdK...cnon """rv<lir oedimen, dnc~mt," """.. ;mp>n.... feal..,..,. nf Sc~mislly lI>d lb< cff«1 of Ell. A "';lieal ilql io II><I< 01_ ii m.ability 10 OIlolI)1io:ally I<JMf"U' di{fcrrn, ""ltniom >p<ciQ. A bydrid<I"...raioIIIlrappilla;.l:l<tcclioa~ ... ~til;t<d fut ,iii• .lt00y has \>eeadeocril>e<l ,n d<tail clKwl>ere Illl, II di"i.l"i,hn b«~ I<Ienalt(S«VI)~ I<knid< (Se(IV)l. dim<thyl "'ko>d<.....tdiud nxtlryt.,cd Sccomp<l'.In<h. ond~ (S«O.·IIll ...k,,;nm.

I. ~...,., rim<n<. ><>Iubili'y of So nnd« r<duced l>I.><odi,........... low.. (eonuolle<! by on iroo ..~id< p/l... lINn ond« ooidl.,.,c""dil;OftJ. Wl>en Eh is in<n::_. 01ida1,,," or Sc(11.0) '0 knit<(Sc(IV)) ..... rapd (lime ",ole '" ........1d>ys). So....q...nl idation'0 ,hoo m(I« 01id;ud ...km'e (ScI VI)) 'pccoes "'u mlOCb.1ow<1" bII.,i,"n suff...... lime. """"', OJlidi!.in, <0",1i""." (i.e.. 1<><:01 ......u)•..1e<\;Ic. iI 'ho< <!onb'WIl ,pecic; in ..,."","'. R.""",bilny of tbcoc""n,r""""",i<::oD< "'a. no< co...>d<f'rd • .o.ph<1l1y in ,hu ~. __,Crilical Eho rOl' 'ho uan<lonnooi<::oD< '" 1lc••nnillOd ar.d .., +50 mVref tl>< Sc(-Il.ol 01i<btion '0 "' ide. Sc(1V) lI>d +200 '"v roo 11>0,,"0d00i0n of ......idc 10 ........... SetVII, J\ddI,..,..... ....me. ....... H)WR....voio. NC -Jimml>121 """fJmocd~ rc.!UIlO. fa lIlia ••,limenl.wl><n Eb "'.. ,ai<el! I" +m mY. 68~ "r the Iotal So "n,,,,,.' .....

on

Ch"""'um min>. "h<miMI}' .;c....... 10 iIIuSl"'''' .., ...l impufuIn.poilU. obouI_lI'" '" $p«'ioliorl "";,h Eh. Fi .... >p<Cialioa chanp..., '"" "ways ",Vl'fSiblc 10< lu~ nl'Jdl diff...,. kill<tito). Bet..... <>l',iii., "......1'" in IIult !o«linl<llt a. It<: nQl a1 ....a}'. """""'P"'icd byd.ang", in .......1 .p<dOli<>ft. StcOlldly. fl>l Cr.....Io.livc n,•• of....... fO<mlllioll procco. i.e.• C.id.,ion of Cr(lIlj and red",",ion ofc.(VI), indicale ..,hd IlIi.. c.virunrncn, ~NO ... '"nIl" Ol' '-="of Cr. S"'tt ,he red"",i.", of Cr(VI) I, rapid and ,,"or> in bolbnood....... and "';I:! (0 l-.;e p(IOl of e.l_ ,Il< ""i....."'" of Cr{llI) iI....... and OC'<"UB O<Ily in n<>o<l"'· \0 .mall pool ore,), ,hi, _~andba • ve- poIC",i" 10 .,,' "'" oiftll: for (:S.

