海水沉积物中总汞甲基汞测定

海水汞

Baseline

Total,methylandorganicmercuryinsedimentsoftheSouthernBaltic

Sea

J.Be dowskia,M.Miotka,M.Be dowskab,J.Pempkowiaka,

ab

InstituteofOceanology,PolishAcademyofSciences,P.O.Box197,Sopot,PolandInstituteofOceanography,GdanskUniversity,Al.Pilsudskiego46,Gdynia,Poland

articleinfoabstract

DistributionofsedimentarymercuryintheSouthernBalticwasinvestigated.SedimentsampleswerecollectedfromtheSouthernBalticintheperiodfrom2009to2011,andconcentrationsofsedimentarytotalmercury(average102ng/g,range5.8–225ng/g)andmethylmercury(average261pg/g,range61–940pg/g)weremeasuredinthemannerthatthein uenceofbothpatchinessandseasonalchangeswereassessed.Moreover,sedimentarymercuryextractedwithorganicsolvent-theso-calledorganicmercurywasalsoanalyzed(average425pg/g,range100–1440pg/g).Thereisastatisticallysigni cantdependencebetweenorganicmercuryandbothmethylmercuryandtotalmercuryconcentrationsinthesediments.Methylmercurycontributiontototalmercuryvariedfrom0.12%to1.05%,whileorganicmercurycontributedto2%oftotalconcentrationonaverage.Theareastudied,althoughmercuryconcentrationsexceedthreefoldthegeochemicalbackground,canberegardedasmoderatelycontaminatedwithmercury,andmethylmercury.

Ó2014ElsevierLtd.Allrightsreserved.

Articlehistory:

Availableonline31July2014Keywords:PatchinessSpeciation

OrganicmercuryExtraction

Mercuryhasbeenasubjectofenvironmentalchemistryinterestforseveraldecades(Pacynaetal.,2006).Althoughallchemicalformsofmercuryaretoxic,publichealthconcernsarefocusedonmethylmercury(MeHg).

Nowadaysloadsofmercurydischargedtotheenvironmentfromanthropogenicsourcesexceedseveraltimesthesefromnatu-ralones(Pacynaetal.,2006).Muchofthemercuryoriginatingfrombothanthropogenicandnaturalsourcesis,eventually,broughttothemarineenvironment.There,owingtoitsaf nitytoparticulatematter,mercuryisreadilyscavengedfromthewatercolumn(Laurieretal.,2003)anddepositedtobottomsediments(CossaandGobeil,2000)inparticularinestuariesandcoastalareas(Boening,2000).

Distributionofmercuryinmarinesedimentsisin uencedbyphysicaltransport,sedimenttexture,mineralogicalcomposition,reduction/oxidationstatusofsediments,adsorptionanddesorp-tionprocessesandorganicmattercontent(Boening,2000;Frenchetal.,1999).Red-oxconditionsareofparticularinterestas,inthereducingenvironment,mercuryisreadilytransferredintoorgano-mercurialspecies(e.g.methylmercury-MeHg)thatarebothmobileandhighlybioavailable.Thus,underspeci ccondi-tionsafractionofmercurydepositedtosedimentsre-enterstheCorrespondingauthor.

E-mailaddress:pempa@iopan.gda.pl(J.Pempkowiak).

http://wendang.chazidian.com/10.1016/j.marpolbul.2014.07.0010025-326X/Ó2014ElsevierLtd.Allrightsreserved.

overlyingwaterandconstitutesthreattolivingorganisms.Asaresult,sedimentscanactasbothsinkandsourceformercuryinaquaticenvironment(Zoumisetal.,2001).

TheBalticSeaisalandlockedbasinsurroundedbyhighlyindustrializedcatchmentarea.Mercuryconcentrationsinthesur-faceBalticsedimentsexceedthegeochemicalbackgroundbyafac-torofthreeto ve(BeldowskiandPempkowiak,2009).Accordingtotherecentpollutionloadcompilation(HELCOM,2011)theinputofmercurytotheBalticSeahadef cientlydecreasedwithintheprevioustwodecades.Despitethis,nocorrespondingdecreaseisobservedinbiotamercuryconcentrations(Saniewskaetal.,2014).Oneofpossiblereasonsisthere-emissionofthepreviouslyaccumulatedmercuryfromsediments,inparticularwithinsedi-mentationbasins,duetoanoxicconditionsprevailingthere(Be dowskietal.,2009).

