Lead exposure and the cognitive development of urban preschool children: the Cincinnati Lead Study cohort at age 4 years

The purpose of this analysis was to determine if significant associations could be observed between prenatal/postnatal blood lead (PbB) levels and the cognitive development of 258 urban, inner-city children at 4 years of age. These children have been followed since birth with frequent assessments of general health, PbB, and neuropsychological status. The Kaufman Assessment Battery for Children (K-ABC) was administered at approximately 4 years of age. Higher neonatal PbB levels were associated with poorer performance on all K-ABC subscales. However, this inverse association was limited to children from the poorest families. Maternal PbB levels were unrelated to 4-year cognitive status. Few statistically significant associations between postnatal PbB levels and K-ABC scales could be found. However, the results did suggest a weak inverse relationship between postnatal PbB levels and performance on a K-ABC subscale which assesses visual-spatial and visual-motor integration skills. In these results we note both contradiction and accord with previously published prospective studies.

[Relationship between internal lead exposure and psychologic performance after occupational medicine interventions]

In order to investigate the influence of hygienic measures (mobilisation yield of lead in urine by CaEDTA, part-time work) on psychological performance 23 lead exposed workers have been psychodiagnostically investigated twice along with biological monitoring (blood lead level, erythrocyte protoporphyrine). In the pre-post comparison 4 of the 6 performance ranges measured showed distinct performance improvements, which could be shown to be statistically significant for group comparisons and in most individual cases. Parameters sensitive to changes were in the motor-sensory choice reaction, concentration and memory while subjective estimations of well-being exhibited no changes. Also after discussing methodological questions (influence of age, test repetition) the changes are interpreted in the direction of a possible reversibility of neurotoxic effects as a consequence of hygienic interventions.

The future challenge of lead toxicity

Five decades ago, lead toxicity in childhood was thought in nonlethal cases to be without residual effect. This misconception was corrected in 1943 by Randolph Byers, who began the modern era of lead neurotoxicology by asserting that lead not only killed cells, but interfered with the normal development of central nervous system neurons. The human data from Byers forward is reviewed, with particular attention on methodological issues that have emerged. The papers on human neurotoxicology presented at the NIEHS lead conference held in Research Triangle Park, NC, in 1974 are examined to demonstrate the progress made over the last 15 years. Seven methodological solecisms have clouded judgment over the question of lead toxicity at low dose: worship of the sacrament of p = 0.05; inaccurate causal modeling; drawing conclusions from studies with inadequate power; positing phantom covariates; underestimating the importance of "small" effects; demanding proof of causality; and evaluating studies in isolation. The principles behind these errors are discussed. Lead exposure is associated with hyperactivity, and hyperactivity is a risk factor for antisocial behavior. The relationship between lead exposure and antisocial behavior is estimated. A plan for the effective removal of one major lead source, housing stock, is presented.

Antecedents and correlates of improved cognitive performance in children exposed in utero to low levels of lead

Up to 2 years of age, children with umbilical cord blood lead levels of 10 to 25 micrograms/dL achieve significantly lower scores on tests of cognitive development than do children with lower prenatal exposures. By age 5 years, however, they appear to have recovered from, or at least compensated for, this early insult. Change in performance between 24 and 57 months of age was examined in relation to level of postnatal lead exposure and various sociodemographic factors. Among children with high prenatal lead exposure, greater recovery of function was associated with lower blood level at 57 months, higher socioeconomic status, higher Home Observation for Measurement of the Environment scores, higher maternal IQ, and female gender. The difference between the scores at 57 months of children with optimal and less optimal values on these variables generally exceed 1/2 standard deviation. Higher prenatal lead exposure is associated with an increased risk of early cognitive deficit. Furthermore, the risk that a deficit will persist through the preschool years is increased among children with high prenatal exposure and either high postnatal exposure or less optimal sociodemographic characteristics.

