TransportationandTransformationofArsenicSpeciesatthe...

Research ArticleTransportation and Transformation of Arsenic Species at theIntertidal Sediment-Water Interface of Bohai Bay China

Xiaoping Yu12 Yafei Guo 12 Qin Wang1 and Tianlong Deng 1

1Tianjin Key Laboratory of Marine Resources and Chemistry College of Chemical Engineering and Materials ScienceTianjin University of Science and Technology Tianjin 300457 China2College of Chemistry and Materials Science Northwest University Xirsquoan 710127 China

Correspondence should be addressed to Tianlong Deng tldengtusteducn

Received 25 October 2017 Revised 15 April 2018 Accepted 22 April 2018 Published 5 June 2018

Academic Editor Wenshan Guo

Copyright copy 2018 Xiaoping Yu et al is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Arsenic species including arsenite As(III) arsenate As(V) monomethylarsenate (MMA) dimethylarsenate (DMA) and somediagenetic constituents (Fe Mn and S2minus) in porewaters along with the unstable arsenic species in sediments collected froma typical intertidal zone of Bohai Bay in China were measured eir vertical distributions were subsequently obtained to revealthe transportation and transformation characteristics of arsenic at the intertidal sediment-water interface (SWI) Results showthat the reduction of As(V) by microorganisms occurred in sediments but the methylation of arsenic by microorganisms wasweak in the intertidal zone e distribution of As(V) was mainly controlled by Mn whereas As(III) appeared to be more likelycontrolled by Fe Arsenic in sediments mainly existed in a stable state so that only little arsenic could be released from sedimentswhen the environmental conditions at the SWI are changed As(III) diffused from porewaters to the overlying water while theopposite was true for As(V) at that time when the samples were collected e total diffusion direction for arsenic across the SWIwas from porewaters to the overlying water with a total diffusive flux estimated at 123mgmiddotmminus2middotaminus1

1 Introduction

At present our knowledge about the arsenic (As) cycles andspecies in marine sediments especially in intertidal sedi-ments is limited e ubiquitous use of anthropogenic ar-senic associated with rapid economic development hassignificantly changed their original distribution patterns innatural environments enabling their delivery to the in-tertidal zone from river catchments via fluvial transportatmospheric deposition and local wastewater dischargeemost common species of arsenic likely to be found in aquaticenvironments are arsenite As(III) and arsenate As(V) [1]but methylation probably occurs by activity of microor-ganisms resulting in the formation of organic arseniccompounds such as monomethylarsenate (MMA) anddimethylarsenate (DMA) [2 3] e strong toxicity of in-organic arsenic leads to the important significance to carryout geochemical studies of arsenic in the environment

Bohai Bay is a semienclosed shallow water basin located inthe western region of the Bohai Sea in the northern ChinaBohai Bay receives a vast amount of industrial and domesticsewage from Beijing and Tianjin through the Haihe RiverJiyunheRiver YongdinxinRiver and so on It was reported thatabout 334times105 kgyear of arsenic was discharged into BohaiBay via rivers [4] Due to the large amount of contaminantinputs and poor physical self-cleaning capacity Bohai Bay hasbecome one of the most degraded marine systems in China

e intertidal zone strongly affected by both humanactivities and tide is the transitional area of ocean and landwhere sediment-water interface (SWI) is the boundary of thesediment and water phase e generation circulation andmigration of chemical substances are exceptionally activethere [5] e toxicity and mobility of arsenic in aquaticenvironment largely depend on its chemical form [6 7]For example inorganic As(III) is generally more toxic thanAs(V) while organic arsenic compounds are generally

HindawiJournal of ChemistryVolume 2018 Article ID 5861358 8 pageshttpsdoiorg10115520185861358

nontoxic [6] erefore studies of arsenic transportationand transformation at the intertidal SWI of Bohai Bay basedon speciation analysis will be more significant However thegeochemical cycle of arsenic is quite complicated here asmany factors have strong effects on this process [8 9] Atpresent available data on arsenic in the intertidal SWI ofBohai Bay are insufficient for the evaluation of theirphysicochemical behaviors and total environmental impactsbecause the chemical states of arsenic in sediment andporewater need to be known to evaluate their mobilitybioavailability and toxicity

In this paper we report the geochemical cycle of arsenicat the intertidal SWI of Bohai Bay based on the extraction ofsediments using the method proposed by Ellwood andMaher [10] along with the measurement of dissolved arsenicspecies in porewaters and related physicochemical param-eters at the SWI

