The History and Impact of Lead Poisoning on Children and Adults
First get the child out of the lead, then get the lead out of the child. -- John W. Graef, M.D., Chief Emeritus, Lead and Toxicity Program, Children's Hospital, Boston, 1997
Department of Health and Human Services Centers for Disease Control reports that lead poisoning represents one of the most common and preventable pediatric health problems in the United States today. While the problem has existed for hundreds of years, researchers are just beginning to understand the actual implications of lead poisoning on the health and well-being of children and adults. In this regard, this paper provides a review of the scholarly and peer-reviewed literature to identify the history of lead poisoning and its various applications, the incidence of the problem today, followed by a discussion of the epidemiology of lead poisoning and the pathophysiological and biochemical basis of lead poisoning in children and adults. Recommendations for preventing lead poisoning in the United States and abroad are followed by a summary of the research and salient conclusions.
Review and Discussion
History of Lead Poisoning.
While lead has been used for various commercial applications for hundreds of years (Miksic, Yap, & Younan, 1994), the dangers associated with its use have only been identified fairly recently. According to Kessel and O'Connor (1997), the average level of lead in children's blood is lower today than it was before lead paint was prohibited from use in homes 25 years ago, and the phasing out of lead in gasoline; nevertheless, the problem of lead poisoning has been the focus of an increasing amount of research because it has been determined that lower and lower blood levels of lead can still adversely affect children's health, particularly the development of the brain. In addition, Kessel and O'Connor report that (1997), "The major cause of lead poisoning is lead-based paint. A child does not, however, have to eat paint chips to become lead poisoned. Any time lead-based paint is disrupted there is a potential for lead poisoning -- whether the paint is rubbed against, sanded or scraped, chewed on, or simply falling off" (p. 3). "Over the last two decades, atmospheric concentrations of lead have decreased significantly around the globe as more and more nations have chosen to remove tetraethylead from gasoline. However, humans may also be exposed to Pb through contaminated food, water, and house dust and through industrial activities such as metal recycling and the battery industry" (Barbosa, Gerlach, Parsons & Tanus-Santos, 2005, p. 1669). Furthermore, as Ryan, Huet, and MacIntosh (2000) emphasize, human activities have significantly changed the natural distribution of lead in the environment, resulting in potentially elevated concentrations of this metal in a number of environmental media; not surprisingly, the occurrence of lead in drinking water is regarded as another important pathway for potential exposure for citizens of the United States and many other countries today (Ryan et al., 2000).
Notwithstanding the costs in human terms, the economic consequences of lead poisoning are staggering. According to Fahs, Landrigan, Lipton, Schechter and Schwartz (2002), "Total annual costs are estimated to be $43.4 billion for lead poisoning. This estimate is likely low because it considers only four categories of illness, incorporates conservative assumptions, ignores costs of pain suffering, and does not include late complications for which etiologic associations are poorly quantified" (p. 721). Furthermore, the costs associated with lead poisoning remain inordinately disproportionate compared to the limited amount of resources devoted to the research, tracking, and prevention of lead poisoning today (Fahs, 2002).
Incidence of the Problem.
According to Dugbatey, Evans, Lienhop and Stelzer (1995), "Childhood lead poisoning is one of the most common preventable pediatric problems in the United States today" (p. 6). In spite of its preventable quality, the consequences of lead poisoning can be severe and even life-threatening and there are millions of children at risk all over the world today, including in the United States. In this regard, Kessel and O'Connor (1997) report that, "Each year, more than one-and-a-half million children have elevated blood lead levels in this country. In most cases of lead poisoning there are no obvious symptoms to alert a parent. Yet these children are at risk for behavioral problems, learning disabilities, and reduced IQ because of exposure to this invisible toxin, which is all around us" (p. 3). Likewise, the U.S. Department of Housing and Urban Development estimates that 3.8 million homes inhabited by children continue to have high levels of lead in dust and lead-based paint in poor condition (Croskey et al., 2005).
