Heavy metal particles can be considered metallic chemical elements, toxic even at low concentrations. They have atomic weight ranges between 63.5 and 200.6, with a specific gravity of 4.5–5.0. Toxic heavy metals in wastewaters and in soil are copper, nickel, zinc, cadmium, lead, mercury, and hexavalent chromium.
This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.
https://doi.org/10.1007%2F978-3-7643-8340-4_6
Heavy metals are toxic metals having density five times greater than water. They are toxic for all living organisms. In humans they enter into body through various ways like ingestion, absorption etc. They become harmful when their accumulation rate is more than their dischargeAny toxic metal may be called heavy metal, irrespective of their atomic mass or density.[1] Heavy metals are a member of an ill-defined subset of elements that exhibit metallic properties. These include the transition metals, some metalloids, lanthanides, and actinides. One source defines heavy metal as one of the common transition metals, such as copper, lead, and zinc. These metals are a cause of environmental pollution from sources such as leaded petrol, industrial effluents, and leaching of metal ions from the soil into lakes and rivers by acid rain.Three principal systems of medicine are practiced in India: Ayurveda, Siddha and Unani-Tibb. These systems utilize drugs of natural origin constituting plants, animals, and mineral preparations.
But some of the heavy metal are useful fo microorganismSome heavy metals such as nickel, iron, copper and zinc are essential to metabolic reactions and are required as trace elements by the organismsOn the one hand, heavy metals have a direct effect on soil enzyme activity, so that the spatial structure of the active groups of the enzyme is destroyed. On the other hand, the growth and reproduction of microorganisms are inhibited, thus reducing the synthesis and metabolism of the microbial enzymeHeavy metals can significantly affect the kinetics of substrate biodegradation and microbial growth, including lag times and specific growth rates. A model to describe microbial metabolic lag as a function of the history of substrate concentration.
Unlike organic contaminants, heavy metals are not biodegradable and tend to accumulate in living organisms. Many heavy metal ions, such as mercury, cadmium, lead, nickel, and chromium, are known to be very toxic or carcinogenic.
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All living organisms are affected by increased concentrations of heavy elements, whether they are in the air, water or soil. The degree of toxic effect of these elements depends on the type of organism, the concentration of toxins and their physical condition. For example, the effect of lead on humans begins with low concentrations, and the obvious symptoms appear at a concentration of 60 micrograms per deciliter, and the concentration becomes fatal when it reaches the limits of 80. Usually the high concentrations of heavy elements in soil, water or air come as a result of external influences. The processes of extracting heavy metals from their ores, especially by thermal methods, are considered one of the most pollutants affecting the environment. The gases released from the chimneys of these factories lead to air and soil pollution, and there are standard parameters for the concentrations of each element in the gaseous emissions that should not be exceeded. For example, for lead, it should not exceed 2 micrograms per cubic meter. The same applies to water pollution. Any study or research of the impact of these elements must be translated into contour maps around the area to be studied, on the horizontal and vertical levels. The effect of water pollution is severe near chemical factories, such as leather tanning, but the effect of thermal extraction plants is more severe on air and soil. Therefore, the type of pollution source determines which of the absolutes is more effective, liquid, gas, or solid.
All living organisms will be affected by increased concentrations of heavy elements, whether they are in the air, water or soil.
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