Influence of blood lead on the ability and attainment of children in Edinburgh

Congenital heart disease and cardiac surgery in childhood: effects on cognitive function and academic ability

OBJECTIVE

To evaluate changes in cognitive and academic functioning following cardiac surgery in children with congenital heart disease.

DESIGN

A prospective cross sectional study in which patients were assessed immediately before treatment and 12 months later.

PATIENTS

Three groups of children aged 3.5-17 years: a group with congenital heart disease awaiting surgery, another awaiting bone marrow transplantation, and a healthy comparison group.

MAIN OUTCOME MEASURES

Intelligence quotient and measures of academic attainment, evaluated with the British Ability Scales.

RESULTS

Preoperatively, children with cyanotic lesions showed deficits in comparison with those with acyanotic lesions. Postoperatively, children with cyanotic lesions showed a deterioration in performance and achieved significantly lower scores than those with acyanotic lesions. While there were significant differences between the congenital heart disease and bone marrow transplantation groups preoperatively, these were no longer apparent at follow up.

CONCLUSIONS

In contrast to previously published findings, the present results suggest that cardiac surgery does not result in early postoperative improvements in cognitive function for children with congenital heart disease. The nature of the cardiac lesion continues to affect cognitive and academic performance, even after surgery.

The Christchurch Health and Development Study: review of findings on child and adolescent mental health

OBJECTIVE

This paper provides an overview of the Christchurch Health and Development Study (CHDS) and a summary of findings relating to child and adolescent mental health.

METHOD

The CHDS is a longitudinal study of a birth cohort of 1265 children born in the Christchurch (New Zealand) urban region during mid 1977. This cohort has now been studied from birth to age 21.

RESULTS

The paper examines the ways in which the study has been able to examine a wide range of issues. Key issues examined include: (i) measurement of disorder (respondent effects; dimensionality; scales vs categories); (ii) prevalence and treatment of disorder; (iii) stability and continuity of disorders; (iv) the contribution of risk and aetiological factors (e.g. lead exposure, parental divorce, child abuse, family adversity, sexual orientation) to psychosocial adjustment; and (v) the psychosocial consequences of mental health problems in adolescence.

CONCLUSIONS

The study findings illustrate the many advantages of a longitudinal study, such as the CHDS, in providing methodologically sound, theoretically relevant and cost effective research that caters for the interests of multiple end-users including the scientific community, clinicians and applied policy makers.

Cognitive deficits associated with blood lead concentrations <10 microg/dL in US children and adolescents

OBJECTIVE

Lead is a confirmed neurotoxicant, but the lowest blood lead concentration associated with deficits in cognitive functioning and academic achievement is poorly defined. The purpose of the present study was to examine the relationship of relatively low blood lead concentrations-especially concentrations <10 micrograms per deciliter (microg/dL)--with performance on tests of cognitive functioning in a representative sample of US children and adolescents.

METHODS

The authors used data from the Third National Health and Nutrition Examination Survey (NHANES III), conducted from 1988 to 1994, to assess the relationship between blood lead concentration and performance on tests of arithmetic skills, reading skills, nonverbal reasoning, and short-term memory among 4,853 children ages 6-16 years.

RESULTS

The geometric mean blood lead concentration for children n the study sample was 1.9 microg/dL; 172 (2.1%) had blood lead concentrations > or =10 microg/dL. After adjustment for gender, race/ethnicity, poverty, region of the country, parent or caregiver's educational level, parent or caregiver's marital status parent, serum ferritin level, and serum cotinine level, the data showed an inverse relationship between blood lead concentration and scores on four measures of cognitive functioning. For every 1 microg/dL increase in blood lead concentration, there was a 0.7-point decrement in mean arithmetic scores, an approximately 1-point decrement in mean reading scores, a 0.1-point decrement in mean scores on a measure of nonverbal reasoning, and a 0.5-point decrement in mean scores on a measure of short-term memory. An inverse relationship between blood lead concentration and arithmetic and reading scores was observed for children with blood lead concentrations lower than 5.0 microg/dL.

CONCLUSION

Deficits in cognitive and academic skills associated with lead exposure occur at blood lead concentrations lower than 5 microg/dL.

Lead intoxication during intrauterine life and lactation but not during adulthood reduces nucleus accumbens dopamine release as studied by brain microdialysis

Environmentally relevant levels of lead (Pb) have been demonstrated to have a neurotoxic action, especially on children. In this study, Long-Evans rats were continuously exposed to Pb acetate in drinking water from early gestational days (2-6) or from 28 days of age. At the 13th week of age, the functional activity of the nucleus accumbens (NAC) dopaminergic system was studied by means of transversal microdialysis. Neither Pb treatment regimen modified dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) extracellular concentrations, with respect to control rats. However, neuronal depolarisation, induced by perfusion with 60 mM KCl, increased extracellular DA levels to a significantly minor degree in rats exposed to Pb during the intrauterine life, with respect to both control and adult Pb treated rats. The in utero treated rats also responded with a lower DA release to amphetamine (1 mg/kg ip) administration. On the other hand, no difference in NAC DA level was found amongst treatment groups in response to different concentrations of the D(2)-D(3) dopaminergic agonist quinpirole, locally administered by means of inverse dialysis. These data indicate a preferential impairment of NAC DA synthesis and/or release in rats exposed to Pb acetate during their intrauterine life.

Exposure to arsenic and lead and neuropsychological development in Mexican children

This cross-sectional study examined the effects of chronic exposure to lead (Pb), arsenic (AS) and undernutrition on the neuropsychological development of children. Two populations chronically exposed to either high (41 children) or low (39 children) levels of As and Pb were analyzed using the Wechsler Intelligence Scale for Children, Revised Version, for México (WISC-RM). Geometric means of urinary arsenic (AsU) and lead in blood (PbB) were 62.9+/-0.03 (microgAs/g creatinine) and 8.9+/-0.03 (microg/dl) for the exposed group and 40.2+/-0.03 (microgAs/g creatinine) and 9.7+/-0.02 (microg/dl) for the reference group. The height for age index (HAI) was used as an indicator of chronic malnutrition and sociodemographic information was obtained with a questionnaire. Lead and arsenic were measured by atomic absorption spectrophotometry. Data on full, verbal, and performance intelligence quotients (IQ) scores, long-term memory, linguistic abstraction, attention span, and visuospatial organization were obtained through the WISC-RM. After controlling for significant potential confounders verbal IQ (P<0.01) decreased with increasing concentrations of AsU. The HAI correlated positively with full-scale and performance IQ (P<0.01). Higher levels of AsU were significantly related to poorer performance on WISC-RM factors examining long-term memory and linguistic abstraction, while lower scores in WISC-RM factors measuring attention were obtained at increasing values of PbB. Our results suggest that exposure to As and chronic malnutrition could have an influence on verbal abilities and long-term memory, while Pb exposure could affect the attention process even at low levels.

