Lead poisoning:
From Detection To Primary Prevention

Public Health of Mexico

Spanish version: Intoxicación por plomo: de la detección a la prevención primaria

May-June 1995, Volume 37, No. 3, pp. 264-275

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Editor’s Note: For be of interest to our readers, we reproduce this work developed by the Environmental Health Committee of the American Academy of Pediatrics, published in Pediatrics 1993; 92 (1): 176-183.

The recommendations contained in this publication does not imply a kind of exclusive treatment and do not constitute a single measure of care. Variants can be appropriate, taking into account the circumstances of each case.

Since the last statement of the American Academy of Pediatrics (ANP) in 1987, has made considerable progress in the understanding of the magnitude and severity of lead poisoning in children.

1, Today it has been shown that blood lead levels that in some time were considered safe, are associated with deficits in intelligence quotient (IQ), behavioral disorders, growth retardation and hearing impairment.

2, In fact, according to the Department of Health and Human Services “the most important health problem in young children” 3 is lead poisoning. The speed at which scientific information is produced allows physicians know the importance of the effects of low levels of lead, changing medical practice.

 
 

In the past 30 years, the Centers for Disease Control (CDC) in the United States have changed the amount of blood lead levels in which lead poisoning occurs, from 60µg/dl in whole blood in the sixties, to 30µg/dl in 1975, and to 25µg/dl in 1985.

The motto of the CDC in 1991 “Preventing Lead Poisoning in Children” recommends reducing the level of community intervention to 10µg/dl, and set various levels of action (Table I).2 In 1987, the ANP postulated that levels lead above 25µg/dl were unacceptable for children. Currently, ANP has been established that the mismatch of cognitive function starts at levels above 10µg/dl, even if clinical symptoms are not noticeable.

At the end of the seventies the average blood lead levels in American children was 16µg/dl. The average blood lead level of children in the United States has decreased since 1976 thanks to the elimination of lead in gasoline and reducing the content of this metal in food, in a way that now level is 4-6µg/dl. However, there are still cases of acute lead poisoning and many children are still at high risk of exposure.

Childhood lead poisoning is preventable. In January 1991, the Public Health Service of the United States (US Public Health Service) launched a strategic plan to eradicate this problem, in which a cost-benefit analysis is included. This is a fundamental change of moving from primary detection and treatment of children exposed to give greater emphasis to the prevention of lead exposure. Although the detection and treatment of poisoned children remain essential, identifying the source of exposure and preventing subsequent exposures in the child and others in the future, becomes extremely important.

Meanwhile children are not in a lead free medium, lead screening in the blood remains basic to prevent serious illnesses and disability in the population. Pediatricians will continue to have a key role in the identification, treatment and eradication of lead poisoning.

Background

Lead poisoning has been known since antiquity. In the second century B.C. Dioscorides, a Greek physician, said “Lead makes you lose your head.” In 1897, in Brisbane, Australia, was first described lead poisoning in children due to paints based on this metal. The cause was associated with the painted railings on porches and in 1920 Brisbane City issued the first act aimed at preventing poisoning from lead-based paint minutes. In the United States lead poisoning caused by this type of painting was described in the first decade of the twentieth century. At first it was thought that if a child was recovering from the acute stage of the disease would not have consequences. In 1943 Byers and Lord refuted this in its report on 20 children who had survived acute lead poisoning: 19 showed clear manifestations of behavioral disorders or mental retardation. At the beginning of the seventies were conducted several studies to analyze this issue in depth and some showed cognitive problems associated with lead; however, these studies were controversial. Since then have been conducted more sophisticated research and with better designs and there is general consensus on the relationship between lead poisoning and cognitive functions.

Epidemiology

Lead poisoning is not exclusively a disease of children from ethnic minorities or low-income. In 1984, the year for which it have available the latest national estimates, 17% of US children had blood lead levels above 15µg/dl. Twelve million children lived in homes with lead-based paint and six million more in housing built before 1940, at the time when painting with higher concentrations of this metal was used. For white children, 7% of those who inhabited the suburbs of higher economic level and 25% of those from poorer communities had blood lead levels above 15µg/dl. The prevalence of black children in poor communities was 55%. Currently are conducting research to meet national estimates of lead levels in children. Although undoubtedly the children who are most at risk deserve all the attention, exposure to which are all social strata represent a problem in pediatric practice. No doubt that every child who lives in a house that has lead-based paint, is at risk and this type of housing, and other sources of exposure are located throughout the US territory and not, as previously thought, only in the cities of the Northeast. The age of the house, and not geographic location, is the best predictor of the presence of lead-based paint.

