Halo initial mass functions (IMFs) heavily biased toward white dwarf (WD) precursors ~1-8 Msun have been suggested as a suitable mechanism for explaining MACHO events. However, by simple chemical evolution argument, Gibson & Mould (1997; GM97) pointed out that such WD-heavy IMFs (wdIMF) cause the overproduction of carbon and nitrogen. We re-examine this problem using numerical simulations.
