Drywall woes have plagued some houses in south Florida, similar to this one. This house has not had any problems.

EMSL started looking at the problem in late 2006 with complaints about a noticeable low-intensity odor, a rotten egg smell. There also were complaints about black sulfur copper corrosion leading to failure of air conditioner evaporator coils. So far there have been no domestic service water problems. “We could not pinpoint anything until early 2007 when client data indicated Chinese-made drywall may be the source,” says Daliessio. “Now we’re seeing about 10 new cases per day. It’s a pretty high-volume concern and will probably increase as publicity generates more inquiries.”

A spokeswoman for the state’s Dept. of Health says it received 53 complaints over the last two years, most in seven south Florida counties. Only 2% of the complaints involved health issues.

Statistics suggest there is a large volume of imported drywall only recently installed or waiting to be used. According to the Gypsum Association, Hyattsville, Md., approximately 300 million sq ft of gypsum board was imported from China in 2006-2007. During that same period approximately 65.7 billion sq ft of gypsum board was used in the U.S.

The material mystery endures and EMSL is trying to get to the bottom of it by pursuing several tracks. Using a U.S. Environmental Protection Agency methodology known as toxic organics 15 they have collected air samples and analyzed them using gas chromatography and mass spectroscopy with inconclusive results. “So far nothing unusual,” says Daliessio. “We are seeing some slightly elevated carbon disulfide and carbonyl sulfide - 2 to 10 ppb, which is well below the EPA guideline of 234 ppb so it doesn't appear to be an acute hazard to human health.”

The firm also is putting samples in an environmental chamber to try to increase the odds of finding the two chemicals or related compounds of hydrogen sulfide and sulfur dioxide, which have not been verified in tests. And they have placed copper strips in contact with the drywall to try and replicate black copper corrosion. But the major problem could be iron and iron disulfide (iron pyrite). “We suspect iron pyrite impurities may be a cause,” says Daliessio. “The drywall contains these compounds, which don't seem to be present in domestic-produced drywall.” He notes there may also be a microbiological component. “We know that certain anaerobic bacteria can degrade calcium sulfate into hydrogen sulfide and this may be implicated,” says Daliessio. “Studies are ongoing.”

According to Daliessio drywall is almost always made up of calcium sulfate. There are two primary sources: gypsum mines and recovered spray dryer residue from coal fired power plants. The plants generate sulfur dioxide and spray calcium oxide and water across the exhaust stream as an emission control technology. The resulting product is gypsum.

Knauf Plasterboard Co., Ltd., Tianjin, China, is one firm that received odor complaints in southern Florida starting in late 2006 and a complaint about copper coils turning black in 2008. The company’s plasterboard was manufactured with naturally mined gypsum rock.

According to a statement from the company, Knauf “is conducting a through investigation and cooperating with builders that have contacted it. Studies and testing by nationally recognized experts are ongoing. The testing has confirmed that copper has blackened and may be caused by low levels of naturally occurring sulfur gasses. The low levels of gasses do not present a health risk to persons within the residences.”

The air quality department at the Florida Dept. of Environmental Protection is not involved in any investigation but the state Dept of Health is seeking more information. “We are trying to determine our next steps,” says Susan S. Smith, a department representative.