Environmental:

EPA – Environmental Protection Agency 
http://www.epa.gov

Asbestos
http://www.epa.gov/asbestos

Indoor Air Quality
http://www.epa.gov/iaq/pubs/insidest.html

Lead
http://www.epa.gov/lead 

Mold 
http://www.epa.gov/mold/index.html

Radon
http://www.epa.gov/radon 

Map of Radon Zones
http://www.epa.gov/radon/zonemap/california.htm