metal interactions in contaminated freshwater sediments from the fly river floodplain, papua new...

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Metal interactions incontaminated freshwatersediments from the flyriver floodplain, Papua NewGuineaBenedict T. Yaru a & Rodney T. Buckney ba Niugini Environmental Consultants , 1/342Mowbray Rd., Artarmon, NSW 2064, AustraliaE-mail:b Department of Environmental Sciences ,University of Technology , Westbourne St.,Gore Hill, Sydney 2007, NSW, AustraliaPublished online: 24 Feb 2007.

To cite this article: Benedict T. Yaru & Rodney T. Buckney (2000) Metalinteractions in contaminated freshwater sediments from the fly river floodplain,Papua New Guinea, International Journal of Environmental Studies, 57:3,305-331, DOI: 10.1080/00207230008711276

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Intern. J. Environ. Studies, 2000, Vol. 57, pp. 305-331 © 2000 OPA (Overseas Publishers Association) N.V.Reprints available directly from the publisher Published by license underPhotocopying permitted by license only the Gordon and Breach Science

Publishers imprint.Printed in Malaysia.

METAL INTERACTIONSIN CONTAMINATED FRESHWATERSEDIMENTS FROM THE FLY RIVERFLOODPLAIN, PAPUA NEW GUINEA

BENEDICT T. YARUa,* and RODNEY T. BUCKNEYb

a Niugini Environmental Consultants, 1/342 Mowbray Rd., Artarmon,NSW 2064 (Australia) ; b Department of Environmental Sciences,

University of Technology, Westbourne St., Gore Hill, Sydney 2007,NSW (Australia)

(Received in final form 22 May 1999)

Field data for sediment pH, Eh, sulphur and organic matter were analysed to determinetheir relationship with measured dissolved and particulate metals from sites in the FlyRiver affected by mine-derived wastes. The above-background concentrations of dis-solved metals correspond to various concentration groups as demonstrated by copperfor background (< 70 mg/kg), moderate (70-500mg/kg) and severe (> 500mg/kg), re-spectively. Dissolved Cu (r = 0.7431, p < 0.0005) and Mo (r = 0.7133,/> < 0.0005) weresignificantly correlated with their sediment component. Dissolved Al, Cd, Cu and Mowere positively correlated with sediment pH. Significant negative correlation betweendissolved copper and sediment (SOM) organic matter (r = -0.3821, p < 0.05), and posi-tive correlation with dissolved Al (r = 0.9358, p < 0.0005) suggest that dissolved Cu ispresent as a complex with either organic matter, Al/Fe oxyhydroxides, or oxyhydroxide-organic matter colloids. Significant interrelations between dissolved Al, Cu and Mowith organic matter and the ratio of Fe/SOM also suggests that sediment physico-chemicalcharacteristics are important in the processes occurring in the Fly River floodplainsediments. These processes appear to be responsible for the significantly increased metalconcentration in the water column.

Keywords: Eh; pH; freshwater sediment; mine derived sediments; metals; Fly River;Papua New Guinea

* Corresponding author, e-mail: [email protected]

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306 B. T. YARU AND R. T. BUCKNEY

1. INTRODUCTION

The Ok Tedi Mining Limited (OTML) operates a copper mine in theStar Mountains in north western Papua New Guinea (see Fig. 1). Cur-rently, overburden and mine residue containing ~ 0.1 % copper are dis-charged into the headwaters of Ok Tedi and transported by the OkTedi and Fly River to the lower reaches of the watershed. Studies[1-8] have shown that copper-rich sediment is being transported into

FIGURE 1 Map of the Fly River system and raunwaras.

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METAL INTERACTIONS 307

the flood plain areas and off-river water bodies, locally known as"raunwaras".

Solids, including suspended and deposited sediments, in lakes,rivers, oceans and other water bodies are the ultimate sink or sourcefor anthropogenic pollutants such as heavy metals [9-16]. However,the ultimate determination of sediments as a source or sink depends onthe chemical, physical and biological processes in the sediment. Theseprocesses (precipitation/dissolution, adsorption/desorption, complexa-tion, organic matter mineralisation, turbation and bioturbation) deter-mine the retention, release and mobility of trace metals in sediments[17-26]. The redox and pH directly affect the adsorption, precipita-tion and mobility of trace metals in sediments. Organic matter com-plexes have been shown to produce stable complexes with heavymetals and organic pollutants.

Recent studies [10, 11] have concluded that the natural Fly Riverand recently deposited mine-derived sediments are a sink rather thansource for copper, with observed elevated copper in the water sourcedto that associated with suspended particles. This conclusion was basedon the results obtained from the study of porewaters, in which copperwas observed in low concentrations, despite the elevated particulatecopper concentrations in the surficial sediments. Co-precipitation withiron- and manganese-oxyhydroxides was identified as the mechanismassociated with removal of copper from the water column.

Processes, which regulate metal behaviour in both water andsediment, are difficult to capture and quantify in both field and labo-ratory experiments. Model predictions of metal behaviour based onthermodynamic calculations are accurate to a certain degree. It is theobjectives of this paper to discuss the relationships between capacitycontrolling factors and metals from recently deposited mine-derivedsediments on the Fly River floodplain.

2. METHODS

2.1. Study Area .

The Fly River flood plains (Fig. 2) include a series of oxbow, blockedvalley lakes and flooded plains. Over a thousand kilometers from the

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N

Bosset Lagoon

O Sample Sites

Bai Lagoon

Kilometers0 5 10

Scale 1:320 000

LakcPangua

Lake Daviambu

FIGURE 2 Raunwara sampling sites in the middle Fly River.

estuary, the river port of Kiunga (Fig. 1) is about 20 meters abovesea level. Seasonal rainfall variation induces fluctuations in the waterlevels in the raunwaras and the main Fly River channel [27-29].Raunwara waters are typically dark brown in color from dissolvedorganic matter and are conveniently classed as "black water". FlyRiver water is turbid ("white water"). Flooding in the main river chan-nel and low water in the raunwaras causes the Fly River water to flowinto the raunwaras. This event transports copper-rich sediment intothe raunwaras and flood plains. At low river levels, the raunwaras maydrain through the tie channels to the Fly.

