2 Introduction Five main heavy metals – Hg, Pb, Cd, Cr, As Widely distributedHigh toxicityNondegradable, c.f. toxic organic compoundsDensities are high compared to othersLook at the table, are all heavy metals toxic?
3 What is a Heavy Metal?Lists of heavy metals differ, assumes all species are toxic.Lists of heavy metals differ, assumes all species are toxic.
4 IntroductionPathwaysAirWaterSinksSoilSedimentAlthough we commonly think of heavy metals as water pollutants, they are for the most part transported from place to place via the air, either as gases or as species absorbed on, or absorbed in, suspended particulate matter. (Baird, 2011)
5 Speciation and Toxicity Mercury illuminated by incandescent and UV lightFree elements not very toxic (except Hg vapor)Highly toxic as cationsPutnam, 1972
6 Speciation and Toxicity Biochemical mode of action: inhibition of enzymesAffinity for -SH (sulfhydryl groups)Occur in enzymes which control metabolic pathwaysM R-S-H → R-S-M-S-R + 2H+
7 Speciation and Toxicity Treatment uses chelating agents
8 Speciation and Toxicity Toxicity depends on speciationInsoluble substances pass through human body without harmMost dangerousImmediate effectsThose that pass blood-brain barrier membrane or placental barrierOrganic compounds of heavy metals (alkyl groups attached to the metal, e.g. methyl mecury, CH3Hg+) are highly toxicsoluble in animal tissueeasily pass through biological membranes unlike Mn+Toxicity of metals in water depends on speciation and water quality (pH / DOC) since complexation and adsorption may make metals less available
9 Bioaccumulation Mercury bioaccumulates, others may(?) All heavy metals bioconcentrate
17 Anthropogenic Sources Mg/yr (N. America)Electrical utilities52.7Incinerators32.2Coal burning: residential and industrial12.8Mining6.7Chlor-alkali6.75Misc64.1Total200.1Coal: ~ 1 ppmAny other material with this content = hazardous wasteHg from coal burning has been found at both PolesCement KilnsTrash incinerationSeigneur et al. 2004
18 Usesindustrial chemicals – e.g. drugs, fungicides, and as a cathode in chlorine and sodium hydroxide production (chlor-alkali process),Cl2 ←NaCl → NaH2 + NaOH ← Amalgam2. electronics – switches, batteries, electrodes, mercury vapor + fluorescent lamps3. scientific instruments – barometer, thermometer, blood-presure meter4. pesticides5. Dentistry – amalgamsGold and silver extraction for miningSkin lightening creamsNa forms amalgam with Hg, otherwise Na would explode on contact with waterHg
19 Collectively Dentists release about the same amount of waste mercury as coal-fired plants Largest source of Hg contamination in wastewaters
21 The Nature of Airborne Mercury How far will airborne Hg travel?flame Clx released by power plantsHg2+ (coal) → Hg0(g) → HgCl2(g)FormFormulaLifetime (Est.)Gaseous Elemental HgHg0(g)Months-yearsParticulate Hg (TPM)Hg2+ (adsorbed), Hg0WeeksReactive gaseous Hg (RGM)HgCl2(g)Days-weeks (water sol.)Covalent molecular compound
22 Mercury Emissions Control TPM captured by electrostatic ppt, or bag filtersHgCl2 removed by wet scrubbingDifficult to remove all mercury, especially GEM (Hg0)Fig 12-1
23 Speciation Organic Inorganic Volatile Reactive Elemental Mercury Hg0Mercury Ion Hg2+AKA ‘reactive gaseous’ mercury’ (RGM) e.g. HgCl2(g)Methyl MercuryCH3Hg+Hg22+ (mercuric ion) is not very toxic since it combines with stomach acid to produce insoluble HgCl2Particulate bound Hg-PDimethyl MercuryCH3HgCH3GlobalRegional?
