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Env. Chemistry, Baird Cann

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Env. Chemistry, Baird Cann

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    1. Env. Chemistry, Baird & Cann

    2. Env. Chemistry, Baird & Cann Heavy Metals Middle & bottom of periodic table; higher density than most common materials Nonbiodegradable; toxic & nontoxic forms; transported by air as gases or in suspended particulates

    3. Env. Chemistry, Baird & Cann Toxicity of Heavy Metals Free elements only Hg is toxic Cations or organometallic species often quite toxic Cations bind to sulfhydryl (-SH) group (cysteine amino acid) in enzymes disrupting the vital metabolic reaction catalyzed by the enzyme

    4. Env. Chemistry, Baird & Cann Compounds that Bind Heavy Metals BAL and Calcium salt of EDTA used for heavy metal poisoning

    5. Env. Chemistry, Baird & Cann Speciation Insoluble forms pass through with little harm Some are acute toxins (arsenic oxide) Some pass through blood-brain barrier (organometallics) In water pH and dissolved and suspended C are important factors (complexation and adsorption will remove some of the metals)

    6. Env. Chemistry, Baird & Cann Bioaccumulation of Heavy Metals Only Hg compounds biomagnify but other bioconcentrate (oyster and mussels [Cd] and [Hg] concentration 105 times water in which they live)

    7. Env. Chemistry, Baird & Cann Mercury Vapor Used in electrical switches (before 2000 automobile convenience & trunk lights); antilock brakes & instrument panels; vapor lights (replaced mostly with Na); fluorescent lamps Most volatile of all metals, vapors are highly toxic Crosses blood brain barrier, oxidized to Hg2+; interferes with central nervous system (coordination, eyesight, tactile senses) Mercury vapors from burning coal, municipal waste (batteries); now rivals emissions of Hg from volcanoes Hg emissions are mostly gaseous as opposed to bound to particles; travel a great distance before being oxidized and dissolved in rain

    8. Env. Chemistry, Baird & Cann Mercury Amalgams Dental: Hg/Ag/Sn; small amounts of Hg released initially, some countries (Germany) banned Hg in fillings for small children and pregnant women; release of Hg from dead human bodies that are cremated? Extract Au & Ag (1g of Hg into environment for each 1g Ag extracted) from dirt by dissolving in Hg filtering & vaporizing Hg; S. & C. America

    9. Env. Chemistry, Baird & Cann Hg & the Chloralkali Process production of Cl2 & NaOH from NaCl Amalgam of Na & Hg to extract Na then conversion to pure NaOH by reaction with water

    10. Env. Chemistry, Baird & Cann The 2+ Ion of Mercury Most common ion Hg+2 e.g. Hg+2 + S-2 HgS(s) HgNO3 used to make felt (mad as a hatter; Hg attacks nervous system but mainly kidney & liver) HgO in mercury cell batteries hearing aids Most of the Hg deposited from air is Hg+2, in waters attached to suspended particulates which are eventually deposited in the sediments The other ion mercury, Hg22+, is not very toxic

    11. Env. Chemistry, Baird & Cann Methylmercury Formation covalent compounds of Hg HgCl2, HgR2 Hg+2 + CH3- Hg(CH3)2 CH3- comes from a derivative of Vitamin B12 (methylcobalamin) with CH3- bound to Cobalt

    12. Env. Chemistry, Baird & Cann Methylmercury Hg(CH3)2 is volatile & escapes from water and is converted to monomethyl HgCH3+ form as HgCH3Cl, HgCH3OH etc. also bind to proteins CH3Hg which may be able to cross the blood brain barrier and human placental barrier; HgCH3+ is the most toxic form of mercury follow by elemental Hg vapor; HgCH3+ also soluble in fatty tissue thus it bioaccumulates & biomagnifies Figure 11-1 Cycling of mercury in freshwater lakes (insoluble inorganic forms are converted to soluble organomettalic forms by bacteria)

    13. Env. Chemistry, Baird & Cann Figure 11-1 Cycling of mercury in freshwater lakes (insoluble inorganic forms are converted to soluble organomettalic forms by bacteria)

    14. Env. Chemistry, Baird & Cann Methylmercury Accumulation Most all the mercury in humans is methylmecury; 80% from fish -binds to S-H groups thus distributed throughout the fish (not like nonpolar compounds which are concentrated in the fatty tissue) Bioconcentration in fish 106 to 107 ; higher in older fish Freshwater [methylmercury] increases with lower pH Figure 11-2

