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

Impact of occupational lead exposure on nerve conduction study data

INTRODUCTION

To investigate nerve conduction data of lead exposed workers.

METHODS

A total of 287 subjects, consisting of 197 lead exposed workers and 90 healthy controls were included. Nerve conduction study of motor (median, ulnar, peroneal and tibial) and sensory (median, ulnar and sural) nerves were performed. The data were analyzed as two and three groups.

RESULTS

The median blood lead level was 40.90 µg/dl. Median sensory, ulnar motor, and ulnar sensory conduction velocity were lower; distal latency of median motor, median sensory and sural sensory were longer than the controls (p < 0.05). There was no difference between the groups in terms of amplitudes.

DISCUSSION

This study was indicated the neurotoxic effect of lead exposure may occur in the peripheral nerves, while the mean blood lead level is 40 µg/dl.

CH3NH3Br solution as a novel platform for the selective fluorescence detection of Pb2+ ions

The development of a simple fluorescent sensor for detecting the Pb²⁺ heavy metal is fundamentally important. The CH₃NH₃PbBr₃ perovskite material exhibits excellent photoluminescence properties that are related to Pb²⁺. Based on the effects of Pb²⁺ on the luminescent properties of CH₃NH₃PbBr₃, we design a novel platform for the selective fluorescence detection of Pb²⁺ ions. Herein, we use a CH₃NH₃Br solution at a high concentration as the fluorescent probe. Incorporation of PbBr₂ into the CH₃NH₃Br solution results in a rapid chemical reaction to form CH₃NH₃PbBr₃. Hence, the nonfluorescent CH₃NH₃Br material displays a sensitive and selective luminescent response to Pb²⁺ under UV light illumination. Moreover, the reaction between CH₃NH₃Br and PbBr₂ could transform Pb²⁺ into CH₃NH₃PbBr₃, and therefore, CH₃NH₃Br may also be used to extract Pb²⁺ from liquid waste in recycling applications.

Lead: Tiny but Mighty Poison

The documentation of lead toxicity (plumbism) dates back to the times when man learnt its various applications. This versatile heavy metal is non-degradable and its ability to get accumulated in the body that goes undiagnosed, makes it a serious environmental health hazard. Lead is now known to affect almost every organ/tissue of the human body. With irreversible effects on neurobiological development of young children and foetus, its toxicity has lasting implications on the human life. Outlining the symptoms, diagnosis and treatment therapy for lead poisoning, the present review elaborates the pathophysiological effects of lead on various organs. This will be of immense help to the health professionals so as to inculcate a better understanding of the lead poisoning which otherwise is asymptomatic. With chelation therapy being the classic path of treatment, new strategies are being explored as additive/adjunct therapy. It is now understood that lead toxicity is completely preventable. In this regard significant efforts are in place in the developed countries whereas much needs to be done in the developing countries. Spreading the awareness amongst the masses by educating them and reducing the usage of lead following stricter industry norms appears to be the only roadmap to prevent lead poisoning. Efforts being undertaken by the Government of India and other organisations are also mentioned.

Neurotoxicants, Micronutrients, and Social Environments

SUMMARY—Systematic research evaluating the separate and interacting impacts of neurotoxicants, micronutrients, and social environments on children's cognition and behavior has only recently been initiated. Years of extensive human epidemiologic and animal experimental research document the deleterious impact of lead and other metals on the nervous system. However, discrepancies among human studies and between animal and human studies underscore the importance of variations in child nutrition as well as social and behavioral aspects of children's environments that mitigate or exacerbate the effects of neurotoxicants.

In this monograph, we review existing research on the impact of neurotoxic metals, nutrients, and social environments and interactions across the three domains. We examine the literature on lead, mercury, manganese, and cadmium in terms of dispersal, epidemiology, experimental animal studies, effects of social environments, and effects of nutrition.

Research documenting the negative impact of lead on cognition and behavior influenced reductions by the Center for Disease Control in child lead-screening guidelines from 30 micrograms per deciliter (μg/dL) in 1975 to 25 μg/dL in 1985 and to 10 μg/dL in 1991. A further reduction is currently being considered. Experimental animal research documents lead's alteration of glutamate-neurotransmitter (particularly N-methyl-D-aspartate) activity vital to learning and memory. In addition, lead induces changes in cholinergic and dopaminergic activity. Elevated lead concentrations in the blood are more common among children living in poverty and there is some evidence that socioeconomic status influences associations between lead and child outcomes. Micronutrients that influence the effects of lead include iron and zinc.

Research documenting the negative impact of mercury on children (as well as adults) has resulted in a reference dose (RfD) of 0.1 microgram per kilogram of body weight per day (μg/kg/day). In animal studies, mercury interferes with glutamatergic, cholinergic, and dopaminergic activity. Although evidence for interactions of mercury with children's social contexts is minimal, researchers are examining interactions of mercury with several nutrients.

Research on the effects of cadmium and manganese on child cognition and behavior is just beginning. Experimental animal research links cadmium to learning deficits, manganese to behaviors characteristic of Parkinson's disease, and both to altered dopaminergic functioning.

We close our review with a discussion of policy implications, and we recommend interdisciplinary research that will enable us to bridge gaps within and across domains.

Protective Effect of Porcine Cerebral Hydrolysate Peptides on Learning and Memory Deficits and Oxidative Stress in Lead-Exposed Mice

In this study, lead acetate solution and porcine cerebral hydrolysate peptides (PCHPs) were administered to developing mice. Porcine cerebral protein pretreated by ultrasound was hydrolyzed with alcalase, and 11 peptide fragments were obtained by Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis of PCHPs. Our data showed that PCHPs significantly decreased Pb2+-induced spontaneous locomotor activity, latencies to reach the platform, and the time in target quadrant. It also decreased the accumulation of lead in the blood and brain of Pb2+-exposed developing mice. Co-administration of PCHPs and dimercaptosuccinic acid (DMSA) did not only reduce the accumulation of lead in blood but also increased the absorption of zinc and iron in Pb2+-exposed mice. Administration of PCHPs individually significantly enhanced hematopoietic parameters compared with the Pb2+-exposed group. PCHPs significantly reduced the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) but increased glutathione (GSH) content and anti-oxidant enzymes and nitric oxide synthase (NOS) activities in Pb2+-exposed brain. Our findings suggest that PCHPs have the ability to protect against Pb2+-exposed learning and memory deficits and oxidative damage.

Levels and source apportionment of children's lead exposure: could urinary lead be used to identify the levels and sources of children's lead pollution?