The cultural parameters of lead poisoning: a medical anthropologist's view of intervention in environmental lead exposure

This article identifies four culturally shaped sources of lead exposure in human societies: modern and historic technological sources: food habits; culturally defined health beliefs; and beauty practices. Examples of these potential sources of lead poisoning are presented from current cultures. They include the use of lead-glazed cooking pottery in Mexican-American households; folk medical use of lead in Hispanic, Arabic, South Asian, Chinese, and Hmong communities; as well as the use of lead as a cosmetic in the Near East, Southeast Asia, and South Asia. Four interacting cultural conditions that create barriers to the reduction of lead exposure and lead poisoning are identified and discussed. These are knowledge deficiencies, communication resistance, cultural reinterpretations, and incongruity of explanatory models.

Lead exposure and neurobehavioral development in later infancy

A prospective methodology was used to assess the neurobehavioral effects of fetal and postnatal lead exposure during the first 2 years of life. Lead was measured in whole blood prenatally in mothers and at quarterly intervals in the infant. Prenatal blood lead levels were low (mean = 8.0 micrograms/dL). However, approximately 25% of the study infants had at least one serial blood lead level of 25 micrograms/dL or higher during the second year of life. Multiple regression and structural equation analyses revealed statistically significant relationships between prenatal and neonatal blood lead level and 3- and 6-month Bayley Mental and/or Psychomotor Development Index. However, by 2 years of age, no statistically significant effects of prenatal or postnatal lead exposure on neurobehavioral development could be detected. Data consistent with the hypothesis that a postnatal neurobehavioral growth catch-up occurred in infants exposed fetally to higher levels of lead are presented.

[Computer-assisted assessment of psychologic performance in patients exposed to neurotoxic substances]

A clinico-experimental investigation was conducted to study subjects exposed to neurotoxic pollutants and contaminants by means of the Combitest 2 computer-aided psychometric method. To this end, sensopsychomotor, mnestic and intellectual performance as well as concentration power were evaluated. Single and multiple choice reaction tasks, termometer tracking and maximal tapping were found to be efficient screening methods. Pronounced relationships were seen to exist between psychometric test results and lead concentration levels in blood.

Behavioral toxicology and risk assessment

In order to establish safe exposure levels to toxic chemicals, risk assessment guidelines have been developed. These guidelines evaluate epidemiologic and animal research data on a particular chemical, as well as dose-response relationships, animal to human extrapolation and assessment of exposure levels of populations. Using the guidelines, risk characterization is established in order to determine a strategy for reducing undesirable risk to human populations. Using both human neonatal lead exposure data and results from rodent and primate studies, this review examines the possibility that behavioral measurements are sufficient to provide adequate risk assessment guidelines for lead intoxication of the developing organism. The overall trend in these data during the past 10 years has been to show that exposures to inorganic lead at levels previously considered safe have long-lasting significant alterations in behavioral measures, suggesting that central nervous system function has been altered irreversibly. The conclusion is drawn that behavioral toxicology can provide sensitive, quantitative and reliable data for risk assessment and that in the future these methodologies could be used to set exposure guidelines for other neurotoxic chemicals.

Results from the European multicenter study on lead neurotoxicity in children: implications for risk assessment

In order to improve dose-response information on neurobehavioral effects of environmental lead exposure in children, the World Health Organization, Regional Office for Europe (WHO/EURO), in collaboration with the Commission of the European Communities, initiated this international study which was planned, executed and evaluated between 1984 and 1989. Eight groups from eight European countries (Bulgaria, Denmark, Greece, Hungary, Italy, Roumania, W. Germany and Yugoslavia) took part. A common study protocol with inherent quality assurance elements was developed to achieve comparability. Blood-lead concentrations (PbB) were the main markers of exposure. The WISC (4 subtests) for psychometric intelligence, the Bender Gestalt test (GFT version) and the Trail-Making test for visual-motor integration, the Vienna Reaction Device and a delayed RT task for reaction performance, and the Needleman scales for behavior ratings served as behavioral endpoints. All individual studies taken together represent a sample size of 1879 school-age children and cover a PbB range from below 5 to about 60 micrograms/100 ml. Overall statistical evaluation of outcome was done by multiple regression analysis using a uniform confounder model. The strongest and most consistent effects occurred for the Bender Gestalt test (GFT version) and for serial choice reaction performance (Vienna Device). The degree of association with PbB was significant for these variables, although the contribution of PbB to the observed variance never exceeded 0.8%. Psychometric intelligence was also negatively affected, although the consistency of outcome between studies was poor, and the association with PbB only borderline. An effort towards risk assessment was made by calculating the proportion of children at risk, using the observed regression coefficients as well as means and standard deviations.