Interactions between environmental lead exposure and sociodemographic factors on cognitive development

A total of 375 children who lived in Port Pirie, South Australia, and surrounding towns were followed from birth to ages 11-13 y. Possible interactions between lifetime average blood lead concentration and sociodemographic factors (including gender, parents' occupational prestige [as a surrogate of socioeconomic status], quality of home environment, and maternal intelligence quotient) on children's intelligence quotients were examined. Although no statistically significant interaction between blood lead concentration and any of these covariates was found, the results suggested that-after adjustment for a wide range of covariates--children from socially disadvantaged backgrounds (adjusted regression coefficient = -9.6 intelligence quotient points per log unit of blood lead concentration; 95% confidence interval = -2.5, -17.7) were more sensitive to the effects of lead than those of a higher socioeconomic status (adjusted regression coefficient = -2.9; 95% confidence interval = 3.8, -9.6). In addition, girls (adjusted regression coefficient = -7.4; 95% confidence interval = -1.7, -13.1) were more sensitive to the effects of lead than boys (adjusted regression coefficient = -2.6; 95% confidence interval = 2.9, -8.0). These results were basically consistent with our findings observed at ages 2 y, 4 y, and 7 y.

Lead absorption and psychological function in Zagreb (Croatia) school children

A cross-sectional study was performed on 275 pupils from the third and fourth grade of three elementary schools (three urban areas with different traffic conditions) in Zagreb. Lead exposure was environmental, mostly through leaded gasoline. The difference in traffic density around the schools was consistent with biological indicators of lead absorption. The aim of the study was to clarify the relationship between characteristic biological indicators of lead absorption including indicators of hematological status with some psychological functions. Lead absorption in pupils was relatively low (mean blood lead: 70.8 +/- 17.88 microgram/L). Pupils' socio-economic status was evaluated by parents' education. The results obtained indicate that gender and school were associated with both biological and psychological variables. After adjusting for age, parental education, and gender, lead appears to have no association with cognitive or psycho-motor measures. The nonstandardized regression coefficients for blood lead-as a measure of the size of lead effect on VIQ, NIQ, and IQ-were -0.016, -0.031, and -0.025, respectively, all nonsignificant.

Clinical lead poisoning in England: an analysis of routine sources of data

OBJECTIVE

To examine the occurrence of clinical lead poisoning in England based on routine sources of data.

METHODS

Three routine data sources were examined, over different periods according to availability of data: (a) mortality for England, 1981-96; (b) hospital episode statistics data for England, for the 3 years 1 April 1992-31 March 1995; (c) statutory returns to the Health and Safety Executive under the reporting of injuries, diseases, and dangerous occurrences regulations (RIDDOR), also for the period 1 April 1992-31 March 1995. Also, analyses of blood lead concentrations carried out by the Medical Toxicology Unit, Guy's and St Thomas' Hospital Trust in London during the period 1 January 1991-31 December 1997 were examined. The analyses were performed both for industrial screening purposes and in response to clinicians' requests where lead poisoning was suspected. This is one of several laboratories carrying out such analyses in the United Kingdom.

RESULTS

One death, of a 2 year old girl, was coded to lead poisoning in England during 1981-96. Analysis of hospital episode statistics data identified 83 hospital cases (124 admissions) over 3 years with any mention of lead poisoning, excluding two with admissions dating from 1965 and 1969. For these 83 cases the median hospital stay per admission was 3 days (range 0-115 days). Five were coded as having received intravenous treatment. Further clinical details of these cases beyond what is routinely recorded on the hospital episode statistics database were not available, except for blood lead concentrations in cases also identified on the Medical Toxicology Unit database. Eighteen cases (22%) were below 5 years of age of whom 10 (56%) came from the most deprived quintile of electoral wards. There was evidence to suggest spatial clustering of cases (p = 0.02). Six occupational cases were reported under RIDDOR in England during the period of study, two of whom were identified on the hospital episode statistics database. One further occupational case was identified on hospital episode statistics. Blood lead analyses for 4424 people carried out by the Medical Toxicology Unit (estimated at about 5% of such analyses in England over 7 years) found that among 547 children aged 0-4, 45 (8.2%) had a blood lead concentration in excess of 25 micrograms/dl, the action level in the United Kingdom for investigation, or removal of environmental sources of lead. At all ages, there were 419 (9.5%) such people, including 106 adults with no mention of industrial exposure.

CONCLUSIONS

Both mortality and hospital admission ascribed to lead poisoning in England are rare, but cases continue to occur and some, at least, seem to be associated with considerable morbidity. Lead poisoning was confirmed as a probable cause of clinical signs and symptoms in only a small proportion of those in whom a blood lead concentration was requested. Where indicated, appropriate remedial action for the safe removal of environmental sources of lead should be taken.

Determinants of blood lead levels in Saudi Arabian schoolgirls

Blood lead levels were measured in 538 girls aged 6 to 12 years who attended primary public schools in Riyadh, Saudi Arabia. Of the 538 screened children, 24.4% had blood lead levels > or =10 microg/dL, the Centers for Disease Control's level of concern. Variation in the blood lead levels was investigated with respect to a number of risk factors. The main determinant of blood lead levels was the regional location of the school. Pupils who attended schools located in the Central region of Riyadh had significantly higher blood lead concentrations than did pupils who attended schools in the peripheral areas. This is most likely to be due to the heavy vehicular emissions in the Central region. Other variables such as low family income, grade, and application of kohl to the child's eyes and/or umbilicus at birth were also contributors to the blood lead levels. These observations emphasize the importance of health education programs to promote the reduction of lead exposure in the general population.