24 Emisson and Deposition Mercury deposition is enhanced by:Oxidizing speciesParticulate matterForest coverProximity to sourcesHg0 → Hg2+‘smog’Cl.OH.‘Watershed Sensitivity’ creates localized ‘hot-spots’ of Hg accumulation
30 Methylmercury Methylmercury is in reality CH3HgCl and CH3HgOH Written: CH3HgX, MeHg or CH3Hg+(Misleading since it is covalent)Occurs in anaerobic portion of lakesdegraded by sunlight, most important sinkAlso Merrian, E. (1991) Metals and their Compounds in the Environment: Occurrence, Analysis and Biological prevalence. VCH.O’neill diagram vs. Winfrey and Rudd, 1990
31 Health Effects Toxicity Toxicity: all formsMeHg >> vapor >> Hg2+ >> liquidLiquid Hg is readily excretedHg2+ not readily transported across membranes – affects liver + kidneysVapor – diffuses from lungs to bloodstream to brainMethylmercury is lipophillic (soluble in fatty tissue)More mobile – bioconcentrates, bioaccumulates and biomagnifiesCrosses blood-brain barrierConverted to Hg2+ in brain (neurotoxin)Usual barrier to Hg2+ is circumvented by vapor and MeHg
32 Health Effects Toxicity Pathways: Inhalation, ingestion, dermalMost Hg in humans is MeHg from fishFDA: 1 ppm fish / EPD: 2.0 ppb waterBrain damage, nervous system disorders, heart disease, liver and kidney failureSymptoms: all brain associated, - numbness of limbs, loss of vision, hearing and muscle coordinationLargest risk to newborns
33 Health Effects Mode of Action Biochemical mode of action: inhibition of enzymesAffinity for -SH (sulfhydryl groups)Occur in enzymes which control metabolic pathwaysM R-S-H → R-S-M-S-R + 2H+
34 Health Effects Mode of Action Christopher C. W. Leong; Naweed I. Syed; Fritz L. Lorscheider CA "Retrograde degeneration of neurite membrane structural integrity of nerve growth cones following in vitro exposure to mercury, Neuroreport 2001;12:Hg dissolves neurons
35 Case Study Minamata, 1953 WHO limit 0.5 mg kg-1 Minamata 50 mg kg-1 Minamata Bay, Japan ( )Plastic manufacturer (Chisso Corp.), used mercury in the production of acetaldehydeDischarged mercury into the bayMain diet of locals was fish + shellfish – 5-20 ppm (106 water)Over 3,000 people suffered (730 deaths): Minamata disease / Dancing Cat Diseasevarious deformities, damage to nervous system, retardation or deathDeveloping embryos are especially vulnerableWHO limit 0.5 mg kg-1Minamata 50 mg kg-1
36 History of Mercury Pollution Site: Almadén, SpainWorld’s largest Hg mineMartínez-Cortizas et al., 1999
37 History of Mercury Pollution Pollution Probe – Mercury in the Environment, A primer
38 PathwaysAcidification of lakes enhances solubility and methylation ratesDouble-whammy effect of burning fossil-fuelsConc. Hg in standardized fish in 84 Ontario lakesLean, 2003
39 Pollution Probe – Mercury in the Environment, A primer
44 Lead Properties and Uses BatteriesFuel additiveChemicalsSolderPigmentsPipingAmmunitionPropertiesLow melting point (327 ºC), easily handled as a liquid – moldedSoft, maleableForms protective oxide layerForms alloys
45 Lead Compounds Pigments Exists in Pb2+ form (PbS is highly insoluble, ore galena, from which most of lead is extracted)e.g. PbO (batteries), PbCO3, PbS, PbCl2Pb3(CO3)2(OH)2 white leadPb3O4 red leadPbCrO4 chrome yellowAlso forms a few ionic Pb4+ compounds such as PbO2Pigments
46 QuestionThe lead level in drinking water is 10 ppb. Assuming an adult drinks 2 L of water per day, calculate the daily total lead intake.10 ppb = 10 g of Pb / 109 g H2OMass of 2 L of H2O = 2000 g2000 g H2O x 10 g Pb = 2.0 x 10-5 g Pb109 g H2O
