Lead is also used by humans to protect themselves from the potentially harmful effects of kryptonite radiation. Dr. Steven Hamilton was one of the first victims of kryptonite exposure to show negative side effects, which eventually proved fatal to him. In the comics, kryptonite radiation has the same effect as more common radioactive materials; for example, Lex gets cancer after wearing a kryptonite ring.
Level 33.1 used lead-lined rooms to store kryptonite. Chloe noticed the building schematic had several rooms lined with lead, and was able to infer that the building probably contained kryptonite.
Inhibit Kryptonite-inspired Metahuman Powers
Alicia Baker is forced by her parents to live in a lead-lined room, to prevent her from teleporting. Later, Clark douses Alicia in lead paint to prevent her from teleporting and allowing her to be captured. As a result, Alicia Baker is also forced to wear a lead bracelet by her doctor, William McBride. The bracelet release small amounts of lead into her blood stream, preventing her from using the kryptonite-inspired teleportation powers she received during the first meteor shower.
Prevent Kryptonian X-ray vision
Lead is the only known substance Kryptonians are unable to see through while using X-ray vision. One is to assume that it does this in the same way that a lead apron obstructs X-ray radiation from harming the human body during a scan. For example, Clark Kent is unable to use his X-ray vision to find Jonathan Kent and Roger Nixon when they are trapped underground in a lead-lined crypt. When Lionel traps Clark so he could show Patricia that he's the Traveler, he completely veils and lines the overlooking room with lead so that Clark couldn't possible see through it.