Lead from Air

The ban on the use of leaded gasoline in the 1970s produced one of the most successful episodes in the search for the control of air pollutants. As already noted, the concentration of lead in the air dropped dramatically and to very low levels within a matter of years after the ban was put into place. Currently, efforts to control lead emissions focus on improving the methods used to remove lead from air and water wastes of smelters, metal processing plants, and other such plants. The most common systems currently used are variations of traditional waste control techniques in which physical devices (such as baghouses) or chemical systems (such as precipitation reactions) are used to extract particles of lead from wastes. 

The above calculations estimate that for a typical adult in a developed country, daily uptake of lead from air, diet, and drinking water is, respectively 1.4 pg, 6 pg, and 1.1 pg. Exposure to lead from all of these sources has fallen rapidly over the past 20-30 years. Figure 12 contrasts the temporal trends in use of lead in petrol (gasoline) and blood leads in the general population of the UK over the period when much of this decline took place. It is interesting to note that from 1971 to 1985 use of lead in petrol was relatively steady, but blood leads declined by a factor of more than two over this period mainly as a response to reductions in dietary exposure, particularly associated with the cessation of use of... 

Inhalation and ingestion (of water, food, paint, soil and/or dust) are the primary routes of human exposure to lead (OECD, 1993). Percutaneous absorption is minimal in humans. The absorption of lead from air to blood involves two processes the deposition of airborne particles in the respiratory tract and the absorption and clearance from the respiratory tract into the circulation. The respiratory deposition of airborne lead is in the range of 30-50% and varies with particle size, chemical speciation, solubility in body fluids and ventilation rate. Higher deposition rates may occur with larger particles, but this deposition takes place in the upper respiratory tract. The smaller particles of inhaled lead (generated by automobile exhaust) are almost (>90%) completely absorbed after deposition in the lower respiratory tract (WHO, 1995). 

Predominant pathways for lead from air to humans are soil, plants, as deposited dusts, and direct exposures of humans through inhalation. 

This is for the typieal PC board-mounted applieation where only the PC board traees are used to eonduet the heat away from the diode. The typieal value range of the lead-to-air thermal resistanee is between 30 to 40°CAV and is a variable whieh is dependent on the lead length. 

Concentric reducers should not be used to reduce suction piping diameter to that of the pump s inlet flange. This type of reducer may create an air pocket in the top of the piping and could lead to loss of pump performance resulting from air entrainment. Eccentric reducers should be installed with the straight side on top. This will reduce the potential for air pocket in the piping or the introduction of air or gas into the pump. 

Focuses on pathways leading from emissions to biota, including air, land, water and sediments, aquatic biota, and wildlife... 

In preparation for one trip, Patterson and his colleagues cleaned 500 plastic containers in vats of nitric acid, rinsed them in pure water, filled them with pure argon to displace lead-contaminated air, and sealed them in plastic bags equipped with breath filters. Even then, the containers contributed about 0.05 millionths of a gram of lead to each sample as they were trucked from the factory to Caltech, automobile exhaust had sprayed them with thousands of micrograms of lead. For Patterson s next trip, he collected the containers directly from the factory production line and sealed them immediately into plastic bags before their trip to his laboratory. 

The release of lead to air is now less than the release of lead to land. Most of the lead in inner city soils comes from old houses painted with paint containing lead and previous automotive exhaust emitted when gasoline contained lead. Landfills may contain waste from lead ore mining, ammunition manufacturing, or other industrial activities such as battery production. 

Information available regarding the chemistry of lead in air is limited. Before the ban on sales of leaded gasoline, lead particles were emitted to the atmosphere from automobiles as lead halides (mostly PbBrCl) and as double salts with ammonium halides (e.g., 2PbBrCl NH4Cl. Pb3[P04]2, and PbS04 [Biggins and Harrison 1979 Ter Haar and Bayard 1971]). After 18 hours, approximately 75% of the bromine and 30-40% of the chlorine disappeared, and lead carbonates, oxycarbonates and oxides were produced. 

Biomass sequestration, which has been embraced by coal companies as the least expensive way to start carbon management, relies on capture from air. Cofiring with biomass followed by sequestration also would lead to a net C02 reduction in the atmosphere (Keith, 2001). On a per ton basis, this option is quite cost effective, but the amount of land area that would be required is extremely large to be practical. Consequently, it is worthwhile to consider other options. Currently, studies that consider capture of C02 directly from the air by chemical means are under way. These processes will require good chemical sorbents that do not pose any environmental concerns in their own right and can be regenerated cost effectively. 

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