ABSTRACT

Heavy metals are recognized relatively as high-density inorganic pollutants, which comprise 75% known elements and are toxic at low concentrations. Industrial wastewater has been considered as the major source of heavy metal pollution in the environment (Chandra et al. 2011; Saxena and Bharagava 2015; Saxena et al. 2016a, 2016b). These metals have been used since the beginning of ancient human civilization and are constantly being added to soil, water, and eventually the biosphere through rapid modernization as well as industrialization around the world via smelting of metalliferous surface finishing industry, combustion of fossils, electroplating, photography, electrical devices, manufacturing, aerospace, waste incineration, transportation, mining, agricultural applications, etc. The accrual of heavy metals, as nonbiodegradable material, not only decreases soil microbial activity along with crop production but also threatens human health due to their persistence in the course of the food chain. Various noxious heavy metals present in different oxidation states such as zinc (Zn), arsenic (As), chromium (Cr), cadmium (Cd), mercury (Hg), copper (Cu), nickel (Ni), and lead (Pb); radioactive elements such as uranium and strontium; as well as organic compounds like trinitrotoluene, 1,3,5-trinitro-1,3,5-hexahydrotriazine, petroleum hydrocarbons (benzene, toluene, xylene, etc.) due to their nonbiodegradable nature, all are difficult to eliminate from the environment, and they become acutely toxic if their concentration exceeds certain threshold (Glick 2010; Ma et al. 2011; Shinwari et al. 2015).