The US government undertook real and widespread environmental monitoring of radioactivity from at least 1947, and perhaps earlier. Many samples were taken of a

The US government undertook real and widespread environmental monitoring of radioactivity from at least 1947, and perhaps earlier. Many samples were taken of air, water, soil, vegetation, human bone and other materials to understand the extent of radioactive fallout. There were international incidents around test fallout in the early 1950s. It was a major political issue in the early 1950s. Presidential candidates RAN on this issue. Consciousness of the problems of test fallout resulted in an above-ground test ban treaty. The US's last above-ground test happened in 1962. So this was a problem that started in 1945, was well known to the general public within a few years, and was solved by 1962. This is obviously not perfect. But it certainly isn't the case that it was ignored until 1997 and people were only finding out about it then.