Relationship between lead mining and blood lead levels in children

The authors studied blood lead levels of 226 randomly selected children, aged 6-92 mo, who lived in either a lead-mining area or a nonmining area, and 69 controls. The authors sought to determine to what extent mining activities contributed to blood lead levels in the children. The mean blood lead levels in the study and control groups were 6.52 microg/dl and 3.43 microg/dl, respectively. The corresponding proportions of children with elevated blood lead levels were 17% and 3%. Soil and dust lead levels were up to 10 times higher in the study than the control group. Elevated blood lead levels appeared to result from exposure to both lead-mining waste and lead-based paint. Mining waste was the cause of the higher prevalence of elevated blood lead levels in these children.

Cognition in children does not suffer from very low lead exposure

We studied the relationship between exposure to lead and memory and attention in children. Participants were 313 boys aged 9 to 12 years who attended special education schools in the Netherlands. Children whose possible attentional or memory problems were obviously due to causes other than lead contamination were excluded from the study. Cognition was assessed by extensive theory- based testing. Blood lead concentration was measured to assess body lead burden. Possible confounding factors that might affect blood lead level and/or cognitive functioning were assessed. Blood lead levels were higher in children with lower socioeconomic status and in children with more hand-to-mouth behavior, and varied seasonally, with higher values in spring and summer. The mean blood lead level was 44.4 microgram lead per liter blood, which is considered low. Only 2% of the children showed a slightly higher blood lead level than the American safety standard. To obtain robust measures of cognitive aspects, we performed a factor analysis. The results showed that blood lead level did not influence any of the cognitive factors. Therefore this study, despite being designed to maximize the chance of finding an effect in asymptomatic children, does not support a relationship between lead at very low doses (below 100 micrograms/liter blood) and cognition in schoolchildren.

Low-level lead exposure selectively enhances dopamine overflow in nucleus accumbens: an in vivo electrochemistry time course assessment

Exposures to even very low levels of lead (Pb) alter behavioral and neurochemical functions. The current study was based on the hypothesis that excess synaptic dopamine (DA) availability may contribute to such disturbances and that the mesolimbic DA projection is more sensitive than the nigrostriatal system to Pb-induced DA-based alterations. In vivo electrochemical measurements of potassium chloride-evoked DA overflow and clearance were compared in dorsal striatum (STR) (nigrostriatal system) and nucleus accumbens (NAC)(mesolimbic system) of male rats after 11 weeks or 11 months of postweaning exposure to 0, 50, or 150 ppm Pb acetate drinking solutions. Pb increased evoked DA overflow selectively in NAC, with biphasic effects at 11 weeks, including increases greater than 400% at 50 ppm and concentration-related effects up to 265% of control at 11 months. Considered relative to 11-week control levels, continued exposure tended to attenuate the magnitude of Pb-related increases in DA overflow in NAC. Pb decreased clearance time in both brain regions, with these effects markedly augmented across time. These changes in DA function were observed at blood Pb values of only 15-16 micrograms/dl, underscoring their environmental relevance. The current findings support the hypothesis of excess DA availability as a mechanism of Pb-induced behavioral alterations and of a particular vulnerability of mesolimbic DA systems (NAC) to such effects. They also suggest that different mechanisms underlie Pb-related changes in amplitude and clearance and confirm previous reports of regional differences of DA systems in response to Pb exposure.

Lead foreign body ingestion in children

Foreign body ingestion is seen commonly in paediatric surgical practice and the vast majority of ingested foreign bodies will pass spontaneously once they have made their way into the stomach. Lead foreign body ingestion in children represents a special case in view of the potential for acute lead intoxication secondary to dissolution and absorption of the ingested lead. Lead dissolves poorly in physiological solutions with the exception of the acid environment of the stomach. We report a case of a 4-year-old child who ingested a lead sinker which was removed from the stomach by emergency endoscopy. This case stimulated a review of the relevant literature and the formulation of a management plan for lead foreign body ingestion in children. The principles of this management plan are observation of the child in hospital and use of a protein pump inhibitor until the foreign body has passed out of the stomach.

Lead levels in deciduous teeth of children in Bahrain

To determine lead exposure among children in Bahrain, a total of 280 shed deciduous whole teeth were collected from 269 children. Teeth were analyzed for lead concentrations using atomic absorption spectrophotometry with electrothermal atomization. Children were between 5 and 15 years old. The study period extended from July 1993 to April 1994. The study showed that the overall mean tooth-lead level was 4.3 micrograms/g dry weight with a range of 0.1-60.8 micrograms/g dry weight. The cumulative frequency distribution revealed that 35% of the teeth had a lead concentration of more than 4 micrograms/g dry weight. The tooth-lead concentrations differed according to the tooth type age. The child's sex, nationality, area of residence and socio-economic status had no impact on tooth-lead level. In conclusion, lead is present in toxic concentrations in 35% of the teeth of the children studied. Urgent measures are needed to eliminate lead from gasoline, paint and other sources in the environment.

Blood lead in Uruguayan children and possible sources of exposure

Blood samples and questionnaire background data were collected from 96 children (age 2-14 years) living in urban, suburban, or rural areas with varying traffic intensity and industrial lead pollution in Uruguay. Spot samples of tap water were collected from the homes of 44 children, and samples of top soil were taken from seven areas. Samples of air-borne dust were collected in central and suburban Montevideo. Blood lead concentrations (B-Pb) in children ranged between 47 and 191 (mean 96) micrograms/L and exceeded in 36% of the children 100 micrograms/L, the intervention level adopted by the United States Centers for Disease Control. Lead in tap water ranged from 0.2 to 230 (mean 15) micrograms/L and exceeded in 39% of the samples the maximum level recommended by WHO, 10 micrograms/L. Lead pipes were used in parts of the water supply systems. Lead in air varied between different locations from 0.15 to 1.7 micrograms/m3, highest in the very center of Montevideo. The median soil lead ranged from 6 to 2100 micrograms/g and was highest in industrially polluted areas. At multiple regression analysis, B-Pb was significantly associated only with age (P = 0.032) and traffic intensity at school (P = 0.045). No significant impact on B-Pb of lead in water or soil could be established.

