  We reconsider the effects of unstable particles on the production and
destruction of the primordial light elements, with a view to reconciling the
high primordial Li7 abundance deduced from Big Bang Nucleosynthesis (BBN), as
implied by the baryon-to-photon ratio now inferred from the anisotropies of the
Cosmic Microwave Background (CMB), with the lower abundance of Li7 observed in
halo stars. The potential destruction of Li7 is strongly constrained by
observations of Deuterium (D), He3 and Li6. We identify ranges for the unstable
particle abundance and lifetime which would deplete Li7 while remaining
consistent with the abundance of Li6. However, in these regions either the D
abundance is unacceptably low or the ratio He3/D is unacceptably large. We
conclude that late particle decay is unable to explain both the discrepancy of
the calculated Li7 abundance and the observed Li7 plateau. In the context of
supersymmetric theories with neutralino or gravitino dark matter, we display
the corresponding light-element constraints on the model parameters.
