Metals as pollutants Flashcards

1
Q

What group of naturally occurring elements most frequently cause toxicity from environmental exposures?

A

Heavy metals

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2
Q

What are some examples of heavy metals?

A
Mercury
Lead
Chromium
Iron
Geranium
Cobalt
Silver
Cadmium
Copper
Molybdenum
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3
Q

What are some examples of lighter elements?

A

Aluminium
Arsenic
Selenium

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4
Q

What is the definition of background concentrations?

A

Concentrations of elements that occur in the environment in situations that have not been significantly influenced by anthropogenic emissions or unusual natural exposures.

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5
Q

What is toxicity?

A

The study of effects of poisonous substances on living organisms, including the way in which they gain entry into the organism.

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6
Q

What 2 factors is a toxic effect related to?

A
  1. the exposure or dose related to:
    - available conc of poison in the environment
    - period of exposure
  2. the susceptibility of an organism to a specific poison being considered. “tolerance”
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7
Q

When can progressive bioaccumulation over time occur until?

A

Until a toxic dose or threshold concentration is exceeded

Long term exposure to a small concentration of some elements may cause a toxic effect

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8
Q

What is toxicity also affected by?

A
  • the chemical form of the toxic element
  • the chemical environment
  • difference in susceptibility among individuals, populations and species
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9
Q

What are some anthropogenic sources of toxic elements?

A
  1. Agricultural/industrial processes
    - inorganic pesticides
    - sewage sludge
    - irrigation systems
  2. Metal mining and processing
    - mining waste
    - Fal estuary
  3. Automobile emissions
    - leaded petrol antiknock compound
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10
Q

What is the role of metals in marine animals?

A
  • at least 20 essential elements and another 6 necessary for healthy growth
  • several of the essential ones are metals e.g. oxygen transport - metallo-enzymes and enzyme cofactors where metals are required in electron transport processes
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11
Q

What is the classification of essential elements?

A

Major:

  • bulk elements: C, H, N, O, S
  • major ions: Na, K, Ca, Mg, P, Cl

Minor:

  • essential: Co, Cu, Fe, Mn, I
  • desirable: As, Cr, Ni, Sn, V, F
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12
Q

What is the effect of metals on cellular metabolism?

A

Memorise figure from lecture!

  • several metals like Cu and Zn are beneficial at low concentrations
  • intracellular concentrations of essential trace metals are controlled by homeostatic mechanisms
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13
Q

What are the toxicity tests?

A
  • Lethal Dose (LD50); acute toxic effects are quantified by controlled experiments to determine the dose causing the immediate death of 50% of the organism exposed
  • Median lethal time (LT50); time for death of 50% of a sample - depends on the concentration
  • Median lethal concentration (LC50); e.g. 4 day LC50; short term tests exposure of aquatic organism to toxin for constant period of time
  • Median Effect Concentration (EC50); e.g. 100 day EC50; reduction in growth response
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14
Q

How do toxic metals interfere with cellular metabolism?

A
  • toxic metals displace essential metals in enzymes to form stronger complexes and thus interfere with cellular metabolism
  • general binding to cellular components disrupts cell activity e.g. damage to cell membrane
  • binding of metals may be specific e.g. Pb with nucleic acids
  • organometallic compounds may be particularly toxic e.g. methyl mercury and tributyl tin
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15
Q

What are some forms of detoxification?

A
  • excretion in waste products
  • production of sulphur (-SH) containing low mol. wt. protein compounds or ‘metallothioneins’
  • in plants similar compounds called ‘phytochelatins’
  • other cellular components that isolate metals e.g. granule formation
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16
Q

When do metals become toxic (in terms of detoxification)?

A

When storage and other detoxification processes are exceeded.

17
Q

What are factors affecting toxicity?

A
  • speciation of metals; dissolved ionic form most toxic; particulate forms important in filter feeders
  • increased temperatures and low salinities
  • compounded or synergistic effects of multiple pollutants
  • condition of organism or life stage
18
Q

What are some detectable effects of metal pollution on marine organisms\?

A
  • biochem response e.g. metallothionein production
  • reduced growth rates
  • morphological changes e.g. imposex in dog whelk
  • reproduction and recruitment
  • behaviour effects
  • changes in community structure
19
Q

Metals are conservative pollutants. What does this mean?

A

They’re not subject to bacterial attack or degradation and are permanent additions to the marine environment.

20
Q

How does bioaccumulation of heavy metals occur?

A

Bioaccumulation occurs through metals binding to cell membranes and intracellular uptake.

It occurs within organisms if they’re unable to excrete the metal.

21
Q

What is biomagnification or bioamplification?

A

When toxic metals are transferred through the food chain by feeding. If predators cannot excrete the metals, they in turn acquire a larger body burden of the metal.

22
Q

What are the natural sources and uses of the toxic metal mercury?

A

Natural sources: weathering of mercury-bearing rocks and volcanic and geothermal vents. Mercury in seawater as hydroxide or chloride. Methyl mercury accumulates in sediments.

Uses: chlor-alkali industry, use of mercury electrodes, switches, slimicides in lumber and pulp industries, seed dressings (fungicide)

23
Q

What is the maximum tolerable consumption of mercury in food according to the WHO?

A

0.03mg per week

24
Q

What form is tin highly toxic in? what is it used in? what can it cause?

A

its organic form as TBT (Tributyl Tin oxide).

used as antifouling paint.

Leaches into sea in harbours and estuaries, causing deformed shells in oysters and imposex in common dog whelk