The Ecotoxicology of Heavy Metals from Various Anthropogenic Sources and Pathways for their Bioremediation

Although Cu and Zn are important microelements with well-defined roles in organisms functioning, their presence in toxic concentrations is related to a contamination process. On the other hand, Pb, Cd, and Hg are toxic xenobiotics with cumulative effects on various organisms, and in the case of Ni the reports are contradictory. All of these heavy metals are found as a naturally content in the earth's crust wherefrom are mobilized through volcanic eruptions or mining activities. Some human activities, such as metals smelting, burning of fossil fuels, cement obtaining, usage of pesticides in agriculture, contribute to the environmental pollution with these heavy metals. The presence of heavy metals is considered a risk factor for all components of the ecosystem due to their geo- and bio accumulative features. In long-term exposure, especially in countries with intensive industrialization and urbanization, toxic and carcinogenic effects based on various mechanisms were reported. However, the extraction and the usage of heavy metals in various industry branches might be considered a necessary evil for the nowadays modern society. In some moments of our evolution there were no alternatives, neither as knowledge, nor as application possibilities. In last decades, alarm signals were pulled by the scientific community and non governmental organizations, and a legislation of heavy metal residues monitoring was developed and applied in many countries all over the world. Moreover, various ecological alternatives were found for the limitation or even excluding of pollutant materials from many of our life aspects (unleaded petrol, insecticides based on pheromones, green concrete manufactured with less cement quantity etc.) and different ways of soil phytoremediation and heavy metals biosorption from aqueous media were tested. The aim of this paper is to review the most important aspects related to heavy metals (Pb, Cd, Hg, Ni, Cu, Zn) ecotoxicology. Various sources of environmental pollution and different mechanisms for physiological homeostasis disruption for each reviewed elementary xenobiotic are critically discussed.