2 Materials and Methods

21 Site Description Bohai Bay is one of the three bays ofBohai Sea in China covering an area of about 16times104 km2

with an average water depth of 125m ere are severalrivers flowing into Bohai Bay by which it receives bothindustrial and domestic wastewater discharged from BeijingTianjin and Hebei All the wastewater through rivers andchannels is directly drained into the near-shore water ofBohai Bay Among 96 sewage outlets monitored in 2008 thewater quality in the adjacent sea of 83 sewage outletscannot meet the water quality requirement of marinefunction area and the ecoenvironmental quality in theadjacent sea of 22 sewage outlets is in quite poor state eexchange of water between Bohai Bay and the central BohaiSea is relatively slow and weak for its semienclosed positionand poor physical exchange capacity thereby most of thepollutants are gradually accumulated there

e sampling site (Figure 1) is a typical intertidalzone of Bohai Bay in the Tianjin section (N39deg12prime236Prime

E117deg54prime542Prime)e Tianjin coast belongs to an alluvial plaincoast where the intertidal zone is quite broad and flat Withthe rapid development of marine economy in Tianjin theecoenvironment of intertidal zone in the Tianjin section wasseriously affected by the deposition of large amounts ofdifferent pollutants

22 SampleCollection andTreatment Overlying water at thesurface was collected using a precleaned polyethylenecontainer when the tide was at its highest in the daytime ofthat day e temperature and pH of the overlying waterwere determined on-site using a thermometer and pHmeterrespectively An undisturbed surface sediment core about30 cm depth was collected at the same place with a tailor-made Teflon sampler when the tide was at its lowest in thedaytime Subsequently all samples were transported to thelaboratory in an icebox e sediment core was extruded ina glove-box bag filled with nitrogen gas to prevent oxidationSediment slices from each 1 cm depth were collected andplaced in precleaned Teflon bottles and kept frozen at minus80degCuntil analysis Porewater sample in each sediment slice wasobtained by centrifugation at 4degC

23 Analytical Methods e method for arsenic speciationanalysis in water was established in our previous work [11]Sulfides dissolved iron (Fe) and manganese (Mn) weremeasured based on the National Standard Method in China(GBT173784-2007) and (GBT11911-89) respectivelyelabile arsenic species including extracted arsenite [EAs(III)]and arsenate [EAs(V)] in sediments were determinedaccording to the methods proposed by Ellwood and Maher[10] Moisture redox potential (Eh) total organic matter(TOM) and total arsenic (TA) in sediments were analyzedbased on the National Standard Method in China (GBT173785-2007) In addition sulfur species including ele-mental sulfur (ES) acid volatile sulfides (AVS) and ma-ture pyrite sulfides (MPS) were determined by continuous

Figure 1 Geographic map of the sampling site

2 Journal of Chemistry

extraction iodometry [12] Total iron (TFe) and totalmanganese (TMn) in sediments were analyzed by flameatomic absorption spectrometry (FAAS) according to theNational Standard Method in China (GBT 20260-2006)

3 Results and Discussion

31 Profiles of Labile Arsenic Species and Related Parametersin Sediments e profiles of labile arsenic species and re-lated physicochemical parameters in sediments are plottedin Figures 2ndash4

Moisture reflects the porosity and the migration-diffusion rate of elements in sediments e average mois-ture of sediments in this studied area was 3865 and sharplydecreased with depth at minus1simminus12 cm (Figure 2(a)) indicatinga high diffusion rate in the top sediments Organic matters insediments provide the necessary survival conditions forbacteria that perform reduction of high valence elementssuch as Fe(III) Mn(IV) and S(VI) We found that TOM inthis investigated site was especially high with an averagecontent of 1062 (Figure 2(a)) Redox potential (Eh) inintertidal sediments is strongly affected by oxygen in air bywhich it presented gradual decrease with depth in the upperlayer in Figure 2(b) e average Eh in this studied site wasminus381mV indicating a weakly reducing environment inintertidal sediments Fe and Mn hydrous oxides are theprimary sources of soluble heavy metals in natural waterTFe in sediments was quite high with an average value of2936 gmiddotkgminus1 while the labile EFe only accounted for about2313 (Figure 2(c)) indicating iron in intertidal sedimentsmainly existed in stable sulfides or in a residual state On thecontrary TMn and EMn in sediments were quite low andthe labile EMn accounted for about 6932 of the TMncontent (Figure 2(d))

