Issues Magazine

Petroleum and Polar Pollution

By Kathryn Mumford and Geoff Stevens

The Arctic and Antarctic often conjure images of pristine expanses of ice and snow, with unique flora and fauna. The unfortunate reality is not nearly as romantic: amid the rare wildlife and extreme conditions, human activities have left a legacy of contamination.

Oil and fuel contaminants are among the most extensive and environmentally damaging pollution problems in polar regions. As well as the immediate negative impact on the sensitive sea and land environments, fuel from spills in polar regions remains for 10–100 years longer than in temperate regions. Low nutrient contents, cold temperatures and dry conditions all preclude the presence of microbial populations that could otherwise degrade the hydrocarbons found in spilled fuel. If significant ongoing environmental damage from spills is to be prevented, intervention is critical.

In the Arctic, the largest source of terrestrial petroleum pollution occurs from ruptured pipelines originating in the Arctic oil fields. These fields have been estimated to contain 5% of the world’s oil. The concentration of petroleum contaminants in Antarctica is lower than Arctic areas because the Madrid Protocol prohibits all Antarctic Treaty member nations from mineral resource activities. However, most research station activities and fuel spills occur on the summer ice-free areas – the same areas in which rare mosses and lichens grow and where Antarctic mammals breed – so these spills still have significant impact.

To date, site remediation in Antarctica has generally involved bulk excavation, exportation and dumping of contaminated material in hazardous landfills. For many countries that occupy Antarctic regions, this process has proven prohibitively expensive. Given site disturbance and the ensuing contaminant mobilisation, site caretakers have concluded that excavation would equal or exceed the damage caused by the initial spill. Under the Madrid Protocol, they are therefore not obliged to act. Unfortunately, alternative remediation technologies are scarce, and so many of these sites and spills continue to damage this sensitive environment.

Likely factors key to this lack of options include the high cost of technological development, uncertainty about adequate performance in such extreme environments, isolation from populated areas and therefore lack of public pressure to clean up the contamination, and the lack of governance over all parties to the obligations under the Madrid Protocol. The development of a remediation system that is easy to deploy, proven and cheap is highly desirable, in particular to entice managers to implement them on their sites.

Researchers at the Australian Antarctic Division, the University of Melbourne and Macquarie University have been developing cost-effective and simple on-site technologies for soil remediation that are suitable for Antarctic conditions. One of these, permeable reactive barriers, removes and (depending on system design) degrades dissolved contaminants from polluted water. Reactive materials halt the moving contaminant plume and, to promote degradation processes, contain components that stimulate the activity of naturally residing microorganisms. This passive treatment technology can be applied and adapted to any site, including those contaminated with heavy metals.

A “funnel and gate” sequential permeable reactive barrier was installed at a fuel plume at Casey Station in Antarctica in 2006. Two high hydraulic conductivity wings funnelled contaminated water through the reactive zone (the gate). The base of the barrier was placed within the permafrost (soil that has been continuously frozen for a minimum of 2 years) to prevent movement of groundwater underneath.

In this design, the entire contaminant plume has to pass through the reactive material of the “gate”, halting further migration of the fuel. The added nutrients and heat stimulate the activity of naturally present hydrocarbon-degrading bacteria, which metabolise the contaminant fuel to carbon dioxide and water.

This system effectively utilises natural processes and eliminates the need to dig up the entire contaminated site, resulting in significant cost savings.

The reactive material selected to do this work is also relatively inexpensive because it is all derived from natural products. It allows the barrier to:

• prevent further movement of petroleum hydrocarbons: The material selected for hydrocarbon sorption was granulated activated carbon. Derived from coconut husks, its ability to “soak up” hydrocarbon is due to its very high surface area (500–1500 m2/g), which can be related to its microporous structure and a high degree of surface reactivity. Sample cores have indicated that, after 6 years of operation, breakthrough of the permeable reactive barrier has not occurred;

• deliver nutrients in a controlled fashion to stimulate microbes that will break down hydrocarbons: Delivering the best concentration of nutrients in a controlled manner is paramount, and it depends on hydrocarbon concentrations, microbe populations, soil water characteristics and soil type. To achieve this, we used a zeolite coated with calcium phosphate. The calcium phosphate dissolves, slowly releasing the important nutrient phosphorus; and

• be mechanically stable under freeze thaw: When wet material is frozen and thawed multiple times, particles often break down. To ensure the mechanical integrity of our selected material, we conducted many trials using different particle sizes.

The permeable reactive barrier is currently in its sixth year of operation, with very positive results. The reactive materials selected have successfully bound contaminants, delivered nutrients in a controlled fashion and supported microorganism growth. Fuel has been degraded within the barrier itself.

This technology has been adopted by companies and researchers in the Northern Hemisphere, and the research team is currently working towards adapting this technology to metal-contaminated sites.