Cosmological deuterium production in non-standard scenarios

It is widely believed that the cosmic baryon density may be obtained by inferring deuterium abundances in low-metallicity quasar absorption line systems. The implicit assumptions which enter this argument are critically assessed. In particular, the production of deuterium in non-standard Big Bang nucleosynthesis scenarios, the putative production of deuterium in astrophysical environments, and the possible destruction of deuterium via non-standard chemical evolution are discussed.