Lead and cadmium levels in violent criminals

Two groups of violent incarcerated male criminals and 30 nonviolent criminals were compared for element content of hair by atomic absorption spectroscopy. Groups did not differ in age, socioeconomic status, or months institutionalized. The groups did differ significantly in lead and cadmium levels. The importance of cadmium in affecting reactivity to stimuli is discussed.

Infantile colic and transient developmental lag in the first year of life

This study investigates the impact of infantile colic on subsequent development. Infants with a history of colic scored significantly lower on the Mental and Psychomotor scales of the Bayley Scales of Infant Development at age 6 months but there was no significant effect of colic on test performance at later ages. The data suggest that this temporary delay in development may be due in part to less favorable patterns of caregiver-infant interaction as a result of the history of colic.

Cross-validation of short forms of the WISC-R in two British samples

Short forms of the WISC-R were computed by multiple linear regression on two samples of British children aged 6 to 12 years. The predictive validity of each short form was assessed both within the sample on which it was developed and cross-validated on the other sample. The empirically determined loss of power of prediction was found to be less than expected on a priori grounds. Predictions of individual scores at the lower end of the IQ distribution were less acceptable. It is concluded that short forms are robust and of value in research and for screening purposes, but cannot be recommended for clinical purposes.

Cognitive functioning in lead workers

In a cross sectional study of occupational exposure to inorganic lead 91 men performed a series of microcomputer based tasks assessing sensor motor reaction time, memory, attention, verbal reasoning, and spatial processing. Performance on the tasks was studied in relation to three ranges of blood lead concentration (low, less than 20 micrograms/dl; medium, 21-40 micrograms/dl; and high, 41-80 micrograms/dl) and exposure response correlations for blood lead concentration, zinc protoporphyrin (ZPP) (range 7-210 micrograms/dl), and urinary aminolaevulinic acid (ALA) (range 0.5-22.0 mg/l). The results show that the high group were impaired on most of the tasks used and, in general, the magnitude of the impairment correlated better with blood lead concentration than ZPP or urinary ALA. An examination of the patterns of task impairment indicated a general slowing of sensory motor reaction time which was relatively independent of the nature of the cognitive functions being tested. There was some evidence, however, suggesting mild impairment of attention, verbal memory, and linguistic processing. In general, workers with high blood lead concentrations showed clear impairment of sensory motor functions in the absence of correspondingly strong evidence for impaired processing and memory functions. It is argued that a general slowness in responding may underlie many previous reports of widespread cognitive impairment in lead workers.

Blood-lead levels and children's behaviour--results from the Edinburgh Lead Study

The effect of blood-lead on children's behaviour was investigated in a sub-sample of 501 boys and girls aged 6-9 years from 18 primary schools within a defined area of central Edinburgh. Behaviour ratings of the children were made by teachers and parents using the Rutter behaviour scales. An extensive home interview with a parent was also carried out. Multiple regression analyses showed a significant relationship between log blood-lead and teachers' ratings on the total Rutter score and the aggressive/anti-social and hyperactive sub-scores, but not the neurotic sub-score when 30 possible confounding variables were taken into account. There was a dose-response relationship between blood-lead and behaviour ratings, with no evidence of a threshold.

The persistent threat of lead: a singular opportunity

Recent data have demonstrated health effects of lead in children at doses previously believed to be harmless. Data from epidemiological studies in many countries, and from experimental studies of animals given lead, demonstrate psychological impairment at blood lead concentrations of 0.5-0.7 mumol/L. Current estimates are that 17 per cent of American children (3-4 million) exceed the level of 0.7 mumol/L. Lead exposure is not a problem for urban poor children alone, but inner-city minorities have a higher rate of exposure. The overabundance of lead coexists in the same area with two serious shortages: affordable housing and jobs. It is argued that a program to train unemployed inner-city residents in safe de-leading, while expensive, makes hygienic, economic, and common sense.