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Site selection within each raunwara was based on the proximityto the main Fly River channel to incorporate sediment affectedand unaffected sites. It was assumed that the furthermost samplingpoint would be least affected. Lake Aesake in the StricklandRiver catchment was chosen as the reference site. A reference sitewithin each raunwara was selected to monitor variations withineach raunwara.

2.2. Sample Collection

2.2.1. Water

Water samples were collected in clean 250 mL high-density poly-ethylene bottles 20-30 cm below the surface and kept in a coolenvironment prior to transportation to the laboratory. Samples werefiltered through a 0.45 um filter, acidified to pH < 2 and analysed formetals in the dissolved fraction using a Perkin Elmer Elan 6000Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Appro-priate reference materials (NIST 1643d Water) were analysed asquality control checks.

2.2.2. Sediment

Sediment core samples were taken using a Wildco™ gravity corer,and collected in Perspex tubes with holes drilled into the full length ofthe tube at 20 mm spacing. The diameter of the holes are 5 mm toaccommodate the size of the Microelectrode™ probes inserted formeasurement of redox and pH at depth intervals (see Fig. 3).

Immediately after a core was retrieved the ends were sealed andredox measurements were taken starting from the bottom, followed bypH. The sediment core was then emptied into HPDE zip-lock plasticbags, sealed and stored to transport to the site laboratory.

Sediment samples were dried at 80° C and ground to uniform size,usually <100um. Analyses of the metals, sulphur and sediment or-ganic matter (SOM) were again performed in triplicates. Trace met-als were digested and analysed using a microwave method [30, 31].Sulphur and SOM were determined using a Leco Analyser™. Ap-propriate external and in-house reference materials were incorporatedas quality control.

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FIGURE 3 Perspex sediment core tube, modified for profile measurement of sedimentEh and pH. Core tube length was ~ lm with holes (0 5 mm) drilled at 10mm intervals toinsert Eh and pH micro-probes.

2.3. Statistical Analysis

Statistical analysis was performed using the Statistica™(Version 5.1)package [32]. Pearson Product Moment Correlation (r) was used tomeasure the relationships between water, sediment and other sedimentcharacteristics. Between-site differences in sediment and water metalconcentration and sediment characteristics were examined using rangestandardised data ((mean x 1000)/range). Dissimilarity matrices (Eu-clidean distances) were obtained using the complete linkage method inCluster Analysis, and ordinated using Multidimensional Scaling.

3. RESULTS

3.1. Water

Dissolved metal concentration results are presented in Table I. It canbe observed from these results that cadmium, lead and manganese were

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TABLE I Dissolved metal concentrations for all sites, expressed as ug/L (± sd)

Site

Bai

Daviambu

Kai

Agu

Aesake

Pangua

123456

123

1234

123456

1234

123456

CM

6.85 ±0.205.86±0.106.96 ±0.199.92 ±0.2728.9 ±0.3029.7 ±0.771.63±0.193.65 ±0.081.53 ±0.3010.5 ±0.4519.6 ±0.3429.4 ±0.4338.9 ±0.404.04 ±0.042.43 ±0.124.34 ±0.434.32 ±0.055.85±0.135.94 ±0.130.92 ±0.300.96±0.171.01±0.171.15±0.5311.4±0.1211.7±0.313.46 ±0.355.86 ±0.542.08 ±0.5536.2 ±0.57

Cd

0.026±0.0130.017 ±0.0020.023 ±0.0100.015 ±0.0060.043 ±0.0100.044 ±0.0100.018 ±0.020

<0.010.012±0.0030.022 ±0.0010.028 ±0.0060.041 ±0.0110.037 ±0.0070.017 ±0.0050.011 ±0.0100.027±0.018

< 0.01 ±0.002< 0.01 ±0.005< 0.01 ±0.002< 0.01 ±0.006< 0.01 ±0.005< 0.01 ±0.0000.025 ±0.0420.008 ±0.001

< 0.01 ±0.002< 0.01 ±0.007< 0.01 ±0.0050.031 ±0.0600.031 ±0.004

Fe

504 ±7546 ±5276 ±4166±4217±1218±4665 ±3609 ±4373 ±265±3

223 ±2312±3310±454±973±3

110±5101 ±0.485 ±38

106 ±2163 ±4187 ±2240 ±1220 ±7337 ±2363 ±5484 ±12374 ±8143±11237 ±6

Mn

2.28±0.145.11 ±0.040.72 ±0.030.31 ±0.011.04±0.140.92 ±0.023.78 ±0.042.45 ±0.011.13±0.010.02 ±0.010.41 ±0.010.95 ±0.011.65 ±0.010.46 ±0.020.14±0.060.33±0.130.20 ±0.000.19 ±0.090.50 ±0.480.36 ±0.023.13 ±4.520.78 ±0.01

13±210.97 ±0.026.02 ±8.681.74±0.131.25 ±0.020.76 ±0.571.09 ±0.02

Pb

1.05 ±0.41.08 ±0.21.22 ±0.40.74 ±0.51.63 ±0.21.48 ±0.10.75 ±1.10.42 ±0.50.71 ±0.20.57 ±0.20.82 ±0.61.98 ±0.51.99 ±1.21.01 ±0.70.59 ±0.71.73 ±1.40.12±0.00.25 ±0.30.21 ±0.10.23 ±0.10.16 ±0.00.20 ±0.11.42±1.80.40 ±0.10.50 ±0.01.02 ±0.81.04 ±0.62.36 ±3.11.03±0.1

Zn

25 ±1.87.8 ±0.38.6±2.12.0 ±0.72.6 ±0.393.0 ±0.941.3 ±0.461.4 ±0.036.2 ±1.66.6 ±0.683.0±0.1615±1.3

