Spill ,~cience& TechnologyBulletin, Vol.4, No. 3, pp. 165-175, 1997 ~
© 1998ElsevierScienceLtd Printed in Great Britain.All rightsreserved 1353-2561/98$19.00+0.0(I
Pergamon PII: S1353-2561 (98)00013-9
The Effect of Sediment Redox Chemistry on Solubility/Chemically Active Forms of Selected Metals in Bottom Sediment Receiving Produced Water Discharge T I N G Z O N G G U O , R. D. D E L A U N E * & W. H. P A T R I C K JR
Wetland Biogeochemistry Institute, Louisiana State University, Baton Rouge, L A 70803- 7511, USA
The effect of sediment redox conditions on the solubility behavior of Fe, Pb, Ni, Ba, and Cu in bottom sediment collected from a produce water discharge site was investigated using kinetics and chemical fractionation procedures. Sediment collected was composited and subsamples incubated in laboratory microcosms under controlled E h - p H conditions. Sediment was sequentially extracted for determining metals in five fractions (exchangeable, carbonate, bound to iron and manganese oxide, bound to organic matter and sulfide, mineral matrix or residue). Metal distribution in the fractions indicates that under oxidizing sediment conditions, the behavior of Fe, Pb and Ni were governed by Fe(III) and Mn(IV) oxides; Ba by insoluble complexation with humic compounds; and Cu by carbonates and humic complexation. Under reducing sediment condition, the behaviors of Fe and Cu were controlled by the formation of insoluble sulfides and humic complexes; the behaviors of Ni and Ba by carbonate and Pb behavior by sulfides, carbonates and humic complexes. With increases in sediment redox potential, the affinity between Fe(III), Mn(IV) oxides and Fe, Pb, Ni, Cu increased, the affinity between insoluble large molecular humic and Ba increased, and the affinity between carbonates and Cu increased. With decreasing sediment redox potential, the affinity between carbon. ates and Fe, Ni, Ba increased; the affinity between sulfides, humic substances and Fe, Pb, Ni, Cu also increased. Upon Fe(III) oxide reduction, it is estimated that 20% of total reducible Fe(III) oxides was reduced by direct bacterial reduction (K = - 4 2 . 6 ppm/day), 80% of total reducible Fe(III) oxides was associated with chemical fractions attributed to sulfide oxidation (K = -171.5 ppm/day). The rate constants (ppm/day) for dissolved Ni (Eh < 0 mV), Pb (Eh < - 8 0 mV) and Cu ( - 8 0 mV < Eh < 0 mV) are - 1 . 6 , -0.047 and --0.16, respectively. In our incubation period, the rate constants (ppm/day) for Ni bound to Fe(III) and Mn(IV) oxides, Ba bound to carbonates and Cu bound to insoluble large molecular humic are - 3 . 2 , 0.91 and 4.3, respectively. © 1998 Elsevier Science Ltd. All rights reserved.
Keywords: metals, sediment, redox chemistry, produced water, coastal
Introduction T h e r e is c o n s i d e r a b l e o n s h o r e a n d n e a r shore activity associated with p e t r o l e u m h y d r o c a r b o n *Corresponding author. Tel: 001 504 388 8810; Fax: 001 504 388 6423.
