The five cities with the highest levels were Norman, Okla.; Honolulu, Hawaii; Riverside, Calif.; Madison, Wis.; and San Jose, Calif.
Studies show chromium 6 can also damage to the gastrointestinal tract, lymph nodes and liver of animals.
Boxer said she plans to co-sponsor legislation to set a deadline for the EPA to establish an enforceable standard for Chromium 6.