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by Joe Hlebica Reprinted with permission by Scripps Instition of Oceanography, UCSD, Explorations Magazine |
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| The mudflats at Green Sands Beach, Mare Island Naval Shipyard, near San Francisco, California. Photo courtesy of Explorations Magazine. | |||||||||
| Mare Island, near San Francisco, is a valuable field site for Scripps researcher Brad Tebo, his students, and associates. They are interested in the attenuation of toxic substances by bacteria and are investigating methods to mitigate heavy metals in marine habitats. As part of this effort, they are participating in a UC systemwide teaching effort known as the Toxic Substances Research & Teaching Program. "Our goal is to rely upon natural processes in bioremediation—not to introduce exotic species of bacteria to the environment," said Scripps graduate student Meriah Arias. The approach, known as natural attenuation, is sometimes faster, cheaper, and more effective than bioengineering methods. Postdoctoral researcher Lee He elaborated, "We want to look at natural processes in terms of dealing with toxic metals in the environment. The question is: How do bacteria naturally detoxify metals? That’s where we’ve been concentrating our studies in the lab." |
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| At the Mare Island site, the Tebo group is searching for answers to this question. Mare Island, established in the 1850s, was the oldest and largest naval shipyard west of the Mississippi at the time of its recent closure. Throughout the years, many shipbuilding technologies were implemented there, and many toxic substances associated with these technologies remain. The yard is like a ghost town now, where once-busy cranes stand still, towering over the half-scrapped hulks of obsolete warships at a site where vast quantities of toxic material were bulldozed into the bay. |
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| Lee He and Meriah Arias take mud core samples at Mare Island Naval Shipyard. Photo courtesy of Explorations Magazine. | |||||||||
| Arias reported, "We want to establish what is going on at the site. Are the metals chromium and copper, among others, being oxidized or reduced?" Supervising this group of researchers from the Tebo laboratory at the Mare Island site is UC Davis vertebrate ecologist Mike Johnson, another participant in the Toxic Substances Research & Teaching Program. On an unseasonably warm autumn morning shortly after dawn, the Tebo group took mud cores on the island’s tidal flats. The site, known as Green Sands Beach, is named for the color of the soil along the shore. The greenish case is evidence of high concentrations of nickel-zinc slag. The abrasive slag was used to sandblast old paint off hulls and superstructures in preparation for repainting. In this environment the remnants of antifouling paint and other similar metals are a major source of toxic metals such as copper and chromium, known carcinogens. Watching shorebirds peck food on the mud flats, Johnson explained that, surprisingly, the levels of metals in the surface sediments and waters are no higher here than anywhere else on the bay. The heavy metals that have settled into the sediments to depths of a foot or more are the ones that pose the problem. Tebo suggested that in the anaerobic zone within the site’s bottom sediments, specially adapted bacteria may already be rendering these metals relatively nontoxic through natural processes of metal and sulfate reduction. "Of course, the toxic metals are still sitting there in the sediments in high concentrations and if the sediments are dredged, exposed, or turned over, you have a potential problem. If organisms are burrowing down, they can be increasing the flux of toxic metals out of those sediments even if they can resist the metals themselves," Tebo pointed out. Before Mare Island and other industrial sites can be declared clean enough to meet public and environmental health standards, these toxic compounds must be neutralized, reduced, or removed. Such a threat might warrant an active cleanup campaign, but the costs—in time, money, and manpower—could prove intractable, as they have in many such situations throughout the industrialized world. As an alternative, Tebo and his research group would like to understand how microorganisms might naturally detoxify the metals. By monitoring the Mare Island site, the Tebo group may be able to predict whether toxic metals will pose a continued threat, and whether more costly remediation is needed. This is valuable information for any community looking forward to the reclamation and safe use of prime waterfront property. |
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