The effect of different concentrations of nickel, copper and zinc on methanogenesis using pure cultures of Methanobacterium formicicum, Methanobrevibacter arboriphilicus, Methanosarcina thermophila and Methanospirillum hungatei over time (1, 15 and 30 d) was evaluated. methanobacterium formicicum showed the highest resistance to all the metals tested, while Methanospirillum hungatei was the most sensitive strain. All strains were sensitive to copper and zinc (10–250 mg 1‐1, but were much more resistant to nickel (200–1200 mg 1‐1). An adaptation process of the methanogenic pure culture with the toxicants was observed over time, which indicates that the inhibitory effects of heavy metals may be reverted in optimal anaerobic conditions.

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