Metals are mainly released into the environment by industrial processes where dissolved organic materials (DOM) are present.  This investigation focused on modification of copper species in the presence of aquatic heterotrophic bacteria assemblage and natural dissolved organic materials. Copper dynamics during bacteria growth was evaluated through the determination of dissolved and particulate copper. The results showed a reduction of organic carbon, an increase of free Cu²⁺ ions followed by adsorbed and internalized copper. This study demonstrated a relevant environmental consequence of heterotrophic bacteria activity related to copper speciation in aquatic ecosystem suggesting that as a result of heterotrophic bacteria activity upon DOM,  more toxic copper species were released into the environment.