Toxicity

Lead is absorbed by ingestion or inhalation. The relationship between exposure and blood lead levels is a dynamic process in which the lead found in the blood represents the product of recent exhibitions, excretion and balance with other tissues. Children who are deficient in iron, protein, calcium and/or zinc, more easily absorb lead, most of which is stored in bones.

In high blood levels (over 70µg/dl), lead can cause encephalopathy and death. Encephalopathies survivors may face disabling sequelae for the rest of their lives, such as seizures and mental retardation. Lead poisoning affects practically all organs but mostly, at the central and peripheral nervous systems, kidneys and blood. Figure 1 shows the levels in which _ has been reported lead poisoning happens. This metal interferes with the enzymes that catalyze the formation of heme. Inhibits pre and postnatal growth and affects hearing acuity. Lead has been carcinogenic in laboratory animals and there is some evidence of its carcinogenic properties in workers exposed to this metal, but not in children.

Although damage has been reported in cognitive functions above of 10µg/dl levels, no threshold has been identified. The levels below this figure may cause no detectable impact on an individual child, but it can be significant in all children. Several studies have found an association between lead levels and intellectual performance of children. In an investigation this association resulted in an increase of 4 to 16% of children with serious deficiencies (less than 80 IQ). In this sample, it was expected that 5% of children had an IQ higher than 125; however, those who had elevated lead levels, none exceeded an IQ of 125.27, 28 This set of studies was examined by meta-analysis and found that the relationship between lead levels and deficiencies in IQ were remarkably consistent. In some studies it was found that for every increase of 10µg/dl of lead in blood, the average IQ in children decreased from four to seven points.

The effects of lead on cognitive functions are found after adjusting for factors such as level of intelligence of parents, socioeconomic status, education and iron deficiency. While in many of the previous studies on lead exposure at lower doses these factors were not handled properly, in investigations that have been published since 1979 these factors were taken into account. However, in some the effects of lead were demonstrated as in the study conducted by Hansen and collaborators with a group of Danish children in whom there was little variability among factors such as ethnicity, educational level and health care.

Moreover, have been also studied the effects of lead exposure in children from birth; Bellinger and collaborators followed up a cohort of children born in the Boston Hospital for Women. Most subjects came from middle class white families. Scores on the quotient of the Bayley Infant Development Scale, adjusted for covariance at the age of three years, were significantly lower in children who had blood lead levels in cordon higher than 10µg/dl (mean 14µg/dl). The blood lead levels at two years of age had a noticeable effect when the children reached 57 months of age. An increase in blood lead level of 10µg/dl in the range 0-25µg/dl at 24 months of age was associated with a decrease of 5.8 points in the Wechsler Intelligence Scale for Children-Revised. At 57 months old, was no longer apparent in development, the effect of prenatal exposure to lead. Several studies conducted in other populations have confirmed the association between levels of prenatal lead and score on the Bayley Infant Development Scale. In two other studies the potential importance of the effects of lead levels at 24 months of age on cognitive function in schools was confirmed. Lead exposures during the first two years of life are a constant risk of developmental delays and deficiencies in cognitive functions.

Recent evidence suggests that the effects of early exposure to lead may persist. Were classified a group of subjects for lead levels in teeth in the first and second years of primary and were followed into adulthood. In this study it was found that those with high levels of lead in teeth during childhood, had seven times more likely to not get to graduate from high school and six times more having scores in reading at least two degrees lower than expected, after adjusting for factors including socioeconomic status and parental IQ. Children also had a more marked absenteeism during the last school year, lower places, more limited vocabulary and lowest points on reasoning, plus slower reactions and poor visual-motor coordination.