MercuryintheBalticsedimentshasbeenasubjectofinvestiga-tionsforseveraldecades(Saniewskaetal.,2010;BeldowskiandPempkowiak,2009;Be dowskiandPempkowiak,2007;BorgandJonsson,1996;KannanandFalandysz,1998;Pempkowiak,1991;Pempkowiaketal.,1998).Concentrationofthemetaliswellchar-acterized(Be dowskiandPempkowiak,2007;BorgandJonsson,1996),asisthemechanismofmercurytransporttothedeposi-tionalbasinsofthesea(Be dowskiandPempkowiak,2007).How-ever,MeHgintheBalticsedimentshavebeenseldomstudied.SofarjustonereportindicatedthepresenceofMeHgintheBaltic

海水汞

J.Be dowskietal./MarinePollutionBulletin87(2014)388–395389

Sediments(KannanandFalandysz,1998).TheauthorsofthereportmeasuredsubstantialcontributionofMeHgtototalmercurybas-ingonseveralresultsofmethylmercuryintheBalticsediments.ThuslittleisknownregardingbothcontemporaryconcentrationsofMeHginthesedimentsandfactorsaffectingtheconcentrations.This,atleastpartly,maybecausedbyrelativelyextensiveanalyt-icalprocedurerequiredtoquantifysedimentaryMeHg(Liangetal.,1994).RecentlythesocalledorganicmercurywassuggestedasamercuryfractioncloselyrelatedtoMeHginfresh-watersediments(BoszkeandKowalski,2008).Theauthorsusedmethylenechloridetoseparateorganicmercuryfromsediments.Otherorganicsol-ventswerealsousedforthepurpose:toluene(Milleretal.,1995),andchloroform(EguchiandTomiyasu,2002;Tomiyasuetal.,2000).TherearenoreportsregardingtheusefulnessoforganicmercuryasasubstituteforMeHginstudiesofmarinesed-imentscontamination.

Theaimofthisstudywastoinvestigateconcentrationsoftotalmercury,andselectedmercuryfractions:totalorganicmercuryandmethylmercuryinsedimentsoftheSouthernBalticSeaandtocomparetheresultswithconcentrationsmeasuredinothermarinecoastalareas.Assamplingstationscharacterizedbyvary-ingred-oxconditions,sedimenttextureandorganicmattercon-tentwerecollectedincloseproximitytooneanother,factorsaffectingsedimentarymercuryconcentrationandspeciationwereassessedtoo,aswererelationsbetweenthemeasuredmercuryfractions.

TheBalticSeaisasemi-enclosedwaterbodysurroundedbyhighlyindustrializedcountries.Twomainfeaturescharacterizehydrologyofthesea.Firstly,thesurfacewaterisbrackishasaresultofalargeriverineinputandthelimitedexchangeofwaterwiththeNorthSea.Secondly,thereisapermanenthaloclineatadepthofabout70m.Thesub-haloclinewatersinthecentralbasinsaredepletedofdissolvedoxygenorevenanoxic.GeochemicalcyclesintheBaltichavebeenstronglyin uencedbyhumanactiv-itiessincethebeginningofthe20thcentury(BorgandJonsson,1996;Pempkowiak,1991).Muchoftheanthropogenicloadiscar-riedtotheBalticSeawiththeriverrunoff.Subsurfacegroundwaterdischargeplayssubstantialroleincaseofnutrientsandorganicmatter,andaminorroleinthecaseofmercury(Szymczychaetal.,2013).ThemajorriversenteringtheBalticcanbedividedintotwobroadcategories:thoseseparatedfromtheseabyalagoon,andthoseenteringtheseadirectly.Thelagoonsactastrapsforsuspendedanddissolvedriverineloads(BorgandJonsson,1996;Pempkowiaketal.,2000).SamplesforthisstudyhavebeencollectedfromtheSouthernandcentralBaltic.Thisareais,onaverage,quiteshallow–meandepthbeing50m(Voipo,1981).SouthernandcentralBalticconsistsofseriesofdeepbasinssepa-ratedbysills.Sedimentationregimeindeepbasins(>80m)maybeconsideredasstable(Zaborskaetal.,2014).Intheintermediateareas(>50m)accumulationtypeofbedprevails,whereasinshal-lowerregionserosionorno-accumulationbottomspredominate(Feisteletal.,2008;Voipo,1981).Sedimentsconsistofsiltand