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    16. Env. Chemistry, Baird & Cann Methylmercury Toxicity T1/2 in humans about 70 days, binds to S-H groups, fat soluble; cumulative poison Drop or two of pure demethylmercury on the gloved hands of Karen Wetterhahn, Dartmouth cancer researcher was fatal http://www.icanbehealthy.com/karen_wetterhahn.htm 1950s Minamata, Japan, Hg+2 catalyst for production of PVC, leaked into bay, fish [Hg] =100ppm, main diet of fish, thousands of people affected, hundreds died Symptoms: target is the brain, central nervous system affected; numbness of limbs, blurring/loss of vision, loss of hearing and muscle coordination, lethargy, irritability, coma & death. Fetuses absorbed from mother show brain damage: symptoms similar to cerebral palsy Levels in hair of pregnant mothers of 10-20 ppm are taken as a warning (WHO)

    17. Env. Chemistry, Baird & Cann Other Sources of Methyl Mercury Fungicide in agriculture & industry; generally broken down in soil & trapped sediment by bonding to sulfur compounds Human deaths from eating seeds that were meant for planting; also reduction in number of birds of prey; agriculture use curtailed in N. America & W. Europe Hg+2 leached from rocks

    18. Env. Chemistry, Baird & Cann Mercury as in Preservatives & Medications Salts of C6H5Hg+ used to preserve paint in can & prevent mildew after application; also formerly as a slimicide in pulp; phenylmercury not as toxic as methyl mercury Mercury (especially Hg2+2) compounds still used in pharmaceuticals & cosmetics because of their preservative & antiseptic qualities

    19. Env. Chemistry, Baird & Cann Safe Levels of Mercury in the Body 99.9 % of Americans daily intake methylmercury below WHO safe limit WHO concluded that mothers wotj10-20 ppm methylmercury in their hair would have levels in their blood that represent a potential threat to the fetus Fetuses in areas where fish are a mainstay of the diet, such as northern Canada, are at risk

    20. Env. Chemistry, Baird & Cann Lead The Free Element mp 327oC; bp 1740oC (Hg 357oC) Uses Flashing, roofing Pipes Bullets, shot (lead poisoning in animals) Sinkers Pb/Sn alloy solder Cooking vessels by the Romans; distillation of alcohol in lead vessels Lead storage battery Not as major environmental problem in its elemental state as mercury

    21. Env. Chemistry, Baird & Cann Pb+2 in Water and Food as an Environmental Hazard to Humans Most lead is extracted from ore PbS (Galena) Pb not soluble even in strong acids (e.g. Pb electrodes in lead storage batteries) but as an alloy with Sn it may dissolve e.g. solder in tin cans, lead dissolves in dilute acids such as canned fruits, also solder in copper pipes especially soft water

    22. Env. Chemistry, Baird & Cann Pb+2 in Water and Food as an Environmental Hazard to Humans Lead pipes leach lead as Pb+2 protective coating of PbCO3 forms; Phosphate may be added to form lead phosphate 20% of lead exposure to Americans comes from drinking water

    23. Env. Chemistry, Baird & Cann Lead Salts as Glazes & Pigments PbO yellow solid used in pottery glaze (water proof, high sheen) gradually leaches especially under acidic conditions Lead pigments PbCrO4 yellow; PbO3 red; Pb3(OH)2 white (taste sweet) replaced with TiO2 as white pigment in paints (Pb banned in 1978 in indoor house paints in U.S.); Pb(AsO4)2 pesticide Lead stabilizers in PVC

    24. Env. Chemistry, Baird & Cann Green Chemistry: Replacement of Lead in Electrodeposition Coatings Electrodeposition surface is dipped in a bath and acts as an electrode as the coating is applied electrophoretically; has many advantages over spray painting, including lower air pollution, due to decreased solvent emissions, better corrosion protection, due to better coverage of poorly accessible areas, reduced waste, due to high transfer efficiency, more uniform coating thickness.

