Some results of quantum gravity suggest possible violations of quantum mechanics in the form of transitions from pure to mixed states. A "quantum violating evolution equation" put forward by Ellis, Hagelin, Nanopoulos and Srednicki is used in the case of rotationally invariant density matrices describing a system of two spin-½ particles. It is shown that the equation may account for the transition from a pure singlet state to a mixture of maximal entropy discussed by Baracca, Bohm, Hiley and Stuart in 1975 in connection with Bohm's version of the EPR experiment. It is argued that similar effects on the evolution of microscopic systems could also arise as a consequence of extra spatial dimensions, such as those introduced in multidimensional unified theories.