3.3 ±0.784.7 ±0.333.1 ±0.689.0 ±1.9

0.74 ±0.073.3 ±0.596.7 ±0.927.5±1.17.3 ±0.278.3 ±2.4

6.1

7.4 ±0.696.3 ±1.7

4.916±4.221 ±1.35.1 ± 1.1

Al

24±1.518±0.8

9.3 ±0.56 ±0.6

91 ±0.298±123 ±0.414±0.2

6.9 ±0.43 ±0.9

42±1.1102 ±2.9152 ±0.412±0.33 ±0.4

11±14.9 ±0.24.9 ±0.46.1 ±0.3ll±0.8ll±0.814±0.612±0.214±0.617 ±0.420±215±1.3

1.5124±1.9

Mo

2.14 ±0.042.43 ±0.032.83 ±0.033.14±0.024.4 ±0.1

4.59 ±0.020.61 ±0.010.77 ±0.010.81 ±0.024.21 ±0.033.12±0.033.52 ±0.054.46 ±0.080.4 ±0.01

1.44 ±0.02I.35±0.011.53 ±0.011.54±0.011.7 ±0.02

0.04 ±00.04 ±00.05 ±00.08 ±0.032.31 ±0.032.16 ±0.040.78 ±0.021.75 ±0.010.42 ±0.026.26 ±0.1

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TABLE I (Continued)

Site

Fid Pin 15

Bosset

1231234

Cu

12.0 ±0.0123.6 ±0.2923.6 ±0.944.95 ±1.229.6 ±6.634.3 ±0.5442.0 ±1.6

Cd

0.017 ±0.0200.044 ±0.0390.022 ±0.0080.014±0.0120.175 ±0.2670.093 ±0.1310.032 ±0.010

Fe

93 ±30112±25205 ±3123 ±40224 ±8352±71308 ±12

Mn

0.10±0.100.49 ±0.530.48 ±0.030.35 ±0.071.01 ±0.351.58 ±0.563.01 ±2.38

Pb

1.33±1.63.69±3.22.89 ±2.51.06±1.03.04 ±2.43.83 ±4.61.83±0.6

Zn

22 ±7.0105 ±1414±4.8

1340 ±3.2

157.4

Al

7 ±2.533 ±0.773 ±1.9l l i l . l26±1.5

159±6177±0.1

Mo

3.54±0.134.16±0.174.26 ±0.051.97 ±0.031.31 ±0.064.19 ±0.084.68 ±0.16

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low at most sites, with concentrations approaching instrument detec-tion limits. Elevated copper concentrations are observed at sites closerto the main Fly River channel. During the time of sampling, Fly Riverwater was flowing into the Bai, Kai, Pangua, Flood Plain 15 and LakeBosset sites, while water from the Agu and Lake Daviambu was flow-ing into the main Fly River channel. Iron and aluminum concentrationsin the dissolved phase were higher than all other metal except copper.

Relationships between dissolved and sediment metals and other sedi-ment chemical characteristics were tested using Pearson Moment Cor-relation [32] (see Tab. II). Dissolved copper (dCu) and molybdenum(dMo) in overlying waters were significantly correlated to sedimentcopper (r = 0.743,p < 0.0005, Fig. 4a) and molybdenum (r = 0.713,p < 0.0005), respectively. Sediment pH and sulphur were also posi-tively correlated with dCu (Figs. 4b and 4c respectively), dCd, dAland dMo. Dissolved copper had a significant positive correlation(r = 0.9358,/? < 0.0005) with dissolved aluminum (Fig. 4d). Dissolvediron was positively correlated with sediment organic matter (SOM).Dissolved aluminum, copper, molybdenum and cadmium were nega-tively correlated (but not significant) with SOM, however, the relation-ship was positive and significant with the reciprocal of SOM (Fig. 4e).No relationships between redox potential and dissolved metals wereestablished through correlation analysis.

Multidimensional Scaling Ordination, or MDS [32], of the rangestandardised data for dissolved metals show three major groupings(Fig. 5). The first group (Group C) encompasses all the dissolved metalconcentrations at background levels. The second group (Group B)constitutes those sites that are influenced by Fly River water. Thesesites may not necessarily be near the main Fly River channel but do ex-change water with the Fly and therefore, mine-derived sediments. Al-though tie channel sites closer to the Fly are expected to have higherdissolved metal concentrations, it is important to note that samplestaken during the flow of black water into the Fly channel will be atbackground concentrations. Results from Lake Daviambu site 3 andsite 4 confirm this observation. Fly River flooded Kai Lagoon whenthe sampling was undertaken, thus elevated dissolved copper concen-trations were found for all sites. The third group (Group A) representssamples from those sites near the tie and main channels with typicalconcentrations for copper ranging from 10 to 42 ng/L.

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TABLE II Pearson Product Moment Correlation (r) coefficients for correlations between dissolved metals and sediment metals, paniculate sulphur,sediment organic matter, pH, Eh, 1/SOM and ratio of sFe/SOM- Varying levels of significance for correlations are superscripted with 5*, 4*, 3*, ** and *for p < 0.0005, p < 0.001, p < 0.005, p < 0.01 and p < 0.05, respectively

sCusCdsFesMnsPbsZnsAlsMosSSOMEhPH1/SOMFe/SOM

dCu

0.74315*0.34560.53843*0.79065*0.54143*0.68485*0.15150.7274s*0.62844*

-0.3821*0.02470.7045*0.65315*0.7036s*

dCd

0.59553*0.0740.36010.6591s*0.4081*0.61084*

-0.06220.61534*0.5078"

