Intellectual impairment and blood lead levels

Low blood lead level effects on intelligence: can a dose-response curve be determined from the epidemiological data?

CONTEXT. Recent publications have graphically demonstrated a curvilinear relationship between measures of intelligence and blood lead levels at low concentrations (< 10 mcg/dl). This led to speculation that a greater biologic effect occurs at lower concentrations. Critics of this conclusion hypothesized that this graphical relationship may be a function of the underlying distributions of these variables. OBJECTIVE. To study the impact of the distribution of data on the shape of apparent dose-response curves. METHODS. Random data based on varied distributions were constructed to simulate a previous study using a single, randomly generated covariate income (Inc) to demonstrate the impact of normally versus exponentially distributed data on the shape of the graph of intelligence quotient (IQ) versus blood lead. We also used an existing database of US blood lead levels and constructed a similar model of income and IQ using both assumptions of distribution for the intermediate variable income. RESULTS. When both lead and income are exponentially distributed, the graph of lead and IQ will be a curve. CONCLUSION. The apparent shape of a dose-response relationship from simulated epidemiological data is nonlinear when one variable and a covariate are exponentially distributed. A non-linear biological relationship should not be assumed and in fact may be the least likely explanation. The use of observational epidemiological data to discern a dose-response relationship between two variables may be misleading.

Pb neurotoxicity: neuropsychological effects of lead toxicity

Neurotoxicity is a term used to describe neurophysiological changes caused by exposure to toxic agents. Such exposure can result in neurocognitive symptoms and/or psychiatric disturbances. Common toxic agents include heavy metals, drugs, organophosphates, bacterial, and animal neurotoxins. Among heavy metal exposures, lead exposure is one of the most common exposures that can lead to significant neuropsychological and functional decline in humans. In this review, neurotoxic lead exposure's pathophysiology, etiology, and epidemiology are explored. In addition, commonly associated neuropsychological difficulties in intelligence, memory, executive functioning, attention, processing speed, language, visuospatial skills, motor skills, and affect/mood are explored.

Blood lead levels in children after phase-out of leaded gasoline in Kinshasa, the capital of Democratic Republic of Congo (DRC)

Background

The phasing out of lead from gasoline has resulted in a significant decrease in blood lead levels (BLLs) in children during the last two decades. Tetraethyl lead was phased out in DRC in 2009. The objective of this study was to test for reduction in pediatric BLLs in Kinshasa, by comparing BLLs collected in 2011 (2 years after use of leaded gasoline was phased out) to those collected in surveys conducted in 2004 and 2008 by Tuakuila et al. (when leaded gasoline was still used).

Methods

We analyzed BLLs in a total of 100 children under 6 years of age (Mean ± SD: 2.9 ± 1.6 age, 64% boys) using inductively coupled argon plasma mass spectrometry (ICP – MS).

Results

The prevalence of elevated BLLs (≥ 10 μg/dL) in children tested was 63% in 2004 [n = 100, GM (95% CI) = 12.4 μg/dL (11.4 – 13.3)] and 71% in 2008 [(n = 55, GM (95% CI) = 11.2 μg/dL (10.3 – 14.4)]. In the present study, this prevalence was 41%. The average BLLs for the current study population [GM (95% CI) = 8.7 μg/dL (8.0 – 9.5)] was lower than those found by Tuakuila et al. (F = 10.38, p <0.001) as well as the CDC level of concern (10 μ/dL), with 3% of children diagnosed with BLLs ≥ 20 μg/dL.

Conclusion

These results demonstrate a significant success of the public health system in Kinshasa, DRC-achieved by the removal of lead from gasoline. However, with increasing evidence that adverse health effects occur at BLLs < 10 μg/dL and no safe BLLs in children has been identified, the BLLs measured in this study continue to constitute a major public health concern for Kinshasa. The emphasis should shift to examine the contributions of non-gasoline sources to children’s BLLs: car batteries recycling in certain residences, the traditional use of fired clay for the treatment of gastritis by pregnant women and leaded paint.

Assessment of potential health risk for inhabitants living near a former lead smelter. Part 2: site-specific human health risk assessment of Cd and Pb contamination in kitchen gardens

Metal contamination of urban soils and homegrown products has caused major concern. In Part 1, we investigated the long-term effects of a former smelter on the degree of kitchen garden-soil contamination and the quality of the homegrown vegetables from these gardens. The results showed that the soils retained a high level of contamination and that a large proportion of the vegetables produced did not comply with the legislation on the levels of metals allowed for human consumption. The present study aims to assess the associated potential health risk to local inhabitants through consumption of homegrown vegetables and ingestion of soil particles using a land use-based approach. For lead (Pb), the standard hazard quotient (HQ)-based risk assessment method was used to determine the HQ. For cadmium (Cd), the approach consisted of calculating the HQs and then deriving site-specific assessment criteria (SSAC) using the SNIFFER method. The results suggested that the exposure pathways considered should not engender any form of deleterious health effects for adults. For children, Pb was the main concern and induced a relatively high health risk through soil particle ingestion, and most total soil Cd concentrations exceeded the derived SSAC, in particular, through consumption of vegetables. The metal bioaccessibility in soils was incorporated into the methods to establish more realistic risk assessment measures. This study proposes an approach to integrate different human health risk assessment methods. Further investigations should complete the assessment to improve risk determination, e.g., the determination of metal bioaccessibility in vegetables.

