HEAVY METALS
Substances
*Hg

13.5

*Pb

11.3

Cu

9.0

*Cd

8.7

*Cr

7.2

Sn

5.8-7.3

*As

5.8

Al

2.7

Mg

1.7

H2O

D...
Figure 1. Relationship between metal generation, exposure pathway and environmental impact.
BIOACCUMULATION OF HEAVY METALS
Pollutants like heavy metals are
CONSERVATIVE pollutants – i.e. they aren’t
broken down by...
BIOMAGNIFICATION


those animals feeding on bioaccumulators
gain even higher inputs of contaminants and
bioaccumulate eve...
SPECIATION AND TOXICITY OF HEAVY METALS
Poisonous in their cations form
 Highly toxic when bonded to short chains of
carb...
CADMIUM (Cd)
Discovered in 1817 by the German chemist
Friedrich Stromeyer
 Cadmium melts at 321°C (610°F), boils at
767°C...
ENVIRONMENTAL SOURCES OF CADMIUM

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Cd compounds form ionic salts with simple anions
Found in water in ...
HUMAN INTAKE OF CADMIUM









High intake for humans living near mines and
smelters
Smokers are also exposed
From ...
PROTECTION AGAINST LOW LEVELS OF
CADMIUM
Cadmium is acutely toxic; lethal dose is 1g
 Humans are protected by methallothi...
EFFECTS IT CAUSE IN THE BODY
Affects important enzymes
 Cause osteomalacia and kidney damage
 Cadmium pneumonitis charac...
CHROMIUM (Cr)


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


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

It has atomic number 24, atomic mass 51.996g/mol
Its melting point and boiling point of 190...
CHROMIUM
Normally occurs in the form of inorganic ions
 Common oxidation states: Cr(VI) and Cr(III)
 In aerobic conditio...
ENVIRONMENTAL SOURCES OF CHROMIUM
Predominantly mined as chromate ore
(FeCr2O4)
 Used to manufacture stainless and in
sup...
CHROMIUM CONTAMINATION OF WATER
Contaminates groundwater beneath areas
with metal-plating
 second most abundant inorganic...
HEALTH EFFECTS OF CHROMIUM
People are exposed to chromium in these four basic ways:
 Breathing (inhalation)
 Eating of c...
Health effects: Trivalent chromium (Cr3+)
Hexavalent chromium (Cr6+) is a danger to human health, it is
carcinogenic. The ...
THE WOOD PRESERVATIVE CCA
Chromated Copper Arsenate
 A waterborne mixture of metal oxides with
which wood is treated usin...
ARSENIC
A metalloid
 It is metallic in appearance and has a specific
gravity of 5.7g·cm-3.
 The atomic weight of arsenic...
COMMON MINERALS OF ARSENIC
arsenopyrite (FeAsS)
 realgar (As2S2)
 orpiment (As2S3)
 arsenic trioxide (As2O3)


When th...
ARSENIC
White arsenic As2O3 is a common poison
 Believed to cure certain ailments, impotence,
prophylactic against plague...
ANTROPOGENIC SOURCES OF ARSENIC
use of its compounds in pesticides
 during mining, smelting of gold, lead. copper,
and ni...
ARSENIC(III) VS. ARSENIC(V) TOXICITY
As(III) commonly exists in aqueous solution
and in solids as arsenite ion AsO33 has ...
acute poisoning
Inorganic As(III) is more toxic than As(V)
methylated arsenic in the liver does not bind tightly so it
...
ARSENIC IN DRINKING WATER
one of the most serious environmental health
hazards
 can cause cancer
 Linked to diabetes and...
DRINKING WATER STANDARD FOR ARSENIC
global average inorganic arsenic content of
drinking water is about 2.5ppb
 WHO and E...
Manifestations of acute arsenic
Bodily system
Symptoms or signs
Time of onset
poisoning
affected

Systemic

Thirst
Hypovol...
REMOVAL OF ARSENIC FROM WATER
to flow the water over activate
alumina(aluminum oxide)
 reverse osmosis can also be used
...
LEAD (Pb)
Its atomic number is 82, atomic weight is 207.2g/mol
 Bluish-white in color.
 It is very soft, highly malleabl...
OCCURRENCE OF LEAD
Lead occurs naturally in the earth crust, usually in
ores such as:
 Galena (PbS) (major ore)
 Cerrusi...
ENVIRONMENTAL SOURCES/USES OF LEAD







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Soundproofing in buildings
Solder- alloy of lead and tin
lining p...
ENVIRONMENTAL SOURCES/USES OF LEAD
(cont.)






Lead in automobile batteries
As additives in gasolines
tetraethyl lea...
EFFECTS OF LEAD IN HUMAN REPRODUCTION
AND INTELLIGENCE
Pb2+ replaces Ca2+ in bones
 Pb2+ remains in bones for decade
 Hi...
HEALTH EFFETC IN ADULTS AND CHILDREN
Blood lead
levels

Adults

Children

10 g/dL

Hypertension may occur

•Crosses placen...
MERCURY
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symbol Hg
From the Latin word, hydrargyrum, “liquid silver,”
Shining, mobile liquid, silvery-w...
ENVIRONMENTAL SOURCES/USES OF MERCURY
Electrical switches in automobiles built
before 2000
 In fluorescent light bulbs an...
ENVIRONMENTAL SOURCES/USES OF MERCURY
(cont.)
Fossil fuel coal lignite (100ppb)
 Discarded laboratory chemicals
 Pharmac...
MERCURY AND THE INDUSTRIAL CHLOR-ALKALI
PROCESS
amalgam of sodium and mercury is used in
some industrial chlor-alkali plan...
MERCURY VAPOR
It is composed of free, neutral atoms.
 If inhaled the atoms diffuse from the lungs to
the bloodstream


...
METHYLMERCURY TOXICITY


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methyl anion combines with Hg2+ to yield volatile
molecular liquid dimethylmercury
t...
(cont.)
between methylmercury in fish muscle and
that dissolved in the water: 1 million to 1, and
can exceed 10 million to...
METHYLMERCURY ACCUMULATION IN THE
ENVIRONMENT AND IN THE HUMAN BODY
Half-life of methylmercury in human body is
70days
 C...
MINAMATA DISEASE
Occurred in a village in Minamata, Japan
 CH3Hg-SCH3
 100ppm of mercury in fish tissues
 Onset symptom...
SOURCES OF METHYLMERCURY
Fungicide in agriculture and industry
 Leaching from rocks and soil into water
systems by natura...
SAFE LEVEL OF MERCURY IN THE BODY