-0.25810.33250.58723*0.33930.3767

dFe

-0.2627- 0.48**

0.0221-0.127-0.3724-0.2057-0.1084-0.2073

0.00780.25690.1048

-0.2904-0.1871-0.1153

dMn

-0.2841-0.4504*-0.1287-0.1954-0.4334*-0.3184-0.3362-0.239

0.06710.4226*0.2199

-0.3018-0 .22-0.1522

dPb

0.2378-0.1099- 0.069

0.27270.13070.1804

-0.3999*0.210.2209

-0.18670.35850.17690.16910.0935

dZn

-0.3661-0.3617-0.56583*- 0.2904- 0.3523- 0.405*-0.56243*-0.3355-0.045

0.09010.0526

-0.2373-0.1601-0.3385

dAl

0.59473*0.20260.4082*0.6714s*0.34160.5078"0.01320.59053*0.65925*

-0.3049-0.0258

0.58493*0.61624*0.63694*

dMo

0.6964s*0.34980.4987"0.7556s*0.55853*0.6624s*0.1920.7133s*0.5074**

-0.38150.07460.6284*0.54983*0.59863*

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8.0

7.6

7.2

68

"

6.0

8.6

e.2

4.8

1.4

1.2

1 0

Figure 4«4b

:OOO ;O

o

0

Q

e o•

&

O

0 0DO

cPD

ng-

nJQ

O pH :

D S«lbu(ing/kg)

O i

D ! ' °! •';

o° ;

D :

a ;D :

0

8

O

a :g> 0 9.

O D

g- a

o

D

1400

1200

1000

600 f

I600 3

400 I

3200

0

5 15 25

dCu |ug/L)

oa

Figure 4c4»4d

<P

O

•

•

B

o ^

Sod S (%w/w)

1/SOM(%W/W)elAI (ugfl.)

6 :

D :. .Q

o ^

D

0

0

a ;

D .;..

o

o :

0

•CO

o0 .o

o

D

... o

8

o

o

D

O

o

ao

°4

0.2

00

-0.2

dCu (ug/L)

FIGURE 4 Dissolved Cu correlations with (a) sediment copper, (b) sediment pH, (c)sediment sulphur, (d) dissolved aluminum and (e) inverse of SOM. Copper was chosen asthe model element because of its abundance in the water column due to the corre-sponding elevated sediment concentrations.

The scatter in the data between Groups A and B are expected, sincefactors such as dilution, presence of mine-derived sediments and or-ganic matter may determine dissolved metal concentrations in thewater column at these sites.

3.2. Sediment

Results for the various sediment parameters are presented in Table III.Values for both redox, Eh (mV), and pH for data analysis in Table III

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C1 =B»1 C2 =Bai2 C3 *Bai3 C4 =Bai4 C5 =Ba<5 C6 "BaB C7 *0av1 C8 *Dav2 C9C10-Ka1 C11 -K»i2C12»Kai3C13>K»4C14-Agu1 C15 >Agu2C16-Agu3 C17 >Agu4C18 -Agu5 C19 «Agu6 C20 «A*«1 C2I =AC«2 C22 =Aes3 C23 = « M C2« =Pan1C25 =Pan2C26*Pan3C27«Pan4C28«P.n5C29»P»i6C30.F151 C31 "F152C32=F153C33 -Bo»1 C34 -BO62 C35=Bo<3 C36 =Boe4

o.o 0.4 o.a-1.S

FIGURE 5 Multidimensional scaling (MDS) ordination of dissolved metal concentra-tions at all sites. Groups A, B and C correspond to sites that have elevated, abovebackground and background concentrations of dissolved metals, respectively. An opti-mum solution was achieved with two dimensions, with a stress of 0.102 for 57 iterations.

are the average of values from the sediment-water interface (0.0 cm) to40 cm depth, taken to represent the rooting zone for aquatic plants.Typical depth profiles for the Eh and pH are represented by data fromBosset Lagoon and Floodplain 15 (Figs. 6 and 7, respectively). BossetLagoon Sites 1 and 2 represent highly oxidised, low pH sites while theother sites are representative of typical sites with varying degree ofmine derived sediment intrusion.

3.2.1. Sediment Metals

Results from this analysis reveal distinct groups, corresponding to thevarious sediment metal concentrations. Thus, sites from the variousraunwaras closer to the main Fly River channel or those sites impactedby mine-derived sediment have higher metal concentrations and there-fore different to other sites within the raunwaras locations. The threedistinct groups represent background (< 70mg/kg Cu), 70-500 and> 500mg/kg Cu. Sediment copper was used as the marker elementto distinguish between natural and mine-derived sediment. The un-contaminated sites based on copper concentrations are Pangua 3, allAesake sites, Bosset 1 and 2 and Daviambu 1 and 2.

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TABLE III Sediment metal concentrations and other sediment variables. All results are expressed as mg/kg except Al, Fe, S and SOM, which areexpressed as % (w/w). Redox potential (Eh) is expressed as mV

Pangua 1Pangua 2Pangua 3Pangua 4Pangua 5Pangua 6Aesake 1Aesake 2Aesake 3Aesake 4Fid Pin 15 1Fid Pin 15 2Fid Pin 15 3Daviambu 1Daviambu 2Daviambu 3Bai 1Bai 2Bai 3Bai 4Bai 5Bai 6Kai 1Kai2Kai 3Kai 4Agu 1Agu2

Cu

321221

19202838

106072284838

1428798802154

964244103180737

10031160864751847905874113

Cd

1.831.700.601.372.804.071.054.002.504.001.703.904.270.952.002.331.601.252.132.803.203.002.702.232.702.773.452.60

Fe

2.433.570.872.404.434.101.471.700.903.803.273.404.133.774.103.532.370.973.033.273.904.403.402.803.674.103.272.37

Mn

15326782

146506699753839

20616041773842

282561231

58155299827792620188578687269127

Pb

4745191798841823393938

1151141329

118582946

10410894

10012788779254

Zn

13414144

134187214

834814

12710619723127

10922513538

14719025222918620619519618977

Al

11.612.78.4

11.911.110.09.3

11.78.1

11.89.8

10.99.9

10.510.09.98.14.2

12.810.88.8

10.69.1

11.48.98.76.7

12.7

Mo

13.512.5

1.310.027.243.0

3.80.72.42.1

10.332.237.42.73.0

45.68.63.78.1

20.251.640.551.819.636.444.622.711.5

% 5

0.100.090.040.190.230.360.420.030.300.100.870.150.340.010.020.250.250.320.110.050.390.390.360.050.290.530.121.25

