EPA/600/R-04/074 

July 2004 

GUIDELINES FOR THE BIOREMEDIATION OF 

OIL-CONTAMINATED SALT MARSHES 

by 

1

Xueqing Zhu, 2Albert D. Venosa, 1Makram T. Suidan, and 3Kenneth Lee 

1

University of Cincinnati 

Cincinnati, OH 45221 

2

U.S. Environmental Protection Agency 

National Risk Management Research Laboratory 

Cincinnati, OH 45268 

3

Department of Fisheries and Oceans-Canada 

Bedford Institute of Oceanography 

Dartmouth, Nova Scotia B2Y 4A2 

EPA Contract No. 68-C-00-159 

Task Order No. 8 

Task Order Manager 

Albert D. Venosa 

Land Remediation and Pollution Control Division 

National Risk Management Research Laboratory 

Cincinnati, OH 45268 

National Risk Management Research Laboratory 

Office of Research and Development 

U.S. Environmental Protection Agency 

Cincinnati, OH 45268 
Disclaimer 

The information in this document has been funded by the United States Environmental Protection 

Agency (U.S. EPA) under Task Order No. 8 of Contract No. 68-C-00-159 to the University of 

Cincinnati. It has been subjected to the Agency’s peer and administrative reviews and has been 

approved for publication as an EPA document. Mention of trade names or commercial products does 

not constitute an endorsement or recommendation for use. 

ii 
Foreword 

The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the 

Nation’s land, air, and water resources. Under a mandate of national environmental laws, the 

Agency strives to formulate and implement actions leading to a compatible balance between human 

activities and the ability of natural systems to support and nurture life. To meet this mandate, EPA’s 

research program is providing data and technical support for solving environmental problems today 

and building a science knowledge base necessary to manage our ecological resources wisely, 

understand how pollutants affect our health, and prevent or reduce environmental risks in the future. 

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for 

investigation of technological and management approaches for preventing and reducing risks from 

pollution that threaten human health and the environment. The focus of the Laboratory’s research 

program is on methods and their cost-effectiveness for prevention and control of pollution to air, 

land, water, and subsurface resources; protection of water quality in public water systems; 

remediation of contaminated sites, sediments and ground water; prevention and control of indoor air 

pollution; and restoration of ecosystems. NRMRL collaborates with both public and private sector 

partners to foster technologies that reduce the cost of compliance and to anticipate emerging 

problems. NRMRL’s research provides solutions to environmental problems by: developing and 

promoting technologies that protect and improve the environment; advancing scientific and 

engineering information to support regulatory and policy decisions; and providing the technical 

support and information transfer to ensure implementation of environmental regulations and 

strategies at the national, state, and community levels. 

This publication has been produced as part of the Laboratory’s strategic long-term research plan. It 

is published and made available by EPA’s Office of Research and Development to assist the user 

community and to link researchers with their clients. 

 Lawrence W. Reiter, Acting Director 

 National Risk Management Research Laboratory 

iii 
EXECUTIVE SUMMARY

Salt marshes are among the most sensitive ecosystems and, therefore, the most difficult to clean. 

Applications of some traditional oil spill cleanup techniques in wetland habitats have caused more 

damage than the oil itself. The objective of this document is to present a detailed technical guideline 

for use by spill responders for the cleanup of coastal wetlands contaminated with oil and oil products 

by using one of the least intrusive approaches – bioremediation technology. This manual is a 

supplement of the previously published “Guidelines for the Bioremediation of Marine Shorelines 

and Freshwater Wetlands” (Zhu et al., 2001), which has focused on the bioremediation of sandy 

marine shorelines and freshwater wetlands. This guidance document includes a thorough review and 

critique of the literature and theories pertinent to oil biodegradation and nutrient dynamics and 

provides examples of bioremediation options and case studies of oil bioremediation in coastal 

wetland environments. It also evaluates current practices and state-of-the-art research results 

pertaining to the bioremediation of hydrocarbon contamination, and presents a procedure for the 

design and evaluation of bioremediation processes applicable to the cleanup of oil contaminated 

coastal wetlands. Special attention is given to oil bioremediation of salt marshes since they are the 

most prevalent type of coastal wetland and have been the subject of the most extensive studies. 

The document consists of two major parts. Part I presents the background and overview of 

bioremediation options, which include the characteristics of coastal wetlands, oil spill threats and 

countermeasures in salt marshes, and relevant state-of-the-art research. Part II provides guidelines 

for design and planning of oil bioremediation in salt marshes, which includes site characterization 

and evaluation, the selection of appropriate bioremediation technologies, and the design of sampling 

and monitoring programs. 

The overall conclusions reached by the guidance manual are as follows. Unlike sandy beaches, oil 

biodegradation on marine wetlands is often limited by oxygen, not nutrient availability. Natural 

attenuation is increasingly becoming the preferred strategy for the restoration of oil-contaminated 

wetlands. However, field studies also show that on some coastal wetlands, nutrients might still be a 

limiting factor for oil biodegradation, particularly if the oil does not penetrate deeply into the anoxic 

zone of the wetland sediment. When biostimulation is selected, it is recommended that nitrogen 

concentrations of at least 2 to as much as 10 mg N/L should be maintained in the pore water to 

achieve optimal oil biodegradation, with the decision on higher concentrations to be based on a 

broader analysis of cost, environmental impact, and practicality. Furthermore, if ecosystem 

restoration is the primary goal rather than oil cleanup, at least one study strongly suggested that 

nutrient addition would accelerate and greatly enhance restoration of the site. Abundant plant growth 

took place in the nutrient-treated plots despite the lack of oil disappearance resulting from the 

addition of extra nutrients. Therefore, the decision to bioremediate a site should depend on cleanup, 

restoration, and habitat protection objectives and other pertinent factors that may have an impact on 

success. 

No effort was made to determine the quality of secondary data reviewed in the literature and the 

conclusions made from these data. 

iv 
TABLE OF CONTENTS 

1 Introduction and Overview of Bioremediation Options .......................................................................................1

1.1 Coastal Wetlands in the U.S. ......................................................................................................................1

1.2 Oil Spills in Salt Marshes: Threats and Countermeasures ..........................................................................2

1.2.1 Threats of oil spills ................................................................................................................................2

1.2.1.1 Impact to wetland plants...............................................................................................................2

1.2.1.2 Impact to wildlife and ecosystems................................................................................................3

1.2.2 Response to oil spills in salt marshes.....................................................................................................4

1.2.2.1 Physical Methods .........................................................................................................................4

1.2.2.2 Chemical methods ........................................................................................................................5

1.2.2.3 In-situ burning ..............................................................................................................................5

1.2.2.4 Restoration ...................................................................................................................................6

1.3 Bioremediation of Oil Spills in Salt Marshes .............................................................................................6

1.3.1 Environmental factors affecting oil biodegradation in salt marshes.......................................................6

1.3.2 Laboratory studies..................................................................................................................................8

1.3.3 Full-scale demonstrations ....................................................................................................................10

1.3.3.1 Nova Scotia, Canada, 1989 ........................................................................................................10

1.3.3.2 San Jacinto Wetland Research Facility (SJWRF), Texas, 1994-1997 ........................................10

1.3.3.3 Terrebonne Parish, Louisiana, 1998 ...........................................................................................11

1.3.3.4 Gladstone, Australia, 1997-1998 ................................................................................................11

1.3.3.5 Nova Scotia, Canada, 2000-2001 ...............................................................................................12

1.3.4 Kinetics of oil biodegradation..............................................................................................................15

1.3.5 Monitoring biological responses to quantify the efficacy of remediation treatment ............................16

1.3.5.1 Bioassessment ............................................................................................................................16

1.3.5.2 Bioassays....................................................................................................................................17

1.3.6 Bioremediation options on salt marshes...............................................................................................18

1.3.6.1 Nutrient Amendment ..................................................................................................................18

1.3.6.2 Microbial amendments ...............................................................................................................19

1.3.6.3 Oxygen amendment....................................................................................................................20

1.3.6.4 Plant amendment (phytoremediation).........................................................................................20

1.3.6.5 Monitored natural attenuation ....................................................................................................21

2 Recommended approaches to bioremediation IN SALT MARSHES ................................................................23

2.1 Pre-treatment Assessment.........................................................................................................................25

2.1.1 Oil penetration and oxygen availability ...............................................................................................25

2.1.2 Background nutrient content................................................................................................................26

2.1.3 Summary of pretreatment assessment ..................................................................................................28

2.2 Treatment Selection and Design ...............................................................................................................28

2.2.1 Nutrient selection.................................................................................................................................29

2.2.2 Concentrations of nutrients needed for optimal biostimulation ...........................................................30

2.2.3 Nutrient application strategies .............................................................................................................31

2.2.3.1 Frequency of nutrient addition ...................................................................................................31

2.2.3.2 Methods of nutrient addition ......................................................................................................31

2.2.4 Sampling and Monitoring Plan for Bioremediation Operations...........................................................32

2.2.4.1 Important variables and recommended measurements ...............................................................32

2.2.5 Environmental assessment of an oil-contaminated salt marsh: a case study ........................................35

2.2.5.1 Bioassessments...........................................................................................................................36

2.2.5.2 Risk assessment..........................................................................................................................46

2.3 Summary and Recommendations..............................................................................................................47

3 REFERENCES...................................................................................................................................................49

v 
1 INTRODUCTION AND OVERVIEW OF BIOREMEDIATION OPTIONS 

1.1 Coastal Wetlands in the U.S. 

Coastal wetlands are subjected to the influence of tidal action. They provide natural barriers to 

shoreline erosion, habitats for a wide range of wildlife including endangered species, and key 

sources of organic materials and nutrients for marine communities (Boorman, 1999, Mitsch and 

Gosselink, 2000). Coastal wetlands can be classified into tidal salt marshes, tidal fresh water 

marshes, and mangrove swamps (Mitsch and Gosselink, 2000). 

•	 Tidal Salt Marshes -- Salt marshes are those halophytic grasslands found in the middle and 

high latitudes along protected coastlines. They are subjected to tidal action as well as high 

salinities. In the United States, they are often dominated by the grass Spartina alterniflora in 

the low intertidal zone, and Spartina patens with the rush Juncus in the upper intertidal zone. 

Most of these wetlands are distributed along the Gulf of Mexico and the Atlantic coast. 

•	 Tidal Freshwater Marshes -- These wetlands are found inland from the salt marshes but 

still close enough to the coast to experience freshwater tidal effects. Since these wetlands 

lack the salinity stress of salt marshes, they are often very productive ecosystems and 

dominated by a variety of grasses and by perennial and annual broad-leafed aquatic plants. 

•	 Mangrove Swamps -- Mangroves are subtropical and tropical coastal wetlands dominated 

by halophytic trees and shrubs. In subtropical and tropical regions of the world, tidal salt 

marshes give way to mangrove swamps. In the United States, they are mostly distributed 

along the southern coast of Florida and generally dominated by the red mangrove 

(Rhizophora) and the black mangrove tree (Avicennia). 

It the early 1990s, it was estimated that the total area of coastal wetlands in the United States was 

approximately 3.2 million ha (32,000 km2

), with about 1.9 million ha or 60 percent of the total 

coastal wetlands as salt marshes and 0.5 million ha as mangrove swamps (Mitsch and Gosselink, 

2000). Coastal wetlands are no longer viewed as intertidal wastelands, and their ecological and 

economic values have been increasingly recognized. Major benefits and functions of coastal 

wetlands include: 

•	 Shoreline Protection – Coastal wetlands provide a buffer between land and sea, protecting 

marine shorelines from the ravages of storms and erosion by wave action. Salt marshes, 

which sustain little damage from ocean storms, can shelter inland developed areas and 

reduce potential storm damage to coastal buildings and structures. 

•	 Support of Coastal Fisheries – Tidal marshes provide spawning site and nursery areas for 

many fish and shellfish species. Due to their high productivity, coastal wetlands produce 

great volumes of detrital organic materials and nutrients, on which many small invertebrates 

and fish feed. It is estimated that over 95 percent of the commercial fish and shellfish species 

in the United States are wetland dependent (Feierabend and Zelazny, 1987). 

•	 Wildlife Habitat – Coastal wetlands are the primary habitat for many plant and animal 

1 
species and provide food, water, and shelter to indigenous and migratory species. More 

importantly, wetland habitats are essential for the survival of a large percentage of 

endangered species. For example, of the 209 animal species listed as endangered by the U.S. 

Department of Interior and the U.S. Fish and Wildlife Service in 1986, about 50 percent 

depend on wetlands for their survival (Mitsch and Gosselink, 1993). 

•	 Water Quality Management – Coastal wetlands maintain and improve water quality by 

acting as sediment and chemical sinks (Baker et al., 1989). Under favorable conditions, 

wetland sediments, plants, and their associated microorganisms are able to contain, take up, 

and degrade various environmental contaminants, such as excess fertilizers, pesticides, and 

heavy metals. 

Wetlands have suffered dramatic losses as a result of human activities, such as drainage for 

agricultural use. Overall, more than 50 percent of the wetlands in the continental U.S. were lost from 

the 1780s to the 1980s (Mitsch and Gosselink, 2000), and at a rate 7,300 ha/year from 1950s to 

1970s (Tiner, 1984). Such losses have greatly diminished the nation's wetlands and their benefits. 

The rates of loss have been declining since the mid 1970s with the enactment of wetland protection 

laws and increased public appreciation. However, threats to coastal wetlands remain, including 

conversion for agricultural, industrial, and residential development, mean sea level rise, and 

chemical contamination from excessive nutrient inputs, chemical accumulations, and oil spills. 

The threat of crude oil contamination to coastal wetlands is particularly high in certain parts of the 

U.S., such as the Gulf of Mexico, where oil exploration, production, transportation, and refineries 

are extensive (Lin and Mendelssohn, 1998). Oil and gas extraction activities in coastal marshes 

along the Gulf of Mexico have been one of the leading causes of wetland loss in the 1970s (Mitsch 

and Gosselink, 2000). Despite more stringent environmental regulations, the risk of an oil spill 

affecting these ecosystems is still high because of extensive coastal oil production, refining, and 

transportation. 

1.2 Oil Spills in Salt Marshes: Threats and Countermeasures 

1.2.1 Threats of oil spills 

Marine wetlands are especially vulnerable to oil spills because the inherently low wave energy of a 

wetland does not physically remove oil effectively. They are flooded at high tide and their complex 

surface can trap large amounts of oil. Impacts of oil spills to coastal wetland ecosystems have been 

described and reviewed extensively (Baker et al., 1989; Fingas, 2001; NAS, 1985; Pezeshki et al., 

2000). A brief summary on these impacts is provided in the following text. 

1.2.1.1 Impact to wetland plants 

Oil spills have been known to cause acute and long-term damage to salt marshes and mangroves 

(Baker et al., 1989; Burns et al., 1993; Lin and Mendelssohn, 1996; Pezeshki et al., 2000). These 

impacts include reduction in population and growth rate or abnormal growth and regrowth after 

initial impact. Mangroves are generally more vulnerable to oil spills than salt marshes because oil on 

the partially submerged roots of mangroves interferes with respiratory activity (Duke et al., 1997; 

2
Evans, 1985). 

The degree of oil impact also depends on various factors, such as the type and amount of oil, the 

extent of oil coverage, the plant species, the season of the spill, the soil composition, and the 

flushing rate. For example, No.2 fuel oil has been found to cause much higher mortality and damage 

to Spartina alterniflora, a dominant salt marsh grass along the Atlantic coast and Gulf of Mexico, 

than Arabian crude oil, Libyan crude oil, and No.6 fuel oil (Alexander and Webb, 1983 & 1985). 

Growth of Spartina alterniflora was not significantly affected by oil contamination at low to 

moderate concentrations (less than 5 mg crude oil/g sediment, Alexander and Webb, 1987; less than 

50 mg crude oil/g sediment, DeLaune et al., 1979) and sometimes was even stimulated (Li et al., 

1990). However, heavy contamination by light oil can lead to widespread mortality, and plants may 

require a decade or more to recover. Different wetland plants also respond differently to oil spills. 

Lin and Mendelssohn (1996) examined the effects of south Louisiana crude oil on three different 

types of coastal marshes and found that the sensitivity of these marshes to the crude oil increased in 

the order of S. lancifolia (freshwater marsh plant), S. alterniflora (salt marsh), and S. patens 

(brackish marsh). Plants are more sensitive to oiling during the growing season than other periods 

(Pezeshki et al., 2000). The sediment type also plays an important role. In general, oil remains 

longer in soils with higher organic matter and, therefore, has greater impact on resident plants. Some 

wetland sediment can act as a reservoir absorbing oil and leaching it out into adjacent coastal 

habitats, causing chronic impacts on biota (Levings et al., 1994). 

1.2.1.2 Impact to wildlife and ecosystems 

Oil spills on coastal wetlands not only damage plants but also have serious consequences for the 

wildlife and other organisms that rely on the wetlands as habitats and nursery grounds. These 

impacts include obvious immediate consequences, such as widespread animal mortality due to 

smothering and toxic effects, and more subtle long-term effects. Oil can affect the fish population by 

both direct toxicity and by a reduction in the benthic species on which they feed (NAS, 1985). 

Seabirds that congregate on the salt marshes suffer from the destruction of their feeding grounds. Oil 

can also change an animal’s feeding and reproductive behaviors. A light oiling of some birds can 

inhibit egg laying (Fingas, 2001). Furthermore, heavy mortality of seabirds is often observed 

because oiling effectively diminishes the natural water-repellant and insulation value of feathers. 

The extent of the impacts also depends on many factors, such as the life cycle and the life habit of 

organisms, the time and season of oil spills, the type and amount of oil, and the duration of oil 

exposure (NAS, 1985). Sediment feeders could be more vulnerable to oil than epibenthic filter 

feeders. Larval fish are more vulnerable to oil than juveniles and adults. Avian mortality would be 

exacerbated by a spill occurring during their feeding and nesting season. 

Considering the different sensitivity of wetland species and populations to oil, spills can 

significantly affect the overall balance of wetland ecosystems, especially if damage occurs to a 

dominant species. On the other hand, some long-term studies have suggested that many oiled marine 

wetlands could recover naturally after a long time (Baker, 1999; Hester & Mendelssohn, 2000; Sell 

et al., 1995). Recovery times vary from a few years for some salt marshes to over a decade for 

mangroves (NAS, 1985; Sell et al., 1995). In a few extreme cases, salt marsh ecosystems have not 

fully recovered decades after the initial oil spills (Baker et al., 1993; Teal et al., 1992). The effects 

3
of oil on wetland ecosystems and recovery still require further investigation. 

1.2.2 Response to oil spills in salt marshes 

Since oil spills can cause serious damage to marine wetland ecosystems, effective countermeasures 

are essential to minimize these ecological impacts. Major oil spill response options in marine 

shorelines and freshwater environments have been briefly reviewed in Chapter 1 of the sandy 

shoreline and freshwater wetland guidance document (Zhu et al., 2001). However, salt marshes are 

among the most sensitive ecosystems and, therefore, the most difficult to clean. Applications of 

some traditional oil spill cleanup techniques in wetland habitats have caused more damage than the 

oil itself (Baker 1999; Owens and Foget, 1982, Sell et al., 1995). Considering the characteristics of 

wetland ecosystems, a number of cleanup and treatment techniques have been proposed and tested to 

deal with oil contamination in coastal wetlands. The feasibility of these methods also depends on 

various factors, such as the type and amount of spilled oil, season of the year, and environmental 

conditions of the spill site. 

1.2.2.1 Physical Methods 

Many oil spill countermeasures based on physical clean up procedures, such as mechanical oil 

removal, high pressure or hot water flushing, and sediment relocation, have been reported to do 

more harm than good to wetland habitats. All physical methods that remain as options for use on 

marine wetland environments require some caution during deployment to minimize environmental 

damage. 

•	 Booming and sorbents – Use of booms to contain and control the movement of floating oil 

at the edge of the wetland and removal of the oil by adsorption onto oleophilic materials 

placed in the intertidal zone. This method can be an effective strategy to prevent floating oil 

from reaching sensitive habitats with minimal physical disturbance if traffic of the cleanup 

crew is strictly controlled. 

•	 Low pressure flushing – Oil is flushed with ambient-seawater at pressures less than 200 kpa 

or 50 psi to the water edge for removal (NOAA, 1992). This technique can be used 

selectively for quick removal of localized heavy oiling with minimal damage to wetland 

vegetation. However, the potential for oil release into the sediments and adjacent water 

bodies should be considered including appropriate containment measures. 

•	 Cutting vegetation-- Cutting vegetation may be a useful cleanup technique to remove oils 

that form a thick coating on the vegetation and to prevent oiling of sensitive wildlife (Baker, 

1989, NOAA 1992). However, the feasibility of this method depends strongly on the season 

in which the spill occurs. In general, winter cutting of dead standing vegetation has little 

effect on subsequence growth, but summer cutting could cause great damage to the regrowth 

of wetland plants and result in shoreline erosion. The use of cutting should also be avoided 

immediately prior to an anticipated rise in water levels because cutting followed by flooding 

could cut off necessary oxygen to plant roots (Pezeshki et al., 2000). Efforts should also be 

made to minimize the inevitable damage due to traffic. 

4
•	 Stripping – Stripping of surface sediments can cause severe environmental impacts and may 

only be considered in the case of extremely oiled wetlands where the oil in the sediments is 

likely to kill the vegetation and prevent plant regrowth. To minimize erosion and habitat 

loss, it is critical to follow the stripping by the restoration of sediment elevation and 

replanting of the wetland species (Krebs & Tanner, 1981). 

1.2.2.2 Chemical methods 

Chemical methods have not been widely used in the United States mainly due to the concerns over 

their toxicity and long-term environmental impacts. However, with the development of less toxic 

chemical agents, the potential for their application will increase. 

