Organic lead

In Britain almost all of the tetraaUcyllead petrol additive is used in the form of tetramethyUead or tetraethyllead with little usage of the mixed alkyl compounds, whilst in the US rather more of the mixed alkyls are in use. Tetra-methyllead is more thermally stable, and generally less chemically reactive than tetraethyllead and European observations indicate that the former compound predominates in the atmosphere [17]. 

Both homogeneous and heterogeneous mechanisms for the removal of tetra-alkyllead compounds from the atmosphere have been investigated [19]. Heterogeneous processes involve adsorption upon particles, with possible subsequent decomposition. These were found to be rather slow. 

Homogeneous gas phase reactions with the reactive hydroxyl species (OH), triplet atomic oxygen (O P) and ozone (O3) together with photol)d ic decomposition were found to be the most important breakdown mechanisms. These are typical reactions of hydrocarbon compounds in the atmosphere. The rates of the various removal processes are highly dependent upon environmental variables such as the intensity of sunlight and the concentrations of other pollutants which act as sources or sinks of the above reactive species. A summary of the breakdown rate predictions appears in Table 2.10. 

Decay path Concentration of reactive species Decay rate (% h ) TML TEL  

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Refining alone can not, economically, provide a fuel to meet specifications the role of organic lead derivatives has long been to make up the difference between the octane number of the clear fuel and the octane required by legislation. 

In addition to their antiknock properties, organic lead compounds possess bactericidal properties and motor fuels with lead are known to inhibit bacterial growth during storage in contact with water. With the disappearance of lead-based compounds, it is necessary to incorporate biocides from the cyclic imine family, (piperidine, pyrrolidine, hexamethyleneimine), alkylpropylene diamines or imidazolines (Figure 9.2). 

It is well known that the luek as well as exeess of ehemieal elements in human organism leads to serious problems in health disorder. The knowledge eoneerning an elemental status of the human organism is very informative from the point of the right medieine diagnose. Therefore a lot of doetors use this information in their praetiee. 

The most common method used to monitor inorganic Pb is the determination of Pb in whole blood by GF-AAS. Exposure to organic lead (i.e. tetraethyl lead) can be monitored by the determination of Pb in mine by GF-AAS (Christensen and Kristiansen 1994). Early effects of exposure to Pb on the heme synthesis can be monitored by determination of the inhibition of the enayme 8-aminolevulinic acid dehydratase in whole blood or 8-aminolevulinic acid in urine by spectrophotometry. 

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Lead is a naturally occurring bluish-gray metal found in small amounts in the earth s crust. It has no characteristic taste or smell. Metallic lead does not dissolve in water and does not bum. Lead can combine with other chemicals to form what are usually known as lead compounds or lead salts. Some lead salts dissolve in water better than others. Some natural and manufactured substances contain lead but do not look like lead in its metallic form. Some of these substances can bum—for example, organic lead compounds in some gasolines. 

Organic Lead. Following a single exposure to vapors of tetraalkyl lead compounds (approximately 1 mg/m3 breathed through a mouthpiece, 10-40 breaths of approximately 1 L volume) in four male subjects, 37% and 51% of inhaled tetraethyl and tetramethyl lead, respectively, were initially found in the respiratory tract, but a considerable percentage of these volatile compounds was lost through exhalation (Heard et al. 1979). Approximately 60-80% of the deposited tetraalkyl lead was absorbed by the lungs. 

Organic Lead. Alkyl lead compounds are actively metabolized in the liver by oxidative dealkylation catalyzed by cytochrome P-450. 

Organic Lead. Urinary lead levels were elevated for 4 days in a man accidentally exposed to an unknown quantity of tetramethyl lead (Gething 1975). Exhalation of the tetraalkyl lead compounds following inhalation exposure is a major route of elimination in humans. At 48 hours postexposure, 40% and 20% of the initially inhaled tetramethyl and tetraethyl lead doses, respectively, were exhaled with low urinary excretion (Heard et al. 1979). 

Berg S, Jonsson A. 1984. Analysis of airborne organic lead. In Grandjean P, ed. Biological effects of organolead compounds. Boca Raton, FL CRC Press, 33-42. 

Booze RM, Mactutus CF. 1990. Developmental exposure to organic lead causes permanent hippocampal damage in Fischer-344 rats. Experientia 46 292-297. 

DeJonghe WRA, Adams FC. 1986. Biogeochemical cycling of organic lead compounds. Adv Environ Sci Technol 17 561-594. 

Nielsen T, Jensen KA, Grandjean P. 1978. Organic lead in normal human brains. Nature 274 602-603. 

D 2547 24 0.05-1.1 g Pb/L Mineralization of organic lead, precipitation of PbCr04, redissolution in HCl/NaCl solution, addition of KI and iodometric titration of liberated I2. 

The vast majority of measurements of organolead compounds in the environment do not constitute evidence for biomethylation of lead. Most environmental organic lead comes from incomplete combustion or spillage of methyl- or ethyl-lead gasoline additives (viz tetraalkylleads or TALs). A literature search will produce several hundred TAL or ionic alkyllead results, but few of them are evidence for methylation in or by the environment. 

Organolead compounds have been handled quite safely in industry for many years. As in the case of inorganic lead, control measures are well defined, and if they are properly applied, neither inorganic nor organic lead intoxication should develop. 

Organic lead compounds were more toxic than inorganic forms... 

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