Is lead in tap water still a public health problem? An observational study in Glasgow

OBJECTIVE

To assess the relation between tap water lead and maternal blood lead concentrations and assess the exposure of infants to lead in tap water in a water supply area subjected to maximal water treatment to reduce plumbosolvency.

DESIGN

Postal questionnaire survey and collection of kettle water from a representative sample of mothers; blood and further water samples were collected in a random sample of households and households with raised water lead concentrations.

SETTING

Loch Katrine water supply area, Glasgow.

SUBJECTS

1812 mothers with a live infant born between October 1991 and September 1992. Blood lead concentrations were measured in 342 mothers.

MAIN OUTCOME MEASURES

Mean geometric blood lead concentrations and the prevalence of raised tap water lead concentration.

RESULTS

17% of households had water lead concentration of 10 micrograms/l (48.3 nmol/l) or more in 1993 compared with 49% of households in 1981. Tap water lead remained the main correlate or raised maternal blood lead concentrations and accounted for 62% and 76% of cases of maternal blood lead concentrations above 5 and 10 micrograms/dl (0.24 and 0.48 mumol/l) respectively. The geometric mean maternal blood lead concentration was 3.65 micrograms/dl (0.18 mumol/l) in a random sample of mothers and 3.16 micrograms/dl (0.15 mumol/l) in mothers whose tap water lead concentrations were consistently below 2 micrograms/l (9.7 nmol/l). No mother in the study had a blood lead concentration above 25 micrograms/dl (1.21 mumol/l). An estimated 13% of infants were exposed via bottle feeds to tap water lead concentrations exceeding the World Health Organisation's guideline of 10 micrograms/l (48.3 nmol/l).

CONCLUSIONS

Tap water lead and maternal blood led concentrations in the Loch Katrine water supply area have fallen substantially since the early 1980s. Maternal blood lead concentrations are well within limits currently considered safe for human health. Tap water lead is still a public health problem in relation to the lead exposure of bottle fed infants.

Low lead levels stunt neuronal growth in a reversible manner

The developing brain is particularly susceptible to lead toxicity; however, the cellular effects of lead on neuronal development are not well understood. The effect of exposure to nanomolar concentrations of lead on several parameters of the developing retinotectal system of frog tadpoles was tested. Lead severely reduced the area and branchtip number of retinal ganglion cell axon arborizations within the optic tectum at submicromolar concentrations. These effects of lead on neuronal growth are more dramatic and occur at lower exposure levels than previously reported. Lead exposure did not interfere with the development of retinotectal topography. The deficient neuronal growth does not appear to be secondary to impaired synaptic transmission, because concentrations of lead that stunted neuronal growth were lower than those required to block synaptic transmission. Subsequent treatment of lead-exposed animals with the chelating agent 2,3-dimercaptosuccinic acid completely reversed the effect of lead on neuronal growth. These studies indicate that impaired neuronal growth may be responsible in part for lead-induced cognitive deficits and that chelator treatment counteracts this effect.

Lifetime exposure to environmental lead and children's intelligence at 11-13 years: the Port Pirie cohort study

OBJECTIVE

To examine the association between environmental exposure to lead and children's intelligence at age 11-13 years, and to assess the implications of exposure in the first seven years of life for later childhood development.

DESIGN

Prospective cohort study.

SUBJECTS

375 children born in or around the lead smelting town of Port Pirie, Australia, between 1979 and 1982.

MAIN OUTCOME MEASURE

Children's intelligence quotient (IQ) measured at 11-13 years of age.

RESULTS

IQ was inversely associated with both antenatal and postnatal blood lead concentrations. Verbal, performance, and full scale IQ were inversely related to blood lead concentration with no apparent threshold. Multivariate analyses indicated that after adjustment for a wide range of confounders, the postnatal blood lead concentrations (particularly within the age range 15 months to 7 years) exhibited inverse associations with IQ. Strong associations with IQ were observed for lifetime average blood lead concentrations at various ages. The expected mean full scale IQ declined by 3.0 points (95% confidence interval 0.07 to 5.93) for an increase in lifetime average blood lead concentration from 0.48 to 0.96 mumol/l (10 to 20 micrograms/dl).

CONCLUSION

Exposure to environmental lead during the first seven years of life is associated with cognitive deficits that seem to persist into later childhood.

The Fremantle Lead Study

OBJECTIVE

To ascertain blood lead levels in a sample of preschool children from Framantle, Western Australia, and to correlate these with possible risk factors.

METHODOLOGY

The study was a cross-sectional prevalence survey of 120 children from day-care centres and 44 hospital inpatients. Blood lead and ferritin levels were determined and a risk factor questionnaire was completed by parents.

RESULTS

Of the 164 children 25.6% had lead levels above the NH&MRC goal (< 10 micrograms/dL). Nine of 133 (6.7%) had ferritin levels below 10 micrograms/L suggesting iron deficiency. Excessive blood lead concentrations as defined by the NH & MRC (> 9 micrograms/dL) related to: child's presence during house renovation (OR 3.35, P = 0.007, 95% CI 1.39-8.81); Aboriginality (OR 6.4, P = 0.008, 95% CI 1.6-24.9), and, in the 9-24 month age group, inversely to distance between home and a road carrying > 7000 vehicles/day (r -0.56, P = 0.009, n = 24).

CONCLUSIONS

A group of Fremantle children with unacceptably high blood lead levels has been identified. Renovation of older housing and Aboriginality are important risk factors.

Adverse health effects of lead at low exposure levels: trends in the management of childhood lead poisoning

An extensive database has provided a direct link between low-level lead exposure during early development and deficits in neurobehavioral-cognitive performance evident late in childhood through adolescence. These consistent studies have demonstrated the presence of a constellation of neurotoxic and other adverse effects of lead at blood lead (BPb) levels at least as low as 10 micrograms/dl). Federal agencies and advisory groups have redefined childhood lead poisoning as a BPb level of 10 micrograms/dl. Before discussing some of these studies in greater detail, the pervasiveness of this entirely preventable disease today in millions of American children must be recognized.