mudintheGdan

´skDeep,theBornholmDeepandtheGotlandDeep-clayintheS upskChannel,andsandwithoccasionalsilt

depositsintheBayofGdan

´sk,theS upskSillandthePomeranianBay(Feisteletal.,2008).Forthisstudy,threesedimentationbasins

oftheSouthernBalticweresampled–Bornholm,Gdan

´skandGot-landDeeps,andtwoshallowareasadjacenttorivermouths–the

Gdan

´skBay,closetotheVistulamouthandthePomeranianBay,closetotheOdramouthduringcruiseontheR/VOceaniainSpring2009and2010fromtheGdanskDeep,theGotlandDeep,thePom-eranianBayandtheGdan

´skBayandinAutumn2009fromtheGdan

´skDeepandtheGotlandDeep.Locationofthesamplingsta-tionsisshowninFig.1.

Sampleswerecollectedwithagravitycorer.Thetopthreecen-timetersofstrati edsedimentsweresampledbycuttingitawaywithaplasticspatula,mixed,transferredintopolyethylenebagsandstoredfrozen(À20°C)untilanalysesinlaboratory.

Beforemercuryanalysisallthesampleswerehomogenizedunderlaminar owhoodandaliquotsweretakenfordetermina-tionsofmoisture,organiccarbonand negrainfractioncontents.Moisturewasusedtocalculatedrymassofsample,andallresultsarereportedasmassperdryweight.Finegrainedfraction(<0.067mm)http://wendang.chazidian.comaniccarboncontentinsedimentswasdeterminedafterremovalofcarbonates(2MHCl)usinganElementalAnalyzerFlashEA1112Seriescom-binedwiththeIsotopicRatioMassSpectrometerIRMSDeltaVAdvantage(ThermoElectronCorp.,Germany)andpresentedaspercentageinthebulkofthedrysample.Qualitycontrolwascar-riedoutwithstandardmaterialssuppliedbytheThermoElectronCorp.Themethodologyusedprovedsatisfactoryaccuracyandpre-cision(averagerecovery99.1±2.0%).

Totalmercurydeterminationwasperformedviasample(500mg)pyrolysisinastreamofoxygen(LecoAMA254,CzechRepublic).TheAMA254techniqueofdirectcombustionfeaturesacombustion/catalysttubewheresedimentdecomposesinanoxygen-richenvironmentandremovesinterferingelements.BothrecoveryandprecisiongivenasRelativeStandardDeviationprovedsatisfactory(97%±3%RSD)basingonareferencematerialanalysis(NIST2584).

Extractablefractionofmercury(organicmercury)wasdeter-minedaccordingtoproceduredescribedforriversediments(Boszkeetal.,2007).Inshort,asedimentsample(5.0g)wastwiceextractedwithchloroform,reextractedbyaqueoussodiumthio-sulphatesolution(0.01M;10mL)Fromtheaqueouslayeranali-quotof5mLwascollected,placedinameasuring ask(50mL)andtreatedwith20lL65%HNO3,7.5mL33%HCland5mLofa1:1solutionof0.0033MKBrO3and0.2MKBrtooxidizeallmer-curyspeciestoHg(II).Resultingsolutionswereanalyzedbymeansofatomic uorescencespectrophotometryonautomatedTekran2600(Canada)apparatus,accordingtoEPA1631method(EPA,2002).