Implications of different residential lead standards on children's blood lead levels in France: predictions based on a national cross-sectional survey

Despite the dramatic reductions in children's blood lead levels (BLLs), there is considerable evidence that low-level lead exposure is associated with intellectual deficits and behavioral problems, without apparent threshold. There are limited data, however, about the contribution of residential sources of lead to contemporary children's blood lead levels. The aim of this study is to calculate the contributions of residential sources of lead to assess the potential impact of setting new standards for lead levels in residential dust, soil and water. We enrolled 484 French children aged from 6 months to 6 years, and collected data on social, housing and individual characteristics. Lead concentrations in blood and environmental samples (water, soils, and dusts) were measured using inductively coupled plasma mass spectrometry. Data were analyzed using a multivariate generalized additive model accounting for the sampling design and the sampling weights. We found that exceedingly low concentrations of lead in dust, soil and water were significant predictors of children's BLLs, after adjustment for potential confounding variables. Lead-contaminated floor dust was the main source of lead in blood. BLLs (GM: 14μg/L) increased by 65%, 13%, 25%, and 5% when lead content in floor dust, loose soil, hard soil and water increased from their 25th percentile to their 95th percentile, respectively. We also observed that the steepest increase in BLLs occurred at the lowest levels of lead-contaminated floor dust, which indicates that lead contamination should be kept as low as possible. Impact of different possible standards on children's BLLs was also tabulated and indicated that unless standards are set low, they will only benefit a small proportion of children who have the highest exposures.

Manioc flour consumption as a risk factor for lead poisoning in the Brazilian Amazon

Recent studies reported elevated blood lead (Pb) levels in riparian populations of the Amazon. For this reason, the aim of the present study was to assess the risk to riparians in the Brazilian Amazon to Pb exposure due to the intake of contaminated manioc flour. Lead levels were determined in whole blood (n = 74) and in manioc flour samples (n = 30) in three different communities. Mean blood Pb levels were 16.8 μg/dl, with individuals living in Açaituba presenting the highest mean blood Pb level (22.4 μg/dl), followed by Nova Canaã (17.3 μg/dl) and Santa Cruz (9.8 μg/dl). The minimum blood Pb level found was 0.83 μg/dl and the maximum was 44.3 μg/dl. The estimated daily intake (EDI) was calculated and compared to the benchmark dose lower confidence limit (BMDL) for neurotoxicity. Mean Pb in manioc flour was 0.34 μg/g while EDI was 79 μg/d, corresponding to 260% of the BMDL (varying from 168 to 308%). This finding is of great importance since this high EDI may exert adverse effects on the nervous system of this population. Manioc flour intake may thus present considerable risk of Pb exposure in this region. Risk management strategies and further studies on adverse effects in this population are needed.

Elevated blood lead levels and sources of exposure in the population of Kinshasa, the capital of the Democratic Republic of Congo

The objective of this study was to determine blood lead levels (BLLs) and the possible sources of exposure in the population of Kinshasa, the capital of the Democratic Republic of Congo. A cross-sectional survey was carried out from January to May 2008 in a representative sample of the Kinshasan population. BLL was measured in 275 individuals (53.4% women) aged 1-70 years in the urban area of Kinshasa and from 60 additional subjects in the rural area. Pb was also determined in environmental specimens (air and soil, indoor and outdoor). BLL in the study population ranged from 2.9 to 49.3 μg/dl (median, 9.9 μg/dl). The median BLL among children aged <6 years was 11.5 μg/dl (range: 3.0-37.8 μg/dl). Of these children, 71% had elevated BLL (≥10 μg/dl) and 22% had BLL ≥20 μg/dl. The proportion of elevated BLL (≥10 μg/dl) was higher for children aged <3 years than for children aged 3 to 5 years (97% vs 56%). A higher prevalence of elevated BLL was observed in urban compared with rural children (71% vs 20%). Significantly higher BLLs were also found in children whose mother consumed fired clay during pregnancy. Residential informal activities in the recycling of car batteries also contributed to elevated BLL in children. The elevated background of Pb exposure in the Kinshasan population indicates a public health issue that requires corrective actions. Pb-contaminated dust and air in children's home is an issue of public health concern. The use of leaded gasoline and the activities of car battery recycling in certain residences appear to constitute the main sources of exposure in the city of Kinshasa. The traditional use of fired clay for the treatment of gastritis by pregnant women is another significant contributor for elevated BLL in children.

Blood lead levels and enzymatic biomarkers of environmental lead exposure in children in Cordoba, Argentina, after the ban of leaded gasoline

Lead (Pb) is a developmental neurotoxicant found in industrial activities, many of them already prohibited worldwide. This study aimed to evaluate current blood Pb (PbB) levels in children in Cordoba, Argentina, and to compare these with similar studies performed before Pb was banned in gasoline in 1996. We also sought to identify mechanistically relevant biomarkers by measuring δ-aminolevulinic acid dehydratase (δ-ALAD), superoxide dismutase (SOD), and catalase (CAT) activities. We finally aimed to determine whether sociodemographic characteristics are associated with Pb toxicity. Blood samples collected from 161 healthy children between September 2009 and February 2010 revealed mean PbB levels of 2.58 ± 0.30 µg/dl. Enzymatic δ-ALAD, CAT, and SOD activities showed no significant variations when plotted against PbB levels. Finally, children living in the suburbs have higher PbB levels than their city counterparts, while low socioeconomic status increased δ-ALAD inhibition compared with that of middle-income children. Overall, these results evidenced a substantial reduction in exposure to Pb in this pediatric population over a decade after Pb was restricted in gasoline and reveal the importance of pursuing novel biomarkers of toxicity along with the sociodemographic profile to complement Pb diagnosis.

