We will review the metallicity of the CIV and OVI phases of the IGM in the redshift range $z\sim 0.1$-5 together with their contributions to the cosmic baryon density. The current studies are limited to regions with overdensities of 3-10; the heavy element enrichment in regions with gas densities close to the mean cosmic density will be probed with future ELTs. We will also investigate the possibilities of detecting metals at $z\sim 10$ and underline the requirements on ELTs due to the anticipated faintness of the early generations of galaxies, QSOs and transient objects.