Originally Posted by Sarge

Here's a few more:

1) Did you have your hardwood floors installed by a contractor? I ask only because as we all should know by now, the manufacture of Asbestos products was outlawed decades ago, but most of the public is unaware that the supplying and installation of these products already produced had been, and may still be legal. It was considered unfair (does anybody smell industry lobbies?) that supply companies who stocked their warehouses should lose their investment.
Small pieces of flooring cannot be nailed because of splitting so the are glued, usually with the industry standard most reliably durable asbestos-based adhesive, which over the years through ambient humidity changes releases the chemical in vapor form.

2) Because of energy conservation concerns in our quest to construct the "green home," the International Energy Conservation Code requires dwelling to be built so tight so as not to allow any natural infiltration. If a wall is unable to "breathe" from one side or the other, "vapor lock" is created which through the course of the annual temperature cycle promotes condensation inside the walls giving rise to the certain production of mold. Our good old drafty houses never had that problem.
As a building official I personally have seen walls opened up for remodeling less than a year after they were built (folks with too much money whom after 6 months got tired of the 75k kitchen that came with the house) and the inside surface of the wall sheathing was solid pitch-black with mold.

3) Another serious problem that we have now (depending on the delineated zone site) that older homes didn't, is Radon. Don't even get me started on that one.

4) Gypsum in its natural state most often has a Sulfur content, the degree of which varies from one area mine to another. China's veins contain a notoriously high level necessitating wide openings at opposing ends to create a constant airflow--as Gypsum can somewhat quickly release the Sulfur through evaporation.
The end of August 2005 brought the southeastern US Hurricane Katrina, coincidentally in the midst of a home-building boom. With all of the necessary rebuilding and reconstruction, coupled with the new construction already underway, there existed a severe shortage of US produced sheetrock, creating a huge demand for imported. China shifted into high gear opening new mines and cranking out high sulfur-content drywall by the cargo ships loads. The immediate inpouring of orders did not permit time for the usual precautionary pre-ventilating, shipping millions and millions of tons of the tainted boards to our suppliers.
An estimated 100,000+ homes were built, between 2005 and 2010, as well as countless remodeling with the drywall. Now particularly in the southeast, with its warmer climate and higher humidity, along with the already present mold, the released SO2 combined with the in-the-wall condensation to manufacture Sulfuric Acid which proceeded to eat up any and all metal inside, while releasing the toxic mix into the living space. Instead of my going on with this and turning it into a 200 page volume, just Google: Tainted Chinese Gypsum Board the next time you have nothing to do for three days.
There was no tracking of the geographical supply distribution so any of us who did any home improvement during that time or who knows how much later involving applied new sheetrock could have used the product.

These are just the items I can just come up with off the top of my head. It's scarier to imagine what is yet to discover.