Lead and Behavior in the Environment

Lead (Z = 82, atomic weight 207.19) is dull gray, soft, and weak but dense (11.35 g cm ). With the electronic configuration (Xe) 4f 5d °6s 6p, Pb exhibits three formal oxidation states (IV), (II), and (0). At Earth surface conditions, Pb(II) is by far the most common oxidation state (Fig. 1). 

Lead readily loses two electrons, yielding Pb , which hydrolyzes above pH 7. While Pb is the dominant inorganic species throughout the pH and Eh range of most natural waters (Fig. 1), sulfate, carbonate, chloride, and phosphate complexes of Pb can also be important, depending on the concentrations of these species and the pH of the solution [24]. Lead carbonate is an effective control on the solubility of Pb in oxic soils and sediments above pH values of 6 (Fig. 1). In 

Typical Pb concentrations in rocks, sods, sediments, and fossil fuels (p-g/g) are basalt, 3 granite, 24 sandstone, 10 limestone, 6 shale, 23 soil, 35 coal 10 sediment, 19. Manganese nodules may contain several hundred p-g/g Pb. In the Earth s crust, the average Pb concentration is estimated to be 15 p-g/g, with 17 pg/g in the upper continental crust, and 13 pg/g in the lower continental crust [26]. Lead is one of the most abundant of the heavy trace elements, for three reasons [27]. First, the cosmic abundance of Pb is relatively high. Second, in addition to common Pb ( Pb), which is non-radiogenic, Pb is derived from the radioactive decay of and Th. In fact, roughly one-half of the ° Pb, 

Pb as a chalcophile element because of its occurrence in galena (PbS), the lithophile character of Pb should not be overlooked. Micas and potassium feldspar, on average, contain 25-30 ag/g- The abundance of Pb in silicates has been summarized by Wedepohl [30]. 

In cases which require extreme accuracy and precision, isotope dilution mass spectrometry (ID-MS) may be used to measure Pb concentrations. This consists of an addition to the sample of a solution of well-known Pb concentration and isotopic composition ( spike ) followed by determination of the isotopic composition of the spiked sample using mass spectrometry, Q-ICP-MS, ICP-SMS, multi-collector ICP-MS (MC-ICP-MS), or thermal ionization mass spectrometry (TIMS). 

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