47 Lead Dissolution of Lead Salts Both PbS and PbCO3 highly insolublePbS(s) ⇌ Pb2+ + S2- Ksp = 8.4 x 10-28PbCO3(s) ⇌ Pb2+ + CO32- Ksp = 1.5 x 10-13The anions behave as strong bases (proton acceptors)S2- + H2O ⇌ OH- + HS-CO32- + H2O ⇌ OH- + HCO3-Removing S2- and CO32- shifts equilibrium to right and more of PbS or PbCO3 dissolvesIncreases solubility
48 Lead can be Mobilized In highly acidic water… The “insoluble” solid dissolves to a much greater extent under acidic conditions. The conversion of S2- to HS- followed by its conversion to H2S facilitates dissolution of PbSS2- + H+ ⇌ HS- K = 7.7 x 1012HS- + H+ ⇌ H2S K’ = 1 x 107So the net dissolution reaction leading to the dissolution of lead in acidic solutionPbS(s) + 2H+ ⇌ Pb2+ + H2SKoverall = Ksp x K x K’ = 6.5 x Or Koverall = [Pb2+][H2S]/[H+]2Since all S2- exists as H2S, from stoichiometry [Pb2+] = [H2S] [Pb2+]2= Koverall x [H+]2 [Pb2+] = 2.5 x 10-4 [H+]
49 [Pb2+] = [2.5 x 10-4] [H+] (linear inc. in solubility with acidity) At pH 4, [H+] = 1.0 x 10-4 mol/L At pH 2, [H+] = 1.0 x 10-2 mol/L[Pb2+] = 2.5 x 10-8 mol/L [Pb2+] = 2.5 x 10-6 mol/LAs the pH drops, the lead concentration increases (linearly proportional to hydrogen ion concentration)Pb2+ is particularly soluble in soft water
50 Lead 4+ lead in Batteries PbO2 in car batteries is a major source
51 Lead Environmental Lead: Gasoline Additive Organic lead: PbEt4Readily absorbed through skinHazard for workers with direct exposureIn the IV oxidation state, it forms covalent compounds with four organic substituents: Pb(C2H5)4 / PbEt4 (tetra ethyl lead). These are volatile and may be soluble in organics and fats, but are not soluble in waterStill used in aviation fuelForm deposits of Pb in engines, organohalides are added to prevent thisEmitted as PbEt4 , lead dihalide (e.g. PbBrCl / PbCl2) which react with sunlight to form PbO
52 Lead Environmental Lead: Gasoline Additive Conversion to unleaded fuel came about due to interference of Pb with catalytic convertersThe historical consumption oflead in gasoline in the USDunlop et al., 2000
53 Lead Effects on Human Reproduction and Intelligence Pb levelMost of the ingested lead initially enters blood, then to soft tissues and other organs, brainEventually lead is deposited in bones as it replaces calcium (Ca2+) and remains for decadesRisk is greater for fetuses and children under 7 yrs and affects normal development of brainsLoss of ~5 IQ per 100 ppb PbBellinger et al., 1987
54 Blood lead levels in US children (1-5 yrs) 20% > 2004% > 300 ppb9% > 100 ppbppb was proposed ‘safe level’…it appears there is no threshold levelGoyer, 1996
55 QuestionConvert these ppb lead levels to μg/dL (standard for blood), assume a blood density of 1.0 g/mL10 ppb = 10 g Pb / 109 mLSince 1 dL = 100 mL10 ppb = 10 g Pb / 107 dL= 1 x 10-6 g Pb / dL = 1 μg / dL
56 Lead Behavior of Lead in the Body Organic Pb – readily absorbedInorganic Pb – lungsPb is stored in bones and teeth – similarities to Ca2+ and Ba2+ (charge, ionic radius)90-95 % of Pb in the body is in the skeletont1/2 is high, 2-3 yrs for whole body half-lifeCan be remobilized during illness into soft tissue/fluidsMajor problem when measuring Pb in the body
57 Lead Body BurdenBody burdens of lead in ancient people uncontaminated by industrial lead (left); typical Americans (middle); people with overt clinical lead poisoning (right). Each dot represents 40 µg of lead. Source: Patterson et al., 1991; adapted from NRC, 1980.