Lead in inner-city soil and its possible contribution to children's blood lead

This study was designed to assess distribution and sources of lead in inner-city soils in Washington, D.C. Duplicate soil samples were collected randomly from 239 unpaved front yards of homes in Washington, D.C. Soil samples were collected 1 m from the houses. Lead concentration in soil was determined by flame atomic absorption spectrophotometry. Presence of lead detected in soil was correlated and traced to the anticipated source of origin. A significantly high concentration of lead was present in inner-city soils. Areas of the city in which the highest lead concentrations were found (Wards 1, 4, 5, 6, 7, 8) were determined to contain a large number of residents who had attained lower education levels than most residents in the remaining wards. It was concluded that lead concentration in inner-city soil plays a significant role in the incidence of lead poisoning in children in the District of Columbia and that paint is the main source of soil lead. Demographic characteristics of the residents appeared to enhance the distribution of lead poisoning.

delta-Aminolaevulinic acid dehydratase as an index of lead toxicity. Time for a reappraisal?

delta-Aminolaevulinic acid dehydratase activity is traditionally accepted as the most sensitive measurable biological index of lead toxicity. We have measured delta-aminolaevulinic acid dehydratase activity and blood lead concentration in 47 healthy controls (A), 42 iron deficient patients (B) and 38 occupationally exposed to lead subjects (C). Blood lead levels [mean (SD)] did not differ between groups A and B [0.51 (0.21) and 0.43 (0.19) mumol L-1, respectively] while those of group C [2.28 (0.56) mumol L-1 were significantly higher (P < 0.001) as compared to the controls. delta-Aminolaevulinic acid dehydratase activity [mean (SD)] was significantly increased [3599 (1909) mumol L-1 h-1] in group B and decreased in group C [1052 (532) mumol L-1 h-1] as compared to the controls [2034 (446) mumol L-1 h-1] (P < 0.001). There was a significantly negative correlation of logarithm of delta-aminolaevulinic acid dehydratase with lead in both groups B (P < 0.05) and C (P < 0.001) but not in group A (P = 0.1). delta-Aminolaevulinic acid dehydratase activity had a high specificity (100%) but a low sensitivity (37%) as an index of toxic lead exposure. According to our data the value of delta-aminolaevulinic acid dehydratase measurement in the diagnosis of lead intoxication is doubtful in cases with low blood lead levels, while in the presence of iron deficiency its reliability is further reduced, since low blood lead levels may be falsely predicted. delta-Aminolaevulinic acid dehydratase activity should be restricted only to monitoring cases with moderate or severe lead poisoning.

Management of childhood lead poisoning: clinical impact and cost-effectiveness

OBJECTIVES

No consensus exists regarding the preferred treatment of childhood lead poisoning. The authors used decision analysis to compare the clinical impacts and cost-effectiveness of four management strategies for childhood lead poisoning, and to investigate how effective chelation therapy must be in reducing neuropsychologic sequelae to warrant its use.

METHODS

The model was based on a 2-year-old child with moderate lead poisoning [blood lead level 1.21 to 1.88 mumol/L (25 to 39 micrograms/dL)]. The following strategies were compared: 1) no treatment; 2) EDTA provocation testing, followed by chelation if testing is positive (PROV); 3) penicillamine chelation with crossover to EDTA provocation testing if toxicity occurs (PCA); 4) EDTA provocation testing with crossover to penicillamine chelation if testing is negative (EDTA).

RESULTS

The EDTA and PCA strategies prevented 22.5% of the cases of reading disability and resulted in an increase of 1.02 quality-adjusted life years compared with no treatment. When the costs of outpatient EDTA testing and chelation are considered, the EDTA strategy is more cost-effective than the PCA strategy; when inpatient costs are considered, the PCA strategy becomes more cost-effective. When costs of remedial education are considered, all strategies are cost-saving compared with no treatment if chelation reduces the risk of lead-induced reading disability by more than 20%.

CONCLUSIONS

Treatment strategies for childhood lead poisoning vary in clinical impact, cost, and cost-effectiveness. Chelation of the 1.4% of United States preschoolers whose blood lead levels are 2.21 mumol/L (25 micrograms/dL) or higher could prevent more than 45,000 cases of reading disability, and save more than $900 million per year in overall costs when the costs of remedial education are considered.

Environmental lead and children's intelligence: a systematic review of the epidemiological evidence

OBJECTIVE

To quantify the magnitude of the relation between full scale IQ in children aged 5 or more and their body burden of lead.

DESIGN

A systematic review of 26 epidemiological studies since 1979: prospective studies of birth cohorts, cross sectional studies of blood lead, and cross sectional studies of tooth lead.

SETTING

General populations of children > or = 5 years.

MAIN OUTCOME MEASURES

For each study, the regression coefficient of IQ on lead, after adjustment for confounders when possible, was used to derive the estimated change in IQ for a specific doubling of either blood or tooth lead.

RESULTS

The five prospective studies with over 1100 children showed no association of cord blood lead or antenatal maternal blood lead with subsequent IQ. Blood lead at around age 2 had a small and significant inverse association with IQ, somewhat greater than that for mean blood lead over the preschool years. The 14 cross sectional studies of blood lead with 3499 children showed a significant inverse association overall, but showed more variation in their results and their ability to allow for confounders. The seven cross sectional studies of tooth lead with 2095 children were more consistent in finding an inverse association, although the estimated magnitude was somewhat smaller. Overall synthesis of this evidence, including a meta-analysis, indicates that a typical doubling of body lead burden (from 10 to 20 micrograms/dl (0.48 to 0.97 mumol/l) blood lead or from 5 to 10 micrograms/g tooth lead) is associated with a mean deficit in full scale IQ of around 1-2 IQ points.

