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Heavy metals definitions

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GEOG 204
Mary Silas

Chapter 4Human Health and Heavy Metal Exposure:  Metals are notable for their wide environmental dispersion from such activity; their tendency to accumulate in select tissue of the body; and their overall potential to be toxic even at relatively minor levels of exposure.  Some metals such as iron and copper are essential life and play a big role. However, some metals are xenobiotics they have no useful role in human physiology.  One of the reflection of the importance of metals relative to other potential hazards in their making by the U.S agency for toxic substances and disease registry (ATSDR) which lists the hazards present in toxic waste sites according to their prevalence and severity of their toxicity  The first, second, third and sixth hazards respectively on the list are heavy metals: lead, mercury, arsenic and cadmium.  Exposure to metals can occur through a variety of routes: metals may be inhaled as dust or fumes. Some metals can be vaporized and inhaled. Metals can also be ingested involuntarily from food and drink.  The amount of actually absorbed from the digestive tract can vary widely, depending on the chemical form of the metal and the age and nutrional status of the individual  Once a metal is absorbed it distributes in tissues and organs.  Excretion typically occurs primarily through the kidneys and digestive tracts, but metals tend to persist in some storage sties like the liver, bones and kidneys for years or decades.  Toxicity of metals commonly involves the brain and the kidney, but other manifestation occurs, and some metals such as arsenic are clearly capable of causing cancer.  Lead:  An exposure remains high or is increasing in many developing countries through a rapid increase in vehicles combusting leaded gasoline and in polluting industries.  Individuals will absorb more lead in their food if their diets are deficient in calcium, iron or zinc.  Toxicity:  Depending on the dose, lead exposure in children and adults can cause a wide spectrum of health problems, ranging from convulsion, cona, renal failure and death at the high end to subtle effects on metabolism and intelligence at the low end of exposure.  Children are particularly vulnerable to the neurotoxin effects of lead  Low level lead exposure in children less then five years of age, results in deficits in intellectual development, as manifested by lost of IQ points.  Maternal bone lead stores are mobilized at an accelerated rate during pregnancy and location are associated with decrements in birth weight, growth rate and mental development.  Mercury:  Exposure:  Mercury has been increasing in importantance as a widespread contaminant.  When deposited in soil, organic mercury compounds are slowly broke down into inorganic compounds; conversely inorganic mercury can be converted by microorganism in soil and water into the organic compound methyl mercury, which is then biocentrated up the food chain.  Toxicity:  At lower but more chronic level of exposure, a typical excitability, memory loos, insomnia, timidity and sometimes delirium- that were once commonly seen to workers exposed to mercury.  Mothers exposed to mercury in 1955 in minmata bay, Japan, gave birth to infants with mental retardation, retention of primitive reflexes, cerebella symptoms, and other abnormalities.  Even at much lower levels, mercury exposure on part of pregnant women through deity intake of fish and whale meat, an important regional food staple is associated with decrements in motor function, language, memory, and neural transmission in their offspring’s.  Arsenic:  Arsenic is a toxic and carcinogenic heavy metal, and human exposures are common.  Exposure:  Significant exposure to arsenic occurs through both anthropological and natural sources.  Widespread dispersion of arsenic is a by-product of the combustion of fossil fuels in which a
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