As a highly toxic heavy metal, the pollution and exposure risks of lead are of widespread concern for human health. However, the collection of blood samples for use as an indicator of lead pollution is not always feasible in most cohort or longitudinal studies, especially those involving children health. To evaluate the potential use of urinary lead as an indicator of exposure levels and source apportionment, accompanying with environmental media samples, lead concentrations and isotopic measurements (expressed as (207)Pb/(206)Pb, (208)Pb/(206)Pb and (204)Pb/(206)Pb) were investigated and compared between blood and urine from children living in the vicinities of a typical coking plant and lead-acid battery factory. The results showed urinary lead might not be a preferable proxy for estimating blood lead levels. Fortunately, urinary lead isotopic measurements could be used as an alternative for identifying the sources of children's lead exposure, which coincided well with the blood lead isotope ratio analysis.

Isotopic ratio based source apportionment of children's blood lead around coking plant area

Lead exposure in the environment is a major hazard affecting human health, particularly for children. The blood lead levels in the local children living around the largest coking area in China were measured, and the source of blood lead and the main pathways of lead exposure were investigated based on lead isotopic ratios ((207)Pb/(206)Pb and (208)Pb/(206)Pb) in blood and in a variety of media, including food, airborne particulate matter, soil, dust and drinking water. The children's blood lead level was 5.25 (1.59 to 34.36 as range) μg dL(-1), lower than the threshold in the current criteria of China defined by the US Centers for Disease Control (10 μg dL(-1)). The isotopic ratios in the blood were 2.111±0.018 for (208)Pb/(206)Pb and 0.864±0.005 for (207)Pb/(206)Pb, similar to those of vegetables, wheat, drinking water, airborne particulate matter, but different from those of vehicle emission and soil/dust, suggesting that the formers were the main pathway of lead exposure among the children. The exposure pathway analysis based on the isotopic ratios and the human health risk assessment showed that dietary intake of food and drinking water contributed 93.67% of total exposed lead. The study further indicated that the coal used in the coking plant is the dominant pollution source of lead in children's blood.

Glucocorticoid potentiation of lead neurotoxicity in the mouse HN9 hippocampal cell line

The biochemical events underlying neurobehavioural deficits following persistent low-level lead exposure during embryonic and early postnatal development remain unclear. Because glucocorticoids have previously been demonstrated to potentiate the action of certain neurotoxins, their role in low-level lead-mediated neurotoxicity was examined using a glucocorticoid-responsive immortalized hippocampal neural cell line (HN9). Low-level lead (10(-10)m) reduced the cell number by approximately 30% over a 5-day treatment period. This effect was potentiated by treatment with the synthetic glucocorticoid dexamethasone, with a 52% decrease in cell number. Lead toxicity in actively differentiating cells was also potentiated by dexamethasone. However, while neither lead nor dexamethasone alone was toxic for cells that had previously been induced to differentiate, a combination of both drugs significantly reduced cell number. These results suggest that lead is preferentially toxic in actively dividing cells and that glucocorticoids may play a role in the potentiation of the lead-induced neurotoxicity.

Early effects of long-term neurotoxic lead exposure in copper works employees

The situation of exposure in a copper works facility in Germany enabled early lead-induced neurotoxic effects to be investigated in the workers. The aim of the investigation was to study the long-term effects of small doses of lead on psychometric/psychophysiological performance of workers. The study involved 70 male lead exposed workers and 27 male controls with no neurotoxic exposure. All test persons were subjected to the method of investigation involving performance data, physiological strain data, and the subjective state. It was found that of the psychometric performance parameters, only the mainly motor performance parameters had a potential for being neurotoxic early indicators. Preferably centrally influenced performance parameters were found to be less suitable early indicators. The lead-exposed subjects exhibited a slowed poststrain resetting behaviour of the vegetative nervous system, which correlated with the individual blood lead level. This was attributed to vagus depression, which had already started in the prevailing situation of exposure and was reflected by diminished cardiac phase duration variability. Our results indicate that it is necessary to more critically choose the lead level standards in the air on the working area. Heart rate variability may be affected even at small lead concentration.

Lead exposure and visual-motor abilities in children from Chennai, India

Lead exposure poses a major environmental hazard in India, but little information is available on the impact of lead exposure on visuo-motor development in Indian children. We hypothesize that higher blood lead levels are associated with poorer visual-motor, visual-spatial and fine motor functioning among children. We conducted a cross-sectional study of 814 school children, aged 3-7 years. Lead in whole blood was measured using the LeadCare Analyzer. The Wide Range of Visual Motor Abilities Test (WRAVMA) was administered to each child by trained examiners. The mean blood lead level was 11.4±5.3 μg/dL. In multivariate analyses adjusting for mother's education level, father's education level, average monthly income, hemoglobin and sex, WRAVMA scores were inversely related to blood lead level. An increase of 10 μg/dL was associated with a decrease of 2.6 points (95% CI: -4.5 to -0.7, P=0.006) in the Visual Motor Composite score and a decrease of 2.9 points (95% CI: -5.1 to -0.7, P=0.011) in the Drawing subtest. Exploration of the shape of the dose-effect relationships using spline functions indicated some non-linearities, with the steepest declines in visual-motor skills occurring at higher blood lead levels. Among urban Indian children, higher blood lead levels are associated with decreased visual-motor abilities, particularly visual-motor integration.

Lead in children's blood is mainly caused by coal-fired ash after phasing out of leaded gasoline in Shanghai

Lead (Pb) is a highly toxic element to the human body. After phasing out of leaded gasoline we find that the blood lead level of children strongly correlates with the lead concentration in atmospheric particles, and the latter correlates with the coal consumption instead of leaded gasoline. Combined with the (207)Pb/(206)Pb ratio measurements, we find that the coal consumption fly ash is a dominate source of Pb exposure to children in Shanghai, rather than vehicle exhaust, metallurgic dust, paint dust, and drinking water. Those particles are absorbed to children's blood via breathing and digesting their deposition on ground by hand-to-mouth activities. Probably the same situation occurs in other large cities of developing countries where the structure of energy supply is mainly based on coal-combustion.

Motor alterations induced by chronic lead exposure

Lead (Pb) as other environmental neurotoxicants substances has the capability to interfere with many biochemical events present in cells throughout the body and it can produce a wide spectrum of alterations in many organs and systems. Among that alterations induced by Pb exposure in adults and children those involving motor system dysfunction represent a common public health problem. The review summarizes the sources of lead exposures in both occupational and residential environments and motor deficits induced by chronic Pb exposure taking in account the last literature in the field. We wish to focus on the current state of knowledge concerning the long-lasting neurological effects of Pb in motor functions and to correlate the neurological deficits induced by Pb exposure in animal models with those reported in humans. The great interest in whether exposure to Pb can cause long-term, progressive declines in central nervous system (CNS) function have revealed that Pb exposure is involved in chronic CNS diseases such Parkinson's and poor motor coordination in children.