58 Summary Lead is not as dangerous as mercury Number of sources and exposure is greaterToxicity: organic > inorganicEnvironmental levels within x10 of the toxic effect level
60 Cadmium http://www.cadmium.org Relatively new metal in terms of humans Sources:natural rock weatheringcopper, lead and zinc smelting auto exhaustcigarette smoke (a cigarette contains 1-2 ug Cd)Uses:metal platingnickel-cadmium batteriessolderspaint pigments (blue)plastic stabilizersphotographic chemicalsfungicidesReadily absorbed and accumulated in plantsFood as most common route of exposure for general populationFrom: Klaassen et al., Chap. 19, Philp, Chap. 6
61 Pharmacokinetics pharmacokinetics: inhalation: smelters, cigarette smoke15-50% absorbedingestion:main source is liver and kidney of meats6% absorbed, greater if deficient in calcium, zinc or ironShenyang Copper Smelter
62 Toxicity Mechanisms Mechanisms binding to –SH groups competing with Zn and Se for inclusion into metalloenzymescompeting with calcium for binding sites (calmodulin)Kidney toxicityLung toxicitySkeletal effectsOsteoporosis and osteomalaciaCancercarcinogenic in animal studies~8% of lung cancers may be attributable to Cd
63 Cadmium (Cd) Epidemics/case studies Japan (1940s)effluent (outflow) from a lead-processing plant washed over adjacent rice paddies for many yearsrice accumulated high level of Cdcommunity was poor (and therefore malnourished with respect to calcium)acute toxicity: renal failure,anemia, severe muscle painnamed "Itai-Itai" disease ("ouch, ouch")Itai-itai victim
65 Arsenic Source: http://www.webelements.com Chemistry: Sources: extremely complex because it can exist in metallic form, can be in trivalent and pentavalent state (charge of 3+ or 5+), and can be organic or inorganicwidely distributed in nature (variety of forms)Sources:smelting of gold, silver, copper, lead and zinc orescombustion of fossil fuelsagricultural uses as herbicides and fungicidescigarette smokeoccupational: largest source is manufacture of pesticides and herbicidesEnvironmental fate:found in surface and groundwater through runoffaccumulates in plants if soil conditions are rightbioaccumulates in aquatic ecosystems (so fish consumption is a source)Source:
66 SourcesEating food, drinking water, or breathing air containing arsenic.Herbal medicines (India/Pakistan Ayurvedic” remediesBreathing contaminated workplace air.Breathing sawdust or burning smoke from wood treated with arsenic.Living near uncontrolled hazardous waste sites containing arsenic.Living in areas with unusually high natural levels of arsenic in rock.
67 pharmacokinetics and dynamics: Arsenic is widespread in the environmentOccupational exposures can occurSmelting industryCoal fired power plantsEpidemiological studies implicate arsenic as a carcinogenInhalation is a common route of exposureDrinking water exposure can also lead to cancerpharmacokinetics and dynamics:absorbed via inhalation, ingestion and dermal exposuremimics phosphate in terms of uptake by cellsDetoxified by methylation: decreased rates lead to increased toxicity (individual susceptibility)Can cross placentaaccumulates in liver, kidney, heart and lung - later in bones, teeth, hair, etc.half-life is 10 hr, excretion via kidneys
68 Arsenic Toxicity Mechanisms binds to sulfhydryl groups (and disulfide groups), disrupts sulfhydryl-containing enzymes (As (III))inhibits pyruvate and succinate oxidation pathways and the tricarboxylic acid cycle, causing impaired gluconeogenesis, and redu ced oxidative phosphorylationtargets ubiquitous enzyme reactions, so affects nearly all organ systemssubstitution for phosphorus in biochemical reactionsReplacing the stable phosphorus anion in phosphate with the less stable As(V) anion leads to rapid hydrolysis of high-energy bonds in compounds such as ATP. That leads to loss of high-energy phosphate bonds and effectively "uncouples" oxidative phosphorylation.