Understanding how brass ball valves passing certification testing can cause elevated lead in water when installed

The lead leaching potential of new brass plumbing devices has come under scrutiny as a significant source of lead in drinking water (>300 μg/L) of new buildings around the world. Experiments were conducted using ball valves that were sold as certified and known to have caused problems in practice, in order to better understand how installed products could create such problems, even if they passed "leaching tests" such as National Sanitation Foundation (NSF) Standard 61 Section 8. Diffusion of lead from within the device into water when installed can increase lead leaching by orders of magnitude relative to results of NSF testing, which once only required exposure of very small volumes of water within the device. "Normalization" of the lead-in-water result tended to produce estimates of lead concentration that were much lower than actual lead measured at the tap. Finally, the presence of flux could also dramatically increase lead leaching, whereas high water velocity had relatively little effect.

When are fetuses and young children most susceptible to soil metal concentrations of arsenic, lead and mercury?

This study was designed to analyze when, during pregnancy and early childhood, the association between soil metal concentrations of arsenic (As), lead (Pb) and mercury (Hg) and the outcome of intellectual disability (ID) is statistically significant. Using cluster analysis, we identified ten areas of land that contained a cluster of ID and areas of average risk for ID. We analyzed soil for As, Pb, and Hg and estimated the soil metal concentration at the residential sites where the woman and children lived during pregnancy and early childhood using a Bayesian Kriging model. Arsenic concentrations were associated with ID during the first trimester of pregnancy and Hg was associated with ID early in pregnancy and the first two years of childhood. The covariates that remained in the final models were also temporally associated with ID.

Health risk assessment of lead for children in tinfoil manufacturing and e-waste recycling areas of Zhejiang Province, China

Tinfoil manufacturing and electronic waste (e-waste) recycling remain rudimentary processes in Zhejing Province, China, which could account for elevated blood lead levels (BLLs) and health impacts on children. We assessed the potential health risks of lead in tinfoil manufacturing and e-waste recycling areas. 329 children in total aged 11-12 who lived in a tinfoil manufacturing area (Lanxi), an e-waste recycling area (Luqiao) and a reference area (Chun'an) were studied. Lead levels in children's blood were determined by inductively coupled plasma mass spectrometer (ICP-MS). Blood urea nitrogen (BUN), serum creatinine, serum calcium, δ-Aminolaevulinic acid (δ-ALA) and intelligence quotient (IQ) were also measured. Geometric mean of BLLs in Lanxi, Luqiao and Chun'an were 8.11 μg/dL, 6.97 μg/dL, and 2.78 μg/dL respectively, with 35.1%, 38.9% and 0% of children who had BLLs above 10 μg/dL. The BLLs in exposed areas were much higher than those in the control area. Lanxi children had higher creatinine and calcium than Chun'an children, and Luqiao children had higher δ-ALA and lower calcium than Chun'an children. No significant differences of IQ were observed between Lanxi, Luqiao and Chun'an, however a negative relationship between BLLs and IQ was shown for the study children. The results indicated that lead pollution from e-waste recycling and tinfoil processing appears to be a potential serious threat to children's health.

Lead neurotoxicity: effects on brain nitric oxide synthase

Lead (Pb), a ubiquitous and potent neurotoxicant, induces several neurophysiological and behavioural changes, while Pb alters the function of multiple organs and systems, it primarily affects the central nervous system. In human adults, encephalopathy resulting from Pb intoxication is often characterized by sleeplessness, poor attention span, vomiting, convulsions and coma; in children, Pb-induced encephalopathy is associated with mental dullness, vomiting, irritability and anorexia; diminished cognitive function resulting in a mental deficit has been also observed during Prolonged exposure to Pb. Pb can produce oxidative stress, disrupt the blood-brain barrier and alter several Ca(2+)-dependent processes, including physiological processes that involve nitric oxide synthesis on central nervous system in development and adult animals. This review summarizes recent evidence showing that Pb can interfere with the production of nitric oxide and can disrupt the function of nitric oxide synthase. Lead interferes with nitric oxide-related physiological mechanisms, and Pb neurotoxicity may affect processes involved in learning and memory.