A method for source apportionment of lead in fine particulate matter based on individual particle analysis using a synchrotron X-ray fluorescence microprobe

A source apportionment method based on individual particle analysis carried out using a synchrotron X-ray fluorescence microprobe was developed for source apportionment of lead in fine particulate matter. Mass contributions of every emission source were obtained by intensity ratios of the characteristic X-ray spectrum of lead in individual airborne particles. The validity of the method was evaluated. The uncertainty of the source apportionment was estimated, which was within 10% in this work. The method was applied to the apportionment of lead in fine airborne particles of Shanghai, indicating that the method has a finer performance for source apportionment.

Atmospheric lead pollution in fine particulate matter in Shanghai, China

The Pb-monitoring program was extended for 6 years from 2002 to 2007 at 17 representative urban sites (6 traffic, 5 industrial, and 6 residential sites), and 3 suburban sites to assess the lead pollution in fine particulate matter (PM2.5) after phasing out leaded gasoline in Shanghai. Compared with Pb levels reported in other places, the Pb pollution in Shanghai is still serious after phasing out leaded gasoline, which remains at high concentration range (213-176 ng/m3) in PM2.5 in winter. Significant spatial variation of Pb concentrations and strong seasonal variation of higher Pb concentration in winter than that in summer were detected. The size distribution of Pb in particulate matter has a unimodal mode that peaks at approximately 0.154-1.59 microm particle diameter, indicating that Pb is mainly concentrated in fine fraction. Lead in the fine fraction is enriched by a factor of 10(3)-10(4) relative to Pb abundance in crust. Eight categories of Pb pollution sources were identified in the PM2.5 in the winter of 2007 in Shanghai. The important emission sources among them are vehicle exhaust derived from combustion of unleaded gasoline, metallurgic industry emission, and coal combustion emission.

Epidemiologic evidence of relationships between reproductive and child health outcomes and environmental chemical contaminants

This review summarizes the level of epidemiologic evidence for relationships between prenatal and/or early life exposure to environmental chemical contaminants and fetal, child, and adult health. Discussion focuses on fetal loss, intrauterine growth restriction, preterm birth, birth defects, respiratory and other childhood diseases, neuropsychological deficits, premature or delayed sexual maturation, and certain adult cancers linked to fetal or childhood exposures. Environmental exposures considered here include chemical toxicants in air, water, soil/house dust and foods (including human breast milk), and consumer products. Reports reviewed here included original epidemiologic studies (with at least basic descriptions of methods and results), literature reviews, expert group reports, meta-analyses, and pooled analyses. Levels of evidence for causal relationships were categorized as sufficient, limited, or inadequate according to predefined criteria. There was sufficient epidemiological evidence for causal relationships between several adverse pregnancy or child health outcomes and prenatal or childhood exposure to environmental chemical contaminants. These included prenatal high-level methylmercury (CH(3)Hg) exposure (delayed developmental milestones and cognitive, motor, auditory, and visual deficits), high-level prenatal exposure to polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and related toxicants (neonatal tooth abnormalities, cognitive and motor deficits), maternal active smoking (delayed conception, preterm birth, fetal growth deficit [FGD] and sudden infant death syndrome [SIDS]) and prenatal environmental tobacco smoke (ETS) exposure (preterm birth), low-level childhood lead exposure (cognitive deficits and renal tubular damage), high-level childhood CH(3)Hg exposure (visual deficits), high-level childhood exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (chloracne), childhood ETS exposure (SIDS, new-onset asthma, increased asthma severity, lung and middle ear infections, and adult breast and lung cancer), childhood exposure to biomass smoke (lung infections), and childhood exposure to outdoor air pollutants (increased asthma severity). Evidence for some proven relationships came from investigation of relatively small numbers of children with high-dose prenatal or early childhood exposures, e.g., CH(3)Hg poisoning episodes in Japan and Iraq. In contrast, consensus on a causal relationship between incident asthma and ETS exposure came only recently after many studies and prolonged debate. There were many relationships supported by limited epidemiologic evidence, ranging from several studies with fairly consistent findings and evidence of dose-response relationships to those where 20 or more studies provided inconsistent or otherwise less than convincing evidence of an association. The latter included childhood cancer and parental or childhood exposures to pesticides. In most cases, relationships supported by inadequate epidemiologic evidence reflect scarcity of evidence as opposed to strong evidence of no effect. This summary points to three main needs: (1) Where relationships between child health and environmental exposures are supported by sufficient evidence of causal relationships, there is a need for (a) policies and programs to minimize population exposures and (b) population-based biomonitoring to track exposure levels, i.e., through ongoing or periodic surveys with measurements of contaminant levels in blood, urine and other samples. (2) For relationships supported by limited evidence, there is a need for targeted research and policy options ranging from ongoing evaluation of evidence to proactive actions. (3) There is a great need for population-based, multidisciplinary and collaborative research on the many relationships supported by inadequate evidence, as these represent major knowledge gaps. Expert groups faced with evaluating epidemiologic evidence of potential causal relationships repeatedly encounter problems in summarizing the available data. A major driver for undertaking such summaries is the need to compensate for the limited sample sizes of individual epidemiologic studies. Sample size limitations are major obstacles to exploration of prenatal, paternal, and childhood exposures during specific time windows, exposure intensity, exposure-exposure or exposure-gene interactions, and relatively rare health outcomes such as childhood cancer. Such research needs call for investments in research infrastructure, including human resources and methods development (standardized protocols, biomarker research, validated exposure metrics, reference analytic laboratories). These are needed to generate research findings that can be compared and subjected to pooled analyses aimed at knowledge synthesis.

Low-level human equivalent gestational lead exposure produces sex-specific motor and coordination abnormalities and late-onset obesity in year-old mice

BACKGROUND

Low-level developmental lead exposure is linked to cognitive and neurological disorders in children. However, the long-term effects of gestational lead exposure (GLE) have received little attention.

OBJECTIVES

Our goals were to establish a murine model of human equivalent GLE and to determine dose-response effects on body weight, motor functions, and dopamine neurochemistry in year-old offspring.

METHODS

We exposed female C57BL/6 mice to water containing 0, 27 (low), 55 (moderate), or 109 ppm (high) of lead from 2 weeks prior to mating, throughout gestation, and until postnatal day 10 (PN10). Maternal and litter measures, blood lead concentrations ([BPb]), and body weights were obtained throughout the experiment. Locomotor behavior in the absence and presence of amphetamine, running wheel activity, rotarod test, and dopamine utilization were examined in year-old mice.