3.2 Sdcnlum

s.~mCMI u;'" ill fOUl di!r"",., _a1.""" "aleS...le."'" (sq_II». ,,"'......... S< (ScIOli. ..,Ie.i,. (SclIYIl. ODd ..lc~ (Se(YI»).$c:ltnium d"",';"')' i. cOIIlp.l&bk ,. OIK>Ihcr G,ooop VIA cit"""...""llIu. AlOIn, majo<r~ lIT«l!n1l1h< r.... and <no:Ispon oflo."niwnin ..dimon!· ....l.' 'I"ems a", it. o.id:l,io.·",du"';",, and "'"...bsequ<IIl <If<<.. Oft ",,.ntion pnx:c>_ ('·1.. ""P'ionl. No"""",,,..clldlcs bave documonotd IUp<C1> of~kn;umbi.Jt<o<h<rniolr)' [lO,3 l J.Stud~. """,plcled by M•...,b<lcyn "al. 1111 on co,,,.miJlaloclK<Sl~ ",,.,rv<li, oedimen, dncU...."' ""'.. iml,,,,II., fnl..,..,. "f Se~"""ry..... lbe off<C1 of E~. A crill.,., '1I:p in llltile " ....... is IllCabil"y 10 .....J)'Iic.lly >CJM'"OIC diff~""" ",kn,um~. A hydrido",~appinJ"'let«lioa"!'IW"' .... ",ilited fut Ibi. 1t00y Iw \occndeocribtd ,n deI.,l tlocwllt", Illl. II <t>"i"IWi.ho. boIWftt:l 110.....10(Sc(VIlJ. ,dtoliilt lSe(IVj). di....lh~ I ,don""'. o,ldiztd mtIlryI.,od Sot<lIf"III""lKh. and rtdu<td (Stlo.-lIn ..ltn;o,",-

I. ~DOIIdlntnl. """",!i'y of So oodtf rtductd cundi'......w," lower (eonl1<>lltd by >II iroo .. lctlidt pII....) 1M. under oaidili"1condilion>. Who. Eh i, ,n<rcaled. o.id.al'Qn of Sc(II.O) '0 ",IcaitoiSc(IV)) ...... ropd {lime ",ole of ........1d.>y>!. S"b..q....nl wddalioa'0 ,ho mo« ""idiud ..,.....'c (Se(VIJ) 'poooes w~ mlOCh.1o'«<1" bu',i'..n ..,lTJCI<nlli..... UIWltro.1dWn, condil (i.e.. ..,>'<01 ....,.,u),""Itnalt ... !be du.m,w" .poe"" in 1oOI R...",bilily of lbeocIn>Iif,,,,,,,,,'''''' .... "'" co...odt<rd tIPI..",>, ,n lhu """y. however.Crilical Ehs 101' 'ho lIllfI'form:&ll<)n< ....n: doto"",1lOd and ......, +50 mV(01' tilt SeHI.O) o.id.."", 10 ..Imido. Sc(1V) .nd ..200 mV (Of ,''''

0 al ..lmidt to ........... Sc(\'ll. Nldi".........I&tito ....... H)WR oir. NC ....imtn.. 121 <;OfIfllrntd lhtx ~ta. In !hi. ,••"menl.....1It. Eh .... ,.iltd to +~ mY. 63% "r "'" '01.1 So IX""'.' ....

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~~h n In . lelal pedal on: ~djDt 179

olubilized. Biomethylalion of Se . pedes w . also importWll undero xtized and modeLe1y reduced c diti (r, 200 and 0 mY).

Sel Ilium redo" hemi t moes semi fealure abouthang • in t 1 _pttialion in r . pon. 10 chang in . Ag in.

di crenc in!be' .ned of Ir.ll1S arm ti bet n different 'ffcctcd the predictability f. pc ilion. Relea..o;e of high percente.g.. > 0 ) of tOla] . lenium "obbeQ dimml

OJlidiUd. COllvusion of lenium to organIc forms also rved.Dr.unali differences in the olubility of oxidized. pecic.'lUCh the.elenium oxyanlon' nd the reduced ped (meroJ lenidesemph.a5ius the imponancc of considering peeilUion change in these' bemi try of this metalloid.

3.3

Arsenic c n exist in [wo pnm:uy fon:ns in sail. 3nienllte (Ai( »nd amlnilC CA... ). Both fom arc I bj I to .iomet.hyL ti n.

resulting inrglllllc:lT ni pede~. 0 id !.ion-reduction. d tubsequcnl effccts Q sorplioniprecipitlltJon major factors affectin

IRe fm afar' nie in,. di menl-Wl1lCr :y. tern . Studic: by. 3Sscheleyn(2.14) docurnnl Qme important features of arsenk geochemi try insoil and dimeDt. At Die w spccialcd usin a Mmilar hydridegener Lion tccbniq a used [or selenlum [33). The m lhod m - u.resnanogr.llll. qUailliliu of arsenite (As(lll). ar en te ( {V •mooomethylarsonic acid ) IIDd dimeth Llll'Sini ocid (0 ).

