Heavy Metals in Sewage Treated Effluents: Pollution and Microbial Bioremediation from Arid Regions

Not all heavy metals are toxic. Some at lower concentrations are essential to the physiological status of the organism. Under certain conditions, induced toxicity occurs when the heavy metals are in the form of cations which tends to bind to certain biomolecules, thus becoming toxic to organisms. In many industries, toxic heavy metals such as As, Cd, Cr, Cu, Hg, Pb and Zn, are released mainly in sewage effluents causing major environmental pollution. Several of the heavy metal contaminations resulted from industrial wastes, along with the mining and burning of fossil fuels, leading to water and soil contamination which causes serious health problems. Rapid population growth plus a steady increase in agriculture and industry are the main cause of environmental pollution. The most common sources of heavy metals are fuel combustion, mining, metallurgical industries, corrosion and waste disposal which infiltrates the soil and underground water. When present at certain levels in the human, metals can cause certain diseases. Most of conventional technologies are inefficient to remove heavy metal contaminants. Microbial bioremediation is a potential method for the removal of heavy metal pollution in sewage effluents before being discharged into the environment. However, further research is needed for isolation and identification of microbes resistant to heavy metals. Industrial regulatory standards must be established to regulate the spread of non-essential metals in the environment. The regulations must be rigidly enforced. The rest of the essential metals must also be regulated since an increase over the physiological limit can also be harmful.