10-20ppm of CH3Hg+ in hair can be
dangerous

INTERNATIONAL CONTROL ON MERCURY



Uni...
heavy metals
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heavy metals
heavy metals
heavy metals
heavy metals
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  • INTRODUCTIONThose metals described as heavy metals are those, which in their standard state have specific gravity (density) of more than 5g/cm3. it is not every heavy metal that is harmful to life. For instance, copper (Cu), nickel (Ni), chromium (Cr) and iron (Fe) are heavy metals which are essential to life. heavy metal refers to a type of chemical element which are poisonous to humans. The five main rae mercury, lead, cadmium, chromium, and arsenic. they are said to be so because of their extensive use, widespread distribution and thir toxicity. Their ultimate sink are soil and sediments. their densities are high compared to the common metals. Mostly transported from place to place via air(as gasses or as species adsorbed in) suspended particulate matter. in general are transition metals and some of the representative elements
  • Increasing industrialization has been accompanied throughout the world by extraction and distribution of metal from their natural deposits. The possible general route and interchange of metal pollutants in the environment is illustrated in Figures 1 as a result of anthropogenic activities, metals a now wide spread in the environment. There is interchange of metals among the different segments of the environment. Civil and industrial activities of man result in various wastes, which could be finely dispersed and/or in solutions, by way of effluents, sewage, dumps and dust. Metals contained in them are thus released into the water, soil or air and thus into food chain. Not all traces of heavy metals are as a result of anthropogenic activities. Metals occur naturally, hence, even foodstuffs produced in completely unpolluted areas are not entirely free of heavy metals. As a result, there is need for preparation of standards for heavy metals in foodstuffs, water among others.
  • *Most plants and animals can regulate their metal content to a certain point – but metals that can’t be excreted build up in an organism over its lifetime *concentrations increase progressively along an ecological food chain
  • alkyl grpups with mercury &/ lead attached are highly toxic. because they are covalent molecules thus soluble to animal tissue. They can pass through biological membranes. whereas charged ions are less able to do so.
  • y-product of zinc smelting, since the two metals usually occur together *burning coals *incineration of waste materials containing cadmium *use as an electrode in rechargeable nicad batteries used in calculators and similar devices *when current is drawn from the battery solid elemental cadmium electrode partially disintegrates to form insoluble Cd(OH)2 by incorporating hydroxide ions from where it is dipped.as the battery is recharged the solid is converted back to cadmium metal---5g Cd,when incinerated most of it is volatilized to the environment *main use is as pigment---CdS depends on the size of the particles-CdS and CdSe use to color plastics *use in paints to produce brilliant yellow colors and thus oppose any ban on them because at present there are no suitable replacements *Van Gogh---cadmium yellow is used in Sunflowers canvas--speculated that it contributed to the artist's anguished and mental state *inceneration of plastics and other materials that contain as pigment or as a stabilizer *when cadmium-plated steel is recycled--since the element isfairly volatile-BP 765degrees C
  • *Cd2+ is soluble in water-unless sulfide ions are present *high intake for humans living near mines and smelters *MCL for drinking water is 5ppb in US and Canada *smokers-Cd that is absorbed from soil and irrigation water by tobacco leaves and then released to the smoke stream when cigarette is burned *from food supply---seafood and organ meats(particularly kidneys)potatoes,wheat rice, grains *ouch-ouch or itai-itai----degenerative bone disease of many women who had borne many children in Japan; severe pain in the joints Ca2+ is replaced by Cd2+ ions since they have sthe same charge and similar size the bones become porous, fracutre and collapse intake of the sufferers are at about 600micro gram per day
  • *Cadmium is acutely toxic; lethal dose is 1g *humans are protected by methallothionen-which functions as regulator of zinc metabolism because it has a lot of sulfhydryl groups it can complex most of the ingested Cd; then eliminated in the urine. if the ingested Cd exceeded the capacity to be complex it is stored in the liver and kidneys *cumulative poison-if not eliminated its lifetime in the body is several decades *at greatest risk of Cd exposure are japan and central europe because of the pollution of the soil by Cd due to contamination from industrial operations--like rice in japan
  • Cadmium adversely affects several important enzymes; it can also cause painfulosteomalacia (bone disease) and kidney damage. Inhalation of cadmium oxide dustsand fumes results in cadmium pneumonitis characterized by edema and pulmonaryepithelium necrosis (death of tissue lining lungs).
  • These materials are vitally important to industrialized societies because oftheir applications in jet engines, nuclear power plants, chemical-resistant valves, andother applications in which a material that resists heat and chemical attack is required.
  • *Cr3+ is deep violet, 6+ is trivalent and hexavalen t *under aerobic condition it occurs as 6+ usually as chromate ion, or under slightly acidic conditions this oxyanionprotonates to HCrO4- ----impart yellowish tinge to water even at 1ppm---high concentration Cr2O7 2- is orangefor COD *6+ is carcinogenic and toxic, soluble,more mobile *chromate ion can oxidize RNA and DNA bases..since it can easily enters biological cells coz of its structural similarity to sulfate inside the cell it oxidizes the rna and dna *under anaerobic conditions it occurs as 3+ *aqeous solubility is not high;often precipitated as Cr(OH)3 under alkaline neutral or even slightly acidic conditons soluble in water *3+ is much less toxic and acts as a trace element
  • *pollutant to groundwater beneath areas with metal plating industries *second most abundant inorganic contaminant under hazardous waste sites *MCL for drinking water in US is 100ppb *most heavy metals are removed by increasing the pH, but not for Cr6+ because it exist as an oxyanion in water *Cr6+ is reduced first to Cr3+ by gaseous SO2 or a solution of sodium sulfite, or adding Fe2+ then adding nase to precipitate Cr3+ is common for purifying wastewater---insoluble Fe3+--Cr3+ compound is formed in soils with fe2+
