  We characterize in detail the very dense $e^- e^+ \gamma$ plasma present
during the Big-Bang Nucleosynthesis (BBN) and explore how it is perturbed
electromagnetically by \lq\lq impurities, {\it i.e.\/}, spatially dispersed
protons and light nuclei undergoing thermal motion. The internuclear
electromagnetic screened potential is obtained (analytically) using the linear
response approach, allowing for the dynamic motion of the electromagnetic field
sources and the damping effects due to plasma component scattering. We discuss
the limits of the linear response method and suggest additional work needed to
improve BBN reaction rates in the primordial Universe. Our theoretical methods
to describe the potential between charged dust particles align with previous
studies on planetary and space dusty plasma and could have significant impact
on interpretation of standard cosmological model results.