Sources

Lead paint is the main source of childhood poisoning, because in so far as the paint deteriorates or falls, the floor and the house dust are contaminated, penetrating then the body of children when they put their hand to mouth.

Children also get to eat paint chips. By 1955 much of the white house paint had 50% lead and 50% linseed oil. In 1955, manufacturers adopted voluntarily standard 1% lead content in these paintings, although it continued to produce those with high lead. By law the proportion of lead allowed in paint was reduced in two stages, 1% in 1971 and, in 1977, to 0.06%. Lead paint for non-residential purposes is occasionally used to paint houses; is estimated to have been applied five million tons of lead in American homes. Moreover, probably 70% of homes built before 1960 have lead-based paint. But most dangerous are the 3.8 million households in which is deteriorating and peeling the lead based paint, and are inhabited by two million children under six years of age.

Unpolluted soil have lead concentrations below 50 parts per million (ppm); those that are contaminated in many urban areas exceed 200 ppm. Areas near the lead mines, industries that employ this metal and foundries can have higher levels of soil contamination (up to 60,000 ppm).56 In the United States, the use of leaded gasoline has launched a 30 million tons of lead into the air. The lead in house dust is a major source of exposure and its origin is in the paint, soil, and other sources.

Acid water of low mineral content may leach large amounts of lead from pipes welds. This is particularly feasible when the water has been sitting in the pipes for long periods, especially hot water. Approximately 16% of domestic water systems have lead levels that exceed the standard of 20µg/dl. In ancient water coolers, as well as in coffee makers, you can still find lead parts and solder. The brass fittings can also be contaminated with lead. Has been associated with contaminated water with lead with poisoning in formula-fed children.

Lead can also contaminate food; The metal found in the ground is absorbed by the plant roots and lead found in the atmosphere may fall on the leaves thereof. Lead can contaminate food during processing: cans with welded seams can contaminate the contents. In the United States has been replaced large-scale soldered cans with seamless aluminum containers; however, some large capacity cans from other countries, still have welded seams. Other forms of contamination exists, such as the use of glazed clay pottery (especially imported), certain “natural” calcium supplements and bright red and yellow paint of bread bags.

Other sources of lead are the traditional remedies of certain ethnicities (Azarcon and greta used by Hispanic and pay-loo-ah of Southeast Asia), cosmetics eyes (kohl of Muslims and the Hindus Surma) hobbies (eg, manufacture of glazed ceramics, artistic painting, target shooting) and accidental ingestion of small lead objects (eg fishing sinkers and curtains). Subjects who work in the industry that employs lead can cause lead dust on their clothes or expose their children when they allow them to visit their workplace. The identification of the source of lead exposure requires conducting a detailed medical history and generally a review of housing.

Preventing Lead Poisoning in Children

There are two basic ways to avoid poisoning: the elimination of lead in the environment and their detection or screening.

Elimination of lead in children’s environment

This is the most effective preventive measure. In cases of prior contamination, reducing the source of exposure involves the removal of lead or modifying the environment to prevent child comes in contact with the metal. The detection of poisoned children is useful to identify areas where environmental cleaning becomes more necessary and to prevent additional cases of exposure.

Detection of lead in children

Lead poisoning can be prevented by routine screening, followed by educational programs and case management. In 1988, the Agency for Toxic Substances and Disease Registry estimated that there were 250,000 children with blood lead levels of 25 ug / dl or more, of which only 12,000 could be identified thanks to screening programs. The measures that had been taken earlier in this respect proved to be inadequate. For example, in 1987-1990 less than 100 children with blood lead levels > 25µg/dl were detected annually in California. At the end of 1991 lead screening was decided in low-income children and in the first eight months of 1992, 707 cases were identified. Although average levels have declined throughout the United States, exposures to lead are still common resulting in concerning blood levels, including children from middle class families, which become much more common than rates of phenylketonuria, hypothyroidism and galactosemia.

In general lead poisoning is clinically imperceptible; even the more careful medical history can walk by many of the sources of lead exposure commonly known. The clinical history can not provide the accuracy of a blood test. In a research conducted recently in a suburban area where it was thought that would not present intoxication problems, 20% of children had blood lead levels of 10µg/dl or more.