  • *chromated copper arsenate-wood preservative *a waterborne mixture of metal oxides with which wood is treated using vacuum-pressure impregnation process wood is placed in a horizontal cylinder and evacuating the cylinder, which draws out much of the moisture from the wood cells the aqueous preservative is then pumped into the cylinder and the pressure is raised forcing the solution into the wood cells duringa period of fixation, which lasts for several weeks after treatment, almost all theCr(VI) is reduced to Cr(III) by reaction with carbon in the wood. This processproduces insoluble complexes that are slow to leach from the treated wood overits lifetime, since the copper and chromium at least are bound to the wood.Leaching of heavy metals from the wood becomes very slow a few months aftertreatment, with more copper and arsenic than chromium being lost.untreated wood--decays in about 3-12 yearstreated-protects from termites, fungi, and other destroying agentsfound in picnic tables, docks, wooden bridges last for 2o-50days
  • Arsenic *a metalloid,have properties of both metals and non-metals. Some of the metalloids such as silicon and germanium are semi-conductors, meaning that they can carry electrical charge under some special condition. This property makes metalloid useful in computers and calculators for convience it is discussed here *whit arsenic As2O3 is a common poison used for murder and suicide from Roman times through Middle Ages *in some European societies, believed to cure certain ailments, impotence, to be prophylactic against plague *50 Chinese drugs contain the element *trace amount is good for human health *small background levels in many food *same group with P and has s2p3 electron configurationin its valence shellArsennic(III) Versus Arsenic(V) Toxicity *As(III) commonly exists in aqeuoussolutioin and in solids as arsenite ion AsO3 3- (As3+ bonded to 3 surounding O2- ions), as protonated forms: HAsO4 2-, H2AsO4 1-, H3AsO4 *overall acts mush like phosporus:phosphatephosphite *has more tendency to form ionic rather than covalent bonds since it is more metal-like *often contaminates phosphate deposits and commercial phosphates because they usually coexist due to similar properties *acute poisoning is due to gastrointestinal damage which results in vomitting and diarrhea *Inorganic As(III) is more toxic than As(V)-due to its ability tostay longer in the body because it becomes bound to sulfhydryl groups in some enzymes---due to subsequent inactivity of enzymes, energy production declines and damage the cells *mthylated arsenic in the liver does not bind tightly so it is largely detoxifiedAntropogenic Sources of Arsenic to the Environment *use of its compounds in pesticides{arsenic compounds used as pesticide before the modern era of organic compoundinsecticide-lead arsenateherbecide-calcium arsenatecalcium arseniteparis green(copper arsenite) *during mining, smelting of gold, lead. copper, and nickel (the leachate fromabandoned gold mines of previous decades and centuries can still be a significantsource of arsenic pollution in water systems) *production of iron and steel *combustion of coal{*it becomes indoor pollutant and contaminates food-coal is burned in a small unventillatedstoven common in developing countries *province of guizhou-coal use for domestic cooking and heating-arsenic level is 10000ppm *most coal worldwide has arsenic less than 5ppm} *arsenic contaminated water brought to ground by wells *added to chicken feed to simulate growth and prevent diseases-scientist worry about the contamination of soil and water by arsenic leached in chicken litter *CCA chromated copper arsenate-to pressure-treat lumber in order to prevent rot and termite damageArsenic in drinking water *one of the most serious environmental health hazards *can cause cancer{lung cancer-ingestion and inhalation of arseniclung,bladder,kidney,skin cancer- ingestion of arsenic including that in waterThe mechanism by which arsenic causes cancer isnot clear. Evidence suggests that it acts as a cocarcinogen, inhibiting the DNArepair mechanism and thereby enhancing the cancer-causing abilities ofother carcinogens. There is evidence from Chile that smoking and simultaneousexposure to high levels of arsenic in drinking water act synergistically incausing lung cancer; i.e., their effect taken together is greater than the sum oftheir individual effects if each acted independently, as discussed in Chapter 4.Other data from Chile show that exposure to arsenic during early childhoodor even in utero increases subsequent mortality in young adulthood from bothmalignant and nonmalignant lung diseases. Indeed, arsenic seems to act synergisticallywith several cofactors—i.e., factors whose presence negativelyaffects the health of an individual to an extent greater than if it or the arsenicoperated independently. Exposure to excessive levels of UV from sunlightand a lack of selenium in the diet (stemming from malnutrition and/or lowselenium levels in local foods) are other cofactors with arsenic. The protectiveeffect of selenium in reducing the amount of active arsenic in the bodymay arise from the formation of a biomolecule containing an bond.Research is under way to determine whether selenium supplementation ofthe diet would be effective in countering the negative health effects of excessarsenic in the drinking water of Bangladesh and the Bengal region of India. *linkedto diabetes and cardiovascular diseases-by disrupting the hormonal process associated with both conditions *drinking water from groundwater of several parts of the world is contaminated with inorganic arsenic(tasteless, odorless, invisible) *affects intellectual levels {Recent research from Bangladesh indicates that increasing levels ofarsenic and/or of manganese in drinking water confer progressively moreand more negative effects on the intellectual levels of six- and ten-year-oldchildren.Major problems from high arsenic levels occur in the Bengal Delta, withthe result that tens of millions of people in Bangladesh and in the West Bengalregion of India drink arsenic-laced water. The World Health Organization hascalled this the “largest mass poisoning of a population in history.” The problemarose from the creation of tens of millions of tube wells, which mine groundwaterthat was previously inaccessible. The concrete tube wells extend 20 m(60 ft) or more into the ground. Ironically, the wells were constructed byUNICEF in the 1970s and early 1980s in an otherwise highly successful projectto eliminate epidemics of diarrhea, cholera, and other waterborne diseasesand to reduce the high child-mortality rate caused by use of microbially unsafewater drawn from streams, ponds, and shallow wells used in the past. Abouthalf the tube wells—affecting about 50 million people in Bangladesh—produce water with arsenic levels as high as 500–1000 ppb, greatly exceedingthe 10 ppb WHO guideline for drinking water (Table 15-2). The sedimentsthrough which the groundwater travels contain the