While there has been some recent progress made in preventing lead poisoning, lead-based paint that has been improperly managed in older homes remains the greatest source of exposure for children in the United States today (Goldman, 1997). The U.S. Secretary of the Department of Health and Human Services recently characterized lead poisoning as being the leading environmental threat to the health of nation's children; a survey in 1992 estimated that more than three million tons of lead in the form of lead-based paints remained a potential threat in American dwellings built prior to 1980 (Goldman, 1997).
Epidemiology of Lead Poisoning.
Today, researchers are well versed with the epidemiology of lead poisoning, although some recent findings have changed some long-held views about its etology. For instance, researchers have determined that when lead enters the body, the substance can be insinuated into the human body via a number of pathways depending on its source and, by extension, its bioavailability (Barbosa et al., 2005). In their study, "Lessons from a Primary-Prevention Program for Lead Poisoning among Inner-City Children," Croskey and her colleagues report that, "From lead-based paint, indoor dust, soil, and probably contaminated water pipes, children living in poor areas are exposed to lead through ingestion, inhalation, or both. Lead-based paint continues to be a problem in older homes and therefore is the major contributor to lead poisoning through ingestion of paint chips or ingestion of dust and soil contaminated with lead paint" (p. 15).
The percentage of lead that is absorbed by the human body primarily depends on the physical and chemical form, particularly particle size and the solubility, of the specific lead-based compound involved. Likewise, some other important factors are specific to the exposed subject, including age, sex, nutritional status and, to a lesser extent, genetic background (Barbosa et al., 2005). One of the earliest toxicokinetics studies reported that once absorbed into the blood compartment, lead has a mean biological half-life of about 40 days in adult males; the half-life in children and in pregnant women has been reported to be longer, because of bone remodeling but another study was unable to confirm this finding (Barbosa et al., 2005).
Similar to a number of other so-called "bone-seeking" elements, lead from blood is incorporated into calcified tissues such as bone and teeth where it is capable of remaining for years. Citing research by Rabinowitz (1991), Barbosa and his colleagues report that the half-life of Pb in bone (bone-Pb) ranges from 10 to 30 years, but the use of the term "half-life" to describe the biological clearance of Pb from bone implicitly makes assumptions about the kinetics of the process by which Pb is released. "Some researchers prefer to use the term 'residence time' to avoid implying more precision than what can be directly determined. From calcified tissue stores, Pb is slowly released, depending on bone turnover rates, which in turn are a function of the type of bone, whether compact (slow turnover) or trabecular (rapid turnover)" (Barbosa et al., 2005).
The studies to date have found that the release rate of Pb from bone varies with age and intensity of exposure, and the transfer of Pb from blood to other compartments determined to be much faster than previous estimates have suggested with the overall clearance rate from blood (sum of rates from blood to cortical bone, to trabecular bone and to other tissue), implying a half-life of 10-12 days (Brito et al. 2005). These latest findings emphasize the difference between the overall clearance viewed from outside, when no allowance can be made for recirculation, and the actual transfer rates identified by researchers conducted thus far (Barbosa et al., 2005).
Pathophysiological and Biochemical Basis of Lead Poisoning in Children and Adults.
The symptoms of lead poisoning are difficult to identify and there is the potential for neurological damage without any discernable symptoms; the only accurate method of determining whether a child has been lead poisoned is through a blood lead level screening (Kessel & O'Connor, 1997). "Because a child is at greatest risk of lead poisoning between the ages of 12 and 36 months, this is the most critical time to screen your child for lead" (Kessel & O'Connor, 1997, p. 33). Even though lead poisoning can be seriously harmful, lead poisoning frequently remains undetected because there are no obvious symptoms involved, a feature that has caused some to refer to lead poisoning as the "silent disease" (Kessel & O'Connor, 1997). Even fairly…