The pyrometallurgical process of mining for obtaining ferronickel involves a stage of calcinations. At this stage a residue is generated described as a calcination dust of fine black grains. Analysis of this material revealed a significant presence of Fe, around 53,000 ppm and Ni, around 14,000, beyond of other metals as Al, Mn, and Cr. Adults and larvae of Oreochromis niloticus were used to evaluate acute toxicity, cytotoxicity and genotoxicity, and histopathological effects. The data obtained show absence of toxicity in concentrations of 5, 10 and 50% but a considerable potential for bioaccumulation in the fish's body.