arsenic. Generally, thedeeper the well beyond about 20 m, the lower the concentration of arsenic.Several million people living in the Bengal Delta region will probablycontract skin disorders from drinking arsenic-laced groundwater if remedialaction is not taken; a fraction of them will also suffer from the more seriousailment of arsenicosis, which can cause cancer of the skin, bladder, kidneys,and lungs. Skin lesions appear after 5–15 years of exposure to high levels ofarsenic in drinking water. A large number of residents of West Bengal, India,have already developed such lesions—the usual outward sign of chronicexposure to arsenic—that may develop into skin cancer because they consumedarsenic-laced groundwater from underground wells. The main cause ofarsenic-related deaths among these people is lung cancer. It has also beenestablished that rice and vegetables grown in Bangladesh using irrigationwater from tube wells are also contaminated by arsenic, and this may be thedominant source of the element for some people. Grains and beans absorbadditional arsenic from the water they absorb when they are cooked.Recent research from Bangladesh indicates that increasing levels ofarsenic and/or of manganese in drinking water confer progressively moreand more negative effects on the intellectual levels of six- and ten-year-oldchildren. The Mn levels in one such study averaged 1.4 ppb, compared to theWHO standard of 0.5 ppb. Elevated manganese levels are also present even inthe United States: Approximately 6% of domestic wells exceed the U.S. EPAlifetime health advisory concentration of 0.3 ppb Mn in drinking water.The origin of the dissolved arsenic in the water in Bangladesh and Indiais controversial. Normally the element, as arsenate ion, is coprecipitated withand adsorbed on the surface of iron oxides in the soil, as would have occurredin ancient times when sediments were being laid down. However, the arsenic,Drinking water standard for arsenic *global average inorganic arsenic content of drinking water is about 2.5ppb *WHO-10ppb *European Union adapeted 10ppb *in developing countries is 50ppb which no longer considered to be protected *10ppb--according to enviromentalist 3-1000 to have bladder or lung cancer, decreasing it to 10ppb it will be 1-1000{one argument raised is that small scale suppliers will be shut down since they cannot afford the cleanup cost..this may lead for consumers to turn to more harmful i other respects..... *difficulty in setting the standard for arsenic is decicing the manner in which the element operates as a carcinogenRemoval of Arsenic from water *to flow the water over activate alumina(aluminm oxide) *reverse osmosis can also be used *water pass through a bed of ferric oxide *capturing arsenic when iron hydroxide is precipitated(similar to removal of colloids)
  • have properties of both metals and non-metals. Some of the metalloids such as silicon and germanium are semi-conductors, meaning that they can carry electrical charge under some special condition. This property makes metalloid useful in computers and calculators
  • *whit arsenic As2O3 is a common poison used for murder and suicide from Roman times through Middle Ages *in some European societies, believed to cure certain ailments, impotence, to be prophylactic against plague *50 Chinese drugs contain the element *trace amount is good for human health *small background levels in many food *same group with P and has s2p3 electron configurationin its valence shell
  • Lead *melting point of 327 *first metal to be extracted from its ore and shapedEnviromental Sources *used as structural metal in ancient times as well as for weather-proofing buildings, in water pipes and ducts, for cooking vessel *use for roofing and flashing for soundproofing in buildings *tin combined with lead is solder-low-melting alloy used in electronics and in other applications to conect solid metals*ammunitions----many hunters use lead shots.ducks and geese are injured and die from chronic lead poisoning beacuase it dissolves inside them and other pellets left on the ground are eaten because they look like food or grit--thus banned in the US canadadenmark etc *lead in solder to seal tin cans However, some lead in the solderthat was commonly used in the past to seal tin cans will dissolve in the diluteacid of fruit juices and other acidic foods if air is present—that is, once the canhas been opened—since lead is oxidized by oxygen in acidic environments: The Pb2 produced by this half-reaction contaminates the contents of thecan; for this reason, lead solder is not usually used any more for food containersin North America. Partially as a result of this change, the average dailyintake of lead for two-year-old children dropped from about 30 mg in 1982 toabout 2 mg in 1991. The 1845 Franklin Expedition to find a Northwest Passage across theArctic is thought to have failed because the members all died from leadpoisoning from the solder in the tin cans that held their food. Canadianwriter Margaret Atwood has written eloquently about the incident in hershort story “The Age of Lead”:It was the tin cans that did it, a new invention back then, a new technology, theultimate defence against starvation and scurvy. The Franklin Expedition wasexcellently provisioned with tin cans, stuffed full of meat and soup and solderedtogether with lead. The whole expedition got lead poisoning. Nobody knew it.Nobody could taste it. It invaded their bones, their lungs, their brains, weakeningthem and confusing their thinking, so that at the end those that had not yetdied in the ships set out in an idiotic trek across the stony, icy ground, pulling alifeboat laden down with toothbrushes, soap, handkerchiefs and slippers, uselesspieces of junk. When they were found (ten years later, skeletons in tatteredcoats, lying where they’d collapsed) they were headed back toward the ships. Itwas what they’d been eating that had killed them.