p r o d u c t i o n a n d recovery in the L o u i s i a n a coastal zone. As a result of p r o d u c t i o n of p e t r o l e u m hydrocarbon, metals a n d radionuclides can e n t e r the e n v i r o n m e n t s u r r o u n d i n g oil and gas p r o d u c t i o n facilities. C o n s i d e r a b l e quantities of p r o d u c e d water c o n t a i n i n g c o n t a m i n a n t s are b e i n g i n t r o d u c e d or have e n t e r e d the s e d i m e n t and water c o l u m n n e a r produc165
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tion sites, especially in offshore and near shore areas (Boesch and Rabalais, 1989). At present there is little information on biogeochemistry or redox chemistry of surface sediment in the vicinity of oil extraction and recovery facilities, as related to metal solubility/behavior. Metal speciation and petroleum hydrocarbon degradation are largely a function of the environmental conditions present in the sediment. One key environmental factor that is common to both heavy metal solubility and the biodegradation of organic matter is sediment redox potential. Anoxic redox potentials can range from only slightly reduced (+300 mV) to highly reduced ( - 3 0 0 m V ) depending on the inorganic electron acceptor present. As sediments become anoxic, different groups of microorganism utilize electron acceptors sequentially in the order: 02, NO~, Mn 4+, Fe 3+, SO] , and CO2. This sequence is often repeated with depth in the profile of sediment beds, where organisms utilizing these acceptors are present in loosely defined zones. Reported concentrations of nine metals were higher in produced water than receiving water (Tillery et al., 1981). The metals included barium, cadmium, chromium, iron, mercury, manganese, strontium and thallium. Barium, cadmium, chromium and manganese also can exceed receiving water by factors of 10-100. Neff (1987) and Lyssj (1981) reported elevated concentrations of As, Cd, Cr, Cu, Hg, Pb and Zn in produced waters. The components of drilling fluids include clays such as benotonite, barium sulfate (barite), chromium lignosulfates and lime/ caustic soda to control pH. Barite is the major source of many of these metals (Kramer et al., 1980). Dames and Moore (1981) in laboratory studies of metal bioaccumulation indicated that barium may be bioaccumulated by a factor of 30, chromium by a factor of up to 15 and lead by a factor of only 2-3. Along the redox gradient found in sediments, the solubility of metals (dissolved metal concentration) can vary by several orders of magnitude. Solubility and speciation of metals is strongly dependent on the redox potential and pH of the sediment (Gambrell et al., 1991b). The purpose of this study was to determine the effect of sediment redox chemistry on metal solubility/behavior in sediment collected from a stream bottom which has received produced water discharge for a number of years.
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Terebonne parish (Fig. 1). The effluent or produced water was discharged from the secondary compartment of the pit into an adjacent canal (St. Pe, 1990). Five active wells contributed produced water to the pit. The average discharge has been reported to be 482 barrels per day (St. Pe, 1990). The sediment had a pH = 7.0 and contained 0.1% Ba, 0.04% Mn and 2% Fe. The heavy metal content of the sediment was determined using wet ashing and ICP procedures. Redox (Eh) control system-microcosm incubation Two hundred grams of sediment (dry weight equivalent, amended with 0.3% (W/W) ground dried plant material) was added to 1.81 5% salinity sea water in laboratory microcosms used to control sediment Eh-pH conditions. The microcosm originally described by Patrick et al. (1973), equipped with a combination pH electrode, Pt-electrodes and refer-
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Materials and methods Sediment Sediment was collected from the discharge point from a waste pit associated with a petroleum recovery operation in the Lirette Oil and Gas field in 166
F i g . 1 Location of Lirette (LRT) site from which sediment samples were collected.
Spill Science & Technology Bulletin 4(3)
EFFECTOF SEDIMENTREDOXCHEMISTRYON METALSOLUBILITY ence electrodes, allows for the continuous recording of Eh and pH. The sediment suspensions were kept stirring with a magnetic stirrer. The suspensions were pre-incubated at 26°C under aerobic condition for 25 days. After the initial pre-incubation, the suspensions were purged with nitrogen gas and maintained under anaerobic conditions. The suspensions were maintained at pH = 7.0 (the normal pH of sediments under flooded conditions) by addition of diluted HC1 or NaOH solution as needed during the pre-incubation and anaerobic incubation periods. Metal was added to sediment suspensions at a rate four times that of the original heavy metal contents of the sediment. The heavy metal contents of the sediment with added metals were: Cu =610, Pb = 300, and Ni = 580. No barium was added to the sediment. Water-soluble fractions
Samples were withdrawn from the suspension by means of a plastic syringe and stainless steel needle. After centrifuging to separate the sediment from the solution phase, the supernatant was filtered through a 0.45/~m membrane filter. The remaining sediment was extracted using the following sequential fractionation scheme. During the above sampling and extraction processes the samples were maintained under nitrogen gas.
Sequential chemical fractionation procedure Many researchers have used fractionation schemes to study heavy metal chemistry in sediment (DeLaune and Smith, 1985; Gambreli et al., 1991a; Giblin et al., 1986; Giesy et al., 1977). Metal contents in the sediment suspension were selectively extracted in this study using the metal fractionation procedure developed by Shannon and White (1991). The various fractions determined in this study are described below FI: Exchangeable phase. Studies have shown that the clay and organic matter surface adsorbed metal ions in sediment will adsorb or desorb heavy metals when the ionic composition or E h - p H change (Keller and Vedy, 1994; Khalid et al., 1981; Gambrell et al., 1980).