CONCLUSION

While low level lead exposure may cause a small IQ deficit, other explanations need considering: are the published studies representative; is there inadequate allowance for confounders; are there selection biases in recruiting and following children; and do children of lower IQ adopt behaviour which makes them more prone to lead uptake (reverse causality)? Even if moderate increases in body lead burden adversely affect IQ, a threshold below which there is negligible influence cannot currently be determined. Because of these uncertainties, the degree of public health priority that should be devoted to detecting and reducing moderate increases in children's blood lead, compared with other important social detriments that impede children's development, needs careful consideration.

Internal lead and cadmium exposure in 6-year-old children from western and eastern Germany

Lead and cadmium levels in blood and deciduous teeth (shed incisors only) of 6-year-old German children were determined in 1991 in a large epidemiological study carried out in rural and urban areas of western Germany (Duisburg, Essen, Gelsenkirchen, Dortmund, Borken) and eastern Germany (Leipzig, Halle, Magdeburg, Osterburg, Gardelelegen, Salzwedel). In total, blood lead and cadmium levels of 2311 German children and tooth lead and cadmium levels of 790 German children were analyzed. Blood lead levels were generally low in all study areas with geometric means between 39.3 micrograms/l and 50.8 micrograms/l in the western German and between 42.3 micrograms/l and 68.1 micrograms/l in the eastern German study areas. The mean blood lead level of Turkish children (n = 213) living in the western German study areas was 50.1 micrograms/l and thus 5.6 micrograms/l higher than the overall geometric mean of the western German children. The higher exposure may be explained by a higher oral uptake from food and different living conditions. These children were excluded from multiple regression analysis because they were all living in the western study areas. The mean tooth lead levels ranged between 1.50 and 1.74 micrograms/g in the western and between 1.51 micrograms/g and 2.72 micrograms/g in the eastern study areas. Thus, they show a distribution pattern similar to blood. Blood and tooth lead levels were higher in urban than in rural areas and higher in the eastern German than in the western German study areas. With regard to the blood and tooth cadmium concentrations, no significant differences between the study areas could be found.(ABSTRACT TRUNCATED AT 250 WORDS)

Home abatement and blood lead changes in children with class III lead poisoning

We studied the effect of home abatement on blood lead (PbB) levels in children from central Massachusetts who had not undergone chelation therapy and whose homes were abated between 1987 and 1990, when stricter abatement guidelines were enacted. One hundred and thirty-two children with a mean preabatement PbB of 25.9 micrograms/dL (1.25 mumol/L) were studied: their mean postabatement PbB (up to 1 year later) was 21.1 micrograms/dL (1.02 mumol/L) (P < .001). This reduction correlated with preabatement PbB; 32 of 33 (97%) with preabatement PbB > or = 30 micrograms/dL (> or = 1.45 mumol/L) were lower postabatement, and 64 of 79 (81%) with PbB 20 to 29 micrograms/dL (0.97-1.40 mumol/L) were lower. However, in children with preabatement PbB < 20 micrograms/dL (< 0.97 mumol/L), only seven of 20 (35%) were lower postabatement and, in fact, there was a significant rise in PbB from 16.8 to 19.3 micrograms/dL (0.81 to 0.93 mumol/L) (P = 0.05). Continued improvement in home abatement technology is needed if that strategy is to be effective in achieving the lower PbB levels now mandated in the 1991 Centers for Disease Control guidelines. Primary prevention of the initial blood lead level elevation remains the most desirable strategy.

Acid precipitation--effects on trace elements and human health

Environmental pollution by acid precipitation increases the solubilization and mobilization of toxic metals. Through the food chain, this may alter the intake of toxic and essential elements in man. Potential adverse health effects could follow after increased human exposure. For the general population, the exposure pattern and health effects caused by aluminium, cadmium, lead and mercury are of particular concern. Although there are several indications that the exposure to toxic elements (e.g. aluminium, cadmium, lead and methylmercury), as well as the intake of essential elements (e.g. selenium), may be affected by acid precipitation, there is presently no firm evidence of adverse health effects in man. However, the present data clearly indicate that the safety margins are small. Thus, the ongoing acidification in many areas must be stopped before such effects become evident. The effects on trace element status and human health by acid precipitation were discussed at the ISTERH (International Society for Trace Element Research in Humans) Conference in Stockholm, May, 1992. The main findings are briefly summarized here.

Clinical and subclinical deficits at 8 years in a geographically defined cohort of low birthweight infants

OBJECTIVE

To determine the prevalence of subclinical deficits in cognitive and motor function in low birthweight infants.

DESIGN

Children of birth weight < or = 2000 g born to mothers resident in Merseyside in 1980-1 assessed using the Wechsler Intelligence Scale for Children (WISC), the Neale analysis of reading ability, and the Stott-Moyes-Henderson test of motor impairment (TOMI). Children attending normal schools assessed with controls matched for age, sex, and class in school. Children attending special schools were assessed unmatched.

SUBJECTS

233 matched index case-control pairs attending normal primary schools and 46 unmatched children attending special schools.

SETTING

Primary and special schools.

MAIN OUTCOME MEASURES

IQ score, reading age in months, and TOMI score.

RESULTS

Index cases when compared with controls had a lower WISC score (mean IQ difference 8.8; 95% confidence interval (CI) 6.8 to 10.7), a lower reading age (mean difference 6.5 months; 95% CI 4.0 to 9.0), and poorer motor performance as shown by the TOMI score (mean difference 1.4; 95% CI 1.1 to 1.8). Of the children attending special schools, 23/46 (50%) had a WISC score < or = 50.

CONCLUSIONS

Low birthweight children have significant subclinical deficits of cognitive and motor function and extra resources, especially in education, may be required to meet their needs.

Efficacy of oral meso-2,3-dimercaptosuccinic acid therapy for low-level childhood plumbism

OBJECTIVE

To compare the response to oral meso-2,3-dimercaptosuccinic acid (DMSA) treatment in children with an initial blood lead (BPb) concentration less than versus more than 2.17 mumol/L (45 micrograms/dl).

DESIGN

Retrospective cohort study.

SETTING

Regional referral lead treatment program in an urban children's hospital.