[Margaret Atwood, “The Age of Lead,” in Wilderness Tips,copyright 1991 by O. W. Toad Limited]lead salts as glazes *PbO is a yellow solid used to glaze pottery--makes the pot waterproof and give brilliant high glosslead salts as pigments *PbCrO4--yellow pigment used in paints applied to school buses and yellow stripes on road *Pb3O4--red lead, as corrosion-resistant paints and has a bright red color.. *Pb(CH2COOH)2--used in preparations to cover gray hai, since Pb2+ ion of this soluble salt will combine with the SH group of hair proteins to give a dark color *Pb3(CO3)2(OH)2-- white lead, fwas used extensively until middle of the twentieth century as indoor white paint(kitchen wcabinets and window trim)lead in automobile batteries Pb4+ can occur in highly oxidizing environment elemental lead and lead oxide employed as the two electrodes in storage batteries in vehicles together now constitute the major use of the element lead can be expelled during recycling if controls are not maintainedused as additives in gasolines tetravalent organic lead compounds are covalent molecules tetraethyl Pb(C2H5)4and tetramethyl lead Pb(CH3)4 found in gasoline about 1g/L to produce leaded gasolinetetraalkyl groups become a neurotoxin as it enters the body through the skin-- PbR3because they can cross the blood-brain barrier--source is the leaded gasoline; tetraalkyl groups become gases atoms of lead liberated from combustion of the tetraalkyl compounds--- they are removed from the vehicles engin, before they from metallic deposits and damage the engine-- small amount of ethylene dibromide and ethylene dichloride are added to the leaded gasoline to form volatile lead compounds and enters the atmosphere from the tailpipe as mixture of PbBrCl and PbBr2 abd PbCl2Lead tetraethyl (Pb(C2H5)4) is the chief constituent of the antiknock compound added to gasoline to prevent premature detonation in internal-combustion engines; it is considered a significant contributor to air pollution. Lead effects on human rep and intel * lead replaces calcium in bomes coz of similar size and same charge *high levels of inorganic Pb2+ is general poison lead remains in bones for decade-accumulate in the body body's lead absorption increases with calcium deficiency dissolving of bone as one ages or coz of illness such as oesteoarthritis and advanced periodontal disease or in times of stress such as pregnancy and menopause results remobolization of bone-stored lead back to the bloodstream whereit become toxic *deterious effects on children's behavior and attentiveness and IQsinterferes with the normal development of the fetus' brainsFIGURE 15-5 The effectof prenatal exposure tolead on the mental developmentof infants. Leadexposure is measured by itsconcentration in the bloodof the child’s umbilicalcord.development score is plotted as a function of age forgroups of young children differentiated by the amountof lead in their umbilical cord at birth. A study ofchildren in a lead-smelting community (Port Pirie) inAustralia indicates that children with a blood leadlevel of 300 ppb had an average IQ 4 to 5 points lowerthan those whose level was 100 ppb. This result isconsistent with other studies that indicate an IQdeficit of about 2–3 points for each increase by100 ppb of blood lead. Some studies indicate thatprenatal exposure to lead—especially during the firsttrimester of pregnancy—has the greatest detrimentaleffect on the IQs measured in children in primarygrades, some indicate it is the lead level at the age oftwo (when blood concentrations usually peak) that ispredominant, and others that it is the concurrent leadlevel—even if lower than that in early childhood—that is the dominant factor. No threshold for theeffects of lead upon IQ are apparent in the studies. * dysfunctional sperm in males---The concentration of leadin the bones of Romans is almost 100 times that found in modern NorthAmericans. Some historians have hypothesized that chronic lead poisoning ofupper-class Romans, from wine and other sources, contributed to the eventualdownfall of the Roman Empire because of the metal’s detrimental effects on theneurological and reproductive systems. *miscarriages and stillbirths in pregnant women--
  • MERCURYenviromental sources/usesmercury amalgams *amalgams-solutions or alloys with almost any other metal or combination of metals *dental amalgamused to fill the cavities in teeth for more than 150years initially has a putty-like consistency prepared by combining approximately equal portions of liquid mercury and a solid mixture that is mainly silver with variable amounts of copper,tin and zinc when first placed and when involved in chewing some mercury vaporized which is the source of long term health problems *but an expert panel of the US national institute of health opposed to this...a recent study found that no measure of exposure to dental mercury—neitherthe concentration of the element in the urine nor the number of dentalfillings—correlated with any measure of mental functioning or fine-motorcontrol; another study found that no IQ or other neurological problems correlatedwith the use of amalgams for filling teeth in children. *some countries in Europe like Germany have banned the use of mercury in fillings-pregnant and small children *porcelain fillings-expensive *liquid mercury is added to soil mixture which has silver or goldmercury forms amalgam then roasted to distill mercury...1gram is lost for every gram silver produced--200000 tonnes...practiced recently in china..before it was in Central and South America...in Brazil a large scale of gold extraction using mercury which pollutes the air and Amazon River because of mishandling *people who live near the mine inhale air with mercury exceeds 50microg/m3 which is 50 times the public exposure guideline of WHO *fungicide(particularly fungicides.These mercury compounds include aryl mercurials such as phenyl mercuricdimethyldithiocarbamate (formerly used in paper mills as a slimicide and as a mold retardant for paper), andalkyl-mercurials such as ethylmercuric chloride, C2H5HgCl, that was used as a seedfungicide. Because of their resistance to degradation and their mobility, the alkylmercury compounds are generally considered to be more of an environmental threatthan either the aryl or inorganic compounds.)*automobiles built before 2000, electrical switches that operate convenience and trunk lighting contained mercury...it is lost in the environment when the cars are recycled for their steel unless they are specifically collected *used in fluorescent light bulbs and in street lamps before *since 1980s, 5-10mg of mercury *most volatile and the vapor is highly toxic*used to make felt for hats fur was immersed in hot solution of mercuric nitrate w/c made the fiber rough and twisted so they would easily mat togethercosequence-nervous disorders like muscle tremor, depprion, memory loss, paralysis, and insanity expression mad as a hatter*crematoria are fitted with selenium filters to remove most mercury from emmisions by forming mercury selenide crystals*dentists are required to install a separator to capture mercury from their wastewater rather than have it flow down drains and become part of municipal sewage-1kg mercury waste per year*preserve paint-- compounds of phenylmercury ion C6H5Hg+ with acetate or nitrate as anion..while in can and to prevent mildew after application of latex paint not as toxic to humans compared to CH3Hg+...but banned for indoor paint because ingestion of element is inevitable*use as slimicides in the pulp-and-paper industry in order to prevent the growth of slime on wet pulp *as topical antiseptic and cosmetics----Mercury and the Industrial Chlor-Alkali Process *amalgam of sodium and mercury is used in some industrial chlor-alkali plants in process that converts aqueos sodium chloride into the commercial products