Natural environmental radioactivity from radon 222.
D000388:Air / Q000032:analysis; D010944:Plants / Q000032:analysis; D011851:Radioactivity; D011883:Radium; D011886:Radon / Q000032:analysis*; D012987:Soil / Q000032:analysis; D014481:United States
D012987:Soil; D011886:Radon; D011883:Radium