•	 Dispersants – Dispersants are chemicals that promote the dispersion of floating oil from the 

water surface into the water column. Fields studies have shown that application of 

dispersants in near shore waters can significantly reduce the retention of oil within the 

intertidal zone and, therefore, the impacts to wetland plants (Duke et al., 2000; Getter & 

Ballou, 1985). However, the use of dispersants in near shore water could have short-term 

toxic effects on adjacent coastal habitats, such as subtidal animal communities. Direct 

spraying or contact of dispersants with wetland plants may also have harmful effects on 

vegetation (Wardrop et al., 1987). 

•	 Cleaners – Cleaners are chemicals that help wash oil from contaminated surfaces. These 

formulations have been used with low-pressure flushing operations to facilitate oil removal 

from wetland vegetation. Studies have shown that the application of cleaners can prevent 

mortality of salt marshes and mangroves (Pezeshki et al., 1995; Teas et al., 1993). However, 

their use has been limited because of the paucity of data available with respect to their longterm effects on wetland habitats. Also, concern has been expressed over the transfer of oil to 

the nearshore waters. 

1.2.2.3 In-situ burning 

In-situ burning involves controlled burning of the oil and oiled vegetation at the contaminated site. 

This technique is capable of rapidly removing large amounts of oil with limited equipment and 

personnel. However, the technique may result in severe damage to wetland habitats, temporary air 

pollution, and possibly toxic combustion residues. The degree of impact to salt marshes is seasonally 

dependent. Like cutting, the likelihood of damage is greatest during the summer and least during the 

period of dormancy in late fall and winter (Baker, 1989). In fact, fall burning of marshes has been a 

commonly used management strategy for controlling wetland overgrowth in many areas. The 

temporary air pollution caused by the airborne emissions are generally not considered a serious 

health threat or environmental concern, especially at distances greater than a few kilometers from the 

fire (Fingas, 2001). Limited data and applications have indicated that in-situ burning can be a viable 

option for removing a large volume of pooled oil at the right season when sediments are saturated 

(Mendelssohn et al., 1995; Pahl et al., 1997). 

5
1.2.2.4 Restoration 

In cases of coastal wetlands being catastrophically damaged, plant and animal species have been reintroduced as restoration strategies. (Bergen et al., 2000; Frink and Gauvry, 1995; Teas et al., 1989). 

S. alterniflora was successfully replanted to restore the salt marshes in New Jersey after the 1990 

Arthur Kill oil spill (Bergen et al., 2000). Three years after the replanting, over 70% of the plant 

coverage was restored as compared to only 5% by natural recolonization at the unplanted reference 

sites. Mangroves were also successfully replanted to restore oil-killed mangrove forest in Panama 

after the 1986 Refineria Panama oil spill (Teas et al., 1989). However, this approach may also upset 

the ecological balance or natural succession processes if it is not carried out appropriately (Fingas, 

2001). 

1.3 Bioremediation of Oil Spills in Salt Marshes 

Bioremediation is an emerging technology that involves the addition of materials (e.g. nutrients or 

other growth-limiting cosubstrates) to contaminated environments to accelerate the natural 

biodegradation processes (OAT, 1991). This technology has been recognized as one of the least 

intrusive methods and has been shown to be an effective tool for the treatment of oil spills in 

medium and low-energy marine shorelines (Lee et al, 1997; Swannell et al., 1996; Venosa et al., 

1996, Zhu et al., 2001). However, until a few years ago, only limited information was available on 

the effectiveness and impacts of the bioremediation of oil spills in coastal wetlands (Lee et al., 1991; 

Wood et al., 1997; Wright et al., 1997). Recently, several long-term field studies on oil 

bioremediation in coastal wetlands have been carried out. These studies provide better understanding 

of the potential of oil remediation in such environments (Burns et al., 2000; Garcia-Blanco and 

Suidan, 2001; Jackson and Pardue, 1999; Shin et al., 1999). In this section, an in-depth review of 

current practices and research on oil bioremediation in coastal wetland environments is presented 

with emphasis on the findings of these field trials. 

1.3.1 Environmental factors affecting oil biodegradation in salt marshes 

The success of oil spill bioremediation depends on our ability to establish and maintain conditions 

that favor enhanced oil biodegradation rates in the contaminated environment. Environmental factors 

affecting oil biodegradation include temperature, nutrients, oxygen, pH, and salinity. These factors 

have been discussed in general in Chapter 2 of the sandy shoreline and freshwater wetland guidance 

document (Zhu et al., 2001) and in Section 5.5 of the document with respect to freshwater wetlands. 

The limiting conditions for oil biodegradation in salt marshes can be significantly different from 

other marine shorelines and even freshwater wetlands. A brief summary of these conditions in salt 

marshes is given here. 

In terms of nutrient supply, coastal marshes are considered high-nutrient wetlands (Mitsch and 

Gosselink, 2000), but most of the nutrients, and nitrogen in particular, are present in the form of 

organic matter and not readily available for microbial or plant uptake (Cartaxana et al., 1999). 

Figure 1.1 illustrates the nitrogen cycling that occurs in a wetland environment. The amount of 

inorganic nitrogen or available nitrogen for oil biodegradation will depend on many processes, such 

as nitrogen fixation, nutrient mineralization, plant uptake and release, denitrification, and wetland 

hydrodynamics. Studies also show that the concentration of inorganic nitrogen (mostly ammonium) 

6
in salt marsh sediments exhibits a seasonal pattern with a concentration peak during the summer 

months probably due to higher mineralization rates associated with elevated temperatures (Cartaxana 

et al., 1999). A similar trend was also reported for available phosphorus (Nixon et al., 1980). 

Therefore, when a major oil spill occurs in salt marshes, it is still likely that nutrient availability 

becomes a limiting factor for oil degradation, depending on the type of sediment, the season, and 

quantity of oil spilled. Hence, nutrient addition may be an important remedy to contemplate when 

considering any or all of these factors. 

N 2 

NH4 

+ NO3 -

N2 & N2O 

NO3 

-

Fixation 

Denitrification 

Mineralization Nitrification 

Plant uptake 

N inflows via 

Surface water 

groundwater 

tidal exchange 

N outflow via 

Tidal exchange 

Aerobic 

soil layer 

Anaerobic 

soil layer 

Organic N 

Algae & Bacteria 

Plant Release 

Figure 1.1 Major processes involved in nitrogen cycles in a coastal wetland 

Unlike other marine shorelines, the substrates of coastal wetlands are saturated or flooded with 

water, and oxygen diffusion rates through these hydric soils are very slow. As a result, available 

oxygen in the soils and in the interstitial water is quickly depleted through metabolism by aerobic 

organisms and chemical oxygen demand due to reduced chemical species. Typically, there is a thin 

layer of oxidized soil (a few millimeters) at the surface, below which the environment becomes 

anaerobic (Gambrell and Patrick, 1978). The thickness of this oxidized layer depends on the 

population of oxygen utilizers, the rate of photosynthetic oxygen production by algae and plants, and 

the rate of oxygen transport through the sediments, which is related to wind, tide and wave action. A 

study of oxygen demand in an oil contaminated salt marsh sediment indicated that oxygen 

availability could be a limiting factor for oil degradation (Shin et al., 2000). These authors reported 

that significant biodegradation occurred only when the tidal cycle exposed the surface of the salt 

marsh to the atmosphere. The dominant electron acceptor in the anaerobic soil layer in salt marshes 

is also different from most freshwater wetlands. In freshwater wetlands, methanogenesis is often the 

dominant process for the oxidation of organic carbon in the reduced soil layer, while in marine 

wetlands, sulfate reduction is usually the most important process when oxygen is limited since 

seawater contains abundant sulfate (Mitsch and Gosselink, 2000). Studies have shown that in some 

marine sediment, PAHs and alkanes can be degraded under sulfate-reducing conditions at similar 

7
rates to those under aerobic conditions (Caldwell et al., 1998; Coates et al., 1997). The importance 

of this process in the biodegradation of oil in salt marsh environments still requires further 

demonstration, especially in the field. The inherent ability of many wetland plant species to transfer 

oxygen to the rhizosphere may also play a role in reducing the effect of oxygen limitation. However, 

little research has been conducted on the capacity of this mechanism in enhancing oil 

biodegradation. 

Other important environmental factors affecting biodegradation of petroleum hydrocarbons include 

pH and salinity. The optimal pH for oil biodegradation is between 6 and 9 (Atlas and Bartha, 1992). 

The pH of wetland sediments and the overlying water depend on both soil type and hydraulic 

condition. Sediments in salt marshes and mangroves are mostly organic and often acidic. In addition, 

the anoxic condition and high sulfur content in coastal wetlands often lead to the production of 

hydrogen sulfide. When exposed to air, sulfide can be reoxidized to sulfate and result in a further 

drop in sediment pH. However, in areas with frequent tidal inundation, the pH of wetland sediments 

and pore water is determined by seawater and is near neutral or slightly alkaline. The salinity of pore 

water in coastal wetlands may also vary dramatically and depends on the frequency of tidal 

inundation, rainfall, coverage of vegetation, groundwater and freshwater inflow, and soil type 

(Mitsch and Gosselink, 2000). In areas adjacent to coastlines or receiving frequent tidal inundation, 

the salinity of wetland water is close to that of seawater. Elevated salinity levels are frequently 

reported at higher elevations or areas with little rainfall and other freshwater supply. Brackish 

marshes are frequently found in estuarine areas and other sites that extend away from the open 

ocean. Salinity can significantly affect the rates of oil biodegradation. Most marine microorganisms 

have an optimum salinity range of 2.5 to 3.5% and grow poorly or not at all at salinity lower than 1.5 

to 2% (Zobell, 1973). Studies have also shown the rates of hydrocarbon degradation to decrease with 

increased salinity above that of seawater (Rhykerd et al., 1995; Ward and Brock, 1978). 

Although many factors can affect oil biodegradation, not many environmental factors can be easily 

manipulated to enhance this natural process. For example, it is not practical to alter wetland salinity, 

and nothing can be done to change the climate. There are two main approaches to oil spill 

bioremediation. (1) bioaugmentation, in which oil-degrading microorganisms are added to 

supplement or augment the existing microbial population, and (2) biostimulation, in which the 

growth of indigenous oil degraders is stimulated by the addition of nutrients or other growth-limiting 

co-substrates. Extensive studies have been carried out recently on the bioremediation of oil 

contaminated coastal wetlands both on a laboratory scale and in the field (see next section). 

1.3.2 Laboratory studies 

Most of the laboratory studies have focused on the potential of using nutrient amendments to 

enhance oil biodegradation in salt marsh environments. This is because studies conducted in other 

shoreline environments have demonstrated that the microbial population is rarely a limiting factor, 

and nutrient addition alone had a greater effect on oil biodegradation than did the addition of 

microbial products (Lee et al, 1997; Venosa et al., 1996). 

Jackson and Pardue (1999) conducted microcosm and mesocosm studies to investigate the effect of 

different nutrient types on enhancing biodegradation of a Louisiana crude oil in Louisiana salt marsh 

sediment. The microcosms contained a 60:1 (water/soil) slurry produced from a salt marsh sediment 

8
at an oil concentration of 0.7 g oil/g soil and were operated in a completely mixed and aerated mode, 

where oxygen limitation was non-existent. Nutrient species examined included phosphate, 

ammonium, nitrate, and phosphate plus ammonium. The results showed that oil degradation was 

limited by nitrogen but not phosphorus under these conditions. Optimal nitrogen concentrations in 

pore water were in the range of 100-670 mg N/L. Among the nitrogen species, ammonium was 

found to be generally more effective in stimulating oil degradation than nitrate. Thus, ammonium 

might be advantageous in the enhancement of the degradation of certain oil components because 

ammonium is less likely to be lost from the system by washout due to its higher adsorptive capacity 

to organic matter. Ammonium is also the more toxic species of nitrogen in the environment. 

In a follow-on mesocosm study in the same paper (Jackson and Pardue, 1999), large intact cores 

(900 cm2

) of salt marsh sediments were contaminated with crude oil and treated with various 

concentrations of ammonium salts. The results showed that ammonium amendments had limited 

success in enhancing oil biodegradation. Even at the highest ammonium loading (10 mg/m2

), the 

nutrient amendment was only able to increase the degradation of lower chain length alkanes (<C20) 

by10-40% and no significant enhancements in the degradation of PAHs and longer chain alkanes 

were observed. 

Wright et al. (1996 and 1997) also conducted a mesocosm study to investigate the influence of 

nitrogen and phosphorus using 7.5-L buckets containing salt marsh sediments with and without 

transplanted Spartina alterniflora under total flooded conditions. The effect of season was also 

examined by conducting this study during winter and summer months. Weathered Arabian crude oil 

was applied to the mesocosms at a rate of 0.46 g oil/m2

. Nutrient treatments included urea, 

ammonium, nitrate, a slow release fertilizer (Max Bac), and an oleophilic fertilizer (Inipol EAP-22). 

Each of them was also evaluated with and without supplemental phosphate. The study showed that 

the effectiveness of bioremediation depended on both the types of nutrients and the season of the 

spill. During the 80 days of the winter experiment, phosphorus was the limiting nutrient for oil 

degradation in this salt marsh sediment. Addition of urea, ammonium, and nitrate without P did not 

enhance hydrocarbon degradation, while phosphorus addition led to an increase in hydrocarbon 

degradation from 43% for the no-nutrient control to 53 -75% for various N and P combinations. 

MaxBac and Inipol EAP-22, which contain both N and P, performed slightly better than inorganic 

nitrogen supplemented with phosphorus. However, during the 40 days of the summer experiment, 

although the overall oil degradation rates were higher than in winter, nutrient addition did not 

significantly stimulate oil degradation beyond the 70% reported for all the treatments. This was 

attributed to the higher mineralization rates of organic nutrients in the sediments during the summer, 

which is consistent with the findings by Cartaxana et al. (1999) and Nixon et al. (1980). The study 

also indicated that the existence of Spartina alterniflora did not significantly affect oil degradation 

as compared to treatments without the wetland plant. 

Garcia-Blanco et al. (2001a) conducted a microcosm study to further simulate the bioremediation of 

oil-contaminated salt marsh under tidal conditions. The study was carried out in glass columns filled 

to a depth of 10 cm with sediment collected from a salt marsh in Nova Scotia, Canada. Each 

microcosm was operated on a 24 hr tidal cycle with a 12-hour submergence period. The entire 

sediment was mixed with weathered No.2 fuel oil to a concentration of 20 g/kg of wet sediment. 

Three inorganic nitrogen sources were tested: (1) a slow-release granular fertilizer (prilled 

ammonium nitrate); (2) sodium nitrate; (3) ammonium chloride. Each nitrogen fertilizer was 

9
supplemented with sodium tripolyphosphate and was added to microcosms at a N:P ratio of 5:1. The 

study showed that the addition of nutrients did not enhance the rate of degradation over the natural 

attenuation rate. The extent of microbial degradation of No. 2 fuel oil in all the microcosms averaged 

only 20% for the total aliphatic hydrocarbons and 12% for the total PAHs. Degradation was greater 

in all cases in the top layers than in the bottom layers of the columns, suggesting that oil degradation 

may have been limited by oxygen availability under the conditions of this study. 

Because these laboratory studies seem to suggest that adding nutrients may be effective under nonoxygen limiting conditions, or during certain seasons, further field experiments are necessary to 

determine the potential of oil bioremediation in coastal wetlands. 

1.3.3 Full-scale demonstrations 

From north temperate salt marshes to tropical mangroves, several field studies on the performance of 

oil bioremediation have been carried out in recent years. These have provided more convincing 

demonstrations of the effectiveness of oil bioremediation since laboratory studies may not consider 

many real world conditions such as spatial heterogeneity, biological interactions, and mass transfer 

limitations. 

1.3.3.1 Nova Scotia, Canada, 1989 

Lee and Levy (1991) conducted one of the first field trials on oil bioremediation in a salt marsh 

environment. The study involved periodic addition of water-soluble fertilizer granules (ammonium 

nitrate and triple super phosphate) to enhance biodegradation of waxy crude oil in a salt marsh 

dominated by Spartina alterniflora and located in Nova Scotia, Canada (Lee and Levy, 1991). Two 

levels of oil concentrations were used (0.3 and 3.0% v oil/v sediment) and two concentrations of the 

NH4NO3 were tested (0.34 and 1.36 g/L sediment). In this study, pristane was used as a biomarker 

for evaluation of biodegradation of crude oils. Results showed that the effectiveness of nutrient 

addition was related to oil concentration. Enhancement by fertilizer was significant at the 0.3% 

contamination level, but no enhancement occurred at 3%, which was attributed to the penetration of 

the oil at higher concentrations into the reduced soil layers where little degradation is expected. This 

study indicated that bioremediation might have a role in the cleanup of coastal wetlands lightly 

contaminated with oil. 

1.3.3.2 San Jacinto Wetland Research Facility (SJWRF), Texas, 1994-1997 

To evaluate the effectiveness of various bioremediation options, a series of field trials were carried 

out in a Texas coastal wetland by a research group from Texas A&M University (Mills et al., 1997; 

Mills et al., 2003; Simon et al., 1999; Townsend et al., 1999; Mills et al., 2003). This brackish 

wetland was set aside for a long-term research program after an oil spill from ruptured pipelines in 

1994. The 21-plot site, named San Jacinto Wetland Research Facility (SJWRF), has been used for a 

series of studies on oil spill countermeasures. Studies on oil bioremediation included three phases. 

Phase I of the research evaluated the intrinsic bioremediation or natural attenuation process after the 

initial oil spill. The effect of biostimulation was investigated in phase II by evaluating the use of 

diammonium phosphate and diammonium phosphate plus nitrate. Phase III involved the evaluation 

of two commercial bioaugmentation products and a repeated diammonium phosphate treatment. The 

10
21 5 x 5 m plots were arranged in a randomized complete block experimental design, and Arabian 

light and medium crude oils were used in phases II and III, respectively. Oil constituents were 

determined using gas chromatography/mass spectroscopy (GC/MS) and were normalized to 17α(Η), 

21β(Η)-hopane to reduce the effects of sample heterogeneity and physical losses. The results of 

phase II showed that the diammonium phosphate treatment significantly enhanced the 

biodegradation rates of both total resolved saturates and total resolved PAHs, and the addition of 

diammonium phosphate plus nitrate only enhanced the biodegradation of total resolved saturates 

(Mills et al., 1997). The field trial on oil bioaugmentation in phase III showed as with other 

shoreline types (Lee et al, 1997a; Venosa et al., 1996), that the addition of microbial products does 

not significantly enhance oil biodegradation rates (Simon et al., 1999). However, the performance of 

the nutrient treatment in this phase also failed to demonstrate the enhancement observed in Phase II. 

1.3.3.3 Terrebonne Parish, Louisiana, 1998 

Due to the mixed results from the earlier trials, field studies were conducted to verify the feasibility 

of oil bioremediation and to determine the limiting factors in oil biodegradation in coastal wetland 

environments. Shin et al. (1999 & 2000) investigated the effect of nutrient amendment on the 

biodegradation of a Louisiana “sweet” crude oil and oxygen dynamics in a Louisiana salt marsh, 

which has a tidal range of 20 cm and is vegetated by Spartina alterniflora. Four treatments (unoiled 

control, oiled control, oil plus ammonium nitrate, and oil plus a slow release fertilizer) were 

examined in forty field plots arranged in a randomized complete block design. Oil components were 

measured by GC/MS, and hopane was used as a biomarker. Oxygen dynamics were investigated by 

monitoring sediment oxygen demand (SOD), and the importance of sulfate reduction was 

2­ determined using a 35SO4 radiotracer technique. Overall, the nutrient amendments did not 

significantly stimulate oil biodegradation, which might have been related to the high background 

nutrient concentrations at this site. Throughout this study, the background nitrogen concentrations in 

the interstitial pore water were higher than the threshold nitrogen concentration of 1 - 2 mg N/L 

required for maximum hydrocarbon biodegradation as found by Venosa et al. (1996) in an unrelated 

field trial on a sandy beach. The addition of oil and fertilizers did increase the SOD and sulfate 

reduction rates in marsh soils. About 2/3 of the oxygen demand was due to aerobic respiration with 

the majority of this demand exerted by hydrocarbon degrading organisms, indicating aerobic 

biodegradation of the crude oil was the main mechanism. The remaining 1/3 of the oxygen demand 

was attributed to sulfide oxidation. Data also showed that significant biodegradation of crude oil in 

the salt marshes occurred only when the tidal cycle exposed the surface of the marsh to air (Shin et 

al., 2000). This study indicated that oxygen availability appears to control the oil biodegradation 

process in salt marshes. 

1.3.3.4 Gladstone, Australia, 1997-1998 

A field study on the performance of oil bioremediation in both mangrove and salt marsh ecosystems 

was carried out recently in a tropical marine wetland located at Gladstone, Australia (Burns et al., 

2000; Duke et al., 2000; Ramsay et al., 2000). This study evaluated the influence of a 

bioremediation protocol on the degradation rate of a medium range crude oil (Gippsland) and a 

Bunker C oil stranded in a tropical Rhizophora sp. mangrove environment and in Haloscarcia sp. 

salt marshes behind the mangroves. The bioremediation strategy used in this study involved 

pumping air beneath sediment that was supplemented with a slow release fertilizer (OsmocoteTM 

11
Tropical fertilizer) for the mangrove sites, and nutrient addition alone for the salt marsh sites. No 

aeration was tested in the salt marsh experiments because the sediment of the salt marshes was much 

less anoxic than that of the mangroves based on preliminary investigations. Four oiled treatments 

(two types of oils with and without the bioremediation treatments) and two unoiled controls 

(enclosure and ambient controls) were tested. Each treatment was studied with replicates of three 

plots for the mangrove sites and replicates of four plots for the salt marsh sites. The oils were added 

to mangrove plots and salt marsh plots at target loadings of 5 L/m2

 and 2 L/m2, respectively. The 

fertilizer was added at a loading of 0.15 kg/m2

 40 hours after oiling for both mangrove and salt 

marsh plots and then again after three months in mangrove plots only. Aeration in mangrove plots 

started 40 hr after oiling and lasted for about four months. In this study, other than total 

hydrocarbons (THCs), only individual alkanes were analyzed using GC-FID, and phytane was used 

as a biomarker. Oil analysis for the mangrove sediments over 13 months showed that no significant 

change in oil composition due to biodegradation was observed until two months after oiling, and by 

that time 90% of the THCs were removed from the sediments through evaporation and dissolution. 

