TOXIC HEAVY METALS Chris Jean Guevarra

HEAVY METALSSubstances Density (gcm-3 )

*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 1.0

Densities of Some Important HeavyMetals and Other Substances

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

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 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

BIOMAGNIFICATION

those animals feeding on bioaccumulators gain even higher inputs of contaminants and bioaccumulate even greater concentrationsand so on.. with animals at the highest trophic level obtaining highest concentrations

Poisonous in their cations form Highly toxic when bonded to short

chains of carbon atomsex. Alkyl groups with mercury and lead attached

SPECIATION AND TOXICITY OF HEAVY METALS

CADMIUM

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

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

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

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

EFFECTS IT CAUSE IN THE BODY

Affects important enzymes Cause osteomalacia and kidney

damage Cadmium pneumonitis characterizes by

edema and pulmonary epithelium necrosis

CHROMIUM

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

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 ionSuspected to be carcinogenic

In anaerobic condition it occurs as +3less toxic and acts as a trace nutrient

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

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)

HEALTH EFFECTS OF CHROMIUMPeople 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).

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.

THE WOOD PRESERVATIVE CCA

Chromated Copper Arsenate A waterborne mixture of metal oxides

with which wood is treated using vacuum-pressure impregnation process

10% of the mass of the lumber Cr(IV) is used here Protects wooden structures Replaced creosote and

pentachlorophenol

ARSENIC

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.

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.

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

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

ARSENIC(III) VS. ARSENIC(V) TOXICITY As(III) commonly exists in aqueous

solution and in solids as arsenite ion AsO3

3-

has more tendency to form ionic rather than covalent bonds since it is more metal-like

often contaminates phosphate deposits and commercial phosphates

Arsenic’s lethal effect when consumed is due to gastrointestinal damage

acute poisoningInorganic As(III) is more toxic than As(V)methylated arsenic in the liver does not bind tightly so it is largely detoxified

ARSENIC IN DRINKING WATER

one of the most serious environmental health hazards

can cause cancer Linked to diabetes and cardiovascular

diseases affects intellectual levels

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

Bodily system affected

Symptoms or signs

Time of onset

Systemic ThirstHypovolemia, Hypotension

MinutesMinutes to hours

Gastrointestinal Garlic or metallic tasteBurning mucosaNausea and vomitingDiarrheaAbdominal painHematemesisHematochezia, melenaRice-water stools

ImmediateImmediateMinutesMinutes to hoursMinutes to hoursMinutes to hoursHoursHours

Hematopoietic system

HemolysisHematuriaLymphopeniaPancytopenia

Minutes to hoursMinutes to hoursSeveral weeksSeveral weeks

Pulmonary (primarily in inhalational exposures)

CoughDyspneaChest PainPulmonary edema

ImmediateMinutes to hoursMinutes to hoursMinutes to hours

Liver JaundiceFatty degenerationCentral necrosis

DaysDaysDays

Kidneys ProteinuriaHematuriaAcute renal failure

Hours to daysHours to daysHours to days

Manifestations of acute arsenic poisoning

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)

LEAD

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.

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)

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

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 roadPb3O4 -as corrosion-resistant paints and has a bright red colorPb(CH2COOH)2 -used in preparations to cover gray hair

Pb3(CO3)2(OH)2 -white lead

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

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 synthesisIncreased 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

MERCURY

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

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

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

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

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

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

(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

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

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

SOURCES OF METHYLMERCURY

Fungicide in agriculture and industry Leaching from rocks and soil into water

systems by natural processes Preservative Thimerosal

SAFE LEVEL OF MERCURY IN THE BODY

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

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

INTERNATIONAL CONTROL ON MERCURY