What are heavy metals?
       What are heavy metals?
      Refers to any metallic chemical element that has a 
       Refers to any metallic chemical element that has a 
       relatively high density and is toxic or poisonous at 
       relatively high density and is toxic or poisonous at 
       low concentrations
       low concentrations
      Natural components of the Earth's crust
       Natural components of the Earth's crust
      Cannot be __________ or __________
       Cannot be __________ or __________
      Essentials:  ___________, ________, ________, _______ and 
       Essentials:  ___________, ________, ________, _______ and 
       ______
       ______
      
      
      Others, such as mercury, lead and cadmium have no 
       Others, such as mercury, lead and cadmium have no 
       known biological role (non-essential)
       known biological role (non-essential)
      All of these metals are toxic if present in excess
       All of these metals are toxic if present in excess
                                     
       
                              Sources
                              Sources
      Industrial and occupational
        Industrial and occupational
          Hg in paper production
            Hg in paper production
          Pb in paint and chemical industry
            Pb in paint and chemical industry
      ________________
        ________________
          Hg in fungicides
            Hg in fungicides
      ________________
        ________________
          Pb in pottery glazes and at one time in pipes
            Pb in pottery glazes and at one time in pipes
      ________________
        ________________
          Hg in amalgam fillings (controversial)
            Hg in amalgam fillings (controversial)
      ________________
        ________________
          Burning of leaded petrol (contains tetraethyl lead, an 
            Burning of leaded petrol (contains tetraethyl lead, an 
            organometal)
            organometal)
                                          
        
      Chemical forms of heavy 
      Chemical forms of heavy 
                         metals
                         metals
     ___________ (inorganic)
       ___________ (inorganic)
        e.g. Hg, Pb
         e.g. Hg, Pb
     As ___________ (inorganic)
       As ___________ (inorganic)
        e.g. MgCl , PbSO …so found in different 
         e.g. MgCl , PbSO …so found in different 
                    2       4
                    2       4
         oxidation states
         oxidation states
     As ___________ compounds (organic)
       As ___________ compounds (organic)
        A metal which is bound directly to the carbon of 
         A metal which is bound directly to the carbon of 
         an organic compound
         an organic compound
        e.g. (C H ) Pb - Tetraethyl lead
         e.g. (C H ) Pb - Tetraethyl lead
                2  5 4
                2  5 4
                                  
       
                   Mercury
                   Mercury
       
                                
                             Mercury
                             Mercury
      50-75% of mercury released into 
        50-75% of mercury released into 
        environment related to human activities 
        environment related to human activities 
        Other Organic examples:  dimethylmercury  Hg(CH )
                                                           3 2
           ____________________ is most commonly found organic mercury 
                                          
                          compound in the environment