The remediation strategy did not significantly enhance the degradation of either the remaining 

Gippsland oil or the Bunker C oil. A similar lag phase before the start of oil biodegradation was 

observed in the 9-month salt marsh experiment. The addition of the fertilizer to the salt marshes did 

show a stimulation of the degradation of the lighter Gippsland oil and resulted in about 20% more oil 

loss as compared with the untreated plots. However, the nutrient amendment did not significantly 

impact the rate of loss of Bunker C oil in the salt marsh plots. Microbial analysis for the mangrove 

sediments showed that the bioremediation treatment had a significant effect on alkane degraders and 

increased the population size by one to three orders of magnitude, as compared to the oil only plots. 

However, the population of aromatic degraders only increased slightly (one order of magnitude). 

Due to the limitation of the experimental design, the study could not distinguish whether nutrient 

addition or aeration stimulated the microbial growth. 

In the same study, Duke et al. (2000) investigated the ecological effects of the bioremediation 

strategy in the mangroves and compared the results to a previous field trial involving use of a 

dispersant at the same site. Although the authors suggested that the dispersant (but not 

bioremediation) significantly reduced the mortality of mangrove trees, the data appeared to show 

that both treatments had some positive effects on the wetland habitats. The increase in the tree 

mortality in bioremediation plots occurred only months after aeration and nutrient addition was 

stopped. Even though some aspects of the design are questionable (e.g., lack of independent tests of 

the effect of nutrients and aeration in mangrove environments, different oiling and treatment 

conditions for the salt marsh and mangrove experiments), the Gladstone field trial did provided 

useful insights on the potential of oil bioremediation, particularly in tropical marine wetland 

environments. 

1.3.3.5 Nova Scotia, Canada, 2000-2001 

A comprehensive field trial conducted on oil bioremediation in a salt marsh environment was carried 

out recently by the U.S. Environmental Protection Agency, University of Cincinnati, and Fisheries 

and Oceans Canada in a coastal salt marsh site situated on the Eastern Shore of Nova Scotia, Canada 

(manuscript not published at the time of this writing). This study explored various options for 

restoring salt marshes heavily contaminated with petroleum hydrocarbons under north-temperate 

conditions. Treatment options included natural attenuation, phytoremediation, and/or bioremediation 

12
by nutrient amendment and disking (gentle tilling). Like most North American salt marshes, this 

tidal salt marsh was dominated by Spartina alterniflora. Tides were semi-diurnal with a range of 

about 2 m. The commencement of the experiment coincided with the spring tide. Test plots for the 

study were set up throughout the wetland in a way that all of them were exposed to the same tidal 

inundation. 

A randomized block design was used in the study. Eighteen 3 m x 3 m plots were set up in three 

replicate blocks. Each block contained six treatments randomly distributed: (a) unoiled, no-nutrient 

control; (b) unoiled with nutrient amendments {NH4NO3 + Ca(H2PO4)2.H2O}; (c) oiled with no 

nutrient amendments and plants intact (natural attenuation); d) oiled with nutrient amendments and 

plants intact; (e) oiled with nutrient amendments and vegetation continually cut back to the ground 

surface and removed to suppress the influence of plants and anaerobiosis associated with the 

accumulation of plant detritus; (f) oiled with nutrient amendments and disked daily to introduce 

oxygen into the rhizosphere. 

A weathered Mesa crude oil was applied to the plots at a rate of 35 mg oil/g dry sediment during the 

first two days of the study. Granular nitrogen and phosphorus nutrients were initially added to each 

of the treated plots at a dosage of 450 g-N and 135 g-P per plot. Subsequent applications took place 

on an as-needed basis as determined by residual nutrient analysis in the interstitial pore spaces. 

When the nitrogen levels fell below a specified concentration range of 5-10 mg N/L in the pore 

water, another application of the same magnitude was made. The effectiveness of various treatments 

was determined by monitoring the reduction of oil constituents in both soil and grass samples using 

GC-MS techniques. Hopane was used as a biomarker to reduce the effects of sample heterogeneity 

and to distinguish bioremediation removal from physical losses. In addition to these detailed 

chemical analyses, this project also used biological endpoints such as evidence of wetland plant 

recovery and reduction of toxic responses to verify the success of the 

bioremediation/phytoremediation treatments (discussed in Section 2.2.4). 

The study showed that the biodegradation of targeted aliphatic hydrocarbons and PAHs took place to 

a very high extent at this north-temperate salt marsh. After 20 weeks, the extent of degradation of 

target n-alkanes within the experimental plots averaged 87% and 97 %, respectively, for the oil in 

sediment and the oil associated with emergent vegetative growth. Reduction of parent and alkylsubstituted PAHs was about 69% in the soil samples and 88% in the plant samples. However, 

targeted alkanes and PAHs only represent a small fraction (less than 10%) of the total petroleum 

hydrocarbons (TPHs). Biodegradation of TPH averaged only 35% in the soil samples and 42% in the 

grass samples (very little of this TPH was comprised of high molecular weight plant waxes). More 

than half of the applied oil remained in the marsh 20 weeks after oil application. Based on the extent 

of oil washout (measured as mg hopane per kg dry soil) and the total oil loss (g TPH per kg dry soil), 

the main mechanism for oil disappearance was attributed to biodegradation. These results contrast 

with those reported in the St. Lawrence River freshwater wetland bioremediation study (Venosa et 

al., 2002) and the study on a tropical marine wetland at Gladstone, Australia, in which most of the 

TPH was removed through physical mechanisms (Burns et al., 2000). 

In this study, as in other reported field studies, no significant differences were observed among 

treatments, either in the degradation of alkanes or PAHs. No significant enhancement of 

biodegradation through the addition of nutrients or the use of disking was observed. The average 

13
nutrient concentrations in the interstitial pore water for various treatments during this study are 

summarized in Table 1.1. Data indicated that the background nitrogen (mostly ammonium nitrogen) 

and phosphorus concentrations in the interstitial pore water were always far in excess of 2-5 mg N/L 

and 1 mg P/L, suggesting that nutrients may not be a limiting factor for oil biodegradation in this salt 

marsh. Enhanced oxygen transfer to the rhizosphere by the plants through their roots or by disking 

did not appear to take place either, at least to the level needed by hydrocarbon degraders to 

metabolize the oil rapidly. From the extent of degradation of the targeted aliphatic and aromatic 

hydrocarbons, it can be inferred that there was no oxygen or nutrient limitation in this particular salt 

marsh site. 

Table 1.1 Average nutrient concentrations in pore water for different treatments during 

Nova Scotia study 

 Treatment A 

Background 

Treatment 

B 

Nutrient 

Control 

Treatment 

C 

Natural 

Attenuation 

Treatment D 

Phytoremediation 

Treatment E 

Nutrient 

Amendment 

Treatment F 

Disking 

NH4-N 

mg N/L 9.43 60.63 18.08 92.49 80.83 104.6 

NO3-N 

mg N/L 0.09 28.57 0.07 37.11 30.56 28.89 

PO4-P 

mg P/L 1.25 12.42 2.17 5.66 9.42 14.75 

However, nutrient addition did stimulate microbial growth, as in the Gladstone study (Ramsay et al., 

2000). Alkane degraders in this wetland seemed to be nutrient limited, since the addition of nutrients 

without oil led to an increase in number of about two orders of magnitude relative to background 

levels. However, when oil was added to the plots without any nutrient amendment (natural 

attenuation plots), the increase in alkane degraders was also on the same order, suggesting the 

existence of different populations that can degrade alkanes under different conditions. However, 

PAH degraders were clearly limited by their carbon sources. Only oiled plots showed an increase in 

the number of PAH degraders. These populations did not seem to be limited by nutrients since the 

addition of nitrogen and phosphorus did not have an effect on either the number of microorganisms 

or on the rate of PAH degradation. 

In summary, these field trials suggest that nutrient amendments may be less effective in stimulating 

oil biodegradation rates in coastal wetlands than sandy beaches. Oil biodegradation on marine 

wetlands is often limited more by oxygen than by nutrient availability. A large fraction of the total 

nutrients in wetland sediments is bound in organic matter (i.e., plants and detritus) that is not readily 

available for microbial uptake. In such cases, natural ongoing mineralization processes may provide 

an effective means to overcome this restraint. However, field experience also suggests that some 

coastal wetlands may be nutrient limited, and in these cases, biostimulation with nutrient enrichment 

may still be an appropriate countermeasure treatment if the oil does not penetrate deeply into the 

anaerobic layer of the wetland sediments (Lee and Levy, 1991; Venosa et al., 2002; Mills et al, 

1997). 

14
1.3.4 Kinetics of oil biodegradation 

Knowledge of the kinetics of oil biodegradation is important for assessing the potential fate of 

targeted compounds, evaluating the efficacy of bioremediation, and determining appropriate 

strategies to enhance oil biodegradation. The rates of biodegradation vary greatly among the various 

components of crude oils and petroleum products and depend on many environmental factors, such 

as temperature, nutrient concentration, and oxygen content. The heterogeneity of oil distribution on 

shorelines or wetland sediments makes kinetics studies even more difficult. To reduce the variability 

associated with heterogeneous oil distribution, Venosa et al. (1996) utilized hopane normalization in 

studying the kinetics of oil biodegradation and developed first-order biodegradation rate constants 

for resolvable alkanes and important two- and three-ring PAH groups present in a light crude oil on a 

sandy beach in the Delaware field study. The first order relationship was expressed as: 







A

H













A

H





0 

e−kt 

=
 ( 1.1 )

where (A/H) is the time-varying hopane-normalized concentration of an analyte, (A/H)0 is that 

quantity at time zero, and k is the first-order biodegradation rate constant for analyte, A. 

Table1.2 Summary of first order biodegradation rate constants from field studies 

Field 

Study 

Location 

Shoreline 

Type 

Oil Type Treatment First order biodegradation rate 

day-1 

Reference 

Alkanes PAHs 

Delaware Sandy 

beach 

Bonny light 

crude oil 

Control 

Nutrient 

Inoculum 

0.026 

0.056 

0.045 

0.021 

0.031 

0.026 

Venosa et 

al., 1996 

Quebec 

Canada 

Tidal 

freshwater 

wetland 

Mesa light crude 

oil 

Control 

Nutrient 

0.0028 

0.0023-0.0034 

0.0028 

0.0016-

0.0041 

Venosa et 

al., 2002 

Texas Brackish 

wetland 

Phase II: 

Arabian light 

crude oil 

Phase III: 

Arabian medium 

Crude oil 

Control 

Nutrient 

Control 

Nutrient 

Inoculum 

0.019 

0.042-0.061 

0.020 

0.024 

0.019-0.030 

0.017 

0.018-0.027 

0.015 

0.013 

0.016-0.017 

Simon et al., 

1999 

Louisiana Salt marsh South Louisiana 

crude oil 

Control 

Nutrient 

0.005 

0.005 

N/A Shin et al., 

1999 

Nova 

Scotia 

Canada 

Salt marsh Mesa light crude 

oil 

Control 

Nutrient 

0.020 

0.026-0.039 

0.010 

0.011-0.013 

Unpublished 

data 

Since the Delaware study, several field trials conducted in other types of environments, including 

salt marshes and a freshwater wetland, have reported first-order oil biodegradation rate constants 

obtained using the same approach (Shin et al., 1999; Simon et al., 1999; Venosa et al., 2002). The 

results of these kinetic studies in the field are summarized in Table 1.2. It can be seen that except for 

15 
Phase II of the San Jacinto field study (Mills et al., 1997; Simon et al., 1999), nutrient amendments 

did not show significant biodegradation rate enhancements in most of these wetland environments. 

Nonetheless, it is encouraging to see that crude oils can be biodegraded intrinsically on marine 

wetlands at similar rates as on sandy beaches (i.e., the Delaware site). The higher intrinsic oil 

biodegradation rates reported for salt marshes when compared to freshwater wetlands may be 

attributed to the generally greater oxygen limitation in freshwater wetland environments (Mitsch and 

Gosselink, 2000). It should be noted here that in the St. Lawrence River freshwater wetland study 

(Venosa et al., 2002), the oil was manually raked into the sediment, causing penetration of oil into 

the anaerobic zone. It is not known whether higher biodegradation rates would have ensued had this 

raking not been done. 

1.3.5 Monitoring biological responses to quantify the efficacy of remediation treatment 

In addition to the demonstration that remedial treatments reduce the concentration of residual oil, it 

is necessary to demonstrate that they do not produce any undesired environmental and ecological 

effects. As discussed in the sandy shoreline and freshwater wetland guidance document (Zhu et al., 

2001), two complimentary approaches are available: (1) bioassessments, which typically monitor 

changes in populations and communities of flora and fauna (Herricks and Schaeffer, 1984); and (2) 

bioassays, which include toxicity tests and bioaccumulation studies (Chapman, 1989). 

1.3.5.1 Bioassessment 

The monitoring of alterations in benthic community structure is frequently used to assess the 

potential impacts of residual oil within sediments. For example, in a follow up of the Exxon Valdez 

oil spill clean up, Driskell et al. (1996) noted negative effects including reductions in size, biomass, 

fecundity, and increased mortality as a result of hot water washing. Changes in epifauna and infauna 

were also used to assess the rates of natural recovery and the impacts of intertidal clean-up activities 

on the coast of Saudi Arabia following the 1991 Persian Gulf oil spill (Watt et al., 1993). The 

possibility of adverse ecological effects such as algal blooms and invertebrate mortality from 

excessive nutrient amendments associated with bioremediation treatments is also a concern (Lee, 

2000a; Lee et al., 2001a, 2001b). 

To date, sediment bioassessments have been largely based on the tracking of changes in 

macroinvertebrate community structure. For a holistic approach, it is recommended that 

consideration should also be given to the bioassessment of fish and other non-benthic community 

organisms (e.g. bacteria, phytoplankton, cladocera, and amphibians). Furthermore, with recent 

advances in biotechnology, micro-scale bioassays are now available to monitor alterations at the 

subcellular or multicellular level of biological organization (Lee et al., 1998; Wells et al., 1998). In 

wetland environments, quantification of potential impacts on vegetative growth can be used to 

document the efficacy of bioremediation strategies. For example, in a tidal freshwater wetland 

experiment, the predominant plant species (Scirpus pungens) was reported to be tolerant to the oil, 

and its growth was significantly enhanced above that of the unoiled control by the addition of 

nutrients (Lee et al., 2001a). Monitoring of recolonization within impacted areas should be 

considered as an endpoint in bioassessments, as it provides integrated information on the impact of 

contaminants on processes such as immigration, emigration, competition, and predation. 

16
1.3.5.2 Bioassays 

As discussed in the sandy shoreline and freshwater wetland guidance document (Zhu et al., 2001), 

acute and/or chronic bioassays can be performed on whole sediment (e.g., solid-phase), suspended 

sediment, sediment liquid phases (pore water, interstitial water), or sediment extracts (elutriates, 

solvent extracts). Since various forms of biota differ in their sensitivity to toxicants, it is highly 

recommended that a test battery approach with species from different trophic levels be utilized in 

environmental assessments to ensure ecological relevance. 

Sediment bioassays have been used extensively to diagnose the effect of oil spills (Teal et al., 1992; 

Gilfillan et al., 1995; Neff and Stubblefield, 1995; Randolph et al., 1998) and their countermeasures 

such as bioremediation (Lee et al., 1995b; Mearns et al., 1995; Mueller et al., 1999). Criteria to 

consider for the selection of bioassays include: (1) sensitivity to test material, (2) ecological and/or 

economic relevance, and (3) the availability of regional expertise for the analysis and interpretation 

of results. 

1.3.5.2.1 Numerous bioassays can be used to document the impact of oil spills in coastal 

environments. Benthic invertebrates such as amphipods and shellfish have been found to be highly 

sensitive to residual hydrocarbons following oil spill incidents (Teal et al. 1992; Gilfillan et al., 

1995; Mueller at al., 1999; Wolfe et al., 1996). They have been used in both field and laboratory 

studies to monitor the impact and effectiveness of oil spill countermeasures such as bioremediation 

(Mearns et al., 1997, 1995; Lee et al., 2001a,b). In terms of quantifying a microbial response, the 

Microtox test is based on the measurement of changes in light emission by a nonpathogenic, 

bioluminescent marine bacterium (Vibrio fisheri) upon exposure to test samples. This commercial 

assay has been used by regulatory agencies for toxicity screening of chemicals, effluents, water and 

sediment, and for contamination surveys and environmental risk assessment, and its application for 

monitoring the efficacy of oil spill remediation methods has been proven (Lee et al., 1995b, 1997; 

Mueller et al., 1999). 

1.3.5.2.2 Due to their economic, recreational, and aesthetic value, fish have been historically 

selected as a primary bioassay organism. Biochemical and physiological alterations induced by 

toxicant exposures can result in: 1) anatomical changes, 2) structural alterations in organelles, cells, 

tissue, and organs, and 3) alteration of metabolic processes. For example, the observation of 

neoplasms in fish was one of the first histopathological indices used in ecotoxicology. Biomarkers, 

defined as biochemical, physiological, or pathological responses measured in individual organisms 

on exposure to environmental contaminants, such as mixed function oxidase (MFO) reactions (Ortiz 

de Montellano, 1986) are also used. MFO reactions induced by PAHs and a variety of halogenated 

hydrocarbons are highly sensitive to contaminants. In the tidal freshwater wetland study with early 

life stages of fish, Hodson et al. (2001) noted that oil alone, oil mixed with sediments in the lab, and 

oiled sediments from the experimental plots all caused induction of MFO (CYP1A) enzyme activity 

relative to unoiled controls, indicating the presence and bioavailability of PAH. Induction did not 

vary markedly among treatments, but declined slowly with time. Concomitant chemical analysis 

suggested that PAHs were depleted primarily by weathering or sediment dispersion rather than by 

bioremediation treatments. 

To date, detrimental effects from nutrient enrichment have not been observed following full-scale 

17
field operations (Prince, 1993; Mearns et al., 1997). However, field experiments have suggested that 

the possibility of detrimental effects from bioremediation treatments cannot be fully discounted 

(Mueller et al., 1999). For example, oxygen depletion and production of ammonia from excessive 

applications of a fish-bone meal fertilizer during one field experiment caused detrimental effects that 

included toxicity and the suppression of oil degradation rates (Lee et al., 1995a). Furthermore, in a 

subsequent bioremediation field trial it was reported that a commercial bioremediation product 

suppressed the rates of toxicity reduction as it increased the retention of residual oil within the 

sediments (Lee et al., 1997). Bioassays used to document the effectiveness of bioremediation 

treatments in sandy intertidal shoreline sediments oiled with a weathered light crude oil showed an 

inhibitory effect on the hatching of grass shrimp due to the addition of nutrients (Mearns et al., 

1995). Furthermore, most recently, in the tidal freshwater study described in the sandy shoreline and 

freshwater wetland guidance document (Zhu et al., 2001), it was noted that amphipod toxicity levels 

became elevated during the study due to excessive nutrient enrichment (Lee et al., 2001a). It is 

recommended that future operational guidelines include ecotoxicological-monitoring protocols. 

1.3.6 Bioremediation options on salt marshes 

Major bioremediation options have been described in the sandy shoreline and freshwater wetland 

guidance document (Zhu et al., 2001). This document provides a summary of the most current 

information on restorative techniques pertaining to salt marshes. 

1.3.6.1 Nutrient Amendment 

As stated in previous sections, biostimulation has been ineffective in accelerating the disappearance 

of oil on certain oil-contaminated salt marshes (Garcia-Blanco and Suidan, 2001; Shin et al., 1999) 

due to either the presence of high background nutrient concentrations or oxygen limitation. 

However, a few field studies did show enhanced oil biodegradation through nutrient addition (Lee 

and Levy, 1991; Mills et al., 1997); therefore, nutrient amendment may still be a viable option for 

removing hydrocarbons from an oil-contaminated wetland when nutrients are limiting. Nutrients 

used for biostimulation can be classified as water-soluble, slow-release, oleophilic, and organic. 

•	 Water-soluble nutrients -- Commonly used water-soluble nutrient products include mineral 

nutrient salts (e.g. KNO3, NaNO3, NH3NO3, K2HPO4, MgNH4PO4), and many commercial 

inorganic fertilizers (e.g. the 23:2 N:P garden fertilizer used in Exxon Valdez case). They are 

usually applied in the field through the spraying of nutrient solutions or spreading of dry 

granules. Compared to other types of nutrients, water-soluble nutrients are more readily 

available and easier to manipulate to maintain target nutrient concentrations in interstitial 

pore water. The main disadvantage is that they are more likely to be washed away by tidal 

and wave action. However, this washout effect is of lesser concern in salt marshes, since 

they generally represent low-energy environments that are subject to little turbulent mixing. 

A field study on nutrient hydrodynamics showed that water-soluble nutrients could remain in 

contact with oiled sediments for weeks on low energy shorelines before being washed out 

(Wrenn et al., 1997a; Harris et al., 1999). 