MethylmercuryhasbeendeterminedintheJosefStefanInsti-tutelaboratoriesinLjubljana(Slovenia),usingtheproceduredevelopedbyLiangetal.(1994)andusedsuccessfullybyothers(Logaretal.,2002;Quevauvilleretal.,1998).Methylmercuryde nedbythisprocedureincludesallmonomethylmercuryspe-ciesfoundinsediments(e.g.CH3Hg+,CH3HgCl,CH3HgOH,andCH3-HgS-R),whichareamenabletocomplexationandextractionasCH3HgBr.Inshort,300mgsampleofwetsedimentwassequen-tiallyelutedwith2.5mlof1.5MHBrsolutionand1mlof1MCuSO4.ThenMeHgwasextractedintomethylenechloride.20mlofdeionizedwaterwereadded,andtheorganicfractionwasevap-oratedafterdilutiontoaknownvolumewithreagentwater,fur-theranalysiswascarriedoutbyaqueousphaseethylation,andthenanalyzedusingtheGC/pyrolysis/CVAFStechniqueinaBrooksandRandModel1Detectorequippedwithagaschromatographycolumnandahightemperature(300°C)desorptionunit.Allsam-pleswereanalyzedintriplicate,andblanksampleswererunforeverysixsamples.Recoveryandprecisionofmeasurementswereassessedbytheuseofcerti edreferencematerial(NIST2584fortotalmercuryandBCR580fororganic/methylmercury).Thosewereequalto98%and3%RSD,fortotalmercury,whileforHgOrgandMeHgRSDsdidnotexceed7.4%whilerecoveryequaled91%.Thecommonproblemwithmercuryanalysisinmarinesedi-mentsistherandomcomponent,associatedwiththesocalled‘‘patchiness’’–mosaicpropertiesofsediments,whichvary,evenonaverylocalscale.TheBalticsedimentswerereportedtobecharacterizedwithsubstantialpatchiness(Zaborskaetal.,2014;ZalewskaandSuplinska,2013;Winterhalter,2001),whichmaycausethemeasuredconcentrationofmercurytobenon-represen-tativeforagivenarea,ifitisbasedonasinglesampleanalyses.

海水汞

Thereforeinthisstudy,coreswerecollectedintriplicate,withinaonesquarekmarea.Moreoverinordertoassesspossibleseasonalvariability,sampleswerecollectedinthreeseasons(Spring2009,

´skandGotlandAutumn2009andSpring2010)intheareaofGdan

Deeps,andintwoseasonsintheremainingstations(Bornholm

´skBay).Deep,PomeranianBayandGdan

ResultsofthesodesignedexercisearepresentedinFig.2,sep-aratelyforeachstation,errorbarsrepresentseasonaldifferences.Sincevariabilityinstationsclosetoshore,especiallyneartheVistulamouth(V)isvisiblygreaterthanintheaccumulationbasins,nearshoreareasanddeeps(accumulationbasins)willbediscussedseparately.

Seasonalvariabilityfortotalmercuryintheaccumulationbasins(GD,BO,andGO)withinthesamestationvariedintherangefrom5%to33%,exceptonecaseinBornholmDeep,whereitreached67%.Thevariabilityrelatedtopatchinessrangedfrom9%to34%.Thustheaverageuncertainty,givenasRelativeStandardDeviation,attachedtoasingulartotalmercuryresultisintherangeof20%.Fororganicmercuryseasonalvariabilityvariedfrom4%to32%,whilethespatialvariabilityrangesfrom4%to31%.Methylmercuryspatialandtemporaldistributionsweresimilar,amountingto4–36%RSDforseasonaland2–34%RSDforspatialdifferences,resultingin15%averageuncertainty.ThustheaverageconcentrationsofmercuryobtainedinthisstudycanberegardedasrepresentativeforthesedimentsoftheSouthernBalticaccumu-lationbasins.Theuncertaintyislessthan20%oftheaveragevalues(Fig.2).

Differentsituationisobservedinthecoastalareas–theresea-sonalvariabilitygivenasRSDreaches103%,115%and121%respec-tivelyfortotal,organicandmethylmercury,whilepatchinessrelateduncertaintyreaches77%,44%and45%fortherespectiveforms.Thistranslatestoanaverageuncertaintyof44%forallstud-iedmercuryspecies.Suchdifferencesmightbeattributedtoboththedynamicsofshallowsedimentsandvariableriverinemercuryinput.Thelatterdirectlycontrolscompositionofmarinesedimentsinthoseareas(Huzarska,2013).EspeciallypronounceddifferencesobservedclosetotheVistulamouthmightbecausedbythe oodinMay2010,thebiggestonesince1850.Atthetimeofthe oodexceptionallylargequantitiesofmercuryweretransportedwiththerun-off(Saniewskaetal.,2014;Wielgat-Rychertetal.,2013).Observedseasonalvariabilityandpatchinessisnotlimitedtomercuryspeciesandresultsfromheterogeneityofsedimentandenvironmentalconditions.Theformercouldbecharacterizedbyorganicmattercontent,granulometryandoxidativestate–factorsthatstronglyin uencesedimentarymercuryconcentration(Pempkowiaketal.,1998).Variabilityofthe nefractioncontribu-tion,organiccarboncontentandredoxpotentialispresentedinTable1.

