One bad thing is that the LEM was never designed to return to earth, so when Apollo 13 came back with the LEM it also brought the RTG back and could have disper

One bad thing is that the LEM was never designed to return to earth, so when Apollo 13 came back with the LEM it also brought the RTG back and could have dispersed the 8.5 lbs of plutonium in the atmosphere. In the grand scheme of things this was probably nothing compared to all the atmospheric nuclear weapon tests that were done in the preceeding years (like the 50 megaton Tsar Bomba blast).