Once they are found as pollutants in some biota, they may be subjected to interactions with organisms, originating phenomena like bioaccumulation and conversion to organometallic species,as examples. Bioaccumulation implies that, as the time goes by,some animals that live in polluted environments will retain in their tissues an increasing amount of such a pollutants. On the other hand, organometallic species are generated by bacterial activity,which forms substances composed by metals covalently bonded to organic carbon chains. Organometallic substances, when excreted in the medium, are generally more harmful than the free metal cations themselves, because they end up acquiring higher affinity with the fat tissues of animals’ bodies increasing greatly their bioconcentration factors