Lead poisoning: Current practice guidelines
The water crisis in Flint, Michigan, has refocused attention on the issue of lead poisoning.
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The water crisis in Flint, Michigan, that began in April 2014 dominated the news, refocusing America's attention to the issue of lead poisoning. In an attempt to cut costs, the city of Flint switched its water source from Lake Huron to the Flint River. Because of the corrosive nature of the water in the Flint River, and the lack of any anticorrosive treatment, the protective lining within the aged pipes of the city's water system was degraded. As a result, high levels of lead were released into the city's drinking water unbeknownst to residents.1
It is important to note that this incident was not an isolated one. It was legal to use lead pipes and solder in the United States until 1986 (Figure 1).1 Many of the pipes in use today across the country are composed of lead or contain lead solder and/or fixtures.1 Although political and regulatory mismanagement were partly responsible for the devastating levels of lead seen in the blood of the children of Flint, another factor contributing to the problem was an aging infrastructure, which exists not only in Flint but also across the country. In the past 20 years, lead has leached into the water supply of other cities, including Sebring, Ohio; Washington, DC; Greenville, North Carolina; and Jackson, Mississippi.2
It is important that the country's continuously aging infrastructure be kept in mind as a risk factor when patients are screened for lead exposure. In light of these events and so that primary care providers can deal as effectively as possible with the problem, this article reviews the epidemiology and presentation of lead poisoning, how to screen for the condition, and guidelines for its management.
In 2012, the Centers for Disease Control and Prevention (CDC) released new guidelines concerning lead. Previously, a blood level of lead at 10 mcg/dL or higher was considered a “level of concern” and resulted in case management. The CDC has now removed the phrase “level of concern,” and a reference level of 5 mcg/dL is currently used to identify children with high levels of lead in their blood.3,4
Any level of lead in the blood can cause negative effects.4-6 Blood levels of lead once thought to be safe are now known to be associated with intelligence deficits and behavioral and learning difficulties in children.6 The level of 5 mcg/dL is simply a statistical reference value for comparison with levels in the population.5 Since the introduction of this new reference level, more children are being identified with blood levels of lead that are too high. In Philadelphia, Pennsylvania, a study of the prevalence of high blood levels of lead in which this new reference value was used reported a 9-fold increase.7
Chronic lead toxicity is much more prevalent than acute lead toxicity. Lead toxicity in adults is more likely to be acute and related to an occupational exposure.8 Adults exposed at work typically inhale lead dust and fumes.9 Lead can cause problems at any age, but lead toxicity in children is of particular concern because of its long-term effects on the developing brain.6,8 The immature blood–brain barrier of children puts them at particularly high risk.9 Children younger than 3 years of age are at greatest risk for lead toxicity for 2 main reasons: They are at a critical stage in brain development, and they tend to put things in their mouth.8,9 Furthermore, the rate of lead absorption is 4 to 5 times higher in children than in adults, and the presence of an iron deficiency increases the risk for toxicity.4 Unborn fetuses are also vulnerable. Lead exposure during pregnancy can lead to miscarriage, stillbirth, and other complications of birth.6
High levels of lead are strongly associated with a low socioeconomic status.4,8 Children of low socioeconomic status are disproportionately at risk, partially because their diet tends to lack adequate amounts of calcium or iron.4,10 Therefore, the provider must recognize that a deficiency of calcium and/or iron is not only a problem in itself but also a marker of increased risk for lead toxicity. Because of decreased access to medical care, the families of these children are less likely to receive sufficient education about the primary prevention of lead poisoning.10 Residence in a low-income urban area increases the likelihood of exposure; typically, exposure to lead will occur in groups within neighborhoods.4 Parents exposed to lead in their occupation may bring lead dust or particles home with them on their clothing, thus exposing the household.4 Any person coming from another country, whether as an immigrant, refugee, or adoptee, is at increased risk for lead toxicity.4 Risk factors for chronic lead poisoning are summarized in Table 1.
Sources of lead
Familiarity with potential sources of lead enables providers to screen for lead in their patients properly and thoroughly. The disaster in Flint may be an extreme case, but the event has highlighted the aging infrastructure of America and the potential for future cases of poisoning with lead traced to old pipes, solder, and fixtures composed of lead. Lead piping is especially common in service lines that link street lines to residential homes.1 In general, treatment plants release water that is mostly lead-free, and many of these treatment plants also use anticorrosion chemicals that protect the inside of pipes down the line. However, the service lines that bring water into homes may contain lead or lead solder if the homes were built before 1986, and these service lines are expensive for homeowners to replace.11 The cost of fixing the nation's service lines would likely be in the billions of dollars, not to mention the millions more it would take to eliminate solder and fixtures composed of lead.1 To complicate matters further, the construction necessary to fix these lines can cause vibrations; as a result, pieces of lead material break off from the piping and enter the water supply.11
Even though lead toxicity due to leaching water pipes has been in the news recently, there are many other sources of lead poisoning that primary care providers should consider when they screen patients for risk factors. Lead-based paint has been banned but continues to be a risk in older homes.8 In fact, most cases of elevated blood levels of lead in recent years have resulted from peeling paint chips in old homes.1 Therefore, the age of a patient's residence is relevant information for discerning risk. After 1978, new homes were less likely to use lead-based paint.8 According to the CDC, lead-based paint or lead dust can be found in 24 million homes in the United States, with 4 million children living in these homes. Chipping paint or simple renovations (Figure 2) result in the formation of lead dust, which children can inhale or consume.12 The use of lead-based gasoline and paint for decades has contaminated the soil, creating another source of exposure.4
The paint in old homes is one of the more common sources of exposure to lead, but there are other sources as well. Although leaded gasoline is no longer used in the United States, it continues to be used in some developing countries.4,6 Products imported from other countries may contain lead, including foods and additives.8 Imported toys and toy jewelry may contain lead, and young children who put such toys in their mouth are exposed.4 The glaze on ceramic pottery can contain lead that contaminates food or drink placed within.4 Engaging in hobbies that involve the use of lead-based products or remodeling old homes can result in lead exposure.8 Parents who are exposed to lead through their occupation or hobby can carry lead dust and particles on their clothing, in turn exposing their children.4 Some folk remedies can also have a high lead content.4 Therefore, it is important for primary care providers to ask their patients about occupations, hobbies, and possible household exposure.