•	 Slow-release fertilizers -- Slow release fertilizers are normally available in solid forms that 

consist of inorganic nutrients coated with hydrophobic materials like paraffin or vegetable 

18
oils or organic nutrients encapsulated by semi-permeable or controlled-rate degradable 

surface coatings. They are designed to overcome the washout problems and provide a 

continuous supply of nutrients to oil contaminated areas. This approach may also cost less 

than adding water-soluble nutrients due to less frequent applications (Lee et al., 1993). The 

Gladstone field trial has shown promise for the application of slow-release fertilizers in 

coastal wetlands (Burns et al., 2000). In this study, the degradation of a Gippsland crude oil 

in salt marsh plots was stimulated by the addition of OsmocoteTM, a slow release fertilizer 

consisting of a mixture of inorganic nutrients coated with an organic resin. 

•	 Oleophilic nutrients -- Another approach to overcome the problem of water-soluble nutrient 

washout is to utilize oleophilic organic nutrients. The rationale for this strategy is that oil 

biodegradation mainly occurs at the oil-water interface, and since oleophilic fertilizers are 

able to adhere to oil and provide nutrients at the oil-water interface, enhanced biodegradation 

should result without the need to increase nutrient concentrations in the bulk pore water. 

Results have been mixed. Some studies have suggested that oleophilic fertilizers might be 

more suitable for use in high-energy, coarse-grained environments due to poor penetration of 

fine sediments by oleophilic fertilizers (Sveum et al., 1994; Sveum and Ladousse, 1989). 

Bioremediation agents containing organic substrates such as meat and fish-bone meal and 

yeast extracts may have the capacity to provide essential micro-nutrients and organic growth 

substrates that may be limiting. However, the large amount of organic carbon within this 

type of amendment may also cause problems. For example, the organic carbon in the product 

may be biodegraded by microorganisms preferentially over petroleum hydrocarbons, thus 

contributing to oxygen depletion and resulting in undesirable anoxic conditions (Lee and 

Levy, 1987,1989; Lee et al., 1995a,b; Swannell et al., 1996). Considering their high cost and 

lack of demonstrated effectiveness, oleophilic fertilizers are unlikely to be the choice 

biostimulation agent for oil cleanup in coastal wetlands. 

1.3.6.2 Microbial amendments 

Addition of oil-degrading microorganisms (bioaugmentation) has been proposed as another type of 

bioremediation strategy. The rationale for this approach includes the contention that indigenous 

microbial populations may not be capable of degrading the wide range of substrates that are present 

in complex mixtures such as petroleum and that seeding may reduce the lag period before 

bioremediation begins (Leahy and Colwell, 1990). Although many vendors of microbial agents 

claim that their product aids the oil biodegradation process based on laboratory tests, the 

effectiveness of microbial amendments has not been convincingly demonstrated in the field (Zhu et 

al., 2001). Actually, results from most field studies indicate that bioaugmentation is not effective in 

enhancing oil biodegradation on marine shores. Field studies conducted on sandy beaches have 

shown that nutrient addition or biostimulation alone had a greater effect on oil biodegradation than 

microbial seeding (Lee and Levy, 1987; Lee et al., 1997, Venosa et al., 1996). The San Jacinto 

study, the only reported field trial on oil bioaugmentation in a coastal wetland environment, also 

revealed that addition of microbial products did not significantly enhance oil biodegradation rates 

(Simon et al., 1999). This is because hydrocarbon-degrading microorganisms are ubiquitous in the 

environment, and their density can increase by many orders of magnitude after exposure to crude oil, 

as evidenced in recent studies of coastal wetlands (Garcia-Blanco and Suidan, 2001; Ramsay et al., 

2000; Townsend et al., 1999). Also, added bacteria may not be able to compete with the indigenous, 

19
well-adapted population (Lee and Levy, 1989; Venosa et al., 1992). The mass of the hydrocarbondegrading bacterial population on coastal wetlands is also limited by factors that are not affected by 

an exogenous source of microorganisms, such as predation by protozoans, the oil surface area, or 

scouring of attached biomass by tidal activity. Therefore, it is unlikely that exogenous 

microorganisms would persist in contaminated wetlands even when they are added in large numbers. 

As a result, microbial amendments will not have any long-term or short term beneficial effects 

in shoreline cleanup operations. 

1.3.6.3 Oxygen amendment 

Because wetland soils are inundated with water, the diffusion rates of oxygen through the soils are 

very slow, and oxygen in the interstitial water is quickly depleted by aerobic metabolism of detritus 

that is abundant in wetlands. A few centimeters, and often only a few millimeters below the 

sediment surface, the wetland sediments are anaerobic. Therefore, oxygen is likely a limiting factor 

for oil biodegradation in marine wetlands. However, an appropriate technology for increasing the 

oxygen concentration in such environments, other than reliance on the wetland plants themselves to 

pump oxygen down to the rhizosphere through the root system, has yet to be developed. Many of the 

oxygen amendment technologies developed in terrestrial environments (e.g. tilling, forced aeration, 

and the addition of chemical oxidants), are currently not considered viable options for use in coastal 

wetlands. There is concern that their deployment is expensive and environmentally intrusive. 

Furthermore, their effectiveness in enhancing oil biodegradation in wetland environments is 

unproven. 

The Gladstone field trial showed that a forced aeration strategy was only able to increase the depth 

of the aerobic layer of the wetland sediments from 1 mm to 2 mm, and could not significantly 

stimulate oil biodegradation in the anaerobic mangrove environment (Burns et al., 2000). Strategies 

involving the mixing of surface sediments, such as tilling or disking, have also been proven 

ineffective in recent field studies (Garcia-Blanco and Suidan, 2001; Garcia-Blanco et al., 2001b; 

Venosa et al., 2002). Not only does this approach cause severe ecological damage to wetlands, it 

also enhances oil penetration deep into the anaerobic sediments, resulting in slower oil 

biodegradation. As for adding alternative electron acceptors, there is no strong evidence yet to 

suggest that the addition of nitrate as an electron acceptor can enhance oil biodegradation when 

oxygen is limiting (Garcia-Blanco and Suidan, 2001; Townsend et al., 1999). The high oil 

degradation rates under sulfate-reducing conditions found in some laboratories (Caldwell et al., 

1998; Coates et al., 1997) have not been convincingly demonstrated in the field. Therefore, further 

research is still required to explore cost-effective oxygen amendment techniques for the 

bioremediation of coastal wetlands. 

1.3.6.4 Plant amendment (phytoremediation) 

Phytoremediation, the stimulation of contaminant degradation by the growth of plants and their 

associated microorganisms, is emerging as a potentially cost-effective option for cleanup of 

petroleum hydrocarbons in terrestrial environments (Banks et al., 2000; Frick et al., 1999a). 

Mechanisms responsible for oil phytoremediation may include degradation, containment, and the 

transfer of contaminants from soil to the atmosphere (Cunningham et al., 1996). Frick et al. (1999b) 

indicated that the primary loss mechanism for petroleum hydrocarbons is the degradation of these 

20
compounds by microorganisms in the rhizosphere of plants. Phytoremediation was hypothesized to 

be particularly effective when used together with nutrient enrichment because hydrocarbon 

contamination may result in nutrient deficiencies in contaminated soil. Added fertilizers could 

increase the rate of oil degradation by indigenous microorganisms in the rhizosphere and 

simultaneously stimulate plant biomass production, thereby increasing the effectiveness of 

phytoremediation and accelerating the recovery of the affected wetland plant ecosystem. 

Extensive studies have been conducted on the phytoremediation of petroleum hydrocarbons in 

terrestrial environments (Frick et al. 1999a,b). Researchers at University of Saskatchewan, Canada, 

recently developed a catalogue of plants with the potential to phytoremediate hydrocarbon 

contaminated soils following a review of information in the literature and the conduct of field 

surveys (Godwin et al., 1999; and Frick et al., 1999c). Nevertheless, only limited studies have been 

carried out on the effectiveness of phytoremediation in enhancing oil degradation in coastal wetland 

environments. Lin and Mendelssohn (1998) found in a greenhouse study that application of 

fertilizers in conjunction with the presence of salt marsh and brackish marsh transplants significantly 

enhanced oil degradation. In another mesocosm study, Dowty et al. (2001) evaluated the effects of 

soil organic matter content, plant species, soil oxygen status and nutrient content on oil degradation 

and plant growth response in fresh marsh environments. The study found that the amount of oil 

remaining after 18 months was lowest in aerated and fertilized mesocosms containing either P. 

hemitomon or S. lancifolia and a substrate of low organic matter content. Field studies, however, 

have not demonstrated such significant effects as in the mesocosm studies. A recent Nova Scotia 

field trial showed that addition of nutrients did not result in significant enhancement of 

biodegradation of crude oil, whether or not plants were left intact or removed (Garcia-Blanco and 

Suidan, 2001). Similar results were also found in the St. Lawrence River freshwater wetland field 

study (Garcia-Blanco et al., 2001b; Venosa et al., 2002). On the other hand, the results of these field 

trials did suggest that although application of fertilizers in conjunction with the presence of wetland 

plants may not significantly enhance oil degradation, it could accelerate habitat recovery. There is 

evidence that nutrient amendments could stimulate vigorous vegetative growth, reduce sediment 

toxicity and oil bioavailability (Lee et al., 2001a). 

In summary, on the basis of field trials conducted to date, the effectiveness of phytoremediation in 

enhancing oil degradation in coastal wetlands is highly site-specific and does not promise to be an 

effective oil cleanup technique per se. However, it does show promise in accelerating the recovery 

and restoration of wetland environments contaminated with oil and oil products, which is the 

ultimate goal of the treatment. 

1.3.6.5 Monitored natural attenuation 

Natural attenuation has been defined as the reliance on natural processes to achieve site-specific 

remedial objectives (USEPA, 1999). When used as a clean up method, a monitoring program is still 

required to assess the performance of natural attenuation. This approach is increasingly viewed as 

the most cost-effective, although the least cosmetically appealing, option for the cleanup of oil spills 

in coastal wetland environments since it causes the least adverse ecological impacts often associated 

with cleanup activities (Baker, 1999; Owens et al., 1999; Sell et al., 1995). Sell et al. (1995); Mills 

et al., 2003) compared the rates of recovery between treated and untreated wetlands based on 20 

case studies of heavily oiled salt marshes. They concluded that most traditional cleanup methods did 

21
not promote significant long-term ecosystem recovery. 

Recent field studies on oil bioremediation have demonstrated that the availability of oxygen, not 

nutrients, is often the limiting factor for oil biodegradation in coastal wetlands. However, as 

discussed earlier, no feasible technique is currently available for increasing the availability of 

oxygen in such an environment. Fortunately, these field studies also showed that the natural 

biodegradation of alkanes and PAHs could occur to a very high extent and at similar rates in coastal 

wetlands as in sandy beaches (See section 1.3.4). Therefore, in consideration of the potential impacts 

associated with physical clean-up procedures in wetlands (i.e. trampling), natural attenuation should 

be given more preference in decision making for oil spill cleanup in coastal wetlands when the oil 

concentration is not high enough to destroy the ecosystem. 

22
2 RECOMMENDED APPROACHES TO BIOREMEDIATION IN SALT MARSHES 

Existing studies have demonstrated that oil biodegradation on marine wetlands is often limited by 

oxygen, not nutrient availability. Natural attenuation is increasingly becoming a promising and even 

a preferred strategy for the restoration of oil-contaminated wetlands. However, field studies also 

showed that on some coastal wetlands, nutrients might still be a limiting factor for oil 

biodegradation, particularly if the oil does not penetrate deeply into the anoxic zone of the wetland 

sediment (Lee and Levy, 1991; Mills et al., 1997; Venosa et al., 2002). Therefore, biostimulation 

with nutrient amendment can still be an appropriate countermeasure treatment under some 

circumstances. General guidelines for the bioremediation of oil-contaminated marine shorelines, 

which are mostly derived from studies and practices on sandy beaches, have been presented in the 

sandy shoreline and freshwater wetland guidance document (Zhu et al., 2001). Although the general 

principles for achieving successful oil bioremediation for all types of marine shorelines are the same, 

a simple transfer of response strategies may not be necessarily the most appropriate since salt marsh 

habitats are significantly different from other marine situations. Therefore, guidelines and special 

considerations for oil bioremediation in coastal wetland environments are presented here based on 

current understandings and field studies, particularly the findings of the Nova Scotia field study 

(Garcia-Blanco and Suidan, 2001). 

Similar to the general protocol presented in the sandy shoreline and freshwater wetland guidance 

document (Zhu et al., 2001), a general procedure or plan for the selection and application of 

bioremediation technology in salt marshes is illustrated in Figure 2.1. The major steps in a 

bioremediation selection and response plan include: 

1. Pre-treatment assessment – This step involves the evaluation of whether bioremediation is 

a viable option based on the biodegradability of the spilled oil, the depth of oil penetration 

and oxygen availability, concentrations of background nutrients, the presence of 

hydrocarbon-degrading microorganisms, the type of shoreline substrate, and other logistic 

and environmental factors (pH, temperature, remoteness of the site, accessibility of the 

site and logistics, etc.). 

2. Design of treatment and monitoring plan – After the decision is made to use 

bioremediation, further assessments and planning are needed prior to the application. This 

step involves selection of the rate-limiting treatment agents (e.g., nutrients), determination 

of application strategies for the rate-limiting agents, and design of sampling and 

monitoring plans. 

3. Assessment and termination of treatment – After the treatment is implemented according 

to the plan, assessment of treatment efficacy and determination of appropriate treatment 

endpoints are performed based on chemical, toxicological, and ecological analysis. 

This document will focus on the operational guidelines for decision-making and planning of oil 

bioremediation in salt marshes. Guidelines with respect to the assessment of field results and 

establishment of appropriate treatment endpoints can be found in the Chapter 6 of the sandy 

shoreline and freshwater wetland guidance document (Zhu et al., 2001). 

23
Step 1: 

Pretreatment Assessment 

Step 2: 

Bioremediation Planning 

Step 3: 

Assessment and Termination 

Oil 

biodegradability 

Background 

nutrient content 

If bioremediation 

is selected 

Climate, prior oil 

exposure and other 

site characteristics 

Nutrient products Nutrient application 

strategy 

Sampling and 

monitoring plan 

Toxicological and ecological 

analysis 

Analysis of oil biodegradation 

and physical loss 

Oil penetration 

and oxygen 

availability 

Figure 2.1 Procedures for the selection and application of oil spill bioremediation in salt marshes 

24 
2.1 Pre-treatment Assessment 

Major considerations in the assessment of the need for biostimulation in salt marshes include the 

evaluation of 1) oil types and concentrations, 2) oil penetration and oxygen availability 3) 

background nutrient content, and 4) other environmental factors such as the prevalent climate and 

prior oil exposures. Among these factors, the assessments of oil penetration, oxygen availability and 

background nutrient content are of particular importance for bioremediation of salt marshes and will 

be discussed in following sections. Detailed discussion on the assessments of oil types and 

concentrations, oil biodegradability, climate and other environmental factors can be found in the 

sandy shoreline and freshwater wetland guidance document (Zhu et al., 2001). 

2.1.1 Oil penetration and oxygen availability 

Unlike other types of marine shorelines (e.g. sandy beaches), the most important limitation for 

cleanup of an oil-contaminated marine wetland is oxygen availability. Wetland sediments become 

anoxic often below a few millimeters to centimeters of the soil surface. When substantial penetration 

of spilled oil into anoxic sediments has taken place, available evidence suggests that biostimulation 

with nutrient addition has limited potential for enhancing oil biodegradation, and it would likely be 

best simply to leave it alone and not risk further damage to the environment by trampling and the 

associated bioremediation activities. Therefore, the evaluation of oil penetration and oxygen 

availability is probably the most important pre-treatment assessment for determining whether 

bioremediation is a viable option. 

The thickness of the oxidized layer within wetland sediments varies from a few millimeters to 

several centimeters, depending on the population of oxygen utilizers, the rate of photosynthetic 

oxygen production by algae, the soil chemical composition, and the rate of oxygen transport into the 

wetland sediments (Mitsch and Gosselink, 2000; Shin et al, 2000). For example, soil organic matter 

is a major oxygen sink in salt marshes and, therefore, oxygen deficiency is more likely to occur in 

wetland soil with high organic matter content. Oxygen limitation will be less severe in the area 

where the wetland surface is exposed to the atmosphere or is subjected to strong surface mixing by 

convection currents and wave action. 

The depth of the aerobic layer can be identified through both visual observation and measurements 

of DO and redox potential. The wetland surface or the aerobic layer is often a brown or brownishred color due to the presence of ferric ions. The anoxic zone in wetland sediments is either bluish 

gray due to the presence of ferrous ions or, more often in salt marshes, black along with a foul odor 

associated with the production of hydrogen sulfide under sulfate reducing conditions. Anoxic 

conditions can also be determined by measuring dissolved oxygen in pore water. Oxygen will 

become a limiting factor when DO concentration in pore water approaches zero. When using DO 

probe, a reading of 0.1 or 0.2 mg/L indicates the depletion of dissolved oxygen. Redox potential is a 

more sensitive measurement of the degree of reduction of wetland sediments. For example, 

denitrification occurs at a redox potential of approximately 250 mV and sulfates are reduced to 

sulfides at a redox potential between –100 and –200 mV (Mitsch and Gosselink, 2000). 

The depth of oil penetration also depends on many factors, such as oil type, concentration and 

shoreline substrate. In general, fresh crude oils and heavy oils tend to adhere to the marsh surface 

25
sediment or pool on the sediment surface. Light oils and oil components can generally penetrate the 

top few centimeters of wetland sediment. However, penetration can be much deeper into burrows 

and cracks extending up to one meter (NOAA, 1992). A microcosm study on the penetration of 

weathered light Arabian crude oil in freshwater wetland sediments showed that the oil was able to 

penetrate about 2.5 cm in 16 weeks for both a flooded condition and a saturated but non-flooded 

condition (Purandare, 1999). However, the amount of the oil able to penetrate into the sediment was 

much less for flooded sediments, where most of the oil floated on the surface of the water. The depth 

of oil penetration also increases with the increase of oil concentration and therefore affects the 

potential of oil biodegradation. In the field trial reported by Lee and Levy (1991), the rates of oil 

degradation in the salt marsh were not stimulated by nutrient amendments at the higher test 

concentration (3.0% v oil/v sediment), where oil penetrated to anaerobic layers of sediment. 

However, bioremediation was effective at the lower test concentration (0.3 % v oil/v sediment), 

where the oil did not penetrate beyond the aerobic sediment surface layers. In the same field study, 

Lee and Levy (1991) also examined the effect of oil concentration on a sandy beach and found that 

oil biodegradation rates were enhanced by the nutrient amendment at the higher oil concentrations 

(3%), where oxygen was not a limiting factor. The result suggested that the favorable concentrations 

for using bioremediation would be much lower in salt mashes than on sandy beaches. 

The type of shoreline substrate is another important factor affecting the oil penetration and the 

feasibility of using bioremediation. Shoreline substrate can affect oil penetration from the 

perspectives of both the sediment texture and the soil chemical composition. Generally, oil 

penetrates coarse sediments more readily than fine sediments. However, because the texture of all 

wetland sediments is normally very fine, the substrate chemical composition plays a more important 

role in oil penetration in salt marsh environments. Studies have shown that the rates of oil 

penetration and biodegradation are strongly related to the soil organic matter content (Dowty et al., 

2001; Lin and Mendelssohn, 1996). Oil is more likely to penetrate into sediments with higher 

organic content since it associates more readily with organic matter than with mineral particles. In a 

greenhouse study, Lin and Mendelssohn (1996) investigated the performance of oil biodegradation 

in three types of coastal wetlands -- salt, brackish, and freshwater marsh. They found that the rates of 

oil degradation were highest in the salt marshes and lowest in the freshwater marshes. The difference 

in oil residue was mainly attributed to the difference in the soil organic content, which was lowest in 

the salt marsh sediments and highest in the freshwater marsh sediments. The study also measured the 

concentrations of the oil that penetrated the soils in digested (to remove the associated organic 

matter) and undigested marsh soil and found that the oil concentrations were 41-279 times higher in 

the undigested soil than the digested one. Similar results were observed by Dowty et al. (2001) in a 

mesocosm study conducted in fresh marsh environments. They found that the rates of oil 

degradation were significantly higher in the inorganic sediments than the organic ones under 

different oil concentrations and nutrient levels. These results are consistent with the notion that 

oxygen demand is higher and oil is more readily able to penetrate into organic sediments. Therefore, 

oil bioremediation seems more likely to be successful when applied in a wetland with lower organic 

matter content. 

2.1.2 Background nutrient content 

To determine whether nutrient amendment is a viable option, it is necessary to assess the 

background nutrient levels in the contaminated site, particularly the nutrient concentrations within 

26
the interstitial water in that environment. There is no need to add nutrients if natural nutrient 

concentrations are high enough to sustain rapid intrinsic rates of oil biodegradation. However, 

because oxygen is often the determining factor in oil degradation on coastal wetlands, the 

assessment of background nutrient concentration is important and needed only after the assessments 

of oil penetration and oxygen availability conclude that oxygen limitation is not a serious 

impediment. In other words, when substantial oil penetration into the anoxic zone of the wetland 

sediments occurs, nutrient amendment is not likely to be effective even if nutrient deficiency exists. 

As shown in the St. Lawrence River field trial (Venosa et al., 2002), the average pore water nitrogen 

concentration in natural attenuation plots was only about 0.74 mg N/L, well below the levels needed 

for maximum hydrocarbon biodegradation (Venosa et al., 1996). However, the dramatic increase in 

nutrient levels in the biostimulation plots did not enhance oil biodegradation above that achievable 

in the natural attenuation plots due to the oxygen limitation within that freshwater wetland sediment. 