69 Arsenic Toxicityorganic arsenicals>inorganic arsenicals>metallic formstrivalent>pentavalentacute: severe abdominal pain, fever, cardiac arrhythmiachronic: muscle weakness and pain, gross edema, gastrointestinal disturbances, liver and kidney damage, swelling of peripheral nerves (neuritis), paralysisliver injury: jaundiceperipheral vascular disease - blackfoot diseasechronic drinking water exposure in Taiwan and Chilecancer (skin, lung, kidney bladder)
70 Black Foot Disease Blisters skin disease: keratosis of hands and feet, and hyperpigmentationBlisters
71 Arsenic Problems: Bangladesh Arsenic is found in groundwater of many countries: particularly South East Asia and BangladeshAs leached from underground sources into village wells of 1 million people, levels of 1000 ppb62% of wells tested exceeded WHO standard~ 35 million people exposed above US EPA standard200,000 people suffering from As-induced skin lesionsproblem may have been exacerbated by large scale withdraw of groundwater for irrigation or by extensive use of fertilizersSkin pigmentation, keratoses andskin cancers were found amongpeople who drank from arseniccontaminated wellsSee Prof. Wilson at Harwad’s Arsenic pageFrom: Klaassen et al., Chap. 19, Philp, Chap. 6
72 Toxic Hazards Associated with Poultry Litter Incineration What Goes In, Must Come Out“One of the most basic principles of incineration is that what goes in, must come out. There is no alchemy going on, so if there are toxic heavy metals like lead, mercury or arsenic going in one end, they must come out in the form of toxic ash and toxic air emissions.”Arsenic Use in Chicken & Turkey FeedRoxarsone, or 3-nitro-4-hydroxyphenylarsonic acid, is currently the most commonly used arsenical compound in poultry feed in the United States, with a usage of 23 to 45 grams of chemical per ton of feed for broiler chickens for increased weight gain, feed efficiency, improved pigmentation, and prevention of arasites. Roxarsone is used in turkeys as well as chickens. By design, most of the chemical is excreted in the manure.
73 Setting the Standard1992: California toxicologist argues that US EPA standard for As in drinking water would constitute a 1:100 risk of cancer for lifetime consumptionEPA standard not originally based on cancer as an endpointachieving a 1:1,000,000 risk would require dropping standard from 50 ppb to 2 pptEPA revising standard to from 50 to 10 ppb in 2006consider cost to small communities
74 Arsenic in US Drinking Waters In the U.S. the arsenic for drinking water was lowered from 50 ppb (μg/L) to 10 ppb – to be complied by 2006Source:
75 Removal of As from Water Pass over alumina (Al2O3)Anion exchange or reverse osmosisPrecipitationIn treatment facilities by precipitating it in the form of insoluble arsanate, AsO43-Fe3+ + AsO43- → FeAsO4(S)GW As is usually reducing so As(III) must first be oxidized to As(V)
76 Steady-State of As in Water Arsenic in Lake OntarioThe lake receives 161 tonnes of As per year through river and lake flows that originate in land based sourcesInput = Output= t = (91-49) tThompson et al, 1999
77 Toxicology LD50 values for some common forms of As Meat and seafood Converted by bio-methylation → excreted
78 ToxicologyAs(III) compounds arsine (AsH3) and trimethylarsince (As(CH3)3) are most toxic
79 Chromated Copper Arsenate (CCA) Chromated copper arsenate (CCA) used to protect decks (45% As2O3)Concern over leaching of As especially in childrens playgrounds76 mg/kg found in soil 10x controlPressure treated woodCCA: 22 percent pure arsenicA 12-foot section of pressure-treated lumber contains about an ounce of arsenic, or enough to kill 250 people."In less than two weeks, an average five-year-old playing on an arsenic-treated playset would exceed the lifetime cancer risk considered acceptable under federal pesticide law."EPA, 2004, banned from residential useSource:
82 Global Arsenic Cycle and Reservoir Sizes 800-1,740 t Asτ = yr = 8 – 10 doceans4.01 x 1013 t As in the earth’s crust1.5 – 2 mg kg-1 upper crust1 – 1.8 mg kg-1 bulk crustlithosphereGlobal As cycle and reservoir sizes from Matschullat, 2000
84 Further Reading (Baird) Hingston, J.a. et al (2001) Leaching of Chromated Copper Arsenate Wood Preservatives. Environmental Pollution, Vol. 111, pp. 53.Lykknes, A. and Kvittingen, L. (2003) Arsenic: Not So Evil After All?. Journal of Chemical Education, Vol. 80, pp. 497.Pearce, F. (2003) Arsenic’s Fatal Legacy Grows. New Scientist. August 9, pp. 4.Smith, A.H. et al. (1992) Cancer Risks from Arsenic in Drinkng Water. Environmental Health Perspecives. Vol. 97, pp. 259.