Reduced sulfur especially AVS (mainly composed ofFeS) in sediments is an important control on the reactivityand toxicity of arsenic [13] e average content of AVS insediments was 015 gmiddotkgminus1 and it was obviously higher in thebottom sediments than that in the upper layers as presentedin Figure 3(b) It is noted that a sharp decrease of MPS in thetop sediments was observed in Figure 3(c) with a maximumof 138 gmiddotkgminus1 at the surface

e average contents of EAs(III) EAs(V) and TAs insediments were 051 218 and 1038mgmiddotkgminus1 respectively(Figures 4(a)ndash4(c)) In order to facilitate the comparison oftrend and contents among EAs(III) EAs(V) and TAs theirprofiles were plotted together in Figure 4(d) As expectedthe average content of TAs was significantly higher than thatof EAs(III) and EAs(V) It means that arsenic in intertidalsediments mainly existed in a stable state or so called ldquoinertrdquostate Labile arsenic [EAs(III) + EAs(V)] only accounted forabout 259 of the TAs content in which EAs(III) was onlyabout quarter of EAs(V)

32 Profiles of Dissolved Arsenic Species and Related Pa-rameters in Porewaters e profiles of dissolved arsenicspecies and related physicochemical parameters in pore-waters are plotted in Figures 5 and 6

e pH of seawater is mainly controlled by the carbondioxide-carbonate system and its pH approximates 81 orfluctuates around this value However since the intertidalzone is affected by many factors the measured pH was 824(Figure 5(a)) Porewaters are often anoxic systems in whichthe physicochemical reactions are remarkably different fromthe overlying water We found that the pH of porewaterswas significantly lower than that of overlying water inFigure 5(a) S2minus is liable to react with dissolved iron to formFeS or FeS2 and thereby the sulfides in overlying water and

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 30 60Moisture and TOM ()

MoistureTOM

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

ndash60 ndash30 0Eh (mV)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 25 50Fe (gkg)

TFeEFe

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 1 2Mn (gkg)

TMnEMn

Dep

th (c

m)

(d)

Figure 2 Profiles of moisture and TOM (a) Eh (b) Fe (c) and Mn (d) in sediments

Journal of Chemistry 3

porewaters were beyond the detection limit (Figure 5(b))Dissolved Fe in overlying water was only 016mgmiddotLminus1 but itreached an average of 060mgmiddotLminus1 in porewaters (Figure 5(c))Although dissolved Mn in bottom porewaters in Figure 5(d)was extremely low an obvious concentration peak waspresented in the profile of dissolvedMn in the upper sedimentwith a maximum of 1113mgmiddotLminus1 at the subsurface

Dissolved oxygen (DO) in overlying water will causea shift of redox equilibrium between As(III) and As(V)

toward As(V) by which the majority of As(III) is oxidized toAs(V) because the tidal action increases the concentration ofDO in the overlying water erefore no As(III) could bedetected in overlying water at the studied site while As(V)reached 814 microgmiddotLminus1 However as it suffers less effects of DOin the porewaters As(III) could be detected in porewaters ateach depth with an average value of 211 microgmiddotLminus1 (Figure 6(a))As(V) was obviously higher than As(III) in porewaters inFigure 6(d) and the average concentration of As(V) was

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

ES (gkg)D

epth

(cm

)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

AVS (gkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20

MPS (gkg)

Dep

th (c

m)

(c)

ES

AVSMPS

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20S (gkg)

Dep

th (c

m)

(d)

Figure 3 Profiles of ES (a) AVS (b) and MPS (c) in sediments and their comparison (d)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 1 2EAs(III) (mgkg)

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 2 4EAs(V) (mgkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14

TAs (mgkg)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14As (mgkg)

EAs(III)

EAs(V)TAs

Dep

th (c

m)

(d)

Figure 4 Profiles of EAs(III) (a) EAs(V) (b) and TAs (c) in sediments and their comparison (d)


775 microgmiddotLminus1 which was about 37 times that of As(III) Noorganic arsenic compounds such as DMA and MMA weredetected in porewaters indicating the methylation of arsenicby microorganisms was weak in intertidal zone of thestudied site

33 Transportation and Transformation of Arsenic Species atthe Intertidal SWI

331 Correlations of Related Parameters at the IntertidalSWI In order to evaluate the correlations of di erent

parameters at the SWI the coecients of statistical corre-lation (r) are calculated and presented in Table 1

Humus in sediments will seriously restrain arsenic ad-sorption onto the surface of iron oxides or hydroxide col-loids by competitive adsorption [14]erefore there shouldbe a negative correlation between TOM and arsenicHowever both EAs(III) and EAs(V) presented positivecorrelations with TOM suggesting that the distribution ofarsenic in intertidal sediments was not dominated by TOMHydrous oxides of Fe and Mn are the main shelters of heavymetals in aqueous systems and thus have important e ects