Lead toxicity is related to both the dose and the exposure time. The role of the pediatrician is to really ensure that early detection and control of the exposure source can minimize the consequences on intellectual ability and behavior of each child. Parents can also be alarmed if pediatricians ignore their concern. It is necessary, as soon as possible, to establish adequate actions to detect and eliminate sources of exposure, in order to ensure the emotional well being of families.

Since the seventies it has resorted to measure blood erythrocyte protoporphyrin (EP) for lead detection Due to the low sensitivity in lower concentrations of lead in blood the CDC recommended in 1991, resorting to samples of venous blood lead instead of the PE. Testing can be done from a finger prick sample, which is more convenient to from a practical point of view. However, this type of sample is easily contaminated with environmental lead, increasing the false positive rate, such that a puncture sample exceeding 15µg/dl must be confirmed by another held in venous blood. Sample reliability puncture depends on the technique used and the problems will be obvious from the false positive rate. If samples have venous blood lead, they can be used for initial screening. Laboratory tests to determine lead levels require high capacity, which it can be acquired by participating in programs offered by CDC for that purpose.

The urgency and scope of the monitoring depend on the risk classification and lead levels in confirmed venous blood. The first step is to conduct a confirmatory test of lead levels in venous blood, which must be carried out immediately if the results of the detection exceed 70µg/dl; or 48 hours if the levels are between 45 and 69µg/dl; a week if the figures are between 20 and 44µg/dl; and in a month if they go from 15 to 19µg/dl (Table II). The individual monitoring of children begins with levels of 15µg/dl and medical assessment at 20µg/dl.

* Del CDC²

Management and treatment of blood lead levels of 10µg / dl or more

General principles

Table I shows the treatment and follow-up recommended by the CDC. The most important aspect of treatment is the removal of the source of exposure.

Patient Education

Providing information to parents about the nutritional sources of calcium, iron, zinc and ascorbate is important for all children, but particularly for those with blood lead levels of 10µg/dl or more. It is necessary to direct the attention of the parents towards the following measures in order to prevent their children from being exposed to lead: a) the removal of lead paint, as well as the renovation and remodeling of the house should be made by trained staff with experience without the family present and the house should be washed properly before re-inhabit; b) control the dust and paint chips; c) prevent children to ingest dust or foreign substances; d) if some job where lead is present is performed, change your clothes and wash before returning home; e) avoid the use of lead near the house for any purpose or hobby; f) wash your hands; and g) drinking water from the cold tap, using mainly this water in the preparation of the formula. In public health agencies, as well as the cdc statement “Preventing Lead Poisoning in Children” 2 there is information available to it.

Nutritional therapy

Children with deficiencies of iron, calcium, zinc and ascorbate are more willing to absorb and / or retain the the lead they ingest. Fat foods may promote absorption of lead. It is important to treat iron deficiency in all children, but especially in those with blood lead levels of 10µg/dl or more.

Environmental intervention

For blood lead levels of 15µg/dl or more, persistent, or 20µg/dl confirmed in venous blood, the patient will be referred in order to investigate environmental conditions in which is the child and improve them. It is necessary to inform the local public health agency and care must be coordinated. The public health agencies will keep the pediatrician informed about the results of the investigation.

Medical evaluation and management of blood lead levels confirmed 20µg/dl and more

Medical record

Physicians should inquire about the type of housing, paint conditionthe habit of pica, the use of own remedies from other ethnic groups, the use of glazed ceramics, hobbies and parents occupation.

Iron

Is necessary to evaluate iron deficiency in children with elevated blood lead levels because they may occur without any anemia. A serum ferritin level below 12µg/dl, or an abnormally low serum iron proportion with respect to the iron binding capacity, is the most specific indicator of iron deficiency.

Other diagnostic procedures

There are many tests for lead poisoning that are unnecessary. Abdominal radiography is useful only in cases of high intake of metal or unusual persistence of high levels of lead in blood. The lead lines on bone radiographs and basophilic stippling of erythrocytes may be associated with chronic exposure to high levels, but can also be negative even in the presence of severe exposure to lead. Because hair and nails testing are exposed to outdoor air pollution, resulting in an unreliable estimate of metal content in the body and are not recommended.