%SOM

8.54.26.1

12.13.41.4

26.44.9

24.87.0

15.60.91.22.13.22.2

18.731.9

5.33.62.21.51.73.01.51.21.9

37.1

Eh

- 1 4 1- 1 2 3- 2 0 5- 1 2 1- 1 9 3- 1 7 4- 1 9 6- 1 8 8

159145

-64 .1139254217302249219155170190192255232

PH

7.275.655.705.186.056.386.726.795.585.956.756.145.716.346.287.337.266.877.016.887.777.036.31

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TABLE III (Continued)

Agu 3Agu 4Agu 5Agu 6Bosset 1Bosset 2Bosset 3Bosset 4Bosset 5Bosset 6

Cu

607391471385

16303155

8051045

Cd

5.104.905.537.002.071.501.831.232.632.13

Fe

3.773.933.702.902.471.831.101.433.104.07

Mn

30123137217056656289

508737

Pb

102837881424229268991

Zn

14714112313247 .482635

186214

Al

4.911.411.010.86.2

12.45.54.89.18.9

Mo

31.512.619.310.6

1.31.50.81.2

31.534.0

%S

0.080.070.050.06

<0.010.020.020.230.430.05

%SOM

2.02.61.24.43.05.86.91.81.39.0

Eh

-41 .9-16 .3122130127127186186116175

PH

6.396.987.436.565.575.576.236.237.037.32

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s4

0•4

•S

-12-1S

•20

-24

-28

•32-3!

-40

-44

-43

•a

- K

-SO

Figure 6 . pH

- O - S1A.PH

-O- S1B.PH

- O - S2A.PH ,

- f t - S2B_PH !

- « - SJ_PH

-* - S4_PH . i

•

/>/

?IT

'• /

I/

?

6.0

pH

S.I 7.0 7.6

FIGURE 6 Redox and pH profiles for Bosset Lagoon sites. The "S" prefix refers tosite, followed by the site number. At this particular raunwara, Site 1 and 2 cores for pHwere sampled in duplicate.

These three groups were confirmed through MDS ordination, asshown by Figure 8. Group A represents sites which have metalconcentrations at background levels while Groups B and C haveconcentrations above lOOmg/kg Cu. The spread of points in the MDSanalysis for the first and third group (Fig. 8) shows the high variabilityas concentrations for sediment metals approach background levels anddilution by natural sediments, especially for Group A. The variation

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840

•4

-8-12-16-20-24-28

_ -32

I 2f •**J> -48° -S2

-66-60-64-68-72-76-80-8448

§§**5t^ i/ K ^fer -^ j '."".'

^^^^^Ti i • ! • • •'••' •" • ' - " " " . ' . . ' . : • . ' " " " : ' " : : . ' . • : :

^ t ^ ^ . ^ )'•"-'••'"..".'.'...""'.".'..\'.'i:.'."Z'. ':":"..'.'.".". :.'••;.'.•

A ^ - " • • • • ' • • • • • • ! • • • • • • • . : : : : : . : . . : . . " ; . . : : ] " " . : : • ; : ' " ' : * : : : •

^R~̂ ;J ^ " " ' i

Figure 7b Eh

-O- S1_EH- 0 - S2_EH

"-A- S3_EH

-300

Eh(mV)

FIGURE 7 Redox and pH profiles for Floodplain 15 sites. The "S" prefix refers to site,followed by the site number.

amongst Group C may be due to various factors. These includekinetics of dispersion and deposition of mine-derived sediments andthe physical sampling of sediment core. Sediment core were not sec-tioned, instead the whole core (core length was approximated at 40 cm)was homogenised and used for metal analysis. This approach wastaken to obtain an average of the conditions prevalent at the time ofsampling, thereby encompassing activities within the 40 cm rootingzone of aquatic plants [33, 34].

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AGU2O

/ GROUPA \/ \

/ BAI2 \/ o AES1 V

/ A " 3 ° I|

PAN3 BOS2

1 ° ° \1 BOS3, AES2 \I o\ , . BOS1\ • BOM o /

\ DAVV

\ V

/ GROUPB \/ \

/ \/FP15 1 *

RA11 /PAN4 O /I o PAN!

° PAN2BAI3 o o I

/ AGU4\AES4 Q A

\DAV2 /\ A0U6/\ 6/

//

\ °BAI4 B OS S

l C // o /

\ PAN5

GROUPC

KAJ3 V

<K ° °v\ i BOS6

FP15_2

-— .—'

-^

\\

DAV3 \

«B \BAllS5 '

o

*-PAN6 /

" /

y

1.0

0.6

0.2

-02

•0.6

-2.0 -1.5 -1.0 -0.5 0,0 0.5 1.0 1.5 2.0

AXIS1

FIGURE 8 Multidimensional scaling (MDS) ordination between sediment metals, par-ticulate sulphur and sediment organic matter, Eh and pH for all sites. Groups C, B andA correspond to sites that have elevated (> 500 mg/kg Cu), above background (70-500mg/kg Cu) and background concentrations of metals (< 70 mg/kg Cu), respectively. Anoptimum solution was achieved with two dimensions, with a stress of 0.089 for 32iterations.

Cadmium, lead and molybdenum were in low concentrations in thesediment as expected for both natural and mine derived sediments.These elements are not enriched in the ore body. Zinc, molybdenumand manganese concentrations show that these elements are associatedwith the mine-derived sediment. Iron and aluminum showed no sig-nificant variation (p > 0.05) from site to site.

Inter-correlation between all sediment parameters (Tab. IV) revealdirect relationships between sulphur, pH, reciprocal of SOM and ratioof sFe/SOM all metals, except Al. SOM is negatively correlated tosediment metals as expected. Increased metals concentrations areobserved in the sediment as pH increases. The sFe/SOM ratio is highlysignificant for all sediment metals, suggesting that the cycling and inter-action between these two elements (Fe, C) have a direct effect on sedi-ment metal behaviour.

