Heavy metals

• Lead - Sources, exposure and effects

  Industrial workers may inhale lead dust.

  Acute exposure to large doses can cause brain damage

  Only likely in accidents ( they can wear facemasks or use water sprays)
• Control of Lead

  • WATER: PIPES: Traces of lead dissolve in the water causing chronic exposure. Most replaced with Copper. phosphoric acid is added to water in high risk areas producing insoluble lead phosphate in pipes.
  • PAINT: added to accelerate drying & increase durability. A risk when old & flaking, especially to children. Removal can be a hazard as vapours produced are inhaled. Use has been phased-out in most countries.
• Mercury - Sources, exposure and effects

  Disposal of batteries, fluorescent lights and thermometers

  SEVERITY DEPENDS ON CHEMICAL FORM:

  • Liquid - not easily absorbed by skin/gut. Lungs absorb vapours if inhaled
  • Inorganic compounds - moderately absorbed by gut
  • Organic compounds - absorbed by skin, gut. Liposoluble so passes through cell membrane entering the brain.
• Control of Mercury

  • mercury thermometers replaced by alcohol/electronic.
  • removed from effluents by osmosis/ activated carbon filters.
  • disposal at high pH (less soluble).
• Cadmium - Sources, exposure and effects

  • disposal of old nickel-cadmium batteries.
  • incineration of waste with cadmium pigments (eg: plastics).
  • drainage water from Cd & zinc mines (often found together).

  LIPOSOLUBLE-- bioaccumulates & magnifies. Causes:

  • brain damage & paralysis.
  • lung cancer.
  • skeletal collapse caused by bone decalcification.
• Control of Cadmium

  Uses were banned (in pigments). Cd waste is disposed in hazardous waste landfills or recycled