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IntroductionHeavy metals are toxic to human healthMost common heavy metals are lead(Pb),
mercury(Hg), cadmium(Cd) and arsenic(As)Indoor concentration of heavy metals is generally less
than their outdoor concentrationThey are mainly produced by industrial activities, and
deposit slowly in the surrounding water and soil
Properties of heavy metalsThey occur near the bottom of the periodic tableHave high densitiesToxic in natureNondegradable
Note: Arsenic is not actually a metal but is a semimetal i.e. its properties are intermediate between those of metals and nonmetals.
Transport phenomenon Water FoodAirAdsorption or absorption onto various materials
Example: Over half of the heavy metal input into Great Lakes is due to deposition from air.
Toxicity of heavy metalsMercury 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).
Toxicity of trace heavy metalsMetal
Route of Entry
Toxicity Effect
TWA by
ACGIH
(mg / m³)
Carcinogen (suspected by
NIOSH)
ArsenicInhalation and ingestion
Irritation of respiratory system, Liver and Kidney damage, Loss of appetite, nausea and vomiting etc
0.20 Yes
CadmiumInhalation 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
Toxicity of trace heavy metals
Metal Route of entry Toxicity EffectTWA by ACGIH
(mg / m³)
Carcinogen (suspected by NIOSH)
MercuryInhalation,ingestion and absorption through skin
Irritation of respiratory system; lung, liver and kidney damage
0.05
(vapor)Yes
LeadInhalation and ingestion
Lung and liver damage; loss of appetite, nausea etc
0.15 No
Nickel InhalationLung, liver and kidney damage
1.00 Yes
MercuryMost volatile of all metalsHighly toxic in vapor formLiquid mercury itself is not highly toxic, and most of that
ingested is excreted
Sources of MercuryElemental 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 operationsUnregulated burning of coal and fuel oilIncineration of municipal wastes Emissions from mercury containing products :batteries,
thermometers, etc.Mercury amalgams: dental fillings
Health effects Skin burnsIrritation of nose and skinRashesExcessive perspirationDamage to the kidneysDamage to visionMinamata disease Dysfunctions of the central nervous systemLoss of hearing and muscle coordinationSevere brain damageDeath
Concentration of Mercury Vapor Indoors
Location
Mercury Concentration
(mg / m³)Comments
House 121 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 room164
4 months after painting with latex paint
House 3:
Bed room262
9 months after painting with latex paint
Concentration of Mercury Vapor Indoors
Source: Foote, 1972.
LocationMercury
Concentration
(ng / m³)Comments
House 4:
Living room1560
New home, painted with latex paint 30 days before
Office building 203
Doctor’s room 4950 Painted with latex paint 6 months before
Dentist’s office
5550 Hg thermometer broken in the past
Dentist’s 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
LeadHas a very low melting point of 327 degrees CUsed as a structural metal in ancient times and for
weather proofing buildingsRomans used it in water ducts and in cooking vesselsAnalysis 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
Sources of leadCommonly used in the building industry for
roofing and flashing and for soundproofingUsed in pipesWhen 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
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
Health effectsAt high levels, inorganic lead is a general metabolic
poisonLead 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
Health effects(contd.)Lead is observed to lower IQ levels in childrenLead is transferred postnatally from the mother in her
breast milkAt elevated levels, lead poisoning would eventually result
in death
Lead content of House Dust
Source: Roberts et al., 1990.
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
Facts about lead poisoningThe human groups most at risk of lead poisoning are
fetuses and children under the age of sevenChronic lead poisoning from wine and other sources is
one of the factors in the downfall of the roman empireEpisodes of lead poisoning were recorded through the
middle ages and even until recent timesA 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.
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
cadmiumIncineration of wastes containing cadmium is an
important source of the metal in the environmentCadmium 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.
Sources of Cadmium Cadmium is used as an electrode in “nicad” batteriesCadmium is used as a pigment in paints(yellow color)It is also used in photovoltaic devices and in TV
screensCigarette smokeFertilizers 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.
Health effects Severe pain in jointsBone diseasesKidney problemsIts lifetime in the body is several yearsAreas of greatest risk are Japan and central EuropeIn very high levels it poses serious health problems
related to bones, liver and kidneys and can eventually cause death.
Arsenic Arsenic oxides were the common poisons used for murder
and suicide from roman times through to the middle agesArsenic compounds were used widely as pesticides before
the organic chemicals eraArsenic is very much similar to phosphorous
Sources of ArsenicPesticidesMining, smelting of gold, lead, copper and nickelProduction of iron and steelCombustion of coalLeachate from abandoned gold minesUsed as a wood preservativeHerbicides Tobacco smokeWallpaper paste and pigments in wallpaper
Health effects Birth defectsCarcinogen: 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 damageSevere vomitingDiarrheaDeath
Recent studies on arsenic exposureArsenic 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
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 ).
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
Methods for measurement of trace metalsMost common method of collecting particulate matter is
through filtersIdentification 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.
Control methodsPeriodic vacuuming of the house can be effective in
removal of these pollutantsReplacement of wood-burning by an equivalent gas
or electrical applianceRemoval of old lead and mercury-based paintsThe effective method for removal of mercury vapors
is by the use of packed bed of absorbentsGold-coated denuder can also be used for the removal
of mercury from air
ReferencesKrishnamurthy, 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.