



"It seems most likely that it's a nasty odor problem, as opposed to something acutely toxic," said Morton Lippmann, a professor of environmental medicine at New York University, who reviewed recent Florida health department's findings on Chinese drywall for The Wall Street Journal. Mr. Lippmann isn't involved in any of the lawsuits that have been filed against drywall manufacturers.

Other researchers said the sulfur-based gases coming from the drywall may exacerbate existing sinus issues and cause respiratory problems. The type of drywall at issue is made primarily from the naturally occurring mineral gypsum. Some of the drywall has been traced to a mine in the Shandong province of China, according to a spokeswoman for one drywall manufacturer, Knauf Plasterboard Tianjin Co., a subsidiary of a large German construction-material company, Knauf International GmbH, that used the mine.

"Sulfur compound gases, even at low levels, have been found to cause respiratory problems," such as asthma, said Nachman Brautbar, a toxicologist and clinical professor emeritus at the University of Southern California School of Medicine, who also reviewed the health-department findings for the Journal, and isn't involved in the legal dispute. "This clearly needs more study."

Black oxidation covers a copper air-conditioner pipe. The owners of the Stuart, Fla., townhome where they discovered faulty drywall say a sulfur gas is being emitted, and it is corroding copper wiring and pipes in the wall. ZUMA

In China, some industry officials defended their drywall's quality and suggested the controversy may be stoked by protectionism.

"The U.S. credit crisis has caused the real estate market to collapse, and as a result domestic drywall manufacturers have seen their sales suffer and their product is relatively expensive compared to the Chinese-made drywall, so we should also consider these issues," Xu Luoyi, head of the National Building Materials Industrial Technology Supervisory Research Center, said in a recent Chinese news report.

A big obstacle facing U.S. authorities investigating the matter is that the Chinese manufacturer isn't always clearly identified on the drywall.

Executives at one Chinese manufacturer named in a drywall-related lawsuit, Taishan Gypsum, couldn't be reached for comment. Meanwhile, Knauf Tianjin said it has been cooperating with U.S. and Chinese authorities. Knauf Tianjin officials said the company has been unfairly singled out because it has acknowledged the issue, while other manufacturers have been less forthcoming.

The U.S. imported roughly 309 million square feet of drywall from China during the housing boom from 2004 to 2007, according to the Gypsum Association, a trade group. While that is a fraction of the drywall used in the U.S., it is enough to build roughly 35,000 houses. The number of houses containing Chinese product could be higher, however, because some houses use a mix of domestic and imported drywall.

Not all of the Chinese drywall is likely to lead to the type of problems that homeowners in Florida, and now Virginia, Alabama and other states are reporting. Drywall problems are also surfacing in the New Orleans area, in homes that were refurbished after Hurricane Katrina.

Some homeowners who have found Chinese-imported drywall in their newly built houses, say their jewelry, pennies and electrical wiring have turned black. Researchers believe the sulfur-based gases from the drywall may be corroding the metal.

The drywall issue is touching nerves that have been frayed by the housing crash. "When the housing market comes back, my home's value isn't coming back," said Rene Galvin, who has moved out of her Bonita Springs, Fla., home that she bought for her retirement and is suing her builder and the drywall manufacturer because of drywall concerns.

—Juliet Ye and Sky Canaves contributed to this article.

Write to Michael Corkery at