    25. Env. Chemistry, Baird & Cann Green Chemistry: Replacement of Lead in Electrodeposition Coatings PGCC Award; PPG, 2001 Yttrium for lead in auto paints High corrosion resistance of lead has lead to exemptions from bans Yttrium twice as effective as lead (Pb3O4) Lead oxide 120 times more toxic than yittrium oxide Also reduces nickel and eliminates chromium that are used in metal pretreatments Potential to eliminate the use of 1 million pounds of lead, but also 25,000 pounds of chromium and 50,000 pounds of nickel on an annual basis

    26. Env. Chemistry, Baird & Cann Dissolution of Otherwise Insoluble Lead Salts Salts of lead (PbCO3, 1.5 x 10-15 & PbS 8.4 x 10-28) generally have low Ksp however the anions are relatively strong bases

    27. Env. Chemistry, Baird & Cann Dissolution of Otherwise Insoluble Lead Salts In acidic solutions PbS & PbCO3 solubilities are significantly increased

    28. Env. Chemistry, Baird & Cann Pb+4 in Automobile Batteries Elemental lead and the lead oxide PbO2 employed as the two electrodes in storage batteries in almost all vehicles now constitute the major use of the element. Majority of used lead storage batteries are recycled for their lead content. Storage batteries that are not recycled constitute the main source of lead in municipal waste.

    29. Env. Chemistry, Baird & Cann Tetravalent Organic Lead as Gasoline Additives Pb(CH3)4 & Pb(C2H5)4 used as additives in gasoline; phased out in most developed countries (interfered with catalytic converters) except in aviation fuel (Figure 11-3), Ethylene dichloride & dibromide also added to combine with liberated lead to prevent buildup of lead deposits; PbCl2 & PbBr2 would then volatilize & be eliminated in the exhaust PbR4 are generally volatile & are readily absorbed through the skin; converted to PbR3+ which acts as a neurotoxin (crosses blood brain barrier) high concentrations of PbR4 are fatal

    30. Env. Chemistry, Baird & Cann

    31. Env. Chemistry, Baird & Cann Pb Effects on Human Reproduction and Intelligence Microorganisms bioconcentrate Pb but it does not biomagnify in the food chain Some Pb directly inhaled, other through plants (bioconc.) Pb absorption increases with Ca or Fe deficiency

    32. Env. Chemistry, Baird & Cann Pb Effects on Human Reproduction and Intelligence High [Pb] general metabolic poison Effects brain function, decreased attention, retardation reproduction including miscarriage, still births Most sensitive are children <7; immature blood-brain barrier; effects mental development Figure 11-4 Passed to children through mothers milk Pb levels in children Figure 11-5 Not as dangerous as Hg but we are exposed to higher levels of Pb

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    34. Env. Chemistry, Baird & Cann Environmental Sources of Cadium Cd is a byproduct of Zn smelting; tends to be pollutant around Zn, Cu & Pb smelters; also from coal burning Used in Ni-Cd (about 5 g in each) batteries (calculators etc.); incineration leads to Cd in environment; some states & European countries outlawing such batteries

    35. Env. Chemistry, Baird & Cann Environmental Sources of Cadium As a pigment: CdS (yellow, Van Gogh?) & CdSe, hue depends on size of particle; used to color plastics CdS also in photoelectric devices & TV screens Cd plated steel Released into environment upon incineration (bp=765oC)

    36. Env. Chemistry, Baird & Cann Human Intake of Cd Most exposure from food supply; seafood & organ meats high [Cd]; most exposure from potatoes & grains (eat much more of these) Plants absorb Cd from irrigation water (contaminant in fertilizers, sewage sludge) Cd uptake increases with decreasing soil pH

    37. Env. Chemistry, Baird & Cann Human Intake of Cd Ouch-ouch degenerative bone disease (severe joint pain); Japan rice grown with irrigation water high in Cd (Jintsu River contaminated from Zn mining & smelting operation); daily intake 600 micrograms/day=10x intake of N. Americans

    38. Env. Chemistry, Baird & Cann Protection Against Low Levels of Cd Cd acutely toxic (about 1 gram); protection from low levels by the S-H rich protein metallothionein, complex is excreted (usual function regulation of Zn metabolism) Cd does not biomagnify Cumulative poison if not eliminated quickly (by metallothionein), lifetime in body several decades

    39. Env. Chemistry, Baird & Cann Arsenic Metalloid properties intermediate between metal and nonmetal As2O3 common poison used for centuries for murder and suicide