Organiccarbonvariabilityinthewholedatasetwassimilarforaccumulationandcoastalareas,andvariedfrom5.56%to13.58%,while nefractioncontributionwasmarkedlymorevariableclosertothecoast.Redoxpotentialsvariedintherangefrom3.9%to309%oftheaverage.Thustheobservedheterogeneityinmercurycon-centrations(Fig.2)canbeattributedtosedimenttexturediffer-ences(incoastalareas)andcombinedeffectofbothorganiccarbonandredoxconditionsvariabilities.

Concentrationsoftotalmercury(THg),organicmercury(HgOrg)andmethylmercuryinmarinesedimentsfromtheSouth-ernBalticvariedintherange5.8–225(average:103)nggÀ1dryweight,90–1240(320)pggÀ1drywt.and60–940(230)pggÀ1

dry

海水汞

Bulletin87(2014)388–395391

Table1

Medianvaluesinthestudiedsedimentsandrangesoforganiccarbon(Corg)concentration(mg/g), nefractioncontribution(<0.063)(%)andredoxpotential(Eh)(mV).

Corg(mg/g)

<0.063(%)

Eh(mV)

GD7.9(6.2–9.1)92.61(89.65–94.87)À76(À129À+9)GO11.8(10.8–12.9)87.94(83.58–91.51)+5(À15À+15)BO7.7(6.3–9.1)62.72(59.41–66.72)+47(+30À+66)V4.4(3.6–5.2)4.23(2.54–5.99)+158(+76À+236)O

2.5(2.1–3.0)

0.93(0.49–1.31)

+234(+221À+245)

wt.,respectively(Fig.3).ThehighestlevelsofTHgandMeHgwerefoundinsedimentsfromtheGdanskDeepandthevicinityoftheVistulamouth,respectively.

ThelowestconcentrationsofbothTHgandMeHgwerefoundinsedimentscollectedclosetotheOdramouthlocatedintheBayofPomerania.ThiscanbeattributedtothemorphologyoftheOdra

riverestuary,wheretheSzczecinLagoonactsas‘ lter’fortheriverrun-offdischargedtothePomeranianBay(seeFig.1).InthecaseoftheVistulaRiverestuary,themorphologyisdifferent–theriverrun-offandtheloadsofchemicalsitcarriesaredischargeddirectly

totheGulfofGdan

´sk(Pempkowiaketal.,2000).Craig(1986)reportedconcentrationrangesof200–400nggÀ1THgforuncontaminatedmarinesediments,whereasheavilypol-lutedsedimentsinurban,industrialorminingareascancontainupto100lggÀ1oftotalmercury.SedimentarylevelsofTHgandMeHgreportedintheliteraturearepresentedinTable2.Ourresultsindicatethatthemercuryconcentrationsaveragesandranges,determinedinsedimentsfromthestudyarea,arelowerthanthosereportedinotherareas(Covellietal.,2001;Jinetal.,2012;KannanandFalandysz,1998;Mzoughietal.,2002;Spadaetal.,2012)withtheexceptionofthelevelreportedbyAsmundandNielsen(AsmundandNielsen,2000)whoindicatedback-groundmercurylevelsof24nggÀ1insedimentsfromtheGreen-landShelf.ThehighestvalueswererecordedinsedimentsfromGulfofTrieste(theAdriatic),in uencedbythecontaminatedriverSoca/Isonzo,forcenturiesdrainingthecinnabar-richdepositsoftheIdrijaminingdistrict,intheNorthwesternpartofSlovenia(Covellietal.,2001).

MeHgconcentrationsmeasuredinthestudyareaarecharacter-isticofanoxicpollutedsediments(Kwokaletal.,2002).Concentra-tionsmeasuredwithinthisstudyarelowerthanthesereportedforperiod1992–1994byKannanandFalandysz(1998)byafactoroftwoforthesameregion,afeaturedif culttoexplaintakingintoaccountthatbothseasonalandspatialvariabilityofmercurycon-centrationsdonotexceed20%oftheaverage,andthefact,thattotalmercuryconcentrationobservedinthisstudyarecomparabletothevaluesobservedin1993–1995(Pempkowiaketal.,1998).ThissuggestsachangeinmethylatingpotentialoftheBalticsedimentssince1990s,whichcouldbeattributedi.e.totheoverallimprovementofoxicconditionsonthebottom(Feisteletal.,2008).Thecontributionofmethylmercurytototalmercuryinsedi-mentsofthestudyarearangedfrom0.14%to1.05%whichfallswithintherangereportedintheliteratureformarineenviron-ments(Cossaetal.,1996;Masonetal.,1994).Thismightsuggestalowmethylationpotentialofmarinesedimentsinthestudyarea.CorrelationanalysesshowedthatTHgwasstronglycorrelatedwithMeHginsediments(SpearmanR=0.82,p<0.01).Theestablishedrelationiscalculatedforallanalyzedsamples,exceptthreesamplescollectedclosetotheVistulamouth,(Fig.4),sincethesamplesinquestionwerecollectedshortlyaftermajor oodinMay,2010.The oodhasintroducedlargeloadsofbothmercuryandorganicmattertotheBalticSea(Saniewskaetal.,2014),andmaywellexplaintheelevatedconcentrationsofbothTHgandMeHgthere.

