1 Bioremediation of Marine Oil Spills Matt Radermacher ABSTRACT Bioremediation of marine oil spills has become a very practical approach to oil spill cleanup efforts in recent years. The tragic Exxon Valdez oil spill in 1989, informed the United States of the lack of preparedness the oil industry and country had in such remediation situations. This catastrophe did however spark further research into the use of bioremediation for marine oil spills, which has proved to be an effective method. Bioremediation for marine oil spills can be approached in two different ways depending on the case at hand. This includes bioaugmentation which involves introducing oil degrading microorganisms to the affected site, and also biostimulation which involves adding supplemental nutrients to the affected site to aid the existing oil degrading microorganisms. Although bioremediation is a new technology, there is continuous research underway which is investigating the practicality and efficiency of this process. There have been downsides found for using bioremediation for marine oil spills, however there are many benefits which make this a feasible technology. KEYWORDS Bioremediation, bioaugmentation, biostimulation, oil spill, oil degrading microorganism, hydrocarbon INTRODUCTION Marine oil spills are very catastrophic events which pose a great threat on the affected environment. Although it is often believed that oil spills affecting marine environments are primarily the result of large oil tanker spills such as the Exxon Valdez incident, most of the oil contamination that occurs is due to surface runoff, the transportation of oil, port activity, and illegal bilge water discharges (Suni et al., 2007). Oil is comprised of many different toxic compounds which endanger the natural habitat involved in the spill, however there are many natural, native microorganisms which are not only capable, but thrive on the decomposition of these toxic compounds. This process of using microorganisms for such cleanup efforts is known as bioremediation and this has proven to be a successful method for the cleanup of marine areas affected by oil spills (Coulon et al., 2006). There are many different approaches which can be taken in the cleanup process, with bioremediation being a very beneficial method. Traditional methods of oil spill cleanup include using mechanical devices such as skimmers and oil booms, however these are very expensive and labor intensive processes. It is found that combining these traditional approaches with bioremediation can allow for a much more successful cleanup process while also reducing cost, as well as man hours. Bioremediation can consist of adding these hydrocarbon degrading organisms to the affected environment, which is known as bioaugmentation, and it can also consist of adding nutrients to the affected site which enhances the biodegradation process of the existing hydrocarbon degraders, and this is known as biostimulation. Bioremediation is a new process and is often questioned as reliable due to uncontrollable variables in an oil spill, such as the composition of the oil, the indigenous microorganisms present at the site, the water characteristics such as temperature and energy, and also the available nutrients at the affected site. Research has been conducted and is still underway, regarding how these different parameters affect bioremediation and its practicality. Research, as well as actual applications to marine oil spills, has shown that bioremediation has many advantages and great potential for many different oil spill cases, however there are also disadvantages, making bioremediation not the best method of cleanup for all marine oil spills.2 BIOREMEDIATION Bioremediation is defined as the use of natural microorganisms, plants, or fungi in the correction of a contaminated or altered environment. Bioremediation for the use of oil spill cleanup is either undergone by bioaugmentation or biostimulation. Bioaugmentation is the addition of microorganism capable of degrading the toxic hydrocarbons, in order to achieve a reduction of the pollutants. Biostimulation is the addition of nutrients needed by indigenous hydrocarbon degrading microorganisms in order to achieve maximum degradation of toxic compounds present in the oil. The degradation of hydrocarbons begins by the conversion of the alkane chain or polycyclic aromatic hydrocarbon (PAH) into an alcohol. Oxidation then converts the compound to an aldehyde and then into an acid and eventually into water, carbon dioxide, and biomass. In the case of the PAH, fission occurs which ultimately leads to mineralization (Venosa). Figure 1: Hydrocarbon Degrading Microorganisms (Zhu et al., 2001) Biostimulation, the addition of nutrients, is practiced for marine oil spill cleanup when there is an existing population of oil degrading microbes present. When an oil spill occurs, the result is a large increase in carbon and this also stimulates the growth of the already present oil degrading microorganisms. However, these microorganisms are limited in the amount of growth and remediation that can occur by the amount of available nitrogen and phosphorus. By adding these supplemental nutrients in the proper concentrations, the hydrocarbon degrading microbes are capable of achieving their maximum growth rate and hence the maximum rate of pollutant uptake. It has been found that when using nitrogen for the supplemental nutrient, a maximum growth rate is achieved by the oil degrading microorganisms at a concentration of 2.0 mg/L (Boufadel et al., 2006). Biostimulation has been proven to be an effective way of achieving increased hydrocarbon degradation by the indigenous microbial population (Coulon et al., 2006). An important factor in achieving successful biostimulation, is obtaining this ideal concentration of nutrients needed for maximum growth of the Figure 2: Pseudomonas Fluorescens (Marinebiotech.org)3 organisms, and keeping this concentration present for the organisms as long as possible. This can become a difficult situation based upon where the nutrients are applied and also because of physical influences, such as differences in densities, wave movements, and tidal influences (Boufadel et al., 2006). When the applied nutrients are dissolved in the water, the nutrients move along with the water and the sand and this movement can vary on the conditions of the site. Tracer studies are often used to