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HEAVY%20METALS

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Title: HEAVY%20METALS


1
HEAVY METALS
(IAQ)
2
Introduction
  • Heavy metals are toxic to human health
  • Most common heavy metals are lead(Pb),
    mercury(Hg), cadmium(Cd) and arsenic(As)
  • Indoor concentration of heavy metals is generally
    less than their outdoor concentration
  • They are mainly produced by industrial
    activities, and deposit slowly in the surrounding
    water and soil

3
Properties of heavy metals
  • They occur near the bottom of the periodic table
  • Have high densities
  • Toxic in nature
  • Nondegradable
  • Note Arsenic is not actually a metal but is a
    semimetal i.e. its properties are intermediate
    between those of metals and nonmetals.

4
Transport phenomenon
  • Water
  • Food
  • Air
  • Adsorption or absorption onto various materials
  • Example Over half of the heavy metal input into
    Great Lakes is due to deposition from air.

5
Toxicity of heavy metals
  • Mercury is highly toxic in vapor form but
    lead,cadmium and arsenic are more toxic in their
    cationic form
  • Toxicity arises from strong affinity of the
    heavy metal cations for sulfur
  • Medicinal treatment for heavy metal poisoning is
    done by chelation therapy by administering
    compounds known as chelates
  • Example British Anti-Lewisite(BAL),
    ethylene diamine tetra acetic acid(EDTA).

6
Toxicity of trace heavy metals
Metal Route of Entry Toxicity Effect TWA by ACGIH (mg / m³) Carcinogen (suspected by NIOSH)
Arsenic Inhalation and ingestion Irritation of respiratory system, Liver and Kidney damage, Loss of appetite, nausea and vomiting etc 0.20 Yes
Cadmium Inhalation and ingestion Lung, liver and kidney damage Irritation of respiratory system 0.05 Yes
Chromium Inhalation, ingestion, and absorption through skin Lung damage and Irritation or respiratory system 0.5 Yes
7
Toxicity of trace heavy metals
Metal Route of entry Toxicity Effect TWA by ACGIH (mg / m³) Carcinogen (suspected by NIOSH)
Mercury Inhalation,ingestion and absorption through skin Irritation of respiratory system lung, liver and kidney damage 0.05 (vapor) Yes
Lead Inhalation and ingestion Lung and liver damage loss of appetite, nausea etc 0.15 No
Nickel Inhalation Lung, liver and kidney damage 1.00 Yes
8
Mercury
9
Mercury
  • Most volatile of all metals
  • Highly toxic in vapor form
  • Liquid mercury itself is not highly toxic, and
    most of that ingested is excreted

10
Sources of Mercury
  • Elemental mercury is employed in many
    applications due to its unusual property of being
    a liquid that conducts electricity
  • Used in electrical switches, fluorescent light
    bulbs and mercury lamps
  • Emission of mercury vapor from large industrial
    operations
  • Unregulated burning of coal and fuel oil
  • Incineration of municipal wastes
  • Emissions from mercury containing products
    batteries, thermometers, etc.
  • Mercury amalgams dental fillings

11
Health effects
  • Skin burns
  • Irritation of nose and skin
  • Rashes
  • Excessive perspiration
  • Damage to the kidneys
  • Damage to vision
  • Minamata disease
  • Dysfunctions of the central nervous system
  • Loss of hearing and muscle coordination
  • Severe brain damage
  • Death

12
Concentration of Mercury Vapor Indoors
Location Mercury Concentration (mg / m³) Comments
House 1 21 months after painting with latex paint
Study room 68.2
Living room 69
Bed room 1 66.5
Bed room 2 139
House 2 Living room 164 4 months after painting with latex paint
House 3 Bed room 262 9 months after painting with latex paint
13
Concentration of Mercury Vapor Indoors
Location Mercury Concentration (ng / m³) Comments
House 4 Living room 1560 New home, painted with latex paint 30 days before
Office building 203
Doctors room 4950 Painted with latex paint 6 months before
Dentists office 5550 Hg thermometer broken in the past
Dentists office 1295 Mixing area for Hg-amalgam
Hospital laboratory 307 Inactive for previous 4 days
Hospital laboratory 930 Near the sink
Laboratory 592 Near the desk
Laboratory 398 Office away from laboratory
Source Foote, 1972.
14
Lead
15
Lead
  • Has a very low melting point of 327 degrees C
  • Used as a structural metal in ancient times and
    for weather proofing buildings
  • Romans used it in water ducts and in cooking
    vessels
  • Analysis of ice-core samples from Greenland
    indicate that atmospheric lead concentration
    reached a peak in roman times that was not
    equaled again until the renaissance

16
Sources of lead
  • Commonly used in the building industry for
    roofing and flashing and for soundproofing
  • Used in pipes
  • When combined with tin, it forms solder, used in
    electronics and in other applications to make
    connections between solid metals
  • Lead is also used in ammunition
  • Note Lead shots have been banned in United
    States, Canada, Netherlands, Norway and Denmark
  • Lead is used in batteries and sinkers in fishing

17
Sources (contd.)
  • Used in paints
  • Lead chromate is the yellow pigment used in
    paints usually applied to school buses. Lead is
    also used in corrosion-resistant paints and has a
    bright red color
  • Used in ceramics and dishware
  • The leaching of lead from glazed ceramics
    used to prepare food is a major source of dietary
    lead, especially in Mexico
  • In the past, lead salts were used as coloring
    agents in various foods
  • Lead is used in some types of PVC mini-blinds

18
Health effects
  • At high levels, inorganic lead is a general
    metabolic poison
  • Lead poisoning effects the neurological and
    reproductive systems, example downfall of roman
    empire
  • Lead breaks the blood-brain barrier and
    interferes with the normal development of brain
    in infants