Monitoring tests

Serial measurements of the lead levels are those that provide the most reliable exposure information. The CDC guidelines (Table I) indicate recommendations regarding the frequency of follow-up tests in children with elevated blood lead levels.

Determinations in other children

Tests are necessary in children living in the same household as one that presents blood lead levels above 20 ug / dl, when you think that the source of exposure is in the house. If you detect lead contamination in other places such as kindergartens, schools, gambling sites or the houses of the people responsible for childcare will be necessary perform tests in children who are in that environment.

Chelation Therapy

Chelation is not recommended in cases with lead levels below 25µg/dl. It has been shown that blood lead level is reduced by chelation, but there are no data regarding prevention or improvement in cases of delay in cognitive functions. It is not a replacement measure to protect children from exposure source. If the doctor does not have experience in the treatment of lead poisoning, you should make another inquiry or refer the patient when considered appropriate chelation therapy and in areas where there are “programs against lead”.

There are four chelating agents: sodium salt of ethylene diamine tetraacetate (CaNaedta), BAL, D-penicillamine and succimer. Chelation accelerates lead urinary excretion. Most of the chelation attendant risks associated with the excretion, at the same time as lead, of base metals (especially calcium, magnesium and zinc). Penicillamine-D causes the same side effects as other penicillins. The bal and succimer are mercaptans and bal and CaNaedta are nephrotoxic.

The common practice has been to submit to chelation therapy to children with blood lead levels of 45µg/dl or more, and to monitor and consider the possibility of using this therapy in cases where levels of 25µg/dl or más. 65 in blood lead levels below 70µg/dl when chelation therapy is justified the following products are used in children: CaNaedta, D-penicillamine and succimer. D-Penicillamine is not cataloged for use in lead poisoning and description of succimer specifies its use in cases where levels exceed 45µg/dl. When blood levels are 70µg/dl or more, usually the treatment that combines CaNaedta and bal is recommended. When your child shows signs of encephalopathy treatment should be applied in an intensive care unit. Chelating agents can significantly stimulate the absorption of lead from the gastrointestinal tract. These therapies can be dangerous if the child is not removed from the lead exposure source exposure is possible that hospitalization is required in the early stages of treatment, when they have not established actions both to prevent exposure to metal, as for ensure absolute treatment compliance and monitoring. For this reason it is more appropriate to give orally the succimer agents and D-penicillamine in outpatients while no actions are taken to reduce exposure to lead in which the child is.

Conclusions

Childhood lead exposure remains a public health problem; is not an disease of poverty or ethnic minorities, nor is it the result of faulty parenting practices. The “problem of lead” has been reduced, but has not been resolved, despite laws banning lead in gasoline and paint, the risks of exposure persist. The problem has not been fully understood, so that an easy solution is impossible. Will be expensive the joint efforts of the public health institutions, environmental protection, housing and pediatricians, but the only way to eradicate this preventable disease. Until lead poisoning is eliminated, screening programs will still be needed. The above recommendations are focused on the need for more acceptable detection methods and monitoring programs and more radical sanitation.

Recommendations of the ANP for pediatricians

1. Previous guidance: Pediatricians should guide and educate parents preventively providing information
   about:
   • Foster a safe environment and safe occupational practices in such a way that parents can prevent lead exposure to their children. This would include metal contact during the performance of a hobby or by
     Contaminated work clothes.
   • The risk involved in the habit of the children in put their hands in their mouths and other similar sources of lead exposure (paint, house dust, floor, drinking water, etc.)
   • Guidance on general prevention measures (hygiene, nutrition).
   • The high risk to children with developmental problems that often have the habit of pica and, given their
     conditions are less suitable for risk losing any cognitive or behavioral skills.
2. Detection of Lead in Blood: The  pediatric services staff should guide further their activities towards
   screening of children exposed to lead. The blood lead screening should be part of routine health monitoring in children, which can be achieved by facilitating the access of children to health services. Because lead is ubiquitous in the environment in the United States, this screening should begin at age 9-12 months and, if possible, be repeated at 24 months of age. CDC has established the possibility of low-risk communities that do not require screening; however they have not developed guidelines to determine the risk of a community. In so far that more data become available, it may become apparent that there are places where it is most appropriate the selective detection of children that routine. In general there are no nationwide properly qualified laboratories to detect each child; however, the need to promote detection should generate these resources.
3. Indications of clicnical order for lead testing: it is necessary to conduct a recount of possible exposure to lead in themedical supervision visits at ages from six months to six years, with specific questions (Table III). Those concerning risks identify children who are at high risk and whose blood lead levels should be checked more frequently (Table I). It is necessary to consider lead poisoning to evaluate the following statements, whether because lead can cause infections or conditions that may be associated with increased intake of lead: developmental delay; learning disabilities; behavior disorders; autism; seizures; anemia due to iron deficiency; infections due to intestinal parasitosis; problems of language and hearing; encephalopathy; recurrent vomiting; and recurrent abdominal pain.

