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
(No Transcript)
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