Determinants of lead exposure in children on the outskirts of Salvador, Brazil

Lead (Pb) is a toxic heavy metal that is widely distributed throughout the environment. Pb is an important neurotoxic metal and children are more susceptible to its effect due to their higher absorption rate and greater susceptibility of the developing nervous system. In this work, we evaluated the lead exposure levels in children living near a metallurgical plant and identified risk factors associated with its internal dose. All children, aged 1-10 years and 11 months, living near a metallurgical plant in the great Salvador area, Brazil were evaluated in this cross-sectional study and compared with children from a non exposed area. Occipital hair and blood were used to assess exposure. Air lead levels in the respirable fraction (PM(2.5)) were also measured in both areas. Blood lead levels (BLL), hair lead levels (PbH) and air lead were determined by graphite furnace atomic absorption spectrometry. Spearman correlations analysis was used to evaluate correlations between BLL, PbH and descriptors. Significant risk factors were modeled using multivariate linear regression analysis. Air lead levels were approximately ten-folds lower than EPA reference concentration (0.15 μg/m(3)). Median BLL and PbH were 1.65 ± 1.45 μg/dL and 1.26 ± 3.70 μg/g, respectively, in exposed children. In the referents, medians were BLL 1.20 ± 1.20 μg/dL; PbH 2.09 ± 2.06 μg/g. No significant difference was observed in biomarkers levels between boys and girls. It was observed a positive weak correlation (Spearman rho = 0.197, p = 0.033) between BLL and PbH. Our data show that children's lead body burden measured as BLL or PbH are low when compared with the recommended reference values. Despite that, we were able to identify four risk factors associated with increased biological lead levels: age, living near industrial site, environmental tobacco smoking and, above all, domestic waste burning. In order to prevent such avoidable exposure, environmental education and proper waste management should be implemented, especially in developing countries.

Integrating susceptibility into environmental policy: an analysis of the national ambient air quality standard for lead

Susceptibility to chemical toxins has not been adequately addressed in risk assessment methodologies. As a result, environmental policies may fail to meet their fundamental goal of protecting the public from harm. This study examines how characterization of risk may change when susceptibility is explicitly considered in policy development; in particular we examine the process used by the U.S. Environmental Protection Agency (EPA) to set a National Ambient Air Quality Standard (NAAQS) for lead. To determine a NAAQS, EPA estimated air lead-related decreases in child neurocognitive function through a combination of multiple data elements including concentration-response (CR) functions. In this article, we present alternative scenarios for determining a lead NAAQS using CR functions developed in populations more susceptible to lead toxicity due to socioeconomic disadvantage. The use of CR functions developed in susceptible groups resulted in cognitive decrements greater than original EPA estimates. EPA’s analysis suggested that a standard level of 0.15 µg/m³ would fulfill decision criteria, but by incorporating susceptibility we found that options for the standard could reasonably be extended to lower levels. The use of data developed in susceptible populations would result in the selection of a more protective NAAQS under the same decision framework applied by EPA. Results are used to frame discussion regarding why cumulative risk assessment methodologies are needed to help inform policy development.

Study of lead level during pregnancy by application of synchrotron radiation micro XRF

In order to study the daily Pb absorption in fetus and to monitor the main Pb sources in prenatal fetus, we have investigated several cases of Pb distribution along the longitudinal axis of fetal hair. The changes of Pb levels in the pregnancy period, even the daily changes of Pb levels can be detected in the hair. Therefore, by analyzing the Pb distribution curves in the fetal hair and the living habits of their mothers, the main sources of Pb in the prenatal fetus can be evaluated. In our study, the main sources of Pb in the two cases of prenatal fetus studied here should be from the polluted aquatics.

Identification of sources of lead exposure in French children by lead isotope analysis: a cross-sectional study

BACKGROUND

The amount of lead in the environment has decreased significantly in recent years, and so did exposure. However, there is no known safe exposure level and, therefore, the exposure of children to lead, although low, remains a major public health issue. With the lower levels of exposure, it is becoming more difficult to identify lead sources and new approaches may be required for preventive action. This study assessed the usefulness of lead isotope ratios for identifying sources of lead using data from a nationwide sample of French children aged from six months to six years with blood lead levels ≥25 μg/L.

METHODS

Blood samples were taken from 125 children, representing about 600,000 French children; environmental samples were taken from their homes and personal information was collected. Lead isotope ratios were determined using quadrupole ICP-MS (inductively coupled plasma - mass spectrometry) and the isotopic signatures of potential sources of exposure were matched with those of blood in order to identify the most likely sources.

RESULTS

In addition to the interpretation of lead concentrations, lead isotope ratios were potentially of use for 57% of children aged from six months to six years with blood lead level ≥ 25 μg/L (7% of overall children in France, about 332,000 children), with at least one potential source of lead and sufficiently well discriminated lead isotope ratios. Lead isotope ratios revealed a single suspected source of exposure for 32% of the subjects and were able to eliminate at least one unlikely source of exposure for 30% of the children.

CONCLUSIONS

In France, lead isotope ratios could provide valuable additional information in about a third of routine environmental investigations.

Lab-on-a-chip sensor for detection of highly electronegative heavy metals by anodic stripping voltammetry

This work describes development of a lab-on-a-chip sensor for electrochemical detection of highly electronegative heavy metals such as manganese and zinc by anodic stripping voltammetry. The sensor consists of a three-electrode system, with a bismuth working electrode, a Ag/AgCl reference electrode, and a Au auxiliary electrode. Hydrolysis at the auxiliary electrode is a critical challenge in such electrochemical sensors as its onset severely limits the ability to detect electronegative metals. The bismuth working electrode is used due to its comparable negative detection window and reduced toxicity with respect to a conventional mercury electrode. Through optimization of the sensor layout and the working electrode surface, effects of hydrolysis were substantially reduced and the potential window was extended to the -0.3 to -1.9 V range (vs. Ag/AgCl reference electrode), which is far more negative than what is possible with conventional Au, Pt, or carbon electrodes. The described lab-on-a-chip sensor for the first time permits reliable and sensitive detection of the highly electronegative manganese. The favorable performance of the bismuth electrode coupled with its environmentally-friendly nature make the described sensor attractive for applications where disposable chips are desirable. With further development and integrated sample preparation, the lab-on-a-chip may be converted into a point-of-care platform for monitoring heavy metals in blood (e.g., assessment of manganese exposure).