In con 10 - lenj m, nic olubilily Wi 0 'n to be gmuerunde:- anaerobic condilion Ih n under ac:robi con hi i II

contaminated olin, Loui5ilUlll soil. P 0 ~ 0 the tOOl! nlcprescnt in tbI! 50i] 1111]£ mobiliz..ed lbe ban in Eh t reducingc ndJli n . This nnbUled prirnaril)' 10 ~Iease of folio ingdissolution 0 iron ox)'bydro ides under mlucin conditi M.

had ihe hi t . occnlmU os nda- a .di .ng coodili hilhc: highest 'e conce.ntrntion under re.d~ conditi()Ql.

not tbemJod. n mit 'j vorab e. i ni6c.Qn1conce~ ofere rved under redu ing nditi .fler the ed

di&solution of iron 0 yhydroxide in the c nlamin .cd Lin, 1...oI1lA1:anait Y"O detec Ie e D er fi e wtcb and ftu flooding

,ub quen changC'. in Eb. Slow un ti of the ) to (lIT)reducti roup with the rel e of i b c cet\lrauon of Mn uponreduction IlJlIdc the prcc-ipitation of ,In) S04}z p under reducedc nditjol1.! like!)' e ent a.~ indie cd b ' G H

4. CONCLUSIONS

ChanIO. in >t<Iimon' Eh in ..._ ,., I'OlUral or onllYoposonicall..ao.ion i< on ~COOlrol OIl 1soJubilil)', UofonwuUty.lho'->riot)" cl<:<Jftdi,"'"' an.d o~mon" il. gononIiUlions aboullho cffoctof Eh on moW >pc<:i.lion .nd >olo~lilY. I' IIlIS ~n ....0<1 lhtIoxidizillJ condi,,,,", favo< moIiI in",iubjlily wbile n:dIIcins conditiOMfa..or molal ..,lu"ilily or moI>iliry 1101- "Thore "'" .. leas! ICVOra!imporllll'll uUplioru to ,hi, rule \0.1 .. C. and So ... di","","" in lbi.pJ.pO., _ Jl<Ol*>ly.....,), ",!loon. In ""'~ ......imon" or ",her areaswilb high coneootrtl'''''' of .ulfide<. lho oppo<ile ,rend (.....1..soIubilily under ocrobic «>ndi'i....) i> Qboc.-J r", mtfIJ molal•. "Tho..lIdits dioen.oed abo... don>of\Ol'~QllIot """l'licariol fea/un:>. FINof til. rho r.:o..... <qUalioo.. rho cr-;ctll'<dox oquUibrium "'luatloa. hasonly limited pttdioti... abili,y fOf n>elal, ",00.. transfotlllalion u...ln......1<)",_ In addi,;"n. It.< <ty...mic ...._ Of ......y soil> and Sl:>fimonl>makn an "'luilibrium IIpllfoaoh difrlO1lllto JUSllty. 10 thcIc CIOet'p:lCialion ,han..,> mu~ be mIl<klcd ~inclk.lty. lhus ,..quirinllhodolem\inalion of • .".",r""Nlli"" rate. S<coodly. ,"""y In<:e mo,aIlr.III.fonnalioM requi", sp:cir", mid..,l> or n:<b:lancs rhol may DOl bepn:ocOI in. Ji.... ..,;l Of scJ.i"",nL llIi.leada 10 im:......I>iliry Of wry.1.... kil1elics for "",naln molal " .... rom>tlions., makinllho Nomse"'lUtlion. ",hore "'luilibriom sswnr:d,~I/:ly ..........

Prodiclina changes io tI speciation in re.pome '" fJl. tho.n:qui..... """""'-1inl ,he rransf,,",,",im. irsoolf WhM i< lhe mIn fJlintensily for lho o.idation·re<!uolion I..",fonnali",,? Wh:ll i. lhocapocily or ,ho oaida", or <Noc'""'l') in It.< ocdi"""ll wbich actuallydri... tho ' ......formalion? "Tho ""((crinl clIpO<'i,y. 01 b<:>w f... bul~ Ellchaoge, ,,"CW' in 'u""o.. '0. change In ....drtio.... muse abo beulldc"lood. Predicr;nl ,he.. tran.formal;"'" ",ill ""'luire bencrrccllo;q-, of ""'~IEll ,nl£1l>ily and C"l'""~y. Monirorinl certainea.ily-lIlU<urcd reclo. coupl.. (e,I.• Fe·llFe·), Mn':'Mn~)mayir>d....e rho ""...iltil~y of I mot.al .p«iI1iOll lRMf<l<mMion in IICdimmL pani<ul..l~ if~ i<Id;oalO)f _pies .... dirtttly involved i.lhe "'...Iion. TIIi, will he~ """"lIle lhan ".in,l ""lk Ell inlplali.om electrodes wbicb .... limilcd b)' """_ilibriom or yrcdoll<W(lleo in lhe- .y".m.