RESULTS

Peak [BPb] were < 1, < or = 10, 24-27, and 33-42 microg/dL in control, low-, moderate- and high-dose GLE groups at PN0-10, respectively. Year-old male but not female GLE mice exhibited late-onset obesity. Similarly, we observed male-specific decreased spontaneous motor activity, increased amphetamine-induced motor activity, and decreased rotarod performance in year-old GLE mice. Levels of dopamine and its major metabolite were altered in year-old male mice, although only forebrain utilization increased. GLE-induced alterations were consistently larger in low-dose GLE mice.

CONCLUSIONS

Our novel results show that GLE produced permanent male-specific deficits. The nonmonotonic dose-dependent responses showed that low-level GLE produced the most adverse effects. These data reinforce the idea that lifetime measures of dose-response toxicant exposure should be a component of the neurotoxic risk assessment process.

Chemically diverse toxicants converge on Fyn and c-Cbl to disrupt precursor cell function

Identification of common mechanistic principles that shed light on the action of the many chemically diverse toxicants to which we are exposed is of central importance in understanding how toxicants disrupt normal cellular function and in developing more effective means of protecting against such effects. Of particular importance is identifying mechanisms operative at environmentally relevant toxicant exposure levels. Chemically diverse toxicants exhibit striking convergence, at environmentally relevant exposure levels, on pathway-specific disruption of receptor tyrosine kinase (RTK) signaling required for cell division in central nervous system (CNS) progenitor cells. Relatively small toxicant-induced increases in oxidative status are associated with Fyn kinase activation, leading to secondary activation of the c-Cbl ubiquitin ligase. Fyn/c-Cbl pathway activation by these pro-oxidative changes causes specific reductions, in vitro and in vivo, in levels of the c-Cbl target platelet-derived growth factor receptor-α and other c-Cbl targets, but not of the TrkC RTK (which is not a c-Cbl target). Sequential Fyn and c-Cbl activation, with consequent pathway-specific suppression of RTK signaling, is induced by levels of methylmercury and lead that affect large segments of the population, as well as by paraquat, an organic herbicide. Our results identify a novel regulatory pathway of oxidant-mediated Fyn/c-Cbl activation as a shared mechanism of action of chemically diverse toxicants at environmentally relevant levels, and as a means by which increased oxidative status may disrupt mitogenic signaling. These results provide one of a small number of general mechanistic principles in toxicology, and the only such principle integrating toxicology, precursor cell biology, redox biology, and signaling pathway analysis in a predictive framework of broad potential relevance to the understanding of pro-oxidant–mediated disruption of normal development.

Chemically different toxins (lead, methylmercury, and paraquat) each cause the intracellular environment to become more oxidized, and thereby activate a common pathway that suppresses signaling from growth factor receptors that may be associated with developmental impairments.

Discovering general principles underlying the effects of toxicant exposure on biological systems is one of the central challenges of toxicological research. We have discovered a previously unrecognized regulatory pathway on which chemically diverse toxicants converge, at environmentally relevant exposure levels, to disrupt the function of progenitor cells of the developing central nervous system. We found that the ability of low levels of methylmercury, lead, and paraquat to make progenitor cells more oxidized causes activation of an enzyme called Fyn kinase. Activated Fyn then activates another enzyme (c-Cbl) that modifies specific proteins—receptors that are required for cell division and survival—to initiate the proteins' degradation. By enhancing degradation of these receptors, their downstream signaling functions are repressed. Analysis of developmental exposure to methylmercury provided evidence that this same pathway is activated in vivo by environmentally relevant toxicant levels. The remarkable sensitivity of progenitor cells to low levels of toxicant exposure, and the discovery of the redox/Fyn/c-Cbl pathway as a mechanism by which small increases in oxidative status can markedly alter cell function, provide a novel and specific means by which exposure to chemically diverse toxicants might perturb normal development. In addition, the principles revealed in our studies appear likely to have broad applicability in understanding the regulation of cell function by alterations in redox balance, regardless of how they might be generated.

Comprehensive study of lead pollution in Shanghai by multiple techniques

Aerosol samples of PM10 particulates were examined with particle-induced X-ray emission (PIXE and micro-PIXE ), inductively coupled plasma-mass spectrometry, and X-ray absorption fine structures (XAFS) to investigate atmospheric Pb concentrations and its chemical species and to decide the source assignment. From the elemental analyses, lead concentrations were averaged at 369 and 237 ng.m-3 in aerosol samples of PM10 collected from 19 monitor sites in Shanghai in the winter of 2002 and 2003, respectively. The XAFS results show that major chemical forms of the lead particulates are probably PbCl2, PbSO4, and PbO. A calculation of isotope ratio and chemical mass balance of the PM10 samples revealed that the atmospheric lead particulates in Shanghai in the two periods were mainly from coal combustors, iron and steel plants, and automobile exhausts, with coal combustion dominating the lead pollution after the phasing out of leaded gasoline in 1997 in Shanghai.

Lead toxicity and chelation therapy

PURPOSE

Common sources of lead exposure, the primary clinical effects of lead toxicity, and current recommendations for managing lead toxicity, including chelation therapy, are reviewed.

SUMMARY

Common sources of lead exposure in children and adults include industrial and mining activities, paint, dust, soil, water, air, the workplace, food, trinkets, ethnic folk remedies, and cosmetics. The absorption and biological fate of lead are affected by a variety of factors, including an individual's nutritional status, health, and age. Children with a blood lead concentration of >10 microg/dL and adults with a blood lead concentration of > or = 45 mug/dL should undergo further evaluation. Symptoms and time to onset of symptoms postexposure may vary, and it can be difficult to identify the early, subtle neurologic effects of lead toxicity. The classic symptoms of lead toxicity generally correlate with blood lead concentrations of 25-50 microg/dL in children and 40-60 microg/dL in adults. Management of lead toxicity requires extensive risk assessment and caregiver education. Chelation is generally not indicated for adults with blood lead concentrations of < 45 microg/dL because of the potential risk of adverse drug events and concerns about remobilized lead, and chelation for children with blood lead concentrations of < 45 microg/dL remains controversial. Dimercaprol, edetate calcium disodium, and succimer are the three agents primarily used for chelation.

CONCLUSION

Lead toxicity remains a significant public health concern. Elimination of elevated blood lead levels in children can be accomplished by educating appropriate health care providers and caregivers, recognizing potential lead sources, and adopting aggressive prevention and case management measures.

