Soil Bacteria Gobble Spilled Diesel Fuel
After the Exxon Valdez met Bligh Reef in spring of 1989, I was among hundreds of newly hired Alaskans who landed on the beaches of Prince William Sound. Using diaper-like cloths, we wiped crude oil off black, greasy rocks. Many of us shared a common thought about the never-ending task: "There must be a better way."
For many types of fuel spills, there is a better way: feed the contaminated soil to bacteria with a hunger for petroleum products. In a process called bioremediation, soil bacteria make a meal out of spilled oil and gasoline.
In theory, everybody wins: the bacteria are happy because they've gained energy from the fuels; humans are happy because the bacteria have transformed the toxic liquids into carbon dioxide and water, the same products we exhale.
Bioremediation is good, but it isn't perfect, according to Mark Tumeo, director of the Environmental Technology Laboratory at the University of Alaska Fairbanks. Tumeo is working on a bioremediation project at McMurdo Station, a research center on Antarctica.
The fuel-eating bacteria, known as Pseudomonas, have evolved a taste for hydrocarbons, the major component of fossil fuels. The molecular structure of a hydrocarbon can be visualized as a backbone-like string of carbon atoms bonded to a rib cage of hydrogen atoms.
Shaped like Tic-Tac breath mints, Pseudomonas are so tiny that 50 of them could line up bumper-to-bumper across the sharp edge of a piece of paper. A shovel-full of soil dug almost anywhere on Earth contains millions of them.
Tumeo found oil-eating Pseudomonas on a diesel spill between two storage tanks at McMurdo Station. Since no natural sources of oil have been found on Antarctica, Tumeo thinks the bacteria he found may have hitched a ride to the continent on an oil tanker. The multinational Antarctic Treaty prohibits exotic species from being introduced to the continent, but since Pseudomonas are already there, Tumeo is hoping to use them to clean up some of the fuel spills that have occurred since McMurdo Station opened in the 1950's.
His work, which is featured in a recent issue of the British journal New Scientist, involves 12 wooden boxes. Into some, he's added the following unsavory ingredients: a cubic foot of diesel-soaked soil, sewage, and surfactants, which are chemicals that break the surface tension of the soil to allow bacteria easier access to the diesel fuel. Tumeo's goal is to create an environment in which the bacteria thrive. At the South Pole, and in Alaska, this might include warming the soil, because at temperatures below freezing Pseudomonas work about as well as squirt guns. Other bacterial boosts include adding oxygen to soil to stimulate the aerobic creatures, and mixing in waste water to provide other nutrients.
After the different mixtures within Tumeo's 12 boxes have reacted for about a year, he should know under what conditions Pseudomonas work best in the Antarctic. If the bacteria work there, he said, they should work anywhere.
As amazing as fuel-eating bacteria are, they can't be counted on to clean up the next big oil spill, Tumeo said. Crude oil has components too thick, waxy and complicated for the bacteria to handle. Even though many fuel-stained soils have been cleaned by bacteria, the number of factors effecting their performance makes bioremediation an inexact, though promising, science.
In the mid-80s, bioremediation was seen as the "silver bullet," by which many hoped to clean all contaminated soil problems, Tumeo said. But, alas, it's not that simple.
"We all want an easy solution to difficult problems," Tumeo said. "But unfortunately we live in a very complex world."
