Heavy Metals Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

This Heavy Metals Essay example is published for educational and informational purposes only. If you need a custom essay or research paper on this topic, please use our writing services. EssayEmpire.com offers reliable custom essay writing services that can help you to receive high grades and impress your professors with the quality of each essay or research paper you hand in.

Heavy metal is a term frequently used by environmentalists to describe a group of metallic elements that frequently have toxic effects. The heavy metals include elements such as mercury, lead, and cadmium. However, as a definition of a class of toxic compounds, the term heavy metals is somewhat problematic. The term implies the toxic material is in metallic form, whereas many heavy metals in the environment may actually be present as a compound, for example methylmercury.

Another problem with the term is that several elements that are sometimes encompassed in the category include the potentially toxic substances arsenic (a semimetal) and selenium (a nonmetal). The definition of “heavy” is also problematic. Various definitions consider metals with densities of anything from 3.5 to 7 g/cm3 or above as heavy. However, some metallic elements that are actually “light” may also be of environmental concern, such as aluminum (density 2.7 g/cm2) and beryllium (density 1.85 g/cm2). Also, using density as a categorization is problematic as such a physical property can vary according to condition or state of an element.

Sometimes atomic weight is used as a defining characteristic of heavy metals; for example, an atomic mass of 63.5 or greater. This again would exclude several elements that are of environmental concern as heavy metal contaminants, such as chromium, nickel, and cobalt (approximate atomic masses 52, 58.7, 59, respectively) and would exclude metals with low atomic masses that form toxic compounds, such as beryllium (approximate atomic mass 9).

Sometimes the term trace element is preferred by many scientists to categorize inorganic contaminants; however, the term trace suggests that quantities of the element occur in the environment in very low amounts, or that even a “trace” of an element might be toxic. The term also may cause confusion with the language of nutrition, in the context of elements that may be required in “trace” amounts in the diet because they have essential functions within the body of organisms.

Many toxic heavy metals are not necessarily toxic in their pure, metallic forms, and the toxicity of the substance varies according to the state or valency of the element. For example, hexavalent chromium (VI) compounds (i.e., Cr6+) can be extremely toxic and carcinogenic, whereas chromium (III) compounds are generally not a health concern.

Whereas some heavy metals have no known role in the nutritional needs of organisms, such as mercury, and even low levels may be of toxicological concern, several heavy metals are actually required in the diet and are trace essential nutrients, including cobalt, a component of vitamin B12; iron, which is a component of hemoglobin, the pigment that carries oxygen in the blood; and zinc, a component of many enzymes that facilitates metabolic reactions in the body. However, high intakes of these elements may be toxic. High concentrations of heavy metals are problematic, but high concentrations of almost any substance in the environment, even relatively benign substances, can also be toxic.

Heavy metals are naturally occurring, and can be released into the atmosphere as the result of forest fires or volcanic emissions; as a gas, particle, or bound to the surface of dust; or they may be released from rocks by erosion and carried by water, in solution, as particles, or bound to the surface of a suspended substance, into rivers or the ocean. Anthropogenic activities also produce heavy metals, such as burning of fossil fuels in power plants or automobiles, as a by-product of mining, the dumping of heavy metal containing waste, or discharges by industry or sewage systems.

Heavy metals may also be transferred via organisms, and are not broken down by biological processes. Although plants and animals can regulate their metal content to a certain point, metals that cannot be excreted bioaccumulate-build up in an organism over its lifetime-especially long-lived species, concentrating in protein-rich tissues such as liver and muscle. Moreover, predators can absorb heavy metals contained within the tissues of their prey species, gaining even higher inputs of contaminants on up the food chain, until animals at the highest trophic level obtain the highest concentrations of heavy metals, a process known as biomagnification.

As humans are a long-lived, top predator, they are at risk from bioaccumulation and magnification of heavy metals. In humans, problems of heavy metal pollution were first brought to world attention with so-called Minamata disease in the 1950s. This primarily neurological condition was caused by consumption of mercury. However, many other so-called heavy metals have effects on the human nervous, immune, and reproductive/hormonal sysyems; for example, lead is of particular concern.

Bibliography:

H. Duffus, “Heavy Metals-a Meaningless Term?” IUPAC, Pure and Applied Chemistry (v.74, 2002);
Morton Lippmann, Environmental Toxicants: Human Exposures and Their Health Effects (John Wiley & Sons, 1997);
Bibudhendra Sarkar, Heavy Metals in the Environment (CRC Press, 2002);
Jun Ui, Industrial Pollution in Japan (United Nations).