Developmental neurotoxicity of industrial chemicals

Neurodevelopmental disorders such as autism, attention deficit disorder, mental retardation, and cerebral palsy are common, costly, and can cause lifelong disability. Their causes are mostly unknown. A few industrial chemicals (eg, lead, methylmercury, polychlorinated biphenyls [PCBs], arsenic, and toluene) are recognised causes of neurodevelopmental disorders and subclinical brain dysfunction. Exposure to these chemicals during early fetal development can cause brain injury at doses much lower than those affecting adult brain function. Recognition of these risks has led to evidence-based programmes of prevention, such as elimination of lead additives in petrol. Although these prevention campaigns are highly successful, most were initiated only after substantial delays. Another 200 chemicals are known to cause clinical neurotoxic effects in adults. Despite an absence of systematic testing, many additional chemicals have been shown to be neurotoxic in laboratory models. The toxic effects of such chemicals in the developing human brain are not known and they are not regulated to protect children. The two main impediments to prevention of neurodevelopmental deficits of chemical origin are the great gaps in testing chemicals for developmental neurotoxicity and the high level of proof required for regulation. New, precautionary approaches that recognise the unique vulnerability of the developing brain are needed for testing and control of chemicals.

Neurobehavioral function in children with low blood lead concentrations

Debate continues as to whether low blood lead level, even below 5 microg/dl, impairs neurodevelopmental function in children. This study assessed the association between neurodevelopmental performance and lead exposure below 5 microg/dl in Korean children. Data were collected from 61 children, aged 7-16 years with a mean blood lead level of 2.9 microg/dl, who participated with their mothers. Neurodevelopmental function was measured with computer-based neurobehavioral tests. The analyzed data included children's performances on five neurobehavioral tests as the dependent variables, and children's blood lead level, sex, age, and mother's performance as the four independent variables. For simple reaction time and digit span, which, respectively reflect attention and short-term memory, there was a small and significant association between the children's neurodevelopmental performance and their blood lead levels (p=0.05, 0.08, respectively). Our study suggests that low blood lead below 5 microg/dl can influence children's neurobehavioral performance.

Lead exposure by drinking water: an epidemiologial study in Hamburg, Germany

Study objective was to investigate the extent of lead exposure via tap water in Hamburg and the relevance of preventive strategies. Two hundred and forty-eight non-smoking young women participated in the cross-sectional study program and 52 women completed the intervention program. In the cross-sectional study program most women (N = 178) didn't know anything about the material of the plumbing system at their homes. Participants with lead in the tap water above the detection limit of 5 microg/l (N = 142) showed significantly higher blood lead levels (median 31 microg/l) compared to those with no detectable lead in the tap water (N = 106; median blood lead 24 microg/l, p < = 0.001). There is a close correlation between the average lead concentration in the tap water and blood lead concentrations (N = 142 value pairs, Spearman's rho 0.43, p < = 0.0001). In the intervention program, the women were asked to minimize exposure by flushing water or to exclude it by consuming bottled water. Intervention lowered blood lead-level significantly (median decrease of 11 microg/l, p < = 0.001). "Minimizers" could lower their blood lead levels by about 21% of the initial value, "excluders" by about 37% (ns, p < = 0.17). The majority judged neither minimizing nor excluding tap water as practicable health preventive behaviour pattern in the long run. Lead in tap water stands for an avoidable surplus exposure. These results underline the relevance of health care preventive measures for the most sensitive groups.

Working memory deficiencies in adults associated with low-level lead exposure: implications of neuropsychological test results

BACKGROUND

Although lead exposure has steadily decreased in the last few years, some lead is still used in the metal processing industry, mostly for wall paints and plumbing. Recent studies on children showed neurobehavioral effects of low-level exposure, but little is known about the neurocognitive effects of lead concentrations in the upper reference range on adults.

METHODS

The neuropsychological effects of lead exposure were examined in 39 adult outpatients at the Unit of Environmental Medicine (UEM), University Hospital, Aachen, Germany. All patients underwent a comprehensive medical examination, including psychiatric. Venous blood and urine samples were collected and tested for heavy metals and selenium. Since the neuropsychological examination was not expected to reveal any severe abnormalities, only specific attentiveness functions were analyzed (alertness, working memory, flexibility, intermodal comparison) since these areas were the likeliest to show objectifiable effects. The tests were conducted using a standardized computerized battery.

RESULTS

Lead blood levels ranged from 1 to 65.6 microg/l (mean 27.4 +/- 16.2 microg/l). Although the neuropsychological test results of all patients were within the normal range, there were significant correlations between blood lead levels and the speed of information processing for working memory.

CONCLUSIONS

The results indicate working memory dysfunctions in adults, the severity of which correlates directly with blood lead levels, supporting the hypothesis that increased blood lead levels can also be associated with measurable neurocognitive abnormalities.

Lead neurotoxicity in children: basic mechanisms and clinical correlates

Lead has been recognized as a poison for millennia and has been the focus of public health regulation in much of the developed world for the better part of the past century. The nature of regulation has evolved in response to increasing information provided by vigorous scientific investigation of lead's effects. In recognition of the particular sensitivity of the developing brain to lead's pernicious effects, much of this legislation has been addressed to the prevention of childhood lead poisoning. The present review discusses the current state of knowledge concerning the effects of lead on the cognitive development of children. Addressed are the reasons for the child's exquisite sensitivity, the behavioural effects of lead, how these effects are best measured, and the long-term outlook for the poisoned child. Of particular importance are the accumulating data suggesting that there are toxicological effects with behavioural concomitants at exceedingly low levels of exposure. In addition, there is also evidence that certain genetic and environmental factors can increase the detrimental effects of lead on neural development, thereby rendering certain children more vulnerable to lead neurotoxicity. The public health implications of these findings are discussed.

Childhood lead poisoning from paint chips: a continuing problem

Although lead poisoning (plumbism) has been recognized for centuries, lead exposures still occur frequently today because of its varied uses and persistence in the environment. Despite the awareness of the adverse effects of lead on adults, childhood plumbism was first reported only about a century ago. Young children are one of the most vulnerable groups to the adverse effects of lead because of their rapidly developing central nervous systems. Federal regulations in the 1970s have been successfully implemented to decrease the amount of environmental lead by decreasing the content of lead in gasoline and indoor paint. However, almost 30 years after these laws were passed, inner-city housing with leaded paint still exists. We describe three children living in New York City who developed plumbism from the ingestion of leaded paint chips.

