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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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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

Transition metals

‘Heavy metals’

Density > 5


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


Nieboer & Richardson toxicity & availability in the hydrologic environment. Wood (1974)

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.


Covalent index = X toxicity & availability in the hydrologic environment. Wood (1974)m2*r Xm - electronegativity

Toxicity rating – B>Intermediate>A

N2-seeking

3.4

Intermediate

1.75

O2-seeking


Toxicity rating toxicity & availability in the hydrologic environment. Wood (1974)

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’


SOURCES & SINKS OF METALS IN THE ENVIRONMENT toxicity & availability in the hydrologic environment. Wood (1974)

Erosion

Biological & Chemical transformations

Volatilization

Uptake

Attachment/release in sediment

Settling/resuspension

Storage


Anthropogenic Enrichment Factor (AEF) toxicity & availability in the hydrologic environment. Wood (1974)

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)


Edu. toxicity & availability in the hydrologic environment. Wood (1974)

Thermostats

Switches (car)

Lamps

Switches

(lights)

Medical

Dental

MERCURY

Liquid at room temperature

Used in fungicides, manufacture of paper & plastics

Dense


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


DEPOSITION in all organisms

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


Toxicity – Dependent on form in all organisms

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


Minamata Bay Incident 1950s in all organisms

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


Fungicide poisoning: in all organisms

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

Used to treat seed grain

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


Some animals concentrate Hg without obvious effects in all organisms

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


LEAD in all organisms

Galena (PbS) – main lead ore

Uses of Lead

Batteries

Pigment

Lead mined for > 6000 years

Cables

Ammunition


No biological role in all organisms

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


(Micrograms per decilitre) in all organisms


BIO- in all organisms

ACCUMULATION


Absorbed into blood in all organisms

Deactivates enzymes that make haemoglobin

Precursor ALA builds up

Paralyses gut,

Fluid on brain,

Affects reproductive system

Anaemia

Pb Inhibits


Start of C20th in all organisms

Large-scale lead poisoning of children noticed

Pica – responsible for Pb ingestion


CADMIUM in all organisms

Produced as by-product from zinc smelting

Believed to be non-essential biologically

Readily accumulated by marine organisms

Essential for diatom sp. Thalassiosira


Poorly absorbed from gut in all organisms

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

Present in cigarette smoke

Causes kidney damage


TIN in all organisms

Heavily mined in Asia, Bolivia & Brazil

Organotin highly toxic

Used in antifouling paints, wood preservatives and stabilizers

Pacific oyster


Metals – do not metabolize in all organisms

Change speciation by binding to chaperones

Prinicipally excreted via gut


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