Title: Heavy Metals
1Heavy Metals
The term heavy metal refers to any metallic
chemical element that has a relatively high
density and is toxic or poisonous at low
concentrations. Examples of heavy metals include
mercury (Hg), cadmium (Cd), arsenic (As),
chromium (Cr), thallium (Tl), and lead (Pb).
2What is a Heavy Metal?
- Heavy metals are those having densities five
times greater than water, and the light metals
are those having lesser densities. - Examples of heavy metallic elements are iron,
lead, and copper. - Examples of light metals are sodium, magnesium,
and potassium. - Humans consume metallic elements through both
water and food.
3Primary Sources For Heavy Metal Soil
Contamination Include
- Fertilizers containing lead and arsenic .
- Pesticides containing lead, arsenic and mercury.
- Sewage sludge containing cadmium, arsenic and
lead (Odum, 2000) . - Irrigation water may transport dissolved heavy
metals to agricultural fields where metals such
as cadmium may be incorporated into plant tissue. - Atmospheric deposition.
- (NCSU Water Quality Group, 1976)
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5Table 1 Lists Metals According to Their Toxicities
6Copper
- Copper naturally occurs in soil and plants
- Copper is a reddish metal that occurs naturally
in rock, soil, water, sediment and air. - Its average concentration in the earths crust
is about 50 parts copper per million parts soil
(ppm). - It is an essential element for all known living
organisms, including humans and other animals.
However, at high concentrations, copper is toxic.
7Copper Sources
- Copper is released into the environment by
mining, farming, and manufacturing operations and
through waste water releases into rivers and
lakes. - It is also released from natural sources
- Volcanoes
- Windblown dusts
- Decaying vegetation
- Forest fires
- Copper released into the environment usually
attaches to particles made of organic matter,
clay, soil, or sand.
8Copper in Plants
- Signs of copper deficiencies
- Wilted leaves
- Chlorosis (yellowing of leaves)
- Root rot
- Functions
- Important for reproductive growth
- Chlorophyll production
- Protein synthesis
- respiration
- Aids in root metabolism
- Helps in utilization of proteins
9Lead
- Lead is by far the most common contaminant of
soils. - Lead in soil is virtually a permanent resident.
Organic matter, especially, will bind and hold
itself in other metals very effectively.
10Lead Sources
- Number one source contamination
- -lead-based paint
- (which has been chipped or scraped off building
exteriors over several decades or centuries.) - Other sources
- -gasoline exhaust
- -motor oil
- - automobile tires
- -industrial activity
- -coal combustion, and pesticides.
11Lead in Plants
- Lead in plants
- - Absorbed through roots
- - Lead builds up in both leaf and root tissue
- - Causes lower concentration of chlorophyll
- - Lead compounds absorb UV light
- - Plants biomass declines, which includes
roots, shoots, and fruits.
12Mercury
- Mercury occurs in two forms
- - organic
- - inorganic
- Inorganic forms most often occur when mercury is
combined with chlorine, sulfur or oxygen. - Organic forms occur when mercury combines with
carbon.
13Mercury Sources
- Metallic forms of mercury are not absorbed by
plants, but are converted by microorganisms to
organic forms such as methylmercury, which are
taken up by plants. - Environmental sources include thermometers,
pesticides, metallurgy, and vapors from burning
coal and other fuels.
14Mercury in Plants
- The uptake of mercury
- - decreases growth
- - induces disorientation of roots and shoots,
plant tissue, and finally the cell wall. - A major portion of Mercury is tightly bound and
remains in the roots.
15Aluminum
- Aluminum toxicity is one of the most common
factors that limit plant growth and development
in many acid soils. - -Aluminum is made available through the process
of cation-exchange when hydrogen ion replaces
aluminum on clay particles the Al is released
into the soil water.
16Aluminum Sources
- Al is found in clay soils, and plays a role in
soil acidity, in aluminosilicates and aluminum
oxides.
17Aluminum in Plants
- Al doesnt effect seed germination, but does
impair growth of new roots and seedling
establishment. - -Roots will be stubby and brittle and may turn
brown. - Plant shoots response to Al by
- -Cellular ultra structural changes in
leaves - -Increases rates of diffusion resistance
reduction of stomatal aperture, and decreased
photosynthetic activity leading to chlorosis. -
18Aluminum in Plants
Which results in Aluminum -Decreases
overall leaf numbers - Size affecting the
biomass Aluminum affects plant growth, crop
yield, uptake and distribution of nutrients in
fruits and reproductive parts.
19Over View of it All..
- Heavy metal soil contamination is a global
problem affecting plant growth and development
and limiting plant distribution and crop
production. Plants do not possess effective
mechanisms to escape the polluted environment,
therefore they should live and survive exposed
directly to stress conditions.
20Sources and References
- Internet
- http//www.agr.state.nc.us/cyber/kidswrld/plant/nu
trient.htmtop - http//web.missouri.edu/umcsnrsoilwww/313_W2004/m
icro2_2004.htm - http//www.probeiternational.org/ebi/contaminants/
cooper.html - http//www.atsdr.cdc.gov/tfacts132.html
- http//www.saanendoah.com/cudefsoil.html
- www.lenntech.com/heavy-metals.htm
- www.nscc.govt.nz
- www.rsc.org/.../Volume/2005/8/heavy_metals.asp
- www.emporia.edu/earthsci/amber/go336/uttinger/
- Books
- Environmental Plant Physiology Edition 2 3- Dgl
- Soils Soil fertility- Dgl / Jean English
- Science and Nutrient Plant Physiology- Jean
English - Plant Nutrition- Jean English