Lead biological half-life

Special precautions Store this radioisotope behind 3 mm thick lead shielding. The effective biological half-life in humans is around 140 days. The thyroid gland is the critical organ in terms of dose, and one would be well... 

On the basis of chemical profile, Wood (38) predicted that arsenic, selenium, and tellurium will be methylated in the environment, and lead, cadmium, and zinc will not. Elemental concentration in the aquatic food chain has been reported for As (39), Hg (40), Cd (41), Pb (42), and Cu (43). The biological half-life of methylmercury in fish, for example, is one to two years (44). Pillay et al. (40) implicated heavy coal burning in the mercurial contamination of plankton and fish populations of Lake Erie. Other metals, notably cadmium, have been shown to be incorporated into the grazing grasses surrounding a coal burning source (27). Trace element contamination, therefore, can enter the food chain at various points. Disposal of solid wastes in the form of ash and slag is yet another environmental consideration (45). 

Measurements of activity in blood of seven subjects were continued for 14 d after inhalation and showed that lead was lost from blood with a biological half-life of 18.0 (s.e.) 0.9 d. Because of radioactive decay, it was not possible to continue measurements for a longer period. Rabinowitz et al. (1976) gave oral doses of the stable lead isotope 204Pb to four subjects daily for several months, and used mass spectrometry to measure 204Pb in blood. The decline in 204Pb in blood was found to be exponential over periods of about 100 d from the end of the period of... 

Over periods of years, resorption of lead from storage in bone gives a longer apparent biological half-life to lead in blood. No tracer experiments with lead have continued for a long enough time to evaluate the entry into blood of resorbed lead. On the assumption that the rates of resorption of lead are similar to those found with Sr and other alkaline earth elements, compartmental analysis suggests that resorbed lead may contribute 40% of the input to blood when exposure has lasted for 50 a (Chamberlain, 1985). 

Major factors that influence distribution are the solubility (see Section 3.3) and stability (see Biological half life, Section 8.4.1) of drugs in the biological environment of the blood. Sparingly water soluble compounds may be deposited in the blood vessels, leading to restriction in blood flow. Drug stability... 

Cumulative absorption of lead over time is a more reliable predictor of adverse effects of lead than a single blood lead measurement. The blood concentration tends to fall markedly within weeks of removal from exposure. The biologic half-life of lead in blood... 

The bioavailability of molecules exclusively screened through in vitro assays can be low. Because of the polarity of the functional groups present in the molecule, they may be poorly absorbed or incorrectly distributed. They may also, as a result of their vulnerability, be the subject of early metabolic destructions, such as first-pass effects or any other kind of degradation leading to a short biological half-life. For such molecules, in vivo administration is limited to the parenteral route, and their clinical usefulness is thus restricted. Sometimes an adequate pharmaceutical formulation (micro-encapsulation, sustained-release or entero-soluble preparations) can overcome these drawbacks, but often the galenic formulation is inoperant, and a chemical... 

Since lead in bone has a biologic half-life measmed in decades, compared to a biologic half-life of lead in blood of only 2-4 weeks [72], the bone more closely reflects cumulative body lead stores. Chelatable lead correlates well with bone lead [4, 31]. The decrease in bone lead stores can be monitored by in vivo tibial K x-... 

Some 20% is assumed to enter the blood compartment. The ICRP biokinetic model for radium has the same general structure as that for strontium and uranium (see Figure 26.2-2). Bone is the critical organ with a biological half-life for radium in the range of 20 years. Since the decay of radium leads to the noble gas radon with a physical half-life of 3.8 days, most of the radioactivity of the decay product escapes from the body before further decays occur. 

BIOLOGICAL PROPERTIES the biological half-life for lead in the bones of humans is 10 yrs can be detected in water by atomic adsorption or by colorimetric analysis or by inductively coupled plasma optical emission spectrometry, dissolved lead by 0.45 micron filtration prior to such analysis... 

Kinetic studies in man show that the lead body burden consists essentially of three compartments (1) a rapid exchange pool in blood and soft tissues (2) an intermediate exchange pool in muscles, skin and bone marrow (3) a slow exchange pool in dense bones and teeth (biological half-life about 20 years). The amount of lead stored in the latter compartment increases throughout life (Steenhout, 1982 Steenhout and Pourtois, 1981). 

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