Effect of produced water discharge on bottom sediment chemistry final report

[From the U.S. Government Publishing Office, www.gpo.gov]

OCS Study
MMS 99-0060

Coastal Marine Institute

Effect of Produced-Water Discharge
on Bottom Sediment Chem istry

Final Report

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Gu4f of Mexico

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195
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1999

U:S. Deppriment of the Interior Cooperative Agreement
AM Minerals management Service Coastal Marine Institute
Gulf of Mexico OCS Region Louisiana State University

OCS Study
MMS 99-0060

Coastal Marine Institute

Effect of Produ'ded-W a"tor'- Discharge
on Bottom Sediment Chemistry

Final Report

Editors

Ronald D. DeLaune
Charles W. Lindau
and
Robert P. Gambrell

November 1999

Prepared under MIVIS Contract
14-35-0001-30660-19907
by
Wetland Biogeochemistry Institute
Louisiana State University
Baton Rouge, Louisiana 70803

Published by

U:S. Depprtment of the Interior Cooperative Agreement
Minerals management Service Coastal Marine Institute
Gulf of Mexico OCS Region Louisiana State University

US Department of Commerce
NOAA Coastal Services Center Library
2234 South Hobson Avenue
Charlestor4 SC 29405-2413

DISCLAIMER

This report was prepared under contract between Louisiana State University Coastal Marine
Institute and the U.S. Dept. of the Interior, Minerals Management Service (MMS). This report
has been technically reviewed by the MMS and it has been approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies of MMS, nor does
mention of trade names or commercial products constitiute endorsement or recommendation for
use. It is, however, exempt from review and compliance with the MMS editorial standards.

REPORT AVAILABILITY

Extra copies of this report may be obtained from the Public Information Office (Mail Stop 5034)
at the following address:

U.S. Department of the Interior
Minerals Management Service
Gulf of Mexico OCS Region
Public.Information Office (M[S 5034)
1201 Elmwood Park Boulevard
New Orleans, Louisiana 70123-2394

Telephone: (504) 736-2519 or
1-800-200-GULF

CITATION

Suggested citation:

DeLaune, R.D., C.W. Lindau, and R.P. Gambrell, eds. 1999. Effect of Produced-Water
Discharge on Bottom Sediment Chemistry. U.S. Dept. of the Interior, Minerals
Management Service, Gulf of Mexico OCS Region, New Orleans, LA. OCS Study MMS
99-0060. 47 pp.

EXECUTIVE SUMMARY

Petroleum hydrocarbons, metals and radionuclides can enter the environment as the result
of petroleum extraction and recovery operations. Produced water discharge associated with oil
recovery has in the past introduced these compounds into Louisiana aquatic environment,
including the sediment column. Investigations were conducted to determine the factors
determining solubility and mobility of these pollutants in sediment.

The effect of sediment redox conditions on the solubility of Fe, Pb, Ni, Ba, and Cu in
bottom sediment collected from a produce water discharge site was invested using kinetics and
chemical fractionation procedures. Under oxidizing sediment conditions, the behavior of Fe, Pb
and Ni were governed by Fe(M) and Mn(IV) oxides; Ba by insoluble complexation with humic
compounds, Cu by carbonates and humic complexation. Under reducing sediment condition, the
behaviors of Fe and Cu were controlled by the formation of insoluble. sulfides, carbonates and
humic complexes.

Kinetics and chemical fractionation procedures were also used in quantifying the effects
of sediment redox (Eh) condition on the behaviors of As, Cd, Cr and Zn in the bottom sediment.
Under oxidizing conditions, As, Zn and Cr behavior were governed by redox chemistry of Fe(IH)
and Mn(M oxides. Cd transformations were controlled by both Fe(1111), Mn(M oxides and
carbonates. Under reducing condition, the behaviors of Zn and Cr was controlled primarily by
insoluble large molecular humic material and sulfides; the behavior of Cd was controlled by
carbonates. When sediment redox potential increased, the affinity between Fe(HI), Mn(IV)
oxides and As. Cd, Cr, and Zn increased. Results suggest reducing conditions in bottom
sediment sites of produced water discharge would limit heavy metal availability.

Sediment collected from a produced water discharge site and in waste pit was extracted
into various chemical fractions and analyzed for radium-226 (fractions included water-soluble,
exchangeable, forms associated with carbonates, reducible, or organic/sulfide). It was.
determined that 95 percent of the radium present was tied up in an unavailable form that could be
extracted only with very strong acids. Radium in this fraction would be released very slowly
into the environment. Results showed that less than 5% of the radium in sediment was in
potentially available forms.

Petroleum hydrocarbon degradation in sediment collected from a low energy brackish
wetland site which had been exposed for a number of years to produced water discharge was also
studied. Recalcitrant or higher molecular weight compounds were the primary hydrocarbon
fractions found in the sediment. Oxidized sediment conditions resulted in a higher rate of
degradation for most hydrocarbons fractions as compared to degradation in reduced sediment
following addition of South Louisiana Crude oil. Nutrient amendments to contan-tinated
sediments significantly increased rate of hydrocarbon degradation.

The effect of chromium (Cr) and lead (Pb) on degradation added South Louisiana Crude
oil in sediment showed that metal concentration normally found at produced water discharge
sites would not influence degradation of hydrocarbon in the sediment profile.

TABLE OF CONTENTS

PAGE

List of Figures ................................................................................ ix
List of Tables .................................................................................. xi

1.0 Introduction ..............................................................................................................I

2.0 Materials and Methods ............................................................................................3

2.1 Effect of Sediment Redox Conditions on Heavy Metal Chemisty .............. 3
2.2 Radium Chemistry ........................................................................................6
2.3 Effect of Heavy Metal Content of Sediment on Petroleum
Hydrocarbon Degradation .............................................................................6
2.4 Degradation of Petroleum Hydrocarbons in Sediment Receiving
Produced Water Discharge ...........................................................................8

2.4.1 Experiment I - Degradation of Residual Hydrocarbons ................... 8
2.4.2 Experiment 11 - Effect of Oxidizing Sediment Conditions
on Degradation of South Louisiana Crude .......................................8
2.4.3 Experiment III - Nutrient Influence on Hydrocarbon
Degradation .....................................................................................9

3.0 Results and Discussion ............................................................................................. I I

3.1 Effect of Sediment Redox Condition on Heavy Metal Chemistry ............... 11
3.2 Radium Chemistry ........................................................................................ 23
3.3 Effect of Heavy Metal on Petroleum Hydrocarbon Degradation .................. 26
3.4 Degradation of Petroleum Hydrocarbons in Sediment Receiving Produced
Water Discharge ............................................................................................ 33
3.4.1 Degradation of Residual Hydrocarbons (Exp. 1) .............................. 33
3.4.2 Effect of Oxidized Sediment Conditions on Degradation of South
Louisiana Crude (Exp. 11) ................................................................. 37
3.4.3 Nutrient Influence on Hydrocarbon Degradation (Exp. 111) ............. 37

4.0 Summary ................................................................................................................... 41

5.0 References ......................I......................... ................................................................. 43

Vii

LIST OF FIGURES

Figure PAGE

I Location of Lirette (LRT) site from which sediment samples were
collected ................................................................................ 4
2.1 The effect of Eh on the distribution of Fe in the chemical fractions ............... 12
2.2 The effect of Eh on the percentage of Fe in the various chemical fractions .... 12
3.1 The effect of Eh on the distribution.of Pb in the chemical fractions .............. 14
3.2 The effect of Eh on the percentage of Pb in the various chemical
fractions .................. ............................................................... 14
4.1 The effect of Eh on the distribution of Ni in the chemical fractions ................ 15
4.2 The effect of Eh on the percentage of Ni in the various chemical fractions .... 15
5.1 The effect of Eh on the distribution of Ba in the chemical fractions ............... 17
5.2 The effect of Eh on the percentage of Ba in the various chemical
fractions ................................................................................. 17
6.1 The effect of Eh on the distribution of Cu in the chemical fractions .............. 18
6.2 The effect of Eh on the percentage of Cu in the various chemical ,,
fractions ................................................................................. 18
7 The effect of Eh on the distribution of As in the chemical fractions............ 20
8 The effect of Eh on the percentage (expressed as g/kg) of As in the
various chemical fractions .............................................................................. 20
9 The effect of Eh on the distribution of Cr in the chemical fractions ................ 21
10 The effect of Eh on the percentage (expressed as g/kg) of Cr in the
various chemical fractions ................................................................................ 21
I I The effect of Eh on the distribution of Cd in the various chemical fractions .... 22
12 The effect of Eh on the percentage (expressed as g/kg) of Cd in the
various chemical fractions ................................................................................. 22
13 The effect of Eh on the distribution of Zn in the various chemical fractions .... 24
14 The effect of Eh on the percentage (expressed as g/kg) of Zn in the
various chemical fractions ................................................................................. 24
15 226Ra activity in various chemical fractions in Humble Canal sediment
incubated under aerobic and anaerobic conditions ............................................ 25
16 226Ra activity in various chemical of waste pit sediment incubation under
aerobic and anaerobic conditions ......................................................... 25
17 Chromium and lead effects on total hydrocarbon degradation in oxidized
and reduced sediment suspensions ................................................................... 27
18 Chromium and lead treatment effects on changes in total petroleum
hydrocarbon (percent) in oxidized and reduced sediment suspensions
during 91 days of incubation ........................................................................... 29
19 Effect of chromium on changes in percent of hydrocarbon degraded in
oxidized and reduced sediment suspensions receiving 0 mglkg (0), 250
mg/kg (11), 1000 mg/kg (V) and 5000 mg/kg (A) Cr added ............................. 31
20 Effect of lead on changes in percent of hydrocarbon degraded in oxidized
and reduced sediment suspensions receiving 0 mglkg (0), 100 mg/kg (0),
500 mg1kg (V) and 2500 mg/kg (A) Pb added ....................................... 32

21 Change in selected hydrocarbon fraction with time under oxidized
conditions ................................................................................ 34
22 Change in selected hydrocarbon fractions with time under reduced
conditions .............................................................................. 35
23 Degradation of selected fractions of South Louisiana Crude under
oxidized conditions (+450 mV) ....................................................................... 38
24 Linear regression degradation rates of selected hydrocarbon fractions as
affected by redox and fertilizer additions (C = Control, R = Reduced,
0 Oxidized, LF Low Fertilization, BF High Fertilization) .................... 39

LIST OF TABLES

Table PAGE

I Sediment characterization .............................................................................. 10
2 Hydrocarbon compounds analyzed ............................................................... 10
3 The rate constants K (mglkg/d) of the pseudo-zero-order reaction
involving Fe .......................................................................... 13
4 Water soluble plus exchangeable chromium and lead concentrations in
oxidized and reduced suspensions .............................................................. 26
5 Chromium and lead effect on total hydrocarbon degradation (total of all
alkane fractions) as affected by oxidized and reduced soil suspensions
(91 days of 28
6 Effect of chromium and lead treatments on the percent total
petroleum hydrocarbons degraded (after 91 days) in oxidized and reduced
sediment suspensions ................................ ........ 30
7 Degradation of residual hydrocarbons in produced water sediment ................ 36