Lead in drinking water of Vienna in comparison to other European countries and accordance with recent guidelines

Due to the decrease of lead intake via inhalation route, the oral route, particularly from drinking water in cities with lead installations, gains relative importance. In two surveys a total of 288 objects were investigated and 1768 samples were analysed. The first series with 51 objects using a field experimental approach systematically investigated the effects of daytime, floor and flushing. Because only objects built before 1945 and suspected of lead plumbing were chosen, the first series approaches worst case conditions. The second series investigating 237 randomly chosen objects stratified according to time of consumption should allow inferences about the present situation in Viennese households. Each sampling procedure comprised one sample without flushing and three further samples with flushing of 1 l, 3 l and 10 l, respectively. Statistically significant decreases occurred between these flushing conditions. The sampling data of the upper floors showed significantly higher lead contents compared to the lower floors, which indicates that house installations are the main causes of lead contamination in Viennese drinking water. In comparison to other European countries the percentage of samples exceeding the guideline levels (50 micrograms/l as current value and 10 micrograms/l as target value) was lower.

On being a whistleblower: the Needleman case

We believe that members of the scientific community have a primary obligation to promote integrity in research and that this obligation includes a duty to report observations that suggest misconduct to agencies that are empowered to examine and evaluate such evidence. Consonant with this responsibility, we became whistleblowers in the case of Herbert Needleman. His 1979 study (Needleman et al., 1979), on the effects of low-level lead exposure on children, is widely cited and highly influential in the formulation of public policy on lead. The opportunity we had to examine subject selection and data analyses from this study was prematurely halted by efforts to prevent disclosure of our observations. Nevertheless, what we saw left us with serious concerns. We hope that the events here summarized will contribute to revisions of process by which allegations of scientific misconduct are handled and that such revisions will result in less damage to scientists who speak out.

Early lead exposure produces lasting changes in sustained attention, response initiation, and reactivity to errors

The present study tested the hypothesis that early lead (Pb) exposure causes lasting attentional dysfunction. Long-Evans dams were fed Pb-adulterated water during gestation and/or lactation; the offspring were tested as adults. The results of a visual discrimination task revealed no Pb effects on learning rate or information-processing speed. However, lasting effects of the early Pb exposure were seen in the subsequent vigilance tasks, particularly in the final task in which onset of the visual cue and cue duration varied randomly across trials. Exposure during both gestation and lactation impaired response initiation. In addition, animals exposed to Pb during lactation only or lactation+gestation committed significantly more omission errors than controls under two specific conditions: (1) trials in which a delay was imposed prior to cue presentation and (2) trials that followed an incorrect response. The pattern of treatment differences indicated that early Pb exposure produced lasting impairment of sustained attention and increased reactivity to errors. Both effects may contribute to the cognitive impairment, problematic classroom behaviors, and increased delinquency associated with early Pb exposure in children. These findings also demonstrate that the developmental timing of the exposure determines the pattern of effects. Thus, conclusions regarding whether or not a particular cognitive or affective function is impaired or spared by early Pb exposure must be limited to the specific timing and intensity of exposure.

Exposure to lead appears to selectively alter metabolism of cortical gray matter

OBJECTIVE

The effects of lead poisoning on the development of children have been examined primarily in the context of behavioral and neuropsychological studies. The purpose of this study was to examine the in vivo use of magnetic resonance spectroscopy (MRS) for the evaluation of the neurotoxic effects of lead on the nervous system. MRS has the ability to monitor brain metabolism by detecting a number of neurochemicals among which is N-acetylaspartate, a metabolite shown to decrease in processes that involve neuronal loss.

METHODS

In the present study we evaluated the metabolism of gray and white matter of frontal cortex using MRS in individuals with elevated blood lead levels and compared the results with those obtained on nonlead-exposed controls.

RESULTS

Although all of the participants had normal MRI examinations of the brain, the lead-exposed individuals exhibited a significant reduction in the N-acetylaspartate/creatine and phosphocreatine ratios in frontal gray matter compared with the nonlead-exposed controls.

CONCLUSIONS

The findings of this study suggest that lead has an effect on brain metabolites as detected by MRS in vivo. More specifically, we have found statistically significant reduced levels of brain metabolites in gray but not white matter in lead-exposed individuals. These results imply that MRS is able to detect metabolic abnormalities in individuals with lead poisoning.

Temporal pattern in the effect of postnatal blood lead level on intellectual development of young children

To determine the temporal pattern of the effect of postnatal blood lead level on the General Cognitive Index (GCI) of the McCarthy Scales of Children's Abilities, we used data from 112 children of the Mexico City Prospective Lead Study with complete evaluations from 36 to 60 months of age at 6-month intervals. We measured blood lead level every 6 months from 6 to 54 months. We controlled for 5-min Apgar, birth weight, birth order, sex, socioeconomic level, maternal IQ, and maximum maternal educational level in a repeated measures ANCOVA using child blood lead level grouped by 6-18 month (geometric mean 10.1 microg/dl, range 3.5-37.0 microg/dl), 24-36 month (geometric mean 9.7 microg/dl, range 3.0-42.7 microg/dl), and 42-54 month (geometric mean 8.4 microg/dl, range 2.5-44.8 microg/dl) averages. There were significant interactions between the 6-18 month blood lead level and age with GCI as the endpoint and between 24-36 month blood lead level and age. The regression coefficient of blood lead at 6-18 months became more negative with age until 48 months, when the rate of decline moderated (linear polynomial contrast p=0. 047). The regression coefficient of blood lead at 24-36 months with CGI became more negative as well from 36 to 48 months but then started decreasing toward zero from 48 to 60 months (quadratic polynomial contrast p=0.019). Significant between-subjects lead effects on GCI were found for 24-36 month blood lead level at 48 months (p=0.021) and at 54 months (p=0.073). The greatest effect (at 48 months) was a 5.8-point GCI decrease with each natural log unit increase in blood lead. Significant between-subjects lead effects on GCI were found for 42-54 month blood lead level at 54 months (p=0. 040) and at 60 months (p=0.060). The effect of postnatal blood lead level on GCI reaches its maximum approximately 1-3 years later, and then becomes less evident. Four to five years of age appears to be a critical period for the manifestation of the earlier postnatal blood lead level effects.

Lead exposure and motor functioning in 4(1/2)-year-old children: the Yugoslavia prospective study

OBJECTIVE

To investigate associations between lead exposure and early motor development.

STUDY DESIGN

We conducted standardized assessments of motor function (Bruininks-Oseretsky Test of Motor Proficiency and Beery Developmental Test of Visual-Motor Integration) at age 54 months in 283 children whose mothers were recruited in pregnancy from a smelter town and a non-lead-exposed town in Yugoslavia and who have been monitored twice yearly since birth. Blood lead concentration (BPb) was summarized in a measure reflecting the average of the child's semiannual serial log BPbs through 54 months.

