METALS

1. METALS • Occur naturally • Released via natural & human activities • Constitute >75% elements in periodic table CHEMICAL DEFINITIONS OF METALS • Metallic shine (lustre) • Usually solid at room temperature • Malleable • Good electrical & heat conductors

2. Alkali metals Alkaline earth metals Transition metals ‘Heavy metals’ Density > 5

3. Classification of naturally-occurring metals according to toxicity & availability in the hydrologic environment. Wood (1974) Non-toxicLow ToxicityMod-high Tox. Aluminium Gold Cadmium Iron Tin Chromium Manganese Copper Lead Mercury Nickel Zinc

4. Nieboer & Richardson Class A (O2 seeking) Borderline Class B (S or N2 seeking) Calcium Zinc Cadmium Magnesium Lead Copper Manganese Iron Mercury Potassium Chromium Silver Strontium Cobalt Sodium Nickel Arsenic Vanadium Nieboer & Richardson (1980); The replacement of the nondescriptive term heavy metals by a biologically and chemically significant classification of metal ions. Environ. Pollut. Ser. B 1:3-26.

5. Covalent index = Xm2*r Xm - electronegativity Toxicity rating – B>Intermediate>A N2-seeking 3.4 Intermediate 1.75 O2-seeking

6. Toxicity rating B>Intermediate>A • Class B most effective at binding with S-H groups, N-containing groups • Displace Intermediate/Class A metals • Can form organometals • Intermediates displace other intermediates/Class A metals • Class A – displace other Class A metals • Metals do not metabolize, change by binding to other molecules • Metals regarded as ‘essential’ or ‘non-essential’

9. SOURCES & SINKS OF METALS IN THE ENVIRONMENT Erosion Biological & Chemical transformations Volatilization Uptake Attachment/release in sediment Settling/resuspension Storage

10. Anthropogenic Enrichment Factor (AEF) Indicates extent to which human activity contributes to global metal cycles Metal Anthropogenic Natural Total (T) AEF Source (A) source ([A/T] x 100) Cadmium 8 1 9 89% Lead 300 10 310 97% Manganese 40 300 340 12% Mercury 100 50 150 66% (All values 106 kg per year)

11. Edu. Thermostats Switches (car) Lamps Switches (lights) Medical Dental MERCURY Liquid at room temperature Used in fungicides, manufacture of paper & plastics Dense

12. No biological role, but abundant in environment and present in all organisms Exposure Medical Used as disinfectant in India in C12th, as diuretics, laxatives, and to treat syphilis. Still part of traditional Chinese medicine Respiratory (e.g. occupational) Gastrointestinal (e.g. Minamata disease) Dental – amalgam used in tooth fillings

13. DEPOSITION DEPOSITION VOLATILIZATION & DEPOSITION VOLATILIZATION & DEPOSITION CH3Hg DEP. & RUNOFF Hg (II) DEP. & RUNOFF Hg(0) REDUCTION DEMETHYLATION OUTFLOW CH3Hg Hg(II) METHYLATION OUTFLOW OUTFLOW BIOMAGNIFICATION DIFFUSION/ SEDIMENT RESUSPENSION SEDIMENTATION SEDIMENTATION Hg(II) CH3Hg

14. Toxicity – Dependent on form Elemental - Hg0 :Vapour, highly toxic Inorganic – Hg+, Hg2+: Not easily absorbed, but risk of kidney damage if ingested Organic – R-Hg, e.g. methyl mercury: More toxic than inorganic, risk of brain & CNS damage. Can cross blood-brain barrier and placenta Attraction for sulphur groups, thus can inactivate enzymes Sodium/potassium-adenosine triphosphate (Na+/K+-ATPase) enzyme particularly sensitive to Hg Na/K-ATPase essential for working of CNS

15. Minamata Bay Incident 1950s JAPAN New factory used mercuric chloride as catalyst New illness apparent in fishermen & their families (memory loss, visual impairment, cerebral palsy) Children & newborns most severely affected Hg discharged principally in inorganic form – bacteria in sediments produced methyl mercury 700 poisonings, > 70 deaths * Minamata Bay

16. Fungicide poisoning: Introduced in 1920s, with Ceresan (2% ethyl mercury chloride) Used to treat seed grain Iraq 1970s: >6000 people poisoned, >500 mortalities

17. Some animals concentrate Hg without obvious effects E.g. Tuna, swordfish, sharks Top predators Active swimmers Seabirds: Majority of Hg in methylated form in feathers Seabirds & marine mammals: High levels of selenium, protects against mercury toxicity

18. LEAD Galena (PbS) – main lead ore Uses of Lead Batteries Pigment Lead mined for > 6000 years Cables Ammunition

19. No biological role Most dangerous via chronic exposure, can be stored in bones as lead phosphate Exposure Medical Used by Romans to treat skin complaints, by Victorians (plus opium) to treat diarrhoea Respiratory (e.g. leaded petrol) Gastrointestinal (e.g. Roman cooking implements & water pipes) Industrial – mining, paints

20. (Micrograms per decilitre)

21. BIO- ACCUMULATION

22. Absorbed into blood Deactivates enzymes that make haemoglobin Precursor ALA builds up Paralyses gut, Fluid on brain, Affects reproductive system Anaemia Pb Inhibits

23. Start of C20th Large-scale lead poisoning of children noticed Pica – responsible for Pb ingestion

24. CADMIUM Produced as by-product from zinc smelting Believed to be non-essential biologically Readily accumulated by marine organisms Essential for diatom sp. Thalassiosira

25. Poorly absorbed from gut Can be taken up by inhalation e.g. Severn Bridge workers 1966 Present in cigarette smoke Causes kidney damage

26. TIN Heavily mined in Asia, Bolivia & Brazil Organotin highly toxic Used in antifouling paints, wood preservatives and stabilizers Pacific oyster

27. Metals – do not metabolize Change speciation by binding to chaperones Prinicipally excreted via gut