An Arizona crematorium became polluted with a plume of radiation after operators inadvertently incinerated the remains of a cancer patient who had undergone a radioactive treatment just days before his unexpected death.

The Phoenix-based Mayo Clinic doctors who reported the contamination were further alarmed when they found that the crematorium’s operator also had trace amounts of radioactive material in his urine—but from a different isotope than the one found in the recently cremated cancer patient. The doctors published their findings Tuesday in a JAMA research letter.

While the levels of radiation they detected in the crematorium and its operator were unlikely to cause harm, the doctors say the issue needs more attention. They conclude: