As noted in Chapter 1, environmental lead can have many sources. It can occur naturally or result from mining or other industrial activities or from the production and use of consumer products that contain lead. This chapter describes the various sources that potentially contribute to lead contamination at or near a Superfund site (see Figure 2-1), and Chapter 3 describes the mechanisms by which environmental dispersal might occur.
Lead is a widespread, naturally occurring element found throughout the Earth’s crust and is commonly enriched in many materials in mining districts. It occurs in virtually all rocks, soils, sediments, and waters at low concentration; however, it can occur at high concentrations over large areas because of natural and human-caused processes. A variety of geologic processes can cause natural lead enrichment, commonly in association with other metal enrichment; in some cases, concentrations of economic interest (ore deposits) are formed. Natural processes that operate at or near the Earth’s surface can concentrate lead further or disperse it into the environment. Such processes could include volcanic emissions, forest fires, and various erosional processes. Similarly, human activity, particularly mining of metallic ores, leads to concentration and dispersion (see Figure 2-1).
In most rocks, lead occurs at low concentrations and behaves geochemically like the alkalis and alkaline earths. As such, it is dispersed in common rock-forming minerals, such as feldspars, amphiboles, micas, and sulfates, where it substitutes for potassium, barium, and similar elements (Sahl et al. 1978). At high concentrations, it forms discrete lead-rich minerals, notably sulfides, carbonates, sulfates, and oxysalts (Sahl et al. 1978). Of the roughly 400 lead-rich minerals known (Back et al. 2008), the most common and essentially the only ore minerals are lead sulfide (galena, PbS), lead carbonate (cerussite, PbCO3), and lead sulfate (anglesite, PbSO4). In this section, the committee briefly discusses the types of lead-bearing mineral deposits, the natural distribution of lead, and mining processes that can lead to dispersal of lead in the environment.
Lead-Bearing Mineral Deposits
Many mineral deposits—rocks that contain materials of potential economic interest—and their surrounding materials contain lead in such concentrations as 0.01 to over 10 wt %, which are well above the typical concentrations (5–80 ppm, and usually less than 20 ppm) in rocks and soils found outside mineralized regions (Faure 1998; Smith and Huyck 1999; Rudnick and Gao 2014). As noted above, human activities have led to environmental dispersal of lead; lead concentrations in post-industrial soils and sediments are about 50–100 ppm (Callender 2005), and concentrations at contaminated sites vary widely—up to thousands of parts per million (Gutierrez et al. 2016).
The decision to recover any particular commodity depends on economics, geology, available technology (extraction methods), and other incentives, not simply on the characteristics of the ores themselves. Thus, anywhere from none to most of the lead might be recovered from mined materials. For example, in Southeast Missouri, lead was the primary product from numerous small operations in the Washington County barite district before the 1920s, at which time production of barite became the focus of mining, and lead from that area became a co-product or a byproduct, or was discarded (Wharton 1972; Mugel 2017). Given the various factors that determine whether a commodity is mined, four categories of mineral deposits might be encountered at a Superfund site, as described below.
- Primary lead deposits in which lead is the primary or sole commodity (primary product) that motivates mining. The classic example is the Southeast Missouri Lead Mining District, where the principal value in most deposits is lead.
- Mineral deposits in which lead is a co-product, and its recovery is an essential part of the economics, but production of other metals is also essential. There are a number of examples, including the midcontinent Tri-State district (Missouri-Kansas-Oklahoma), where lead was co-produced with zinc; Coeur d’Alene, Idaho, where most deposits produced lead and silver; and Leadville, Colorado, where lead was co-produced with silver, gold, and zinc.
- Mineral deposits in which lead is recovered as a byproduct because it is economically profitable to do so but not necessary for profitability. Examples include the vein deposits of the Silverton district, Colorado, which include the Gold King, Sunnyside, and related mines that were produced primarily for gold and silver, but where other metals, including lead, were common byproducts.
- Mineral deposits where lead at lower concentrations (commonly less than 0.5%) is mined with the ore but is not recovered. An example is the Ducktown district, Tennessee, which produced copper and iron sulfide (for sulfuric acid).
Metallic mineral deposits form when geologic processes concentrate metals into small volumes of rock from much larger, relatively dilute sources. As in the case of lead, concentrations in ores are typically a thousand times as great as in the source rocks. Lead-bearing deposits form in many geologic settings with a corresponding diversity in ore types and characteristics. The geologic occurrence and the geochemical nature of lead-bearing ores have fundamental effects on how lead gets into the broader environment, whether through natural dispersion or by mining and related human activities (du Bray 1995; Plumlee 1999). The most important lead-bearing deposits and some of their principal characteristics are summarized below.
- Deposits associated with sedimentary basins. These deposits constitute the most important lead ores globally and include the Mississippi Valley Type (MVT) ores of the middle of North America (Leach et al. 2005, 2010) and the ores of the Southeast Missouri Lead Mining District. The deposits are typically stratabound (confined to favorable layers), and the rocks that host the deposits are commonly rich in carbonate minerals. The low iron sulfide and high carbonate concentrations of these deposits limit acid production during weathering and thus limit lead solubility and mobility in the surface environment.
- Deposits associated with hot waters generated from or circulated by magmatism. These deposits include carbonate replacement, polymetallic veins, and seafloor massive sulfides. They are the most common types of mineral deposits and typically have small to moderate quantities of lead with other base and precious metals (Ridley 2013). They commonly have abundant sulfide minerals, and their host rocks might lack appreciable acid-neutraliz-
ing capacity. Thus, lead can be appreciably mobile under these circumstances.
- Deposits associated with waters circulated during metamorphism. These deposits are mainly vein gold deposits with relatively low lead concentrations (Goldfarb et al. 2005), although the Coeur d’Alene silver–lead deposits of Idaho fit this category (Ramos and Rosenberg 2012). The moderate sulfide and carbonate mineral concentrations result in moderate acid production and acid-neutralizing capacity.
- Residual deposits associated with weathering. Chemical weathering processes can substantially increase the concentration of lead minerals because of removal of other, more soluble components. This situation is common in the weathered zone of many metal deposits and in the clay-rich soils formed on lead-bearing carbonate host rocks, such as in the Washington County barite district, Missouri (Wharton 1972; Kaiser et al. 1987). Acid production is minimal, and neutralization capacity is moderate.
Geologic differences are important because they lead to different environmental consequences, they allow possible fingerprinting of sources, and they influence the choice of mining and processing methods by which lead and other commodities are produced. Among the important ore characteristics are the capacity to produce acid waters when weathered, the content of toxic elements, and the geologic form and hydrologic setting of the deposits (du Bray 1995; Plumlee 1999; Smith and Huyck 1999; Smith 2007). As summarized above, acid production correlates with the abundance of iron sulfide minerals (pyrite, pyrrhotite, and marcasite), whereas acid-neutralizing capacity is highest in carbonate-hosted deposits, such as those of the midcontinent and many igneous-related replacement deposits. Conversely, seafloor massive sulfide deposits and many vein deposits have relatively high sulfide concentrations and host rocks that are poor acid neutralizers, and these characteristics lead to the wide availability of acid and dissolved metals in groundwater and surface waters.
Lead concentrations (and other element concentrations) vary greatly among ore deposit types and within individual deposits or districts (du Bray 1995; Plumlee 1999; Smith and Huyck 1999). Some ore deposits and ore districts have relatively uniform compositions and host rocks (for example, many MVT deposits and districts), but many exhibit strong spatial variation (zoning) in metals, other elements, and the nature of the local host rocks (for example, magmatic-related hydrothermal systems; Ridley 2013). Lead concentrations can span several orders of magnitude, depending on position; for example, ores at Bingham, Utah, ranged from greater than 10% in the carbonate rock-hosted part of the system to less than 0.1% in the igneous rock-hosted copper-rich core. Because the geochemical signatures vary with deposit type and location of a particular ore-forming system, they can be used to aid in the forensic identification of sources.
A particularly useful geochemical variable is the isotopic composition of lead itself (Box 2-1). Extensive study of lead isotopes in ores shows that different deposit types and regions have compositions that reflect the geologic history of the terrain and the processes involved in ore formation (Doe and Zartman 1979). For example, ores of the midcontinent have distinctively high ratios of the radiogenic isotopes of lead (206Pb, 207Pb, and 208Pb) to non-radiogenic, or primordial, lead (204Pb).1 Such differences have the potential to distinguish geologic sources and even individual districts and deposits (Goldhaber et al. 1995; Sangster et al. 2000). Application of isotopic differences is discussed further in Chapter 4, and case studies are provided in Chapter 5.
Over 200 mining districts in the United States have produced appreciable amounts of lead (Long et al. 1998), and many more have accessory lead minerals. However, the principal lead production has come from only a large handful of districts. The most important are the Mississippi Valley ores of Southeast Missouri and the Missouri–Kansas–Oklahoma tristate district; the vein silver–lead ores of the Coeur d’Alene, Idaho; and various igneous-related polymetallic carbonate replacement deposits of Colorado (Leadville) and Utah (Bingham, Park City, and Tintic). Of those districts, Southeast Missouri (Box 2-2; Figure 2-2) has produced more than the others combined (Long et al. 1998) and collectively contains the world’s largest known concentration of lead (Appold and Garven 1999).
Natural Distribution of Lead
When lead deposits form from hydrothermal fluids, the lead concentration rarely terminates abruptly at the edge of an ore body but rather falls off gradually; this is primary dispersion.2 The original geologic dispersion reflects the facts that ore-forming fluids typically invade a considerable volume of rock and that the metal-trapping (precipitating) process is commonly inefficient (Rose et al. 1979). Such primary distributions can be highly focused, around a few meters or less, if the flow of mineralizing fluids was strongly focused (Barnes and Lavery 1977). In other cases, where fluid flow and conditions for precipitation were not localized, tremendous volumes of rock over large areas (tens to thousands of square kilometers) might contain anomalous metals. For example, minor quantities of galena and sphalerite (ZnS) are widely distributed in the
1 Radiogenic indicates an isotope that has been created from radioactive decay.
2 The edge of an ore body is an economic boundary that is influenced by a combination of geologic and technologic factors. In many cases, what might be waste under one set of conditions can become ore under more favorable conditions, or vice versa.
Paleozoic sedimentary rocks of the midcontinent, where they represent the sparse products of the metalliferous fluids that flowed regionally along these sedimentary layers (McLimans et al. 1980; Goldhaber et al. 1995; Leach et al. 2005; Figure 2-2).
Weathering and erosion of primary metal concentrations lead to dispersion at or near the Earth’s surface. Given the relatively low solubility of lead in most surface fluids, chemical weathering concentrates lead in residual materials in gossans (weathered ores) and clay-rich soils (Rose et al. 1979; Smith and Huyck 1999). The residual materials are ultimately eroded (mechanically removed by running water) and contribute to the overall sediment load in rivers and streams. Only in sulfide-rich deposits that have poor neutralizing capacity is lead dispersed mainly in solution. Environmental dispersal of lead through those various processes is discussed in detail in Chapter 3.
Concentration and Dispersal of Lead by Mining
Lead is concentrated to yield a product but also dispersed by mining (Figure 2-1). Mining begins by physically extracting ore; this is followed by processing of the ore to obtain a concentrate of lead minerals and then by smelting to obtain metallic lead, which is ultimately shipped to market. At each stage, materials are discarded. In the extraction process, waste consists of materials that are moved to mine the ore but that lack economic concentrations of metal. Waste rock can vary greatly in mineralogy, composition, and size. Because the distinction between ore and waste is economic, large volumes of waste can have elevated lead concentrations compared with those of ordinary rocks. Indeed, what is waste under one set of conditions or at one time might be ore in other circumstances, and reprocessing for environmental or economic reasons is common in many long-lived mining districts. Historically, waste disposal was driven by what was easiest; thus, waste was generally discarded in the most efficient manner for the time and place, such as on the surface in dumps or replaced in mine openings. However, by the latter part of the 20th century, waste rock disposal was subject to regulatory controls and handled systematically in a mine’s plan of operation.
Processing of lead-bearing ores typically involves physical separation as is the case with all lead minerals. However, some lead-bearing ores might be chemically processed; for example, a cyanidation process is used to treat lead-bearing gold deposits. Tailings are the residua of mineral processing after much of the valuable content has been removed in the form of a concentrate. The efficiency of concentration reflects available technology and economics, and recovery of valuable components can vary from less than 50% to 95%. For example, early and primitive techniques used hand-picking or simple gravitational separation with rockers to upgrade the content of the valuable fraction of the ore; the techniques were inefficient and often resulted in less than 50% recovery, and the balance went into the mine waste or tailings (Mugal 2017). Given the high lead content of ores, tailings typically contain lead concentrations of a few hundred to thousands parts per million, depending on recovery efficiency.
Most mineral processing depends on the characteristic properties of ore minerals that allow separation of the valuable constituents from the unwanted minerals, for example, by using density or distinctive surface properties. Gravity-based methods operate by separating dense ore minerals—such as galena, cerussite, and barite—from a less-dense waste fraction. If the lead-bearing materials are not consolidated, as is the case in residual ores, simple washing and gravity separation might suffice. For example, such methods were widely used in the barite-lead districts of Southeast Missouri, notably in Washington County. In that case, the efficiency of recovery depended on the main product—barite or lead—and, in many cases, a substantial fraction of lead was not recovered and thus discarded in the tailings. See Box 2-3 for additional information on the history of lead mining in Southeast Missouri (Wharton 1972; Mugal 2017).
In hard-rock mining, ores require crushing (milling) to liberate the valuable minerals from the unwanted gangue (waste) minerals. The degree of crushing depends on the nature of the ore, particularly on the grain size of the ore minerals. Except in unusually coarse-grain ores, efficient separation (for example, greater than 90%) commonly requires crushing to fine sand or smaller. How finely to crush the ore is a tradeoff in cost vs recovery. After the ore is milled, the ore minerals are separated from the waste to make an ore concentrate. Gravity separation is still commonly applied, but most sulfides are recovered through selective froth flotation. In froth flotation, hydrophobic surfactants specific to particular minerals are added to a slurry of the crushed ore. When air is bubbled through the slurry, the surface-coated minerals attach to the air bubbles and float to the surface. The metal-laden froth is continuously removed and dried to leave a high-grade mineral concentrate. The concentrate is the feedstock for the final steps in metal production.
Tailing characteristics—such as mineralogy, grain size, and chemical composition—reflect differences in processing, economics, and the broad social and regulatory environment. Over time, tailings disposal has seen an increasing focus on engineered impoundments. In recent decades, designed and built impoundments control not only the bulk tailings themselves but their potential water and dust effects. Early mining operations paid little or no attention to disposal methods; often, there was no effort at impoundment, and some tailings were discarded directly into streams. With time, tailings were typically discarded in designated areas, but often the areas were not designed
to control slope failure, other types of erosion, wind effects, and water discharges.
The final steps in the recovery of lead are broadly termed smelting; they reflect conversion of the ore concentrate into metal and various waste products, including slag, gases, and dust (Vignes 2013). Smelter feed can include both primary sources (concentrates) and secondary sources (from recycling). As smelters became larger industrial operations through the 20th century, their feedstock evolved from local sources (one or more nearby mines) to a mix of sources.
Depending on the nature of the feed (recycled metals or ore concentrate), the smelting process begins with pretreatment that might include mechanical separation (secondary sources) or drying, calcining, or roasting (primary sources). The materials are then smelted and converted to metal by reduction from the sulfide or oxide form. The molten waste product (slag) contains iron, silica, calcium, some residual metal, and other minor components. Sulfide smelting involves passage of gases that carry off the sulfur, mainly as sulfur dioxide. The emitted gases also contain appreciable amounts of particulate matter in the form of melts or solids. As with mine waste and tailings, early smelting operations were typically inefficient and operated with no emission controls. Gases, slag, and dust were discharged directly into the environment. In more recent times, particularly with the passage of the Clean Air Act and resulting regulation, smelter emissions have been greatly reduced by treatment of sulfur-bearing gases and by control of dust and other particles. Slag is typically disposed of in heaps, where it is poured, cools, and solidifies. Ultimately, the metals produced by smelting might be further processed in a refinery to recover precious metals (notably silver in the case of lead) or to remove impurities that are not wanted in the final salable product. Like the earlier stages, solid and liquid refinery wastes have had a checkered history of disposal and might still contain appreciable metals. After smelting and mining, lead is distributed to other regions where it is converted into manufactured or chemical products, providing other opportunities for lead dispersion in areas that are typically well outside mining areas.
There are possible sources of environmental lead in addition to natural sources and those associated with mining (Figure 2-1). Indeed, the 2014 National Emissions Inventory estimated that less than 1% of atmospheric lead emissions in the United States was the result of mining activities (Table 2-1). Mining-related emissions of lead in Missouri accounted for one-third of the national mining-related emissions but only 10% of the total lead emissions in the state. This section briefly discusses other sources of lead that could contribute to environmental contamination.
|Sector or Source||US Lead Emissions (tons/yr)||Sector or Source Fraction (%)|
|Energy, all sources||88.9||12.2|
|All other sources or sectors||17.0||2.3|
a Data compiled from the 2014 National Emission Inventory.
b Mining refers to mineral-extraction activities.
c Metals refers to smelting, refining, and other metal-processing activities.
Source: EPA (2017).
Gasoline and Other Fuels
In the United States, lead has been added to gasoline and other fuels since 1929 to prevent engine knocking. Mielke (1999) estimated the total consumption of lead in gasoline in the United States from 1929 to 1986 as 5.9 × 106 metric tons. The use of alkyl–lead additives in automobile fuels has been nearly eliminated since US Environmental Protection Agency (EPA) promulgated guidelines in the 1970s that mandated that new cars run on unleaded gasoline. The sale of leaded automobile fuels was discontinued in 1986, although a small amount of alkyl–lead continues to be used in racing sports and by owners of classic cars. The sharp decline in lead consumption in gasoline (Figure 2-3) resulted in a 98% decrease in total national lead emissions from 1970 to 1995 (EPA 2013).
Alkyl–lead additives are still used in aviation fuel, specifically for small piston-engine aircraft. Although emissions that result from the operation of those airplanes was a tiny fraction of total atmospheric lead emissions in most of the 20th century, they accounted for more than half the national lead emissions by 2008 (Rao et al. 2013) and for nearly two-thirds in 2014 (Table 2-1). Aircraft-related lead emissions are highly variable; areas near airports experience the highest loadings.
Although automobile-related lead emissions are now near zero, the legacy lead that remains in soils and sediments is a potentially important lead source at or near Superfund sites. Smith (1976) found that lead concentrations in the top 5 cm of roadside soils were up to 30 times the concentrations in soils away from the roadside. Emissions of gasoline lead, however, were widely dispersed around the country and resulted in deposition and accumulation of lead in soils and surface waters even in remote areas. Johnson et al. (1995) estimated that the total lead deposition in precipitation at the Hubbard Brook Experimental Forest in New Hampshire in 1926–1989 was 8.66 kg/ha. Because Hubbard Brook is remote from point sources of lead pollution, the lead deposition was interpreted as an estimate of gasoline-lead input into the forest. Lead is readily adsorbed in soil organic matter and clay particles (see Chapter 3), so nearly all the lead remains in the soil and makes up a large fraction (about 10%) of total lead in the soil (Johnson et al. 2004). At Hubbard Brook, the mass of the O soil horizon (surface soil layer), where most of the atmospherically deposited lead is stored, is 8.7 kg/m2 (Johnson et al. 1991); thus, gasoline lead might account for up to 100 ppm of the total lead in the O soil horizon. Furthermore, the 1926–1989 atmospheric lead input was similar in magnitude to that of total lead released from soil minerals by chemical weathering in the 12,000–14,000 years since the last glacial retreat. The burden of gasoline-derived lead in soil can thus be quantitatively important in studies aimed at lead-source apportionment.
The use of lead in paints in the United States dates back to the colonial era. White lead provided a consistent base color for interior and exterior paints and made the paint more durable and easy to wash (Browne 1930; Hallett and Rose 1935). Widespread use of lead in US paint manufacturing began in 1884 and peaked in the 1920s,
but lead-based paints continued to be widely used, especially on exterior surfaces, into the 1970s (Figure 2-3). Baltimore, Maryland, passed the first municipal law that banned the use of interior lead paints in 1951. In 1978, the federal government banned the sale of all lead-based paints. The total consumption of lead by the US paint industry was similar in magnitude to that used in gasoline additives for automobile fuels (Mielke 1999). Therefore, as with gasoline, old paint could represent a quantitatively important source of lead in some soils.
Because of the durability of lead paints and the tendency to paint over, rather than remove, previous paint layers, a large amount of lead is associated with older buildings and with construction debris. Chipping, physical abrasion, and breakdown of paint surfaces by atmospheric chemicals, such as ozone and nitrogen dioxide (Edwards et al. 2009), lead to the release of particulate, aerosol, and gaseous lead from interior and exterior surfaces of residential, commercial, and industrial structures. Soils near buildings constructed before the 1970s often have high lead concentrations, especially near the drip lines where water runs off rooftops. In an extensive study in New Orleans, lead concentrations were substantially higher in soils collected along drip lines of residential homes than in soils near streets or in parks (Mielke 1994; Mielke and Reagan 1998).
Paints used for road markings have also historically contained lead. Abrasion of those paints by vehicles results in road dust with high lead concentrations, much of which is deposited along the sides of the road (Murakami et al. 2007). Some oil paints used by artists continue to contain lead.
Lead pipes were used extensively in indoor plumbing and for residential service lines in most American communities well into the 20th century. Most municipal building codes now prohibit new installations of lead piping, but many homes and older buildings still have lead risers inside and lead service lines outside. In some municipalities—notably Flint, Michigan—lead service lines deliver large amounts of the domestic water supply. Furthermore, lead solder has been used to join copper pipes and pipe fittings and might also be a source of lead in domestic plumbing systems. Corrosion and chipping of the pipes are potential sources of lead contamination in drinking water and in soils outside residential and commercial buildings.
Demolition of aging buildings can result in large releases of lead into the environment if lead pipes and other building materials that contain lead are not removed. Construction debris is thus an important source of lead in many reclaimed urban sites. Superfund sites associated with industrial activities dating back to the first half of the 20th century or earlier might thus have substantial stocks of lead from plumbing and building materials.
The manufacture of batteries is one of the largest industrial uses of lead globally. The lead-acid (Pb–PbO2) battery remains the standard means for generating electricity in most vehicles. In the United States, there is an efficient recycling program for lead-acid batteries of all types, which has greatly reduced the amount of battery lead released into the environment generally and deposited in municipal landfills specifically. Smith (2004) estimated a recycling efficiency of 95% for lead in batteries in the United States. The domestic recycling efficiency was estimated to be 77% owing to the export of spent batteries (primarily to Mexico) for recycling. Papp (2013) used a different accounting approach and reported a similar value of 81% for 2011. Wilburn (2014) estimated that 95.5% of the mass of lead-acid batteries was recovered from the municipal waste stream in 2000–2010.
Estimates of lead recycling do not account for long-term storage of batteries before recycling. Substantial lead release can occur from batteries experiencing corrosion. Battery lead might thus be an important source of contamination at sites that host automotive repair businesses.
Mining wastes have been used as agricultural amendments because metals are commonly associated with carbonate or phosphate rocks (Davies et al. 1993). In the Southeast Missouri Old Lead Belt, for example, chat left over from the extraction of lead from the Bonneterre limestone was crushed and sold for use as agricultural lime through much of the 20th century. Much of that material was used in the surrounding region, but some was shipped by train and barge to towns and ports along the Mississippi River.
Pesticide use has also contributed to environmental contamination with lead. Arsenicals were widely used as pesticides and insecticides in the United States until they were banned in 1988. Lead arsenate—PbHAsO4 or Pb5(OH)(AsO4)3 (EPA 1986)—is believed to have been the most commonly used arsenical pesticide (Peryea 1998). It was used for a wide array of crops, but its use in orchards, especially for grapefruit and apples (EPA 1986; Peryea 1998), was particularly widespread. Lead arsenate was typically applied by handgun spraying, and application rates depended on the crop species and the target pest (Peryea 1998).
Extensive use of lead arsenate in orchard lands has necessitated remedial action when those lands have been reclaimed for residential use. Schooley et al. (2008) highlight cases from Virginia, North Carolina, Washington, New Jersey, and Wisconsin in which soil lead concentrations of up to 800 ppm were observed in former apple orchards. Contamination at pesticide manufacturing sites has also been documented. The Industri-plex Superfund site in Woburn, Massachusetts—the site of a former chemical plant that made arsenate pesticides—contained soils contaminated with lead, arsenic, and other metals (DOJ 2012). Ayuso et al. (2004) were able to use lead isotopic analysis to characterize the isotopic signature of lead-arsenate pesticides and concluded that the use of these products could be an important source of lead in soils of formerly agricultural lands in New England.
Other Consumer Products
Lead is an important component of a number of consumer products. Perhaps most notable is ammunition for firearms. Lead shot was nearly ubiquitous until the early 1990s. In 1991, its use in waterfowl hunting was banned. In January 2017, the use of lead shot on federal wildlife refuges was also banned—a regulation overturned in February 2017. The burden of lead in soils and wetlands in or near shooting ranges and popular hunting sites can be high enough to be a threat to wildlife, especially waterfowl and raptors (Kendall et al. 1996; Fisher et al. 2006). Lead sinkers can also be an important source of lead in lakes and rivers that are frequented by fishermen (Jacks et al. 2001; Scheuhammer et al. 2003).
Lead-containing toys, jewelry, and decorative arts are other potential sources that could be important in residential areas. Antique toys and toys that are imported from countries where the use of lead paint is permitted are particularly likely to have high lead concentrations. In some cases, the lead is found in the paint used to decorate the toys. Lead might also be incorporated into the plastics of inexpensive toys. Because lead helps to make plastic more malleable, it is likely to be found in soft plastic toys. Similarly, other household plastics, such as vinyl window blinds, can be an important source of household lead. Sunlight and heat can degrade the material and result in release of dust that has high lead concentrations (EPA 2016). In older homes, lead might also have been used in counterweights in windows.
Lead is abundant in several forms of glass. Leaded glass, which is used for artisan crystal and stained glass, is composed of 12–60% lead oxide, and opal illumination glass contains an average of 3.0% lead oxide (Spinosa et al. 1979). In the late 19th and early 20th centuries, Southeast Missouri hosted an active glass industry, including extraction of local sand for glass-making (Burchard 1907). Many glazes and solders have high lead concentrations. Leaded glazes are used because they provide a smooth finish that highlights bright colors. Terra cotta pottery from Latin America, such as Mexican bean pots, often has high lead concentrations, as do some highly decorated ceramics from Asia. Lead solder is often used in electronic parts and in inexpensive jewelry, and lead is used to make jewelry heavier.
The interested reader is directed to Tables 3-3 and 3-4 in EPA (1998), which contain comprehensive lists of industrial and commercial uses of lead alloys and lead compounds, respectively. Lead derived from the decay of consumer products or present in demolition debris is a potential source to consider in attribution studies in lead-contamination investigations, especially those associated with exposures in the residential environment.
Appold, M.S., and G. Garven. 1999. The hydrology of ore formation in the southeast Missouri district: Numerical models of topography-driven fluid flow during the Ouachita orogeny. Econ. Geol. 94(6):913-935.
Ayuso, R., N. Foley, G. Robinson Jr., G. Wandless, and J. Dillingham. 2004. Lead Isotopic Compositions of Common Arsenical Pesticides Used in New England. U.S. Geological Survey Open File Report 2004-1342. Reston, VA: U.S. Geological Survey [online]. Available: https://pubs.usgs.gov/of/2004/1342/2004-1342.pdf [accessed June 20, 2017].
Back, M.E., J.A. Mandarino, and M. Fleischer. 2008. Fleischer’s Glossary of Mineral Species, 2008. Tuscon, AZ: Mineralogical Record Incorporated.
Barnes, H.I., and N.G. Lavery. 1977. Use of primary dispersion for exploration of Mississippi Valley-type deposits. J. Geochem. Explor. 8(1-2):105-115.
Browne, F.L. 1930. Effect of priming-coat reduction and special primers upon paint service on different woods. Ind. Eng. Chem. 22(8):847-854.
Burchard, E.F. 1907. Glass sand of the Middle Mississippi Basin. Pp. 452-472 in Contributions to Economic Geology, 1905, S.F. Emmons, and E.C. Eckel, eds. U.S. Geologic Survey Bulletin 285N [online]. Available: https://pubs.usgs.gov/bul/0285n/report.pdf [accessed June 28, 2017].
Callender, E. 2005. Heavy metals in the environment—Historical trends. Pp. 67-105 in Environmental Geochemistry, Treatise on Geochemistry Vol. 9, B. Sherwood Lollar, ed. Amsterdam: Elsevier.
Davies, B.E., C.F. Paveley, and B.G. Wixson. 1993. Use of limestone wastes from metal mining as agricultural lime: Potential heavy metal limitations. Soil Use Manag. 9(2):47-52.
Doe, B.R., and R.E. Zartman. 1979. Plumbotectonics, the phanerozoic. Pp. 22-70 in Geochemistry of Hydrothermal Ore Deposits, 2nd Ed., H.L. Barnes, ed. New York: John Wiley.
DOJ (U.S. Department of Justice). 2012. Companies Agree to $4.25 Million Natural Resource Damages Settlement at Industri-Plex Superfund Site, Woburn, Mass. Press Release 12 603. May 10, 2012 [online]. Available: https://www.justice.gov/opa/pr/companies-agree-425-million-natural-resource-damages-settlement-industri-plex-superfund-site [accessed August 3, 2017].
du Bray, E.A., ed. 1995. Preliminary Descriptive Geoenvironmental Models of Mineral Deposits. U.S. Geological Survey Open-File Report 95-831. Reston, VA: U.S. Geological Survey [online]. Available: https://pubs.usgs.gov/of/1995/0831/report.pdf [accessed June 20, 2017].
Edwards, R.D., N.L. Lam, L. Zhang, M.A. Johnson, and M.T. Kleinman. 2009. Nitrogen dioxide and ozone as factors in the availability of lead from lead-based paints. Environ. Sci. Technol. 43(22): 8516-8521.
EPA (U.S. Environmental Protection Agency). 1986. Lead Arsenate. EPA Pesticide Fact Sheet 12/86 [online]. Available: https://quicksilver.epa.gov/work/03/2087981.pdf [accessed June 20, 2017].
EPA. 1998. Locating and Estimating Air Emissions from Sources of Lead and Lead Compounds. EPA-454/R-98-006. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC. May 1998 [online]. Available: https://www3.epa.gov/ttnchie1/le/lead.pdf [accessed June 20, 2017].
EPA. 2013. Integrated Science Assessment for Lead. EPA/600/R-10/075F. U.S. Environmental Protection Agency, National Center for Environmental Assessment, Research Triangle Park, NC.
EPA. 2016. Lead. Home Danger Zone Finder [online]. Available: https://www.epa.gov/lead/home-danger-zone-finder-0 [accessed August 4, 2017].
EPA. 2017. 2014 National Emissions Inventory (NEI) Data [online]. Available: https://www.epa.gov/air-emissions-inventories/2014-national-emissions-inventory-nei-data [accessed June 20, 2017].
Faure, G. 1998. Principles and Applications of Geochemistry: A Comprehensive Textbook for Geology Students, 2nd Ed. Upper Saddle River, NJ: Prentice Hall.
Faure, G., and T.M. Mensing. 2004. Isotopes: Principles and Applications, 3rd Ed. Hoboken, NJ: Wiley. 493 pp.
Fisher, I.J., D.J. Pain, and V.G. Thomas. 2006. A review of lead poisoning from ammunition sources in terrestrial birds. Biol. Conserv. 131(3):421-432.
Goldfarb, R.J., T. Baker, B. Dubé, D.I. Groves, C.J.R. Hart, and P. Gosselin. 2005. Distribution, character, and genesis of gold deposits in metamorphic terranes. Pp. 407-450 in Economic Geology: One Hundredth Anniversary Volume 1905-2005, J.W. Hedenquist, J.F.H. Thompson, R.J. Goldfarb, and J.P. Richards, eds. Littleton, CO: Society of Economic Geologists.
Goldhaber, M.B., S.E. Church, B.R. Doe, J.N. Aleinikoff, J.C. Brannon, F.A. Podosek, E.L. Mosier, C.D. Taylor, and C.A. Gent. 1995. Lead and sulfur isotope investigation of Paleozoic sedimentary rocks from the southern Midcontinent of the United States; Implications for paleohydrology and ore genesis of the Southeast Missouri lead belts. Econ. Geol. 90(7):1875-1910.
Graney, J.R., A.N. Halliday, G.J. Keeler, J.O. Nriagu, J.A. Robbins, and S.A. Norton. 1995. Isotopic record of lead pollution in lake sediments from the northeastern United States. Geochem. Cosmochim. Acta 59(9):1715-1728.
Gulson, B.L., K.G. Tiller, K.J. Mizon, and R.H. Merry. 1981. Use of lead isotope in soils to identify the source of lead contamination near Adelaide, South Australia. Environ. Sci. Technol. 15(6):691-696.
Gutiérrez, M., K. Mickus, and L.M. Camacho. 2016. Abandoned Pb–Zn mining wastes and their mobility as a proxy to toxicity: A review. Sci. Total Environ. 565:392-400.
Gwiazda, R.H., and D.R. Smith. 2000. Lead isotopes as a supplementary tool in the routine evaluation of household lead hazards. Environ. Health Perspect. 108(11):1091-1097.
Hallett, R.L., and C.H. Rose. 1935. Lead pigments. Pp. 81-87 in Symposium on Paint and Paint Materials. STP38728S. West Conshohocken, PA: ASTM International [online]. Available: https://doi.org/10.1520/STP38728S [accessed May 22, 2017].
Jacks, G., M. Byström, and L. Johansson. 2001. Lead emissions from lost fishing sinkers. Boreal Environ. Res. 6:231-236.
Johnson, C.E., A.H. Johnson, T.G. Huntington, and T.G. Siccama. 1991. Whole-tree clear-cutting effects on soil horizons and organic-matter pools. Soil Sci. Soc. Am. J. 55:497-502.
Johnson, C.E., T.G. Siccama, C.T. Driscoll, G.E. Likens, and R.E. Moeller. 1995. Changes in forest lead cycling in response to decreasing atmospheric inputs. Ecol. Appl. 5(3):813-822.
Johnson, C.E., R.J. Petras, R.H. April, and T.G. Siccama. 2004. Post-glacial lead dynamics in a forest soil. Water Air Soil Pollut. Focus 4(2):579-590.
Kaiser, C.J., W.C. Kelly, R.J. Wagner, and W.C. Shanks. 1987. Geologic and geochemical controls of mineralization in the Southeast Missouri barite district. Econ. Geol. 82(3):719-734.
Kendall, R.J., T.E. Lacker. Jr., C. Bunck, B. Daniel, C. Driver, C.E. Grue, F. Leighton, W. Stansley, P.G. Watanabe, and M. Whitworth. 1996. An ecological risk assessment of lead shot exposure in non-waterfowl avian species: Upland game birds and raptors. Environ. Toxicol Chem. 15(1):4-20.
Leach, D.L., D.F. Sangster, K.D. Kelley, R.R. Large, G. Garven, C.R. Allen, J. Gutzmer, and S. Walters. 2005. Sediment-hosted lead-zinc deposits: A global perspective. Pp. 561-607 in Economic Geology: One Hundredth Anniversary Volume 1905–2005, J.W. Hedenquist, J.F.H. Thompson, R.J. Goldfarb, and J.P. Richards, eds. Littleton, CO: Society of Economic Geologists.
Leach, D.L., R.D. Taylor, D.L. Fey, S.F. Diehl, and R.W. Saltus. 2010. A Deposit Model for Mississippi Valley-Type Lead-Zinc Ores, Chapter A of Mineral Deposit Models for Resource Assessment. U.S. Geological Survey Scientific Investigations Report 2010–5070–A [online]. Available: https://pubs.usgs.gov/sir/2010/5070/a/ [accessed September 18, 2017].
Long, K.R., J.H. DeYoung, and S.D. Ludington. 1998. Database of Significant Deposits of Gold, Silver, Copper, Lead, and Zinc in the United States. U.S. Geological Survey Open-File Report 98-206. Reston, VA: U.S. Geological Survey.
Manton, W.I. 1985. Total contribution of airborne lead to blood lead. Br. J. Ind. Med. 42(3):168-172.
McHenry, R.E. 2006. Chat Dumps of the Missouri Lead Belt, St. Francois County, With an Illustrated History of the Lead Companies that Built Them. Park Hills, MO: Missouri Department of Natural Resources, Missouri Mines State Historic Site.
McLimans, R.K., H.L. Barnes, and H. Ohmoto. 1980. Sphalerite stratigraphy of the upper Mississippi Valley zinc-lead district, southwest Wisconsin. Econ. Geol. 75(3):351-361.
Mielke, H.W. 1994. Lead in New Orleans soils: New images of an urban environment. Environ. Geochem. Health 16(3):123-128.
Mielke, H.W. 1999. Lead in the inner cities: Policies to reduce children’s exposure to lead may be overlooking a major source of lead in the environment. Am. Sci. 87(1):62-73.
Mielke, H.W., and P.L. Reagan. 1998. Soil is an important pathway of human lead exposure. Environ. Health Perspect. 106(Suppl. l):217-229.
MO DNR (Missouri Department of Natural Resources). 2017. Missouri Lead Mining History by County. Missouri Department of Natural Resources [online]. Available: https://dnr.mo.gov/env/hwp/sfund/lead-mo-historymore.htm [accessed February 15, 2017].
Mugel, D.N. 2017. Geology and Mining History of the Southeast Missouri Barite District and the Valles Mines, Washington, Jefferson, and St. Francois Counties, Missouri. U.S. Geological Survey Scientific Investigations Report 2016-5173 [online]. Available: https://pubs.usgs.gov/sir/2016/5173/sir20165173.pdf [accessed June 20, 2017].
Murakami, M., F. Nakajima, H. Furumai, B. Tomiyasu, and M. Owari. 2007. Identification of particles containing chromium and lead in road dust and soakaway sediment by electron probe microanalyser. Chemosphere 67(10):2000-2010.
Papp, J.F. 2013. Recycling metals. Pp. 61.1–61.5 in Minerals Yearbook 2013, Vol. 1. Metals and Minerals [online]. Available: https://minerals.usgs.gov/minerals/pubs/commodity/recycle/myb1-2013-recyc.pdf [accessed June 20, 2017].
Peryea, F.J. 1998. Historical use of lead arsenate insecticides, resulting soil contamination and implications for soil remediation. Scientific Registration No. 274 in Proceedings of the 16th World Congress of Soil Science,
August 20-26, 1998, Montpellier, France [online]. Available: http://soils.tfrec.wsu.edu/leadhistory.htm [accessed May 22, 2017].
Plumlee, G.S. 1999. The environmental geology of mineral deposits. Pp. 71-116 in The Environmental Geochemistry of Mineral Deposits, Part A. Processes, Techniques, and Health Issues. Review of Economic Geology Vol. 6A. Littleton, CO: Society of Economic Geologists.
Ramos, F.C., and P.E. Rosenberg. 2012. Age and origin of quartz-carbonate veins associated with the Coeur d’Alene mining district, Idaho and western Montana: Insights from isotopes and rare-earth elements. Econ. Geol. 107(6):1321-1339.
Rao, V., L. Tooly, and J. Drukenbrod. 2013. 2008 National Emissions Inventory: Review, Analysis, Highlights. EPA-454/R-13-005. U.S. Environmental ProtectionAgency, Office of Air Quality Planning and Standards, Research Triangle Park, NC [online]. Available: https://www.epa.gov/sites/production/files/2015-07/documents/2008report.pdf [accessed June 20, 2017].
Ridley, J. 2013. Ore Deposit Geology. New York: Cambridge University Press.
Rose, A.W., H.E. Hawkes, and J.S. Webb. 1979. Geochemistry in Mineral Exploration. London: Academic Press. 657 pp.
Rudnick, R.L., and S. Gao. 2014. Composition of the continental crust. Pp. 1-51 in Treatise on Geochemistry, Vol. 4. The Crust, 2nd Ed., H. Holland, and K. Turekian, eds. Amsterdam: Elsevier.
Sahl, K., B.R. Doe, and K.H. Wedepohl. 1978. Lead. Pp. 80A-1 to 82-O-1 in Handbook of Geochemistry Vol. 2, K.H. Wedepohl, ed. New York: Springer.
Sangster, D.F., P.M. Outridge, and W.J. Davis. 2000. Stable lead isotope characteristics of lead ore deposits of environmental significance. Environ. Rev. 8(2):115-147.
Scheuhammer, A.M., S.L. Money, D.A. Kirk, and G. Donaldson. 2003. Lead Fishing Sinkers and Jigs in Canada: Review of Their Use Patterns and Toxic Impacts on Wildlife. Canadian Wildlife Service Occasional Paper 108. Ottawa, Canada: Environment Canada. 48pp.
Schooley, T., M.J. Weaver, D. Mullins, and M. Eick. 2008. The history of lead arsenate use in apple production: Comparison of its impact in Virginia with other states. J. Pest. Saf. Educ. 10:22-53.
Smith, G.R. 2004. Lead recycling in the United States in 1998. Chapter F in Flow Studies for Recycling Metal Commodities in the United States, S.F. Sibley, ed. U.S. Geological Survey Circular 1196. Reston, VA: U.S. Geological Survey [online]. Available: https://pubs.usgs.gov/circ/2004/1196am/c1196a-m_v2.pdf [accessed June 20, 2017].
Smith, K.S. 2007. Strategies to predict metal mobility in surficial mining environments. Pp. 25-45 in Understanding and Responding to Hazardous Substances at Mine Sites in the Western United States, J.V. DeGraff, ed. Reviews in Engineering Geology Vol. 17. Boulder, CO: Geological Society of America [online]. Available: https://minerals.usgs.gov/east/mea/Smith2007_508.pdf [accessed June 20, 2017].
Smith, K.S, and H.L.O. Huyck. 1999. An overview of the abundance, relative mobility, bioavailability, and human toxicity of metals. Pp. 29-70 in The Environmental Geochemistry of Mineral Deposits, Part A: Process, Techniques and Health Issue. Littleton, CO: Society of Economic Geologists.
Smith, W.H. 1976. Lead contamination of the roadside ecosystem. J. Air Pollut. Control Assoc. 26(8):753-766.
Spinosa, E.D., D.T. Hooie, and R.B. Bennett. 1979. Summary Report on Emissions from the Glass Manufacturing Industry. EPA/600/2-79/101. U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH.
USGS (U.S. Geological Survey). 2015. Mineral Resources Data System (MRDS) [online]. Available: https://mrdata.usgs.gov/mrds/ [accessed February 2, 2017].
Vignes, A. 2013. Extractive Metallurgy, 3. Processing Operations and Routes. London: iSTE.
Wharton, H.M. 1972. Barite Ore Potential of Four Tailings Ponds in the Washington County Barite District, Missouri. Rolla, MO: Geological Survey and Water Resources.
Wilburn, D.R. 2014. Comparison of the U.S. Lead Recycling Industry in 1998 and 2011. U.S. Geological Survey Scientific Investigations Report 2014-5086. Reston, VA: U.S. Geological Survey [online]. Available: https://pubs.usgs.gov/sir/2014/5086/pdf/sir2014-5086.pdf [accessed June 20, 2017].
Winslow, A. 1894. Lead and Zinc Deposits. Jefferson City, MO: Missouri Bureau of Geology and Mines.
Zientek, M.L., and G.J. Orris. 2005. Geology and Nonfuel Mineral Deposits of the United States. U.S. Geological Survey: Open-File Report 2005-1294-A. Reston, VA: U.S. Geological Survey [online]. Available: https://pubs.usgs.gov/of/2005/1294/a/of2005-1294a.pdf [accessed September 17, 2017].