Relationship between lead exposure indicators and neuropsychological performance in children

This study surveyed 237 schoolchildren in a lead-polluted industrial area in northern Italy to assess the relationship between various biological indicators (lead in blood, hair and teeth, and delta-aminolevulinic dehydratase [ALA-D] activity) and some neuropsychological functions, assessed by a battery of five psychometric tests. The geometric means of lead measured in blood, hair and teeth were 10.99 micrograms/dl, 6.79 micrograms/g and 6.05 micrograms/g, respectively. Mean ALA-D activity was 51 mU/ml RBC. By analysis of covariance, after regressing out the variance accountable to confounding variables (age, sex, occupation/education of parents), Total and Verbal WISC-R IQ and Toulouse Pieron test results were significantly affected by the levels of lead in teeth. ALA-D values also appeared to be related to WISC-R IQ results (Total, Verbal and Performance).

The effects of low to moderate lead levels on neurobehavioral functioning in children: toward a conceptual model

The purpose of this article is to present a working model of the way in which low to moderate levels of lead toxicity may affect the neurological and behavioral functioning of young children. The model is used to organize representative data on the subject, to evaluate the state of the field, and to suggest directions for future research.

Neurobehavioural consequences of prenatal low level exposures to lead

A cohort of 318 children born in three Sydney hospitals between April 1982 and March 1983 were recruited into a five year prospective study designed to investigate the relationship between low level lead exposures and neurobehavioural development. Blood samples were obtained at the time of birth, then at 6 month intervals to 4 years and then at 5 years; neurobehavioural and physical measures were taken at 6 months, 12 months and hence annually to 5 years. This paper presents some of the findings from the first three years of the study and addresses the issue of the relationship between fetal exposures to lead and child development to three years. Maternal and cord blood lead levels were in range 0-29 microgram/dl with the majority less that 15 micrograms/dl. The geometric means were, respectively, 9.1 micrograms/dl and 8.1 micrograms/dl. The analyses presented do not support the hypothesis of a relationship between maternal and cord blood lead levels in this range and developmental deficits in young children to the age of three years.

Neurobehavioral deficits after low level lead exposure in neonates: the Mexico City pilot study

Gestation age and ability of the baby to self-quiet and to be consoled during the first 30 days of life decrease when mother's blood lead levels rise from 36 weeks of pregnancy to birth of child. These effects appear to be independent of the absolute lead levels of mother and child (N = 42). Since pre- and perinatal stress predicts higher maternal birth lead, further work could determine the relative contributions of undetected stress during pregnancy and elevated lead levels upon subsequent development. Several cases, not included in the statistical analyses, showed associations between cord leads greatly elevated over maternal leads and poor outcome.

Low level lead exposure in the prenatal and early preschool periods: intelligence prior to school entry

The hypothesis that low level lead exposure in the fetal and early preschool years is related to neuropsychological deficit is being examined in a prospective study of development through the preschool years. Clear and consistent support for the hypothesis was not obtained in previously reported findings relating maternal and cord blood lead level (PbB) and PbB from venous samples through age three years to a series of developmental tests. It was concluded the relationship of lead level and cognitive development was primarily a function of the dependence of each on the quality of the caretaking environment. The cohort has now been examined at age four years, ten months, an age selected to assess development just prior to school age. The test used was the Wechsler Preschool and Primary Scale of Intelligence. We found statistically significant correlations between most of the PbB measures and the intelligence test scores, but these were attenuated, not statistically significant and not consistent in direction when relevant confounding variables were considered. Possible biases or threats to validity were reviewed. Effect sizes relating both prenatal and preschool lead exposure to intellectual development were small, not statistically significant, and not consistent in direction.

