Sources of lead in the environment
Lead paint residuePrior to 1950, lead was a major ingredient in most interior and exterior oil house paint and was still used in some paints until 1978, when residential use of lead paint was banned (US GAO 1999). In the late 1980s, the U.S. Department of Housing and Urban Development (HUD) and the EPA conducted a national survey of lead-based paint in housing to estimate the extent of lead-based paint in housing, where a home was classified as having lead-based paint if the measured lead concentration on any painted surface was ≥1.0mg/cm 2. Based on these studies, an estimated 64 ±7 million privately owned homes (83% ±9%) built before 1980 have lead-based paint somewhere in the building. Approximately 12 ±5 million of these homes are occupied by families with children under the age of 7 years (ATSDR 2002). The older the house, the more likely it is to contain lead-based paint and to have a higher concentration of lead in the paint. Before 1955, most house paint contained up to 50% lead; however, in 1971 the amount of lead allowed in paint was lowered by federal law to 1% and then to 0.06% in 1977. Of the 4.9 million tons of white lead pigment used between 1910 and 1989, 92% was used prior to 1950, most of it between 1910 and 1939. The greatest concentration of older homes is located in the Northeast and upper Midwest of the United States (Farquhar 1994; ATSDR 2000). Damaged lead-based paint has been associated with excessive dust lead levels. Approximately 14 million homes (19% of the pre-1980 housing) have more than 5 square feet of damaged lead-based paint, and nearly half (47%) of those homes have excessive dust lead levels (ATSDR 2002). As lead paint deteriorates, peels, chips, is removed, or pulverizes because of friction (e.g., in window sills), house dust and surrounding soil may become contaminated. Releases from lead-based paints are frequently confined to the area in the immediate vicinity of painted surfaces, and deterioration or removal of the paint can result in high-localized concentrations of lead in indoor air (from sanding and sandblasting) and on exposed surfaces. Disturbance of older structures containing lead-based paint is now a significant contributor to total lead releases (ATSDR 2002). Lead in household paints is the most frequent cause of lead poisoning. Lead enters the body through transfer of particulates from normal hand-to-mouth activity and inhalation. Children are also at increased risk from the ingestion of paint chips, and children with pica behavior are at even greater risk (ATSDR 2000). Lead concentrations of 1-5mg/cm 2 have been found in chips of lead-based paint, suggesting that consumption of a single chip of paint would provide greater short-term exposure than any other source of lead. An estimated 40-50% of currently occupied housing in the United States may contain lead-based paint on exposed surfaces (Farquhar 1994; ATSDR 2002). Several tactics can be employed to decrease exposures to lead-based paint by either making the paint inaccessible or removing it completely. Two main methods can be used to lessen exposure to damaged lead paint. Encapsulation involves covering paint with a material that bonds to the surface, such as acrylic or epoxy coatings, or with flexible wall coverings and enclosure, which uses approved wallboards or paneling that cover the contaminated surface. Removal is also an accepted method; however, proper procedures must be followed to prevent the creation or dispersal of lead-contaminated dust. Removal requires the complete stripping or removal of contaminated surfaces and replacement with lead-safe components. Physical removal can be done by wet-scraping with mechanical, chemical paint removers or by hand-scraping using a heat gun at recommended levels. On-site removal of lead-based paint requires worker safeguards, including protective clothing, respirators, personal hygiene protocols, and periodic blood lead testing. Removal costs 30 to 50% more than enclosure or encapsulation (Farquhar 1994). Auto emissions from leaded gasolineLead in gasoline was recognized as a significant contribution to human health risk in the US. as early as 1973 when the EPA decided to reduce lead in gasoline down to 0.10g. By 1975, small trucks and cars were required to have a catalytic converter, which necessitated the use of unleaded gasoline. In 1986, the EPA announced that lead would be reduced by 90% in gasoline, and it had already set an interim standard of 0.50 grams of lead effective on July 1, 1985 (EPA History Lead 2002). As recently as 1990, the amount of lead in gasoline had decreased by 99.8% (Pirkle et al. 1994). However, emissions from cars predating this time, and the small amount of lead that has not been eliminated from gasoline, have left residual traces of lead along roadways and may contribute to human exposure to lead in soils. Three surveys conducted by the National Health and Nutrition Examination (NHANES) found that the BLL of participants aged 1 to 74 dropped 78%, and in participants aged 1 to 5 years old it dropped 77% over a 15-year period from 1976 to 1991. Many factors contributed to this significant drop, but the reduction of lead in gasoline was singled out as the largest factor in the drop in blood lead levels (Pirkle et al. 1994). The combustion of leaded gasoline releases lead into the air, at which time it is dispersed turbulently. The dispersion of lead is impacted by wind speed and direction, topography, and variations in source strength. One urban study found that over 80% of lead emissions reached the surface by gravitational settling or was removed by