The four categories of metals are ferrous, non-ferrous, noble, and heavy metals. Ferrous metals are those composed of iron and carbon, and an example of such metals is iron. They have high strength but undergo corrosion with time. Air is the source of exposure to these metals. The rust in these metals pollutes the air and when inhaled causes lung irritation and coughing (Nriagu & Pacyna, 1988). Nonferrous do not contain iron and are different from ferrous metals in that they are less corroded, have less strength, and require less pressure to be molded. Examples of such metals are aluminum and lead. The soil is the source of exposure to these metals. Small particles from these kinds of metals especially from lead find their way into the topsoil hence affecting the plant growth of crops such as rice (Mukherji & Maitra, 1976). Another category is noble metals which are less reactive just like noble gases unlike when in liquid and powder forms. They do not rust and are easily molded. An example of a noble metal is Gold. Air is a source of exposure in that metals such as gold emit mercury vapor during mining which affects the respiratory tracts of humans (Lacerda, 1997). Heavy metals are the last category, and it comprises metals that have a high atomic mass and density but are less strong than ferrous metals. These metals are limited in supply, and an example is an arsenic. Contaminated water, air, and soil are the sources of exposure to heavy metals such as arsenic. The metals are carcinogenic and are reportedly one of the causes of skin cancer in humans and other body parts such as the lungs (Smith et al. 1992). An advantage of heavy metals is that they can be used as a wood preservative against bacteria and fungi (Baldrian, 2003).
References
Baldrian, P. (2003). Interactions of heavy metals with white-rot fungi. Enzyme and Microbial Technology, 32 (1), 78-91.
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Lacerda, L. D. (1997). Global mercury emissions from gold and silver mining. Water, Air, and Soil Pollution, 97 (3-4), 209-221.
Mukherji, S., & Maitra, P. (1976). Toxic effects of lead on growth & metabolism of germinating rice (Oryza sativa L.) seeds & on mitosis of onion (Allium cepa L.) root tip cells. Indian journal of experimental biology.
Nriagu, J. O., & Pacyna, J. M. (1988). Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 333 (6169), 134-139.
Smith, A. H., Hopenhayn-Rich, C., Bates, M. N., Goeden, H. M., Hertz-Picciotto, I., Duggan, H. M., ... & Smith, M. T. (1992). Cancer risks from arsenic in drinking water. Environmental health perspectives, 97, 259.
