Biokinetics of neutron activated nanoparticles. (A) Lung clearance of cerium-141 (141Ce) after instillation of cerium-141 dioxide (141CeO2) nanoparticles and cerium-141 chloride (141CeCl). Reprinted from Environmental Science: Nano 1, Molina RM, Konduru NV, Jimenez RJ, Pyrgiotakis G, Demokritou P, Wohlleben W, Brain, JD, Bioavailability, distribution and clearance of tracheally instilled, gavaged or injected cerium dioxide nanoparticles and ionic cerium, 561–573, Copyright 2017, with permission from the Royal Society for Chemistry. (B) Extrapulmonary retention of 141Ce and barium-131 (131Ba) after intratracheal instillation of 141CeO2 and barium-131 sulfate (131BaSO4) nanoparticles (Konduru et al. 2014; Molina et al. 2014).