impactation (Piver 1977). These two processes, along with precipitation, cause lead in the air to be re-deposited onto the Earth’s surface. Once lead is in the soil it does not biodegrade but can be washed away. It is the runoff and erosion associated with precipitation that causes the removal of lead because lead binds well with soil particles. The intensity of the precipitation correlates directly with the rate of removal of lead. Additionally, chemical processes and uptake of lead by plants can remove lead from soils (Piver 1977). Because these processes have not changed and lead has been mostly eliminated from gasoline since 1990, lead exposure from gasoline combustion has decreased significantly, so as not to contribute a new source of terrestrial deposition of lead. Consequently the amount of residual lead in roadside soils that has the potential to be exposed to children is stable or decreasing. Some lead remains, as it does not biodegrade, and it tends to remain in the top several inches of soil because it is not prone to leaching, but this increases the potential of the lead to wash away with the erosion of soil particles because it adheres to them (Wisconsin Dept of Health 2004). The two main factors that influence the level of lead deposited on soil by gas emissions are distance from roads and traffic volume. Both atmospheric and soil lead levels have been found to be a function of traffic volume and distance from the roadway with numerous studies finding that soil and dust lead levels increase with increased traffic volume and decrease with distance from the road (Francek et al. 1992). Because of the positive correlation between traffic volume and roadside lead content, urban children are more at risk from auto-emitted lead (Piver 1977). One study found that roadside dust had an average lead level of 353 micrograms, while rural/suburban roads had an average of just 125 micrograms (Hashisho et al. 2004). Three additional factors contribute to soil lead levels. The speed and acceleration of a car influence the rate of lead emissions into the air. As acceleration increases the rate of emissions increase as it does when the cruise speed increases. Acceleration and increased speed free particulates that have gathered in the exhaust system. Additionally, the age of the exhaust system and engine can have an effect on lead emissions, with older engines emitting greater amounts of lead due to the buildup of lead particulates in the exhaust system (Piver 1977). A case study done in 1992 in Mt. Pleasant, Michigan, found that the age of houses was the most significant factor in the amount of lead found in Mt. Pleasant homes and soils compared to traffic volume and distance from the road. The study sampled 42 houses with pre-school children in 1991. Higher traffic volumes and houses located closer to roads were the two factors that increased lead concentrations. Traffic volume on streets that averaged less than 2,000 cars per day was found to not impact lead levels in the soil. Homes with a median road distance of 16 meters were found to have higher lead in both their soils and at their entranceways than homes located farther away. The explanation for this has been consistently described in studies as the result of fallout from lead particulater from leaded gasoline due to cars being closer to yards and homes. However, the most consistent relationship found in the study was increasing lead levels correlated with increasing home age. Overall, the study determined that Mt. Pleasant had much lower lead levels than most large cities and were relatively low in general (Francek et al. 1994). Mt. Pleasant could be described as a similar community to our study sites in terms of population, % children, and in age of homes, so we believe that we will see a minimal impact of lead in gasoline to the homes that we are testing except for the homes very close to main roadways, as this study did. Because almost 14 years have passed since the vast majority of lead was removed from gasoline and the natural processes such as precipitation and the corresponding runoff and plant uptake that remove lead from the soil, we do not believe that lead combustion from gasoline will be a significant variable in our study. By 1989 the EPA found that solid waste and industrial processes had surpassed transportation as the highest emitters of lead (ATSDR 2002). The houses that may be impacted the most by lead combustion are those homes located closest to the roads. Because of the fact that lead stays in the soil for long periods of time, there will be lead present from gasoline combustion, but it is definitely not the largest source of lead emissions today. We also feel that because Meadville is a small town that does not experience high volumes of cars traveling at high speeds, lead exposure in soil as a result from gasoline will be a lesser variable than in an urban area. Lead pipes and lead solderWater is a pathway for lead exposure by ingesting lead-contaminated water from sewer and plumbing systems. This form of lead exposure can be caused by the presence of lead in old pipes or lead solder in newer, copper pipes. In an interview with Meadville Area Water Authority (MAWA) Project Manager Donald Nold, it was discovered that Meadville is fortunate enough to have had all of its lead pipes removed sometime in the mid-1990s and to have all copper pipes installed that do not have any lead solder in them. This means there isn’t any potential problems associated with lead solder eroding from copper pipes. However, there are other places where lead can enter the water, such as household plumbing systems that MAWA is not required to maintain and test (Nold, Personal Communication). The Environmental Protection Agency (EPA)’s Lead and Rule of 1991, document number 383-0300-107, requires each state to have standards equal to or lower than the federally mandated levels, so the state has set the action level at 0.015 mg/L in compliance with Federal regulations (Lead and Copper 1997). For MAWA to be in compliance, 90 percent of samples must be below 15 parts per billion (ppb) or 0.015 mg/L. In April, 2000 the EPA made minor changes to the Lead and Copper Rule that included revisions that relax monitoring and reporting, and reduce the amount of public education and language required by the Lead and Copper Rule of 1991 (Lead and Copper Rule Minor Revisions 2001). MAWA tests every three years because that is the minimum requirement established by the EPA when a community’s water is not in violation of federal standards, and in 2001-2003 they had only one sample out of a total of 20 exceed the 15 ppb limit (Consumer Confidence Report 2003). If MAWA were ever in violation, they would have to increase the frequency of testing to every year. They predicted that this was either due to poor sampling procedure by the customer or corrosion of household plumbing systems. Out of the 30 sampled homes, 21 had a lead composition of less than 0.001 ppb in their water (Nold Personal Communication). MAWA serves 16,000 people in Meadville, West Mead, and Vernon Townships, and obtains water from seven wells located on Rogers Ferry Road. MAWA monitors water through licensed operators at the source, during treatment processes, and as the water flows through the local distribution pipes to the homes in their customer area. Additionally, MAWA conducts customer testing, as required by the Lead and Copper Rule, and uses groups of 30 customers that are chosen to sample their water following standardized guidelines distributed by MAWA, which MAWA then analyzes (Nold Personal Interview). The customers are chosen based on a 3-tier system in which the first tier is single-family structures that have lead or copper pipes with lead solder installed after 1982, and if possible the sample population will be made up entirely of the first tier. If sufficient structures are not available that meet this description, the second tier is used, the only difference being that the second tier consists of buildings and multi-family residences installed after 1982 and/or are served by lead service lines. If necessary, there is a third tier that is made of single-family houses containing only copper pipes installed before 1983 (Lead and Copper 1997). Titusville Public and Water Works also operate a public water supply that is obtained from ten local wells. Like Meadville they perform lead testing every three years, and their water has met federal and state requirements. The last sampling came in September of 2001, and it reported a lead level detected of two micrograms per liter. This is a value far below the action level of 15 micrograms per liter, so Titusville’s water was found to be in compliance with federal and state standards. They believe the contamination came from corrosion of household plumbing systems and erosion of natural deposits. Titusville also has an extensive Wellhead protection plan in place, and they have classified their susceptibility to potential contaminants as not susceptible (2003 Annual Drinking Water Quality Report). From these findings we believe that public water lines do not pose a significant risk of exposure of lead to residents. Although specific evaluation of other variables such as low income, private household plumbing facilities could yield information contributing to lead found in water, the overall risk of exposure at present is determined to be low. Therefore, we do not believe lead present in the water, especially in public, residential lines, is a major factor in causing lead exposure in our study locations. Occupational exposureSecondary occupational exposure, also known as paraoccupational or indirect exposure, can present an additional threat in homes where one or both parents work in an industry using lead (McDiarmid and Weaver 1993). These occupations include but are not limited to asbestos removal, construction, bricklaying, bridge, tunnel and tower demolition or construction, electrical work, lead smelter, production, or refining, mining, painting, paint manufacturing, plastic manufacturing, printing, and jobs in the tool and die industry. Workers can be exposed to lead dust when removing paint from pre-1978 homes during renovation, remodeling or demolition work, when cutting through leaded cables, and also when sanding or sand blasting walls or steel structures coated with lead paint (e.g. bridgework) (Department of Labor and Industries 1999). Workers can be exposed by breathing in lead dust or fumes when working with lead, by eating, drinking, or smoking in work areas, by handling contaminated objects, or by accidentally swallowing lead dust. Unfortunately, children of occupationally exposed adults and pregnant women living in a household with those who work in lead-related industries may be at increased risk. These family members exposed to take-home agents may be more vulnerable than workers due to differences in their physiology (age and health status), behaviors (hand-to-mouth and pica behaviors of young children), and education (worker awareness and use of personal protective equipment) (DHHS 2002). Lead dust collected on work clothes during the day and worn home, particularly on pants, shoes, socks or other fomites can contaminate the car and home, exposing households to increased levels of lead-contaminated dust (McDiarmid and Weaver 1993). A multitude of studies have been conducted to determine whether children of lead workers are at a higher risk of lead absorption than non-exposed children, and if so, what factors can influence their levels of absorption. According to several of these studies (Table #), significantly higher dust concentrations were found in exposed workers’ homes, and their children were found to have higher blood lead levels (BLL) (Baker et al 1977; Dolcourt et al 1978; Watson et al 1978; Piacitelli et al 1997; Roscoe et al 1999; Aguilar-Garduno et al 2003) Childhood lead exposure via parental occupational hazards can present significant lead levels in the home. Failure to screen these children may mean that their lead poisoning will be missed because they may not live in neighborhoods or houses that otherwise make them candidates for targeted screening. Consequently, training efforts should be encouraged to increase employee and employer awareness of hazards and acceptance of safe work and material-handing procedures. Measures to protect workers’ families should focus primarily on identifying and preventing the transport of hazardous substances from the workplace. Workers should change clothes and shower before going home; work areas should be separated from living or eating areas; and personal protective equipment should be used as needed. Equally important are the development and distribution of information and education programs designed for family members and health care professionals (Dept Health and Human Services 2002; McDiarmid and Weaver 1993). Existing standards that require employers to reduce risks to workers will inherently protect the workers’ families as well. In 1978, OSHA set the standard permissible exposure limit (PEL) for inorganic lead at 50μg/m 3 averaged over an 8-hour workday, with an action level beginning at 30μg/m 3 where employers must establish comprehensive programs to reduce exposure (Roychowdhury 1998). A BLL > 40μg/dL requires that the worker be notified in writing and be provided a medical examination. Annual medical examinations must be performed on all workers who have had a BLL ≥40μg/dL in the past 12months. OSHA allows workers to continue to work with a blood levels up to 50μg/dL; however, after this level is exceeded, the employer is obligated to remove the worker from the high-exposure job until his or her BLL has fallen below 40μg/dL on two consecutive blood lead levels (Levin and Goldberg 2000). In order to prevent the worker from being economically penalized following this removal, OSHA requires that the employer provide the worker full pay and maintenance of seniority until the worker’s BLL falls below 40μg/dL (ATSDR 2003). GardeningDietary risk of lead ingestion can occur when gardens are established on sites where soil has been contaminated with a high content of lead from a variety of possible sources such as air-borne from nearby heavily trafficked roads, placement near a lead smelter, waste disposal area or coal burning power plant, soil-borne particles from lead based paint on housing or from natural deposits (Peryea 1999). Lead contaminated soil found in home gardens may therefore be transferred to food from gardening, creating another avenue for exposure. Plant uptake of lead is a key to increasing bioavailability to humans. Food quality may be reduced when lead from soils enters the garden produce, accumulating in the leaves, stems, roots and outer skin of many fruits and vegetables (Scheyer 2000). Though the distribution pattern of lead concentration in plant parts is highly variable, seeds and fruits tend to have lower concentrations than leaves, stems and roots. Outer parts of the roots and tubers usually having the highest concentrations due to direct contact with the soil; therefore, root crops such as beets, carrots, turnips and radishes should be avoided in lead contaminated soils. Furthermore, leafy vegetables are also more likely to become contaminated because of their high water content, and large surface exposure (Wisconsin Dept of Health 2004). Fruits and vegetables that produce edible fruits, such as tomatoes, peppers, cucumbers and squash, can be grown as lead does not highly concentrate in the fruits (Ameroso and Mazza 2004). Lead can be passed along to children through handling and consumption of produce grown in soils with lead; however, this exposure can be reduced by careful cleaning and food preparation (Ameroso and Mazza 2004). Contaminated soil should be kept out of the house and children should not eat soil. Produce should be washed thoroughly outside of the house to remove loose soil particles and residue before bringing into the house. Once inside, the produce should be washed and scrubbed with a 1% vinegar solution or 0.5% dishwashing liquid solution before cooking or consumption to remove remaining soil particles (Peryea 1999). Root and tuber crops should be peeled before cooking or consumption and the peelings should be discarded. Unused plant parts and peelings should not be composted in the garden to eliminate recycling of lead into the garden (Ameroso and Mazza 2004). When gardening, several steps can be taken to reduce the levels of lead exposure to children. First, gloves should be worn during gardening or hands should be washed thoroughly afterwards. Although complete elimination of lead in soils may be costly or in some cases not possible, other steps can be taken to significantly reduce the level of lead exposure to children. If lead sources come from air-borne particles from heavily trafficked roads, the garden should be placed as