A Russian doctor found to have a radioactive isotope in his body after treating victims of an Aug. 8 rocket engine explosion had been contaminated by food and not radiation, authorities said Friday. Earlier, The Moscow Times reported that a group of doctors who treated the radiation victims had been flown to Moscow for medical checkups. One of the doctors was reportedly found to have Cesium-137 — a radioactive isotope that is a byproduct of the nuclear fission of uranium-235 — in their muscle tissue.

“Subthreshold” traces of Cesium-137 have been found in the unnamed doctor’s muscle tissue, the Arkhangelsk region’s administration said in a statement published on Friday. “But specialists don’t associate this fact with [the doctor’s] participation in the incident relief effort” in the military town of Nyonoksa, it added. The Health Ministry’s biomedical agency says Cesium-137 “tends to accumulate in fish, mushrooms, lichens and algae,” the Arkhangelsk region administration said. “We can say with a fair degree of probability that it got into his body via food products which he'd eaten,” the administration added.