Monte Carlo track chemistry simulations of the B-10(n, alpha)Li-7 radiolysis of water show that the in situ formation of H3O+ by the two He and Li recoiling ions renders the native track regions temporarily very acidic. For these irradiating ions, the pH remains near 0 at times less than similar to 100 ps after which the system gradually returns to neutral pH at similar to 0.1 ms. These 'acid spikes' have never been invoked in water or in a cellular environment exposed to densely ionizing radiations. The question of their implications in boron neutron capture therapy and, more generally, in hadrontherapy, is discussed briefly. (C) 2017 Elsevier B.V. All rights reserved.