Lead deposition

Note that for certain older engines, small quantities lead deposits from combustion could have a positive effect as a solid lubricant and prevent exhaust valve recession. For these motors which still represented in 1993 from 20 to 30% of the French automotive fleet, the use of unleaded fuel is not possible. 

Bromine is used in the manufacture of many important organic compounds including 1,2-dibromoethane (ethylene dibromide), added to petrol to prevent lead deposition which occurs by decomposition of the anti-knock —lead tetraethyl bromomethane (methyl bromide), a fumigating agent, and several compounds used to reduce flammability of polyester plastics and epoxide resins. Silver(I) bromide is used extensively in the photographic industry... 

The mechanism of poisoning automobile exhaust catalysts has been identified (71). Upon combustion in the cylinder tetraethyllead (TEL) produces lead oxide which would accumulate in the combustion chamber except that ethylene dibromide [106-93-4] or other similar haUde compounds were added to the gasoline along with TEL to form volatile lead haUde compounds. Thus lead deposits in the cylinder and on the spark plugs are minimized. Volatile lead hahdes (bromides or chlorides) would then exit the combustion chamber, and such volatile compounds would diffuse to catalyst surfaces by the same mechanisms as do carbon monoxide compounds. When adsorbed on the precious metal catalyst site, lead haUde renders the catalytic site inactive. 

Blei, n. lead, -abgang, m. lead dross, lead scoria, -ablagerung,/. lead deposit, -acetat, n. lead acetate, -ader, /. lead vein, -anti-monerz, n., -antimonglanz, m. zinkenite. -arbeit, /. lead smelting plumbing, -arse-nat, n. lead arsenate, -arsenglanz, m. sarto-rite. -arsenik, m. lead arsenate lead arsenide, -art, /. kind or variety of lead. 

Analyzing the samples back at Caltech, Patterson, Masayo Murozumi, and Chow demonstrated that polar ice is naturally extremely pure but that snow deposited in modern times on Greenland contained roughly 100 times more lead than did preindustrial snow. Most of the lead deposits dated from the twentieth century. Geochemists later used the unique ratio of lead-206 and lead-207 isotopes in the lead to prove that these deposits originated in the United States. 

Lead may also interact detrimentally with aquatic life. Once lead deposits in soil, it sticks to soil particles and is only displaced by rain water, ending up in water sources where it affects the aquatic life. Some plants accumulate Pb from both contaminated soils and water sources or more specifically water in the rhizosphere. Besides, contaminated soils are liable to remain polluted with lead this will affect soil fertility.3,4 The fact that large changes in the lead content of soil are required to produce changes in the aerial parts of the plants as compared to changes in aerial lead concentration is closely reflected in the leaf lead concentration. Accumulation of Pb in grasses remains a potential hazard to livestock.3... 

Phosphorus Rat Lead retention Low dietary phosphorus enhances both lead retention and lead deposition in bone Barton and Conrad 1981... 

Alga, Fucus distichus distance from lead deposit 1 km 1 DW 10... 

No effect on hepatic ALAD activity renal ALAD decreased with increasing lead deposition in kidney... 

Ghazaly, K.S. 1991. Influences of thiamin on lead intoxication, lead deposition in tissues and lead hematological responses of Tilapia zillii. Comp. Biochem. Physiol. 100C 417-421. 

In order to decrease urban atmospheric lead concentrations, lead deposition, and subsequent children s exposure via hand to mouth activity, urban lead contaminated soils should be remediated or isolated. 

Figure 7. Spatial distribution of lead depositions in Europe in 2002 (Ilyin et al., 2004).

Figure 8. Relative contribution of external anthropogenic sources to lead depositions in European countries in 2002.

Figure 17. Contribution of different regions and countries of the Northern Hemisphere to the total annual lead deposition to Kazakhstan (a) and Kyrgyzstan (b) in 1990 (Ilyin et al., 2004).

Similar equations can be written for Pb and Pb using their appropriate radioactive parents and decay constants. If t = 0 is taken to represent the time of the formation of the Earth s crust, then these three equations describe the trajectory of the isotopic composition of terrestrial lead from that time. If T is the time elapsed since the formation of the Earth, (i.e., the age of the Earth), and tm is the time before present at which the lead minerals were formed, then, using the assumptions of the Holmes Houtermans model given above, the isotopic composition of a common lead deposit formed tm years ago is given as follows ... 

Figure 9.2 Holmes-Houtermans model for the evolution of common lead deposits.

Figure 9.5 Schematic diagrams to illustrate some of the models for the evolution of the lead isotope ratios in lead deposits (a) Holmes-Houtermans, (b) Stacey-Kramers, (c) mixing model.

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