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Toxic Elements Dr. Sherin Bakhashab. 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
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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 NIOSH: National Institute for Occupational Safety and Health
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 • 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: sever neurological disease • Dysfunctions of the central nervous system • Loss of hearing and muscle coordination • Sever brain damage • Death
Lead • Has a very low melting point of 327 degrees C • 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
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 Ammunition
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 • 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
Facts about lead poisoning • The human groups most at risk of lead poisoning are fetuses and children under the age of seven • 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 • Burning 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, melting of gold, lead, copper and nickel • Production of iron and steel • Combustion of coal • 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-melting 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
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
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.