However, when oxygen availability is not a limiting factor, the decision to use nutrient amendments 

should be based on how high the natural levels are relative to the optimal or threshold nutrient 

concentrations. It has been recommended in the sandy shoreline and freshwater wetland guidance 

document (Zhu et al., 2001) that the threshold concentration for optimal hydrocarbon biodegradation 

on marine shorelines is in the range of 2 to 10 mg N/L based on the field experiences on sandy 

beaches (Bragg et al., 1994; Venosa et al., 1996) as well as in an estuarine environment (Oudet et 

al., 1998). Although no such threshold concentration has been experimentally identified in salt 

marsh environments, recent field experiences did provide some insights. The Nova Scotia study 

found that the average background nitrogen concentration in pore water was about 10 mg N/L at the 

experimental site. Thus, nitrogen limitation was not an important factor (Garcia-Blanco and Suidan, 

2001). The ineffectiveness of nutrient amendments in enhancing oil biodegradation under this high 

background nutrient level suggested that the nitrogen threshold concentration should be lower than 

10 mg N/L. However, the San Jacinto River study suggested that the threshold nitrogen 

concentration may be higher than 2 mg N/L on coastal wetlands. During Phase II of the study, 

nutrient addition apparently enhanced oil degradation even when the background nitrogen 

concentration was about 5 mg N/L (Harris et al, 1999; Mills et al., 1997). This study, however, was 

inconclusive because the same enhancement was not observed when the treatment was repeated 

during the following year (Simon et al., 1999). Although further research is still needed, it appears 

from existing evidence that the threshold nitrogen concentration for optimal oil biodegradation in 

salt marshes is likely similar to that obtained in other shoreline types (e.g. 2-10 mg N /L). 

The investigation of background nutrients should also determine whether the present nutrient 

concentrations are typical of the area or sporadic (i.e., determine the impact of chronic runoff from 

nearby agricultural practices and local industrial and domestic effluents). As described in Part I, 

coastal marshes are generally considered high-nutrient wetlands. However, inorganic bioavailable 

nutrient concentrations in salt marsh sediments may exhibit a strong seasonal pattern with a 

concentration peak usually during the summer months probably due to a high mineralization rate at a 

higher temperature (Cartaxana et al., 1999; Nixon et al., 1980). The available nutrient levels can also 

be elevated as a result of runoff, fire and death of plants. If these events are sporadic, biostimulation 

may still be appropriate when the nutrient levels fall below threshold concentrations. 

27
2.1.3 Summary of pretreatment assessment 

Based on the current understandings discussed in the previous sections as well as in the sandy 

shoreline and freshwater wetland guidance document (Zhu et al., 2001), the following pretreatment 

assessments should be conducted to determine whether bioremediation is a viable option in response 

to a spill incident in salt marsh environments: 

•	 Determine whether the spilled oil is potentially biodegradable – Light petroleum products 

and light crude oils (API gravity > 30°) are relatively biodegradable; products rich in normal 

alkanes are also relatively biodegradable; heavy crude oils (API gravity < 20°) and residual 

fuel oils, which are high in polar compounds (asphaltenes and resins) are less biodegradable. 

High concentrations of oil (of any weight) may also inhibit biodegradation. For details, see 

Zhu et al. (2001). 

•	 Determine whether oxygen is a factor limiting oil biodegradation by measuring the depth of 

oxidized sediment layer and the extent of oil penetration – When a substantial portion of the 

spilled oil has penetrated into anoxic sediments, biostimulation with nutrient addition has 

limited potential for enhancing oil biodegradation. Oxygen limitation is less likely to occur 

in wetland sediments with lower organic matter and/or contaminated with oil at moderate 

concentrations. 

•	 Determine whether the nutrient content at the impacted area is likely to be a limiting factor 

by measuring the background nutrient concentrations within the interstitial water in that 

environment – If oxygen is not the limiting factor, the decision to use bioremediation by 

addition of nutrients should be based on how high the natural levels are relative to the 

optimal or threshold nutrient concentrations (e.g., > 5 mg N/L). It should also be determined 

if the natural nutrient concentrations present are typical of the area or sporadic. If sporadic, 

biostimulation may still be appropriate when the nutrient levels fall to limiting values; if 

chronic, biostimulation may not be necessary. 

•	 Determine whether climatic or seasonal conditions are favorable for using bioremediation – 

Bioremediation may be more effective during warmer seasons, particularly in cold 

environments, since oil biodegradation rates are higher during these seasons. However, this 

does not necessarily mean that summer is the most favorable season. Because inorganic 

nutrient levels in salt marsh sediments often peak during the summer, biostimulation will not 

be effective if the nutrient content is no longer the limiting factor during warmer seasons. 

Prior exposure to oil will also be a favorable but not a solely determinative condition for 

selecting bioremediation. 

2.2 Treatment Selection and Design 

If biostimulation by nutrient addition is determined to be a potentially effective cleanup option based 

on the pretreatment assessments, further evaluation and planning are needed before its application. 

This step involves selection of the rate-limiting nutrients, determination of optimal nutrient 

concentrations and application strategies, and design of sampling and monitoring plans. 

28
2.2.1 Nutrient selection 

One of the first tasks during the stage of treatment selection and design would be to select 

appropriate nutrient products. The laboratory treatability tests, especially well-designed microcosm 

or mesocosms tests, are most commonly used approaches to determine the type and level of 

amendments. However, responders will likely not have time or resources to conduct a treatability 

study. This section, therefore, serves to support a reasonable approach to deciding which type of 

formulation to use. 

Screening and treatability tests that have been reported in the literature involve the determination of 

rate limiting nutrients as well as optimal forms of nutrient species. Nitrogen, phosphorus, or both can 

limit oil degradation in salt marshes. In a microcosm study, Jackson and Pardue (1999) found that 

nitrogen but not phosphorus was the rate-limiting nutrient for oil degradation in sediment from a 

Louisiana salt marsh. Wright et al. (1996, 1997) reported the opposite result for a mesocosm study 

where oil degradation was mainly limited by the concentration of phosphorus in sediment from a 

Texas salt marsh. 

The molecular form of nutrients is also important. For example, although both ammonium and 

nitrate are capable of enhancing oil degradation when nitrogen is a limiting factor, their 

effectiveness may differ depending on the type of oil and the properties of shoreline substrate. 

Jackson and Pardue (1999) found that addition of ammonium appeared to stimulate degradation of 

crude oil more effectively than nitrate in salt marsh soils in a microcosm study. The ammonium 

requirement was only 20% of the concentration of nitrate to achieve the same increase in 

degradation. The authors concluded that ammonium was less likely to be lost from the microcosms 

by washout due to its higher adsorptive capacity to sediment organic matter. A recently completed 

study at a salt marsh in Nova Scotia also showed that the ammonium spikes after nutrient addition 

were always substantially higher than the nitrate spikes, even though the only exogenous source of 

nitrogen was NH4NO3 (Table 1.1). The lower pore water nitrate concentrations can be attributed to 

the higher washout rate for nitrate and its loss through denitrification within the anoxic sediments. 

Under such circumstances, ammonium based nutrients may be superior to nitrate based nutrients 

because the nutrient dosage will be much lower when using ammonium than nitrate to achieve the 

same pore nitrogen concentration. However, this may not always be the case. Actually, the St. 

Lawrence River field study showed that the pore water nitrate concentrations were always higher 

than the ammonium concentrations after NH4NO3 was added (Venosa et al., 2002). This finding was 

attributed to the adsorption of NH4

+

 onto the negatively charged soil particles and its uptake by the 

root systems of the wetland plants. This result also suggests that the effects of nitrate washout and 

denitrification were less important in this fresh water marsh. 

Nutrient selection might also be influenced by temperature conditions. In a field study, Lee et al. 

(1993) investigated the efficacy of water-soluble inorganic fertilizers (ammonium nitrate and triple 

super phosphate) and a slow release fertilizer (sulfur-coated urea) to enhance the biodegradation of a 

waxy crude oil in a low energy shoreline environment. The results showed that at temperate 

conditions above 15°C, the slow-release fertilizer appeared to be more effective in retaining elevated 

nutrient concentrations within the sediments and more effective in enhancing oil degradation than 

water-soluble fertilizers. However, lower temperatures were found to reduce the permeability of the 

coating on the slow-release fertilizer and suppress nutrient release rates. Water-soluble fertilizers 

29
such as ammonium nitrate were then recommended under these temperature conditions. Based on 

the above discussion, it is recommended that, if temperature conditions allow use of slow-release 

fertilizer (i.e., temperatures in excess of 15°C), then that would be the preferred fertilizer to use in a 

salt marsh. If the temperature were lower, then ammonium nitrate would be appropriate. In either 

case, the amount of fertilizer to use should be based on maintenance of a minimal amount that would 

not limit biodegradation (i.e., something greater than about 5 mg N/L and 0.5 mg P/L). 

In addition to demonstrating the efficacy of nutrient products in enhancing oil degradation, it is also 

critical to demonstrate that bioremediation products have low toxicity and do not produce any 

undesired environmental and ecological effects, especially when applied to such sensitive 

ecosystems as salt marshes. Various toxicity test protocols have been discussed in part I as well as in 

the sandy shoreline and freshwater wetland guidance document (Zhu et al., 2001). A case study on 

the assessment of bioremediation treatment through monitoring biological responses in an oilcontaminated salt marsh will also be presented later in this document. 

2.2.2 Concentrations of nutrients needed for optimal biostimulation 

Since oil biodegradation largely takes place at the interface between oil and water, the effectiveness 

of biostimulation depends on the nutrient concentration in the interstitial pore water of oily 

sediments (Bragg et al., 1994; Venosa et al., 1996). The nutrient concentration should be maintained 

at a high enough level to support maximum oil biodegradation based on the kinetics of nutrient 

consumption. Higher concentrations will provide no added benefit but may lead to potentially 

detrimental ecological and toxicological impacts. 

Only a few studies have been reported on the optimal nutrient concentration in salt marsh 

environments. In a microcosm study using salt marsh sediment slurry, Jackson and Pardue (1999) 

found that oil degradation rates could be increased with increasing concentrations of ammonia in the 

range of 10 – 670 mg N/L, with most of the consistent rate increases occurring between 100 -670 mg 

N/L. They further proposed a critical nitrogen concentration range of 10-20 mg N/L. Harris et al. 

(1999) examined the nutrient dynamics during natural recovery of an oil-contaminated brackish 

marsh and found that there was an interdependency between the natural nutrient levels and the extent 

of oil degradation when the background nitrogen concentration in pore water declined from 40 mg 

N/L to 5 mg N/L. Evidence from bioremediation field studies also suggested that concentrations of 

approximately 5 to 10 mg/L of available nitrogen in the interstitial pore water is sufficient to meet 

the minimum nutrient requirement of the oil degrading microorganisms (Garcia-Blanco and Suidan, 

2001; Mills et al., 1997; See Section 2.1.2). As mentioned earlier, the threshold concentration range 

for optimal hydrocarbon biodegradation on marine shorelines is around 2 to 10 mg N/L based on 

field experiences on sandy beaches (Bragg et al., 1994; Venosa et al., 1996) and in an estuarine 

environment (Oudet et al., 1998). The apparent higher threshold nitrogen concentrations in salt 

marshes are mainly due to the lack of information with respect to oil biodegradation under lower 

nitrogen concentrations, since all the existing field studies were conducted in salt marshes with 

background nitrogen concentrations of at least 5 mg N/L (Garcia-Blanco and Suidan, 2001; Harris et 

al., 1999; Mills et al., 1997; Shin et al., 1999). Therefore, it is reasonable to recommend, as for other 

types of shorelines, that biostimulation of oil impacted salt marshes should occur when nitrogen 

concentrations of at least 2 to as much as to 5-10 mg N/L are maintained in the pore water with the 

decision on higher concentrations to be based on a broader analysis of cost, environmental impact, 

30
and practicality. In practice, a safety factor should be used to achieve target concentrations, which 

will depend on anticipated nutrient washout rates, selected nutrient types, and application methods. 

The safety factor used in salt marsh environments may generally be smaller than that used in higher 

energy beaches due to the reduced degree of nutrient washout expected in salt marshes. One needs 

always to keep in mind, however, that nutrient toxicity might exist if too much nutrient is applied to 

a coastal wetland (Mueller et al., 1999). The factors that lead to higher nutrient losses in wetland 

environments may also be important, such as sediment adsorption, plant uptake, and denitrification 

(if applicable). 

2.2.3 Nutrient application strategies 

Once the optimal nutrient concentrations have been determined, the next task is to design nutrient 

application strategies, which include nutrient application frequency and delivery methods. 

2.2.3.1 Frequency of nutrient addition 

The frequency of nutrient addition to maintain the optimal nutrient concentration in the interstitial 

pore water mainly depends on shoreline nutrient loss rates. A tracer study conducted on a lowenergy beach and a high-energy beach in Maine demonstrated the influence of shoreline types on 

nutrient washout rates (Wrenn et al., 1997a; Zhu et al., 2001)). The study shows that during spring 

tide, nutrients can be completely removed from a high-energy beach within a single tidal cycle. But 

it may take more than two weeks to achieve the same degree of washout from a low-energy beach. 

Washout during the neap tide can be much slower because the bioremediation zone will be only 

partially covered by water during this period. Salt marshes are low-energy systems and nutrient 

washout rates in such environments should be similar to the observations made on the low energy 

beach in the Maine study. In salt marshes, the washout rates may be further reduced when using 

ammonium-based nutrients due to their higher affinity to adsorb onto the sediment as compared to 

nitrate-based fertilizers (Jackson and Pardue, 1999). Therefore, weekly to monthly additions may be 

sufficient for biostimulation of salt marshes when the nutrients are applied during neap tide. It is 

even possible that only one nutrient dose is required for the bioremediation of some coastal marshes. 

A study on the nutrient dynamics in an oil contaminated brackish marsh showed that it took more 

than one year for nutrient concentrations to decrease to background levels after being naturally 

elevated by flooding and perturbations due to the spill (Harris et al., 1999). However, this may not 

be truly indicative of nutrient application dynamics, since exogenous nutrients were not added in this 

case. Nutrient sampling, particularly in sediment pore water, must be coordinated with nutrient 

application to ensure that the nutrients become distributed throughout the contaminated area and that 

target concentrations are being achieved. The frequency of nutrient addition should be adjusted 

based on the nutrient monitoring results. 

2.2.3.2 Methods of nutrient addition 

Nutrient application methods should be determined based on the characteristics of the contaminated 

environment, physical nature of the selected nutrients, and the cost of the application. In many 

intertidal environments, particular high-energy shorelines, the primary consideration in developing 

and selecting a nutrient application method has been how to overcome the washout problems. Many 

attempts have been made in this regard, including the use of slow release and oleophilic fertilizers 

31
(Prince, 1993) and the subsurface application of nutrients (Wise et al., 1994). However, since 

nutrient washout in coastal wetland environments is relatively slow, the more important 

considerations in such cases should be on the use of less expensive and less environmentally 

intrusive application methods. As discussed in the sandy shoreline and freshwater wetland guidance 

document (Zhu et al., 2001), current experience indicates that surface application of dry granular 

fertilizer (either slow-release or water-soluble) to the impact zone at low tide is probably the most 

cost-effective and less environmentally intrusive way to control nutrient concentrations. 

2.2.4 Sampling and Monitoring Plan for Bioremediation Operations 

2.2.4.1 Important variables and recommended measurements 

Important variables to be monitored in an oil bioremediation project include the environmental 

factors that limit oil biodegradation rates (e.g., temperature, interstitial nutrient and oxygen 

concentrations), evidence of oil biodegradation (e.g., concentrations of oil and its components), 

microbial activity (e.g., bacterial numbers and activity), and toxicological effects. Primary variables 

recommended for monitoring of bioremediation field programs in coastal wetland environments are 

listed in Table 2.1. 

If pretreatment assessments determine that oil biodegradation in the field is likely to be limited by 

nutrient rather than oxygen availability, pore water nutrient analysis becomes one of the most 

important measurements in developing proper nutrient addition strategies and assessing the effect of 

oil bioremediation. The frequency of nutrient sampling must be coordinated with nutrient 

application. This is to make certain that (1) the treatment is reaching and penetrating the impact 

zone, (2) target concentrations of nutrients are being achieved, and (3) toxic nutrient levels are not 

being reached. The location from which nutrient samples are collected is also important. Recent 

research on solute transport in the intertidal zone has shown that nutrients may remain in the beach 

subsurface for much longer periods than in the bioremediation zone (Wrenn et al., 1997b). Nutrient 

concentration profiles along the depth of the oil-contaminated region may be monitored by using 

multi-port sample wells or by the extraction of sediment samples collected from the oilcontaminated region (Venosa et al., 2002; Lee et al., 2001a). The sampling depth should be 

established from the results of site surveys to determine the maximum depth of oil penetration. To 

counter the inherent heterogeneity observed in field studies, a positive “margin of error” should be 

added to ensure that the samples will encompass the entire oiled depth throughout the project. The 

sampling depth must be modified if observations during the bioremediation application suggest that 

the depth of oil penetration has changed. 

The success of oil bioremediation will be judged by its ability to reduce the concentration and 

environmental impact of oil in the field. As discussed in Chapter 3 of the sandy shoreline and 

freshwater wetland guidance document (Zhu et al., 2001), to effectively monitor biodegradation 

under highly heterogeneous conditions, it is necessary that concentrations of specific analytes (i.e., 

target alkanes and PAHs) within the oil be measured occasionally using chromatographic techniques 

(e.g., GC/MS) and are reported relative to a conservative biomarker such as hopane. However, from 

an operational perspective, more rapid and less costly analytical procedures are also needed to 

satisfy regulators and responders on a more real time, continual basis. Existing protocols for the 

measurement of TPH, especially those using infrared absorption of Freon-extracts, are generally not 

32
reliable and have limited biological significance. Using GC/FID and integrating the area under the 

chromatogram is better. TLC-FID appears to be a promising screening tool for monitoring oil 

biodegradation (Stephens et al., 1999), although not enough experience is available to make any firm 

recommendations on its use at this time. 

As suggested in the foregoing paragraph, GC/MS operated in the selected ion monitoring mode 

(SIM) is the preferred method to use to assess the progress of biodegradation. One sampling per 

month of composited samples from the site analyzed by GC/MS should suffice to provide evidence 

that hydrocarbons are being biodegraded. To this end, normalization of biodegradable constituents in 

the oil to hopanes, steranes, and/or other potential biomarkers (e.g., highly substituted 4- or 5-ring 

PAHs like C4-chrysene) is essential to ensure that the disappearance observed is due to the 

bioremediation action rather than physical washout. Samples are normally extracted with 

dichloromethane and cleaned up using column chromatography prior to conducting the GC/MS. 

However, due to the expense and expertise involved with GC/MS analysis, more frequent analysis of 

TPH is appropriate to follow the temporal progress of treatment. It is suggested that at least one TPH 

sampling event per week be conducted at the spill site. Either the gravimetric or GC/FID method of 

TPH analysis should be used. Interpretation of chromatographic methods may be confounded by the 

presence of plant lipids and other biogenic compounds present in the environment; thus, care should 

be exercised in interpreting results. For example, plant lipids normally give rise to peaks in the 

chromatograms at retention times that coincide with odd-numbered higher molecular weight alkanes 

in the range of C25, C27, C29, C31, and C33. Thus, it is essential that the chromatogram of the spilled 

oil be known to compare to actual samples analyzed. 

In addition to monitoring treatment efficacy, the bioremediation monitoring plan should also 

incorporate reliable ecotoxicological endpoints to document treatment effectiveness for toxicity 

reduction. Commonly used ecotoxicity monitoring techniques, such as the Microtox® assay and an 

invertebrate survival bioassay, have also been summarized in the sandy shoreline and freshwater 

wetland guidance document (Zhu et al., 2001). These micro-scale bioassays may provide an 

operational endpoint indicator for bioremediation activities on the basis of toxicity reduction (Lee et 

al., 1995b). A summary of criteria for selecting an appropriate bioremediation endpoint based on 

both oil degradation and toxicity reduction has been presented in the sandy shoreline and freshwater 

wetland guidance document (Zhu et al., 2001). Examples for a salt-marsh study are presented in the 

following sections. 

33
Table 2.1 Monitoring plan for an oil bioremediation project in a coastal wetland environment 

Analysis Matrix Recommended Methods References 

*Dissolved nitrogen Sediment 

(interstitial 

pore water) 

Extract in acidified 0.1% NaCl. 

4500-NH3 H (Automated 

Phenate Method) and 

4500-NO3 

-

 F (automated Cdreduction) 

Eaton et al., 1995 

Page et al, 1986 

Dissolved phosphorus Sediment 

(interstitial 

pore water) 

Extract in acidified 0.1% NaCl. 

4500-P E (ascorbic acid method) 

Eaton et al., 1995 

Page et al, 1986 

*Residual oil 

constituents 

Sediment Extract into dichloromethane 

(DCM). 

Analyze components by GC/MSSIM 

Venosa et al, 1996 

*Total petroleum 

hydrocarbons 

Sediments Gravimetric analysis 

(dichloromethane extraction) or 

GC/FID analysis of DCM 

extracts. 

NETAC, 1993 

Redox and sulfide Sediment 

(interstitial 

pore water) 

Redox and sulfide electrodes ATI Orion,1991a,b 

*Dissolved oxygen of 

pore water 

Aqueous Hach® high range assay Hach Company, 

Loveland, CO 

pH of pore water Aqueous Potentiometric with combination 

electrode 

Page et al, 1986 

Microbial populations Sediment MPN for alkane and PAH 

degraders 

Genetic biomarkers 

Wrenn and Venosa, 

1996 

Macnaughton et al., 

1999 

Microbial activity Sediment Uptake/respiration of 

radiolabelled substrates. 

In-situ respiration 

Lee and Levy, 1989 

Prince et al, 1999 

*Toxicity of residual 

oil 

Sediment, 

pore water 

Biotests (e.g. Microtox Test, 

Amphipod survival test, MFO 

induction, etc.) 

See Section 1.3.5 

and 2.2.4.2 

Shoreline profile Contaminated 

site 

Intertidal/supratidal zone surveys 

using fixed benchmarks at the 

study site.(e.g., wells, plot 

boundary markers). 

