I’m told that Chinese sheet rock contains combustion ash from fluidized bed (limestone injection to control SO2) combustion. It can be quite reactive.
This is heavily reported in the media, but is not accurate.
They are confusing two issues. Fly ash is the particulate matter from unburned coal in power plants. It is widely used as an additive to concrete, where it doesn’t seem to cause any problems.
Synthetic gypsum, OTOH, is a byproduct of the removal of sulfur gases from the smokestack. It is chemically a good deal more pure than the gypsum they dig out of the ground. It is used in both Chinese and US drywall. It is widely considered a “green” product. It is produced entirely separately from the fly ash and could not be mixed with it during production. Somebody could add it later, of course.
EPA tests that just came out this week found no fly ash in the Chinese drywall. But the tests were of only two samples.
Lord only knows what the Chinese put into drywall. But people should be aware that six months of testing has found nothing that is obviously the cause of the problem.