3.2.2. Sediment Redox/pH

The pH profiles at each site were different but not significant(p > 0.05). Results in Table III show lowly acidic conditions, with a

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TABLE IV Pearson Product Moment Correlation (r) coefficients for sediment metalsand other sediment variables. Varying levels of significance for correlations aresubscripted with 5*, 4*, 3*, ** and * for p < 0.0005, p < 0.001, p < 0.005, p < 0.01 andp < 0.05, respectively

sCusCdsFesMnsPbsZnsAlsMo

0.447"-0.1367

0.07610.55574*0.20890.3793*

-0.18770.56194*

SOM

-0 .4509"-0.3915*-0.6635*- 0 . 4 2 5 5 "-0.4792**-0.4689**-0.3056- 0 . 4 4 3 3 "

Eh

0.0956-0.334

0.01140.04430.02540.0495

-0.24950.0381

pH

0.84625*0.4052*0.68225*0.8075*0.73925*0.82295*0.13090.796s*

IJSOM

0.6164s*0.34660.57224*0.591s*0.54584*0.52143*0.08410.6376s*

sFe/SOM

0.6857s*0.3938*0.7028s*0.697s*0.5864*0.6137s*0.16020.7118s*

few sites approaching pH 4. Acidic conditions were encountered atseveral sites, including Bosset SI and S2 and Daviambu SI and S2 (seeFig. 6a for Bosset Lagoon Sites 1 and 2). However, copper concen-trations at these sites were low, an indication of the absence of mine-derived sediments. Generally, a decrease of between one half to twopH units were observed with depth for sediments from all sites.

The pH of these bottom sediments ranged from 4 to 8, spanning4pH units. In most cases, pH dropped by up to 0.5 pH units near thetop 0-20 cm of the sediment. This drop coincided (in all observations)with a drop in redox potential. At some sites, pH dropped by up to0.4 pH units as measured Eh increased. The pH measured at BossetLagoon Sites 1 and 2 were decreasing with increasing depth (Fig. 6, Ehand pH for Site 1 and 2). Duplicate cores were taken to confirm thisobservation and at both sites, the trend was similar. Sediment pH cor-related positively with dissolved copper, lead, aluminum and molybde-num, and negatively with manganese.

Sediment pH was positively correlated (Pearson Product MomentCorrelation) with sediment metals, confirming the general understand-ing that an increase in pH increases precipitation of metals (thus theirassociation with particulate phase) and a decrease in pH increases insoluble metals.

The redox conditions at all these sites ranged from strongly reducing( - 274 mV) to strongly oxidising (+ 324 mV). Mobilisation of metals isthought to occur within the intermediate zone of the redox conditionsthat range from - 150 to +200mV [35]. Eh was poorly (positive butnot significant p < 0.05) correlated with dissolved metals except Al,

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which was negative and not significant (p < 0.05). Although Eh meas-urement was initiated from the bottom of the core, some effect on ex-posure to air was observed from this end. The appearance of a tail,towards a more positive Eh is obvious for sites such as Bai Lagoon site3 and 4, Bosset Lagoon Sites 1 and 2, and Floodplain 15 sites (see Figs.6 and 7). The region below the sediment-water interface (0-20 cm)was found to be more reducing than any other section of the sediment.

3.2.3. Sediment Sulphur/SOM

Sediment sulphur was significantly (p < 0.05) correlated with dCu(r = 0.628), dCd (r = 0.508), dAl (r = 0.659), dMo (r = 0.507), sCu(r = 0.511), sMn (r = 0.619), sZn (r = 0.422) and sMo (r = 0.614).Sediment organic matter correlation with dissolved and sediment metalswas negative except for dFe, dMn and dZn. The role of sediment organicmatter in metal cycling is also illustrated by Figure 9, with SOMincreasing and decreasing sediment Cu (Fig. 9a), Fe (Fig. 9c) and Mn(Fig. 9d). An increase in SOM causes the pH to decrease (Fig. 9b).

Significant positive correlation (p<0.05) exist for pS and SOM.Figures 4(c and d) show that values clustered around the low SOM/high pS reflect the pS associated with the mine-derived sediments.Mine-derived sediments have typically low sediment organic matterassociation. However, as SOM increases, pS associated with the plantmatter are obvious. Results from Agu Site 2 and Flood Plain 15 Site 1confirm this observation. Highly significant correlations were observedbetween the reciprocal of SOM and Cu (e.g., see Fig. 4e), Al and Moin the dissolved phase. Similarly, this relationship was also observedfor the ratio of sFe to SOM (Figs. lOa-dCu and lOb-dAl). The SOMdata was treated because the relationship between this parameter anddissolved metals was exponential. Correlation data also showed thatthe relationship between SOM and sFe, sMn and sZn was positive.

4. DISCUSSION

Decreasing sediment pH may result in a significant mobilisation ofmetals. Results from this study show that there were increaseddissolved metal concentrations in the water column, however, the

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10 15 20 25

SOM (%w/w)

5.0

4.5

40

3.5

3.0

25

2.0

1.5

1.0

0.5

Figure 9o OSdQ SadMnfrngftg)

O

D

O

: °

500

10 15 20 25 X 35 40

SOM

FIGURE 9 Correlation between SOM and (a) sCu, (b) pH, (c) sFe and (d) sMn.

correlation with corresponding sediment pH was positive. Mobilisa-tion of copper in the water column is independent of pH because thechanges are not significant (typically between 7-8.5) to warrant asudden increase in the dissolved copper levels in the waters of the FlyRiver and raunwaras [36,37]. However, increasing copper concentra-tions observed in the middle Fly River area was observed to corre-spond to increasing dissolved organic matter concentrations [11].Recent complexing capacity data show that copper in the dissolved

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8 15

o

D

< & _ - *

Figure 10a10b

O

o

— L

°oa

a «i|

o

D

o

CCP

oO;o

n

- • • ; -

o

o

a

a

o

a

o

D

6

D

o

.. D..