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

60 75 90pH

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

000 01 02

Sulfides (mgL)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 1 2Fe (mgL)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 6 12Mn (mgL)

Dep

th (c

m)

(d)

Figure 5 Proles of pH (a) suldes (b) dissolved Fe (c) and Mn (d) in porewaters

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 7 14As(III) (microgL)

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20As(V) (microgL)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20TAs (microgL)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20As (microgL)

As(III)

As(V)TAs

Dep

th (c

m)

(d)

Figure 6 Proles of dissolved As(III) (a) As(V) (b) and TAs (c) in porewaters and their comparison (d)


on the distributions and speciation of arsenic at the SWI[15] Arsenic is adsorbed on Fe andMn oxideshydroxides insediments to form stable states and positive correlationswere obtained between TAs and TFe as well as between TAsand TMn with correlation coefficients of 058 and 068respectively Usually iron extracted by 25 hydroxylaminehydrochloride in acetic acid mainly exists as FeOOH insediments and a high correlation was found betweenextracted Fe and As (EFe and EAs) (Table 1)

A dynamic equilibrium exists between EAs(III) andEAs(V) in sedimentsey will present negative correlationif the equilibrium is only controlled by Eh However thecoefficient was 071 indicating that their distributions werenot only controlled by Eh EAs(III) will be oxidized at highEh and a negative correlation will thus be observed be-tween Eh and EAs(III) if the distribution of EAs(III) is notinfluenced by other factors However a positive correlation(r 081) was observed between Eh and EAs(III) dem-onstrating that the distribution of EAs(III) was notdominated by Eh No significant negative correlation wasfound between As(III) and As(V) showing that the dis-tribution of arsenic in porewaters was also not dominatedby Eh e correlation coefficients between As(III) and Feand As(V) and Mn were minus008 and minus029 respectivelyMeanwhile positive correlations between EAs(III) and EFeas well as between EAs(V) and EMn in sediments werepresented It is speculated that the distribution of As(V)was controlled by Mn while As(III) was likely to bedominated by Fe

332 5e Flux of Dissolved Arsenic at the Intertidal SWIProfiles of dissolved arsenic in porewaters and overlyingwater (Figures 6(a) and 6(b)) suggest probable diffusion ofarsenic at the intertidal SWI Based on the assumption thatall dissolved arsenic diffusing upwards (or downwards) istransferred to the overlying water (or porewaters) thediffusive flux was estimated using the method applied byCiceri et al [16]

J ϕDsdAsdz

11138681113868111386811138681113868111386811138680 (1)

where J is the flux of dissolved arsenic φ is the porosity ofsediment (050 calculated from the water content using thefollowing formula φ Vwater(Vwater + Vsolid) in which V isthe volume obtained from mass and density of water andsediment) (dAsdz)0 is the concentration gradient calcu-lated from the linear portion of dissolved arsenic concen-tration at the SWI and Ds is the bulk sediment diffusioncoefficient and is obtained from the formula [17]

Ds ϕD0 ϕlt 07

Ds ϕ2D0 ϕgt 07(2)

where D0 is the free solution diffusion coefficientD0 is affected bymany factors such as pH salinity and so

on It is estimated based on the study by Tanaka et al [18]e average pH at the depths where the concentrationgradient of arsenic species was calculated was used in cal-culating D0 of As(III) and As(V) which are 107times10minus6 and76times10minus6 cmmiddotsminus1 respectively e estimated diffusive fluxesfor As(III) and As(V) across the SWI were 140 and017mgmiddotmminus2middotaminus1 respectively However it is noted that As(III) diffused from porewaters to the overlying water whilethe opposite was true for As(V) based on the variationdirection of the concentration gradient erefore the totaldiffusive flux for arsenic at the SWI was about123mgmiddotmminus2middotaminus1 and the direction was from porewaters tothe overlying water

333 Transportation and Transformation of Arsenic at theIntertidal SWI Arsenic occurrence forms in the environ-ment are affected by many factors ermodynamicallyarsenic should mainly exist in As(V) species (H2AsO4

minusHAsO4

2minus and AsO43minus) under oxidizing conditions and in As

(III) species (H3AsO3 and H2AsO3minus) under reducing con-

ditions Commonly there is an oxidized zone above the SWIand a reduced zone below the SWI As shown in this

Table 1 Statistical correlations (r) between profiles of parameters at the intertidal SWI