PATIENTS

Thirty consecutive children, median age 34 months (range, 5 to 161 months), with an initial BPb concentration 0.97 to 2.90 mumol/L (20 to 60 micrograms/dl) selected for DMSA use. Reasons for DMSA use included BPb concentration > 2.17 mumol/L (11 children), complications with penicillamine therapy (11), chronic renal failure (1), and compassionate use (7). All patients received required environmental hazard reductions before drug administration.

RESULTS

Group 1 (n = 23) had a mean BPb concentration of 1.50 mumol/L (31 micrograms/dl), and group 2 (n = 7) had a mean BPb concentration of 2.41 (51 micrograms/dl). Sixteen patients (70%) in group 1 and five patients (71%) in group 2 had had previous chelation therapy (p value not significant). No significant difference was found in the mean percentage of the reduction of BPb concentration during treatment of group 1 (60%) versus group 2 (58%). The mean BPb concentration in group 1 rebounded to 70% of pretreatment values by mean day 41; the BPb concentration in group 2 rebounded to 69% by day 37 (p value not significant). Prior chelation therapy did not result in a significant difference in either the percentage reduction of BPb concentration or the percentage of rebound BPb.

CONCLUSION

DMSA is equally effective in acutely lowering BPb concentration in children with BPb concentrations less than and greater than 2.17 mumol/L.

The influence of pH and household plumbing on water lead concentration

The water lead concentrations measured in the homes of children who were part of the Edinburgh Lead study are related to the characteristics of the water supply and the household plumbing. At the time of the study one of the City of Edinburgh's two water supplies was lime treated to reduce plumbosolvency but in the second supply this treatment had not yet become effective. This allows us to estimate the extent to which this type of water treatment reduces water lead concentrations, in houses with lead plumbing, to comply with existing and proposed limits for lead in water. The kitchen cold water was supplied from a lead storage tank in 69 (15%) of the houses. These houses had the highest lead concentrations and water tre.

Relative exposure of children to lead from dust and drinking water

The Blackpool, Wyre and Fylde Health Authority, in the North West of England, could be described as a "low-level lead exposure area." Primary sources of lead exposure are atmospheric fallout (both indoors and outdoors) and potable water consumption. Deciduous teeth were collected from children living in this area as were water samples and outdoor dust samples. Both total lead concentrations and 206Pb:207Pb ratios were determined for a defined subset of teeth. Significant differences in the total lead concentrations were found for teeth collected from children resident in different targeted areas (i.e., Blackpool, Fleetwood, and Garstang). No significant differences were found between the total lead concentrations or the 206Pb:207Pb ratios from dust and water samples in these areas. Examination of the 206Pb:207Pb ratios for dust, water, and teeth obtained from each area separately revealed differing patterns of exposure to lead. Determination of 206Pb:207Pb ratios, in addition to total lead concentrations, enabled the differences in sources of exposure to be identified in these communities. The authors conclude that isotopic analyses are an important aspect of community survey work, and these analyses can be helpful in accurately targeting intervention strategies aimed at reducing exposure to lead.

Mental retardation in ten-year-old children in relation to their mothers' employment during pregnancy

We conducted a case-control study to examine relationships between potential risk factors in women's prenatal occupational histories and subsequent mental retardation in their 10-year-old children. Children with mental retardation (intelligence quotient less than 71) were identified from special education records maintained by the public school systems in the metropolitan Atlanta area and from records of various medical and social service agencies serving children with special needs. Control children were chosen from the rosters of 10-year-olds who were enrolled in regular education classes in the local public school systems. To obtain occupational histories, sociodemographic data, and other information, we interviewed 352 natural mothers (67%) of 525 case children and 408 natural mothers (64%) of 636 control children. We computed odds ratios for each of 25 selected occupation, industry, and agent categories controlling for maternal education, birth order, and race. Most comparisons yielded odds ratios that were not indicative of unusual risks, but we did find lower than expected risks among children of teachers and health-care professionals. We also found a strong, positive association between mental retardation and maternal employment in the textile and apparel industries. The findings are useful for planning the direction of future studies of childhood cognitive ability to focus on specific parental occupations or industries.

Identification and apportionment of sources of lead in human tissue

A brief review of the use of stable lead isotope ratio measurements to identify and apportion sources of lead in human tissue is followed by examples of the use of inductively coupled plasma source mass spectrometry for such studies.Inductively coupled plasma source mass spectrometry (ICP-MS) has only recently been used for measurements of coupled ratios in body tissues and fluids and in environmental sources of lead. Generally, the inaccuracy of these measurements is about -0.2% and the imprecision less than 0.5%. This analytical performance is sufficient to detect the much larger changes in(206)Pb:(207)Pb ratios of -2% or higher, seen in environmental lead exposure and in childhood lead poisoning.Measurements of lead isotope ratios by ICP-MS have been used to identify specific sources of childhood lead poisoning and to indicate the relative importance of environmental sources, such as drinking water and lead from petrol. Populations in the United Kingdom with low lead uptake usually have(206):Pb(207)Pb ratios in body tissues within the range 1.13 ± 0.01. Significant deviations from this range have been seen in response to increased uptake from lead in: drinking water in parts of Scotland (source ratio ∼1.18 and petrol lead in inner London (source ratio ∼1.07). The dominant source for some Scottish subjects with high concentrations of lead in blood or in teeth was water, which contributed approximately 60% to body lead. Petrol lead was shown to be a significant contributor (30-40%) to the body lead of inner London children.

A review of persistent, low-grade lead challenge: neurological and cardiovascular consequences

Although acute toxicity following heavy intake of lead (Pb) is a well-established clinical entity, the harmful effects of persistent, low-dose challenge, a situation commonly found among the general population, is uncertain. The major dangers of persistent, low-dose challenge that have been hypothesized are controversial: first, mentation and behavioral perturbations and second, development of hypertension with its consequences on the cardiovascular system. Accordingly, one cannot exclude some contributions from persistent Pb exposure to chronic disease and the aging process. Despite these potential adversities, many sources for Pb contact still remain with us. Current estimates are that 10-50% of American children (over 3-4 million) harbor unsafe levels according to present-day standards. Therefore, it is reasonable to conclude that more work is needed in this area. Clearcut evidence concerning the deleterious influence of Pb on the nervous and/or cardiovascular-renal systems would lead to greater attempt to lessen exposure, to ameliorate symptomatology by providing supplemental agents which obviate the unwanted effects of Pb (iron, calcium, zinc), and to consider therapy with binding agents, like CaNa2EDTA, in the afflicted.