RESULTS

Multiple regression showed that taken together, anthropometric measures (birth weight, body mass index) and markers of a stimulating and organized home life (HOME scale, parental education and intelligence, availability of siblings) explained a significant 10% to 18% of the variance in motor functioning. Beyond these contributions, BPb was significantly associated with poorer fine motor and visual motor function but was unrelated to gross motor coordination.

CONCLUSIONS

Modest associations between early lead exposure and fine motor and visual motor functioning appear even after statistical adjustment is done for other contributors to motor development. Associations with BPb are specific to these areas of motor skill; gross motor development was unaffected.

Developmental considerations of neurotoxic exposures

In this article, the authors provide a conceptual framework in which to consider alternative approaches to identify the developmental consequences of exposing the developing brain to neurotoxic substances. Concepts underlying brain development and issues regarding neurobehavioral testing in children are reviewed. In addition, the authors selectively review preclinical data identifying mechanisms contributing to neurobehavioral compromise, and clinical data identifying deficits resulting from exposure to two classes of neurotoxins: exposure to drugs of abuse, including alcohol, nicotine, and cocaine; and exposure to environmental agents, including lead, methyl-mercury, PCBs, and organophosphorus compounds.

Effects of chronic lead exposure on learning and reaction time in a visual discrimination task

Long-Evans rats exposed chronically to lead (Pb) acetate (0, 75, or 300 ppm) were tested as adults on an automated, three-choice visual discrimination task as part of a larger study designed to elucidate the cognitive effects of developmental Pb exposure. Median adult BPb levels for the groups were <5, 20, and 36 microgram/dl. The pattern of results suggested a linear effect, with increasing lead dose producing progressively slower learning and an increased incidence of "impaired" individuals. This latter measure proved to be slightly more sensitive than the former, suggesting individual differences in susceptibility to Pb neurotoxicity. Additional analyses revealed that the impairing effect of Pb was seen in both the chance and post-chance learning phases, indicating that the deficit was not limited to (but could include) attentional function. Reaction time on incorrect trials was reduced in the 300-ppm group, whereas no Pb effect was seen for correct trials. The present findings suggest that chronic developmental Pb exposure produces an associative deficit as well as a tendency to respond rapidly, but does not affect information-processing speed.

Neuropsychological Toxicology

Humans exposed to neurotoxins may exhibit alterations in cognitive and affective functioning and report a wide range of subjective symptoms. The multidisciplinary field of “neuropsychological toxicology” provides a framework for the systematic assessment and interpretation of adverse effects. Neuropsychological assessment is of interest not only to clinicians, but also to regulatory and legislative authorities. The importance of neuropsychological toxicology in the area of occupational risk research is increasingly being recognized. Possible fields of application include behavioral monitoring for preventive purposes, expert assessment in the context of compensation cases, and treatment in rehabilitation programs. This article reviews common research approaches, selected findings, and methodological problems of this emerging discipline and summarizes the implications for related fields of psychological research.

Neurodevelopmental evaluation of 9-month-old infants exposed to low levels of lead in utero: involvement of monoamine neurotransmitters

The objective of this work is to investigate the neurotoxicty of low-level lead exposure in utero on infants and the possible involvement of dopaminergic and serotonergic neurotransmitters. The correlation analysis for cord blood lead level, the concentrations of dopamine metabolite homovanillic acid (HVA) and serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cord plasma and the neurodevelopmental scales of infants were conducted on 244 9-month-old children. Both score of sociability subscale and 5-HIAA concentration were correlated with cord blood lead level. The sociability score was negatively correlated with the concentration of HVA, whereas both the coordination score and the global score were negatively correlated with the concentration of 5-HIAA. With partial correlation analysis, after taking HVA into account, the significant negative correlation between the sociability score and the cord blood lead level that existed in the linear correlation analysis disappeared, and the score of global scale correlated negatively with lead level in cord blood. When taking 5-HIAA into account, the scores of all the neurodevelopmental subscales except the language subscale were significantly negatively correlated with lead level in cord blood. The results indicated that low-level lead exposure in utero could produce a neurotoxic effect on the developing serotonergic system in infants. The neurotoxicity of low-level lead exposure in utero may affect the sociability of infants. Serotonergic activity was shown to have a potential effect on neurodevelopmental assessment. It may interfere with the association between low-level lead exposure in utero and other neurodevelopmental performances of 9-month-old children.

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.

Cognitive and sensorimotor functions in 6-year-old children in relation to lead and mercury levels: adjustment for intelligence and contrast sensitivity in computerized testing

Within a larger environmental health screening program neurobehavioral measures were taken in 384 6-year-old children (mean age 74 months) in the cities of Leipzig, Gardelegen, and Duisburg. Lead concentrations in venous blood samples (PbB) and urinary mercury excretion in 24-h samples (HgU) were measured as markers of environmental exposure by electrothermal AAS. Dependent variables included two subtests from the WISC [vocabulary (V) and block design (BD)] as well as five tests from the NES2 [pattern comparison, pattern memory, tapping, simple reaction time, and the continuous performance test (CPT; child version)]. In addition, visual functions [visual acuity (TITMUS-test) and contrast sensitivity (FACT)] were tested as covariates. The overall average PbB (geometric mean) was 42.5 microg/l (upper 95% value = 89 microg/l). The overall average mercury excretion (HgU) was 0.16 microg/24 h. Whereas no significant or borderline associations between HgU and any of the target variables was found, significant negative associations were observed between PbB and verbal intelligence (WISC vocabulary but not WISC Block Design) and false-positive responses (false alarms), as well as false-negative responses (miss) in the CPT. Whereas parental education was the most important confounder for WISC performance, visual contrast sensitivity and computer familiarity also proved predictive for performance in several computer-based NES subtests. It is concluded that non-IQ measures, namely measures of sustained attention, are negatively affected in children with 95% of blood-lead levels below 90 microg/l, even after adjustment for intelligence and contrast sensitivity, whereas the causative role of lead in altering IQ functions remains somewhat equivocal, because important covariates could not be controlled for.

