CORVALLIS, Ore. -- Oregon Sea Grant researchers at Oregon State University (OSU) are testing a novel approach to reducing chemical pollution: They're using lowly seaweeds.
In an ongoing Sea Grant project, Gregory L. Rorrer, a professor in OSU's Department of Chemical Engineering, is studying whether the metabolic processes of certain marine seaweeds can be harnessed to break down a class of pollutants into less toxic constituents.
"We're trying to understand how these pollutants interact with a large class of marine macro-organisms in the environment," Rorrer said.
The pollutants, polycyclic aromatic hydrocarbons (PAHs), are naturally released into the environment by forest fires and volcanic eruptions. However, a greater volume is formed by the incomplete combustion of petroleum fuels.
PAHs are commonly found in low concentrations in the sediment of coastal and estuarine waterways, Rorrer explained, but they often occur at harmful levels in areas of concentrated maritime activity, such as shipping ports, harbors and in other industrial areas where fuel oil or coal is burned. Not only are high concentrations of some PAHs toxic to marine invertebrates, particularly clams and oysters, but several compounds within the class are known carcinogens.
Unlike many other byproducts of human activity, PAHs do not readily degrade in the environment but instead persist by binding with organic materials found in marine sediment, Rorrer said. Current options for treating areas of PAH contamination involve either dredging and removal of the affected sediment or "capping" contaminated deposits with a layer of PAH-free material. Both methods of remediation are extremely costly and often ultimately ineffective in keeping PAH compounds out of the environment, according to the researcher.
Seaweeds are known to take up and tolerate a wide variety of the organic compounds normally found in sea water, and related research in Rorrer's laboratory demonstrates that a tropical red seaweed (Portieria hornemannii) was effective in taking up and metabolizing another compound, which is also an aromatic hydrocarbon, the explosive substance TNT. Preliminary results by Rorrer and graduate student Kristi Christensen using a green Oregon seaweed (Acrosiphonia coalita) and the red seaweed Portieria strongly suggest that seaweeds are indeed capable of removing PAH compounds from sea water.
Whether they break PAHs down into environmentally acceptable compounds or merely sequester the intact compounds within their tissues is not yet known.
"The next question is, 'Where are the PAHs?" said Rorrer. "We're trying to find out if they're metabolized, or where they're hiding in the organism."
PAHs are fat-soluble and tend to accumulate in the fatty tissues of animals. When one animal is consumed by another, the PAH molecules become part of the higher organism. In this way, the PAH concentration increases, or biomagnifies, within the food chain. While it appears unlikely that PAHs are broken down completely by the marine seaweeds, Rorrer hopes to find that the compounds degrade into forms that are less harmful to marine organisms.
The results of this Sea Grant study may have far-reaching implications for seaweed's role as a component of engineered bioremediation systems and PAH monitoring programs. While field applications using seaweed as a bioremediation tool are beyond the scope of Rorrer's current Sea Grant project, he speculates that seaweeds could be deliberately cultivated near PAH-contaminated "hotspots," or grown near PAH-sensitive aquaculture facilities.
Further research will also be needed to explore how seaweeds interact synergistically with other microorganisms in the environment to metabolize PAHs. But for now, it's a primary question that is being investigated in the controlled systems of Rorrer's lab.
"Are these materials being remediated by these organisms? Nobody knows at present," said Rorrer. "This is the first step that will address that."
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