Bacteria colonizing heavily polluted tailing ponds in Southern Venezuela exhibit multiple resistances against mercurial compounds and antibiotics. The corresponding genetic determinants, mainly acquired through horizontal gene transfer, might also be transferred to pathogenic bacteria, an issue which represents an important risk to public health. In this work we show that indigenous, mercury-resistant bacterial strains isolated from a model tailing pond, located in El Callao (Bolivar State, Venezuela) and exhibiting a high concentration of soluble Hg, were able to transfer in vitro both heavy metal- and antibiotic resistance markers to potential human- and animal- pathogens (i.e. Escherichia coli and Pseudomonas aeruginosa). The frequencies of transfer ranged between 1.2x10 -6 and 5.5x10 -7 transconjugants per recipient. Transconjugants were also detected in the field, in model biofilms previously grown in natural sponges (Luffa cylindrica ) and submersed in the ponds, at frequencies ranging from 1x10 -4 to 5x10 -3 transconjugants per recipient. These results are of particular relevance from the public health viewpoint, especially in light of the potential risk of horizontal flow of antibiotic resistance genes between indigenous bacteria and potential human pathogens.