1.5 2.5

Ratio of S«d Fe/SOM

100 5

FIGURE 10 Correlation between sFe/SOM and (a) dCu and (b) dAl.

phase is complexed by organic matter, with complexing capacitiesof these waters averaging 30mg/L [11]. Relationship between organicmatter from the sediment and dissolved metals observed from thisstudy confirm that organic matter is playing an important role in thecomplexation of metals.

The sediments are mildly acidic at most sites except for unaffectedsites with values approaching pH 4. Metal dissolution from sedimentand release at such pH from these sites would be significant, however,the metal concentrations at these sites are at background levels.Therefore, if re-mobilisation of metals at these low sediment pH sitesoccurred, the presence in the water column would be low due to thedilution effect from low-copper water. The low background pHs isattributed to the properties of these soils, i.e., natural acid sulfate soils.The pH of sediment at other sites is between 6 to 8. The slightly acidicconditions of these sediments are attributed to the presence of highconcentrations of organic acids, and not necessarily due to acid minedrainage from mine-derived sediments.

The oxygenated, alkaline nature of the Fly River water is conduciveto the formation and presence of aluminum and iron oxyhydroxides.The relationships between pH and metals in sediment (e.g., see Figs,l la and lib), and water (Fig. lie) show that this is an importantprocess, with increased metal concentration in sediments as pH in-creases. Correlations between sediment pH and dissolved metals in the

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5.0

4.6

4.0

3.5

8? 3.0

S.

I"2.0

1.6

1.0

Figure 11a11b

D6

O SodF«rMn 5<KlCu(mj,

0

o

o

n o~5o

Oo

o

DO

D {P

Oc

oo

oD

0

o

D

.0

a ° DLJ :

0 n ;

DB

no

4.8 6.6 6.4

pH

6.8 7.2 7.6

1400

1200

1000

800 _a%

600 .§aU

400 |

200

0

-200

4.8 5.2 5.6 6.0 6.4 6.8 7.2 7.6 8.0

FIGURE 11 Relationships between metals and pH (a) sFe (%), (b) sCu (mg/kg) and(c) dissolved aluminum (jig/L).

overlying water also show that dissolved metals increase as pHincreases. This observation is interesting because an increase in acidityshould coincide with an increase in dissolved metals. The mechanismresponsible for this behaviour is the adsorption of metals onto oxi-dised surfaces, or complexation with organic matter and subsequentadsorption or co-precipitation onto Al- and Fe-oxyhydroxide col-loids. The Al/Fe-oxyhydroxides and oxyhydroxide-organic complexes

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less than 0.45 um are expected to pass through the mentioned mem-brane pore size [38,39]. Copper in the dissolved phase at these sitesare expected to be present as complexes with organic matter and ad-sorbed onto fine particles until such when ionic copper concentratesexceed complexing capacity of the system [11].

Organic matter is important in this system because of its role inthe regulation and storage of metals, if the mine-derived sediments be-come a source for metals in the water column. Most transformation af-fecting metals in surface sediments are driven directly and indirectly bydecomposition of organic detritus deposited from the water column.The spatial and temporal distributions of oxidation of organic mattercontrol the cycling of metals in sediments [15,16,40]. In the sedimentsof these raunwaras, organic matter is crucial in the complexationof mdbilised copper in the surface and interstitial waters. Copper ispreferentially complexed to organic matter in natural waters andsediment porewaters [41-44]. Significant negative correlations (p <0.05) between sediment metals and organic matter show that either theSOM is readily consumed by the new material during the reductivedissolution of iron oxides [13,45] or there is dilution of high organicmatter sediment by recently deposited mine-derived sediments.

Cycling of carbon, Fe, Mn, nitrogen and sulphur is expected toinfluence the changes in capacity controlling factors such as pH andredox, thereby controlling metal solubility. The ratio of sFe/SOMshows that, the interaction between these two variables appears tohave an influence on the dCu, dCd, dAl and dMo. The interactionbetween sFe and SOM is also influencing the metals in sediment, withmore metals associated with the particulate phase as the ratio in-creases. Although there could be a simple dilution of SOM with low-organic matter sediment, a variety of Fe-humate complexes can beformed with subsequent hydrolysis and oxidation-reduction reactionsto form Fe2+ and oxidised organic matter [46].

Sediment sulphur is directly related to sediment metals and dis-solved metals. The direct relationship with dissolved copper reveals thatmine derived sediments are a source, especially with results from thisstudy showing direct correlation with sulphur and sediment metals.Copper in the dissolved phase may be present as fine copper sulphideparticles or as copper-organo-sulfide complexes. This may be possiblebecause results from recent laboratory based studies [47] show that

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adsorbed copper may react with sulfide under reducing conditions toform covellite (CuS) or chalcocite (Cu2S). Bacterial oxidation of sulfideminerals in suspended and benthic mine derived particles may alsocontribute to the increased dissolved metal concentration (Apte perscomm.) observed in this system.

The redox state of sediment determines the speciation of metalions in porewaters and the formation of Fe/Mn oxyhydroxides. Theinteraction between dissolved metal ions and particulate matter deter-mine the fraction of metal ions that will be bound to particulate mat-ter and that will be removed to the sediments. Copper and other tracemetals may be affected by these processes in different ways; inter-action with iron and manganese oxyhydroxides, precipitation, andcomplexation with sulphides. Changes in redox chemistry are alsoknown to influence metal mobilisation. Studies involving oxidationof reduced sediments in experimental plots and in laboratory mixingexperiments show that there is rapid oxidation of reduced metals, con-sequently decreasing bioavailability as metals are immediately adsorb-ed or complexed with oxidised compounds and organic matter [48].The solubility and mobilisation of metals in sediment and interstitialwaters are increased in between a —150 and +150mv Eh range.Results from this field study show that redox conditions of at thesesites are ideal for the release and flux of metals to the surficial waters.These results (Tab. I for dissolved Fe and Al and Tab. II for sedimentmetals) also illustrate that an abundance of organic material and anaturally high Fe and Al concentrations are important in maintain-ing ionic metal species in complexed forms. The fine colloidal mattersprovide a high surface for adsorption.