TAs EAs(III) EAs(V) As(III) As(V) TFe EFe Fe TMn EMn Mn ES AVS MPS TOM Eh pHTAs 100 053 011 040 003 058 044 004 068 070 052 minus005 028 012 066 030 minus049EAs(III) 100 071 048 minus037 037 046 minus030 070 069 071 017 minus006 045 068 081 minus078EAs(V) 100 011 minus027 001 029 minus041 044 046 045 000 minus043 038 038 071 minus058As(III) 100 minus007 046 039 minus008 061 046 074 018 017 057 067 057 minus066As(V) 100 008 016 038 minus007 minus004 minus029 minus001 026 minus030 minus004 minus040 036TFe 100 086 minus028 080 078 026 minus002 058 minus003 042 029 minus021EFe 100 minus046 078 085 029 minus009 033 minus007 046 045 minus025Fe 100 minus037 minus043 minus037 minus014 019 minus033 minus032 minus060 041TMn 100 088 064 012 026 035 076 067 minus064EMn 100 055 minus010 020 013 062 061 minus055Mn 100 029 minus015 078 086 085 minus096ES 100 011 040 023 017 minus022AVS 100 minus025 minus001 minus025 023MPS 100 063 069 minus082TOM 100 073 minus084Eh 100 minus090pH 100


research As(III) in the overlying water was below the de-tection limit but it was detectable in the porewaters wherereducing conditions prevailed It is deduced that the trans-formation of arsenic species occurred in the sedimentsGenerally arsenate cannot be reduced by other reagents in theenvironment and thus arsenite in porewaters mainly resultsfrom the reducing action of microorganisms [19] Redoxcondition also has important e ects on the release of arsenicin sediments Arsenic can be adsorbed or coprecipitated intosediments in the oxidized layers during its migration towardthe upper sediments Suldes of As(III) are thermodynami-cally stable in the presence of S2minus which usually exists ina strongly reducing environment erefore arsenic di usingdownward will be xed by reacting with dissolved or par-ticulate suldes [20] As shown in Figure 3(b) a high contentof AVS in sediments was benecial to the xation of arsenic

Arsenic is usually adsorbed on Fe oxideshydroxides inan oxidizing environment while Mn(IV) and Fe(III) areeasily reduced to low valence and highly soluble Fe(II) andMn(II) in a reducing environment and then they migrateinto the porewaters Mn(II) is more stable than Fe(II) andmore dicult to oxidize so it can di use further than Fe(II)resulting in a peak ofMn(II) approaching the SWI (Figure 5(d))Eh decreased with depth in sediments but EFe did not de-crease signicantly (Figure 2(c)) implying that EFe was notvisibly reduced to Fe(II) and subsequently entered intoporewaters with the decrease of Eh erefore no obviousincrease of As(V) in porewaters appeared in Figure 6(b) Itprobably results from the slow dynamics of Fe(III) reductionafter Fe(III) adsorbs arsenic and subsequently enters intosediments in the eodiagenesis Based on the aforementionedanalysis the migration and transformation of arsenic at theintertidal SWI of Bohai Bay can be summarized and is shown

in Figure 7 It is obvious that the process is extremelycomplicated and further studies are required

4 Conclusions

Di erent arsenic species and some diagenetic constituents (FeMn and S2minus) in porewaters along with the unstable arsenicspecies in sediments collected from a typical intertidal zone ofBohai Bay in China were measured to reveal the transportationand transformation characteristics of arsenic at the intertidalsediment-water interface (SWI) Results show that the re-duction of As(V) bymicroorganisms occurred in sediments bywhich 21 of the arsenic in porewaters was presented as As(III) No organic arsenic compounds were detected indicatingthe methylation of arsenic by microorganisms was weak in theintertidal zone Distribution of As(V) was mainly controlled byMn whereas As(III) appeared to be more likely dominated byFe Arsenic in sedimentsmainly existed in a stable state andwasnot easy to extract by the reagents used in this study Signicantdi usion of arsenic occurred at the SWI at that time when thesamples were collected As(III) di used from porewaters tothe overlying water whereas the opposite was true for As(V)e net di usion direction of arsenic across the SWI was fromporewaters to the overlying water with a total di usive pounduxestimated at 123mgmiddotmminus2middotaminus1 Early diagenesis of arsenic at theintertidal SWI is quite complicated Further studies need to becarried out to better understand andmanage the overall systemof the intertidal zone in Bohai Bay

Conflicts of Interest

e authors declared that there are no conpoundicts of interestregarding the publication of this paper

Mic

robe

Redu

ctio

n Diff

usio

n

As(III)

As(III)middotFe(III)

Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)

As2S3Sediment Porewater

Fe(III) reduction Des

orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion

Figure 7 Transportation and transformation of arsenic at the intertidal SWI of Bohai Bay


