Post on 25-Dec-2015
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
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
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 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 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
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 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