First-principles electronic band structure investigations of monoclinic, tetragonal, and cubic ZrO2 reveal the highly anisotropic nature of the conduction and valence band topologies in the monoclinic phase with electron and hole effective masses differing by over an order of magnitude in perpendicular directions. The planes of relatively high implied electron and hole mobilities intersect along a single crystallographic direction, making this the only direction readily available for exciton motion. Conversely, in the tetragonal and cubic phases, charge carrier effective masses are more isotropic and exciton motion is less restricted. These findings may explain recent experimental observations suggesting that exciton production via gamma irradiation in zirconia crystallites immersed in water is responsible for the accelerated dissociation of adsorbed water molecules on crystallite surfaces, and for the specificity of the effect to the tetragonal zirconia phase.