Probability of intellectual disability is associated with soil concentrations of arsenic and lead

BACKGROUND

The association between metals in water and soil and adverse child neurologic outcomes has focused on the singular effect of lead (Pb), mercury (Hg), and arsenic (As). This study describes the complex association between soil concentrations of As combined with Pb and the probability of intellectual disability (ID) in children.

METHODS

We used a retrospective cohort design with 3988 mother child pairs who were insured by Medicaid and lived during pregnancy and early childhood in South Carolina between 1/1/97 and 12/31/02. The children were followed until 6/1/08, using computerized service files, to identify the diagnosis of ID in medical records and verified by either school placement or disability service records. The soil was sampled using a uniform grid and analyzed for eight metals. The metal concentrations were interpolated using Bayesian Kriging to estimate concentration at individual residences.

RESULTS

The probability of ID increased for increasing concentrations of As and Pb in the soil. The Odds Ratio for ID, for one unit change in As was 1.130 (95% confidence interval 1.048-1.218) for Pb was 1.002 (95% confidence interval 1.000-1.004). We identified effect modification for the infants based on their birth weight for gestational age status and only infants who were normal size for their gestational age had increased probability of ID based on the As and Pb soil concentrations (OR for As at normal weight for gestational age=1.151 (95% CI: 1.061-1.249) and OR for Pb at normal for gestational age=1.002 (95% CI: 1.002-1.004)). For normal weight for gestational age children when As=22 mg kg(-1) and Pb=200 mg kg(-1) the risk for ID was 11% and when As=22 mg kg(-1)and Pb=400 mg kg(-1) the probability of ID was 65%.

CONCLUSION

The probability of ID is significantly associated with the interaction between Pb and As for normal weight for gestational age infants.

Reduction of blood lead levels in lead-exposed mice by dietary supplements and natural antioxidants

BACKGROUND

Lead exposure is a global environmental problem that induces lifelong adverse health effects. Our aim was to investigate the effect of dietary supplements and natural antioxidants on blood lead levels (BLL) in lead-exposed mice, and observe their impact on the absorption of calcium, iron and zinc in vivo.

RESULTS

All of selected dietary supplements (calcium lactate, zinc sulfate, ferrous sulfate, ascorbic acid and calcium-rich milk) and natural antioxidants (extract of Chinese wolfberry, extract of Hangzhou white chrysanthemum and antioxidant extract of bamboo leaves) have promising capacity of reducing BLL in lead-exposed mice with an reduction range from 56.2% to 65.1%. The metal ion-mediated chelating and competitively inhibitory mechanisms may elucidate their reduction effect. Besides, blood calcium, iron and zinc levels were not significantly changed in all of the experimental groups, indicating that the intake of all additives does not disturb the absorption of essential mineral elements in mice.

CONCLUSION

All the studied additives not only effectively reduce BLL, but also maintain normal calcium, iron and zinc absorption in mice. The formulation of calcium, iron and zinc supplements and/or polyphenol and vitamin-rich antioxidants may constitute an important secondary prevention effort to reduce BLL and lead exposure.

Is dental amalgam safe for humans? The opinion of the scientific committee of the European Commission

It was claimed by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)) in a report to the EU-Commission that "....no risks of adverse systemic effects exist and the current use of dental amalgam does not pose a risk of systemic disease..." [1, available from: http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_016.pdf].SCENIHR disregarded the toxicology of mercury and did not include most important scientific studies in their review. But the real scientific data show that:(a) Dental amalgam is by far the main source of human total mercury body burden. This is proven by autopsy studies which found 2-12 times more mercury in body tissues of individuals with dental amalgam. Autopsy studies are the most valuable and most important studies for examining the amalgam-caused mercury body burden.(b) These autopsy studies have shown consistently that many individuals with amalgam have toxic levels of mercury in their brains or kidneys.(c) There is no correlation between mercury levels in blood or urine, and the levels in body tissues or the severity of clinical symptoms. SCENIHR only relied on levels in urine or blood.(d) The half-life of mercury in the brain can last from several years to decades, thus mercury accumulates over time of amalgam exposure in body tissues to toxic levels. However, SCENIHR state that the half-life of mercury in the body is only "20-90 days".(e) Mercury vapor is about ten times more toxic than lead on human neurons and with synergistic toxicity to other metals.(f) Most studies cited by SCENIHR which conclude that amalgam fillings are safe have severe methodical flaws.

Association between children's blood lead levels, lead service lines, and water disinfection, Washington, DC, 1998-2006

OBJECTIVE

Evaluate the effect of changes in the water disinfection process, and presence of lead service lines (LSLs), on children's blood lead levels (BLLs) in Washington, DC.

