Essay, Research Paper: Heavy Metals And Their Uptake By Plants

Heavy Metals and Their Uptake by Plants

What are Heavy Metals?
Heavy metals are natural constituents of the Earth's crust
and trace amounts are always present in biological
materials. They are defined more specifically as
electropositive elements having a density greater than five.

Some examples of heavy metals are mercury, plutonium,
uranium, chromium, and lead.

What are their effects on the environment?
Small amounts of some of these metals are necessary for
proper life functions, but too much can cause sickness or
even death. Their major routes of exposure are inhalation
and ingestion. These metals are absorbed very easily into
the brain and lead is accumulated in the bone. Heavy metals
can also damage animals in the wilderness.

How can they be removed?
They can be removed in many ways, including acid leaching
and delectroosmosis, or immobilization by vitrification.
These methods remove all biological activity from the
treated material. They are also expensive and often
require special equipment and specially trained operators. Phytoremediation and rhizofiltration are two cost effective, environmentally sound methods of removing heavy metals. These processes are defined as the use of plant roots to remove toxic heavy metals from water or soil. This technology will lead to improved and lower cost methods for conserving water resources and restoring water quality.

The plants utilized are called hyperaccumulators. These
hyperaccumulators accumulate the metals mostly in the leaf
and stem vacuoles. Some terrestrial plants used include
Indian mustard and sunflower. The main problems with these
new methods include the fact that most hyperaccumulators
are fairly rare and the disposal of large amounts of
harvested metal-enriched biomass.

What is plutonium?
Plutonium is one of the most toxic materials known to man.
It is a manmade byproduct of nuclear reactions. It has
been shown that plants tend to absorb plutonium very well,
although the mechanism that accomplishes this is not yet
known. Five processes each influence the uptake of heavy
metals, including plutonium, by plants; these are
mobilization, root absorption, complexation, transport, and
compartmentalization. Many common plant species are being
tested for the ability to absorb dangerous heavy metals,
like plutonium. Some of these test species are clover,
soybean, tomato, pea, oat, barley, and corn.

What is Mercury?
Found in red sulfide and other ores containing compounds of
zinc, tin and copper, rocks such as limestone, sandstone,
shale, balsalt, and fossil fuels, mercury is a highly toxic
heavy metal. The larger part of atmospheric mercury is
present in vapor form. This is often removed through
precipitation into water and works its way up the aquatic
food chain until, finally, humans can come in contact with
it and, in big enough quantities become ill from mercury
poisoning. Humans can also come in contact with mercury in
freak accidents in labs or broken mercury thermometers.
In most cases, exposures are identified because symptoms
develop.

What is lead?
Lead is yet another poisonous heavy metal. Most exposure
has been prevented with the elimination of leaded gasoline
and paint. Also, it is now illegal to use lead solder on
food and drink cans. Still, older buildings often still
have lead paint. Therefore, low-income Hispanic and
African-American children living in major cities have the
highest lead levels (10 micrograms/ deciliter). There is
also the question of the transfer of lead through breast
milk, but since very low levels of lead actually end up in
the milk, this is still safe. Lead poisoning is also
usually caught early, due to extensive screening processes.

Are Heavy Metals dangerous to humans?
Certain heavy metals, namely lead and mercury, are
incredibly poisonous to humans. Key symptoms of lead
poisoning are gastrointestinal discomfort, constipation,
anorexia, nausea, fatigue, personality changes, headache,
hearing loss, and lack of coordination in adults and
irritability, abdominal pain, ataxia, seizures, loss of
consciousness, chronic learning deficits, hyperactivity,
and reduced attention span. Sign of mercury poisoning are
muscle cramps or tremors, headache, tachycardia,
intermittent fever, acrodynia, personality change, and
neurological dysfunction. If these symptoms are present
and the individual could've possibly been exposed to either
mercury or lead, the person should seek professional help.

Where can I get more information?
1. soilcrop.tamu.edu/webpages/rloepper/PlantCr.htm
2. www.epa.gov/iedweb00/pubs/hpguide.html
3. www.manufactur…hives/1995/po10201.95/02adp1f0.htm
4. es.epa.gov/ncerqa_abstracts/sbir/other/water/dushenkor.html
5. A Primer of Environmental Toxicology Roger P. Smith 1992
6. www.anl.gov/LabDB/Current/Ext/H603-text.002.html