Wrenn et al, 1997a,b 

* Critical measurements 

The sandy shoreline and freshwater wetland guidance document (Zhu et al., 2001) presents other 

important variables in a comprehensive monitoring plan, including site background conditions (e.g., 

oxygen, redox, pH, sediment grain size, and temperature) and shoreline profiles. Oxygen availability 

34 
is crucial for rapid bioremediation since hydrocarbon biodegradation is primarily an aerobic process. 

Although the pretreatment assessments may have determined that oxygen availability might not be a 

serious concern for the on-going project, oxygen limitation is always a potential problem in a 

wetland environment. Therefore, dissolved oxygen (DO) in the pore water should be monitored on a 

regular basis. The frequency of DO sampling should also be coordinated with nutrient application, 

particularly when organic nutrients are used (Lee et al., 1995b; Sveum and Ramstad, 1995; See 

Section 4.1.3), to insure that anoxic conditions do not result. When available oxygen does become 

limiting, the nutrient dosage and application frequency should be adjusted accordingly. Monitoring 

oil penetration and analyzing redox potential and sulfide concentrations with depth of wetland 

sediments will assist in determining whether oil has penetrated into the anoxic zone during the 

process of bioremediation. This assessment can also be used as a criterion in determining treatment 

endpoints. 

Measurement of pH in the pore water is also important in monitoring oil bioremediation. 

Biodegradation of oil in marine environments is optimal at a pH of about 8 (Atlas and Bartha, 1992). 

The pH of seawater is usually around 8.5, which is adequate to support rapid oil biodegradation. For 

accurate interpretation of field data, analysis of sediment grain size should be conducted to verify 

study site homogeneity. 

2.2.5 Environmental assessment of an oil-contaminated salt marsh: a case study 

Since environmental assessment is a relatively new approach in evaluating the effectiveness of oil 

bioremediation treatments, a case study outline is presented as a means to provide operational 

guidance to spill responders. This example is based on a controlled oil spill field trial recently 

conducted in a salt marsh at Conrod’s Beach, Nova Scotia, Canada, to determine if bioremediation 

by nutrient enrichment or phytoremediation by enhanced plant growth would accelerate the rates of 

residual oil loss and habitat recovery. The experimental design and bioremediation performance with 

respect to oil biodegradation has been reviewed (Section 1.3.3). Standard bioassessment and biotest 

procedures (Section 1.3.5) were used to quantify the rates of habitat recovery and to identify 

detrimental treatment effects (e.g., toxicity of the bioremediation agent or oil degradation byproducts). The overall success of the remedial operations was based on the integration of results 

from a suite of assays, which were chosen on the basis of ecological relevance to the site of concern, 

cost considerations, and the availability of technical expertise (Venosa and Lee, 2002). 

35
2.2.5.1 Bioassessments. 

2.2.5.1.1 Recovery of vegetation. Growth (biomass) of the predominant plant species (Spartina 

alterniflora) within the salt marsh was significantly suppressed by oiling, and recovery was not 

observed during the first growing season. While initial results showed some recovery in all oiled 

plots in the following spring, there was also evidence of changes in species composition within the 

treated plots. Another opportunistic plant species that was more tolerant to the altered site conditions 

increased its percentage of cover. By the end of the second growing season, the treated plots showed 

substantial evidence of recovery in the sections of the plots that were not removed by sampling. 

2.2.5.1.2 Microbial responses. 

•	 Oil degradation potential. Potential hydrocarbon degradation rates of representative alkane 

and PAH components within sediment samples were determined by quantifying the 

respiration rate of added 14C-labelled hexadecane and 14C-labelled phenanthrene as 

representatives of n-alkane and PAH class components within the test oil (Lee and Levy, 

1989, Caparello and LaRock 1975, Walker and Colwell, 1976). Time-series changes (Week: 

4, 7, 9, 12, 16, 20) in the turnover time of these specific tracers were calculated with the 

actual concentrations of residual hexadecane and phenanthrene in each sample determined 

by GC/MS to account for dilution by the unlabelled fraction of the specific substrates under 

study. 

Results of the added 14C-labeled hexadecane studies clearly illustrated the stimulation of 

indigenous organisms with the potential to degrade alkanes within the first 10-weeks after 

the application of oil (Figure 2.2). The lower the turnover time, the greater is the stimulatory 

effect (lower turnover times mean higher biodegradation rates). A stimulatory effect on 

potential hexadecane degradation rates by the addition of nutrients to unoiled sediments was 

also observed. However, within the oiled sediments, remedial treatments based on nutrient 

additions did not appear to cause a stimulatory effect that could be adequately resolved by 

measurement of hexadecane respiration rates. Natural attenuation (Treatment C: oil without 

nutrients in the figure) appeared to be relatively effective. These radiotracer studies are in 

agreement with detailed chemical analysis that showed that 87% of the target n-alkanes were 

degraded in the test sediments within 20 weeks. Similar observations were made for the 

biodegradation of PAHs (represented by phenanthrene, a 3-ringed polycyclic aromatic 

hydrocarbon) with the exception that nutrient amendments to the unoiled control sediments 

had no stimulatory effect (Figure 2.3) as contrasted with the hexadecane results. These 

observations are in full agreement with the corresponding field studies on microbial growth 

by MPN analysis. It was noted that besides oil, the addition of nutrients to unoiled plots also 

resulted in an increase in the number of potential n-alkane degraders by two orders of 

magnitude with respect to background levels. Only oiled plots showed an increase in the 

number of PAH degraders. 

•	 Denitrification activity. Denitrification is a primary process that regulates the nitrogen cycle 

in wetland sediments (Figure 1.1). Microbial denitrification activity was monitored on each 

sampling occasion by placing a gas chamber on each plot and taking headspace samples over 

a 30-minute period, which were subsequently analyzed for nitrous oxide, an intermediate in 

36
the denitrification of nitrate. The seasonal average denitrification activity, plotted against 

treatment type showed that in all cases where nutrients were applied (Treatments D = oil + 

nutrients, E = oil + nutrients + cut plants, F = oil + nutrients + disking), there was a net 

positive denitrification potential (Fig. 2.4). Natural attenuation (Treatment C: oil without 

nutrients) and Treatment A (unoiled control) showed a net negative denitrification potential. 

These results indicate that nutrient application resulted in increased denitrification activity in 

the sediments. 

Turnover Time (Days) 

900

800

500

400

300

200

100

0 

4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 

Control Control Oil Oil Oil Oil 

Nutrients Nutrients Nutrients Nutrients 

Cut Disking 

Figure 2.2. Average turnover time of hexadecane. Error bars = 1 standard error. 

37 
Turnover Time (Days) 

30000

20000

10000

400

300

200

100

0

4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 4 7 9 12162062 4 7 9 12162062

Control Control Oil Oil Oil Oil 

Nutrients Nutrients Nutrients Nutrients 

Cut Disking 

Figure 2.3. Average turnover time of phenanthrene. Error bars = 1 standard error. 

38
Nitrous oxide fluxes (g N ha -1 d-1) 

800

600

400

200

C 

A

0 

D E F B 

-200

-400

ANOVA (P = 0.019) 

-600 Error bars = SEM

Nutrients 

Figure 2.4. Seasonal average in denitrification activity with different treatments from Conrod’s 

Beach sediments from June to November, 2000. Letter designations are the same as in Figure 2.2. 

•	 Structural deformity of Foraminifera. For ecological relevance in the monitoring of potential effects 

in contaminated environments, it is preferred to use native (indigenous) species as indicators. In this 

study, Foraminifera (forams), single-celled microorganisms (protozoa) that construct a shell from 

available mineral particles or secrete one of calcium carbonate or of silica, were found to be a unique 

indicator species, due to their sensitivity to residual oil. This is attributed to the fact that the process 

of forming their shell has been reported to be highly susceptible to certain types of environmental 

pollution resulting in deformities. Foram skeletons are also resistant to decay, and many are found as 

fossils. Having these properties, foram tests and deformities can be used to monitor the ecological 

effects of oil spills and treatments. 

39

Oil No oil 
The forams under observation at the study site were typically between 63-500 μm. They occurred in 

the sediment at an abundance of 400-4000 species per sample. Sediment samples (1 cm depth) were 

taken with a metal 10-cc core bi-weekly for the first two months and monthly for the last three 

months until the end of the study. The samples were sieved, processed, and analyzed under a 

stereomicroscope to determine the types of species, the number of living vs. dead, and normal vs. 

deformed populations. Preliminary results from the first study season suggest that the oil impacted at 

least one particular species of forams, Miliamina fusca, resulting in a high percentage of structural 

deformity in comparison to non-oiled specimens. Time-series studies can prove an estimate of the 

time required for natural attenuation or remedial treatments to reverse this biological effect. 

2.2.5.1.3 Bioassays. Establishing the actual exposure level of biota to residual oil is difficult. While 

chemical measures of oil in sediments, water, and tissues are routine, there is no guarantee that all 

biological organisms accumulate oil or its components equally or in proportion to environmental 

concentrations. Further, many of the components of oil such as alkanes and PAHs are metabolized, 

so that chemical analyses of tissue may not represent the true dose or dose rate. The key to sediment 

assessment is bioavailability since elevated concentrations of toxic compounds may not necessarily 

result in adverse effects to the organisms living within the sediments. The only means of measuring 

bioavailability is by measuring or determining biological response. Such testing has often involved 

measures of bioaccumulation (the ability of an organism to accumulate contaminants in tissues). 

However, because bioaccumulation is a phenomenon, not an effect (and can be relatively expensive 

to determine due to costly chemical analyses), emphasis has shifted towards indicative endpoints 

that are based on sediment toxicity tests, which are effects-based and relatively inexpensive. 

•	 Microtox solid phase test. In the Microtox® Solid Phase Test (AZUR Environmental, 1999; Lee et 

al., 1995b; Microbics Corporation, 1992), the bacterium, Vibrio fisheri, is exposed to test sediments. 

A significant decrease in bioluminescence relative to water-only controls is indicative of sediment 

toxicity. Toxicity levels are calculated as the concentration of sample that would result in a 50% 

reduction in luminescence (‘effective concentration,’ EC50). To account for interference from 

differences in sample grain size distribution, turbidity, and to a lesser extent, color of the sample 

dilutions, sample test results were compared with results from unoiled sediments from the 

immediate study area. 

Oil toxicity was evident on comparison of oiled with unoiled plots (Figure 2.5a). If one sets an 

arbitrary EC50 toxicity threshold at 1,000 mg/L [which Environment Canada uses in its regulations 

(Tay et al., 1997)], then even though there was a detrimental response observed in the control 

sediments treated with nutrients only, all unoiled sediment samples would be deemed non-toxic 

according to this guideline, while toxicity was identified following oil treatments (Fig. 2.5a). There 

is no implied suggestion that the 1,000 mg/L threshold is being or should be adopted by EPA. The 

threshold was reported as an example to demonstrate how one may utilize toxicity data in decisionmaking. On comparison of results, it appears that natural attenuation (the bars labeled Oil in the 

figure) could account for most recovery. By week 9, all treatments were non-toxic. The significance 

of natural attenuation was also illustrated by a comparison of the relative recovery of the plots using 

EC50’s for each treatment and sampling time normalized to the unoiled control (Fig. 2.5b). 

40
a

Normalized EC50 (%) EC50 (mg/L) 

13000 

12000 

11000 

10000 

9000 

8000 

7000 

6000 

5000 

4000 

3000 

2000 

1000 

140 

120 

100 

80 

60 

40 

20 

Control Control Oil Oi Oi Oil 

Nutrients Nutrients Nutrients Nutrients

Cut Disking 

Figure 2.5. Sediment toxicity for sediment samples from Conrod’s Beach, Nova Scotia, at weeks 0 

to 62, as reflected by (a) EC50 for experimental treatments and (b) EC50 normalized to the mean 

control value at each sampling time. Error bars = 1 standard deviation. 

41 

a 

l l 

0 

0 

16

b 

16

20 2062 62

02479

12

02479

12

02479

12

02479

12

02479

12

02479

12

02479

12

02479

12

02479

12

02479

12

02479

12

02479

1612

16

20 2062 6216 1620 2062 6216 1620 2062 6216 1620 2062 6216 1620 2062 62 
•	 Amphipod survival test. The Amphipod Test measured the effects of sediment samples on survival 

of sediment-dwelling Eohaustorius estuarius (Environment Canada, 1992). Both the mean percent 

survival and the mean weight of animals in each treatment were compared with mean percent 

survival and mean weight of amphipods in reference control sediments to determine if the treatments 

caused a significant decrease in organism survival or growth. The results are reported as percent 

mortality (Figure 2.6). Mortality was high in all of the oiled treatments, but it began to decrease by 

Week 12 largely as the result of natural processes. Addition of nutrients accompanied by disking 

appeared to cause the most rapid rates of detoxification (recovery) within the oiled plots as measured 

by this test. However, the results of chemical analyses (GC/MS) indicated that this observation 

could also be attributed to the physical removal of oil (enhanced dispersion with tides) mediated by 

disking operations. By Week 62, the difference between the disked plots and the natural attenuation 

plots was highly significant (32% vs. 5% mortality). 

100

90

80

Mortality (%)70 

60 

50 

40 

30 

20 

10 

0 0

27

122062

027

122062

027

122062

027

122062

027

122062

027

122062 

Oil

Control Control Oil Oil Oil 

Nutrients Nutrients Nutrients Nutrients 

Cut Disking 

Figure 2.6. Changes in sediment toxicity from 0 to 62 weeks as quantified by the Amphipod 

Survival Test. Error bars = 1 standard deviation 

•	 Gastropod survival. Although many organisms have been used as sentinels or bio-monitors of 

environmental contaminants (LeBlanc and Bain, 1997), there is still a need to identify and exploit 

alternative species that are sensitive and amenable to ecotoxicological testing. Mollusks are 

42
abundant and widely distributed, and their use as in situ bio-monitors has been on the rise (Lagadic 

and Caquet, 1998). Saltwater marshlands present unique restoration challenges following oil spills 

due to the sediment's high capacity for oil absorption, low oxygen content, fluctuating salinity, and 

tidal flow. The mud-snail, Ilyanassa obsoleta, an abundant detritovore inhabiting these marshlands, 

was evaluated for its suitability as a bio-monitor to assess the impacts or efficacy of the 

bioremediation treatments. It was selected for use as an in situ bio-monitor as it feeds on sediment 

detritus, algae and decaying organic matter within the wetland. Snails (n = 50/treatment/sampling 

time) were caged in 20 × 20 × 22 cm open mesh polypropylene baskets moored to the sediment 

surface of experimental plots. At the end of the second year, cages were recovered after being 

exposed to the experimental plots for 30, 60 and 90 days to evaluate effects on survival at the end of 

the second field season (Week 62). Healthy snails were also exposed for a 30-day period under 

laboratory conditions to test sediments recovered from the plots, and to determine survival rates. The 

mud snails did not survive long in captivity in the field, and laboratory exposures were erratic. 

Mortality in the field was likely due to environmental factors as mortality was high even in control 

cages. It is unlikely that anoxia due to crowding and/or eutrophic conditions was a factor since these 

snails are tolerant of anoxic conditions and can grow in dense aggregates. Mortality after 5 d 

exposure was generally higher for snails caged within the experimental plots amended with 

nutrients. This toxic response was attributed directly to the use of fertilizers. 

•	 Acute and chronic effects on fish. Fish biotests were performed with salt marsh sediments recovered 

from the experimental site at Conrod’s Beach, Dartmouth, Nova Scotia using euryhaline rainbow 

trout. Bioavailability was assessed by quantifying the extent of CYP1A (MFO enzyme, see Section 

1.3.5.2) induction (Guiney et al., 1997) in fingerling trout following 96 h exposures to test 

sediments. S-9 fractions from liver homogenates were prepared for the measurement of 

ethoxyresorufin-o-deethylase (EROD, CYP1A enzyme) activity (Hodson et al.,1996). Each 

bioassay included negative controls (water only), un-oiled sediment controls, and positive water 

controls (fish exposed to the compound ß-naphthoflavone, which is a model inducer). 

All data were analyzed after log transformation and the extent of induction calculated by 

normalizing to control activity, i.e. induction equaled activity of treated fish divided by activity of 

control fish, and hence had no units. The Mesa crude oil contained sufficient PAH to cause high 

levels of EROD induction in trout, as shown by a preliminary bioassay of clean sediments spiked 

with oil in the lab (10 mL oil/L of sediment). By diluting the spiked sediment with clean sediment, a 

clear exposure-dependent gradient of induction was found (Figure 2.7). The plateau of activity at the 

highest oil concentrations suggests acute toxicity (Hodson et al. 1996), likely due to the combined 

narcotic effects of all the components of oil. A similar effect was observed when oil was simply 

added to water (data not shown). The threshold concentration causing induction was about 0.1 mL 

oil/L of reference sediment (Figure 2.7). 

43
Figure 2.7. EROD activity of rainbow trout exposed to reference sediments spiked with oil. Error 

bars are 95% confidence limits while the shaded zone represents the 95% confidence limits of 

control activity. Numbers represent sample sizes. 

Study results showed that PAHs were bioavailable from Conrod’s Beach oiled sediments. While 

EROD induction was evident for fish exposed to sediments sampled 1 d after oiling, induction 

actually increased in July (50 d later) before decreasing somewhat in October (140 d; Figure 2.8). 

The initial low extent of induction may have been caused by oil toxicity. With higher oil 

concentrations, it is likely that EROD induction was inhibited, as was evident from the leveling-off 

of the exposure-response curve in the test of sediments spiked with oil in the lab (Figure 2.7). There 

did not appear to be a major effect of bioremediation treatments, with the possible exception of 

disking. Plots disked to aerate the sediment showed 45% lower EROD induction potency (p<0.05) 

than plots with or without nutrients (Figure 2.9). The plots with plants cut showed 44% lower 

induction potency, but the difference was just below the level of statistical significance. Disking may 

have reduced induction potency by facilitating the transport of oiled surface sediments into deeper 

underlying sediments, enhancing the dispersion of disturbed surface sediments by tides, and 

stimulating microbial activity by improving oxygen availability within the wetland sediments (Lee 

2000b). 

44
Figure 2.8. MFO induction in fish exposed to oiled sediments. Each point is the average of data 

pooled across all treatments. Error bars = 95% confidence limits. Numbers = sample size. 

Figure 2.9. Effect of experimental treatments on EROD induction of trout exposed to oiled 

sediments. Asterisk indicates induction was significantly lower than the highest activity. Error bars = 

95% confidence limits. N = 15/treatment. 

In summary, because there was a strong link between concentrations of PAHs in beach sediments 

and the extent of induction in exposed trout, the induction bioassay successfully tracked the changes 

over time in the concentrations and bioavailability of PAH and of the crude oil itself. Over the long 

term, we would expect that the relationship between induction and uptake of non-PAH hydrocarbons 

would weaken due to the differential rates of degradation and weathering of different components of 

oil. However, within the time frame of this study, it appears that both the bioremediation and 

phytoremediation treatments did not markedly affect the rate of PAH degradation. While there 

appeared to be a significantly greater loss of PAH from aerated sediments, the overall enhancement 

was less than two-fold, which is at the limit of detection of the induction bioassay for the sample 

sizes tested. 

45
Preliminary studies with eyed-eggs (about 15 d post fertilization) of trout also suggested that 

symptoms of Blue sac disease (BSD - characterized by yolk sac and pericardial edema, 

hemorrhaging, deformities, and induction of mixed function oxygenase enzymes) were more 

frequent in fish exposed to oiled than to un-oiled sediments (Zambon et al., 2000); indicating a risk 

to early life stages of species that spawn on tidal beaches. 

These laboratory bioassays with fish represent a ‘worst-case’ scenario as the test organisms could 

not avoid exposure to sediments that have been mixed, thereby destroying surface layers that might 

be depleted of oil due to weathering. The ratio of water to sediment was also fixed, which is very 

different from the situation in well-flushed tidal beaches. Finally, the test species is a useful model, 

but is not a beach spawner. Nevertheless, the model fish do provide a useful surrogate for other 

species, such as smelt, capelin, and herring that spawn on both freshwater and marine beaches or in 

marine littoral zones. In many estuaries, contaminated water is often not well mixed, but moves back 

and forth with the tide, thereby causing prolonged exposure of fish entrained in the water mass 

(Elson et al. 1972). As illustrated by the Exxon Valdez spill, eggs deposited in beach sediments 

cannot move and are also subject to continuous exposure. The utility of freshwater species as a 

surrogate for marine species might also be questioned. However, it is worth noting that eggs of pink 

salmon, a species closely related to rainbow trout, were exposed to oil from the Exxon Valdez 

because they were spawned in river mouth shoals (Marty et al. 1997). The eggs were bathed 

alternately in fresh and salt water as the tide rose and fell, so that an exposure of trout to oiled 

sediments in saline water is not entirely unrealistic. To resolve the uncertainties associated with 

assessing exposure and effects, it is clear that the next step is to refine and adapt bioassays for 

application in situ, using species endemic to the test sites. 

2.2.5.2 Risk assessment 

In this case study, overall sediment quality was determined from the integration of results from 

analysis of sediment chemistry, community structure, alteration of primary metabolic processes, and 

sediment toxicity. The results of detailed chemical analysis, bioassessments, and bioassay tests 

suggested that in the Conrod Beach study, natural attenuation was the primary process that reduced 

residual oil concentrations and toxic effects. The biotest results showed that the remediation 

strategies under evaluation, stimulation of bioremediation and phytoremediation activity by nutrient 

amendments and physical mixing (disking), were not highly effective in regards to restoration. It 

was also evident in the results of some biotests (e.g. Amphipod Survival Test, Microtox Test) that 

possible detrimental effects may be linked to the addition of fertilizers. 

It is imperative that one fully understands the various processes that may affect biotest endpoints. 