METHODS

Three cross-sectional analyses examined the relationship of LSL and changes in water disinfectant with BLLs in children <6 years of age. The study population was derived from the DC Childhood Lead Poisoning Prevention Program blood lead surveillance system of children who were tested and whose blood lead test results were reported to the DC Health Department. The Washington, DC Water and Sewer Authority (WASA) provided information on LSLs. The final study population consisted of 63,854 children with validated addresses.

RESULTS

Controlling for age of housing, LSL was an independent risk factor for BLLs ≥ 10 μg/dL, and ≥ 5 μg/dL even during time periods when water levels met the US Environmental Protection Agency (EPA) action level of 15 parts per billion (ppb). When chloramine alone was used to disinfect water, the risk for BLL in the highest quartile among children in homes with LSL was greater than when either chlorine or chloramine with orthophosphate was used. For children tested after LSLs in their houses were replaced, those with partially replaced LSL were >3 times as likely to have BLLs ≥ 10 μg/dL versus children who never had LSLs.

CONCLUSIONS

LSLs were a risk factor for elevated BLLs even when WASA met the EPA water action level. Changes in water disinfection can enhance the effect of LSLs and increase lead exposure. Partially replacing LSLs may not decrease the risk of elevated BLLs associated with LSL exposure.

Low-level Pb and cardiovascular responses to acute stress in children: the role of cardiac autonomic regulation

OBJECTIVE

A number of studies suggest that Pb exposure increases cardiovascular disease risk in humans. As a potential mechanism for this effect, we recently reported a significant association between early childhood Pb levels and cardiovascular response to acute stress. The current study considers the association between current Pb levels and the autonomic nervous system activation pattern underlying the cardiovascular response to stress in a new cohort of children.

METHODS

We assessed blood Pb levels as well as cardiovascular responses to acute stress in 9-11 year old children (N=140). Sympathetic activation (measured with pre-ejection period) and parasympathetic activation (measured with high frequency heart rate variability) were also assessed.

RESULTS

In a sample with very low levels of blood Pb (M=1.0 μg/dL), we found that increasing blood Pb was associated with coinhibition of sympathetic and parasympathetic activation in response to acute stress. In addition, increasing Pb levels were associated with the hemodynamic stress response pattern typical of coinhibition--significantly greater vascular resistance and reduced stroke volume and cardiac output.

CONCLUSIONS

Blood Pb levels were associated with significant autonomic and cardiovascular dysregulation in response to acute psychological stress in children. Moreover, these effects were significant at Pb levels considered to be very low and notably well below the 10 μg/dL, the Centers for Disease Control and Prevention definition of an elevated blood Pb level. The potential for autonomic dysregulation at levels of Pb typical for many US children would suggest potentially broad public health ramifications.

Prenatal and adolescent blood lead levels in South Africa: child, maternal and household risk factors in the Birth to Twenty cohort

INTRODUCTION

The risk factors for lead exposure in developing countries have not been fully described. This study looks at child, maternal and household factors associated with increased risk of lead exposure at birth and at 13 years of age in the Birth to Twenty cohort.

METHODS

Mothers were recruited from antenatal clinics in the Johannesburg-Soweto metropolitan area in 1990 (n=3273). Lead levels were analysed in cord blood collected at birth (n=618) and at 13 years (n=1546). Data on selected child, maternal and household factors were collected using a structured questionnaire in the third trimester and at 13 years of age. Statistical analyses were conducted to determine the associated risk factors.

RESULTS

The mean blood lead level at birth was 5.85 microg/dl, and at 13 years of age it was 5.66 microg/dl. The majority of children had blood lead levels above 5 microg/dl (52% at birth and 56% at 13 years). At birth, being a teenage mother and having low educational status were strong predictors for elevated cord blood lead levels. Being a male child, having an elevated cord blood level, and lack of household ownership of a phone were significant risk factors for high blood lead levels at 13 years.

CONCLUSION

Significant associations found in the study point to the low socio-economic status of lead-affected mothers and children. These poor circumstances frequently persist into later childhood, resulting in continued high lead levels. Thus broader measures of poverty alleviation and provision of better education may help decrease the risk of exposure.

The relationship between mental retardation and developmental delays in children and the levels of arsenic, mercury and lead in soil samples taken near their mother's residence during pregnancy

This study was designed to evaluate the association between lead, mercury, and arsenic in the soil near maternal residences during pregnancy and mental retardation or developmental disability (MR/DD) in children. The study was conducted using 6,048 mothers who did not move throughout their pregnancies and lived within six strips of land in South Carolina and were insured by Medicaid between January 1, 1997 and December 31, 2002. The mother child pairs were then followed until June 1, 2008, through their Medicaid reimbursement files, to identify children diagnosed with MR/DD. The soil was sampled for mercury (Hg), lead (Pb), and As based on a uniform grid, and the soil concentrations were Kriged to estimate chemical concentration at individual locations. We identified a significant relationship between MR/DD and As, and the form of the relationship was nonlinear, after controlling for other known risk factors.

Blood lead (Pb) levels: further evidence for an environmental mechanism explaining the association between socioeconomic status and psychophysiological dysregulation in children

OBJECTIVE

The authors recently reported that blood lead (Pb) was a significant mediator for the positive association between socioeconomic status (SES) and peripheral vascular responses to acute stress in children (B. B. Gump et al., 2007). The present study considers the possibility that Pb may also mediate an association between SES and cortisol responses to acute stress.