Position paper of the American Council on Science and Health: lead and human health

The potential human health risk of lead in the environment remains a topic of current debate and concern. Given sufficient exposure, lead can exert severe and chronic health effects. Today, due to successful efforts to reduce the commercial use of lead and control its release to the environment, lead "poisoning" is uncommon in our society. Blood-lead levels among the U.S. population, including those of children, have decreased dramatically over the past decade and according to current surveillance programs continue to decline. Because lead poisoning among children is no longer as prevalent as it once was, the focus has shifted to the long-term effects lead may exert on the intellectual development of children. Continued toxicological and epidemiological research will expand the understanding of this important facet of the lead issue. Trace levels of lead in consumer products remain a low health risk to humans, despite the fear and uncertainty which often accompany such concerns. Future efforts to reduce lead exposure should be aimed at high-risk groups which include the socioeconomically disadvantaged and certain minority sectors of the population. Through educational programs, improvement in personal hygiene practices, and abatement of lead-containing paint (when warranted), blood lead levels should continue to decline, reducing the health risk to lead in the environment.

Effects of lead on the somatic growth of children

Studies on the effects of lead on the somatic growth of children are limited and contradictory. The authors investigated the adverse effects of blood lead concentration on the somatic growth of primary-school-age children. In this study, there was a total of 522 children, aged 6-9 y, who resided in three areas of Greece (i.e., Loutraki, Lavrion, and Elefsina). The medical evaluation included medical history; physical examination; and measurements of height, head circumference, and chest circumference. The authors also evaluated dietary information, socioeconomic status, and height of parents. The authors conducted laboratory tests for hematological parameters and blood lead levels. The mean blood lead level was 12.3 microg/dl (standard deviation = 8.9 microg/dl), and levels ranged from 1.3 microg/dl to 51.2 microg/dl. There were negative monotonic relationships between growth parameters and blood lead levels, even after the authors allowed for confounding effects. An increase in blood lead level of 10 microg/dl was associated with a decrease of (a) 0.33 cm in head circumference (95% confidence interval = 0.12, 0.55; p = .002); (b) 0.86 cm in height (95% confidence interval = 0.14, 1.16; p = .020); and (c) 0.40 cm in chest circumference (95% confidence interval = -0.22, 1.02; p = .207). These findings led the authors to conclude that a decrease in growth in children may be associated with blood lead concentrations.

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.

The neurobehavioural toxicology and teratology of lead

When comparing neurobehavioural observations from occupational lead-exposure of adults on the one hand, and environmental lead exposure of children on the other, it appears that the developing relative to the mature brain is more at risk. Neurobehavioural toxicity in occupational lead-exposure has typically not been observed at blood lead-concentrations (PbBs) below 400 micrograms/l, whereas ih environmentally exposed children such deficit has been reported to occur down to PbB of 100-150 micrograms/l and, perhaps, even below this range. Both cross-sectional and prospective studies have arrived at similar conclusions in this respect. The preferred endpoint in most such studies has been the IQ-measure, which has good psychometric qualities, is sufficiently well standardized to be comparable across studies, and exhibits attractive simplicity for the regulator in a public health context. At the same time, however, this IQ-focus has also interfered with systematic efforts to identify more specific lead-induced functional deficits by means of more detailed neurobehavioural analyses (Bellinger 1995). Metanalyses on both cross sectional and prospective studies in lead-exposed children have concluded that a typical doubling of PbB from 100 to 200 micrograms/l is associated with an average IQ-loss of 1-3 points (Pocock et al. 1994; WHO 1995), and no threshold has as yet been identified. Since, however, cause-effect contingencies necessarily remain doubtful in epidemiological studies if the observed effects are as subtle as these, experimental studies in animals have become helpful in supporting the causative role of lead to produce neurobehavioural deficit at steady-state PbB down to about 150 to 200 micrograms/l. Such deficit has been demonstrated by means of a variety of learning/memory models with positive and negative reinforcement contingencies in the rat--and in primates as well. It has also been shown in such studies that neurobehavioural deficit subsequent to early developmental exposure extends long into adulthood after cessation of exposure at weaning. It, therefore, appears that the neurobehavioural teratology of lead has more convincingly been demonstrated in animal models than in human exposure conditions, so far. A coherent theory to explain the particular vulnerability to lead of the developing brain is still lacking. Recent data do suggest, however, that Pb-induced disruption of calcium homeostasis in the immature brain might interfere with normal brain development.

Blood lead levels in 2- to 3-year-old children in the Greater Bilbao Area (Basque Country, Spain): relation to dust and water lead levels

The objectives of this study were to determine blood lead levels in 2-y-old children in the Greater Bilbao Area (Basque Country, Spain) and to compare those levels with the lead content of different media (i.e., house dust, park dust and soil, and water) in the child's environment. Between May and September of 1992, 138 children, aged 2 to 3 y, were studied. All children were attended by pediatricians within the public health-care network, and their parents volunteered for the study. A venous blood sample was drawn from each child and was analyzed for lead level, and the parents answered a questionnaire that addressed the socioeconomic background and habits of the children. The environment was investigated in 42 cases. Blood lead levels exceeded 15 micrograms/dl in 2% of the children, and 14% of the children had levels that exceeded 10 micrograms/dl (geometric mean = 5.7 micrograms/dl [4.7-6.7 micrograms/dl]. Blood lead levels were higher among (a) children whose mothers worked outside the home, (b) children whose fathers had only a primary-level education, and (c) children who lived in houses constructed prior to 1950. The geometrical averages of lead in house dust, park soil, and park dust were 595, 299, and 136 micrograms/g, respectively. Statistically significant linear correlation was found between blood lead level and lead content in park dust, a finding that explained a 9% variation in blood lead level; a subgroup of these children was also found to have a strong linear association between blood lead and lead content in house dust.

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.

An unknown risk group of lead poisoning: the gypsy children

The differences in average blood lead levels (PbB) between iron-deficient children of both gypsy and Caucasian origin were determined. PbB were assayed in 89 iron-deficient children (Group ID): 25 gypsies and 64 Caucasians. Two sub-groups were established: sub-group ID1, 57 iron-deficient children without anaemia (11 gypsies, 46 Caucasians), and sub-group ID2, 32 children with iron deficiency anaemia (14 gypsies; 18 Caucasians). Group IS composed of 41 iron-sufficient children (11 gypsies and 30 Caucasians) served as controls. Blood counts, red-cell indices, serum iron concentrations, serum ferritin, and PbB were determined for the entire study population. The average PbB for gypsy and Caucasian iron-deficient children, were 14.25 and 7.25 micrograms/dl (P < 0.01) respectively. The prevalence of iron-deficient children with toxic PbB (> 20 micrograms/dl) was higher in gypsies (24%) than in Caucasians (1.5%) (P < 0.01). A difference in average PbB between the two ethnic groups was also seen in children with normal iron metabolism (average PbB, 10.23 vs 5.65 micrograms/dl for gypsies and Caucasians, respectively, P < 0.001). CONCLUSION Gypsy children should be considered as a population group at risk of lead poisoning in our environment.