TABLE III Estimated risk of lead exposure in high doses : survey shows*

Your child… 1. Live or regularly visit homes in which the paint is peeling or that were built before 1960? This may include kindergartens, schools, the home of the caregiver or relatives, etcetera. 2. Live in or regularly visit a house built before 1960, recently remodeled, or with a renewal in progress or plans? 3. Have any sibling, playmate or housing being followed or treated for lead poisoning (ie, blood lead>15µg/dl)? 4. Lives with an adult whose job or hobby involves exposure to lead? 5. Live near a smelter, battery recycling plant or other industry that release lead?

* From CDC²

Recommendations to the Government

1. Monitoring through public health agencies and housing. Lead testing carried out in children become void when there are no public health programs that ensure an investigation of the environmental conditions and the monitoring of each case. The government should establish and fund these programs.

The lead screening programs in high-risk areas should be integrated with other public health activities.

2. Environmental sanitation. The ANP is in favor of the measures and actions that the environmental protection agencies and housing carried out to remove lead both residential areas and other areas where children are at risk of exposure. Is necessary to have inspectors and workers with the training and certification required, as well as the approved training programs, in order not to create more lead-related risks.

Health departments in some states have lists of experts and certified contractors. Moreover, it is necessary to develop economic and safe technologies to eliminate lead, in a way that basic prevention actions are convenient from the point of view of cost-effectiveness.

3. Reduction of new sources of lead contamination in the environment. The ANP is in favor of any legislation through which it seeks to reduce the entry of lead in the environment in general.
4. Identification of areas at risk of lead contamination. It requires more information about the percentages of elevated blood lead levels in specific communities. The ANP encourages the government to carry out research aimed at small areas to determine if lead screening is required, as well as whether the actions to eradicate lead have been positive. A better understanding of the distribution of lead poisoning would enable to perform actions of successful screening.
5. Research to develop more effective lead tests. There is an urgent need for tests lead levels and poisoning more effective and less invasive. The ideal test would be applied routinely in outpatient, be economical, rapid, sensitive, resistant to contamination and reliable.
6. Lead poisoning should be part of the conditions that are reported to CDC. The ANP is in favor of laboratories nationwide, notify lead poisoning.
7. Promoting clinical studies. The ANP recommends conducting further research to determine the degree of effectiveness of various strategies to prevent and treat lead poisoning, and the comparison of methods to eliminate this metal from housing and conduct controlled clinical trials with chelators agents, with long-term follow-up.
8. Periodic updating of the recommendations concerning the screening. It is necessary for CDC to conduct research on the effectiveness of screening for lead and to be aware the bibliographic production about it, in order to ensure that screening is carried out in a way that ensures greater protection from the point of view of public health and, moreover, be less invasive and the best from the point of view of cost-effectiveness. In particular, it is necessary to study and assess the issues of risk, as well as recommendations on the monitoring frequency. The recommendations for screening should be reassessed especially in the light of research that have been published since the 1991 guidelines.
9. Adequate funding for screening tests. The Department of Health and Human Services should reconsider its decision to continue using outdated erythrocyte protoporphyrin test in children who have Medicaid insurance and, instead, cover the costs of testing lead in blood. The  Early Periodic Screening, Diagnosis and Treatment Program should include blood lead test as an element separately invoiced, nationwide.

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