  One of the notable modifications of General Relativity (GR) is the Rastall
gravity. We have studied the polarization modes of Gravitational Waves (GWs) in
this gravity. It is found that at a very far distance away from the source of
GWs, Rastall gravity behaves identically to GR. That is, we get only two
massless tensor polarization modes of GWs in the theory. Afterwards, we have
extended our study to quasinormal modes of black holes in Rastall gravity in
presence of non-linear electrodynamic sources. Here the impacts of cosmological
field, dust field, phantom field, quintessence field and radiation field on the
quasinormal modes in presence of electrodynamic sources have been investigated.
Apart from this, we have also checked the dependency of quasinormal modes with
the Rastall parameter $\lambda$, black hole structural constant $N_s$ and
charge of the black hole $Q$. The study shows that the quasinormal modes
corresponding to the black hole with non-linear electrodynamic sources show
significant deviations from a general charged black hole in Rastall gravity
under certain conditions. Further, the behaviour of black holes and hence the
quasinormal modes depend on the type of surrounding field considered.