F2: Bound to carbonate phase. Significant heavy metal contents are associated with sediment carbonates (Ramos et al., 1994; Gambrell, 1994). This fraction would be susceptible to pH change and the degradation of organic matter in sediment. If, however, the pH becomes moderately to strongly acidic, as can sometimes occur when reduced sediment (containing sulfides) become oxidized, these metals may be transformed into the dissolved form. Spill Science & Technology Bulletin
4(3)
I :~ ~'~ ~
: ( ~ ~I
F3: Bound to iron and manganese oxides phase. Iron and manganese oxides exist as nodules and concretions, cemented between particles or on particle coatings in sediment. These oxides are excellent scavengers for heavy metals and are active when Eh and pH change in the sediment (Feijtel et al., 1988; I~vy Jet al., 1992). When sediments become reducing, the metals bound to Fe and Mn oxides will be transformed into readily available forms due to the dissolution of Fe and Mn oxides. F4: Bound to organic matter and sulfide phase. This fraction represents heavy metals bound to various insoluble organic matter such as living organisms, detritus, coatings on mineral particles (Gambrell et al., 1980; Ramos et al., 1994). Such organic matter can be degraded under aerobic and anaerobic conditions, releasing soluble heavy metals. Heavy metals can exist as sulfides under anaerobic conditions (Gambrell et al., 1980, Gambrell et al., 1991b) which are susceptible to Eh and pH changes. Metal complexed with insoluble large molecular humic are effectively immobilized. There is some evidence that these metals are less effectively immobilized if a reduced sediment is oxidized (Gambrell and Patrick, 1978, 1988). On the other hand, when reduced sediment is oxidized, all sulfides will be oxidized into sulfate, and all bounded metals with sulfides will be released and transformed into readily available forms. F5 Mineral matrix phase. The residual sediment fractions represent primary and secondary materials. These heavy metals are relatively stable in a natural sediment environment (Gambrell, 1994). The methods for extracting metals from each fraction are described below.
FI: The sediment was extracted at room temperature for 30rain with 8ml 0.5 M Mg(NOa)2/g dry weight sediment, adjusted to pH 7.0 with nitric acid. The samples were agitated continuously. F2: The sediment residue from F1 was leached at room temperature for 5 h with 8ml, 1 M NaOAc, adjusted to pH 5.0 with acetic acid for I g dry weight sediment. These samples were also agitated continuously. F3: The sediment residue from F2 was extracted at 96°C for 6 h with 20 ml 0.08 M NHzOH.HCI in 25% (v/v) acetic acid for 1 g dry weight sediment. These samples were occasionally agitated. F4: For 1 g of dry weight sediment, the sediment residue from F3 was extracted at 85°C for 2 h with 3 ml 0.02 M HNO3 and 5 ml 30% H202 (adjusted to pH =2.0 with HNO3) was added, and extraction continued at 85°C for another 3 h. The sample was then cooled, 5 ml 3.2 M NH4OAc in 2% (V/V) HNO3 was added, and the sample was diluted to 20 ml with
167
T. G U O et al.
deionized water. The samples were agitated continuously for 30 min. NHaOAc was added to prevent adsorption of extracted metals onto the oxidized sediment. F5: The sediment residue from F4 was extracted with 25 ml concentrated HNO3 for 1 g of dry weight sediment at 105°C, the sediment was digested to 5 ml solution left, and the sample was diluted to 25 ml with deionized water.
residues were rinsed with 8 ml of deionized water for 1 g dry weight sediment and centrifuged at 5000 rpm for 30min. These second supernatants were discarded. Metals from water-soluble and sediment extracts were analyzed by ICP methods.