Finally. it >bould be ''''''In;,J:<! thla any raIe dcpc'ldl on.\~numbe, of voriable•. of which Ell II only one, Ocneroli.tin,l""roo>group> of _ral. tnd envim",nen" will t.< diffICul1 bc<:ause of rhovadable. C<lnltibul;nl to ,he ~inelic rate Ie,m, Ben.. ""'Ihodo ofn..-.rin11OflV: <if I..... varial>lcs (e.l.. Ell) lIIlIy i....,.,.,.e prtdicIab~i1y

4. CONCLUSIONS

Ch",O. in It'dimrn' Ell in <npJ<I>O '" .....mor "llvoposonicaUnation is ..~ cone,.,1 on mo..1!l<llullilit)'. UnronUIUlltcIy. lho'-ariory ofcondi'ioDl; and o~mo... resi,. gonon!i.taliono aboullho effoctof Eh on moll! .pu;o';o" and ""'ubillt)'. I' Iw boon ....ed !halolidizlllJ coodllioos fl'.... meta! inlOlubillly ..Mo roducl"l condlriOMfa'"," mota! ""lo"ilily or """'ilily 110). "Thoro ""' .. k.aol ""vora!1m""".... uuplioru to thi> 101e 14•• C. on<! So .. di",u...d;" lbi.pape., _ Jl<IlMbly many Q1~. Tn ''''''tal _mon" or OIhor.uowith high CO"'O""I'''''' of .ulfides. lho "A""ile ' ...nd (l"'alOr..,.LJbility urdor ocrobic """"I,iort» h oboo<lYftI fgr many motoll. "Thoaludics di",o<SCll ._domon.u.1e OIhor """"licali., f<alo"",- F"""of all. til< No""" ...,...u"". til< <~a! redox oquUihrium equolioll. hasonly limited predictive ability fOf n""aI, ..ho5e lflWfonnaiion ~li<s.....!ow. In addit;" ... tb< d)'n>"'k n""'" of """'y ""I._ oedi".,nlSmaktll All eqolll"""", lJIllft>a<h dimwit 10 JUSlity. In tboK <asu.poo:i...ion ,!I;m..,. IIlUII be modoled ki""lioally. tllw requlrin,lbedolermu.a.i"" of. """'f"''''''li'''' talc. Soooodly. many t~ "."a!"""'f""""'ions roqul... opo:;lf>c •• id....... <>:duo'''''''llIol may DOl b<prn<nt in a Ii"''' SOIiI Of sedi"",nL TIli.lclltb to ;rte..nil>ilily Of wry.1"... kitltlin fOf ..,...in mot.l " ....rom>ali....... makinllb< Nom..equation. ,.,horo equilibriu", IS ...wnod. oompkltly UI\USIIIlJoo.

Predictin£ .hanges i. """oJ """,laIi"" in rospom<O 10 Ell. lb<nroqui....~nllho""""fonnalion. iI5clf. Who! io lho min EllInl.noity fOf the o.idation·...ducllon uandormallOfl? Wb:oIl i. tho<.pacily of tho Ollidanl Of rcdu<taIl1(1j in lho _"",n, ...-hich actuallydri'I'C tho t......,f~ion? "Tho buff.rinl OMpaCi,y. Of J>t:t-- f... bulk Ell<hongo. ""<IU in IU,,""" '0 a <h....B. in """dilio.... It\U$O abo beundtutood. PnodiclinB the.. Itan.fonn>liona ,.,ill rtqu;r< belli::.technique> or me""';nl a. lo~ty on<! c.ll*~J. Monito<irl, CUllin••oily-mcaoun:d miDI coupl.. ('.8.• Fc,Z/Fe.J. Mn':'Mn~) mayindic... the po..iltili'y of I ".,W .peci""",, ItOn>fonnation i~ I..<limEnt. particularly ir lhcl< indio...". OOIIpI<> oro diroctIy iD\'Ol"<4 inII>< .....lion. .!"II" willI>< more OCCUfll" thon l1!IinB bulk Ell Olin,plOfloum c1cetro<lcs which .... liIDucd I>}' """'<q";hhrium of nu.ny

raIoI«lUJIleI In lhe 'j''''''''.Fi....ly. il >hQo.lkl be mllOlni'M! ,hal. a.ny 1»1< dopc'l<b "" I I....

