From what I've read, the scientists were at least partially aware, but the secrecy of the project caused compartmentalization. Just as an indicator, only two p

From what I've read, the scientists were at least partially aware, but the secrecy of the project caused compartmentalization. Just as an indicator, only two people died of acute radiation exposure in the Manhattan Project, and both people were avoiding the established safety protocols. That seems prima facie evidence that they were aware that high-dose radiation was bad. I think there was also pushback against those facts becoming more public after the war both due to the fact that the US used the atomic bomb, and also due to industrial uses of radioactive materials that no one wanted to pay for (a la the Radium Girls).