Photosynthesis shines as remediation tool

Marine construction, wood treatment, agricultural chemical production, chlorine production-- for decades we have been dumping waste into our harbors, many of which are now considered some of the most contaminated hazardous waste sites in the United States.

Battelle researchers at PNNL's Marine Sciences Laboratory have developed a promising technique for remediating contaminated sediments in seawater and freshwater ecosystems.

"The main limiting factor affecting the biodegradation of many organic contaminants is the availability of oxygen," said Michael Huesemann, who manages the project. "Oxygen is required for naturally occurring bacteria to oxidize, or biodegrade, organic contaminants."

Under normal conditions, very little oxygen gets into the sediment, diffusing only a few millimeters and allowing for the bioremediation of only a thin layer of sediment.

Huesemann believes he has found a solution with eelgrass and the simple process all plants use for nourishment--photosynthesis. "In eelgrass, we have a photosynthesis-driven oxygen pump that delivers oxygen into sediment for free, as long as there is sunlight," he said.

Although eelgrass roots grow only about six inches, they deliver oxygen much deeper into the sediment and therefore stimulate biodegradation in a much thicker layer than would occur by natural biodegradation where only the top few millimeters are bioremediated. "If you can remediate the top six inches of sediment with eelgrass, you have created a clean cap where animals can live," Huesemann said.

Tests at the Marine Sciences Laboratory showed that within five months about 60 percent of polycyclic aromatic hydrocarbons (PAHs) were removed in sediments planted with eelgrass, while during the same period only 24 percent of the PAHs were removed in unplanted sediments.

Readers interested in field testing this insitu sediment treatment technology should contact Huesemann at michael.huesemann@pnl.gov.