properties of pollutants

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  • properties of pollutants
    • toxicity: a measure of how poisonous a substance is, (usually caused by enzyme inhibition).
      • toxic pollutants
        • carbon monoxide binds to haemoglobin in blood and prevents it from carrying oxygen.
        • lead inhibits enzymes in nerve cells
        • DDT prevents normal passage of nerve impulses between nerve cells by inhibiting enzyme action.
        • acids change the shape of cell membrane and enzyme proteins so they don't function properly.
    • specificity: a measure of differing toxicities of a substance on different organisms. A specific substance is very toxic to some organisms and much less toxic to others.
      • e.g. pyrethroid insecticides kill both insects and mammals, but insects are more sensitive than mammals so farmers use a dose that kills insects but won't harm mammals.
    • persistence: a measure of the rate at which a material breaks down and therefore the length of time it remains in the atmosphere.
      • CFCs are chemically stable and break down slowly
      • DDT is stable but gradually breaks down, it hasn't been used for over 30 years but some still remains in wildlife
      • both sewage and pyrethroid insecticides break down rapidly in the right conditions.
    • biodegradability: the ease with which a material is broken down by living organisms, usually bacteria.
      • sewage, paper and cardboard are biodegradable
      • most plastics and DDT are less biodegradable
    • mobility: a measure of how easily a material moves in the environment.
      • CFCs are persistent gases which travel long distances in the atmosphere as they aren't very soluble in water so aren't removed by rain
      • smoke particles rarely travel  far as they are washed out by rain or settle due to gravity
      • currents in rivers will carry sediments, smaller\lighter particles travel furthest
    • solubility: the ease with which the molecules of a material separate and disperse into a liquid.
      • nitrate fertilisers are very soluble in water so get washed off fields by rain and carried into local river bodies
    • liposolubility: a measure of how easily a substance dissolves in fats and oils.
      • organochlorine insecticides, dioxins and PCBs are liposoluble
      • heavy metals are liposoluble,e.g. mercury and lead
    • bioaccumulation: the increase in concentration of a substance in living tissue.
      • organochlorine insecticides, dioxins, PCBs, and heavy metals like lead and mercury
    • biomagnification: the progressive bioaccumulation of a material along a food chain.
      • insecticides like DDT can biomagnify
    • synergism: the process where the presence of two materials produces a greater effect than the sum of their individual effects.
      • nitrogen oxides, sulfur dioxide, zinc and cadmium are synergistic
    • mutagenicity: a mutagen is a material that can cause changes in DNA structure.
      • ionising radiation, asbestos, dioxins and PCBs are mutagenic
    • carcinogenicity: a carcinogen is a substance that can cause cancer.
      • asbestos, DDT and cadmium are carcinogenic
    • teratogenicity:a teratogen is a substance that interferes with gene function in a growing embryo so that a non-inherited birth abnormality is produced.
      • the herbicide 2,4,5T is a teratogenic pollutant- it was used in defoliant spray used by the USA in the Vietnam war and to control broad-loaf weeds
      • mercury is teratogenic

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