chlorine and sodium hydroxide and gaseous hydrogen by electrolysis. *In order to form a concentrated, pure solution ofNaOH, flowing mercury is used as the negative electrode (cathode) of theelectrochemical cell. The metallic sodium that is produced by reduction inthe electrolysis immediately combines with the mercury and is removed fromthe NaCl solution without having reacted with the aqueous medium: *When metals such as sodium are dissolved in amalgams, their reactivityis greatly lessened compared to that for the free state, so that the otherwisehighly reactive elemental sodium in the Na–Hg amalgam does not react withthe water in the original solution. Instead, the amalgam is removed and laterinduced by the application of a small electrical current to react with water ina separate chamber, thereby producing sodium hydroxide that is free of salt.The mercury is recovered after NaOH production and is recycled back tothe original cell. The recycling of mercury is not complete, however, andsome finds its way into the air and into the water body from which the plant’scooling water is obtained and to which it is returned. Although liquid mercuryis not soluble in water or in dilute acid, it can be oxidized to soluble form bythe intervention of bacteria that are present in natural waters. By this means,the mercury becomes accessible to fish.The mass of mercury lost to the environment from the average chloralkaliplant has decreased enormously since the problem was identified in the1960s. Nevertheless, installations in North America that use mercuryelectrodes have largely been phased out. They were replaced by ones thatuse a fluorocarbon membrane that separates the NaCl solution from thechloride-free solution at the negative electrode. The membrane is designedsuch that Na, but not anions, can pass through it. In both types of cells, theoverall reaction is----mercury vapor *mercury is a liquid that conducts electricity well *it is composed of free, neutral atoms. *Elemental mercury vapor can enter the body through inhalation diffuse from the lungsand be carriedby the bloodstream to the brain where it penetrates the blood-brain barrier.because they are electrically neutral It disruptsmetabolic processes in the brain causing tremor and psychopathological symptomssuch as shyness, insomnia, depression, and irritability.causes diffuculties with coordination, eyesight, and tactile senses *liquid mercury is not highly toxic,when ingested most are excreted *Hg2 2+ is not so toxic since it combines with chloride in the stomach to form Hg2Cl2------Methylmercury toxicity *methyl anion combines with Hg2+ to yeild volatile molecular liquid dimethylmercury *the formation occurs in muddy sediments of rivers and lakes, under anaerobic condition *methylmercury(or monomethylmercury) less volatile: CH3HgCl, CH3HgOH---CH3HgX or CH3Hg+X- since this substances consist of covalent molecules readily formed in the same way as dimethylmercury at the surface of sediments in anaerobic water its production predominates over dimethylmercury in acidic or neutral aqueous systems *sulfate ions stimulates sulfate-reducing bacteria that methylate mercury *sulfide ions results in fomation of mercury sulfide complexes that do not undergo methylation *The pathways for the production and fate of dimethylmercury andother mercury species in a body of water are illustrated in Figure 15-1. Methylationof inorganic mercury does occur in anaerobic regions of lakes, especiallynear the interface of the epilimnion and the hypolimnion, and at the interfaceof the latter with sediments, but not in aerobic water. Organic-rich sedimentsat the bottom of warm, shallow lakes are important sites of methylmercuryproduction. Wetlands are also active sites of methylmercury production.Methylmercury in surface water is photodegraded (to as yet unknown products)and is the most important sink for this substance in some lakes. *The ratio between methylmercury in fish muscle andthat dissolved in the water in which the fish swims is often about 1 million to1, and can exceed 10 million to 1. The highest methylmercury concentrations(over 1 ppm) are usually found in large, long-lived predatory marine speciessuch as shark, king mackerel, tilefish, swordfish, and large tuna (sold as steaksand sushi), as well as in fresh-water species such as bass, trout, and pike. *us has EPA maximum conc of 0.3ppm in fish tissue *the lower the pH the more soluble mercury is amdmethylmercury is faster-----methylmercuryaccuumulation in the enviro and human body *half life of methylmercury in human body is 70days coz of its greater solubility in lipid enviro *cummulative poison *dialkylmercury including dimethylmercury is supertoxic coz they are lethal in small amounts-----Minamata diseaseMinamata, Japan--a chemical plantemployed Hg2+ as catalyst un process that produced polyvinyl chloride discharged mercury containing resudue into the bay CH3Hg-SCH3--formed from inorganic mercury methylation by mciroorg in the bay's sediment and then bioaccumulate 100ppm in the fish compare to 0.3ppm in US onset symptoms were first seen in cats who ate discarded fish--began jumping around, twitching, ran in cricles and finally threw themselves into the water and then drowned symptoms in humans arise from dysfunctions of the central nervous system--numbness in arms, legs, blurring even loss of vision, loss of hearing and muscle coordination and lethargy and irritabilitymethylmercury can be passed to fetus--caused brain damage, some to fatal extent, symptoms similar to those of cerebral palsy: mental retardation, seixure, motor disturbance and even paralysis-----Sources of Methyl Mercury *as fungicides in agriculture and industry to prevent seedling losses from fungus attack *deaths in america, china, iraq-- fungicide containing ethylmercury CH3CH2Hg+ which its toxicity is similar to methylmercury *mercury is leached from rocks and soil into water systems by natural processes-- mercury becomes attached trapped as insoluble compounds by attachment to sulfur ions present in clays and inorganic matterflooding: CH3Hg+ formed from the natural mercury content of the soil and soil bound Hg2+ comes in contact with anaerobic bacteria thus insoluble mercury was converted to CH3Hg+ w/c readily dissolves in water--enters food chain through its absorption in fish *from preservative Thimerosal prevent micorbial growth in many vaccine preparations administered to infantsCH3CH29Hg9S9C6H4COOH; contains ethylmercury ion *as a toical disinfectant----Safe level of Mercury in the body *10-20ppm of CH3Hg+ in hair indicates that a pregnant woman has sufficient CH3Hg+ in her bloodstream to represent a to a developing fetusInternational Controls on Mercury *United Nations Environment Programme in 2005 devised a global treaty to curb the production if mercury and to ban completely the export of mercury between countries
  • heavy metals