Acknowledgments

is work was financially supported by the National NaturalScience Foundation of China (U1607129 U1607123 and21773170) the Application Foundation and AdvancedTechnology Program of Tianjin (15JCQNJC08300) theYangtze Scholars and Innovative Research Team in ChineseUniversity (IRT_17R81) and the Chinese PostdoctoralScience Foundation (2016M592827 and 2016M592828)

References

[1] A R Lopez S C Silva S M Webb D Hesterberg andD B Buchwalter ldquoPeriphyton and abiotic factors influencingarsenic speciation in aquatic environmentsrdquo EnvironmentalToxicology and Chemistry vol 37 no 3 pp 903ndash913 2018

[2] S M Su X B Zeng L Y Bai et al ldquoConcurrent methylationand demethylation of arsenic by fungi and their differentialexpression in the protoplasm proteomerdquo EnvironmentalPollution vol 225 pp 620ndash627 2017

[3] K Huang Y Xu C Packianathan et al ldquoArsenicmethylation bya novel ArsM As(III) S-adenosylmethionine methyltransferasethat requires only two conserved cysteine residuesrdquo MolecularMicrobiology vol 107 no 2 pp 265ndash276 2018

[4] L Q Duan J M Song X G Li and H M Yuan ldquoebehaviors and sources of dissolved arsenic and antimony inBohai Bayrdquo Continental Shelf Research vol 30 no 14pp 1522ndash1534 2010

[5] W R Boynton M A C Ceballos E M BaileyC L S Hodgkins J L Humphrey and J M Testa ldquoOxygenand nutrient exchanges at the sediment-water interfacea global synthesis and critique of estuarine and coastal datardquoEstuaries and Coasts vol 41 no 2 pp 301ndash333 2018

[6] L Ronci E De Matthaeis C Chimenti and D DavolosldquoArsenic-contaminated freshwater assessing arsenate andarsenite toxicity and low-dose genotoxicity in Gammaruselvirae (Crustacea Amphipoda)rdquo Ecotoxicology vol 26 no 5pp 581ndash588 2017

[7] D M Prieto V Martin-Linares V Pineiro and M T BarralldquoArsenic transfer from As-rich sediments to river water in therresence of biofilmsrdquo Journal of Chemistry vol 2016 ArticleID 6092047 14 pages 2016

[8] S Y Li C L Yang C H Peng et al ldquoEffects of elevated sulfateconcentration on the mobility of arsenic in the sediment-water interfacerdquo Ecotoxicology and Environmental Safetyvol 154 pp 311ndash320 2018

[9] T L Deng Y Wu X P Yu Y F Guo Y W Chen andN Belzile ldquoSeasonal variations of arsenic at the sediment-water interface of Poyang Lake ChinardquoApplied Geochemistryvol 47 pp 170ndash176 2014

[10] M J Ellwood and W A Maher ldquoMeasurement of arsenicspecies in marine sediments by high-performance liquidchromatographyndashinductively coupled plasma mass spec-trometryrdquo Analytica Chimica Acta vol 477 no 2 pp 279ndash291 2003

[11] X P Yu T L Deng Y F Guo and QWang ldquoArsenic speciesanalysis in freshwater using liquid chromatography combinedto hydride generation atomic fluorescence spectrometryrdquoJournal of Analytical Chemistry vol 69 no 1 pp 83ndash88 2014

[12] W M Duan M L Coleman and K Pye ldquoDetermination ofreduced sulphur species in sediments an evaluation andmodified techniquerdquo Chemical Geology vol 141 no 3-4pp 185ndash194 1997

[13] Y Hashimoto and Y Kanke ldquoRedox changes in speciationand solubility of arsenic in paddy soils as affected by sulfurconcentrationsrdquo Environmental Pollution vol 238 pp 617ndash623 2018

[14] J M Galloway G T Swindles H E Jamieson et al ldquoOrganicmatter control on the distribution of arsenic in lake sedimentsimpacted by similar to 65 years of gold ore processing insubarctic Canadardquo Science of the Total Environment vol 622-623 pp 1668ndash1679 2018

[15] X W Xu C Chen P Wang R Kretzschmar and F J ZhaoldquoControl of arsenic mobilization in paddy soils by manganeseand iron oxidesrdquo Environmental Pollution vol 231 pp 37ndash47 2017

[16] G Ciceri C Maran W Martinotti and G QueirazzaldquoGeochemical cycling of heavymetals in amarine coastal areabenthic flux determination from powerwater profiles and insitu measurement using benthic chamberrdquo Hydrobiologiavol 235-236 no 1 pp 501ndash517 1992