To conclude, this study has demonstrated that dissolved metals inthe surface waters were associated with colloidal matter in suspension.Initially, dissolved metals would increase as more mine-derived parti-culate matter from the benthic sediments and suspension increases.Increases in dissolved metals are expected to be associated primarilywith the organic matter. Dissolved metals at these sites are associatedwith fine Al- and Fe-oxyhydroxides, especially at neutral to alkalinepH (7-8.5 in the water) through complexation and adsorptionprocesses. Colloidal Al particles and organic matter coatings on theAl/Fe-oxyhydroxides may be responsible. The increase in dissolvedmetals as a result of these processes should not result in an increase

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in ionic metal concentrations, unless there is an increase in ionicmetal concentration which exceeds the complexing capacity. Low-pH sediments and observed redox conditions are ideal for metalmobilisation, however acidity of sediments are not an issue since it isestimated that an adequate buffering capacity, with adequate complex-ing capacity exist to render ionic metal species non-toxic.

References

[1] Ok Tedi Mining Limited (OTML) Acceptable Paniculate Level (APL) andAdditional Monitoring Program (Terms of Reference for Compliance Monitoring)(1990).

[2] Ok Tedi Mining Limited (OTML) "APL Compliance and Additional MonitoringProgram: 1991", Annual Report. OTML Internal Report ENV91-00 (1991).

[3] Ok Tedi Mining Limited (OTML) "APL Compliance and Additional MonitoringProgram: 1991", Annual Report, Fly River Floodplain Copper Monitor. OTMLInternal Report ENV92-06 (1992).

[4] Ok Tedi Mining Limited (OTML) "Fly River Floodplain Copper Monitor(Appendum to the APL Compliance and Additional Environmental MonitoringProgram: 1993", Annual Report. OTML Internal Report ENV93-06 (1993).

[5] Ok Tedi Mining Limited (OTML) "Fly River FloodPlain Copper Monitor(Appendum to the APL Compliance and Additional Environmental MonitoringProgram: 1992/93", Annual Report. OTML Internal Report ENV94-14 (1994).

[6] Ok Tedi Mining Limited (OTML) "Fly River Flood Plain Copper Monitor(Appendum to the APL Compliance and Additional Environmental MonitoringProgram: 1993/94", Annual Report. OTML Internal Report ENV95-08.

[7] G. M. Day, "Particle size and shape of characteristics of deposited sediments in themiddle Fly River, and Sediment deposition rates in the tie-channels and off-riverwater bodies", Consultants Report to Ok Tedi Mining Ltd. Report #: C/R 001:06Main Report 1 (1996).

[8] W. E. Dietrich and G. Parker, "Analysis of the copper contamination of the FlyRiver floodplain", Consultant's Report to OTML (1992).

[9] H. E. Allen (Ed.), Metal Contaminated Aquatic Sediments (Ann Arbor Press;Chelsea, Ml , 1995).

[10] S. C. Apte, G. E. Batley, G. M. Day and I. B. Wood, "Factors influencing thepartitioning and fate of copper in the Ok Tedi and Fly River systems", OTMLjCSIRO collaborative research program. First Year Report (1993).

[11] S. C. Apte, G. E. Batley, G. M. Day, E. C. Schwamberger and I. B. Wood (1995)."Factors influencing the partitioning and fate of copper in the Ok Tedi and FlyRiver systems", OTML/CSIRO collaborative research program. Final Report.

[12] A. G. Burton Jr., "Assessing the toxicity of freshwater sediments", EnvironmentalToxicology Chemistry 10, 1585-1627 (1991).

[13] W. Salomons and W. M. Stigliani (Eds.), Biogeodynamics of Pollutants in Soils andSediments: Risk Assessment of delayed and non-linear responses. (Springer-Verlag,Berlin, 1995).

[14] W. Salomons and U. Forstner, Metals in the Hydrocycle. (Springer-Verlag,Heidelberg, 1984).

[15] W. Salomons and U. Forstner, Chemistry and Biology of Solid Wastes: DredgedMaterial and Mine Tailings. (Springer-Verlag, Berlin, 1988).

[16] W. Salomons and U. Forstner, Environmental Management of Solid Waste.(Springer-Verlag, Berlin, 1988).

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[17] W. Davison, "Conceptual models for transport at a redox boundary", In:(W. Stumm, Ed.) Chemical Processes in Lakes. (John Wiley & Sons, New York,1985), pp. 35-53 (1985).

[18] L. J. Jackson, J. Kalff and J. B. Rasmussen, "Sediment pH and redox potentialaffect the bioavailability of Al, Cu, Fe, Mn and Zn to rooted aquaticmacrophytes", Canadian Journal of Fisheries and Aquatic Sci. 50, 143-138 (1992).

[19] W. Petersen, K. Wallmann, P. Li, F. Schroeder and H. D. Knauth, "Exchange oftrace elements at the sediment-water interface during early diagenesis processes",Marine and Freshwater Research 46, 19-26 (1995).

[20] A. Tessier, R. Carignan and N. Belzile, "Processes occurring at the sediment-waterinterface: Emphasis on trace elements", In: (J. Buffle and R. R. De Vitre, Eds.)Chemical and Biological Regulation of Aquatic Systems. (Lewis Publishers, BoeaRaton, Florida, 1994), pp. 137-173.

[21] A. Tessier and P. G. C. Campbell, "Partitioning of trace metals in sediments:relationship with bioavailability", Hydrobiologia 149, 43-52 (1987).

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metal interactions in contaminated freshwater sediments from the fly river floodplain, papua new...

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