Introduction Heavy metals are toxic to human health


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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

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.

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 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 metals

  • Metal
  • Route of Entry
  • Toxicity Effect
  • TWA by
  • ACGIH
  • (mg / m³)
  • Carcinogen (suspected by NIOSH)
  • Arsenic
  • Inhalation and ingestion
  • 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

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
  • 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

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

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

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 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

Concentration of Mercury Vapor Indoors

  • Source: Foote, 1972.
  • Location
  • Mercury Concentration
  • (ng / m³)
  • Comments
  • House 4:
  • Living room
  • 1560
  • 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
  • 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

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

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

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 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.)

  • 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 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 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.

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

  • 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

  • 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 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 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

  • 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 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

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 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 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

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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