Poisoning, by lead

In the treatment of poisoning by lead or other metal ions, higher concentrations of chelant can be safely obtained in humans by administering Na2CaEDTA rather than Na EDTA. The metal ion is bound by displacing small amounts of Ca " that the body can tolerate. Use of Na EDTA would result in calcium chelation and thus serious depletion of calcium in the body fluids (44). Removal of iron in Cooley s anemia is accompHshed by using chelants that are relatively specific for iron (45). 

Lead compounds were not found on the surrounding activated coating layer, rather only associated with the precious metal. The Pt sites are less poisoned by lead than are Pd or Rh sites because the Pt sites are protected by the sulfur in the fuel. Fuel sulfur is converted to SO2 in the combustion process, and Pt easily oxidizes SO2 to SO on the catalyst site. The SO reacts with the lead compounds to form PbSO, which then moves off the catalyst site so that lead sulfate is not a severe catalyst poison. Neither Pd nor Rh is as active for the SO2 to SO reaction, and therefore do not enjoy the same protection as Pt. 

Vehicle data represents the complex interaction of many variables, including vehicle performance, reactor design and location, as well as catalyst properties. For a catalyst that has failed, one must ponder whether the converter design used in the vehicle is suitable for the catalyst, the quantity of the catalyst used is correct, the distance of the converter from the exhaust manifold is suitable, the catalyst has been inadvertantly overheated to above 2000°F or poisoned by lead and sulfur, or whether the catalyst can be modified to produce a far superior product. 

Three-way automotive catalysts based on palladium, rather than the more expensive metals platinum and rhodium, have long been desired. However, Pd is more sensitive than R to poisoning by lead (Pb) compounds [1-4], Consequently, widespread commercial use of Pd-based automotive three-way catalysts (TWC) was delayed in the U.S. until the early 1990s, by which time residual Pb concentrations in unleaded gasoline had decreased to negligible levels. The past five years have witnessed... 

Kendall, R.J. and P.F. Scanlon. 1983. Histologic and ultrastructural lesions of mourning doves (Zenaida macroura) poisoned by lead shot. Poult. Sci. 62 952-956. 

If we were to judge of the interest excited by any medical subject by the number of writings to which it has given birth, we could not but regard the poisoning by lead as the most important to be known of all those that have been treated of, up to the present time. 

CO is more pronounced which is exactly opposite to the poisoning by lead. Also opposite to the lead poisoning behavior is the observation, by the same workers, that phosphorus poisoning affects Pt more strongly than Pd. 

In another of the many interactions between problems and their solutions, catalysts in catalytic converters are poisoned by lead. For this reason, cars with catalytic converters are required to use only unleaded gasoline. One negative side effect of the use of catalytic converters is an increase in N2O emission. The converters reduce NO and NO2 to N2O, which has less immediate effects but has a greenhouse effect (described later in this chapter). 

Lead poisoning in horses is characterized by neurological effects. Affected horses will be either depressed or excited. Colic and diarrhea are also seen. Because of laryngeal nerve paralysis, horses poisoned by lead also present with difficult respirations and a roaring syndrome. Abortions may also occur. 

Thermal aging, S02 poisoning, and reaction of the active phase with the support are factors that are known to be important in the deactivation of solid catalysts. Noble metals are usually poisoned by lead, whereas base metal oxide catalysts are more susceptible to poisoning by sulfur (88,286-289). Indeed, the deactivation of oxides when used in oxidation or reduction processes and particularly as catalysts for exhaust gas purification has been attributed to a large extent to S02 (14,174,290). In this section, some aspects of the S02 poisoning effect and the nature of the interactions of S02 with perovskite oxides are reviewed. 

The experience of automotive catalysis indicates that Rh is only somewhat less susceptible to poisoning by lead traces than Pd while Pt is by far the most resistant. 

Platinum Catalysts for Exhaust Emission Control The Mechanism of Catalyst Poisoning by Lead and Phosphorus Compounds... 

Figure 11. Catalyst poisoning by lead as a function of catalyst bed temperature...

The Mechanisms of Poisoning. The curves in Figure 8 depict typical deactivation characteristics of oxidation catalysts poisoned by lead and... 

The ability of catalysts to recover after poisoning by lead has been noted (9, 11). The platinum catalyst recovered part of its activity when lead was removed from the fuel (see Figure 11). Furthermore, the regen-... 

Actions and Uses.—Internally —In excessive doses, irritant poison in medicinal doses, astringent in diarrhoea, dysentery, and obstinate diabetes as an antidote to poisoning by lead, and to arrest the secretion of milk in cows. Eccternally —Astringent to open joints and wounded thec as a collyrium in chronic conjunctivitis also styptic. 

Actions and Uses.—Cathartic, diuretic, and febrifuge. Chiefly employed, combined with ginger, as a purgative for cattle and sheep. Used also as a febrifuge for the horse, and as an antidote to poisoning by lead. 

B. Symptomatic poisoning by lead (without encephalopathy). Oral unithiol, 4-8 mg/kg orally every 6-8 hours, may be considered an alternative to suc-cimer (see p 501). Note Parenteral therapy with EDTA (see p 440) is preferable for treatment of severe lead intoxication (lead encephalopathy or lead colic), or for patients with extremely high blood lead concentrations (eg, blood lead >150 mcg/dL). 

Since 1975 catalysts have been fitted to vehicles in the USA to control emissions, initially of HC and CO (oxidation catalysts), and latterly also of NOx (three way catalysts). The mode of operation of these catalyst systems in the USA and Japan is now well characterised (1). The catalysts typically comprise the precious metals platinum, palladium and rhodium, either singly or in combination, together with base metal promoters or stabilisers, supported on alumina pellets or alumina coated ceramic monoliths. Catalysts for the US market are designed to withstand 50,000 miles of road use and must be operated in conjunction with lead free fuel since they are poisoned by lead. 

---