far from the road as possible to reduce the risk of lead fallout from automobile emissions. A fence may also be erected between the road and the garden to create a barrier from the lead source. If lead sources come mainly from soil-borne particles from paint on housing or other natural resources, the garden can be located as far from the house as possible and may be built in containers or raised beds where clean soil has been imported. If contamination is severe, ornamental plants such as flowers, shrubs and trees could be grown in place of edible plants, or the soil could be subject to abatement, where contaminated soil is replaced with fresh soil (Peryea 1999). While gardening in lead contaminated soils may introduce another source of lead exposure for children, sufficient steps can be taken to reduce these risks and is not considered a major avenue for lead exposure in children. Furthermore, while soil properties (pH, element level in soil, organic matter, cation exchange capacity, and level of other elements in the soil) and plant properties (plant age, species, type of crop edible portion [leafy or root vegetable, or garden fruit]) may affect absorption, lead is not easily translocated to plant foliage in harmful amounts (Chaney, Sterrett, and Mielke 1984). While this exposure may be relevant in particular cases, gardening has not been shown as a large pattern of exposure in this region and will not be further evaluated in this particular study. High lead content itemsHumans can be exposed to lead through a variety of sources that are usually not easily recognizable as basis for lead exposure. For instance, lead has been found in practically all the major food groups, with the highest concentrations being found in vegetables and fruits. But before these items are thrown out of the US., be aware that the lead content in foods in general is very negligible. However, fish are the one food that should be examined closely for lead poisoning before consuming. If a state has fish advisories and limits on the amount of fish that should be eaten weekly, it could be due to high lead content in the fish tissues. Then fish consumption should be limited to fish caught from water bodies that are below the specified EPA lead levels (ATSDR 2002). Another unusual form of lead exposure from foods comes from the tamarind candies imported from Mexico. In one case study, environmental analyses of the home of a 2-year-old Hispanic child with an unusually high blood lead level (BLL), revealed negative tests of household paint, soil and dusts. Further studies determined that the child had eaten many types of tamarind candy, one of which had lead levels of 404 ppm in the stick and 21,000 in the wrapper. Another Hispanic child had a BLL level of 26 m g/dL, and tests done on imported candies found the wrapper had a lead concentration of 16,000 ppm. After two years since the child stopped consuming the candy, the child’s BLL level decreased to 13.2 m g/dL (CDC 2002) Lead is also present in tobacco in the amount of about 2.5—12.2 m g/cigarette, but only 2—6% of this may be inhaled by the smoker, some of which may be residually available as second-hand smoke inhaled by children in these households (ATSDR 2002). Some non-food items in which the presence of lead has been detected include wine bottles and glasses made from lead crystal decanters in which the lead leaches from the decanters and glasses into the liquids inside them. After four months of storage in decanters, port wine was found to have lead concentrations of over 5,000 m g/L. Hair dyes along with other cosmetic items can contain lead compounds such as lead acetate. Because lead acetate can easily be moved from one surface to another, it can be readily transferred from hair product to hand to mouth. In one experiment, a dry hand that was passed through dyed dry hair that was lead-based picked up 786 m g of lead. Finally, lead ammunition when fired exposes a person to lead dust in concentrations of up to 1,000 m g/m 3, or this same lead ammunition could be ingested if the animal shot is eaten (ATSDR 2002). Some children’s toys and products that are imported from other countries may have high lead content. Items that have been found to contain lead in the past include any toys, furniture, vinyl blinds, candles with lead wicks, and car keys. Dishware, cans, and pottery are three other items that, if imported, may contain lead, which can leach into foods and drink stored and eaten from these materials (Wisconsin Dept. of Health). Some traditional home remedies from foreign regions and some powder cosmetics have been found to contain significant lead levels. These lead containing products are imported from countries that do not have the strict lead guidelines as in the US. Lead exposure can also occur as a type of point-source pollution. These sources can take the form of lead smelters, battery disposal factories, or superfund sites. In Crawford County, nine active superfund sites have been identified. These are mostly steel or other metal manufacturing plants that are classified as non-active by the National Priority List (NPL) of Superfund sites except for the Saegertown industrial area site. The list also includes a landfill and the Cambridge Springs lead site. There are also numerous archived sites in the County that are non-active on the Superfund Information Systems (NPL 2003, Superfund Information Systems 2004). Lead has been identified on at least 1,026 of about 1,467 NPL sites, so it is obviously one of the major contaminants in any Superfund site, past or present (ATSDR 2002).
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