In previous posts, we’ve discussed both sapphires and rubies, which are varieties of corundum. This popular, colorful, and durable gemstone is highly prized.
Corundum is now being diffusion treated with titanium and chromium, where the stone is irradiated to get the colorant to absorb into the outer layer of the stone. Another treatment, beryllium diffusion, has been common for years. Stones treated with any of these methods may lose part or all of their color if the stone is damaged or repolished.
It is possible that there are health hazards from these stone treatments. For example, chromium is toxic and may damage DNA cells.  “There is disturbing evidence that suggests the beryllium treatment poses a health hazard to the workers who process and cut the gemstones and to the merchants who handle them.” 
Surprisingly, irradiated gemstones are generally considered safe because of the mandated cooling off period and monitoring requirements. “NRC [Nuclear Regulatory Commission] requires that the initial distribution of these stones be by a distributor licensed by the NRC. This distributor would conduct radiological surveys of each batch of gemstones to ensure that any residual radioactivity falls below regulatory limits.” 
Sellers in the United States are required by law to disclose all treatments to stones they sell.
 The Jeweler’s Directory of Gemstones by Judith Crowe, p.50