    1. 1. HEAVY METALS Substances *Hg 13.5 *Pb 11.3 Cu 9.0 *Cd 8.7 *Cr 7.2 Sn 5.8-7.3 *As 5.8 Al 2.7 Mg 1.7 H2O Densities of Some Important Heavy Metals and Other Substances Density (gcm-3 ) 1.0 their standard state have specific gravity (density) of more than 5g/cm3  occur near the middle and bottom of the periodic table type of chemical element which are poisonous to humans
    2. 2. Figure 1. Relationship between metal generation, exposure pathway and environmental impact.
    3. 3. BIOACCUMULATION OF HEAVY METALS Pollutants like heavy metals are CONSERVATIVE pollutants – i.e. they aren’t broken down by bacteria etc and are effectively permanent  Most plants and animals can regulate their metal content to a certain point-but metals that can’t be excreted buildup in an organism over its lifetime  BIOACCUMULATION
    4. 4. BIOMAGNIFICATION  those animals feeding on bioaccumulators gain even higher inputs of contaminants and bioaccumulate even greater concentrations and so on.. with animals at the highest trophic level obtaining highest concentrations
    5. 5. SPECIATION AND TOXICITY OF HEAVY METALS Poisonous in their cations form  Highly toxic when bonded to short chains of carbon atoms ex. Alkyl groups with mercury and lead attached 
    6. 6. CADMIUM (Cd) Discovered in 1817 by the German chemist Friedrich Stromeyer  Cadmium melts at 321°C (610°F), boils at 767°C (1413°F)  Has a specific gravity of 8.64g·cm-3  Its atomic number is 48 and atomic weight is 112.41g·mol-1 .  When heated, cadmium burns in air with a bright light, forming the oxide CdO.  Cadmium occurs as the principal constituent of a mineral only in the rare greenockite 
    7. 7. ENVIRONMENTAL SOURCES OF CADMIUM           Cd compounds form ionic salts with simple anions Found in water in the +2 oxidation state By-product of zinc smelting Burning coals Incinerating waste materials containing cadmium As an electrode in rechargeable NiCad batteries Incinerating plastics and other materials that contain as pigment or as a stabilizer As pigment Use in paints to produce brilliant yellow color recycling cadmium-plated steel
    8. 8. HUMAN INTAKE OF CADMIUM      High intake for humans living near mines and smelters Smokers are also exposed From food supply-wheat rice, grains, seafood, organ meats Maximum containment level is 5ppb in US and Canada Acute environmental problem occurred in Jintsu River Valley region of Japan- ouch-ouch or itai-itai
    9. 9. PROTECTION AGAINST LOW LEVELS OF CADMIUM Cadmium is acutely toxic; lethal dose is 1g  Humans are protected by methallothionein  It is a cumulative poison  Greatest risk of Cd exposure is Japan and Central Europe 
    10. 10. EFFECTS IT CAUSE IN THE BODY Affects important enzymes  Cause osteomalacia and kidney damage  Cadmium pneumonitis characterizes by edema and pulmonary epithelium necrosis 
    11. 11. CHROMIUM (Cr)        It has atomic number 24, atomic mass 51.996g/mol Its melting point and boiling point of 1907oC and 2672oC respectively. From Greek word chroma refers to its many colorful compounds It is a silvery, lustrous , brittle hard metal It does not tarnish in air. Chromium is unstable to oxygen i.e. it react with oxygen to produce a thin oxide layer that is impermeable to oxygen and thus protects the metal below. Is considered also as crucial metal
    12. 12. CHROMIUM Normally occurs in the form of inorganic ions  Common oxidation states: Cr(VI) and Cr(III)  In aerobic condition it occurs as +6 as chromate ion Suspected to be carcinogenic  In anaerobic condition it occurs as +3 less toxic and acts as a trace nutrient 
    13. 13. ENVIRONMENTAL SOURCES OF CHROMIUM Predominantly mined as chromate ore (FeCr2O4)  Used to manufacture stainless and in superalloys  Tanned leather  Metal plating industries  CCA treated wood  Smelters 
    14. 14. CHROMIUM CONTAMINATION OF WATER Contaminates groundwater beneath areas with metal-plating  second most abundant inorganic contaminant under hazardous waste sites  MCL for drinking water in US is 100ppb  Cr(VI) is extracted by reducing it to Cr(III) 
    15. 15. HEALTH EFFECTS OF CHROMIUM People are exposed to chromium in these four basic ways:  Breathing (inhalation)  Eating of contaminated food)  Drinking of contaminated water  Skin contact (with chromium compounds/salts). Health effects: Trivalent chromium (Cr3+) Chromium (III) is an essential nutrient to humans and its deficiency may cause diseases such as heart problems, diabetes and metabolic disorders. Yet when consumed in excess can be harmful. It can cause adverse health effect such as skin rashes. Chromium (III) is not yet classified as carcinogenic according to International Agency for Research on Cancer (IARC).
    16. 16. Health effects: Trivalent chromium (Cr3+) Hexavalent chromium (Cr6+) is a danger to human health, it is carcinogenic. The most dangerous compounds of Cr6+ are:  Calcium chromate  Chromium trioxide  Lead chromate  Strontium chromate  Zinc chromate Health problem caused by chromium (VI) compounds are:  Skin rashes  Upset stomach and ulcers  Respiratory problems  Weakened immune systems  Kidney and liver damage  Alteration of genetic materials  Lung cancer  Death.
    17. 17. THE WOOD PRESERVATIVE CCA Chromated Copper Arsenate  A waterborne mixture of metal oxides with which wood is treated using vacuumpressure impregnation process  10% of the mass of the lumber  Cr(IV) is used here  Protects wooden structures  Replaced creosote and pentachlorophenol 
    18. 18. ARSENIC A metalloid  It is metallic in appearance and has a specific gravity of 5.7g·cm-3.  The atomic weight of arsenic is 74.9216.  Gray arsenic is the most common. When gray arsenic is heated under standard pressure it sublimes, passing directly from solid to gaseous form at 613°C (1135°F).  A yellow, nonmetallic form also exists and has a specific gravity of 2.0. 
    19. 19. COMMON MINERALS OF ARSENIC arsenopyrite (FeAsS)  realgar (As2S2)  orpiment (As2S3)  arsenic trioxide (As2O3)  When these ores are roasted, the arsenic sublimes and can be collected from the dust in the flues as a by-product.
    20. 20. ARSENIC White arsenic As2O3 is a common poison  Believed to cure certain ailments, impotence, prophylactic against plague  50 Chinese drugs contain the element  Trace amount is good for human health  Used to treat syphilis 
    21. 21. ANTROPOGENIC SOURCES OF ARSENIC use of its compounds in pesticides  during mining, smelting of gold, lead. copper, and nickel  production of iron and steel  combustion of coal  added to chicken feed to simulate growth and prevent diseases  Manufacturing of glass to eliminate a green color caused by impurities of iron compounds  CCA preservative 
    22. 22. ARSENIC(III) VS. ARSENIC(V) TOXICITY As(III) commonly exists in aqueous solution and in solids as arsenite ion AsO33 has more tendency to form ionic rather than covalent bonds since it is more metal-like  often contaminates phosphate deposits and commercial phosphates 
    23. 23. acute poisoning Inorganic As(III) is more toxic than As(V) methylated arsenic in the liver does not bind tightly so it is largely detoxified  Arsenic’s lethal effect when consumed is due to gastrointestinal damage