    40. Env. Chemistry, Baird & Cann As(III) Versus As(V) Toxicity to some extent mimics P (same group; same subshell electrons), although more tendency to form ionic compounds; found with phosphorus compounds in nature Acute poisoning due to severe vomiting & diarrhea As(III) more toxic than As(V) (reduced to III in the body) due to bonding to S-H groups (in enzymes) & longer retention in the body

    41. Env. Chemistry, Baird & Cann Anthropogenic Sources of As in the Environment Contamination of phosphates use as a pesticide: Pb3(AsO4)2, insecticide; herbicides Na3AsO3, Cu3(AsO3)2 (also wood preservative) Mining & smelting Au, Pb, Cu, Ni Combustion of coal 1% As in parts of China, global average 5 ppm) Iron & steel production Copper chromated arsenic (CCA) used to pressure treat lumber; 90% of the use of As in US is for wood preservatives

    42. Env. Chemistry, Baird & Cann Arsenic in Drinking Water As (much from natural sources;) in Drinking water (particularly groundwater) is one of the most serious environmental health hazards Bangladesh tube wells drilled by UNICEF for potable water (surface water high bacteria concentrations), high concentration of As soils some well exceed the 10 ppb WHO guideline by 50X; also used for irrigation thus contaminating rice & vegetables Carcinogen Lung, skin, (liver & bladder?) Synergistic effect between As and smoking

    43. Env. Chemistry, Baird & Cann Drinking Water Standards for As Global average As in drinking water 2.5 ppb EU, US & WHO limits 10 ppb; Canada 25 ppb; Australia 7 ppb

    44. Env. Chemistry, Baird & Cann Removal of As from Drinking Water Passing water over basic alumina; ion exchange & reverse osmosis are promising Precipitation as an insoluble salt addition of ferric chloride requires oxidation to AsV

    45. Env. Chemistry, Baird & Cann Steady State of As in Water

    46. Env. Chemistry, Baird & Cann As in Organic & Other Molecular Forms Most are water soluble thus can be excreted & thus less toxic

    47. Env. Chemistry, Baird & Cann As in Organic & Other Molecular Forms Majority of daily As intake from food: meat, seafood (mostly organic form such as As(CH3)4+ which are readily excreted), LD50 Table 11-2 As(CH3)3 & AsH3 by contrast are the most toxic forms of As Molds form As(CH3)3 from arsenic containing pigments in wallpaper releasing this as a gas into the room Cancer risks from As on the same level as ETS & radon

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    49. Env. Chemistry, Baird & Cann Chromium Common oxidation states Cr+3 & Cr+6, in aerobic conditions Cr exists primarily as the chromate ion highly soluble, toxic, can dimerize to dichromate Anerobic (reducing) conditions Cr exists the +3 ion; not very toxic or soluble under basic neutral or even acidic conditions

    50. Env. Chemistry, Baird & Cann Cr Contamination of Water Used for electroplating, corrosion resistance & tanning Second most abundant inorganic contaminant of groundwater under hazardous waste sites MCL in US 100 ppb Removal most heavy metals increase the pH but Cr+6 soluble at any pH but Cr+3 low solubility so Cr+6 usually reduced to +3

    51. Env. Chemistry, Baird & Cann Green Chemistry: Removing the As & Cr from Pressure Treated Wood Untreated exposed exterior wood decays in 3-5 years by termites, fungi etc. Pressure treated wood, ptw (lasts 10 -20 times longer) is first placed under vacuum to dehydrate the wood cells & then under pressure is treated with CCA solution (35.3% CrO3, 19.6% CuO, & 45.1% As2O3) 2001 7 billion board feet (enough to build 450,000 homes) of ptw was produced. 150 million pound of CCA was used containing 60 million pounds of Cr+6, and 40 million pounds of As

    52. Env. Chemistry, Baird & Cann Green Chemistry: Removing the As & Cr from Pressure Treated Wood A single 12-ft long 2 X6 board contains about 27 g of arsenic, enough to kill more than 200 adults. Although the preservatives are locked the wood some are leached out & there is also concern over direct contact with the wood US CCA treated lumber as of 1/1/04 was phased out for consumer use

    53. Env. Chemistry, Baird & Cann Green Chemistry: Removing the As & Cr from Pressure Treated Wood CCA preservative has been replaced by quaternary ammonium salts (ACQ) low toxicity (unrestricted pesticide) Quaternary Ammonium salts are also used in detergents, and disinfectants as well as fungicides & algaecides in lakes, rivers, streams, fish hatcheries & potable water supplies

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