Failure of the Gastropod Survival Test to resolve differences in experimental treatments could be 

attributed to adverse environmental conditions that caused high levels of inherent variability within 

the test matrix. The Biotox Solid-Phase Flash Assay (Lappalainen et al, 1999) is currently being 

considered as a relevant adjunct (or alternative) test to the Microtox solid-phase assay, since it 

allows the evaluation of large numbers of environmental samples at a more reasonable cost using the 

same test organism. This assay was used with success to provide evidence of toxicity reduction by 

remedial activities in an oil-impacted freshwater environment (Blaise et al., 2002). However, in this 

case study, all sediments collected during the first 2 sampling events (Week 0, 2) show marked and 

46
similar levels of toxicity. It is hypothesized that the assay was unable to discriminate between 

toxicity of oiled and unoiled sediments, as it was responding to the presence of natural contaminants 

present in the anaerobic sediments (e.g., NH3 and/or H2S) and possibly also to their degree of oil 

contamination (in the case of the oiled sediments). Similarly, the Algal Toxicity Test with 

Selenastrum capricornutum (Blaise and Ménard, 1998) that readily identified the inhibitory effects 

of residual oil in sediments on esterase enzyme activity in the previous freshwater marsh case study 

was ineffective in this test case. This was attributed to interferences associated with benthic diatom 

growth. This has necessitated the development of a new algal toxicity test using the marine macroalga Champia parvula to assess archived sediments from this study. 

With further refinement, guidelines for selection of bioassessment and bioassay test suites will be 

provided to oil spill response managers that are tasked to implement and verify the success of 

countermeasure operations including the extent of habitat recovery. For this case study in a marine 

salt marsh environment, the results of the ecological risk assessment with all available quantitative 

chemical and biological data suggest that natural attenuation may be the most environmentally sound 

and cost-effective treatment option. Although there was some evidence of changes in microbial 

community structure and activity, no significant differences were observed among treatments in oil 

degradation rates or toxicity reduction. Active remedial treatment is not supported by cost-to-benefit 

analyses. 

2.3 Summary and Recommendations 

Most of the information presented in this guidance document was based on only a few field studies 

of oil bioremediation. Not many studies have been done in a definitive manner. The Conrod Beach 

experiment in Dartmouth, Nova Scotia, demonstrated that biodegradation of the alkane fraction and 

some of the PAH fraction was stimulated following the application of inorganic fertilizers directly to 

the plots. Disking (or tilling) caused substantial damage to the rhizosphere, and such drastic 

measures cannot be recommended as a means of increasing oxygen content in the root zone. Not 

much can be done in that regard. Thus, if significant penetration has taken place into the subsurface, 

then not much hope of acceleration in hydrocarbon disappearance is possible since anaerobic 

conditions rapidly set in at greater depths. If, however, penetration is limited to the top several mm, 

then sufficient oxygen might be available to permit biostimulation to accelerate greater hydrocarbon 

disappearance than via natural attenuation. So, of major importance in the event of an oil spill in a 

salt marsh (or any wetland oil spill) is to assess the degree to which penetration has taken place 

below the surface. If it is minor, then biostimulation could be considered as a viable strategy for 

cleanup. If it is more than a few mm penetration, then biostimulation will have diminished 

effectiveness due to the increased likelihood of limiting oxygen concentration in the oil impact zone. 

Salt marshes are among the most sensitive ecosystems and, therefore, the most difficult to clean. 

Applications of some traditional oil spill cleanup techniques in wetland habitats have caused more 

damage than the oil itself. Several long-term field studies have been carried out in coastal wetlands 

to evaluate the potential of oil bioremediation, one of the least intrusive technologies. The studies 

have shown that oil biodegradation on coastal wetlands is often limited by oxygen, not nutrient 

availability. Natural attenuation is increasingly becoming the preferred strategy for the restoration of 

oil-contaminated wetlands. However, field studies also indicate that nutrient amendments may still 

be a viable option for removing hydrocarbons from an oil-contaminated wetland if the oil does not 

47
penetrate deeply into the anoxic zone of wetland sediments and when nutrients are limiting. When 

biostimulation is selected, it is recommended that nitrogen concentrations of at least 2 to as much as 

10 mg N/L should be maintained in the pore water to achieved optimal oil biodegradation, with the 

decision on higher concentrations to be based on a broader analysis of cost, environmental impact, 

and practicality. The overall success of the remedial operations should be not only based on the 

efficiency of oil degradation but also the integration of results from a suite of assays, which are 

chosen on the basis of ecological relevance to the site of concern, cost considerations, and the 

availability of technical expertise. 

48
3 REFERENCES 

Alexander, S.K. and Webb, J.W. (1987) Relationship of Spartina alterniflora growth to sediment oil 

content following an oil spill. Proceedings of 1987 International Oil Spill Conference. American 

Petroleum Institute, Washington, DC, pp 445-449. 

Alexander, S.K. and Webb, J.W. (1985) Seasonal response of Spartina alterniflora to oil. 

Proceedings of 1985 International Oil Spill Conference. American Petroleum Institute, Washington, 

DC, pp 355-357. 

Alexander, S.K. and Webb, J.W. (1983) Effects of oil on growth and decomposition of Spartina 

alterniflora. Proceedings of 1983 International Oil Spill Conference. American Petroleum Institute, 

Washington, DC. 

ATI Orion (1991a) Instruction manual platinum redox electrodes model 96-78-00 model 97-78-00. 

Orion Research Inc., Boston. 

ATI Orion (1991b) Model 94-16 silver/sulfide electrode instruction manual. Orion Research Inc., 

Boston. 

Atlas, R.M. and Bartha R. (1992) Hydrocarbon biodegradation and oil spill bioremediation. In K.C. 

Marshall (ed.), Advances in Microbial Ecology, Vol. 12, Plenum Press, NY, pp287-338. 

AZUR Environmental. (1999) MicrotoxOmni for Windows 95/98, ver. 1.18, CD-ROM. AZUR 

Environmental, Carlsbad CA. 

Bachoon, D.S., Hodson, R.E., Araujo, R. (2001) Microbial community assessment in oil-impacted 

salt marsh sediment microcosms by traditional and nucleic acid-based indices. Journal of Microbial 

Methods, 46, 37-49. 

Baker, J.M. (1999) Ecological effectiveness of oil spill countermeasures: how clean is clean? Pure 

Appl. Chem., 71(1), 135-151. 

Baker, J. M., Guzman, L. M., Bartlett, P. D., Little, D. I., and Wilson, C. M. (1993). Long-term fate 

and effects of untreated thick oil deposits on salt marshes. Proceedings of 1993 International Oil 

Spill Conference, American Petroleum Institute, Washington, D.C., pp. 395-399. 

Baker, J,M, Bayley, J.A., Howells, S.E., Oldham, J., Wilson, M. (1989) Oil in wetland. In B. Dicks 

(ed): Ecological Impacts of the Oil Industry, John Wiley & Sons Ltd, Chichester, U.K., pp 37-59. 

Banks, M.K., Govindaraju, R. S., Schwab, A. P., Kulakow, P., and Finn, J. (2000). Phytoremediation 

of Hydrocarbon-Contaminated Soil. Lewis Publishers, Boca Rotan, FL. 

Bergen, A., Alderson C., Bergfors, R., Aquila, C., Matsil, M.A. (2000) Restoration of a spartina 

alterniflora salt marsh following a fuel oil spill, New York City, NY. Wetlands Ecology and 

Management, 8, 185-195. 

49
Blaise, C., Gagné, F., Chèvre, N., Harwood, M., Lee, K., Lappalainen, J., Persoone, G., Chial, B. 

and Doe, K. 2002. Toxicity assessment of oil-contaminated freshwater sediments. J. Bioremediation 

(submitted). 

Blaise C and Menard L. (1998) A micro-algal solid-phase test to assess the toxic potential of 

freshwater sediments. Water Qual. Res. J. Can. 33, 133-151. 

Boorman, L.A. (1999) Salt marshes—present functioning and future change. Mangroves and Salt 

Marshes, 3, 227-241. 

Boufadel, M.C., Reeser, P., Suidan, M.T., Wrenn, B.A., Cheng, J., Du, X., Huang, T.L., Venosa, 

A.D. (1999a) Optimal nitrate concentration for the biodegradation of n-Heptadecane in a variablysaturated sand column. Environmental Technology, 20, 191-199. 

Burns, K.A., Codi, S., Duke N.C. (2000) Gladstone, Austrilia field studies: weathering and 

degradation of hydrocarbons in oiled mangrove and salt marsh sediments with and without the 

application of an experimental bioremediation protocol. Marine Pollution Bulletin, 41, 392-402. 

Burns, K.A., Codi, S., Swannell, R. P. J., Duke N.C. (1999) Assessing the oil degradation potential 

of endogenous micro-organisms in tropical marine wetlands. Mangroves and Salt Marshes, 3, 67-83. 

Burns, K.A. and Codi, S (1998) Contrasting impacts of localised versus catastrophic oil spills in 

mangrove sediments. Mangroves and Salt Marshes, 2, 63-74. 

Burns, K.A., Levings, S., and Garrity, S. (1993) How many years before mangrove ecosystems 

recover from catastrophic oil spills? Marine Pollution Bulletin, 26, 239-364. 

Caldwell, M.E., Garrett, R.M., Prince, R.C., Suflita, J.M. (1998) Anaerobic biodegradation of longchain n-alkanes under sulfate-reducing conditions. Environ. Sci. Technol., 32, 2191-2195. 

Caparello D. M. and P. A. LaRock (1975). A radioisotope assay for the quantification of 

hydrocarbon potential in environmental samples. Microbial Ecology 2, 28-42. 

Cartaxana, P., Cacador, I., Vale, C., Falcao, M., Catarino, F. (1999) Seasonal variation of inorganic 

nitrogen and net mineralization in a salt marsh ecosystem. Mangroves and Salt Marshes, 3, 127-134. 

Chapman, P. M. (1989) A bioassay by any other name might not smell the same. Environmental 

Toxicology and Chemistry 8 (7), 551. 

Coates, J.D., Woodward, J., Allen, J., Philip, P., Lovley, D.R. (1997) Anaerobic degradation of 

polycyclic hydrocarbons and alkanes in petroleum-contaminated marine harbour sediments. Appl. 

Environ. Microbiol., 63, 3589-3593. 

Cunningham, S.D., Anderson, T.A., Schwab, A.P., and Hsu, F.C. (1996) Phytoremediation of soils 

contaminated with organic pollutants, Advances in Agronomy, 56, 55-114. 

50
Delaune, R.D., Patrick, W.H. Jr. and Buresh, R.J. (1979) Effect of crude oil on a Louisiana Spartina 

alterniflora salt marsh. Environmental Pollution, 20, 21-30. 

Dowty, R.A., Shaffer, G.P., Hester, M.W., Childers, G.W., Campo, F.M., Greene, M.C. (2001) 

Phytoremediation of small-scale oil spills in fresh marsh environments: a mesocosm simulation. 

Marine Environmental Research, 52, 195-211. 

Driskell, W. B., Fukuyama, A. K., Houghton, J. P., Lees, D. C., Mearns, A. J. and G. Shigenaka, G. 

(1996) Recovery of Prince William Sound intertidal infauna from Exxon Valdez oiling and shoreline 

treatments, 1989 through 1992. American Fisheries Society Symposium 18, 362-378. 

Duke, N.C., Burns, K.A., Swannell, R. P. J., Dalhaus, O., Rupp, R.D. (2000) Dispersant use and a 

bioremediation strategy as alternate means of reducing impacts of large oil spills on mangroves: The 

Gladstone field trials. Marine Pollution Bulletin, 41, 403-412. 

Duke, N.C., Pinzon, Z.S., Prada, M.C. (1997) Large scale damage to mangrove forests following 

two large oil spills in Panama. Biotropica, 29, 2-14. 

Eaton, A.D., Clesceri, L.S., and, Greenberg, A.E. eds. (1995) Standard Methods for the Examination 

of Water and Wastewater, 19th Edition. American Public Health Association, Washington, DC. 

Elson, P.F., L.N. Lauzier and V. Zitko. (1972) A preliminary study of salmon movements in a 

polluted estuary. In: M. Ruivo (ed.), Marine pollution and sea life. Food and Agric. Org. of U.N., 

Fishing News (Books) Ltd., London. pp325-330. 

Environment Canada, (1992). Biological test method: Acute test for sediment toxicity using marine 

or estuarine amphipods, Report EPS 1/RM/26, Environment Canada, Ottawa, 83 p. 

Evans, C.W. (1985) The effects and implications of oil polution in mangrove forests. Proceedings of 

1985 International Oil Spill Conference. American Petroleum Institute, Washington DC, pp367-371. 

Feierabend, S.J., and Zelazny, J.M. (1987) Status Report on Our Nation’s Wetlands, National 

Wildlife Federation, Washington, DC. 

Field, D.W., Reyer, A.J., Genovese, P.V., and Shearer, B.D. (1991) Coastal Wetlands of the United 

States. National Oceanic and Atmosphere Administration and U.S. Fish and Wildlife Services, 

Washington DC. pp59. 

Fingas, M. (2001) The Basics of Oil Spill Cleanup. Lewis Publishers, Boca Raton, FL, p203. 

Frick, C.M., Germida, J.J., Farrell, R.E. (1999a) Assessment of Phytoremediation as an in-situ 

technique for cleaning oil-contaminated sites, Proceedings of the Phytoremediation Technical 

Seminar, Environment Canada, Ottawa, pp105-124. 

Frick, C.M., Germida, J.J., Farrell, R.E. (1999b), Assessment of Phytoremediation as an In-situ 

51
Technique for Cleaning Oil-contaminated Sites, Report prepared for the Petroleum Technology 

Alliance Canada (PTAC), University of Saskatchewan, Saskatoon, SK, 82 p. Available on-line (in 

pdf format373K) at:http://www.ag.usask.ca/departments/scsr/department/research/index.html. 

Frick , C.M., R.E. Farrell, and J.J. Germida. (1999c). PhytoPet: A Database of Plants That Play a 

Role in the Phytoremediation of Petroleum Hydrocarbons. Prepared for the Petroleum Technology 

Alliance of Canada, Calgary, AB (November 1999). University of Saskatchewan, Dept. of Soil 

Science, Saskatoon, SK. 

Frink, L, and Gauvry, G. (1995) Response to oiled wildlife in Tampa Bay. Proceedings of 1995 

International Oil Spill Conference. American Petroleum Institute, Washington DC. 

Gambrell, R.P., and Patrick, W.H. (1978) Chemical and microbial properties of anaerobic soils and 

sediments, in: Hooks and Crawford (Eds), Plant Life in Anaerobic Environments, Ann Arbor Sci. 

Pub. Inc., Ann Arbor, MI, pp375-423. 

Garcia-Blanco, S. and Suidan, M.T. (2001) Ecosystem Restoration of Oil-Contaminated Coastal Salt 

Marshes: Field Study. Research Report for USEPA, University of Cincinnati, Cincinnati, OH, in 

preparation. 

Garcia-Blanco, S., Suidan, M.T., Venosa, A.D., Huang, T., Cacho-Rivero, J. (2001a) Microcosm 

study of effect of different nutrient addition on bioremediation of fuel oil #2 in soil from Nova 

Scotia coastal marshes. Proceedings of 2001 International Oil Spill Conference. American 

Petroleum Institute, Washington DC. 

Garcia-Blanco, S., Motelab, M., Venosa, A.D., Suidan, M.T., Lee, K., King, D.W. (2001b) 

Restoration of the oil-contaminated Saint Lawrence River shoreline: Bioremediation and 

Phytoremediation. Proceedings of 2001 International Oil Spill Conference. American Petroleum 

Institute, Washington DC, pp. 303-308. 

Gauthier J. (2001) Bioremediation of a crude oil-contaminated riverine shoreline : Sediment toxicity 

assessment with ASPA an algal solid phase (direct contact) assay. Maurice Lamontagne Institute, 

Fisheries and Oceans Canada. 15p. 

Getter C.D. and Ballou, T.G. (1985) Field experiments on the effects of oil and dispersant on 

mangroves. Proceedings of 1985 International Oil Spill Conference. American Petroleum Institute, 

Washington DC, pp577-582. 

Gilfillan, E. S., Suchanek, T. H., Boehm, P. D., Harner, E. J., Page, D. S., and Sloan, N. A. (1995) 

Shoreline impacts in the Gulf of Alaska region following the Exxon Valdez oil spill. In: Exxon 

Valdez Oil Spill: Fate and Effects in Alaskan Waters. P. G. Wells, J. N. Butler and J. S. Hughes 

(eds.), American Society for Testing and Materials, Philadelphia, ASTM STP 1219. pp. 444-481. 

Greene, T.C. (1991) The Apex Barges Spill, Galveston Bay , July 1990. Proceedings of 1991 

International Oil Spill Conference. American Petroleum Institute, Washington DC, pp291-297. 

52
Guiney, P. D., R. M. Smolowitz, R. E. Peterson, and J. J. Stegeman. (1997) Correlation of 2,3,7,8-

tetrachlorodibenzo-p-dioxin induction of cytochrome P4501A in vascular endothelium with toxicity 

in early life stages of lake trout. Toxicology and Applied Pharmacology, 143, 256-273. 

Harris, B.C., Bonner, J.S., and Autenrieth, R.L. (1999) Nutrient dynamics in marsh sediments 

contaminated by an oil spill following a flood. Environmental Technology. 20, 795-810. 

Hester, M.W. and Mendelssohn, I.A. (2000) Long-term recovery of a Louisiana Brackish marsh 

plant community from oil-spill impact: vegetation response and mitigating effects of marsh surface 

elevation. Marine Environmental Research, 49, 233-254. 

Herricks, E. E. and Schaeffer, D. J. (1984) Compliance monitoring – Standard development and 

regulation enforcement using biomonitoring data. In: Freshwater Biological Monitoring, D. Pascol 

and R. W. Edwards (eds.), Pergammon Press, N.Y., pp. 153-166. 

Hodson, P.V., I. Ibrahim, A. Ewart, S. Zambon, and K. Lee. (2001) Bioavailability to fish of 

sediment PAH from an experimental oil spill. MS in prep. 

Hodson, P.V., S. Efler, J.Y. Wilson, A. El-Shaarawi, M. Maj and T.G. Williams. (1996) Measuring 

the potency of pulp mill effluents for induction of hepatic mixed function oxygenase activity in fish, 

Journal of Toxicology and Environmental Health, 49, 101-128. 

Jackson, A.W. and Pardue, J.H. (1999) Potential for enhancement of biodegradation of crude oil in 

Louisiana salt marshes using nutrient amendments. Water, Air, and Soil Pollution, 109, 343-355. 

Jackson, A. W. and Pardue, J.H. (1997) Seasonal variability of crude oil respiration potential in salt 

and fresh marshes. J. Environ. Qual., 26, 1140-1146. 

Jackson, A.W., Pardue, J.H., and Araujo, R. (1996) Monitoring crude oil mineralization in salt 

marshes: use of stable carbon isotope ratios. Environ. Sci. Technol., 30, 1139-1144. 

Krebs, C.T. and Tanner, C.E. (1981) Restoration of oiled marshes through sediment stripping and 

Spartina propagation. Proceedings of 1997 International Oil Spill Conference. American Petroleum 

Institute, Washington DC, pp386-390. 

Lagadic, L and Caquet, T., (1998). Invertebrates in Testing of Environmental Chemicals: Are They 

Alternatives? Environmental Health Perspectives, 106, 553-561. 

Lappalainen, J., R. Juvonen, K. Vaajasaari, and M. Karp. (1999) A new flash method for measuring 

the toxicity of solid and colored samples. Chemospshere 38, 1069-1083. 

Leahy, J.G.; Colwell, R.R. (1990) Microbial Degradation of hydrocarbons in the environment. 

Microbial Reviews, 53(3), 305-315. 

LeBlanc, G. A. and Bain, L. J., (1997) Chronic Toxicity of Environmental Contaminants: Sentinels 

53
and Biomarkers. Environmental Health Perspectives, 105, 65-79. 

Lee, K., Doe, K. G., Lee, L. E. J., Suidan, M. T., and Venosa, A. D. (2001a) Remediation of an oilcontaminated experimental freshwater wetland: Habitat recovery and toxicity reduction. 

Proceedings of the 2001 International Oil Spill Conference. American Petroleum Institute, 

Washington, DC. pp323-328. 

Lee, L. E. J., McDonald, A., Stassen, J., and Lee, K. (2001b). Effect of oil-spill bioremediation 

strategies on the survival, growth and reproductive success of the mystery snail, Viviparus 

georgianus. In: Environmental Toxicology and Risk Assessment: Science, Policy, and 

Standardization – Implications for Environmental Decisions: Tenth Volume, ASTM STP 1403, 

B.M. Greenburg, R.N. Hull, M.H. Roberts Jr., and R.W. Gensemer (eds.), American Society for 

Testing and Materials, West Conshohocken, PA., 2001. 

Lee, K. (2000a) In situ bioremediation of oiled shoreline environments. Opportunities for 

Advancement of Environmental Applications of Marine Biotechnology. Proceedings of the October 

5-6, 1999, Workshop. The National Research Council of the National Academy of Sciences and the 

National Academy of Engineering, National Academy Press, Washington, DC., pp. 44-60. 

Lee, K. (2000b) “Canadian Environmental Assessment Act. Screening Report: Evaluation of Salt 

Marsh Oil Spill Countermeasures”, Fisheries and Oceans Canada, Environment Canada, Ottawa, 

ON. 

Lee, K., Blaise, C. and Wells, P. G. (1998) Microscale testing in aquatic toxicology: Conclusions 

and future directions. In: Microscale Aquatic Toxicology: Advances Techniques and Practice, P.G. 

Wells, K. Lee and C. Blaise (eds.), CRC Press, Incorporated, pp647-652. 