The above extractions were conducted in 250 ml centrifuge tubes, which prevented any loss of sediment between the successive extractions. Separation was conducted by centrifuging at 5000 rpm for 30min. Supernatants were filtered using 0.45ym millipore filters and then analyzed for metals. The
Metal kinetics are influenced by many factors. These factors include temperature,' organic matter, surface activity of Fe and Mn compounds, microorganism species and other sediment characteristics. Since it is difficult to individually quantify the variables, in this investigation the factors were
R e s u l t s and d i s c u s s i o n
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Fig. 2 The effect of Eh on the (a) distribution or content; and (b) percentage of Fe in various chemical fractions. 168
Spill Science & Technology Bulletin 4(3)
EFFECT OF SEDIMENT REDOX CHEMISTRY ON METAL SOLUBILITY combined into one parameter - - the rate constant of the assumed zero-order reaction, the so-called pseudo-zero-order reaction model. In our discussion below the pseudo-zero-order reaction model was used. When the rate constant was positive, the reaction released constituents of metals into solution. When the rate constant was negative, the metals are
K, (direct microbial reduction) 1<2 (indirect reduction by sulfide)
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removed from solution. When considering metals bound to organic matter and sulfide phase, we assumed that the formation of insoluble organic matter (complexation of insoluble, large molecular weight humic) (Gambrell and Patrick, 1978; Gambrell et al., 1980) and sulfides were independent. At sediment E h = - 1 3 0 m V and above (the Eh at sulfate is reduced) the changes in metals in this fraction was attributed to insoluble, large molecular weight humic substances.
Table 1 The rate constants K (ppm/day) of the pseudo-zero-order reaction involving Fe Soluble
I
Fe behavior
Figure 2a shows the effect of sediment Eh (redox potential) on the content of Fe in the various
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Spill Science & Technology Bulletin 4(3)
169
T. G U O e t
chemical fractions. As Eh decreased, Fe(III) oxides were microbialy reduced to soluble Fe(II), therefore increasing soluble Fe concentration ( K = 42.5 ppm/ day) in solution. When Eh further decreased to - 1 3 0 m V , a reduction in exchangeable iron was observed which was attributed sulfide formed as a result of sulfate reduction precipitating dissolved Fe(II) to form insoluble FeS. Based on the fractionation data at all redox levels studied, dissolved Fe(II) was also removed through Fe becoming associated with insoluble organic matter (primarily as a result of complexation of Fe with insoluble, large molecular humic). The above two factors result in the reduction of soluble Fe concentration in . solution ( K = - 2 5 . 8 p p m / d a y ) . The rate constants of the removed reactions for dissolved Fe(II) are 40.7 and
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31.4ppm/day for the formation of sulfides and complexation of insoluble, large molecular humic respectively. Fe(IIl) oxides in the sediment were reduced to the more soluble Fe(II) during anaerobic incubation. Under reducing conditions (Eh > - 1 3 0 m V ) , the reduction of Fe(III) oxides occurred only by direct microbial reduction ( K = - 4 2 . 6 p p m / d a y ) involving organic carbon turnover. This part of Fe(III) reduction was equivalent to approximately 2071 ppm (20% of total reducible Fe(III)). At sediment (Eh < - 1 3 0 m V ) , Fe(III) reducing microorganisms can inhibit sulfate reduction by outcompeting sulfate reducers for electron donors (Lovley and Phillips, 1987). We assume that a portion of Fe(III) reduction occurred by sulfides reducing Fe(III) oxides. Only a
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Fig. 4 T h e effect of E h on the (a) distribution; a n d (b) p e r c e n t a g e of Ni in v a r i o u s c h e m i c a l fractions. 170
Spill Science & Technology Bulletin 4(3)
i
EFFECT OF S E D I M E N T R E D O X C H E M I S T R Y ON METAL SOLUBILITY
small amount of the Fe(III) reduction at these redox levels can occur by direct bacteria reduction involving organic carbon turnover (Jacobson, 1994). Accordingly, almost 8571 ppm (80% of total reducible Fe(III)) was reduced by the sulfide oxidation pathway (K = - 171.5 ppm/day). The rate constant of indirect Fe(IlI) oxide reduction by sulfides is significantly greater than that by direct bacteria reduction. The rate constants of the pseudo-zero-order reaction are listed in Table 1. Figure 2b shows the percentage distribution of Fe found in the various chemical fractions. During anaerobic incubation approximately half of the reduced Fe(III) was converted to sulfide bound Fe(lI). The remaining half of the reduced Fe(III) was
Pb behavior Figure 3a shows the effect of sediment Eh on the actual distribution content of Pb in the various chemical fractions. As Eh decreased, Fe(IIl) and Mn(IV) oxides were released into solution. Adsorbed Pb decreased ( K = - 1 . 1 ppm/day) with a significant portion of the released Pb going into solution
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converted to carbonate bound Fe(II). Under oxidizing sediment conditions Fe(llI) oxide predominated by Fe behavior was controlled by Fe(III) oxides. Under reducing sediment conditions, sulfide and insoluble large molecular humic bound Fe(II) was the dominant fraction controlling iron behavior.