Blood lead level and neurobehavioral development among children living in Mexico City

This cross-sectional study examined the association between blood lead levels and neuropsychological and behavioral development of 139 children (7-9 y of age) who attended school in the southwestern part of Mexico City. A trained psychologist administered an IQ test to 84% of the children, and teachers graded them for agility, socialization, expression, and knowledge. Parents also answered a questionnaire on demographic and socioeconomic variables. Anodic stripping voltametry was used to determine blood lead levels. Regression models were used to determine the best predictors of IQ and teachers' rating scores. The mean blood lead level was 19.4 micrograms/dl (standard deviation [SD] = 7.6), with a geometric mean of 17.8 micrograms/dl (95% confidence interval [95% CI] = 16.5-19.1). Blood lead was the strongest predictor of full-scale IQ, and there was a significant negative trend between blood lead, full-scale IQ, and teachers' rating scores. In this study, children with higher levels of blood lead performed more poorly on psychometric tests and had poorer educational attainment than their counterparts. These results suggest an association between neuropsychological and behavioral impairment and lead exposure.

Dentine lead and intelligence prior to school entry: a statistical sensitivity analysis

The relationship between circumpulpal dentine lead and IQ at age 4 years 10 months was examined in 164 urban children. Negative correlations were observed between dentine lead and IQ scores, but were reduced in magnitude after adjustment for social covariates. Analyses using errors-in-variables regression models indicated that the degree of this reduction depended on difficult-to-verify assumptions regarding the magnitudes of (i) measurement error in the lead variable and the covariates, and (ii) possible changes in the caretaking environment resulting from conjectured effect of lead on the child's cognitive and behavioral development. Sensitivity analyses were conducted in which estimates of the lead effect were repeatedly computed and compared for a range of possible values for factors (i) and (ii). It was found that the statistical significance of the lead effect on Full Scale IQ depended on the relative magnitudes of these factors, and that failure to incorporate measurement error in the analysis would have led to gross overestimation of the precision of the findings.

Early dentine lead levels and subsequent cognitive and behavioural development

While a number of studies have reported associations between lead levels and cognitive development and behaviour in cross-sectionally studied child samples, there have been relatively few studies of the long term effects of early lead exposure. This issue was studied in a birth cohort of 1265 New Zealand children who were assessed with respect to: (a) dentine lead levels at ages 6-8 years; (b) cognitive and behavioural outcomes at 12, 13 years; (c) various confounding factors. The results of the analysis show: (a) the presence of small but consistent bivariate associations (ranging in absolute size from r = .08 to .20) between early lead levels and later school performance and behaviour; (b) after adjustment for both errors of measurement in test scores and lead levels and adjustment for confounding factors these correlations reduced to between .07 and .14. Nonetheless these correlations remained statistically significant. The evidence is consistent with the view that early mildly elevated lead levels are associated with small but relatively long term deficits in cognitive ability and attentional behaviours.

Environmental exposure to lead and children's intelligence at the age of seven years. The Port Pirie Cohort Study

BACKGROUND

Exposure to lead in early childhood is thought to result in delayed neuropsychological development. As yet there is little longitudinal evidence to establish whether these effects persist into later childhood.

METHODS

We measured IQ scores in 494 seven-year-old children from the lead-smelting community of Port Pirie, Australia, in whom developmental deficits associated with elevated blood lead concentrations had already been reported at the ages of two and four years. Exposure to lead was estimated from the lead concentrations in maternal blood samples drawn antenatally and at delivery and from blood samples drawn from the children at birth (umbilical-cord blood), at the ages of 6 and 15 months and 2 years, and annually thereafter. Data relating to known covariates of child development were collected systematically for each child throughout the first seven years of life.

RESULTS

We found inverse relations between IQ at the age of seven years and both antenatal and postnatal blood lead concentrations. After adjustment by multiple regression for sex, parents' level of education, maternal age at delivery, parents' smoking status, socioeconomic status, quality of the home environment, maternal IQ, birth weight, birth order, feeding method (breast, bottle, or both), duration of breast-feeding, and whether the child's natural parents were living together, the relation with lead exposure was still evident for postnatal blood samples, particularly within the age range of 15 months to 4 years. For an increase in blood lead concentration from 10 micrograms per deciliter (0.48 mumol per liter) to 30 micrograms per deciliter (1.45 mumol per liter), expressed as the average of the concentrations at 15 months and 2, 3, and 4 years, the estimated reduction in the IQ of the children was in the range of 4.4 points (95 percent confidence interval, 2.2 to 6.6) to 5.3 points (95 percent confidence interval, 2.8 to 7.8). This reduction represents an approximate deficit in IQ of 4 to 5 percent.

CONCLUSIONS

Low-level exposure to lead during early childhood is inversely associated with neuropsychological development through the first seven years of life.

Lead neurotoxicity and disorders of learning

Preventable and treatable causes of disorders of learning caused by lead exposure can be recognized by heightened awareness of this potential hazard. The Centers for Disease Control using data from many studies of neurobehavioral effects of lead in children and animals, has redefined the lead exposure threshold for clinical and social intervention from 25 micrograms/dL to 10 micrograms/dL. This article reviews the pertinent studies that provide evidence of the effects of lead exposure on development of the nervous system, effects on neural structures involved in memory and learning, and the impact of early lead encephalopathy on adolescent and adult learning skills and cognitive performance. Physicians, teachers, and child care personnel are responsible for identifying children with behavioral signs of subclinical lead intoxication as early as possible. Screening programs and preventive strategies, such as the multitier Centers for Disease Control approach referred to in this article, are necessary. It is no longer reasonable to assume that lead-exposure children not demonstrating severe encephalopathy will recover completely, without residual brain damage after removal from exposure. Sufficient evidence now exists to clearly demonstrate measurable effects of low levels of lead body burden on behavioral and intellectual performance, resulting in learning disorders.