heavy Metal toxicology in natural science

1. BIOACCUMULATION OF HEAVYMETALS
Pollutants like heavy metals are
CONSERVATIVE pollutants – i.e. they aren’t
broken down by bacteria etc and are
effectively permanent
Most plants and animals can regulatetheir
metal content to a certain point-but metals
that can’t be excreted buildup in an organism
over its lifetime

2. *short note BIOACCUMULATION
Bioaccumulation is essentially the buildup
of contaminants such as heavy metals or
pesticides in living organisms

3. BIOMAGNIFICATION
those animals feeding on bioaccumulators
gain even higher inputs of contaminants and
bioaccumulate even greater concentrations
and so on.. with animals at the highest
trophic level obtaining highest concentrations
*short note

5. SPECIATION ANDTOXICITY OF HEAVY METALS
 Poisonous in their cations form
 Highly toxic when bonded to short chains of
carbon atoms
ex. Alkyl groups with mercury and lead
attached

7. MERCURY
• Symbol Hg
• From the Latin word, hydrargyrum, “liquid silver,”
• Shining, mobile liquid, silvery-white in color
• It is liquid at -38.9oC
• Becomes solid when subjected to a pressure of
7,640 atmospheres
• Freezing point of about -39°C (about -38°F), a boiling
point of about 357°C
• Density of 13.55 grams per cu cm. The atomic weight
of mercury is 200.59gmol-1
• Conducts electricity well
• Its principal ore is cinnabar

8. ENVIRONMENTAL SOURCES/USES OFMERCURY
Electrical switches in automobilesbuilt
before 2000
In fluorescent light bulbs and in streetlamps
before
dental amalgam
Gold and silver mining
Pesticides
Used to make felt forhats

9. ENVIRONMENTAL SOURCES/USES OFMERCURY
(cont.)
Fossil fuel coal lignite(100ppb)
Discarded laboratorychemicals
Pharmaceuticalproducts
Crematoria
Wastewater from dentists’offices
Preservepaint
Used as slimicides in pulp-and-paper
industry
As topical antiseptic and in cosmetics

10. MERCURY ANDTHE INDUSTRIAL CHLOR-ALKALI
PROCESS
 amalgam of sodium and mercury is used in
some industrial chlor-alkali plants in process
that converts aqueos sodium chloride into
the commercial products chlorine and
sodium hydroxide and gaseous hydrogen by
electrolysis.
 Flowing mercury is used as the cathode
 Some of the mercury find its way to the air
and water

11. MERCURY VAPOR
It is composed of free, neutralatoms.
If inhaled the atoms diffuse from the lungsto
the bloodstream
liquid mercury is not highly toxic, when
ingested most are excreted

12. METHYLMERCURY TOXICITY
Methyl anion combines with Hg2+ to yield
volatile molecular liquid dimethylmercury.
The formation occurs in muddy sediments
of rivers and lakes, under anaerobic
condition
Methylmercury(or monomethylmercury)
• Its production predominates over
dimethylmercury in acidic or neutral aqueous
systems
• Sulfate ions stimulates sulfate-reducing
bacteria that methylate mercury
• Sulfide ions results in formation of mercury
sulfide complexes that do not undergo
methylation

14. (cont.)
between methylmercury in fish muscle and
that dissolved in the water: 1 million to 1, and
can exceed 10 million to 1
High methylmercury concentration inlarge,
long-lived predatory marine species

15. METHYLMERCURY ACCUMULATION INTHE
ENVIRONMENT AND IN THEHUMANBODY
• Half-life of methylmercury in human bodyis
70days
• Cumulativepoison
• dialkylmercury including dimethylmercuryis
supertoxic

16. MINAMATA DISEASE
• Occurred in a village in Minamata, Japan
• CH3Hg-SCH3
• 100ppm of mercury in fish tissues
• Onset symptoms were first seen in cats
• Symptoms in humans arise from dysfunctions of
the central nervous system
• Methylmercury can be passed to fetus
• U.S. has EPA maximum conc of 0.3ppm in fish
tissue

17. SOURCES OFMETHYLMERCURY
Fungicide in agriculture andindustry
Leaching from rocks and soil intowater
systems by natural processes
PreservativeThimerosal

18. SAFE LEVEL OF MERCURY IN THE BODY
10-20ppm of CH3Hg+ in hair can be
dangerous
INTERNATIONAL CONTROL ONMERCURY
United Nations Environment Programme in
2005 devised a global treaty to curb the
production if mercury and to ban completely
the export of mercury between countries

20. Drinking Water Guidelines for Heavy
Metals

22. *AdditionalNoteon: THE WOOD PRESERVATIVECCA
Chromated CopperArsenate
A waterborne mixture of metal oxideswith
which wood is treated using vacuum-
pressure impregnation process
10% of the mass of thelumber
Cr(IV) is usedhere
Protects woodenstructures
Replaced creosote andpentachlorophenol