85 Further Reading Smith, A.H. et al (2002) Science Welch, A., Ryker, S., Helsel, D., and Hamilton, P. (2001) Arsenic in Ground Water of the United States: A Review. Well Water Journal. February, pp
88 Mills, A.L. (19) Lead in the environment. Chemistry in Britain. Bryce-Smith, D. (19) Lead Pollution – a growing hazard to public health. Chemistry in Britain.Bryce-Smith, D. (19) Lead pollution from petrol. Chemistry in Britain.
89 BooksHarrison, R.M. and Laxen, D.P.H. (1981) Lead Pollution: Causes and Control. Chapman and Hall.NRC Committee on Lead in the Human Environment (1980) Lead in the Human Environment. National Academy of Sciences, Washington DC.Stoker, H.S. and Seager, S.L. (1976) Environmental Chemistry: Air and Water Pollution. Scott Foreman and Company.
90 Further Reading Hg Journals and Reports Betts, K. (2003) Dramatically improved mercury removal. Environmental Science and Technology, pp A.Cleckner, L.B., Garrison, P.J., Hurley, J.P., Olson, M.L., and Krabbenhoft, D.P. (1998) Trophic transfer of methyl mercury in the northern Florida Everglades. Biogeochemistry, Vol. 40, No. 2-3, ppCrenson, S.L. (2002) Study Records Elevated Mercury. Associated Press. Sunday Oct 20th.Fitzgerald, W.F., Engstrom, D.E., Mason, R.P., and Nater, E.A. (1998) The case for atmospheric mercury contamination in remote areas. Environmental Science and Technology, Vol. 32, pp. 1-7.Lean, D. (2003) Mercury pollution a mind-numbing problem: high levels of mercury lurk in our water supply, and it is time to sound a global alarm. Canadian Chemical News, January, p. 23.Martínez-Cortizas, A., Pontrevedra-Pombal, X., Garcia-Rodeja, E., Nóvoa-Muñoz, J.C., and Shotyk, W. (1999) Mercury in a Spanish peat bog: Archive of climate change and atmospheric deposition. Science, Vol. 284, ppPacya, E.G., and Pacya, J.M. (2002) Global emission of mercury from anthropogenic sources in Water, Air and Soil Pollution, Vol. 137, ppRenner, R. (2004) Mercury woes appear to grow. Environmental Science and Technology, Vol. 38, No. 8, pp. 144A.Rouhi, A.M. (2002) Mercury Showers. Chemical and Engineering News. April 15, p. 40Sarr, R.A. (1999) New Efforts to Uncover the Dangers of Mercury. New York Times, Health and Fitness Section, p. D7, Tuesday, November 2.Seigneur, C., Vijayaraghaven, K., Lohman, K., Karamchandanai, P., and Scott, C. (2004) Global source attribution for mercury deposition in the United States. Environmental Science and Technology, Vol. 28, No. 2, ppWinfrey, M.R., Rudd, J.W.M., Environmental factors affecting the formation of methylmercury in low pH lakes. Environmental Toxicology and Chemistry, Vol. 9, ppWright, K. (2005) Our Preferred Poison. Discover, March.
91 Hg BooksBerry, L.G. and Mason, B. (1959) Mineralogy: Concepts, Descriptions, and Determinations. W.H. Freeman, San Francisco.Gribble, C.D. (1978) Rutley’s Elements of mineralogy, 27th edition. Unwin Hyman, LondonHBRF (2007) Mercury Matters. Hubbard Brook Research Foundation.O’neill, P. (1993) Environmental Chemistry (2nd edition). Chapman and Hall.
92 Movies FHS: the Ocean Sink (1990) 29 mins FHS: Chemicals from NaCl: 1 20 minsFHS: Salt 1992Minamata movie:People's Century: Endangered Planet (1999)
93 Mills, A.L. (19) Lead in the environment. Chemistry in Britain. Bryce-Smith, D. (19) Lead Pollution – a growing hazard to public health. Chemistry in Britain.Bryce-Smith, D. (19) Lead pollution from petrol. Chemistry in Britain.
94 BooksHarrison, R.M. and Laxen, D.P.H. (1981) Lead Pollution: Causes and Control. Chapman and Hall.NRC Committee on Lead in the Human Environment (1980) Lead in the Human Environment. National Academy of Sciences, Washington DC.Stoker, H.S. and Seager, S.L. (1976) Environmental Chemistry: Air and Water Pollution. Scott Foreman and Company.