Inorganic lead

The recent report by Chamberlain and co-workers provides one of the most comprehensive investigations of the intake, uptake and metabolism of lead, presenting both new data and a review of the literature [10]. In their studies 

The lead that remains in the bloodstream is lost steadily with a short-term half-life of ca. 20 days (adult males, normal blood lead concentration). The half-life for excretion of the lead from the body is, however, somewhat longer at ca. 28 days [10]. This latter figure is consistent with the half-life of lead in the bloodstream found in the long-term studies of Rabinowitz [8], which suggests that some of the lead initially lost to storage re-enters the bloodstream before being excreted. 

There is now considerable evidence to show that the half-life for excretion of lead from the body is not constant, but is a function of the blood lead concentration (henceforth, blood lead concentration will be called simply blood lead or PbB). As the blood lead increases, so the half-life of lead in the body decreases. There is thus a certain natural protective mechanism against exposure to increased amounts of lead. The evidence for this takes the form of an increased rate of urinary excretion of lead, the major pathway for removal of absorbed lead, per unit of blood lead, as PbB increases. This observation is also consistent with the numerous epidemiological studies which approximate the relationship of blood lead levels to exposure by a log-linear or log-log plot of a slope 1, i.e. one in which the incremental increase in blood lead per unit of intake decreases as the intake increases. It may also be that the fractional uptake of lead into the bloodstream decreases as the body is exposed to higher concentrations. 

The uptake and metabolism of lead is summarized in Fig. 7.7. This model represents a synthesis of the information presented by Chamberlain et al [10] and Rabinowitz et al [8, 15]. It must, nevertheless, remain somewhat speculative at the present time, although it is numerically self-consistent. Furthermore, it represents typical conditions, at least in so far as one can typify 

The metabolism of tetraalkyllead is different from that of inorganic lead. Initial entry is still into the bloodstream but the lead is more evenly distributed between blood plasma and red blood cells. Tetraalkyllead, in contrast to inorganic lead, is lost rapidly from the bloodstream, although after 5 to 10 h some of the lead re-appears, associated this time almost exclusively with the red blood cells [14]. The lead is now probably present as trialkyllead, with some possibly having been converted to inorganic lead. 

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In general, the chemistry of inorganic lead compounds is similar to that of the alkaline-earth elements. Thus the carbonate, nitrate, and sulfate of lead are isomorphous with the corresponding compounds of calcium, barium, and strontium. In addition, many inorganic lead compounds possess two or more crystalline forms having different properties. For example, the oxides and the sulfide of bivalent lead are frequendy colored as a result of their state of crystallisation. Pure, tetragonal a-PbO is red pure, orthorhombic P PbO is yeUow and crystals of lead sulfide, PbS, have a black, metallic luster. 

The alimentary symptoms may be overshadowed by neuromuscular dysfunction, accompanied by signs of motor weakness that may progress to paralysis of the exterior muscles or the wrist (wrist drop), and less often, of the ankles (foot drop). Encephalopathy, the most serious result of lead poisoning, frequendy occurs in children as a result of pica, ie, ingestion of inorganic lead compounds in paint chips this rarely occurs in adults. Nephropathy has also been associated with chronic lead poisoning (147). The toxic effects of lead may be most pronounced on the developing fetus. Consequendy, women must be particulady cautious of lead exposure (148). The U.S. Center for Disease Control recommends a blood level of less than 10 p.m per 100 mL for children. 

OSHA regulations (149) limit exposure to inorganic lead compounds of an employee without a respirator to 50 air as a time-weighted... 

This combustion process results in the reduction of inorganics, leading to a molten smelt of sodium carbonate (Na2C03) and sodium sulfide (NajS) on the furnace floor, which is discharged to a tank and dissolved to form green liquor. 

Separation and detection methods Very interesting hyphenated techniques have been developed for the separation and measurement of organic and inorganic lead spe-... 

Byrne RH (1981) Inorganic lead complexation in natural seawater determined by UV spectroscopy. Nature 290 487-489... 

Deaths associated with occupational exposure to inorganic lead (which is predominantly by the inhalation route of exposure) are discussed in Section 2.2.1.1. No studies were located regarding death in animals after inhalation exposure to inorganic lead. 

No increase in kidney weight was noted in mice continuously exposed to 1.6 mg lead/m3 as lead nitrate for 28 days (Hillam and Ozkan 1986). No other studies were located regarding renal effects in animals after inhalation exposure to inorganic lead. These results are presented in Table 2-2 and plotted in Figure 2-1. 

No studies were located regarding developmental effects in humans after inhalation exposure to inorganic lead. See Section 2.2.1.6 for a discussion of the developmental effects of lead in humans after multi-route exposure. 

Ocular Effects. No studies were located regarding ocular effects in humans after oral exposure to inorganic lead. 

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