Environmental geochemistry of lead

The noticeable changes of lead content in the environment are dated as long ago as about 2700-3000 years. These results come from glacier and peat monitoring using deep drilling. 

The common compounds of lead derive from the +2 oxidation state. As a member of the periodic group IV-A, lead also forms tetravalent compounds which are covalent. The most important are the tetraalkylleads, which are used as gasoline additives. The Pb - C bond is very non-polar, and the organolead species tend to be kinetically inert, like organomercurials. 

The speciation of lead(II) in aqueous solution involves several polymeric hydroxo-complexes. Below pH5.5, (aq) predominates. However, with increasing pH, Pb4(OH)g , and PbslOH) form consequently with the following deposition of Pb(OH)2(s). 

Lead occurs in nature as the sulfide, galena, PbS. Lead is more electropositive than mercury, and roasting the sulfide in air forms lead oxide, reaction (7) 

The oxide is then reduced to a metal with coke. The impure metal is refined by electrolysis. 

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The greatest contribution to our knowledge of the environmental geochemistry of lead was made by Professor C.C. Patterson and his associates at the California Institute of Technology. An entire issue of Geochimica et Cosmochimica Acta (vol. 58, No. 15, 1994) was devoted to Professor Patterson upon his retirement. The effect of environmental lead on public health was also considered in a major work on medical geochemistry edited by Selmus et al. (2005). 

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