The majority of drywall entered the US through Florida, California, Louisiana, and Virginia. Much of the contaminated drywall was used in rebuilding areas after catastrophes such as hurricanes and areas with the biggest boom in housing. Most Chinese drywall was imported from six factories in China located in Beijing, Dongguan, Wuhu, Tianjin, Taian, and Shandong. The large manufacturers of Chinese drywall are Knauf Plasterboard Tianjian and L&W Supply Corp, Beijing New Building Materials, Taian Taishan Plasterboard, and Taishan Gypsum Co.. Since 2006 alone more than 550 million pounds of drywall was imported from China. The contaminated Chinese drywall problem was first reported in December, 2008.
Contaminants in the drywall include several sulfide and disulfide compounds, including hydrogen sulfide, strontium sulfide, and carbon disulfide, among others. The origin of these contaminants is not known, but is thought to be from mined gypsum, coal fly ash, or radioactive phosphogypsum. Contaminated drywall off-gases compounds into the air as a function of heat, humidity, and the amount of defective drywall in the building. Indications of contaminated drywall include a foul sulfur smell similar to rotten eggs or used fireworks, black corrosion of copper and other metals, and nosebleeds and respiratory problems.