Retention of lead

Ziegler EE, Edwards BB, Jensen RE et al. 1978. Absorption and retention of lead by infants. Pediatr Res 12 29-34. 

Absorbed lead is distributed in various tissue compartments. Several models of lead pharmacokinetics have been proposed to characterize such parameters as intercompartmental lead exchange rates, retention of lead in various pools, and relative rates of distribution among the tissue groups. See Section 2.3.5 for a discussion of the classical compartmental models and physiologically based pharmacokinetic models (PBPK) developed for lead risk assessments. 

The Leggett Model simulates lead biokinetics in liver with two compartments the first simulates rapid uptake of lead from plasma and a relatively short removal half-life (days) for transfers to plasma and to the small intestine by biliary secretion a second compartment simulates a more gradual transfer to plasma of approximately 10% of lead uptake in liver. Different transfer rates associated with each compartment are calibrated to reproduce patterns of uptake and retention of lead observed in humans, baboons, and beagles following intravenous injection, as well as blood-to-liver concentration ratios from data on chronically exposed humans. Similarly, the Leggett Model simulates lead biokinetics in three compartments of soft tissues, representing rapid, intermediate, and slow turnover rates (without specific physiologic correlates). 

Barton JC, Conrad ME. 1981. Effect of phosphate on the absorption and retention of lead in the rat. 

Morrow PE, Beiter H. Amato F, et al. 1980. Pulmonany retention of lead An experimental study in man. Environ Res 21 373-384. 

In the cladoceran Daphnia magna, about 90% of the total body lead burden is adsorbed to the exoskeleton (Berglind et al. 1985). In animals with a vertebral column, total amounts of lead tend to increase with age. By far the most lead is bound to the skeleton, especially in areas of active bone formation (Barth et al. 1973 Tsuchiya 1979 USEPA 1980 Hejtmancik et al. 1982 Mykkanen etal. 1982 Peter and Strunc 1983 De Michele 1984 Eisler 1984 Berglind etal. 1985 Marcus 1985). The retention of lead stored in bone pools poses a number of difficulties for the usual multicompartmental loss-rate models. Some lead in bones of high medullary content, such as the... 

Lead is toxic to all phyla of aquatic biota, but its toxic action is modified by species and physiological state, and by physical and chemical variables. Wong et al. (1978) stated that only soluble waterborne lead is toxic to aquatic biota, and that free cationic forms are more toxic than complexed forms. The biocidal properties of soluble lead are also modified significantly by water hardness as hardness increases, lead becomes less bioavailable because of precipitation increases (NRCC 1973). In salmonids, for example, the toxicity and fate of lead are influenced by the calcium status of the organism, and this relationship may account for the reduced effects of lead in hard or estuarine waters. In coho salmon (Oncorhynchus kisutch), an increase in waterborne or dietary calcium reduced uptake and retention of lead in skin and skeleton (Varanasi and Gmur 1978). 

Varanasi, U. and D.J. Gmur. 1978. Influence of water-borne and dietary calcium on uptake and retention of lead by coho salmon (Oncorhynchus kisutch). Toxicol. Appl. Pharmacol. 46 65-75. 

As to the effect of the operating parameters on the retention of lead, there exists only a limited amount of information on some of these factors, such as TEL concentration in the fuel, catalyst temperature, and position. 

When varying the temperature of the catalyst, while keeping all other variables constant, it was noticed in laboratory devices (30), burning iso-octane containing TEL, that the retention of lead on monolithic catalysts does increase with temperature (10) in the 350°-760°C range. In burner experiments with monolithic base metal catalysts (21) lead retention doubled when the temperature was increased from 600° to 850°C. In dynamometer studies of pelleted catalysts, again, a temperature increase from 550° to 750°C caused a sevenfold increase in lead retention (23). 

Since the retention of lead is primarily determined by the thermodynamic stability of the lead deposits, the influence of the temperature may vary with the composition of the lead deposits, which in turn, depends on the fuel and catalyst composition. We shall briefly discuss how such reasoning pertains to lead retention. 

Morrow, P.E., Beiter, H., Amato, F. Gibb, F.R. (1980) Pulmonary retention of lead an experimental study in man. Environmental Research, 21, 373-84. 

Potter, H.A.B. and Yong, R.N., Influence of iron/aluminium ratio on the retention of lead and copper by amorphous iron-aluminium oxides, Appl. Clay Sci., 14, 1, 1999. 

Stockl NK. 1989. [Experimental investigations of the retention of lead and other trace elements (Ee, Cu, Zn, Mn) in juvenile and adult rats exposed to different levels of alimentary lead.] Munich, Germany ... 

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