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METALS - PowerPoint PPT Presentation


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METALS. Lead, Pb. Unique properties - used since antiquity Mostly anthropogenic sources (Greenland snow pack data, 1954) Banned as paint additive Europe 1921 USA 1978 Sources: smelters, refineries, power plants, incinerators, manufacturing and recycling operations. Exposure to Pb.

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lead pb
Lead, Pb
  • Unique properties - used since antiquity
  • Mostly anthropogenic sources

(Greenland snow pack data, 1954)

  • Banned as paint additive
    • Europe 1921
    • USA 1978
  • Sources: smelters, refineries, power plants, incinerators, manufacturing and recycling operations
exposure to pb
Exposure to Pb

Annual US air emissions:

1981 56,000t

1990 7,100t

  • Pb in air NAAQS level =1.5ug/m3 (quarterly)
    • Mostly (90%) from leaded gasoline, until 1978

(400t/day worldwide)

    • Industrial emissions
  • Pb in water Action water level =15ppb (0.015ppm)
    • Airborne Pb deposition in water
    • Water supply pipes
    • Lead shots in lakes (Whatcom county, WA)
  • Pb in food
    • From water to plants --> animals --> food
    • Pb-based glaze for pottery
    • Pica for children - leaded paint flakes
  • Pb in soil
    • From industrial emissions, home paint disposal, gasoline (~600,000t/year)
    • Pica for children
pb health effects
Pb Health effects
  • Young animals and humans more susceptible
  • Aquatic organisms and birds affected (directly or by water acidification)
human health effects of pb

Action blood level =25ug/dl (2.5ug/ml)

Human health effects of Pb

In blood - 25 days

Half life In soft tissue - 40 days

In bone - 25 years !

  • Accumulates (95% in bone and teeth) - remobilized
  • Possible human carcinogen (IARC)

(phosphate and acetate forms)

  • Systemic poison
    • Inhibits hematopoiesis - anemia (heme synthesis)
    • Causes renal tubular dysfunction
    • Lung function (asthma, bronchitis, tissue damage)
    • Muscle and joint pains, skeletal growth effects
    • Immune system damage
    • Miscarriage, stillbirth
children more vulnerable
Children more vulnerable

CNS effects from blood level =10ug/dl (1ug/ml) - CDC

  • Pb poisoning is the most common and serious environmental disease
  • Primary target CNS
    • Retardation and brain damage
    • Behavioral changes
    • Cognitive development
  • Levels dropped since 1974 from 15-18 to 2-3ug/dl - still 2.2% US children are above the 10ug/dl limit
mechanism of action
Mechanism of action
  • Binds to -SH groups on enzymes (inactivation)
    • adenyl cyclase (ATP to AMP),
    • aminotransferase (protein metabolism)
  • Competition with Ca++
    • Mitochondria respiration
    • Synaptic regulation
    • Skeletal calcium substitution
    • tRNA interaction with aminoacids and ribosomes
  • Heme synthesis inhibition
    • -aminolevulinic acid dehydratase (Zn++) ( serum ALA levels)
    • Ferrochelatase (Fe++)
  • Nutritional factors affect Pb absorption

(Fe deficiency)

cadmium cd
Cadmium, Cd
  • Itai-itai byo disease (Japan 1945)
    • Irrigation of rice fields with contaminated water from Zn-Cd-Pb mine
  • Bone fractures, deformations, decalcification, pains
  • Persistent (t1/2=10-25y), one of the most toxic trace metals
  • Byproduct of smelting, fossil fuel combustion, phosphate fertilizers
  • Used with other metals as anticorrosive, multiple other uses
  • Similar to Zn++ (binds proteins), and to Ca++
exposure to cd t 1 2 7 4 18y
Exposure to Cd - t1/2 = 7.4-18y