EFFECTS OF PRODUCED WATER DISCHAR GE
ON BOTrOM SEDII"NT CHENUSTRY

Project Personnel:
T.Z. Guo, B.C. Banker, 1. Devai, R.D. DeLaune, C.W. Lindau, C. Mulbah
and R-P. Gambrell

Louisiana State University
Wetland Biogeochemistry Institute

1.0 INTRODUCTION

During the production of crude oil, condensates or natural gas and water may also be
brought to the surface. This water is called formation water, produced water or oil field brine.
Produced waters are one of a variety of wastes generated from oil and gas production wells (Neff
et al. 1987). The volume ofwater produced may be quite large (Neff et al. 1989). It has been
estimated that a total of 2 million barrels of oil and gas produced waters are discharged into the
State waters of Louisiana per day from nearly 700 sites among the 70 oil and gas fields. At the
time of the study, 23%, 22% and 17% were discharged into fresh, brackish and saline wetland
environments, respectively, with the remainder discharged into open embayments or nearshore
Gulf waters (Boesch and RabaWs 1989). Petroleum production and recovery activity in Louisiana
coastal zone can discharge a considerable amount of produced waters (Boesch and Rabalais 1989).
The produced waters can contain elevated concentrations of toxic metals radium and petroleum
hydrocarbons as compared to the receiving water (St. Pe 1990). It is estimated that annually 1.7 to 8.8
million metric tons of petroleum hydrocarbons are released into the environment (Leahy and Colwell
1990). Metals in produced water can include bariurn, cadmium, chron-@iurn, iron, mercury, manganese,
strontium and thallium (Tillery et al. 1981; Koons et al. 1977; Lyssj 1981). As the produced water
enters wetland environments, toxic metals can enter the sediment column.
Produced water discharge can lead to contamination of sediments, streams and wetlands.
Production waters from oil recovery process are passed through pits for an indeterminate time
until being discharged into the environment. Petroleum hydrocarbons, metals, and radionuclides
are prevalent pollutants in produced waters and sediments (Neff et al. 1989; St. Pe' 1990).
Petroleum components, specifically polycyclic aromatic hydrocarbons, can contain numerous
carcinogenic and mutagenic compounds. Substantial contamination of fine-grained sediments
with petroleum hydrocarbons of produced water origin has been observed with distance fi7om
produced water sites in coastal Louisiana (Rabalais et al. 1991).
Analysis of total metal concentration in sediment quantifies the degree of trace metal
enrichment. Total metal content does not provide infon-nation on transfon-nation and mobilization of
trace metals. Speciation studies can: 1) provide an insight into metal distribution patterns, 2) identify
metal bioavailability and toxicity in ecosystems, and 3) explain transformation and mobility of metal
species. Metal species distribution has been studied in various ways (Gambrell et al. 1991 a; Giblin et
a . 1986; Giesy et al. 1977; Keller and Vedy 1994). These techniques have included multistep
extractions in which a chemical solution removes various metal forms. Such fractionation schemes can
provide information on the general behavior of metals in sediment and provides an estimate of their

potential mobility (Keller an d Vedy 1994). Metals in sediment are generally considered to be present in
the following forms: water soluble, exchangeable, carbonate bound, ferric and manganic oxide bound,
organic matter and sulfide bound, silicate bound and residual.
The oxidationlreduction state (redox potential) of sediment is an important parameter affecting
heavy metal transformation and hydrocarbon degradation. The redox. conditions (Eh) of estuarine
sediment varies widely from approximately +500 rnV (surface sediments) to approximately -300 mV
(strongly reducing sediments). Sediment redox levels can greatly affect to)dc metal uptake by plants
(Gambrell and Patrick 1988; Giblin et al. 1986), leaching losses of toxic metals by runoff or ground
water (Folson et al. 1988; Palermo et al. 1989), bU there is little information on redox chemistry of
toxic metals in different geochemistry forms in sediment.
Heavy element species kinetics in wetland soil kinetics are influenced by many factors. T'hese
factors include temperature, organic matter, surface activity of Fe and Mn compounds, microorganism
activity and other sediment characteristics. Since it is difficult to study these factors individually, the
factors were combined in this study into one parameter, the rate constant of the assumed zero-order
reaction. This pseudo-zero-order reaction model was used in this study. When the rate constant is
positive, the metal content increases in the specific fraction. When the rate constant is negative, the
metals are removed from the specific fraction. When considering trace elements bound to the organic
matter and sulfide phase, it was assumed that the formation of insoluble organic matter (complexation
of insoluble, large molecular weight humic fi7action) and sulfides was independent (Gambrell and
Patrick 1978; Gambrell et al. 1980). At sediment Eh = -130 mV or Eh> -130 mV, the changes in
heavy elements in this fraction were due to insoluble, large molecular weight humic substances.
Surface of clays, organic matter, and iron oxides in sediment will absorb or desorb heavy

Gambrell et al. 1980). Significant heavy element content is also associated with sediment carbonates
elements when the ionic composition or Eh-pH changes (Keller and Vedy 1994; Khalid et al. 1981;

(Ramos et al. 1994; Gambrell 1994). This fraction would be susceptible to pH change. Iron and
manganese oxides existing as nodules and concretions, cemented between particles or on particle
coatings in sediment are excellent scavengers for heavy-elements and are affected by sediment Eh and
pH change (Feijtel et al. 1988; Levy et al. 1992). Heavy elements are also bound to various insoluble
organic fon-ns such as living orgar-@isms, detritus, and hurnic material (Gambrell et al. 1980; Ramos et al.
1994). Sediment redox conditions can affect the degradation and solubility of such organic material
and then influence the release of heavy elements. Heavy elements can also exist as suffides under
anaerobic conditions (Gambrell et al. 1980; 1991b) which are susceptible to Eh and pH changes.
Heavy elements found in primary and secondary minerals are relatively stable in a natural sediment
environment (Gambrell 1994).
Radionuclides in produced waters include naturally occurring radium-226. Produced
water and drilling muds are commonly stored in waste pits created at the production site. In
Louisiana alone, an estimated 20,000 oil-production sites are known to have radioactive
contamination significant enough to require permitting. Produced water brines in the Gulf of
Mexico region can contain up to 37 Bq L-1 of Radium 226 (Kraemer and Reid 1984), an amount
ten times the levels found in natural water. Little is known about the fate of radium in sediment
and waste pits. In order to improve our ability to predict its migration into aquatic environments
and the food chain, we must understand the physical and chemical processes controlling solubility
and movement.
Cocontaminants (e.g., heavy metals) at sites contaminated with petroleum hydrocarbon has
raised the question of the reliability of natural detoxification and engineered remediation processes in

these complex mixtures. Interactions between the contaminants may inhibit biodegradation processes
occurring in the site. One example is the inhibition of biodegradation in contaminated sediments by the
presence of toxic heavy metals such as Cd, Cr, Zn, and Hg. Studies have documented the toxicity of
metals to microorganisms in culture (Farrell et al., 1990) and in soils and sediments (Capone et al.,
1980). However, few studies have concentrated on non-lethal effects of heavy metals on microbial
functions (e.g., biodegradation of orgar:iic chernicals), particularly in sediments.
Studies which have been perforined on these processes indicate that effects of metals on
biodegradation processes are complex and dependent on the type, concentration, and speciation of the
metals added (Said and Lewis 1991). Understanding metal impact on petroleum hydrocarbon
degradation is important in the implementation of remediation at waste or spill sites.
Hydrocarbon biodegradation is influenced by both physicochemical and biological properties of
the environment. Extensive research has been carried out on the biodegradation of sludge (Boyd and
Shelton, 1984; Bossert et al., 1984) and other hydrocarbon compounds (Zhang and NMer, 1992;
Nfiller and Bartha, 1989; Oberbremer et al., 1990). There is little information on degradation of
petroleum hydrocarbon in sediment receiving produced water discharge.
In this study, the kinetics and transforinations of heavy metals, radiurn, and petroleum
hydrocarbon degradation in estuarine sediment at a site in Coastal Louisiana receiving produced water
discharge were examined. The effects of sediment redox potential (Eh) on the kinetics of
transfori-nation of toxic metals and radium in sediments are detailed. Petroleum hydrocarbon
degradation was also studied.

2.0 MATERIALS AND METHODS

2.1 Effect of Sediment Redox Conditions on Heavy Metal Chemistry

Studies were designed to determine the speciation and solubility of heavy metals in
sediment receiving produced water discharge. Sediment was collected from a canal (Humble
Canal) from a waste pit at the point of discharge associated with a petroleum recovery operation
in the Lirette Oil and Gas field in Terebonne _parish (Fig. 1). The effluent or produced water was
discharged from the secondary compartment of the pit into the canal (St. Pe, 1990). Five active
wells contributed produced water to the pit. 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.
Two hundred grams of sediment (dry weight equivalent, amended with 0.3% (W/W)
ground dried plant material) was added to 1.8 L of 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 reference
electrodes, allows for the continuous recording Eh and pH.
The sediment suspensions were kept stirring with a magnetic stirrer. The suspensions
were preincubated at 26 OC under aerobic condition (+430 mV) for 25 days. After the initial
preincubation, the suspensions were purged with nitrogen gas and maintained under anaerobic

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Figure 1. Location of Lirette (LRT) site from wbich sediment samples were collected
(from Guo et al. 1997a, 1997b).

condition (-170 mV). The suspensions were maintained at pH=7.0, (the normal pH of.sediments
under flooded conditions), by addition of diluted HCI or NaOH solution as needed during the
preincubation and anaerobic incubation periods.
Metal was added to the sediment suspension at a rate four times of the original heavy
metal contents of the sediment. The heavy metal contents of the sediment with added metals
were: Cu--610 mg/kg, Pb--300 mgtkg, Cd=21 mg/kg, Zrt=800 mg/kg, Cr--210 mgtkg, As=370
mg/kg, and Ni=580 mg/kg. No barium was added to the sediment.
Samples from the sediment suspensions were taken at selected intervals. The suspension
samples were centrifuged and the supernatant filtered through a 0.45 [un membrane filter. This
supernatant was assumed to be water soluble. The remaining sediment was extracted sequentially as
described below. The sediment sample was kept under nitrogen or oxygen free atmosphere during
extraction. Following removal of the water soluble phase, the sediment was sequentially extracted into
fine fractions (F I to F5) described below.

FI-Exchangeable Phase. The solid phase from the water soluble fraction was extracted at
room temperature for 30 min.-,,with 8 ml 0.5 M Mg(NO3)2/g dry weight sediment, adjusted to pH 7.0
with nitric acid. The samples were agitated continuously.

F2-Bound to Ca-bonale Phase. The sediment residue from F1 was leached at room
temperature for five hours with 8 ml, IM NaOAc, adjusted to pH 5.0 with acetic acid for I g dry
weight sediment. These samples, were also agitated continuously.

