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METALS

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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METALS

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  1. METALS

  2. 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

  3. 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

  4. Pb Health effects • Young animals and humans more susceptible • Aquatic organisms and birds affected (directly or by water acidification)

  5. 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

  6. 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

  7. 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)

  8. 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++

  9. 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)

  10. 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

  11. 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

  12. 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?

  13. 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?

  14. 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

  15. 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)

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