Yet some environmentalists remain concerned about the secrecy surrounding the 840-acre, pork chop-shaped island off northeastern Long Island - and they're dubious of any claims that pollution has been remedied.
"We are highly concerned that when the government acts alone they may not be doing the best job," said Adrienne Esposito, executive director of the Citizens Campaign for the Environment.
"Every government cleanup needs the public's involvement and independent oversight to ensure its validity."
The Department of Homeland Security is preparing to sell the island 100 miles east of Manhattan and build a new high-security laboratory in Kansas to study animal diseases.
Documents, some obtained by the AP under the Freedom of Information Law, reveal that hundreds of tons of medical waste, contaminated soil and other refuse have been shipped off the island for disposal. Other island sites have been cleaned in compliance with federal regulations, the reports indicate.
Also, the U.S. Army Corps of Engineers determined in 2006 that no munitions or ordnance remain from the Army base on Plum Island that once housed as many as 4,000 troops from the Spanish-American War through World War II. And as late as 2007, New York government inspection reports said there is no environmental threat on the island.
Plum Island's remote location, restricted public access, and best-selling books have all helped fuel a mystique about what goes on there. It wasn't until the early 1990s that tours of the facility were given to the news media - about the time the government declassified files revealing secret germ warfare research there in the 1950s. The last media tour was in 2004.
Before the island, its ferry dock and mainland offices can be sold, the General Services Administration, which manages federal properties, is studying the environmental impact of the research activities. A draft is expected by summer's end and public hearings will follow.
"There has been some EPA investigation and remediation," said Bob DeLuca, president of the Group for the East End, which focuses on environmental issues. What has not been assessed - and what we have asked for is - what is the legacy of contamination?"
The Preserve Plum Island Coalition, a new consortium of more than two dozen environmental groups, opposes the sale. Spokesman John Turner said the island should not be developed because it is home to a number of endangered bird species and other wildlife.
"We want it (the sale) to be reversed," Turner said. "We think there are very significant ecological, natural and cultural resources on the island."
That's a view shared by author Nelson DeMille, who wrote a 1997 murder mystery with Plum Island as the backdrop. He says it would be best to close the lab and open a nature preserve.
Democratic U.S. Rep. Timothy Bishop questions the wisdom of moving the lab to Kansas. He estimates the sale could fetch $50 to $80 million but says building the new facility would cost 10 times that much. DHS, which took over Plum Island operations in 2003, considered several locations, including Plum Island, before choosing a site at Kansas State University in Manhattan, Kan.
But questions remain; the Senate last year ordered DHS to study whether operating a lab and studying pathogens in the "beef belt" could imperil America's livestock industry. DHS has determined that an accidental release of foot-and-mouth disease would have a $4.2 billion impact on the economy, regardless of the lab's location.
A 2006 Army report noted how the Chemical Warfare Service researched pathogens in the 1950s that could be used for "both defensive and offensive purposes" on a variety of animals. The island was used because of federal laws banning germ warfare research on the U.S. mainland.
Army records also indicate at least hog cholera virus and Newcastle disease, a virus of poultry and other birds, were "field tested" on Plum Island, but the report noted it was never clearly established "how many other viruses the CWS may have used in their research."
A former Plum Island administrator, David Huxsoll, told the AP that anthrax, a lethal disease affecting humans and animals, was studied for decades in the facility's bio-containment lab. The bacteria can form dormant spores able to survive long periods in the environment. Scientists have also studied foot-and-mouth disease, swine fever, and other foreign animal diseases.
Gigi Gronvall, a senior associate at the University of Pittsburgh-based Center for Biosecurity, said there was little need to worry about any residual disease contamination. "I'd say it's extremely unlikely that any pathogens could have been released," Gronvall said. "Those labs are designed to be one of the barriers between the pathogens and the environment."
A 2007 DEC letter confirmed the island's motor pool and nearly 20 other locations on the island had been cleaned to comply with the federal Resource Conservation and Recovery Act. In some instances, sites were excavated and contaminated soil was removed to landfills.
DEC spokesman Bill Fonda added that between 2000 and 2007, some 970 tons of medical waste - material that could not be burned in one of the lab's incinerators - was taken from 10 Plum Island sites to landfills in Pennsylvania.
Another building which DEC says was certified as clean was Building 257, the subject of the 2004 best-selling book "Lab 257" by attorney Michael Carroll. He believes Plum Island's mysterious past inspired the move to Kansas.
"Plum Island raised too many red flags," Carroll said. "I think that's why they decided to pick up and move somewhere else."