F3-Bound to Iron andMcwganese Oxides Plum. The sediment residue from F2 was extracted
at 96 T for six hours with 20 rrA 0.08 M NH20H HCI in 25% (v/v) acetic acid for I g dry weight
sediment. These samples were occasionally agitated.

F4-Bound to Organic Matter and Suodes Phase. For I g of dry weight sediment, the
sediment residue from F3 was extracted at 85 OC for 2 hrs. with 3 n-d 0.02 M HN03 and 5 nil 30%
H-202 (adjusted to pH = 2.0 with HN03) was added, and extraction continued at 85 T for another 3h.
The sample was then cooled, 5 nil 3.2 M NILOAc in 2% (V/V) UN03 was added, and the sample was
diluted to 20 ml with deionized water. The samples were agitated continuously for 30 n-dn. NH40Ac
was added to prevent adsorption of extracted metals onto the oxidized sediment.

F5-Mineral Matrbc Phase. The sediment residue from F4 was extracted with 25 nil
concentrated EN03 for I g of dry weight sediment at 105 OC, the sediment was digested until 5 ml
solution was let and the sample was diluted to 25 ml with deionized water.
The above sequential extractions were conducted in 250 n-A centrifuge tubes which prevented
any loss of sediment between the successive extractions. Separation was conducted by centrifuging at
5000 rpm for 30 min. Supernatants were filtered using 0.45 @irn millipore filters and then analyzed for
metals. The residues were rinsed with 8 ml deionized water for I g dry weight sediment and
centrifuged at 5000 rpm for 30 min, These second supernatants were discarded.
Metal concentrations in the water soluble phase and the chemical extracts were determined by
ICP. Quality assurance was conducted by spiking extracts with certified element standards.

2.2 Radium Chemistry

Another set of experiments were conducted to determine the speciation and solubility of
radium. The primary study site from which sediment was collected was also located in the Lirette
Oil and Gas field (Humble Canal located in a tidally influenced brackish marsh environment).
Additional sediment samples were collected from waste pits located in Quarantine Bay. Sediment
at both sites had been exposed to produced water. Microcosm studies were initiated for studying
the partitioning of radium as influenced by either oxidized and reduced sediment conditions at the
two sites.
Sediment was incubated in the microcosms in a similar manner as heavy metal studies.
Two hundred grams of sediment on a dry weight basis (amended with 0.2% (W/W) ground dried
plant material) was added to 1.8 L deionized water in laboratory microcosms under controlled
Eh-pH condition. The fticrocosm described by Patrick et al. (1973) originally, equipped with a
combination pH electrode, Pt-electrodes and reference electrodes, allowed for the continuous
recording or controlling sediment Eh and pH.
The sediment suspensions were kept suspended with a magnetic stirrer. The suspensions
were preincubated at 260C under aerobic conditions for 25 days. After the initial preincubation,
the suspensions were purged with nitrogen gas and maintained in anaerobic condition. The
suspensions were maintained at pH=7.0, the natural pH of the sediments, by addition of diluted
HCI or NaOH solution as needed during the preincubation and anaerobic incubation periods. Eh
was maintained at preset conditions ranging from +600 mV (oxidized) to -250 mV (reducing).
After incubation and equilibration of sediment under oxidized (+600 mV) and reduced
250 mV) conditions aliquots were removed from each microcosm and chemically extracted. The
sequential extraction procedures adopted from R.D. Shannon (1991) as described previously (in
the metal section) with a minor modification of the residue fraction was used for determining the
partitioning phase of the radium over time under various sediment redox conditions.
Direct y-ray spectrometry of daughter products using a shielded, Ge(Li) detector
interfaced with a multichannel analyzer was used for determining 22@Ra activity in the fractions
(Michel et al., 1981). Primary quantification of 226Ra was made by analysis of 214Bi daughter
product (energy 609 keV, 43*0 y per 100 disintegrations). The instrument was. calibrated using a
22@Ra standard from the National Bureau of Standards (NBS), Washington, DC. Extract samples
were placed in polycarbonate bottles and sealed for daughter in-growth for I month.. Samples
were counted until at least 1000 counts were detected.

2.3 Effect of Heavy Metal Content of Sediment on Petroleum Hydrocarbon Degradation

Sediment used in this study was also collected from a stream in the Lirette Oil and Gas field in
Terebonne Parish (Fig. 1). Five hundred grams of homogenized wet sediment was placed into each of
eight 2 L flask microcosms and water added to produce a sediment: water ratio of 1: 10 (on weight
basis). Each suspension was kept continuously stirred with a magnetic stirrer. The soil pH and
temperature were maintained at 6.5 and 250C, respectively. Breathing air was continuously bubbled
through the suspensions for oxidation (redox potentials ranging from +500 mV to +600 mV).
Nitrogen was bubbled through the reduced microcosms. Two milliliters of South Louisiana Crude oil
(API Gravity 36.0) was added to each flask and allowed to homogenize for two weeks. South

Louisiana Crude was weathered in shallow open pans for four days (for removal of volatile
hydrocarbons) prior to addition. Weathered loss was I I percent. The addition of weathered oil and
allowing two weeks of equilibration in microcosms was to eliminate volatilization losses from the study
which is directed at determining effects of heavy metal concentrations on hydrocarbon degradation.
Twenty milliliters of each suspension was then removed and placed in Teflon tubes for extraction and
analysis of hydrocarbons..
Next, 50 ml of Cr solution equivalent to 0, 250, 1000 and 5000 @Lg Cr per gram of sediment
(dry weight) were added to separate flasks. Similarly, 50 ml of Ph solution equivalent to 0, 100, 500
and 2500 gg added Pb per gram of dry sediment were added to an additional four flasks. Twenty
milliliters of suspension were removed from the flask two days after metal additions for ICP analysis.
Ten milliliters were taken for dry matter determinations. Subsequent aliquots were removed over a
period of 91 days to determine changes in petroleum hydrocarbon levels.
Extraction for petroleum hydrocarbons (alkane fractions) was conducted by the addition of a
solvent (1:1 hexane:acetone) to each 20 ml portion of suspension taken from the rnicrocosms. This
mixture was shaken for 7 hours to facilitate extraction, The mixture was then centrifuged at 10,000
rpm for 13 n-dn. to separate the solvent, microbial mat, water and sediment fractions. The top three
fractions were decanted off into a separatory funnel and the sediment particulates washed -with solvent.
The microbial mat was rinsed three times and the hydrocarbon laden solvent decanted off The
decanted solvent was passed through pre-dried anhydrous sodium sulfate to remove water. The final
solvent-hydrocarbon mix was evaporated down to 10 n-A under the fume hood. One n-d sample was
placed into a vial and 20 gg mr' of internal standard added for GC/MS analysis.
The hydrocarbon analysis will be performed on a gas chromatograph (Hewlett Packard 5890
Series II Plus) equippedwith an HP-5 high resolution capillary column (30 m, 0.25 prn fihn thickness,
0.25 mrn i.d.) which will be directly interfaced to a quadrupole mass spectrometer (Hewlett Packard
5972 Mass Selective Detector). The carrier gas helium of ultra high purity) flow-rate will be 1.0
ml/min, the injector temperature will be 300 OC, the column temperature will be programed from 50 OC
to 310 at 9OC/min rate with initial 3.0 min delay and 15.0 min hold at the end. The interface to the
mass selective detector will be maintained at 280 OC. Injections will be made using a Hewlett Packard
7673 automatic liquid sampler into a splitless injection port.
Hewlett Packard Vectra 486/66)CN4 computer system and Hewlett Packard G1034C Software
for the MS ChemStation (DOS Series) was used in collecting and analyzirig data. G1033A NIST
PBM Library was used for the peak identification. ASTM Crude Oil Quantitative Standard (Supelco,
Inc., Bellefonte, PA) was used for the quantification and Sernivolative Internal Standard Mix (Supelco,
Inc., Bellefonte, PA) was used as internal standard.
At the end of incubation, subsamples of sediment (oxidized and reduced) were removed from
the microcosms with a syringe. The samples were extracted with NaOA, (pH 4.5) and the extracts
were analyzed for metals using ICP procedures.
All data was subjected to analysis of variance and Duncan's Multiple Range Test (SAS 1995).
Comparisons were made between two or more regression functions describing changes in percent
hydrocarbon with time at Cr and Pb rates of 0, 250, 1000, 5000 and 0, 100, 500 and 2500 Ag/g,
respectively. This analysis used the method of comparison of two or more linear functions (Neter et
al., 1990).

2.4 Degradation of Petroleum Hydrocarbons in Sediment Receiving Produced Water
Discharge

Studies were also designed to determine (1) residual petroleum degradation, (2)
degradation of applied South Louisiana Crude and (3) fertilizereffect on hydrocarbon degradation
in sediment (oxidized and reduced) collected from a produced water discharge site. Sediment
samples collected were homogenized and air-dried for 3 days. Total salts were calculated from
electrical conductivity measurements and pH was measured with a combination electrode. Cation
exchange capacity (CEC) measured the sum of exchangeable K, Na, Ca and Mg. Oil percent was
determined by gravimetric methods following extraction with petroleum ether. Total petroleum
hydrocarbon content (TPH) was determined by Freon-113 (1, 1, 2-trichloro-1, 2, 2-
trifluoroethane) extraction. Twenty grams of wet sediment was extracted with 90 n-d of Freon-
113 and compared with a calibrated standard to obtain total concentration. Sediment parameters
and concentrations are summarized in Table 1.
Microcosms were also employed to study effects of sediment redox conditions on
hydrocarbon degradation in sediment suspension (Patrick, et a]., 1973). Wet sediment from the
point of discharge (0 m) was used in all microcosm experiments. Sediment suspensions were
prepared in 2,000 " ErIenmeyer flasks by mixing 85 grams of wet homogenized sediment with
1700 ml distilled water. Suspensions were constantly stiffed using a magnetic stirrer and purged
with oxygen free nitrogen gas. A period of about two weeks was needed for microcosms to
attain the desired reduced redox level before petroleum additions. Oxidized conditions were
maintained by pumping air through the microcosms.
The redox control systems maintained sediment redox level within +20 mV of the desired
potential. This was accomplished with platinum electrodes and a calomel reference electrode
connected to a millivolt meter which monitored sediment redox potential. The output of the
millivolt meter was connected to a meter relay which activated an air pump. When sediment
redox dropped below the set point, a small amount of air was pumped into the apparatus in order
to maintain the desired potential.

2.4.1 Experiment I - Degradation of Residual Hydrocarbons

A microcosm study was designed to determine rate of residual hydrocarbon loss from
sediment collected from the discharge site. Six redox controlled microcosms were set up and
divided into oxidizing (+450 mV) and reducing (-150 mV) sets. Sediment samples were removed
at 1, 14, 30, 60 and 103 days and extracted for hydrocarbon components.

