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Heavy Metals

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Title: Heavy Metals


1
Heavy 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).
  • Nicole, Noah, Megan

2
What 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.

3
Primary 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)

4
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5
Table 1 Lists Metals According to Their Toxicities
6
Copper
  • 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.

7
Copper 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.

8
Copper 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

9
Lead
  • 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.

10
Lead 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.

11
Lead 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.

12
Mercury
  • 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.

13
Mercury 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.

14
Mercury 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.

15
Aluminum
  • 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.

16
Aluminum Sources
  • Al is found in clay soils, and plays a role in
    soil acidity, in aluminosilicates and aluminum
    oxides.

17
Aluminum 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.

18
Aluminum 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.
19
Over 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.

20
Sources 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
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