BIO206H5 Chapter Notes - Chapter 4: Methylmercury, Arsenic, Intellectual Disability
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Chapter 4Human 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
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
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
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.
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
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
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