2.4.2 Experiment 11 - Effect of Oxidizing Sediment Conditions on Degradation of South
Louisiana Crude

Based upon the results from Exp. 1, a second laboratory study was initiated to determine
degradation rates of hydrocarbon components of South Louisiana Crude oil added to oxidized
sediment suspensions. Redox potential was controlled (+450 mV) in three microcosms followed
by addition of 20 ml of South Louisiana Crude. At 1, 4, 7, 16 and 28 days after oil addition,
sediment samples were removed and analyzed for hydrocarbon fractions and concentrations.

The oil used for this experiment was a low sulfur oil rich in light aromatics, paraff@ns and
olefins. It is moderately toxic and has been shown to be degraded by indigenous microorganisms
under aerobic sediment conditions.

.2.4.3 Experiment III - Nutrient Influence on Hydrocarbon Degrad ation

This experiment determined the effects fertilizer and redox conditions had on hydrocarbon
degradation. Nitrogen and phosphorus were added to. the 1700 n-d sediment slurries in the
controlled redox microcosms. Four grams of NE4N03 and 2 g of K21HP04 was the high treatment
and 2 g of NH4N03 and I g of K2HP04 was the low treatment. Twenty n-d of South Louisiana
Crude oil was added to the controlled redox microcosms (+450 mV and -150 mV) and samples
were removed at 1, 6, 10, 14, 28 and 42 days after fertilization. Sediment samples were analyzed
for concentration of C-10 (decane) through C-17 (heptadecane) hydrocarbons. Treatments
consisted of reduced and oxidized sediment conditions with two levels of fertilizer amendment
and reduced and oxidized controls (oil only). Treatments were not replicated due to the limited
number of available microcosm apparatus.
Extraction techniques followed EPA Method 8270 and were used for all three petroleum
degradation experiments, A 20 ml sediment sample was removed from the redox controlled
microcosm and pipetted into a Teflon tube. Ten H of 1: 1 hexane:acetone solvent was added and
tubes were shaken for 7 hours followed by centrifugation at 10,000 rpm for 13 minutes. The
petroleum laden solvent layer was transferred into a separatory funnel and the Teflon tube rinsed
several times with the hexane:acetone solvent. Anhydrous sodium sulfate removed trace amounts
of water and the petroleum laden solvent was evaporated to 10 " using dry nitrogen. Samples
were stored at 50C until GC/MS analysis,could be performed. One n-d of each sample was
transferred into a LoVial and 0.4 pl of an internal standard added. A Hewlett Packard 5890
Series 11 plus GUMS was used for analyzing the samples for selected petroleum hydrocarbons. A
HP-5 high resolution capillary column (30 m x .250 mrn i.d., 0.25 gm film thickness) was used
and directly interfaced with a quadrapole mass spectrometer (HP 5972 Mass Selective Detector).
The carrier gas (ultra high pure He) flow rate was 1.0 n-A rr@n-, injection temperature 3000C,
column temperature programmed from 500C to 3 1 OOC at 80C min ' with an initial 3 minute delay
and 15 minute hold time at the end. Sample injections were made using a HP 7673 automatic
liquid sampler into a splitless injection port. A HP Vectra 486/66 computer system equipped with
HP G1034C software and G1033A NIST PBM Library for the MS ChemStation was used for
collecting and analyzing mass spectrometer results. Table 2 displays the hydrocarbons analyzed in
this study. Not all fractions are discussed for each of the three laboratory experiments.
Hydrocarbon data were analyzed using the Statistical Analysis System (SAS 1995) to fit
the simple linear regression model:
Y=Bo+Blx+E
where Y and X represent the dependent and independent variables respectively (Freund and
Wilson 1993). E is the random error term and slope is change in Y(hydrocarbon concentration)
with respect to change in X(days), which is the degradation rate of selected petroleum
hydrocarbons. Comparison between redox levels and other treatments utilized the General Linear
Model and Post-Anova Duncan's Techniques of the SAS programs.

Table I

Sediment Characterization

Location P Na K Ca Mg A] S B

--- - --- - --- - - - - ---------- - --- - -------------- - ----- - - ------
Outfall 208 24938 423 3217 584 0.4 171 28
15 m, 335 2905 520 2843 1644 1.5 286 3

.Salts TPH Oil CEC pH

kg ---------- -- meq 100 g-1
Outfall 95260 66510 9.3 130 6.9
15m. 8300 2010 1.7 42 6.7

Table 2

Hydrocarbon Compounds Analyzed

n-alkane C# Polycyclic aromatic hydrocarbons (PAH)
decane 10 Naphthalene
undecane 11 Acenaphthene
dodecane 12 Fluorene
tridecane 13 Phenanthrene
tetradecane 14 Pyrene
pentadecane 15 Benzo(a)anthracene
hexadecane 16 Chrysene
heptadecane 17 Benzo(b)fluoranthene
octadecan.e 18 Benzo(a)pyrene
eicosane 20 Benzo(k)fluoranthene
tetracosane 24 Dibenzo(ah)anthracene
octacosane 28 Benzo(g,hi)perylene
dotriacotane, 32 Isoprenoids
hexatriacotane 36 2, 6, 10 c-trimethyldodecane
2, 6, 10, 14-tetramethylbeptadecane-pristane
2, 6, 10, 14-tetramethylpentadecane-pristane

3.0 RESULTS AND DISCUSSION

3.1 Effect of Sediment Redox Conditions on Heavy Metal Chemistry

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 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 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
hurnic) (Gambrell and Patrick 1978, 1980) and sulfides were independent. At sediment Eh=-130
mV, (the Eh where sulfate is reduced) and above the changes in metals in this fraction was
attributed to insoluble, large molecular weight hurnic substances.

Iron

Figure 2.1 shows the effect of sediment Eh (redox potential) on the content of Fe in the
various chemical fractions. As Eh decreased, Fe(111) oxides were ri-@icrobialy reduced to soluble
Fe(11), therefore increasing the soluble Fe concentration (K=42.5 mg/kg/d) in solution. When Eh
further decreased to -130 mV, a reduction in exchangeable iron was observed which was
attributed to sulfide formed as a result of sulfate reduction, precipitating dissolved Fe(H) to form
insoluble FeS. Based on the fractionation data at all redox levels studied, dissolved Fe(Il) was
also removed through Fe becoming associated with insoluble organic matter (primarily as a result
of complexation of Fe with insoluble, large molecular humic material). The above two factors
result in the reduction of soluble Fe concentration in solution (K=-25.8 mg/kg/d). The rate
constants of the removal reactions for dissolved Fe(11) are 40.7 mg/kg1d and 31.4 mg/kg/d for the
formation of sulfides and complexation of insoluble, large molecular humic, respectively.
Fe(III) oxides in the sediment were reduced to the more soluble Fe(R) during anaerobic
incubation. Under reducing condition (Eh > -130 mV), the reduction of Fe(M) oxides occurred
only by direct microbial reduction (K=-42.6 mglkg/d) involving organic carbon turnover. This
part of Fe(I11) reduction was equivalent to approximately 2071 mg/kg (20% of total reducible
Fe(Hl)). At sediment (Eh < -130 mV), Fe(III) reducing microorganisms can inhibit sulfate
reduction by out competing sulfate reducers for electron donors (Lovley and Phillips, 1987). We
assume that a portion of Fe(RI) reduction occurred by sulfides reducing Fe(HI) oxides. Only a
small amount of the Fe(M) reduction at this redox level can occur by direct bacteria reduction
involving organic carbon turnover (Jacobson, 1994). Accordingly, almost 8571 mg/kg (80% of
total reducible Fe(111)) was reduced by the sulfide oxidation pathway (K=-171.5 mg/kg/d). The
rate constant of indirected Fe(III) 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
3.

12500 2000

100oo-
1500 F I
C)- - 0- -
0-
7500- 1 -@! ------ - F2
Ei Do
Ei
0 ---- F3
1000 .2
M
U 5000 ---- F4

500 --- --- Soluble
2500

0. ...... ------
0 .0 0
0 1 20 30 40 50 60 T(day)
(a) 430 0 -80 .130 -1,50 -170 Eh(mV)

80 10

IEH I

I
60- 7.5 F I
'0 EB
. ........ 0 ........ F2

-0 EB
2i 40- 3 _0 ---- F3
0
U
---- F4
U- b
20 2.5 --- ER --- Soluble
............ 0.,
0 ........ ........0

0 0
0 10 20 30 40 50 60 T(day)
(b) - 430 0 -80 -130 -150 -170 Eh(MV)

Figure 2.1 The effect of Eh on the distribution of Fe in the chemical fi7actions (from
Guo et al. 1997a).

Figure 2.2 The effect of Eh on the percentage of Fe in the various chemical fractions
(from Guo et al. 1997a).

Table 3

The Rate Constants K (mg/kg/d) of the Pseudo-Zero-Order Reaction Involving Fe

soluble F2 F3 F4

KI (direct microbial
reduction) 42.5 -17.5 42.6 31.4

K2 (indirect reduction
by sulfide) -25.8 124.1 -171.5 72.1

Figure 2.2 shows 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(II). The remaining half of the reduced Fe(III) was converted to carbonate bound
Fe(II). Under oxidizing sediment condition Fe(IH) oxide predominated with Fe behavior was
controlled by Fe(111) oxides. Under reducing sediment conditions, sulfide and insoluble large
molecular humic bound Fe(111) was the dominant fraction controlling iron behavior.

Lead

Figure 3.1 shows the effect of sediment Eh on the actual distribution content of Pb in the
various chemical fractions. As Eh decreased Fe(III) and Mn(IV) oxides were reduced and
released into solution. Adsorbed Pb decreased (K=- 1. 1 mg/kg/d) with a significant portion of the
released Pb going into solution (K=17 mglkgld). Continued decrease in Eh resulted in dissolved
Pb concentration decreases (K=-47 mg/kg/d) as a result of the formation of insoluble lead
associated with sulfides (K=1.72 mg/kg/d), insoluble complexes of insoluble large molecular
hun-iic material (K=O. 17 mg/kg/d) and carbonates. As a result of the above processes, most of the
Pb released by Fe(III) and Mn(IV) reduction was apparently converted to lead sulfide.
Figure 3.2 shows the effect of Eh on the percentage of Pb in the various chemical
fractions. Under oxidizing conditions, Pb was bound to Fe(HI) and Mn( M. oxides. Pb behavior
in the sediment was apparently controlled by chemical adsorption on Fe(M) and Mn(M 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.

Nickel

Figure 4.1 shows the effect of Eh on the content of Ni in solution and changes among the
fraction over the redox range studied. When sediment Eh decreased, Fe(M) and Mn(M oxides
were reduced to soluble Fe(H) and Mn(II). The Ni adsorbed on Fe(M) and Mn(M oxides
decreased (K=-3.2 mg/kg/d) resulting in the release of Ni into solution (K=1.5 mg/kg/d). When
sediment Eh decreased further, dissolved Ni concentration decreases (K=-1.6 mg/kg/d) may be
attributed to the formation of nickel bound to carbonates (K=3.2 mg/kg/d), sulfides

150 3.