OSHA air 200ug/m3

  • Air - 25-40% retention
    • Mostly occupational
    • Ambient air 1ng/m3 (20-50ng/day)
    • Tobacco smoke major inhalation source (1.5-2ug/cig)
  • Water (naturally at <10ng/l)
    • In salt waters as CdCl2, in fresh waters as CdCO3
  • Soil
    • Deposition from air
    • Municipal sewage on agricultural soil
    • Phosphate fertilizers
  • Food - 5-10% retention (10-50ng/d to 200-1000ug/d)
    • Main source of human exposure (plants bioaccumulate Cd)
    • Leafy vegetables, grains, cereals
    • Some seafoods

EPA max 0.01mg/l, (goal 5ug/l)

cd health effects
Cd Health effects
  • Known human carcinogen (lung cancer) (air 1ug/m3)
  • Accumulation in liver, kidney (t1/2=10-20y), and skeleton over lifetime - Very low excretion (0.005%/day)
  • Nephrotoxicity due to Ca++ ion uptake inhibition (free intracellular Cd ions; Metallothionein)
  • Mechanisms: Enzyme inhibition, metal co-factor displacement, oxidative damage (lipid peroxidation)
  • Antagonist of nutritional metal intake (role of deficiencies in toxicity, protein in diet, vit. C)
  • Newborns and children most sensitive
mercury hg
Mercury - Hg
  • Unique properties and rare on earth crust, but also ubiquitous
  • Multiple uses (thermometers, UV light lamps, catalyst, batteries, electrical apparatus)
  • US sources: chloralkali industry and coal fired power plants (40%); also pulp and paper industry, incineration, smelters, gold mining (Amazon)
  • Also natural sources (volcano eruptions)
  • Elemental Hg is oxidized to Hg++ and biotransformed to organic forms (mostly methyl)
  • Bioaccumulates in fat tissue - fish intake
hg health effects

FDA guideline for fish 0.5ug/g

Critical daily dose 300mg

Hg Health effects
  • Brain is target organ: Neurotoxicity, psychomotor effects, brain damage (fetus)
  • Poisonings
    • Minamata Bay acute toxicity (Japan) (11mg/g)
    • Iraq 1971-72, bread - MeHg as fungicide
  • Women of childbearing age and children are subpopulations of highest concern
  • Enzyme inhibition (-SH binding)
  • Na+ and K+ membrane permeability
  • Nephrotoxicity
  • Se protective?
nickel ni

OSHA air level 7ug/m3 (occupational)

No drinking water safety level

Nickel - Ni
  • Occupational toxicity - inhalation - Ni(CO)4
  • Water contamination through leakage
  • Carcinogenic forms - Ni, Ni2S3, NiOx
    • DNA and protein crosslinking
    • Chromosomal aberrations
    • Oxidative processes
  • Competition with essential metals
  • Skin contact exposure
  • Crosses the blood-placenta barrier
  • Mg protective?
arsenic as

EPA safe level 50ug/l (drinking water)

Arsenic -As
  • Oxides, AsO3, H3AsO3, H3AsO3
  • Uses: Insecticides, rodenticides, herbicides, fungicides, preservatives, pigments, vet med.
  • Sources: Natural processes, fossil fuel combustion (fly ash particulates), smelting (AsH3)
  • Microorganismal oxidation, methylation (organic forms)
  • Groundwater and surface water contamination
    • 350,000 US residents above safe level
    • Mostly in Asia (India, China), South America (Chile)
  • Urban air (0.02ug/m3), soil (0.2-40ug/g)
  • Food - fish
arsenic health effects
Arsenic Health Effects
  • Inhalation, ingestion, skin contact
    • Liver, kidneys, spleen, intestine (lung), skin, hair, nails
  • Toxicity higher for water soluble forms (As3+), metabolic transformation (methylation detox)
  • CNS effects (motor activity)
  • Carcinogen (bladder, kidney, skin, liver, blood, lung and colon (inorganic forms) (0.35-1.14mg/l)
  • Capillary injury - “Blackfoot” (gangrene)
  • Teratogen
  • Reacts with -SH: enzyme inhibitor (antidote BAL)
  • Uncouples oxidative phosphorylation
  • Oxidative processes (SOD, CAT, GPX, GST inhibition)