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Fig. 5 The effect of Eh on the (a) distribution; and (b) percentage of Ba in various chemical fractions. Spill S c i e n c e & Technology Bulletin 4(3)
171
T. G U O et al.
( K = 17ppb/day). A continued decrease in Eh resulted in dissolved Pb concentration decreases ( K = - 4 7 ppb/day) as a result of the formation of insoluble lead associated with sulfides (K = 1,72 ppm/ day), insoluble complexes of insoluble large molecular humic (K = 0.17 ppm/day) and carbonates. As a result of the above processes, most of the released Pb by Fe(III) and Mn(IV) reduction was apparently converted to lead sulfide. Figure 3b shows the effect of Eh on the percentage of Pb in the various chemical fractions. Under oxidizing conditions Pb was bound to Fe(III) and Mn(IV) oxides. Pb behavior in the sediment was apparently controlled by chemical adsorption on Fe(III) and Mn(IV) oxides. Under reducing sediment
conditions, Pb behavior was also governed by sediment carbonate and sulfide since lead was found in both the carbonate and sulfide fractions. Ni behavior
Figure 4a shows the effect of Eh on the Ni content in solution and changes between fractions over the redox range studied. When sediment Eh decreased, Fe(llI) and Mn(IV) oxides were reduced to soluble Fe(II) and Mn(II). The Ni adsorbed on Fe(llI) and Mn(IV) oxides decreased (K = - 3.2 ppm/day) resulting in the release of Ni into solution ( K = 1.5ppm/day). When sediment Eh decreased further, dissolved Ni concentration decreases
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Fig. 6 T h e effect of E h o n the (a) distribution; a n d (b) p e r c e n t a g e o f Cu in v a r i o u s c h e m i c a l fractions. 172
Spill Science & Technology Bulletin 4(3)
•
E F F E C T O F SEDIMENT R E D O X CHEMISTRY ON METAL SOLUBILITY
B :~ $ t
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0
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10
20
30
40
50
430
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Eh(mV)
Fig. 7 The effect of Eh on the soluble contents of Pb, Ba, and Cu.
The Ni bound to insoluble sulfides only increased slowly as the Eh sediment decreased to low levels, suggesting that Ni was not strongly influenced by sulfide. Similar results have been reported by Griffin et al. (1989) for reducing sediment conditions. Ni behavior in sediment in this study was controlled primarily by the formation of nickel bound to carbonates.
(K = - 1 . 6 ppm/day) were attributed to the formation of nickel bound to carbonates ( K = 3.2ppm/day), sulfides (K = 1.1 ppm/day) and insoluble large molecular humic ( K = 1.1 ppm/day). Most of the nickel released is transformed into nickel bound to carbonates. A small percentage of the nickel released was bound to sulfides and with a large molecular humic compound, making nickel less soluble. Figure 4b shows the effect of Eh on the percentage of Ni in the various chemical fractions. Under oxidized sediment conditions, Ni was bound to Fe(III) and Mn(IV) oxides. Under reducing sediment conditions, the Ni was mainly bound to carbonates.
2000
B a behavior
Figure 5a shows the effect of sediment Eh on levels of Ba in the various chemical active fractions.
80
...."~............,0 1
1500 -
-60
1000-
-40~
"~
....[] ........ O ........
• °%*1~,,.
500-
0q
i
i
I
I
I
0
10
20
30
40
50
430
0
-80
-130
-150
-
Fe Ni
20
0 60 -170
T(day)
Eh(mV)
Fig. 8 The effect of Eh on the soluble contents of Fe and Ni.