2.5
100

a ....... F2
C60
Ei
0 ---- F3
0
U ID "/,<)
0
50 EB ---- F4

EB 1.5 --- E9 --- Soluble

0
0 10 20 30 40 50 60 T(day)
(a) 430 0 -80 -130 -150 -170 Eh(mV)

60 ).4
@o
0'

1.2 F 1
40-
........ ........ F2

30 1 ---- F3
0
U "0
-a 11 o
F4
20-
Eb
---EEI--- Soluble
0.8

0 0.6
0 10 20 30 40 50 60 T(day)
N 430 0 -80 -130 -150 -170 Eh(mV)

Figure 3.1 The effect of Eh on the distribution -of Pb in the chemical fractions (from
Guo et al. 1997a).

Figure 3.2 The effect of Eh on the percentage of Pb in the various chemical fractions
(from Guo et al. 1997a).

300 80

250

-60 F

200
F2
Ei or
150- -40 0 ---- F3

0
U ---- F4
7- 100 . ............. --- EB --- Soluble
-20

0 0
0 10 20 30 40 so 60 T(day)
(a) 430 0 -80 -130 -150 -170 Eh(mV)

60 20

50-

15
ER
40- Fl
E8
I t 0 F2
@O

30- -10
0 A
U -6 ---- 0 ---- F3
CIO
z20 . .. ......... 10 ---- A ---- F4

10 --- EEI --- Soluble

0 F- I 1 0
0 10 20 30 40 50 60 T(day)
(b) 430 0 -80 -130 -150 -170 Eh(mV)

Figure 4.1 The effect of Eh on the distribution of Ni in the chemical fractions (from
Guo et al. 1997a).

Figure 4.2 The effect of Eh on the percentage of Ni in the various chemicaffractions
(from Guo et al. 1997a).

(K=1.1 mgtkg/d) and insoluble large molecular hurnic (K--1.1 mg/kg/d). Most of the nickel
released is transformed into nickel bound to carbonates. A small percentage of the nickel released
was bound to sulfides and large molecular weight hurnic compounds, making nickel less soluble.
Figure 4.2 shows the effect of Eh on the percentage of Ni in the various chemical
fractions. Under oxidized sediment condition, Ni was bound to Fe(III) and Mn(M oxides.
Under reducing sediment conditions, the Ni was mainly bound to carbonates. The Ni bound to
insoluble sulfides only increased slowly as 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.
Barium Figure 5.1 shows the effect of sediment Eh on .levels of Ba in the various chemicay active
fractions. 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.
Sediment Eh had little effect on dissolved Ba levels in the sediment since Ba has only one valence
state. Ba(H) has a lower affinity than other metals to ferric and manganic oxides. As sediment Eh
decreased the Ba bound to sulfides and insoluble large molecular hurnic fraction did decrease. We
know that at Eh>-130 mV no sulfide exists. The only possible explanation is that as Eh
decreased, the Ba bound to insoluble, large molecular hurnic material also decreased. This
decreased Ba is converted to Ba bound to carbonates. The rate constant of the fon-nation of
barium bound to carbonates is 0.91 mg/kg/d.
Figure 5.2 shows the effect of Eh on the percentage of Ba in the various chemical
fractions. It is obvious that under oxidizing conditions, Ba behavior was controlled by
complexation of Ba with insoluble, large molecular humic compounds. Under reducing
conditions, Ba behavior was controlled primarily by Ba bound to carbonates.

Copper

Figure 6.1 shows the effect of sediment Eh on the solubility and distribution of Cu in the
various chemical fractions. As Eh decreased to 0 mV, dissolved Cu content increased (K=70
mg/kg/d) apparently as the result of the dissolution of copper associated with Fe(IR) and Mn(IV)
oxides and carbonates. Continued decrease in sediment Eh resulted further reduction in dissolved
Cu level (K=-O. 16 mg/kg/d) attributed to the formation of the insoluble complexation of Cu with
large molecular humic compounds (K=4.3 mg/kg/d) and copper bound to sulfides (K=0.6
mg/kg/d) . 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(111) and Mn(1V) oxides also decreased
slightly. The rate constants of the pseudo-zero-order reaction are -2.1 mg/kg/d and -0.67
mg/kg/d for the dissolution of copper bound to carbonates and Fe(IH), Mn(IV) oxides
respectively. Upon sediment reduction, Cu solubility decreased, thus reducing Cu toxicity,
Figure 6.2 shows the effect of sediment Eh on the percentage distribution of Cu in the
various chemical fraction. Under oxidizing sediment conditions, copper was bound primarily to

100- 1.6

80 - 1.4
F I

0 F2
E60- -1.2 I@i
0 to
Ei ....0 ---- F3
C
0 V
40 0 M ---- F4

--- ES --- Soluble
20 Y4 ... 0.9

0EP, 0.6
0 10 20 30 40 50 60 T(day)
(a) 4300 -80 -130 -150 -170 Eh(mV)

60 1
EB

50- 0.8
--13- F I

40 0 . ........ 0....... F2

-0.6 0.... F3

30- F4
CO

--- EB--- Soluble
0 - 0.4
20

10 +-0,2
0 io- 20 30 40 50 60 T(day)
(b) 430 0 -80 -130 -150 -170 Eh(mV)

Figure 5.1 The effect of Eh on the distribution of Ba in the chemical fractions (from
Guo et al. 1997a).

Figure 5.2 The effect of Eh on the percentage of Ba in the various chemical fractions
(from Guo et al. 1997a).

400- 4

300 F I
IObr-) ----- -3

...... . 0------ F2
ES

u 200 ----0 ---- F3
C
0 -0.
U
---- F4
U -2
100 133 --- EB--- Soluble

433
0..

0
0 10 20 30 40 50 60 T(day)
(a) 430 0 -80 -130 -150 -170 Eh(mV)

80- 0.8
IEB
0.7

60 F I
0.6 ........0........ F2

0 ---- F3
40 0.5
0
U
:3 F4
U
0-.-B - 0.4
, -z".,O --- E13--- Soluble
20- 1 ,
------ -EBI EB - 0.3
.-0

0 - 0.2
0 10 20 30 40 50 60 T(day)
N 430 0 -80 -130 -150 -170 Eh(mV)

Figure 6.1 The effect of Eh on the distribution of Cu in the chemical fractions (from
Guo et al. 1997a).

Figure 6.2 The effect of Eh on the percentage of Cu in the various chemical fractions
(from Guo et al. 1997a).

carbonates and large molecular hurnic material. Under reducing sediment condition, Cu was
found to be bound to a insoluble sulfides and to some extent humic compounds.

Arsenic

Figure 7 shows the effect of Eh on the level of As in the water soluble chemical fraction. When
Eh decreased to 0 mV, As(V) was reduced to As(M) (K7-0.21 mg/kg/d). At sediment Eh=O to -100
mV, dissolved arsenic concentration was essentially zero. This may be due to the fact that the fresh
AsM which was formed from As(V) reduction became insoluble.
Following manganic oxide and ferric oxide reduction, the As bound with these oxides
decreased OCF-0.88 mg/kgtd). Similar results have been reported by McGeehan and Naylor, (1994).
Parallel increases in As bound to insoluble large molecular humic compounds correlated with reduction
of manganese and iron oxide. The rate constant of pseudo-zero-order reaction for the formation of As
with insoluble large molecular humic substances was 0.97 mg/kg/d. There was no evidence to show
that As associated with sulfides was formed.
At Eh levels between 430 mV to -130 mV, As bound to carbonates decreased (K=-0.51
mglkg/d). Further decreases in Eh (< -130 mV) caused the As bound to carbonates to increase
(K=0.59 mg/kg/d).
Figure 8 shows the effect of Eh on the percentage of As in the various chemical fractions. The
dominant active As fraction is As bound to FqIII) and Mn(M oxides.

Chromium

Cr fractions were also affected by sediment redox conditions (Figures 9 and 10). As Eh
decreased to 0 mV, Fe(M) and Mn(M oxides in the sediment were reduced to more soluble Fe(II)
and Mn(II) and the Cr adsorbed on Fe(E[I) and Mn(M oxides was apparently released increasing
dissolved Cr concentration. At Eh<100 mV, soluble Cr(VI) was apparently reduced to insoluble
Cr(M) (mostly as Cr(OH)3) (Masscheleyn et al. 1992). Cr(IH) also apparently reacted with organic
matter to forrn dissolved Cr(rV)-organic complexes (Masscheleyn et al. 1992). The above three
reactions controlled dissolved Cr concentration in the sediment. The combination of these three
reactions resulted in little difference in dissolved Cr content being measured under the various redox
conditions studied.
As sediment Eh decreased, Cr associated with Fe(M), Mn(M oxides decreased (K=-0.32
mg/kgtd), while Cr associated with insoluble large molecular hurnic material increased (K=0.81 mg/kgI
d). There was no evidence to show that any Cr associated with sulfides was formed.
Figure 10 shows the effect of Eh on the percentage of Cr in the various chemical fractions.
Under oxidizing conditions, Cr associated primarily with Fe(IM and Mn(M oxides, with Cr activity
being controlled by chemical adsorption of Cr on Fe(M) and MnWV) oxides. Under reducing soil
conditions, Cr was bound to insoluble large molecular burnic substances.

Cadmium

Fig. I I shows the effect of Eh on the levels of water soluble Cd and Cd in the various chenical
fractions. As sediment Eh decreased, dissolved Cd decreased from 4.6 mg/kg to 0.3 mg/kg (K=-0.09
mg/kg/d), and Cd associated vAth Fe(M) and Mn(M oxides also decreased (K=-0.01 mg/kg/d).

200 4

150- 'Ju.. -EEr -3 F I
0.%
,a @..%,
I@i '13 'Q ---0--- F2
@O
100 - -2 0---- F3

---- F4

--- EH --- Soluble
50

-0
0 10 20 30 40 50 60 T(day)

430 0 -80 -130 -150 -170 Eh(mV)

800 15

600- 10" F I
10
10.-0... EB F2

400 -E 3 ---- F3

0
---- F4

200- -E9- - - Soluble

0 0
0 10 20 30 40 so 60 T(day)

430 0 -80 -130 -150 -170 Eh(mV)
Figure 7. The effect of Eh on the distribution of As in the chemical fractions (from
Guo et al. 1997b).
Figure 8. The effect of Eh on the percentage (expressed as g/kg) of As in the various
chemical fractions (from Guo et al. 1997b).

100 0.65

75- 0.6 FI
0, C@
"0 F2
or 0.55
bo
"Cor
"1 0---- F3
50

0
U EQ 0.5 F4

U
EE--- Soluble

'0
25- 0.45

0 41 0.4
0 10 20 30 40 50 60 T(day)
430 0 -80 -130 -150 7170 Eh(mV)

600 4

----A

500 -
0-, 3.5
F I

400
... OL.. F2
0

CIO
-@4 3 ---- F3
300 :9
E
0
200- ---- A ---- F4
--- E13- - - Soluble
Z, 2.5
-0-
100 \0
V,
0-1 .......................... . .1-- 12
0 10 20 30 40 50 60 T(day)

430 0 -80 -130 -150 -170 Eh(mV)

Figure 9. The effect of Eh on the distribution of Cr in the chemical fractions (from
Guo et al. 1997b).