Effects of combined lead and cadmium exposure: Changes in schedule-controlled responding and in dopamine, serotonin, and their metabolites

Adult male rats were maintained on 1 of 4 ad-lib diets: Group Control-Diet received a normal laboratory diet that contained no added chemicals: Group Lead-Diet received a diet containing 500 ppm (parts per million) lead: Group Cadmium-Diet received a diet containing 100 ppm cadmium: and Group Lead-Cadmium-Diet received a diet containing both 500 ppm lead and 100 ppm cadmium. After 60 days of exposure to their respective diets, animals were placed on restricted diets (15 g/day) of the identical food received during the exposure period. Each animal was trained to lever press on a fixed-interval 1-min schedule for 21 sessions (1 session day). The results of schedule training showed that lead alone or cadmium alone was associated with increased lever pressing relative to control diet. However, when lead and cadmium were exposed jointly, performance was not significantly different from control performance. Similar attenuation of effects were observed for central neurotransmitter functions. Specifically disturbances in dopamine and serotonin turnover that were produced by lead alone were attenuated by the cotreatment of cadmium and lead. Possible accounts of the apparent antagonism between cadmium and lead are discussed.

Long-term effects of chronic postnatal lead exposure on delayed spatial alternation in monkeys

Two cohorts of monkeys chronically exposed to lead during the first year after birth and their controls were tested during adulthood for choice accuracy on a learning and memory task, delayed spatial alternation (DSA). Neither cohort showed significant lead-related deficits, as had been seen in a previous experiment with monkeys exposed to similar chronic levels of lead during the first year with an additional high pulse given five-six weeks after birth (18,19). On the contrary, the lead-exposed monkeys in the present experiment actually performed slightly better than controls. In the previous (pulse-chronic) study, the deficit occurred at short intertrial delays, suggesting an attentional rather than mnenomic deficit. A lead-induced decrease in attentiveness could also explain the present results. The lower level lead intoxication may have decreased attentiveness to a lesser degree, so that the monkeys were less susceptible to irrelevant stimuli and performed better.

Low-level lead exposure, social class, and infant development

A prospective cohort study was conducted to assess the association between early development and low-level prenatal and postnatal lead exposure. Infants' performance between 6 and 24 months on the Mental Development Index of the Bayley Scales of Infant Development declined with increasing concentration of lead in blood, but the decline varied with children's age at exposure, level of exposure, and socioeconomic status. Within the second year of life, the performance of children in lower socioeconomic strata was adversely affected at lower levels of prenatal exposure (blood lead levels of 6 to 7 micrograms/dl) than was the performance of children in higher socioeconomic strata. However, even the performance of these advantaged infants was lower when cord blood lead level exceeded 10 micrograms/dl, well below the figure currently regarded as the maximum permissable level for young children. Exploratory analyses suggested that early postnatal blood lead levels between 10 and 25 micrograms/dl were also associated with lower Mental Development Index scores, but only among children in lower socioeconomic strata.

Behavioral effects of developmental lead exposure in rhesus monkeys

Postnatal lead exposure has been found to cause long-term learning and memory deficits in monkeys. Pulse-chronic exposure, consisting of acute high-level exposure followed by chronic lower-level exposure, has been particularly effective in causing these impairments. We investigated possible antecedents of lead-induced cognitive dysfunction by evaluating the behavioral effects of pulse-chronic lead exposure in rhesus monkeys during the first 6 months of postnatal life. Blood lead concentrations in the monkeys reached a peak of 55.8 +/- 7.8 ug/dl during week 5 after birth and then averaged between 33.1 and 42.9 ug/dl during the rest of the first 6 months after birth. Zinc protoporphyrin levels were increased by lead exposure, but hematocrits were unaffected. Significant lead-related effects were detected on a visual exploration test and a neonatal behavioral assessment battery. Lead-treated monkeys exhibited decreased looking behavior on the visual exploration test and decreased muscle tonus and increased arousal or agitation on the behavioral assessment battery. No effects were seen on a Piagetian object permanence task and no toxic effects on health or growth were detected. In addition to providing indices of behavioral dysfunction during postnatal lead exposure, performance on these early behavioral tests may predict later lead-induced cognitive dysfunction.