Spill Science & Technology Bulletin 4(3)
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T. GUO et al. Sediment Eh had little effect on dissolved Ba levels in the sediment since Ba has only one valence state and Ba(II) has lower affinity to ferric and manganic oxides than other metals. As sediment Eh decreased (Eh < - 1 3 0 m V ) the Ba bound to sulfides and insoluble large molecular humic fractions did decrease. We know that when Eh > - 1 3 0 m V no sulfide exists. The only possible explanation is that as Eh decreases, the Ba bound to insoluble, large molecular humic also decreases. This decreased Ba is converted to the Ba bound to carbonates. The rate constant of the formation of barium bound to carbonates is 0.91 ppm/day. Figure 5b shows the effect of Eh on the percentage of Ba in the various chemical fractions. It is obvious that under oxidizing conditions, the dominant active Ba fraction is the Ba bound to insoluble, large molecular humic. Ba behavior under oxidized conditions was controlled by complexation of Ba with insoluble, large molecular humic. Under reducing conditions Ba behavior was controlled primarily by Ba bound to carbonates. Cu behavior
Figure 6a shows the effect of sediment Eh on the solubility and distribution of Cu in the various chemical fractions. As Eh decreased to 0 m V , dissolved Cu content increased ( K = 7 O p p b / d a y ) apparently as the result of the dissolution of copper associated with Fe(III) and Mn(IV) oxides and carbonates. Continued decrease in sediment Eh resulted in further reductions in dissolved Cu ( K = - 0 . 1 6 ppm/day) attributed to the formation of the insoluble complexation of Cu with large molecular humic compounds (K = 4.3 ppm/day) and copper bound to sulfides ( K = 0.6 ppm/day). Griffin et al. (1989) also reported that under reducing conditions, Cu behavior was controlled by sulfides. Under very reducing sediment conditions, Cu bound to carbonates was apparently converted to Cu bound to insoluble sulfides and large molecular humic compounds. Paralleling this sediment reduction, Cu bound to Fe(III) and Mn(IV) oxides also decreased slightly. The rate constants of the pseudo-zero-order reaction are - 2 . 1 and - 0 . 6 7 ppm/day for the dissolution of copper bound to carbonates and Fe(III), Mn(1V) oxides, respectively. Upon sediment reduction, Cu solubility decreased, thus reducing Cu toxicity. Figure 6b shows the effect of sediment Eh on the percentage distribution of Cu in the various chemical fractions. Under oxidizing sediment conditions, copper was bound primarily to carbonates and large molecular humic material. Under reducing sediment 174
conditions, Cu was found to be bound to insoluble sulfides and, to some extent, humic compounds.
Summary Sediment redox chemistry is important in both the sequestering and mobility of metals entering the sediment column in Louisiana water bottoms. Sediment redox potential, a measure of the oxidation-reduction status of sediment would be a excellent indicator of potential metal release from sediment. In these studies of sequential extraction of metal in sediment as influenced by oxidation-reduction, we have identified some key parameters determining metal solubility behavior. Under reducing sediment conditions, Fe and Cu solubility were controlled by the formation of insoluble sulfides and humic complexes. Ni and Ba solubility/behavior under reducing conditions were governed by carbonate levels in the sediment. Pb solubility/behavior in reduced sediment was controlled by sulfides, carbonates and humic complexes. Upon oxidation, the affinity between Fe(III), Mn(IV) oxides and Fe, Pb, Ni, and Cu increased. The affinity between insoluble large molecular humic and Ba increased with sediment oxidation. The affinity between carbonates, and Cu also increased following sediment oxidation. As sediment redox potential redox potential decreased, the association between carbonates and Fe, Ni, and Ba increased. The affinity between sulfides, humic substances and Fe, Pb, Ni. and Cu also increased as redox potential decreased. The soluble Ni content of the sediment was strongly affected by sediment redox conditions. There was approximately 6 - 7 times more soluble nickel in oxidized sediment as compared with reduced sediment (Fig. 7). The increase in nickel was inversely related to the exchangable iron content of the sediment. Soluble copper was also influenced by the redox chemistry of the sediment. There were 2-3 times greater soluble copper levels in oxidized sediment as compared with reduced sediment conditions (Fig. 8). Soluble Pb, although not as drastic, was also influenced by sediment redox conditions. Pb decreased with decreasing sediment redox levels. Only a slight increase in soluble barium was observed with decreased sediment redox potential. In summary, sediment redox condition was shown to be important in predicting the mobility and transport of metal in sediment receiving metal input from produced water or other sources. Acknowledgements--The research was supported by Louisiana State University Coastal Marine Institute funded by the Minerals Management Service (Contact No. 14-35-0001-30660,T.U. 19907). Spill Science & TechnologyBulletin 4(3)
EFFEC* OF SEDIMEN* R DO× CHEM,STR
ON METAL sOLUB,LI,
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