IAQ 1

HEAVY METALSHEAVY METALS

IntroductionIntroduction

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

Properties of heavy metalsProperties 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.

Transport phenomenon 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.

Toxicity of heavy metalsToxicity 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).

Toxicity of trace heavy Toxicity of trace heavy metalsmetals

Toxicity of trace heavy metalsToxicity of trace heavy metals

Yes0.5

Lung damage and Irritation or respiratory system

Inhalation, ingestion, and absorption through skin

Chromium

Yes0.05

Lung, liver and kidney damage; Irritation of respiratory system

Inhalation and ingestion

Cadmium

Yes0.20

Irritation of respiratory system, Liver and Kidney damage, Loss of appetite, nausea and vomiting etc

Inhalation and ingestion

Arsenic

Carcinogen (suspected by NIOSH)

TWA by

ACGIH

(mg / m³)

Toxicity EffectRoute of Entry

Metal

Toxicity of trace heavy Toxicity of trace heavy metalsmetals

Toxicity of trace heavy metalsToxicity of trace heavy metals

Yes1.00

Lung, liver and kidney damageInhalationNickel

No0.15

Lung and liver damage; loss of appetite, nausea etc

Inhalation and ingestion

Lead

Yes0.05

(vapor)

Irritation of respiratory system; lung, liver and kidney damage

Inhalation,ingestion and absorption through skin

Mercury

Carcinogen (suspected by NIOSH)

TWA by ACGIH

(mg / m³)Toxicity EffectRoute of entryMetal

MercuryMercury

MercuryMercury

Most volatile of all metalsHighly toxic in vapor formLiquid mercury itself is not highly toxic,

and most of that ingested is excreted

Sources of MercurySources 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

Health effects 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

Concentration of Mercury Concentration of Mercury Vapor IndoorsVapor Indoors

Concentration of Mercury Vapor IndoorsConcentration of Mercury Vapor Indoors

9 months after painting with latexpaint262

House 3:

Bed room

4 months after painting with latexpaint164

House 2:

Livingroom

139 Bed room 2

66.5 Bed room 1

69 Livingroom

68.2 Study room

21 months after painting with latexpaint

House 1

Comments

MercuryConcentration

(mg / m³)Location

Concentration of Mercury Concentration of Mercury Vapor IndoorsVapor Indoors

Concentration of Mercury Vapor IndoorsConcentration of Mercury Vapor Indoors

Office away from laboratory398Laboratory

Near the desk592Laboratory

Near the sink930Hospital laboratory

Inactive for previous 4 days307Hospital laboratory

Mixing area for Hg-amalgam1295Dentist’s office

Hg thermometer broken in the past5550Dentist’s office

Painted with latex paint 6 months before

4950Doctor’s room

203Office building

New home, painted with latex paint 30 days before1560

House 4:

Living room

Comments

Mercury Concentration

(ng / m³)Location

Source: Foote, 1972.

LeadLead

LeadLead

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

Sources of leadSources 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

Sources (contd.)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 effectsHealth 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

Health effects(contd.)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

Lead content of House DustLead content of House Dust

Lead content of House DustLead content of House Dust

214013501530860Lead content of soil, ppm

1320430780320Lead content of dust, ppm

636.7263.5Total amt. Of dust, g / m²

72767173Home age (yrs)

96325No. of homes studied

After RemodelingWalk-off MatShoes onShoes offActivities

Source: Roberts et al., 1990.

Facts about lead Facts about lead poisoningpoisoning

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.

Cadmium Cadmium

Cadmium 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.

Sources of Cadmium 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.

Health effects 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.

Arsenic Arsenic

Arsenic 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

Sources of ArsenicSources 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

Health effects 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

Recent studies on Recent studies on arsenic exposurearsenic 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

Recent studies..(contd.)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 General sources of heavy metals in residential housesmetals 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

Sampling and Sampling and MeasurementMeasurement

Methods for measurement of Methods for measurement of trace metalstrace 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.

Control strategiesControl strategies

Control methodsControl 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

ReferencesReferences

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.