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Lead

 

Lead: From Water Technology Magazine Volume 31, Issue 8 - August 2008



Chemical symbol: Pb

Atomic number:
82

What it is:
  • Lead is a toxic metallic element that was regularly used in industrial capacities for most of the 20th century.

  • Lead constitutes only 0.00013 percent of the Earth’s crust, but easy mining and refinement keep it from being considered rare.

  • Lead is usually found in these ores/compounds:

    • Lead sulfide (galena): PbS

    • Lead sulfate (anglesite): PbSO4

    • Lead carbonate (cerussite): PbCO3
Where found:
  • Lead rarely occurs naturally in water. Source waters that contain lead have usually been affected by industrial, smelting or mining wastes.

  • Lead can enter water by leaching from pipes by way of corrosion, a reaction of water with metal caused by low pH, low mineral content in water, and dissolved O2.

  • Plumbing installed before 1930 is most likely to contain lead.

  • Lead can also leach from copper and brass.
Health effects:
The risk of lead poisoning is highest in children and pregnant women. Children absorb 30-75 percent of the lead they ingest; adults absorb only 11 percent. Effects of lead poisoning include:
  • Damage to the brain, kidneys and red blood cells

  • Coma and convulsions

  • High blood pressure

  • Slowed physical growth, hearing problems and reduced intelligence in children.

Regulation:
  • US Environmental Protection Agency (EPA) maximum contaminant level (MCL) in drinking water for lead is 15 parts per billion.

  • US EPA MCL goal: zero

  • Amendments to the Safe Drinking Water Act in 1986 set the maximum allowable lead limit at 0.2 percent for solder and flux and at 8.0 percent for pipes.
Water treatment:
  • Removal of lead source

  • Corrosion control methods in pipes, including: pH and alkalinity adjustment; calcium adjustment; silica or phosphate-based corrosion inhibition

  • Ion exchange softeners operated at no more than 2.0 to 3.0 gallons per minute flow rate per cubic foot

  • Reverse osmosis removes 90-95 percent of the soluble lead impurities and also acts as a barrier to lead.


Sources: Water Quality Association, US EPA, NYS Department of Health, American Water Works Association, Minnesota Department of Health, industry sources.