Metals are natural components in soil. Some of
these metals are micronutrients necessary for plant
growth, such as Zn, Cu, Mn and Co, while others
have unknown biological function, such as Cd, Pb, Ni,
Cr, As and Hg (Gaur and Adholeya 2004; Lasat,
2000). Many species of plants have been successful
in absorbing contaminants such as lead, cadmium,
chromium, arsenic, and various radionuclides from
soils. Toxic heavy metals such as Pb, Co, Cd, Ni, As,
Cr are accumulated in the plants and animals. Since
they are not biodegraded thus causing various
diseases and disorders even in relatively lower
concentrations (Pehlivan et al., 2009). Heavy metals
are the major environmental contaminants and pose
a severe threat to human and animal health by their
long-term persistence in the environment (Gisbert et
al., 2003; Halim et al., 2003). Heavy metals
constitute an ill-defined group of inorganic chemical
hazards, and those most commonly found at
contaminated sites are lead (Pb), chromium (Cr),
arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu),
mercury (Hg) and nickel (Ni) (GWRTAC, 1997). Heavy
metals, with soil residence times of thousands of
years, pose numerous health dangers to higher
organisms. They also effect on plant growth, ground
cover and have a negative impact on soil microflora
(Roy et al., 2005). For instance, lead (Pb) has a soilretention time of 150–5,000 years and was reported
to maintain a high concentration for as long as 150
years after application of sludge to the soil
(Nandakumar et al., 1995).
The problems of ecosystems are increasing with the
advancement in technology. The elevated level of
lead and other heavy metals, e.g. cadmium,
chromium and mercury, in the local water streams is
a major concern to public health. Soils contaminated
by the accumulation of heavy metals and metalloids
through emissions from the rapidly expanding
industrial areas, mine tailings, disposal of high metal
wastes, leaded gasoline and paints, land application of fertilizers, animal manures, sewage sludge,
pesticides, wastewater irrigation, coal combustion
residues, spillage of petrochemicals, and
atmospheric deposition (Khan et al., 2008; Zhang et
al., 2010). Plants have evolved highly specific and
very efficient mechanisms to obtain essential
micronutrients from the environment, even when
present at low ppm levels. Plant roots, aided by
plant-produced chelating agents and plant induced
pH changes and redox reactions, are able to
solubilize and take up micronutrients. Plants have
also evolved highly specific mechanisms to
translocate and store micronutrients. These same
mechanisms are also involved in the uptake,
translocation, and storage of toxic elements, whose
chemical properties simulate those of essential
elements. Thus, micronutrient uptake mechanisms
are of great interest to phytoremediation (USDE
1994). Some metals with unknown biological
function (Cd, Cr, Pb, Co, Ag, Se and Hg) are also
accumulated (Cho-Ruk et al., 2006). Contaminated
soils and waters pose a major environmental and
human health problem, which may be partially
solved by the emerging phytoremediation
technology (Salt et al., 1998). Phytoremediation is
the use of vegetation for in situ treatment of
contaminated soils, sediments, and water. It is
applicable at sites containing organic, nutrient, or
metal pollutants that can be accessed by the roots of
plants and sequestered, degraded, immobilized, or
metabolized in place. The generic term
“phytoremediation”consists of the Greek prefix
phyto (plant), attached to the Latin root remedium
(to correct or remove an evil) (USEPA 2000;
Erakhrumen and Agbontalor, 2007). Heavymetals
uptake, by plants using phytoremediation
technology, seems to be a prosperous way to
remediate heavymetals contaminated environment.
(Bieby et al., 2011). Techniques used for removal of
heavy metals, like chemical precipitation, lime
coagulation, ion exchange, reverse osmosis and
solvent extraction are expensive and nonenvironmental friendly.
Summarize and write a main points for the above information
1. Metals such as Zn, Cu, Mn, and Co are essential micronutrients for plant growth, while others like Cd, Pb, Ni, Cr, As, and Hg have unknown biological functions and can be toxic.
2. Heavy metals like Pb, Co, Cd, Ni, As, and Cr can accumulate in plants and animals, causing various diseases and disorders even in lower concentrations.
3. Heavy metals pose a severe threat to human and animal health due to their long-term persistence in the environment.
4. Lead, chromium, arsenic, zinc, cadmium, copper, mercury, and nickel are the most commonly found heavy metals at contaminated sites.
5. Heavy metals have negative effects on plant growth, ground cover, soil microflora, and higher organisms due to their long soil residence times.
6. The accumulation of heavy metals in soil and water is a major concern for public health, caused by industrial emissions, mine tailings, waste disposal, and other sources.
7. Phytoremediation, the use of vegetation for in situ treatment of contaminated soils, sediments, and water, is an emerging technology that may help mitigate the impact of heavy metal contamination.
8. Techniques like chemical precipitation, lime coagulation, ion exchange, reverse osmosis, and solvent extraction are expensive and non-environmentally friendly for heavy metal removal.