[17] W J Ullman and R C Aller ldquoDiffusion coefficients innearshore marine sedimentsrdquo Limnology and Oceanographyvol 27 no 3 pp 552ndash556 1982

[18] M Tanaka Y Takahashi N Yamaguchi K W KimG D Zheng and M Sakamitsu ldquoe difference of diffusioncoefficients in water for arsenic compounds at various pH andits dominant factors implied by molecular simulationsrdquoGeochimica et Cosmochimica Acta vol 105 pp 360ndash3712013

[19] R S Oremland and J F Stolz ldquoe ecology of arsenicrdquoNature vol 300 no 5621 pp 939ndash944 2003

[20] K F Pi Y X Wang X J Xie T Ma C L Su and Y Q LiuldquoRole of sulfur redox cycling on arsenic mobilization inaquifers of Datong Basin northern Chinardquo Applied Geo-chemistry vol 77 pp 31ndash43 2017


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nontoxic [6] erefore studies of arsenic transportationand transformation at the intertidal SWI of Bohai Bay basedon speciation analysis will be more significant However thegeochemical cycle of arsenic is quite complicated here asmany factors have strong effects on this process [8 9] Atpresent available data on arsenic in the intertidal SWI ofBohai Bay are insufficient for the evaluation of theirphysicochemical behaviors and total environmental impactsbecause the chemical states of arsenic in sediment andporewater need to be known to evaluate their mobilitybioavailability and toxicity

In this paper we report the geochemical cycle of arsenicat the intertidal SWI of Bohai Bay based on the extraction ofsediments using the method proposed by Ellwood andMaher [10] along with the measurement of dissolved arsenicspecies in porewaters and related physicochemical param-eters at the SWI

2 Materials and Methods

21 Site Description Bohai Bay is one of the three bays ofBohai Sea in China covering an area of about 16times104 km2

with an average water depth of 125m ere are severalrivers flowing into Bohai Bay by which it receives bothindustrial and domestic wastewater discharged from BeijingTianjin and Hebei All the wastewater through rivers andchannels is directly drained into the near-shore water ofBohai Bay Among 96 sewage outlets monitored in 2008 thewater quality in the adjacent sea of 83 sewage outletscannot meet the water quality requirement of marinefunction area and the ecoenvironmental quality in theadjacent sea of 22 sewage outlets is in quite poor state eexchange of water between Bohai Bay and the central BohaiSea is relatively slow and weak for its semienclosed positionand poor physical exchange capacity thereby most of thepollutants are gradually accumulated there

e sampling site (Figure 1) is a typical intertidalzone of Bohai Bay in the Tianjin section (N39deg12prime236Prime

E117deg54prime542Prime)e Tianjin coast belongs to an alluvial plaincoast where the intertidal zone is quite broad and flat Withthe rapid development of marine economy in Tianjin theecoenvironment of intertidal zone in the Tianjin section wasseriously affected by the deposition of large amounts ofdifferent pollutants

22 SampleCollection andTreatment Overlying water at thesurface was collected using a precleaned polyethylenecontainer when the tide was at its highest in the daytime ofthat day e temperature and pH of the overlying waterwere determined on-site using a thermometer and pHmeterrespectively An undisturbed surface sediment core about30 cm depth was collected at the same place with a tailor-made Teflon sampler when the tide was at its lowest in thedaytime Subsequently all samples were transported to thelaboratory in an icebox e sediment core was extruded ina glove-box bag filled with nitrogen gas to prevent oxidationSediment slices from each 1 cm depth were collected andplaced in precleaned Teflon bottles and kept frozen at minus80degCuntil analysis Porewater sample in each sediment slice wasobtained by centrifugation at 4degC

23 Analytical Methods e method for arsenic speciationanalysis in water was established in our previous work [11]Sulfides dissolved iron (Fe) and manganese (Mn) weremeasured based on the National Standard Method in China(GBT173784-2007) and (GBT11911-89) respectivelyelabile arsenic species including extracted arsenite [EAs(III)]and arsenate [EAs(V)] in sediments were determinedaccording to the methods proposed by Ellwood and Maher[10] Moisture redox potential (Eh) total organic matter(TOM) and total arsenic (TA) in sediments were analyzedbased on the National Standard Method in China (GBT173785-2007) In addition sulfur species including ele-mental sulfur (ES) acid volatile sulfides (AVS) and ma-ture pyrite sulfides (MPS) were determined by continuous

Figure 1 Geographic map of the sampling site










ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


MoistureTOM

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 25 50Fe (gkg)

TFeEFe

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 1 2Mn (gkg)

TMnEMn

Dep

th (c

m)

(d)






ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

ES (gkg)D

epth

(cm

)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

AVS (gkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20

MPS (gkg)

Dep

th (c

m)

(c)

ES

AVSMPS

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20S (gkg)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 2 4EAs(V) (mgkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14

TAs (mgkg)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14As (mgkg)

EAs(III)

EAs(V)TAs

Dep

th (c

m)

(d)








ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

60 75 90pH

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

000 01 02

Sulfides (mgL)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 1 2Fe (mgL)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 6 12Mn (mgL)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20As (microgL)

As(III)

As(V)TAs

Dep

th (c

m)

(d)






J ϕDsdAsdz

11138681113868111386811138681113868111386811138680 (1)


Ds ϕD0 ϕlt 07

Ds ϕ2D0 ϕgt 07(2)




minusHAsO4










4 Conclusions




Mic

robe

Redu

ctio

n Diff

usio

n

As(III)


Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)



orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion



Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls












ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


MoistureTOM

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 25 50Fe (gkg)

TFeEFe

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 1 2Mn (gkg)

TMnEMn

Dep

th (c

m)

(d)






ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

ES (gkg)D

epth

(cm

)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

AVS (gkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20

MPS (gkg)

Dep

th (c

m)

(c)

ES

AVSMPS

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20S (gkg)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 2 4EAs(V) (mgkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14

TAs (mgkg)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14As (mgkg)

EAs(III)

EAs(V)TAs

Dep

th (c

m)

(d)








ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

60 75 90pH

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

000 01 02

Sulfides (mgL)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 1 2Fe (mgL)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 6 12Mn (mgL)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20As (microgL)

As(III)

As(V)TAs

Dep

th (c

m)

(d)






J ϕDsdAsdz

11138681113868111386811138681113868111386811138680 (1)


Ds ϕD0 ϕlt 07

Ds ϕ2D0 ϕgt 07(2)




minusHAsO4










4 Conclusions




Mic

robe

Redu

ctio

n Diff

usio

n

As(III)


Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)



orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion



Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

ES (gkg)D

epth

(cm

)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 05 10

AVS (gkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20

MPS (gkg)

Dep

th (c

m)

(c)

ES

AVSMPS

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

00 10 20S (gkg)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 2 4EAs(V) (mgkg)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14

TAs (mgkg)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0 7 14As (mgkg)

EAs(III)

EAs(V)TAs

Dep

th (c

m)

(d)








ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

60 75 90pH

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

000 01 02

Sulfides (mgL)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 1 2Fe (mgL)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 6 12Mn (mgL)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20As (microgL)

As(III)

As(V)TAs

Dep

th (c

m)

(d)






J ϕDsdAsdz

11138681113868111386811138681113868111386811138680 (1)


Ds ϕD0 ϕlt 07

Ds ϕ2D0 ϕgt 07(2)




minusHAsO4










4 Conclusions




Mic

robe

Redu

ctio

n Diff

usio

n

As(III)


Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)



orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion



Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls









ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

60 75 90pH

Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

000 01 02

Sulfides (mgL)

Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 1 2Fe (mgL)

Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 6 12Mn (mgL)

Dep

th (c

m)

(d)


ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(a)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(b)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0


Dep

th (c

m)

(c)

ndash30

ndash25

ndash20

ndash15

ndash10

ndash5

0

0 10 20As (microgL)

As(III)

As(V)TAs

Dep

th (c

m)

(d)






J ϕDsdAsdz

11138681113868111386811138681113868111386811138680 (1)


Ds ϕD0 ϕlt 07

Ds ϕ2D0 ϕgt 07(2)




minusHAsO4










4 Conclusions




Mic

robe

Redu

ctio

n Diff

usio

n

As(III)


Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)



orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion



Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







J ϕDsdAsdz

11138681113868111386811138681113868111386811138680 (1)


Ds ϕD0 ϕlt 07

Ds ϕ2D0 ϕgt 07(2)




minusHAsO4










4 Conclusions




Mic

robe

Redu

ctio

n Diff

usio

n

As(III)


Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)



orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion



Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







4 Conclusions




Mic

robe

Redu

ctio

n Diff

usio

n

As(III)


Fe(II)+

Oxidation

As(V)

Ads

orpt

ion

Oxi

datio

n

Mn(IV) + As(V)

+S2ndash

As(V)middotMn(IV)

FeSFeS2

Diff

usio

n

+S2ndash

(Tra

ce)



orpt

ion

O2

Overlying water

SWI

Diff

usio

nD

iffus

ion

Fe(III) + As(III)

Diff

usio

n

Prec

ipita

tion



Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




Acknowledgments


References



























Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls









Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




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