19
Health effects(contd.)
  • Lead is observed to lower IQ levels in children
  • Lead is transferred postnatally from the mother
    in her breast milk
  • At elevated levels, lead poisoning would
    eventually result in death

20
Lead content of House Dust
Activities Shoes off Shoes on Walk-off Mat After Remodeling
No. of homes studied 5 32 6 9
Home age (yrs) 73 71 76 72
Total amt. Of dust, g / m² 3.5 26 6.7 63
Lead content of dust, ppm 320 780 430 1320
Lead content of soil, ppm 860 1530 1350 2140
Source Roberts et al., 1990.
21
Facts about lead poisoning
  • The human groups most at risk of lead poisoning
    are fetuses and children under the age of seven
  • Chronic lead poisoning from wine and other
    sources is one of the factors in the downfall of
    the roman empire
  • Episodes of lead poisoning were recorded through
    the middle ages and even until recent times
  • A recent study in Mexico indicated that pregnant
    women can decrease the lead levels in their blood
    and presumably in the blood of their developing
    fetus by taking calcium supplements.

22
Cadmium
23
Cadmium
  • Cadmium lies in the same subgroup of the periodic
    table as zinc and mercury, but is more similar to
    zinc
  • Coal burning is the main source of environmental
    cadmium
  • Incineration of wastes containing cadmium is an
    important source of the metal in the environment
  • Cadmium is most toxic in its ionic form unlike
    mercury
  • Note Mercury is most toxic in vapor form and
    lead, cadmium and arsenic are most toxic in their
    ionic forms.

24
Sources of Cadmium
  • Cadmium is used as an electrode in nicad
    batteries
  • Cadmium is used as a pigment in paints(yellow
    color)
  • It is also used in photovoltaic devices and in TV
    screens
  • Cigarette smoke
  • Fertilizers and pesticides
  • Note The greatest proportion of our exposure
    to cadmium comes from our food supply- seafood,
    organ meats, particularly kidneys, and also from
    potatoes, rice, and other grains.

25
Health effects
  • Severe pain in joints
  • Bone diseases
  • Kidney problems
  • Its lifetime in the body is several years
  • Areas of greatest risk are Japan and central
    Europe
  • In very high levels it poses serious health
    problems related to bones, liver and kidneys and
    can eventually cause death.

26
Arsenic
27
Arsenic
  • Arsenic oxides were the common poisons used for
    murder and suicide from roman times through to
    the middle ages
  • Arsenic compounds were used widely as pesticides
    before the organic chemicals era
  • Arsenic is very much similar to phosphorous

28
Sources of Arsenic
  • Pesticides
  • Mining, smelting of gold, lead, copper and nickel
  • Production of iron and steel
  • Combustion of coal
  • Leachate from abandoned gold mines
  • Used as a wood preservative
  • Herbicides
  • Tobacco smoke
  • Wallpaper paste and pigments in wallpaper

29
Health effects
  • Birth defects
  • Carcinogen
  • Lung cancer results from the inhalation of
    arsenic and probably also from its ingestion.
    Skin and liver cancer, and perhaps cancers of the
    bladder and kidneys, arise from ingested arsenic
  • Gastrointestinal damage
  • Severe vomiting
  • Diarrhea
  • Death

30
Recent studies on arsenic exposure
  • Arsenic emitted from a copper-smelting plant in
    Bulgaria has been shown recently to have produced
    a three-fold increase in birth defects in new
    born children in that area
  • Most daily exposure of arsenic by north American
    adults is due to food intake, especially of meat
    and seafood
  • Under humid conditions of molds in wallpaper
    paste and arsenic pigments in wallpaper,
    instances of mysterious illness and death have
    been reported

31
Recent studies..(contd.)
  • Recent studies have shown that about 1 of
    Americans consume drinking water that has arsenic
    levels of 25 ppb or more, and in Utah and
    California water supplies have been found to
    contain as much as 500 ppb
  • Scientists have estimated that there is a
    one-in-a-thousand lifetime risk of dying from
    cancer induced by normal background levels of
    arsenic ( this equals the risk estimate due to
    tobacco smoke and radon exposure ).

32
General sources of heavy metals in residential
houses
  • Infiltration from outside, along with the dust
    carried on shoes and clothes
  • Indoor sources include old-lead and latex based
    paints, domestic water supply, burning of wood,
    and tobacco smoke
  • Pesticides and fungicides are major sources of
    arsenic and mercury indoors

33
Sampling and Measurement
34
Methods for measurement of trace metals
  • Most common method of collecting particulate
    matter is through filters
  • Identification and concentration of individual
    trace metals like lead,cadmium, arsenic, mercury
    and chromium is determined by
  • ? Atomic absorption
    spectrophotometer
  • ? X-ray fluorescence
  • ? Atomic absorption spectrophotometry is a
    destructive method and requires at least 1 to 2
    ml of solution
  • ? X-ray fluorescence is a nondestructive
    method and works independent of the chemical
    state of the sample.

35
Control strategies
36
Control methods
  • Periodic vacuuming of the house can be effective
    in removal of these pollutants
  • Replacement of wood-burning by an equivalent gas
    or electrical appliance
  • Removal of old lead and mercury-based paints
  • The effective method for removal of mercury
    vapors is by the use of packed bed of absorbents
  • Gold-coated denuder can also be used for the
    removal of mercury from air

37
References
  • Krishnamurthy, S. 1992. Biomethylation and
    environmental transport of metals. Journal of
    Chemical Education 69(5)
  • Colin Baird.2000. Environmental Chemistry, W.H.
    Freeman and Company, New York.
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