Figure 10. The effect of Eh on the percentage (expressed as g/kg) of Cr in the various
chemical fractions (from Guo et al. 1997b).

12.5- 5
E 3,

10- EB 4

to F I
G 7.5- -3
EI F2
0
5 ------ 0.
2 0---- F3
Cn
2.5- F4
EQ %% --- EB--- Soluble
A-----& "In, @
0 -0
0 10 20 30 40 50 60 T(day)
430 0 -80 -130 -150 -170 Eh(mV)

600- 250

500- -200
F I
400 % %% 150 z ------ F 2
to
-'A 300 Ct 0---- F3

100 6 ---- F4
A LO
200-
--- Soluble

so
100-

%ER
0 0
0 10 20 30 40 50 60 T(day)

430 0 -80 -130 -150 -170 Eh(mV)

Figure 11. The effect of Eh on the distribution of Cd in the chemical fractions (from
Guo et al. 1997b).

Figure 12. The effect of Eh on the percentage (expressed as g/kg) of Cd in the various
chemical fractions (from Guo et al. 1997b).
0.-
/&

In contrast Cd associated with carbonates QC==0.01 mg/kg/d), and Cd associated with insoluble large
molecular hurnic substances and sulfides increased as Eh decreased. The rate constants of pseudo-
zero-order reaction on the formation of Cd associated with insoluble sulfides and large molecular
humic material were 0.16 mg/kg/d and 0.01 mg/kg/d respectively. These results are similar to the
findings of Kerner and Wallman (1992) for Cd associated with dissolved and sulfide forms.
Fig. 12 shows the effect of Eh on the percentage of Cd in the water soluble and chemical
fi-actions. Under oxidizing sediment conditions, Cd was associated with Fe(P and MnqV) oxides,
carbonates, and soluble phase Cd. Soluble Cd accounted for 230 g/kg of the total concentration under
oxidized conditions. Under reducing sediment conditions, Cd bound to the carbonates fi-action
accounted for most of the Cd while water soluble Cd accounted for only 15 g/kg of total Cd
concentration. As Eh decreased, the decreased Cd associated with Fe(Ell) and N4nM oxides and
soluble phases was transformed into Cd associated with insoluble carbonates and sulfides.

Zinc

Fig. 13 shows the effect of sediment Eh on the distribution of Zn in the water soluble and
chemical fi7actions. As Eh decreased, dissolved Zn decreased from 100 mg/kg to 0.8 mg/kg OC=-1.78
mg/kg/d, Fig. 14), Zn associated with Fe(III) and Mn(M oxides also decreased (K=-6.5 mg/kg1d). In
contras;t, Zn associated with carbonates (K=3.3 mglkg/d) and Zn associated with insoluble large
molecular humic substances and sulfides increased as sediment Eh decreased. The rate constants of the
pseudo-zero-order reaction for the formation of Zn associated -,krith insoluble sulfides and large
molecular hurnic material were 5.4 mg/kg/d and 2.9 mg/kgId respectively. These results are similar to
that reported by Kerner and WaHman (1992) who determined Zn existed primarily in dissolved and
sulfide forms.
Fig. 14 shows the effect of sediment Eh on the percentage distribution of Zn in the various
fractions. Under oxidizing conditions, Zn was associated with Fe(IH) and Mn(M oxides and soluble
phases. Soluble Zn accounted for 140 g/kg of total content of all fractions. Under reducing
conditions, Zn was found to be associated with insoluble sulfide, large molecular hurnic compounds
and carbonates. Soluble Zn accounted for I g/kg of the total content found in the fi-actions. As
sediment Eh decreased, the Zn associated with Fe(M) and MhM oxides and soluble phases was
transformed into Zn fractions associated with insoluble carbonates, sulfide and large molecular humic
compounds. The data collected show that Zn becomes less mobile under reducing sediment
conditions.

3.2 Radium Chemistry

Selective extraction of wastepit and Humb le Canal sediment exposed to produced water
showed that greater than 95% of the 226Ra could be detected only in the residual fractions (Figure
15 and 16). Only a small amount of 226Ra activity was detected in exchangeable or carbonate
fractions that would indicate the presence of more readily available forms of radium. The
extraction data suggest that 226Ra solubility may be controlled by the mineral phase. Due to the
large ionic radius of radium, it is unlikely that 226Ra is incorporated within the clay lattice of the
sediment.

500 125

400 100
% F I
%% .0
% 0 ...... <y-, , 1. A
1. F2
tl@ 300- EH 75
C4 %
G %%% Ei ---- 0---- F3
Y.
,A,,,7Z `
0
C
0 200- so F4

--- EB--- Soluble
100 4 %% 0 25
%

0 0
0 10 20 30 40 50 60 T(day)
430 0 -80 -130 -150 -170 Eh(mV)

600 150

500-
01...
% 0
% F1
% '01"
400- % E9 -loo F2
%%
300- % 0 F3
0
EH *I-I A ---- R
0
200- 50 V) ---
-0.,. EEI--- Soluble

100 %

0 0
0 10 20 30 40 50 60 T(day)
430 0 -80 -130 -150 -170 Eh(mV)

Figure 13. The effect of Eh on the distribution of Zn in the chemical fractions (from
Guo et al. 1997b).

Figure 14. The effect of Eh on the percentage (expressed as g/kg) of Zn in the various
chemical fractions (from Guo et al. 1997b).

Bayou sediment
H20 AEROBIC (+600 mV)
EXCH ANAEROBIC (-250 mV)

CARB

REDUCE

ORG/S

RESID - AMR-

0 50 100 600 800
22'Ra Activity (pCilgram)

Waste pit sediment
HO [ED AEROBIC (+600 mV)
ANAEROBIC (-250 mV)
EXCH

CARB

REDUCE

ORG/S

RESID

0 50 100 8010 1000
226Ra Activity (pCilgram)

Figure 15. 226 Ra activity in various chemical fractions in Humble Canal sediment
incubated under aerobic and anaerobic conditions.

Figure 16. "'Ra activity in various chen-dcal of waste pit sediment incubation under
aerobic and anaerobic conditions.

The co-precipitation with other minerals such as barite, gypsum and anhydrite has been
reported (Langmuir and Melchior 1995). The presence of elevated levels of barite in the sediment
would suggest that precipitation with barite would be the most likely sink for 226Ra as indicated by
the detection of 226Ra only in the residue.

3-3 Effect of Heavy Metal on Petroleum Hydrocarbon Degradation

Water soluble plus exchangeable Cr and Pb concentrations are shown in Table 4. The majority
of the added metal was sequestered or precipitated by other sediment fractions. Only under reducing
sediment conditions were significant water soluble plus exchangeable metal concentrations observed.
At 5,000 mg/kg added Cr only 145 mg/kg remained in the water soluble plus extractable phase. At
2,500 mg/kg added Pb, 183 mg/kg remained in the more bioavailable water soluble plus exchangeable
fraction.
Figure 17 depicts changes in total hydrocarbon concentration (alkane fractions) under oxidized
and reduced conditions. The data shows that total hydrocarbon concentration decreased with time in
all treatments. Total hydrocarbons were greater in suspensions treated with 1000 mg/kg Cr compared
to suspensions receiving no Cr. Sediment suspensions treated with 5000 mg/kg Cr had higher
hydrocarbon concentrations remaining than suspensions that received 1000 mg/kg Cr. Since the actual
amounts of hydrocarbons varied for the oxidized and reduced suspensions, comparisons are difficult to
make. It was evident that total hydrocarbon concentration measured at the end of the anaerobic
incubation of suspensions treated with higher Cr levels was greater than the lower Cr treatments.

Table 4

Water Soluble Plus Exchangeable Chromium and
Lead Concentrations in Oxidized and Reduced Suspensions

Treatment Amount found
(mg/kg) (mg/kg)
Cr Oxidized Reduced
0 0.59 0.99
250 1.50 22.60
1000 2.44 61.60
5000 32.52 145.40

0 3.85 5.90
100 4.08 16.40
500 4.40 40.30
2500 11.46 183.20

800 0 M@kg Cr keduced
250 mgtkg Cr
a 1000 mgtkg Cr
600 00 mgtkg Cr

Oxidized

400

200

0 20 40 6 0 80 100 0 20 40 60 80 100

Time (days) Time (days)

500 r I
0 mgfkgPb Reduced
400 100 mgfkg Pb
500 mg(kg Pb
9 2500 mglkgPb
W
U 300
Oxidized

200

100

0
0 20 40 60 80 100 0 20 40 60 80 100
Time (days) Time (days)
Figure 17. Chron-@iurn and lead effects on total hydrocarbon degradation in oxidized
and reduced sediment suspensions (from DeLaune et al. 1998).

The change in total hydrocarbon degraded (percent) provides some information on treatment
effects (Figure 18, Table 5). Little difference in petroleum hydrocarbon degradation existed between 0
and the 1000 mg/kg Cr treatment levels. However at 5000 mg/kg Cr, percent total hydrocarbon
remaining was ligher compared to the other treatments, thus showing reduced degradation of the total
hydrocarbon fractions. The difference was not statistically significant.
In the case of the Pb treated sediment suspensions, data (Figure 18, Table 6) shows that under

kg Pb rates after the third sampling. However, under reducing conditions, remaining hydrocarbons
oxidized conditions 50 to 601/6 of the added hydrocarbons were still present for the 500 and 2500 mg/

were even higher (50-801/6) after the third sampling date. This shows that total hydrocarbon
degradation rates were slower compared to oxidized treatments. At the end of the oxidation
incubation the highest total remaining hydrocarbon percentage in the Pb treatments was around 10%.
Total remaining hydrocarbons measured in the Pb treated suspensions under reduced conditions ranged
from 10 to 55%. The percent degraded (Table 6) shows very little treatment effect. However, unlike
the Cr treatments, there was a much larger difference between the percent degraded during the
oxidation and reduction phases for all Pb treatment levels.

Table 5

Chromium and Lead Effect on Total Hydrocarbon Degradation (total of all alkane fractions) as
Affected by Oxidized and Reduced Soil Suspensions (91 days of incubation)

Degradation Rate (mg/kg soil/day)
Treatment Oxidized Duncan Reduced Duncan
(mg/kg) Grouping Grouping

Chromium
0 3.65 A 2.49 A
250 5.28 A 2.40 A
1000 7.18 A 3.20 A
5000 4.62 A 1.54 A

Lead
0 3.68 A 1.68 A.
100 3.69 A 2.96 A
500 3.20 A 2.22 A
2500 3.69 A 1.60 A

Note: Means in columns followed by the same letter are not significantly different.

The differences observed may be explained by examining the observed degradation rates (Table
5). Petroleum hydrocarbon degradation in the oxidized suspensions was faster than that measured
under reducing conditions. The disparity was observed in all concentration rates in the individual
flasks.

