Industrial sources of lead

It has been indicated in earlier chapters that industrial emissions of lead contribute little on a nationwide basis to lead in the air, in comparison with automotive sources. This is largely a result of the very tight control exercised over industrial sources of lead, using techniques which will be described in this chapter. Nevertheless, as shown in Chapter 2, industrially emitted lead may have a considerable local effect upon air quahty, and if ambient air quality standards such as that in the USA (1.5 jUg mT ) are to be met, then considerable improvements in emission control installations will be required. 

Before methods of pollution control can be discussed, it is pertinent to examine the processes from which lead emissions arise. These will be covered in the following sections. It is especially important to consider the nature of the effluent gas streams (e.g. temperature, lead particle size distribution) in order that an appropriate control method may be selected. 

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If you are at risk for soil contamination either because you live near a busy street or industrial source of lead or because you have had lead paint deteriorating on your property or a history of lead arsenate pesticide spraying, you should take precautions, unless and until you have had your soil tested and are told that it is safe. Limit your children s exposure to the soil, and exercise caution regarding any vegetable gardening. 

Industrial sources of lead are typically point sources of emission. Such sources give rise to a narrow plume of pollution, and hence considerable temporal variations in pollutant levels are encountered dependent upon the wind direction. Close to a large lead refinery at Tower Hamlets, London, the mean atmospheric lead concentration measured over a six month period was 3 /xg m, whilst concentrations up to 92 Mg were observed during 3 hourly periods [4]. Far higher mean concentrations were measured in the vicinity of a lead smelter in Silver Valley, Idaho. Annual average results are summarized in Fig. 2.3. The difference between the 1974 and 1975 results arises from a reduction in smelter emissions in the intervening period [8]. 

The results in Table 23 indicate that there is no marked increase in translocation of lead to the aerial parts of the plants up to the two highest levels studied, but at these levels, the plant lead content is markedly enhanced. The latter levels, fortunately, correspond to a degree of soil contamination with this element which is generally unusual, even in urban environments. Such levels in the soil are normally found only in the vicinity of industrial sources of lead contamination such as smelters, or near natural deposits of lead ores. 

Davis, W. E. Emission study of industrial sources of lead air pollutants, 1970. PB— 223 652. NTIS (1973). 

Although the naturally occurring concentration of ozone at the earth s surface is low, the distribution has been altered by the emission of pollutants, primarily by automobiles but also from industrial sources which lead to the formation of ozone. The strategy for controlling ambient ozone concentrations arising from automobile exhaust emissions is based on the control of hydrocarbons, CO, and NO via catalytic converters. As a result, peak ozone levels in Los Angeles, for instance, have decreased from 0.58 ppm in 1970 to 0.33 ppm in 1990, despite a 66% increase in the number of vehicles. 

Certain minerals may be mined and processed for more than one purpose. For instance, bauxite, on the one hand, can be utilized for making bricks or abrasives and, on the other, is used for the production of aluminum. It is often found that many nonmetallic minerals are associated with metalliferous minerals. As an example mention may be made of galena, the main mineral source of lead, which is found very frequently to be associated with fluorite (CaF2) and barytes (BaS04), both of which are important industrial minerals. 

Sources of lead in surface water or sediment include deposits of lead-containing dust from the atmosphere, waste water from industries that handle lead (primarily iron and steel industries and lead producers), urban runoff, and mining piles. 

Of the known aquatic releases of lead, the largest ones are from the steel and iron industries and lead production and processing operations (EPA 1982a). Urban runoff and atmospheric deposition are significant indirect sources of lead found in the aquatic environment. Lead reaching surface waters is sorbed to suspended solids and sediments (EPA 1982a). 

Major sources of lead in Atlantic coast streams included wastes from metal-finishing industries, brass manufacturing, lead alkyl production, primary and secondary lead smelting, coal combustion, and manufacture of lead oxide. 

Natural products have been, and remain, a rich source of leads for the pharmaceutical industry and many marketed drugs are either natural products or are modifications of such substances. Hence, considerable effort is spent in isolating and characterising chemicals from natural sources which can be tested in a variety of biological screens. Often, it is necessary to carry out laborious extraction and purification steps and the advent of directly coupled HPLC-NMR has been explored as an alternative technique for natural product identification. The use of HPLC-NMR, and other hyphenated techniques such as HPLC-MS-MS, for identification of natural products from plant sources has been reviewed by Wolfender and co-workers [40,41],... 

Because of the long-term and widespread use of lead, it is one of the most ubiquitous of the toxic metals. Exposure may be through air, water, or food sources. In the United States the major industrial uses, such as in fuel additives and lead pigments in paints, have been phased out, but other uses, such as in batteries, have not been reduced. Other sources of lead include lead from pipes and glazed ceramic food containers. 

Of the six heavy metals discussed in this chapter, Pb has been studied extensively with respect to the environmental effects. Clair Patterson, the father of environmental Pb studies, in one of his many major publications concerning the global Pb cycle (Patterson and Settle, 1987), noted that during pre-industrial times Pb in the troposphere originated from soil dusts and volcanic gases. In modern times (1950-1980) the proportion of natural Pb in the atmosphere is overwhelmed by the industrial sources of smelter emissions and automobile exhausts. Lead air pollution levels measured near our Nation s roadways decreased 97% between 1976 and 1995 due to the consequence of the Clean Air Act that eliminated leaded gasoline which interfered with the performance of catalytic converters. 

Lead occurs naturally in the environment. However, most of the lead dispersed throughout the environment comes from human activities. Before the use of leaded gasoline was limited, most of the lead released into the US environment came from car exhaust. Since the EPA has limited the use of leaded gasoline, the amount of lead released into the air has decreased. Other sources of lead released into the air include burning fuel, such as coal or oil, industrial processes, and burning solid waste. 

Control and reduction of ambient air pollutants in the United States has met with varying degrees of success. Unleaded gasoline now accounts for 99% of all gasoline sales. This change has virtually eliminated mobile sources as emitters of lead and reduced ambient lead levels by more than 75%. Likewise, stationary point sources of lead emissions, primarily industrial smelters, have dropped by more than 90% over the past three decades, although significant... 

The lead content in the skeleton in occupationally unexposed subjects varies in different geographical areas of the world. It is around a few milligrams in prehistoric subjects, living in a world with no traffic or industries (Ericson etal. 1979), about 10 mg in temporary Scandinavians (Schiitz et al. 1987a), and about 100 mg in subjects from the UK (Barry 1975) and the US (Ericson et al. 1979). In long-term and heavily exposed lead smelter workers, the skeletal lead content may be in the order of 1 g. There is a continuous turn-over of the skeletal bone, and in long-term-exposed subjects, the skeletal pool functions as an endogenous source of lead. 

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