no",be, of vori.abl••• of .. bi<h a. i. ""Iy OfIC. ac.....lizln ......B""'P' of ....t.l. U1d cn.-iron""'nts will he diffICul1 bee of lb<vlfiabl •• contribulinl 10 tbe kine,i. ro" lerm. Be".. ""'lbodo orn...-.riflB ....... <if lhcoc v..~ ('.B.• Ell) may i"-"",,," prcdicubiIny

IS1

ud imp",,'e our "o<lentandioS of me,.1 fl .., from ..,di"",nlSlIn<krJoinl <!wile< in Ell.

I. Ke""". M. and K. WallflW\. ··Remol>ilil.>tion EvnllS Jn~oI"ina:

Cd Odd Zn from lllleni<l.ol M..d f1IIIo. S<dimt<IIS;" tho Efbe Bolliif}'Durinl'he Tid&1 C)'<'le." f:.r, Ct><l'f. Slulf S<j. 35:)71_393lim).

2 Maucheleyn. P.II•• 11..0. Del.une .nd W.H. Polric.l<, Jr.,"AJ1aUc _ Sdtllium 0Ernt>uy .. AITecl<ld by Sedimrnl Re<IoA""""'liol and pH." J. &I,,;...... QNt>J. 1(H22·'27 (1991).

l. Mo.ucheley., 1'.11.. 1.11. P~rd"". 11..0. DeL.ou"" ODd W,HPatric:l<. k, "Chrom,um Redo, ClIonuscry ill • l.-.er Missmippi"'&1Jcy BouomlancIII........ood We'land," Eo.;"",. Sci. T«"'ol26:1217-1226 (Im~

4, DeLoom<. R.D. _ CJ. Smilh. ~Rekti<: ()f:-:~ one! M<tobfoil_ina O.idalion of Fr<slI"'",el 3nd s,oline Sedimenl." J.£I"...... Qt.aL 14:'64-168 (19~1,

,. Stumm. W, and 1.1. Mo"aII, Ilq",,,lr CA<",;Jlrylnd <dirioft.I""" Wiley'" Son•• (Ne,," "'ort. 1981).

6. Spooito, G. and S..... Mltlilod, "GEOCHEM: A CC>IlIpur","""'.m for rhe Caleul31;OIl of Cben,ical Equilibria,~ in S<>ils<>lll,ilM, IUI<I OrA.. Har'TIlI Wm",. I]ni."....y of C.lifornia,(P.r,ef1Jde,CA 1979).

7. Bm..", D.S. and 1.0. Al)ison, Ml"7£QIlI £Ij.llil1rI.", M<141~pt<Wi<>ot Mahl: " U..,', MIlI".al. EPAlblXlf.!·87IOJ2. U.S.EPA. (A'hen>, GA 1m).

S. Lindhe,•. 11..0. _ D.O. Runnell,. -Ground W.,e, Redo.Re""l;on>: An Analy.•i. of Equilibrium S,.", Apptied 'a EllM.--.... oncI Gcochomical Moo.lio,,· Sc/;oru225:9ll-927(191$-11.

9. Turne" F.T. Ind W.II. ,,"triel<, Jr.• "Ch<mie.1 Chanll"" inWOIorSlc:u«I $oils ... Rc«.lt of o..)'P llcpletiool," in T"",," 9IhIn•. C""I. SoIl 5<:1.. "<ld<>M., l.W. Hol~ Ed., pp, 53-65,El",''''''. (New YorI<, 19611).

181

lod imp.o.'e 011' """""IOn<!i08 of DleI.J nu, f",m ..,di"",n"lItMkrJoinle~ in Eh.

I. Ke""". M. and K. WallflWl. "Remnbili>.ation Ev.nu lnvolvilllCd MIl Zn from lIIlMi<LaI Mud f10l S<dimt<d> ill ,lie EIbe EslUJIYDurinlllle Ti...1 C)'<'I.>~ f:sr, Ct><lJI. Sltt:/f Sri. 35:371_393om).

2. Muscholeyn. P,H •. R.O. lIeLlun. In<! W.H. Patrick. Jr.,~Alotaic MIl Sdcoiwn 0J<m&>uy .. Affet1lld by Sedi"""" IWlo>;I'oIIfn,ill and rH.~ J. &0,,;...... QNaJ. 2IB22-'17 (1991).

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