O.UgIg Cr
250 pglg Cr
100 - Reduced
1000 jig/g Cr
500 #g1g Cr
80, -

Oxidized
60

U
'W' 20

0
0 20 40 60 80 100 0 20 40 60 80 100
Time (days) Time (days)

Oxidized Reduced
0100
.0 0 pglg Pb
100pg1g Pb
0
t- 500 pg/kg Pb
80
2500 pg/g Pb

0 60

U
40 -

20 -

0
0 20 40 60 80 100 0 20 40 60 80 100
Time (days) Time (days)
Figure 18. Chrornium and lead treatments effects on changes in total petroleum
hydrocarbon (percent) in oxidized and reduced sediment suspensions
during 91 days of incubation (from DeLaune et al. 1998).

Effect of Cr and Pb on Deuadation of Individual Hydrocarbon Fractions in Oxidized and Reduced
Sediment Suspension

Eleven hydrocarbon fractions were quantified but three (pentadecane, hexadecane, and
octadecane) were individually graphed for analysis of degradation under both oxidized and reduced
conditions. Since the effects of treatments on the total hydrocarbon degradation result from the
degradation rates of its individual components, the percent of each fraction is graphically presented in
Figure 19.
The results show that under both oxidized and reduced environments the low molecular weight
hydrocarbons tend to disappear much faster than heavier hydrocarbons. In generaL the degradation of
the three hydrocarbon fractions decreased as Cr treatment increased.
Under oxidized conditions, the percent of the three individual hydrocarbons in Pb treated
suspensions decreased quite rapidly with time (Figure 20). Under reduced conditions, less than 20% of
the original hydrocarbon fraction remained. But there were no visible treatment trends observed from
this set of data. However, it must be noted that much larger fractions of the original concentrations
were present at the termination of the study.

Table 6

Effect of Chromium and Lead Treatments on the Percent Total Petroleum Hydrocarbons
Degraded (after 91 days) in Oxidized and Reduced Sediment Suspensions

Compound Treatment Rate Oxidized Reduced
(mg/kg) %

Chromium 0 82.88 79.83

250 88.84 64.17

1000 80.48 78.12

5000 66.56 40.43

Lead 0 89.20 50.85

100 83.48 95.51

500 91.69 66.74

2500 89.52 42.68

Following a statistical analysis of Cr. and Pb on the degradation (percent) of three selected
hydrocarbon fractions (pentadecane, hexadecane and octadecarie), we could only show a significant
difference of Cr on octadecane degradation. Chromium only sh owed degradation under reducing

Oxidized Reduced

100 100

80 -
80 -
Cd
C) 60 -
CU 60 -
10 Cd
40
40

20
20
0 0

100 - 100

80 - 80

Cd
60 - 60
Cl

40 -
40 -

20 - 20 -

0 0

120 - 120

100 100

80 - 80

0 60 - 0 60 -

40 40 -

20 20

0 0
0 20 40 60 80 100 0 20 40 60 80 100
Time (days) Tune (days)

Figure 19. Effect of chromium on changes in percent of hydrocarbon degraded in
oxidized and reduced sediment suspensions receiving 0 mglkg (0), 250
mg/kg (0), 1000 mg/kg (V) and 5000 mg/kg (A) Cr added (from DeLaune
et al. 1998).

%Octadecane %Hcxadecane %Pentade

K) IN 0) co C) K) a) C"0
0 0 CD0 0 0 0 0 0
CD 1
.C)

CD
Q

Cl.
CD @3*w
1:4w
<

C,
(D co
zs

CD 0
:z blZI 0
w 4- CD
m 011
0

0 %Pentadecaj
%Octadecane %]Efexadecane

CL
CL 4- cr) co0 w 0 C)
0 0 0 0 C 0 0
CL 00

0
1@

CD 0
CD m

cl.
rq
00
00

conditions at 5,000 mg/kg added Cr. There were no significant differences in degradation as influenced
by metal content for the oxidized treatments (cv-- 0.05). The slope of octadecane degradation of the
reduced 5000 mglkg Cr treatment was significantly different than the 0 and 250 mg/kg Cr treatments
(a7- 0.05). There was no statistical influence of Cr and Pb on degradation of pentadecane and
hexadecane.
Chromium and Pb at the levels used in this study had no significant impact on degradation of
South Louisiana Crude oil. The Cr and Pb added was bound by the sediment into insoluble or
unavailable forms. Results suggest that heavy metals would not influence degradation of petroleum
hydrocarbon in sediment at the produced water discharge site. Data presented should not be
extrapoled to sites containing sandy substrates in which heavy metals were not sequestered or removed
from the solution or exchangeable fractions.

3.4 Degradation of Petroleum Hydrocarbons in Sediment Receiving Produced Water
Discharge

3.4.1 Degradation of Residual Hydrocarbons (Exp. I

Initial residual sediment concentrations of hexadecane, heptadecane, eicosane,
tetradecane, tridecane and hexatriacotane in the oxidized and reduced nidcrocosms were similar
and averaged (6 replications) 88.4, 87.5, 65.5, 50.3, 28.6, 1.6 pg/g dry sediment, respectively.
(Figs. 21 and 22). Hgh concentrations (day 1) of octadecane (82. 1), pentadecane (78.0) and 2, 6,
10, 14 tetramethylpentadecane (70.5 pg/g) were also measured but not graphed. Initial
concentrations of tetracosane and the remaining isoprenoids ranged from about 20 to 35 pg/g and
decane, undecane, dodecane and dotriacotane concentrations were less than 10 Pg/g. At the end
of the study (103 days), initial concentrations of residual hexadecane, heptadecane, eicosane,
tetradecane and tridecane were reduced an average of 87% under oxidized sediment conditions
compared to only 54% reduction under reducing conditions. Hexatricotane concentrations were
reduced only 41% under oxidizing conditions and no change in concentration was measured under
reduced sediment conditions. Remaining hydrocarbons investigated (not graphed) averaged 77%
reduction under oxidizing conditions and 44% reduction under reducing conditions over the 103
day experiment.
Degradation rates were faster under oxidizing conditions (Fig. 21) compared to a reducing
environment (Fig. 22). All other alkanes analyzed (see Table 2) displayed similar rates of
degradation. Degradation rates under oxidized sediment conditions ranged from a low of 0.029
(decane) to a high of 0.721 pg/g/d for hexadecane. Higher degradation rates (oxidized
conditions) were also observed for tetradecane, pentadecane, heptadecane, octadecane, eicosane
and 2, 6, 10, 14 tetramethyl pentadecane (Table 7). Degradation of residual hydrocarbons under
controlled reducing conditions was slower. Rates ranged from 0.012 (decane) to 0.351
(hexadecane) pg/g/d. Degradation rates (reducing conditions) of all investigated hydrocarbon
fractions averaged 58% (ranged from 30 to 96%) slower compared to corresponding rates
measured under oxidizing conditions (Table 7).
Significant differences in degradation rates of hydrocarbon fractions were observed as
affected by sediment redox conditions. All petroleum fractions displayed a significantly (P<0.05)
greater loss from the oxidized treatment compared to the reduced treatment.

100

80
Z Tridecane
Tetradecane
60 -- Hexadecane
Heptadecane
40 Eicosane
Z
@4 Hexatriacontane
U 20
Z

Q
0 1 f - I
1 14 3.0 60 103

DAYS

Figure 2 1. Change in selected hydrocarbon fraction writh.time under oxidized conditions.

100 -

80
z Tridecane
60 Tetradecane
A Hexadecane
40 x Heptadecane
a Eicosane
I --*-Hexatriac@ @ane
20
z
0
1 14 30 60 103

DAYS

Figure 22. Change in selected hydrocarbon fractions with time under reduced conditions.

Table 7

Degradation of Residual Hydrocarbons in Produced Water Sediment

Compound Oxidized Rate Reduced Rate
(pg/g/d) (pg/g/d)
decane 0.029 0.012
undecane 0.050 0,022
dodecane, 0.128 0.070
tridecane 0.294 0.150
tetradecane 0.449 0.235
pentadecane, 0.649 0.340
hexadecane 0.721 0.351
heptadecane 0.715 0.326
octadecane 0.620 0.175
eicosane 0.533 0.237
tetracosane 0.279 0.058
octacosane 0.106 0.014
dotriacontane 0.067 0.022
Hexatriacontane 0.18 0.006
2, 6, 10trimethyl-dodcane 0.153 0.075
2, 6, 10, 14tetramethyl heptadecane 0.253 0.149
-2, 6, 10, 14tetramethyl pentadecane 0.400 0.281

3.4.2 Effect of Oxidized Sediment Conditions on Dep-radation of South Louisiana Crude (Exp.
M

Degradation of selected South Louisiana Crude hydrocarbons under controfled redox
conditions (+450 mV) is graphed in Figure 23. Initial concentrations (day 1) of tridecane,
dodecane, undecane, dotricotane, phenanthrene and pyrene were 299.4, 292.6, 182.7, 25.0, 9.3
and 0.6 pg/g, respectively. Initial concentrations of remaining hydrocarbons analyzed (not
graphed) ranged from 66.9 (octacosane) to a high of 240.5 Pg1g for octadecane. Starting
concentrations of heptadecane, hexadecane and pentadecane averaged 195.1 [tg/g dry sediment.
After 28 days of laboratory incubation, initial concentrations of undecane, dodecane and tridecane
were reduced an average of 81% with the largest reduction (96%) observed for the shortest n-
alkane (undecane, C-11). Dotriacotane and ph6nanthrene concentrations were reduced 51.5%
and pyrene 28% under oxidizing conditions.
Degradation rates of shorter n-alkanes; undecane (3.01), dodecane (4.41) and tridecane
(3.58 pg/g/d) were much faster than the longer n-alkane; dotriacotane (0.20) and polycyclic
aromatic hydrocarbons; phenanthrene (0.09) and pyrene (0.002 pg/g/d). Degradation of
tetradecane (2.62), pentadecane (2.12), hexadecane (1.71), heptadecane (0.89), octadecane
(2.18), eisocane (1.80), tetracosane (0.86), octacosane (0.61) and naphthalene (0.22 pg/g/d) are
not graphed in Figure 23. All compounds investigated showed significant (P<0.05) degradation
over the 28 day study except pyrene (P=0.233).

