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METALS - PowerPoint PPT Presentation


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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. Alkali metals. Alkaline earth metals.

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slide1

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
slide2

Alkali metals

Alkaline earth metals

Transition metals

‘Heavy metals’

Density > 5

slide3

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

slide4

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.

slide5

Covalent index = Xm2*r Xm - electronegativity

Toxicity rating – B>Intermediate>A

N2-seeking

3.4

Intermediate

1.75

O2-seeking

slide6

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’
slide9

SOURCES & SINKS OF METALS IN THE ENVIRONMENT

Erosion

Biological & Chemical transformations

Volatilization

Uptake

Attachment/release in sediment

Settling/resuspension

Storage

slide10

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)

slide11

Edu.

Thermostats

Switches (car)

Lamps

Switches

(lights)

Medical

Dental

MERCURY

Liquid at room temperature

Used in fungicides, manufacture of paper & plastics

Dense

slide12

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

slide13

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

slide14

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

slide15

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

slide16

Fungicide poisoning:

Introduced in 1920s, with Ceresan (2% ethyl mercury chloride)

Used to treat seed grain

Iraq 1970s: >6000 people poisoned, >500 mortalities

slide17

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

slide18

LEAD

Galena (PbS) – main lead ore

Uses of Lead

Batteries

Pigment

Lead mined for > 6000 years

Cables

Ammunition

slide19

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

slide21

BIO-

ACCUMULATION

slide22

Absorbed into blood

Deactivates enzymes that make haemoglobin

Precursor ALA builds up

Paralyses gut,

Fluid on brain,

Affects reproductive system

Anaemia

Pb Inhibits

slide23

Start of C20th

Large-scale lead poisoning of children noticed

Pica – responsible for Pb ingestion

slide24

CADMIUM

Produced as by-product from zinc smelting

Believed to be non-essential biologically

Readily accumulated by marine organisms

Essential for diatom sp. Thalassiosira

slide25

Poorly absorbed from gut

Can be taken up by inhalation e.g. Severn Bridge workers 1966

Present in cigarette smoke

Causes kidney damage

slide26

TIN

Heavily mined in Asia, Bolivia & Brazil

Organotin highly toxic

Used in antifouling paints, wood preservatives and stabilizers

Pacific oyster

slide27

Metals – do not metabolize

Change speciation by binding to chaperones

Prinicipally excreted via gut

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