  The Adler-Bell-Jackiw anomaly for massive particles is studied in an external
magnetic field. The contributions of the mean spin and the pseudoscalar are
accounted for in the quasiclassical approximation. The equation for the
evolution of the magnetic helicity with the new quantum corrections is derived.
We show that the quantum contribution to the helicity evolution can overcome
the classical one in the dense degenerate matter which can be present in the
core of a neutron star. The application of the obtained results for the
interpretation of magnetar bursts are discussed.