Lee, K., Tremblay, G.H., and Gauthier, J., Cobanli, S.E., Griffin, M. (1997) Bioaugmentation and 

biostimulation: a paradox between laboratory and field results. Proceedings of 1997 International 

Oil Spill Conference. American Petroleum Institute, Washington DC, pp697-705. 

Lee, K., Tremblay, G.H. and Cobanli, S.E. (1995a) Bioremediation of oiled beach sediments: 

Assessment of inorganic and organic fertilizers., Proceedings of 1995 Oil Spill Conference. 

American Petroleum Institute, Washington, DC, pp107-113. 

Lee, K., Siron, R., Tremblay, G.H. (1995b) Effectiveness of bioremediation in reducing toxicity in 

oiled intertidal sediments. In Hinchee et al.(Eds): Microbial Processes for Bioremediation, Battelle 

Press, Columbus, OH, pp117-127. 

Lee, K., and Trembley, G. H. (1993). Bioremediation: Application of slow-release fertilizers on low 

energy shorelines. Proceedings of the 1993 Oil Spill Conference, American Petroleum Institute, 

Washington, D. C., pp449-454. 

Lee, K., and Levy, E. M. (1991). Bioremediation: Waxy crude oils stranded on low-energy 

shorelines. Proceedings of the 1991 Oil Spill Conference, American Petroleum Institute, 

Washington, D. C., pp541-547. 

54
Lee, K., and Levy, E.M. (1989) Enhancement of the natural biodegradation of condensate and crude 

oil on beaches of Atlantic Canada. Proceedings of 1989 Oil Spill Conference. American Petroleum 

Institute, Washington, DC, pp 479-486. 

Lee, K., and Levy, E.M. (1987) Enhanced biodegradation of a light crude oil in sandy beaches. 

Proceedings of 1987 Oil Spill Conference. American Petroleum Institute, Washington, DC, pp411­

416. 

Levings, S., Garrity, S., and Burns, K.A. (1994) The Galeta Oil Spill III. Chronic reoiling and long 

term toxicity of hydrocarbon residues in the mangrove fringes community. Estuarine Coastal and 

Shelf Science, 38, 365-395. 

Li, Y., Morris, J.T. and Yoch, D.C. (1990) Chronic low level hydrocarbon amendments stimulate 

plant growth and microbial activity in salt-marsh microcosms. J. Appl. Ecol., 27, 159-171. 

Lin, Q., Mendelssohn, I.A., Henry, C.B. Jr., Hester, M.W., and Web, E.C. (1999) Effect of oil 

cleanup methods on ecological recovery and oil degradation of Phragmites marshes. Proceedings of 

1999 Oil Spill Conference. American Petroleum Institute, Washington, DC. 

Lin, Q. and Mendelssohn, I.A.(1998) The combined effects of phytoremediation and biostimulation 

in enhancing habitat restoration and oil degradation of petroleum contaminated wetlands. Ecological 

Engineering, 10, 263-274. 

Lin, Q. and Mendelssohn, I.A.(1996) A comparative investigation of the effect of South Louisiana 

crude oil on the vegetation of freshwater, brackish, and salt marshes. Marine Pollution Bulletin, 32, 

202-209. 

Macnaughton S.J., Stephen, J.R., Venosa, A.D., Davis, G.A., Chang, Y. and White D.C. (1999) 

Microbial Population changes during bioremediation of an experimental oil spill. Applied and 

Environmental Microbiology, 65, 3566-3574. 

Marty, G. D., J. W. Short, D. M. Dambach, N. H. Willits, R. A. Heintz, S. D. Rice, J. J. Stegeman, 

and D. E. Hinton. (1997) Ascites, premature emergence, increased gonadal cell apoptosis, and 

cytochrome P4501A induction in pink salmon larvae continuously exposed to oil-contaminated 

gravel during development. Canadian Journal of Zoology, 75, pp 989-1007. 

Mearns, A. J., Venosa, A.D., Lee, K., Salazar, M. (1997) Field-testing bioremediation treating 

agents: lessons from an experimental shoreline oil spill. Proceedings of 1997 International Oil Spill 

Conference. American Petroleum Institute, Washington DC, pp707-712. 

Mearns, A., Doe, K., Fisher, W., Hoff, R., Lee, K., Siron, R., Mueller, C. and Venosa, A. D. (1995) 

Toxicity trends during an oil spill bioremediation experiment on a sandy shoreline in Delaware, 

USA. Proceedings of the 18th Arctic and Marine Oilspill Program (AMOP) Technical Seminar, 

Edmonton, Canada, June 14-16, 1995, pp1133-1145. 

55
Mendelssohn, I.A., Lin, Q., Debusschere, K., Henry, C. B., Overton, E.B., Penland, S., Rabalais, 

N.N. (1995) The development of bioremediation for oil spill cleanup in coastal wetlands: products 

impacts and bioremediation potential. Proceedings of 1995 International Oil Spill Conference. 

American Petroleum Institute, Washington DC. 

Microbics Corporation. (1992) Detailed Solid-Phase Test Protocol, in Microtox Manual – A Toxicity 

Testing Handbook, Vol. II, Detailed Protocols. Microbics Corporation, Carlsbad CA, pp. 153-178. 

Mille, G., Munoz, D., Jacquot, F., Rivet, L., Bertrand, J.-C. (1998) The Amoco Cadiz oil spill: 

evaluation of petroleum hydrocarbons in the Ile Grande salt marshes (Brittany) after a 13-year 

period. Estuarine, Coastal and Shelf Science, 47, 547-559. 

Mills, M.A., Bonner, J.S., McDonald, T.J., Page, C.A., and Autenrieth, R.L. 2003. Intrinsic 

bioremediation of a petroleum-impacted wetland. Marine Pollution Bulletin 46(7):887-899. 

Mills, M.A., Bonner, J.S., Simon, M.A., McDonald, T.J., Autenrieth, R.L. (1997) Bioremediation of 

a controlled oil release in a wetland. Proceedings of the 20st Arctic and Marine Oilspill Program 

(AMOP) Technical Seminar, Environment Canada, Ottawa, pp606-616. 

Mitsch, W.J. and Gosselink, J.G. (2000) Wetlands, John Wiley & Sons, Inc., New York. 

Mitsch, W.J. and Gosselink, J.G. (1993) Wetlands, Van Nostrand Reinhold, New York. 

Mueller, D.C., Bonner, J.S., Autenrieth, R.L., Lee, K., Doe, K. (1999) The toxicity of oil 

contaminated sediments during bioremediation of a wetland. Proceedings of 1999 International Oil 

Spill Conference. American Petroleum Institute, Washington DC. 

National Academy of Sciences (1985) Oil in the Sea: Inputs, Fates and Effects, National Academy 

Press, Washington DC. 

Neff, J. M. and Stubblefield, W. A. (1995) Chemical and toxicological evaluation of water quality 

following the Exxon Valdez oil spill. . In: Exxon Valdez Oil Spill: Fate and Effects in Alaskan 

Waters. P. G. Wells, J. N. Butler and J. S. Hughes (eds.), American Society for Testing and 

Materials, Philadelphia, ASTM STP 1219. pp. 141-177. 

NETAC (1993) Evaluation Methods Manual: Oil Spill Response Bioremediation Agents. National 

Environmental Technology Application Center, University of Pittsburgh, Pittsburgh, PA. 

Nixon, S.W., Kelly, J.R., Furnas, B.N., Oviatt, C.A. and Hale, S.S. (1980) Phosphorus regeneration 

and metabolism of coastal marine bottom communities. In K.R. Tenore and B.G. Coull (eds): Maine 

Benthic Dynamics, University of South Carolina Press, Columbia, SC, pp219-242. 

NOAA (1992) Shoreline Countermeasure Manual, National Oceanic & Atmospheric 

Administration, Seattle, Washington. 

Ortiz de Montellano, P. R. (1986) Cytochrome P450. Structure, Mechanism, and Biochemistry. 

56
Plenum Press, N.Y., 556 p. 

Oudet, J., Merlin, F.X., and Pinvidic, P. (1998) Weathering rates of oil components in a 

bioremediation experiment in estuarine sediments. Marine Environmental Research, 45(2), 113-125. 

Owens, E.H., Scienkiewicz, A.M., Sergy, G.A. (1999) Evaluation of shoreline cleaning versus 

natural recovery: the Metula spill and the Komi operations, Proceedings of 1999 International Oil 

Spill Conference. American Petroleum Institute, Washington DC. 

Owens, E.H. and Foget, C.R. (1982) A small river oil spill: a large step back for cleanup technology. 

Spill Technology Newsletter, Jan-Feb, 7-10. 

Page, C.A., Autenrieth, R.L., Bonner, J.S., and McDonald, T. (2001) Behavior of chemically 

Dispersed oil in a wetland environment. Proceedings of 2001 International Oil Spill Conference. 

American Petroleum Institute, Washington DC, pp821-823. 

Page, A.L., Miller, R.H., Keeney, D.R. (1986) Methods of Soil Analysis. Part II: Chemical and 

Microbial Properties, 2nd Edition. ASA (American Society of Agronomy and Soil Science Society 

of America). 

Pezeshki, S.R., Hester, M.W., Lin, Q., Nyman, J.A. (2000) The effects of oil spill and clean-up on 

dominant US Gulf coast marsh macrophytes: a review. Environmental Pollution, 108, 129-139. 

Pezeshki, S.R., Delaune, R.D., Nyman, J.A., Lessard, R.R., Canevari, G.P. (1995) Removing oil and 

saving oiled marsh grass using a shoreline cleaner. Proceedings of 1995 International Oil Spill 

Conference. American Petroleum Institute, Washington DC, pp203-209. 

Prince, R.C., R.E. Bare, R.M. Garrett, M.J. Grossmann, C.E. Haith, L.G. Keim, K. Lee, G.J. Holtom, 

P. Lambert, G.A. Sergy, E.H. Owens, and C.C. Guenette (1999) Bioremediation of a marine oil spill 

in the Arctic. In Situ Bioremediation of Petroleum Hydrocarbon and Other Organic Compounds, 

B.C. Alleman and A. Leeson (eds.), Battelle Press, Columbus, Ohio, USA. pp. 227-232. 

Prince, R.C. (1993) Petroleum spill bioremediation in marine environments. Critical Rev. Microbiol. 

19, 217-242. 

Purandare, J.A., Huang, T., Suidan, M.T., Johnston, B., Venosa, A.D., Pier, P. (1999) Microcosm 

study of bioremediation of oil-contaminated freshwater wetlands, Proceedings of 1999 International 

Oil Spill Conference. American Petroleum Institute, Washington DC. 

Ramsay, M.A., Swannell, R.P.J., Shipton, W.A., Duke, N.C., Hill, R.T. (2000) Effect of 

bioremediation on the microbial community in oiled mangrove sediments. Marine Pollution 

Bulletin, 41, 413-419. 

Randolph, R.C., Hardy, J. T., Fowler, S. W., Price, A. R. G., and Pearson, W. H (1998) Toxicity and 

persistence of nearshore sediment contamination following the 1991 Gulf War. Environment 

International, 24, 33-42. 

57
Rhykerd, R.L., Weaver, R.W., McInnes, K.J. (1995) Influence of salinity on bioremediation of oil in 

soil, Environmental Pollution, 90(1), 127-130. 

Sell, D., Conway L., Clark, T., Picken, G.B., Baker, J.M., Dunnet, G.M., McIntyre, A.D., and Clark, 

R.B. (1995) Scientific criteria to optimize oil spill cleanup, Proceedings of 1995 International Oil 

Spill Conference. American Petroleum Institute, Washington DC, pp595-610. 

Shin, W.S., Pardue, J.H., and Jackson, W.A. (2000) Oxygen demand and sulfate reduction in 

petroleum hydrocarbon contaminated salt marsh soils. Water Research, 34(4), 1345-1353. 

Shin, W.,S., Tate, P.T., Jackson, W.A., Pardue, J.H. (1999) Bioremediation of an experimental oil 

spill in a salt marsh. In Means and Hinchee (Eds): Wetlands and Remediation: An international 

Conference. Battelle Press, Columbus, OH, pp.33-40. 

Simon, M., Autenrieth, R.L., McDonald, T.J., Bonner, J.S.(1999) Evaluation of bioaugmentation for 

remediation of petroleum in a wetland. Proceedings of 1999 International Oil Spill Conference. 

American Petroleum Institute, Washington DC. 

Stephens, F.L. Bonner, J.S., Autenrieth, R.L. (1999) TLC/FID analysis of compositional 

hydrocarbon changes associated with bioremediation, Proceedings of 1999 International Oil Spill 

Conference. American Petroleum Institute, Washington DC. 

Suidan, M.T. and Wrenn, B.A. (2000) The Effect of Pulsed Applications of Ammonium-N or NitrateN on the Bioremediation of Crude-Oil-Contaminated Shorelines. Final Report for USEPA, 

University of Cincinnati, Cincinnati, OH. 

Sveum, P., Faksness, L.G., and Ramstad (1994) Bioremediation of oil-contaminated shorelines: the 

role of carbon in fertilizers. In R.E. Hinchee, B.C. Alleman, R.E. Hoeppel, and R.N. Miller (eds.), 

Hydrocarbon Bioremediation, Lewis Publishers, Inc., Boca Raton, FL. pp. 163-174. 

Sveum, P. and Ladousse, A. (1989) Biodegradation of oil in the Arctic: Enhancement by oil-soluble 

fertilizer application. Proceedings of 1989 International Oil Spill Conference. American Petroleum 

Institute, Washington DC, pp439-446. 

Swannell, R.P.J., Mitchell, D., Jones, D.M., Petch, S.P., Head, I.M., Willis, A., Lee, K., Lepo, J.E. 

(1999a) Bioremediation on oil contaminated fine sediments. Proceedings of 1999 International Oil 

Spill Conference. American Petroleum Institute, Washington DC, pp 751-756. 

Swannell, R. P. J., Mitchell, D., Lethbridge, G., Jones, D., Heath, D., Hagley, M., Jones, M., Petch, 

S., Milne, R., Croxford, R., and Lee, K. (1999b) A field demonstration of the efficacy of 

bioremediation to treat oiled shorelines following the Sea Empress Incident. Environmental 

Technology, 20, 863-873. 

Swannell, R.P.J., Lee, K., and Mcdonagh, M. (1996) Field evaluations of marine oil spill 

bioremediation. Microbiological Reviews, 60(2), 342-365. 

58
Tay, K.L., K.G. Doe, A.J. MacDonald, and K. Lee. (1997) Monitoring of the Black Point Ocean 

Disposal Site, Saint John Harbour, New Brunswick, 1992-1994. Environment Canada, Atlantic Region, 

Internal Report, ISBN: 0-662-25655-5, Cat.no. En40-214/9E, 133 pp. 

Teal, J.M., Farrington, J.W., Burns, K.A., Stegeman, J.J., Tripp, B.W., Woodin, B., and Phinney, C. 

(1992) The West Falmouth Oil Spill after 20 years: Fate of fuel oil compounds and effect on 

animals. Marine Pollution Bulletin, 24, 607-614. 

Teas, H.J., Lessard, R.R., Canevari, G.P., Brown, C.D., Glenn, R. (1993) Saving oiled mangroves 

using a new non-dispersing shoreline cleaner. Proceedings of 1993 International Oil Spill 

Conference. American Petroleum Institute, Washington DC. 

Teas, H.J., Lasday, A.H., Luque, L.E., Morales, R.A., Diego, M.E.D., Baker, J.M. (1989) Mangrove 

restoration after the 1986 Refineria Panama oil spill. Proceedings of 1989 International Oil Spill 

Conference. American Petroleum Institute, Washington DC, pp433-437. 

Tiner, R.W. (1984) Wetlands of the United States: Current Statue and Recent Trends. National 

Wetland Inventory, U.S. Fish and Wildlife Service, Washington, DC. 

Townsend, R.T., Bonner, J.S., Autenrieth, R.L.(1999) The effect of bioremediation on microbial 

populations in an oil-contaminated coastal wetland. Proceedings of 1999 International Oil Spill 

Conference. American Petroleum Institute, Washington DC. 

U.S. EPA (1999) Monitored Natural Attenuation of Petroleum Hydrocarbons, EPA 600-F-98-021, 

Office of Research and Development, U.S. Environmental Protection Agency. 

U.S. EPA (1978a) Protection, Cleanup and Restoration of Salt Marshes Endangered by Oil Spills: A 

Procedural Manual. EPA 600-7-78-220, Office of Research and Development, U.S. Environmental 

Protection Agency. 

U.S. EPA (1978b) Response of a Salt Marsh to Oil Spill and Cleanup: Biotic and Erosional Effects 

in the Hackensack Meadowlands, New Jersey. EPA 600-7-78-109, Office of Research and 

Development, U.S. Environmental Protection Agency. 

Venosa, A.D. and K. Lee. (2002) Introduction to the special section on freshwater wetland 

bioremediation and phytoremediation. Bioremediation J. 6(3): 257-259. 

Venosa, A. D., Lee, K., Suidan, M. T., Garcia-Blanco, S., Cobanli, S., Moteleb, M., Haines, J.R., 

Tremblay, G., and Hazelwood, M. (2002) Bioremediation and biorestoration of a crude oilcontaminated freshwater wetland on the St. Lawrence River. Bioremediation Journal, 6 (3), 261­

281. 

Venosa, A. D., Suidan, M. T., Wrenn, B. A., Strohmeier, K. L., Haines, J. R., Eberhart, B. L, King, 

D.W., and Holder, E. (1996) Bioremediation of experimental oil spill on the shoreline of Delaware 

Bay. Environmental Science and Technology, 30, 1764-1775. 

59
Venosa, A.D., Haines, J.R., and Allen, D.M. (1992) Efficacy of commercial inocula in enhancing 

biodegradation of crude oil contaminating a Prince William Sound beach. J. Ind. Microbiol., 10, 1­

11. 

Walker J. D. and R. R. Colwell (1976). Measuring potential activity of hydrocarbon degrading 

bacteria. Appl. Environ. Microbiol., 31, 189-197. 

Ward, D.M., and Brock, T.D. (1978) Hydrocarbon biodegradation in hypersaline environments. 

Appl. Environ. Microbiol., 35, 353-359. 

Watt, I., Woodhouse, T., and Jones, D. A. (1993) Intertidal clean-up activities and natural 

regeneration on the Gulf coast of Saudi Arabia from 1991 to 1992 after the 1991 Gulf oil spill. 

Marine Pollution Bulletin, 27, 325-331. 

Wells, P. G., Blaise, C., and Lee, K. (1998) Microscale Aquatic Toxicology: Advances Techniques 

and Practice, P.G. Wells, K. Lee and C. Blaise (eds.), CRC Press, Incorporated, 679pp. 

Wise, W.R., Guven, O., Molz, F.J., and McCutcheon, S.C. (1994) Nutrient retention time in a highpermeability, oil-fouled beach. J. Environ. Eng. 120, 1361-1379. 

Wolfe, D.A., Krahn, M. M., Casillas, E., Sol, S., Thompson, T. A., Lunz, J. and Scott, K. J. (1996) 

Toxicity of intertidal and subtidal sediments contaminated by the Exxon Valdez oil spill. American 

Fisheries Society Symposium, 18, 121-139. 

Wood, T.M., Lehman R.L., Bonner J. (1997) Ecological impacts of a wetland oil spill and 

bioremediation experiments, Proceedings of 1997 International Oil Spill Conference. American 

Petroleum Institute, Washington DC. 

Wordrop, J.A., Butler, A.J., and Johnson, J.E. (1987) A field study of the toxicity of two oils and 

dispersant on the mangrove Avicennia Marina. Marine Biology, 96, 151-156. 

Wrenn, B.A., Boufadel, M.C., Suidan, M.T., and Venosa, A.D. (1997a) Nutrient transport during 

bioremediation of crude oil contaminated beaches. In: In-Situ and On-Site Bioremediation: Volume 

4, Battelle Press, Columbus, OH, pp. 267-272 

Wrenn, B.A., Suidan, M.T., Strohmeier, K.L., Eberhart, B.L., Wilson, G.J., and Venosa, A.D. 

(1997b) Nutrient transport during bioremediation of contaminated beaches: Evaluation with lithium 

as a conservative tracer. Wat. Res., 31, 515-524. 

Wrenn, B.A. and Venosa, A.D. (1996) Selective enumeration of aromatic and aliphatic hydrocarbon 

degrading bacteria by a most-probable-number procedure. Can. J. Microbiol. 42, 252-258. 

Wright, A.L., Weaver, R.W. and Webb, J.W. (1997). Oil bioremediation in salt marsh mesocosms as 

influenced by N and P fertilization, flooding, and season. Water, Air and Soil Pollution, 95, 179-191. 

60
Wright, A.L., Weaver, R.W., Webb, J.W. (1996) Concentrations of N and P in floodwater and 

uptake of 15N by spartina alterniflora in oil-contaminated mesocosms. Bioresource Technology, 56, 

257-264. 

Zambon, S., N.M. Fragoso, S.P. Tabash, S.M. Billiard, and P.V. Hodson. (2000) The bioavailability 

and toxicity of sediment-borne retene, in Proceedings of the 21st Annual Meeting of the Society 

Environmental Toxicology and Chemistry, Nashville, TN, Nov. 12-16, 2000, Abstract PTA 083. 

Zhu, X., Venosa, A.D., Suidan, M.T., and Lee, K. (2001) Guidelines for the Bioremediation of 

Marine Shorelines and Freshwater Wetlands, Report under a contract with Office of Research and 

Development, U.S. Environmental Protection Agency. Available on-line at: 

http://www.epa.gov/oilspill/pdfs/bioremed.pdf 

Zobell, C.E. (1973) Microbial degradation of oil: Present statue, problems, and perspectives. In 

Ahearn and Meyers (Eds.), The Microbial Degradation of Oil Pollutants, Publication No. LSU-SG73-01, Louisiana State University, Baton Rouge, LA, pp3-16. 

61