2 Toxicity and Sources of Pb , Cd , Hg , Cr , As , and Radionuclides in the Environment

2.1 Metal Toxicity ..................................................................................................................... 14 2.1.1 Selected Heavy Metals ............................................................................................ 14 2.1.1.1 Lead ......................................................................................................... 14 2.1.1.2 Cadmium .................................................................................................. 16 2.1.1.3 Mercury .................................................................................................... 18 2.1.1.4 Chromium ................................................................................................ 21 2.1.2 Radionuclides ......................................................................................................... 22 2.1.2.1 Uranium ................................................................................................... 22 2.1.2.2 Radon ....................................................................................................... 24 2.1.3 Arsenic Pollution .................................................................................................... 25 2.1.3.1 Arsenic Speciation and Toxicity .............................................................. 25 2.1.3.2 Arsenic-Contaminated Countries ............................................................. 25 2.1.3.3 Clinical Effects ........................................................................................ 26 2.2 Metals in Groundwaters ...................................................................................................... 27 2.2.1 Heavy Metals in Aquifers ....................................................................................... 28 2.2.2 Cases and Remediation ........................................................................................... 33 2.3 Heavy Metal Pollution Sources ........................................................................................... 35 2.3.1 Acid Mine Drainage ................................................................................................ 35 2.3.1.1 Chemistry of Acid Mine Water ................................................................ 35 2.3.1.2 Extent of the Damage .............................................................................. 36 2.3.1.3 Radioactive AMD .................................................................................... 37 2.3.1.4 Treatment of AMD ................................................................................... 38 2.3.2 Metal Finishing and Surface Treatment Operations ............................................... 40 2.3.2.1 A Typical Electroplating Process ............................................................. 43 2.3.2.2 Future Trends in Electroplating ............................................................... 45 2.3.3 Leather Tanning Process ......................................................................................... 45 2.3.3.1 Description of the Chromium Tanning Process ....................................... 46 2.3.3.2 Wastes Generated in the Chromium Tanning Process ............................. 48 2.3.3.3 Effl uent Treatment ................................................................................... 50 2.3.4 Ferrous Metal Industries ......................................................................................... 51 2.3.4.1 Ferrous Metal Processing ........................................................................ 52