3.4.3 Nutrient Influence on Llydrocarbon Degradation (Exp. 111).

Linear regression degradation rates for undecane, tridecane, pentadecane and heptadecane
as affected by redox and fertilizer are graphed in Figure 24. A general overview shows
degradation rates in oxidized sediments amended with fertilizer were much higher (except
undecane) compared to the reducing sediment treatments. Hghest degradation rates were
observed for tridecane, pentadecane and heptadecane (4.4 to 5.1 pg/g/d) in sediments amended
with the high rate of fertilizer. Undecane's highest, degradation rate occurred in reduced sediment
plus high fertilizer (3.9 pg/g/d). In most cases, hydrocarbon degradation rates decreased as level
of fertilizer decreased and lowest rates were observed for the control treatments (oil only). Under
reducing conditions, many treatments showed an increase (production) in tridecane, pentadecane
and heptadecane over the 42 day experiment (Fig. 24). Net production rates ranged from 0. 1
(tridecane) to 0.6 (pentadecane) pg/g/d. An increase in sediment heptadecane concentration was
also observed for the oxidized control (0.2 pg/g/d). The observed net increases were thought to
be due to faster production rates from higher molecular weight compounds compared to slower
degradation rates of the hydrocarbons.
Degradation and production rates of decane, dodecane, tetradecane and hexadecane (not
graphed) followed the same general distribution as undecane, tridecane, pentadecane and
heptadecane. High degradation rates were calculated for dodecane, tetradecane and hexadecane
(4.6 to 5.0 gg/g/d) in oxidized sediment amended with high fertilization. Net production of
dodecane, tetradecane and hexadecane (0.3 to 0.5 pg/g/d) was observed in some reduced
sediment treatments.
Averaged over the eight hydrocarbons (C-10 through C-17) degradation rates (net
production included) for the control, low and high fertilization (oxidizing conditions) were 1.0,

350

300
250 Undecane
Dodecane
200 Tridecane
150 Dotriacontane
Pyrene
100 - Phenanthrene
CO U
Z 50
U 0 7 -Ir T
1 4 7 16 28

DAYS

Figure 23. Degradation of selected fractions of South Louisiana Crude under oxidized conditions (+450 mV).

FERTILIZER EFFECT

"/C3 6
'-6b
'@b 5
ED CR
4-- CO
3
0 LFR
Z 2 - LFO
M HIR
r-) 0 E:i HFO
-1 Undecane Tridecane Pentadecane Heptadecane
-2
HYDROCARBON FRACTION

Figure 24. Linear regression degradation rates of selected hydrocarbon fractions as affected by redox and fertilizer addition (C
Control, R = Reduced, 0 Oxidized., LF = Low Fertilization, HF = High Fertilization).

2.7 and 4.3 gg degraded g7' dry sediment d_', respectively. Under controlled reducing conditions,
degradation rates averaged 0.3, 0.8 and 1. 1 pg g-' d-, respectively. Initial concentrations of the
eight n-alkanes investigated were reduced approximately 25, 67 and 99% over 42 days for the
control, low fertilizer and high fertilizer treatments, respectively, under oxidized sediment
conditions. Reducing conditions reduced initial concentrations approximately (production
included) 27, 3 and 13%, respectively.
A general linear statistical model was used to test the interaction of the main effects (redox
and fertilization), sorted by individual hydrocarbon compound. Additional analysis used the entire
model, grouping all hydrocarbon fractions (C-10 through C-17) together. Analysis revealed
fertilizer amendment had a greater effect on degradation rates of decane, undecane, tridecane and
tetradecane than sediment redox. A post-analysis of variance technique was used to check for
significant differences between redox and fertilizer effects. Duncan's Multiple Range Test for
variable concentration of petroleum hydrocarbons found redox effects produced significant
differences (P<0.05) in degradation rates. The two fertilizer treatments and control were also
significantly different. These studies support previously published research showing fertilization
or enhancing degradation of crude oil (Wright et al. 1997).
can be used as a method f
Multiple regression was performed with both main effects and interactions. The
interaction of fertilizer and redox had the greatest effect on change in hydrocarbon concentration
over time. The most significant main effect was time followed by redox and fertilization. None of
the main effects or interactions were found to be insignificant compared to controls.
Oxygen concentration has been reported to be a critical rate lin-fting factor in
biodegradation of hydrocarbons (Atlas and Cerniglia 1995). In this study, oxidation status or
sediment redox condition was also shown to govern hydrocarbon degradation at the wetland site
impacted by produced water discharge. Hgh concentrations of recalcitrant isoprenoids were
encountered in sediment gathered at the outfall from a produced water pit. Degradation of these
more resistant hydrocarbons was slow but showed a response to sediment redox condition.
Oxidized sediment conditions showed a significant increase in the degradation rate for all
compounds studied at the site compared to reducing sediment conditions. Even the recalcitrant
isoprenoids showed appreciable degradation rates under oxidizing conditions.
South Louisiana Crude oil was added to sediment to determine rate of degradation of
lighter hydrocarbon crude oil fractions. Oxidizing conditions resulted in an increased degradation
rate of added South Louisiana Crude. This was especially true for the shorter n-alkane (<C-14).
Concentration of some of the longer n-alkanes showed an increase with time, apparently caused
by stripping of methyl groups during biodegradation, resulting in formation of n-alkanes. The
oxidizing conditions increased the susceptibility of the branched long-chained hydrocarbons
(isoprenoids), that are more difficult to degrade than the n-alkanes.

4.0 SUMMARY

The effect of sediment redox conditions on the solubility behavior of Fe, Pb, Ni, Ba, and
Cu in bottom sediment collected from a produced water discharge site was investigated using
kinetics and chemical fi-actionation procedures. Sediment collected was composited and
subsamples incubated in laboratory microcosm's under controlled Eh-pH 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 indicate that under oxidizing sediment conditions, the
behavior of Fe, Pb and Ni were governed by FeQH) and Mn(IV) oxides; Ba by insoluble
complexation with hurnic compounds, 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, 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 carbonates and Fe, Ni, Ba increased,
affinity between sulfides, humic substances and Fe, Pb, Ni, Cu also increased. Upon Fe(III) oxide
reduction, it is estimated 20% of total reducible Fe(III) oxide were reduced by direct bacterial
reduction (k--42.6 mg/kg/d), 80% of total reducible Fe(III) oxides was associated with chemical
fractions attributed to sulfide oxidation (K=-171.5 mg/kg/d). The rate constants (mg/kg/d) for
dissolved Ni (Eh < 0 mV), Pb (Eh < -80 mV) and Cu (-80 mV < Eh < 0 mV) are - 1.6, -0.047 and
-0. 16 respectively. In our incubation period, the rate constants (mg/kg/d) for Ni bound to Fe(1111)
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.
Kinetics and chemical fractionation procedures were also used in quantifying the effects of
sediment redox (Eh) condition on the behaviors of As, Cd, Cr and Zn in the bottom sediment collected
from a Louisiana Coastal site receiving produced water discharge. Sediment samples were incubated
in rnicrocosms in which Eh-pH conditions were controlled. Sediment was sequentially extracted for
determining metals in various chemical fractions (water soluble, exchangeable, bound to carbonates,
bound to iron and manganese oxides, bound to insoluble organic and sulfides) and chemical inactive
fraction (mineral residue). Under oxidizing conditions, As, Zn and Cr behavior were governed by
redox chemistry of Fe(IH) and WON) oxides. Cd transformations were controlled by both Fe(M),
Mn(M oxides and carbonates. Under reducing condition, the behaviors of Zn and Cr was controlled
primarily by insoluble large molecular hun-@c material and sulfides; the behavior of Cd was controlled
by carbonates. When sediment redox potential increased, the affinity between Fe(M), Mn(M oxides
and As, Cd, Cr, and Zn increased. When sediment redox potential decreased, the affinity between
carbonates and Cd and Zn increased; the affinity between insoluble sulfides, large molecular humic
matter and As, Cd, Cr, Zn increased; the soluble Cd and Zn decreased; the soluble As and Cr remained
constant. Results suggest reducing sediment conditions would reduce Cd and Zn toxicity. Under
reducing or anaerobic conditions, the solibilization rate constants (mg/kg/d) for As, Cr, Cd, Zn bound
to Fe(E11) and Mn(M oxides were -0.88, -0.32, -0.01, -6.5 respectively, the rate constants (mg/kg/d)
for dissolved Cd and Zn were -0.09 and -1.78 respectively.
Sediment from oil recovery pit and stream bottom sediment receiving produced water
discharge were incubated in laboratory microcosm under oxidized and reduced sediment conditions.

The sediment was then extracted into various fractions and analyzed for radium-226. The results
orm
indicated that very fittle (5 percent) of the total radium in the sediment material was present in a f
that was extractable or otherwise available from the waste-pit material and/or bottom sediment (such
forms include water-soluble, exchangeable, associated with carbonates, reducible, or organictsulfide).
Approximately 95 percent of the radium present was tied up in a residual form that could be extracted
only with very strong acids. Radium in this fraction would be released very slowly into the
environment from the contaminated sediment,
Rate of petroleum hydrocarbon degradation was measured in sediment collected from a low
energy brackish wetland site which had been exposed for a number of years to produced water
discharge. Recalcitrant or higher molecular weight compounds were the primary hydrocarbon
fractions found in the sediment. Degradation rates were determined by measuring loss of selected
petroleum hydrocarbons components with time in laboratory incubation. South Louisiana Crude oil
was added to the sediment to measure degradation rates of soluble hydrocarbons which were too low
in concentration in the original sediment. Oxidized sediment conditions resulted in a higher rate of
degradation for most hydrocarbon fractions as compared to reduced sediment. Fertilizer or nutrient
amendments to contaminated sediments significantly increased the rate of hydrocarbon degradation.
Fertilizer enhanced the degradation of the lower and more soluble molecular weight fiWfions as
compared to the higher molecular weight fractions.
The effect of chromium (Cr) and lead (Pb) on degradation of South Louisiana Crude oil in
sediment collected from a produced water discharge site was measured in laboratory microcosms
under oxidized and reduced conditions. Metal content had no impact on total hydrocarbon
degradation content based on changes in concentration. Even on a percentage basis, which normalizes
for differences in hydrocarbon concentrations, no statistical influence of Cr (5,000 pg/g) and Pb (2,500
gg/g) on degradation could be measured under reducing conditions. A more sensitive analysis of metal
impact on degradation depicted by an analysis of reduction of selected alkane fractions also showed
little effect on degradation. Only degradation of octadecane was shown to be statistically inhibited at
5,000 pg/g of added Cr and only under reducing conditions. The sediment due to the clay content,
sequested much of the added metals. Under reducing conditions, 25 percent of water soluble and
exchangeable Cr and Pb remained in solution at the highest Pb (2,500 Vg1g) and Cr (5,000 gg/g) levels
compared to oxidized sediments. The amount in solution was not great enough to impact hydrocarbon
degradation. The study demonstrates that Cr and Pb entering sediment at this produced water site
would have minimal impact on petroleum hydrocarbon degradation.
In sunu-nary, heavy metal solubility was shown to be low in anaerobic and neutral pH
estuarine sediment found at a coastal Louisiana produced water discharge sties. Solubility of Ba
found in barite was low under alkaline and either anaerobic or aerobic sediment conditions. Over
95% of radium found in contaminated sediment existed as an unavailable form which could be
extracted only with strong acids. Typical heavy metal pollution levels found in the surface
sediment environment at produced water discharge sites would not impact microbial degradation
of petroleum hydrocarbons in the sediment column. Oxidized sediment conditions resulted in a
faster rate of petroleum hydrocarbon degradation as compared to reducing sediment conditions in
a produced water impacted sediment column.

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