    24. 24. ARSENIC IN DRINKING WATER one of the most serious environmental health hazards  can cause cancer  Linked to diabetes and cardiovascular diseases  affects intellectual levels 
    25. 25. DRINKING WATER STANDARD FOR ARSENIC global average inorganic arsenic content of drinking water is about 2.5ppb  WHO and European Union-10ppb  in developing countries is 50ppb 
    26. 26. Manifestations of acute arsenic Bodily system Symptoms or signs Time of onset poisoning affected Systemic Thirst Hypovolemia, Hypotension Minutes Minutes to hours Gastrointestinal Garlic or metallic taste Burning mucosa Nausea and vomiting Diarrhea Abdominal pain Hematemesis Hematochezia, melena Rice-water stools Immediate Immediate Minutes Minutes to hours Minutes to hours Minutes to hours Hours Hours Hematopoietic system Hemolysis Hematuria Lymphopenia Pancytopenia Minutes to hours Minutes to hours Several weeks Several weeks Pulmonary (primarily in inhalational exposures) Cough Dyspnea Chest Pain Pulmonary edema Immediate Minutes to hours Minutes to hours Minutes to hours Liver Jaundice Fatty degeneration Central necrosis Days Days Days Kidneys Proteinuria Hematuria Acute renal failure Hours to days Hours to days Hours to days
    27. 27. REMOVAL OF ARSENIC FROM WATER to flow the water over activate alumina(aluminum oxide)  reverse osmosis can also be used  water pass through a bed of ferric oxide  capturing arsenic when iron hydroxide is precipitated(similar to removal of colloids) 
    28. 28. LEAD (Pb) Its atomic number is 82, atomic weight is 207.2g/mol  Bluish-white in color.  It is very soft, highly malleable, ductile and a relatively poor conductor of electricity.  It melts at 327oC and its boiling point is 1750oC.  Lead has low water solubility, is very resistant to corrosion but tarnishes upon exposure to air.  Lead is a highly toxic trace element with no recognized biological requirement in organisms. 
    29. 29. OCCURRENCE OF LEAD Lead occurs naturally in the earth crust, usually in ores such as:  Galena (PbS) (major ore)  Cerrusite (PbCO3)  Anglesite (PbSO3)  Lanarkite (PbO·PbSO3)
    30. 30. ENVIRONMENTAL SOURCES/USES OF LEAD           Soundproofing in buildings Solder- alloy of lead and tin lining pipes, tanks, X-ray apparatus Weather-proofing buildings Protective shielding for radioactive material Smelters Sheathing electric cables Additives for gasoline Ammunitions Lead in solder to seal tin cans
    31. 31. ENVIRONMENTAL SOURCES/USES OF LEAD (cont.)     Lead in automobile batteries As additives in gasolines tetraethyl lead Pb(C2H5)4 and tetramethyl lead Pb(CH3)4 Lead salts as glazes in pots (PbO) Lead salts as pigments PbCrO4 -paints applied to school buses and yellow stripes on road Pb3O4 -as corrosion-resistant paints and has a bright red color Pb(CH2COOH)2 -used in preparations to cover gray hair
    32. 32. EFFECTS OF LEAD IN HUMAN REPRODUCTION AND INTELLIGENCE Pb2+ replaces Ca2+ in bones  Pb2+ remains in bones for decade  High levels of inorganic Pb2+ is general poison  deleterious effects on children's behavior and attentiveness and IQs  Dysfunctional sperm in males  Miscarriages and stillbirth in pregnant women 
    33. 33. HEALTH EFFETC IN ADULTS AND CHILDREN Blood lead levels Adults Children 10 g/dL Hypertension may occur •Crosses placenta •Impairment IQ, growth •Partial inhibition of heme synthesis 20 g/dL Inhibition of heme synthesis Increased erythrocyte protoporphyrin Beginning impairment of nerve conduction velocity 30 g/dL •Systolic hypertension •Impaired hearing( ) Impaired vitamin D metabolism 40 g/dL •Infertility in males •Renal effects •Neuropathy •Fatigue, headache, abd pain Hemoglobin synthesis inhibition 50 g/dL Anemia, GI sx, headache, tremor Colicky abd pain, neuropathy 100 g/dL Lethargy, seizures, encephalopathy Encephalopathy, anemia, nephropathy, seizures
    34. 34. MERCURY          symbol Hg From the Latin word, hydrargyrum, “liquid silver,” Shining, mobile liquid, silvery-white in color It is liquid at -38.9oC Becomes solid when subjected to a pressure of 7,640 atmospheres Freezing point of about -39°C (about -38°F), a boiling point of about 357°C Density of 13.55 grams per cu cm. The atomic weight of mercury is 200.59gmol-1 Conducts electricity well Its principal ore is cinnabar
    35. 35. ENVIRONMENTAL SOURCES/USES OF MERCURY Electrical switches in automobiles built before 2000  In fluorescent light bulbs and in street lamps before  dental amalgam  Gold and silver mining  Pesticides  Used to make felt for hats 
    36. 36. ENVIRONMENTAL SOURCES/USES OF MERCURY (cont.) Fossil fuel coal lignite (100ppb)  Discarded laboratory chemicals  Pharmaceutical products  Crematoria  Wastewater from dentists’ offices  Preserve paint  Used as slimicides in pulp-and-paper industry  As topical antiseptic and in cosmetics 
    37. 37. MERCURY AND THE INDUSTRIAL CHLOR-ALKALI PROCESS amalgam of sodium and mercury is used in some industrial chlor-alkali plants in process that converts aqueos sodium chloride into the commercial products chlorine and sodium hydroxide and gaseous hydrogen by electrolysis.  Flowing mercury is used as the cathode  Some of the mercury find its way to the air and water 
    38. 38. MERCURY VAPOR It is composed of free, neutral atoms.  If inhaled the atoms diffuse from the lungs to the bloodstream   liquid mercury is not highly toxic, when ingested most are excreted
    39. 39. METHYLMERCURY TOXICITY       methyl anion combines with Hg2+ to yield volatile molecular liquid dimethylmercury the formation occurs in muddy sediments of rivers and lakes, under anaerobic condition methylmercury(or monomethylmercury) its production predominates over dimethylmercury in acidic or neutral aqueous systems sulfate ions stimulates sulfate-reducing bacteria that methylate mercury sulfide ions results in formation of mercury sulfide complexes that do not undergo methylation
    40. 40. (cont.) between methylmercury in fish muscle and that dissolved in the water: 1 million to 1, and can exceed 10 million to 1  High methylmercury concentration in large, long-lived predatory marine species 
    41. 41. METHYLMERCURY ACCUMULATION IN THE ENVIRONMENT AND IN THE HUMAN BODY Half-life of methylmercury in human body is 70days  Cumulative poison  dialkylmercury including dimethylmercury is supertoxic 
    42. 42. MINAMATA DISEASE Occurred in a village in Minamata, Japan  CH3Hg-SCH3  100ppm of mercury in fish tissues  Onset symptoms were first seen in cats  Symptoms in humans arise from dysfunctions of the central nervous system  Methylmercury can be passed to fetus  U.S. has EPA maximum conc of 0.3ppm in fish tissue 
    43. 43. SOURCES OF METHYLMERCURY Fungicide in agriculture and industry  Leaching from rocks and soil into water systems by natural processes  Preservative Thimerosal 
    44. 44. SAFE LEVEL OF MERCURY IN THE BODY  10-20ppm of CH3Hg+ in hair can be dangerous INTERNATIONAL CONTROL ON MERCURY  United Nations Environment Programme in 2005 devised a global treaty to curb the production if mercury and to ban completely the export of mercury between countries
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