(IAQ)

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.