  The quark determinant in the presence of a background gluon field is
calculated in a large quark mass derivative expansion by considering quark
sources. The resulting low-energy QCD Effective Field Theory (EFT) is valid for
non-homogeneous fields and it presents, besides the usual Euler-Heisenberg type
gluon self-interactions, different types of corrections to the minimal
quark-gluon interaction among which there are several imaginary terms. The
Abelian limit of this effective action, i.e. an expanded Euler-Heisenberg
effective action with fermion sources, is exhibit and it contains, therefore,
corrections to the fermion-photon interactions, including imaginary parts.
Different resulting properties are calculated such as: their contributions to
the energy-momentum tensor and its trace, the Poynting vector, the
chromo-electric permittivity and chromo-magnetic permeability. Conditions for
these quantities, as well as for the corresponding Abelian limits, to be real
are exhibited.