Intheremainingareas,reducingconditionswereobservedinsediments(themeasuredred-oxpotentialwasintherangefromÀ122to66mV).Themeasuredredoxpotentialindicatesthattheconditionsinsedimentswereappropriateforthesulfatereducingbacteriatoreducesulfatetosul de.Asaresultlabilemercuryformsaretransformedtomercurysul de(Be dowskiandPempkowiak,2007)thatissparinglysolubleinaqueoussolution.OncedepositedasHgS,mercuryispresumablynotavailableformethylation(Boening,2000).However,bioturbationorphysicalmixingcanintroduceoxygentosedimentsthatleadstooxidationofHgSandthusremobilizeafractionofHgS(Steinetal.,1996).Moreover,evenwithinthesamelocation,thepercentageofmethylmercuryvariedtosomeextendsuggestingthatotherfactorssuchasorganicmatterandmicrobialactivitymayin uenceorevenplayasigni cantroleinthemethylationprocess(Be dowskietal.,2009)MostpronounceddifferenceswereobservedintheBorn-holmDeep(0.21–1.03%)andinthevicinityofrivermouths(Vistula–0.14–0.61%;Odra–

0.64–1.05%).

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392J.Be dowskietal./MarinePollutionBulletin87(2014)388–395

Table2

Totalmercuryandmethylmercurylevelsreportedforsedimentsindifferentcoastalseas.Studyarea

THgconc.(nggÀ1)Average

GulfofTriesteAdriaticsea

LagoonofBizerte

MediteraneanoffTunisiaGulfofTarantoIonianSeaJadeBayNorthSea

VistulaMouth(GulfofGdansk)Odramouth

(PomeranianBay)

´skDeepGdan

GulfofGdanskBalticSea

´skBasinGdan

´skDeepGdan

BornholmDeepBornholmDeep

524013027701087193151641761906456

Range100–23,30010–650360–773035–24317–1536–13220–42037–88028–473130–37025–84

MeHgconc.(pggÀ1)Average1690053010800–35475–645

Range200–60,100nd–32001000–40,000–68–94061–94–

35–1700

Covellietal.(2001)Mzoughietal.(2002)Spadaetal.(2012)Jinetal.(2012)ThisstudyThisstudy

Thisstudy

KannanandFalandysz(1998)Be dowskiandPempkowiak(2007)Pempkowiaketal.(1998)

Be dowskiandPempkowiak(2007)ThisstudySource

Organomercurycompoundsarethoseinwhichmercuryisbondeddirectlytothecarbonatome.g.CH3Hg(I)andC2H5Hg(I)(Hintermann,2010).Severalextractingagentswereusedforsepa-ratingorganomercurycompoundsfromsedimentssofar:toluene(Milleretal.,1995),chloroform(EguchiandTomiyasu,2002;Tomiyasuetal.,2000)anddichloromethane(RennebergandDudas,2001).However,withtheuseofthesesolventsnotonlytheorganomercurycompoundsbutalsoafractionofthemercurycomplexedbyorganicligandsisextracted(EguchiandTomiyasu,2002).Inthisstudychloroformwasusedasanextractingagenttoseparatethisoperationallyde nedfractionofmercury,calledhereorganicmercury(HgOrg).Obviouslyorganicmercurycom-prisesmethylmercuryasde nedinthisstudy.Theaveragecon-centrationofmercuryinthisfractioninthestudyareais0.42nggÀ1(range0.10–1.44nggÀ1).Concentrationsoforganicmercuryintherange:0.9–26nggÀ1weredeterminedinthemar-inebottomsedimentsfromtheYatsushiroSeainJapan(Tomiyasuetal.,2000),inthesoilsamplesfromtheareastronglypolluted