There are few things that evoke more irrationality in humans than radioactivity. The naturally occurring radiation from cosmic rays, UV, man-made (X-rays etc) and even compounds inside our bodies (Potassium 40, Carbon 14) will completely overshadow any dose you may receive from your Kodak Ektar or Pentax Takumar lens. The thorium is vitrified, and the decay particles will be arrested inside the glass matrix. This incidentally is why the glass eventually turns yellowish.

There has never been proof that low doses of radiation are harmful, but it was poorly understood why. It has recently been discovered that cell repair following radiation damage happens at extraordinary efficiency up to a certain dose rate. Above that rate, the repair mechanism starts to get overloaded, and the efficiency drops to the point where permanent cell damage becomes linear with dose. Think of it as a repair shop with a single technician. If he services fewer units than his capacity, each unit can be fully repaired, but if he is overloaded, he will rush and make mistakes. The international radiation dose limits are several orders of magnitude below the linear rate, though, as is the natural radiation dose a person will receive from natural sources (other than skin exposed to UV in large doses).