RFID uses the low-end of the electromagnetic spectrum. The waves coming from readers are no more dangerous than the waves coming to your car radio. They have nothing to do with ionizing radiation (X-ray). The chips respond to the magnetic field of the readers with such weak signals that even the readers have difficulties in perceiving them. Thus, even at a distance of just a few meters the radio emissions are no longer measurable.
RFID tags and readers work with regular radio waves. They have nothing to do with ionizing radiation