DESIGN

Early childhood Pb exposure was tested as a mediator for cross-sectional associations between SES and cortisol responses.

MAIN OUTCOME MEASURES

The primary outcome was cortisol responses to acute stress in 9.5-year-old children (N = 108).

RESULTS

Lower family income was associated with significantly greater cortisol levels following an acute stress task. A mediational analysis confirmed that Pb was a significant mediator for this association.

CONCLUSION

These results reaffirm the importance of considering the chemical environment as well as social and psychological environment when evaluating psychophysiological effects of low SES.

Mass lead intoxication from informal used lead-acid battery recycling in dakar, senegal

BACKGROUND AND OBJECTIVES

Between November 2007 and March 2008, 18 children died from a rapidly progressive central nervous system disease of unexplained origin in a community involved in the recycling of used lead-acid batteries (ULAB) in the suburbs of Dakar, Senegal. We investigated the cause of these deaths.

METHODS

Because autopsies were not possible, the investigation centered on clinical and laboratory assessments performed on 32 siblings of deceased children and 23 mothers and on 18 children and 8 adults living in the same area, complemented by environmental health investigations.

RESULTS

All 81 individuals investigated were poisoned with lead, some of them severely. The blood lead level of the 50 children tested ranged from 39.8 to 613.9 microg/dL with a mean of 129.5 microg/dL. Seventeen children showed severe neurologic features of toxicity. Homes and soil in surrounding areas were heavily contaminated with lead (indoors, up to 14,000 mg/kg; outdoors, up to 302,000 mg/kg) as a result of informal ULAB recycling.

CONCLUSIONS

Our investigations revealed a mass lead intoxication that occurred through inhalation and ingestion of soil and dust heavily contaminated with lead as a result of informal and unsafe ULAB recycling. Circumstantial evidence suggested that most or all of the 18 deaths were due to encephalopathy resulting from severe lead intoxication. Findings also suggest that most habitants of the contaminated area, estimated at 950, are also likely to be poisoned. This highlights the severe health risks posed by informal ULAB recycling, in particular in developing countries, and emphasizes the need to strengthen national and international efforts to address this global public health problem.

The role of metabotropic glutamate receptor 5 in developmental lead neurotoxicity

A complete explanation of the mechanisms of lead-induced developmental neurotoxicity remains unknown. The glutamate receptor is one of the most important targets of lead. More recently, metabotropic glutamate receptor 5 (mGluR5) has been shown to have a functional relationship with learning and memory. We investigated the impact of developmental lead exposure on hippocampal mGluR5 expression and its potential role in lead neurotoxicity. Both in vitro model of lead exposure with Pb(2+) concentrations of 0, 10 nM, 1 microM, and 100 microM in cultured rat embryonic hippocampal neurons, and the in vivo model of rat maternal lead exposure involving both gestational and lactational exposure with 0, 0.05%, 0.2%, and 0.5% lead acetate were utilized. Immunoperoxidase and immunofluorescent analyses, quantitative PCR and western blotting were used. In vitro studies revealed that expression of mGluR5 mRNA and protein was decreased dose-dependently after lead exposure, which was further confirmed by the results of in vivo studies. These data suggest that mGluR5 might be involved in lead-induced neurotoxicity by disturbing mGluR5-induced long-term depression and decreasing N-methyl-D-aspartic acid receptor (NMDAR)-dependent or protein synthesis-dependent long-term potentiation. These results might improve the understanding of the mechanism and potential treatments for moderate to severe lead poisoning in children.

Gender specific differences in neurodevelopmental effects of prenatal exposure to very low-lead levels: the prospective cohort study in three-year olds

The primary purpose of this study was to assess the relationship between very low-level of prenatal lead exposure measured in the cord blood (<5 microg/dL) and possible gender-specific cognitive deficits in the course of the first three years of life. The accumulated lead dose in infants over the pregnancy period was measured by the cord blood lead level (BLL) and cognitive deficits were assessed by the Bayley Mental Development Index (MDI). The study sample consisted of 457 children born to non-smoking women living in the inner city and the outlying residential areas of Krakow. The relationship between prenatal lead exposure and MDI scores measured at 12, 24 and 36 months of age and adjusted to a set of important covariates (gender of child, maternal education, parity, breastfeeding, prenatal and postnatal environmental tobacco smoke) was evaluated with linear multivariate regression, and the Generalized Estimating Equations (GEE) longitudinal panel model. The median of lead level in cord blood was 1.21 microg/dL with the range of values from 0.44 to 4.60 microg/dL. Neither prenatal BLL (dichotomized by median) nor other covariates affected MDI score at 12 months of age. Subsequent testing of children at 24 months of age showed a borderline significant inverse association of lead exposure and mental function (beta coefficient=-2.42, 95%CI: -4.90 to 0.03), but the interaction term (BLL x male gender) was not significant. At 36 months, prenatal lead exposure was inversely and significantly associated with cognitive function in boys (Spearman correlation coefficient=-0.239, p=0.0007) but not girls (r=-0.058, p=0.432) and the interaction between BLL and male gender was significant (beta coefficient=-4.46; 95%CI: -8.28 to -0.63). Adjusted estimates of MDI deficit in boys at 36 months confirmed very strong negative impact of prenatal lead exposure (BLL>1.67 microg/dL) compared with the lowest quartile of exposure (beta coefficient=-6.2, p=0.002), but the effect in girls was insignificant (beta coefficient=-0.74, p=0.720). The average deficit of cognitive function in the total sample over the first three years of life (GEE model) associated with higher prenatal lead exposure was also significant (beta coefficient=-3.00; 95%CI: -5.22 to -0.70). Beside prenatal lead exposure, presence of older siblings at home and prenatal environmental tobacco smoke had a negative impact on MDI score. Better maternal education showed a strong beneficial effect on the cognitive development of children.

CONCLUSION

the study suggests that there might be no threshold for lead toxicity in children and provides evidence that 3-year old boys are more susceptible than girls to prenatal very low lead exposure. The results of the study should persuade policy makers to consider gender-related susceptibility to lead and possibly to other toxic hazards in setting environmental protection guidelines. To determine whether the cognitive deficit documented in this study persists to older ages, the follow-up of the children over the next several years is to be carried out.

The U.S. Food and Drug Administration risk assessment on lead in women's and children's vitamins is based on outdated assumptions

BACKGROUND

Following a recent report of lead in certain commercial vitamin products, the U.S. Food and Drug Administration (FDA) conducted a nationwide survey to determine the Pb content in 324 multivitamin/mineral products labeled for use by women and children. The FDA compared estimated Pb exposures from each product with safe/tolerable exposure levels, termed provisional total tolerable intake (PTTI) levels, previously developed for at-risk population groups in 1992.

OBJECTIVE

We investigated the FDA's conclusions that Pb concentrations in all vitamin products examined do not pose a hazard to health because they are below the PTTI levels for all groups considered.

DISCUSSION

For their initial estimations of PTTI levels, the FDA used a blood lead level (BLL) of 10 microg/dL as the threshold for adverse effects in children and in pregnant or lactating women. Studies have repeatedly linked chronic exposure to BLLs < 10 microg/dL with impairments in cognitive function and behavior in young children despite the absence of overt signs of toxicity. The FDA analysis also omitted any consideration of nonfood sources of Pb exposure, which is inconsistent with our current understanding of how most children develop elevated BLLs.

CONCLUSION

We feel that based on these oversights, the FDA's conclusions are unduly reassuring and that reconsideration of their current recommendations appears warranted.

Blood lead levels of children and its trend in China

To evaluate Chinese children's blood lead levels (BLLs) and identify its distribution features, we collected articles on children's BLLs published from Jan, 2004 to Aug, 2007 with sampling time since 2001, by searching Chinese Biomedical Disk (CBMDisk), Chinese Journal Full-test Database (CJFD) and other ways. After a rigorous investigation, 35 articles eligible for inclusion criteria were reviewed. Meanwhile, to reveal the trend of Chinese children's BLLs, the data was compared with the results from our former study carried out in 2004, which reviewed the articles published since 1995 to 2003. The results showed that the mean BLLs of Chinese children from 2001 to 2007 was 80.7 microg/L (45.5-165.3 microg/L), and 23.9% (3.2%-80.7%) of children's BLLs was higher than 100 microg/L. Both BLLs and prevalence of BLLs higher than 100 microg/L were lower than that of 1995 to 2003. Of 24 provinces or cities, only 4 showed higher BLLs and higher prevalence rates of lead poisoning (BLLs > or =100 microg/L) than that of 1995 to 2003. The mean BLLs of children living in industrial areas were higher than those in urban and suburban areas, and suburban higher than urban areas. Boys' BLLs were 79.3 microg/L, significantly higher than girls 76.9 microg/L (P<0.001). The results also showed that children's BLLs increased with their ages, and the decreased BLLs for all age were observed comparing with the results of our former study in 2004. Overall, our study revealed that the BLLs of children in China showed a decreasing trend after gasoline with lead was banned in China in 1st July 2000. Our study also showed that the BLLs of children in China were still higher than that in developed countries, which suggested that children's lead poisoning prevention and controlling would be a long-term mission in China.

Screening for lead poisoning: a geospatial approach to determine testing of children in at-risk neighborhoods

OBJECTIVE

To develop a spatial strategy to assess neighborhood risk for lead exposure and neighborhood-level blood lead testing of young children living in the city of Atlanta, Georgia.

STUDY DESIGN

This ecologic study used existing blood lead results of children aged <or=36 months tested and living in one of Atlanta's 236 neighborhoods in 2005. Geographic information systems used Census, land parcel, and neighborhood spatial data to create a neighborhood priority testing index on the basis of proxies for poverty (Special Supplemental Nutrition Program for Women, Infants and Children [WIC] enrollment) and lead in house paint (year housing built).

RESULTS

In 2005, only 11.9% of Atlanta's 18,627 children aged <or=36 months living in the city had blood lead tests, despite a high prevalence of risk factors: 75,286 (89.6%) residential properties were built before 1978, and 44% of children were enrolled in WIC. Linear regression analysis indicated testing was significantly associated with WIC status (P < .001) but not with old housing.

CONCLUSIONS

This neighborhood spatial approach provided smaller geographic areas to assign risk and assess testing in a city that has a high prevalence of risk factors for lead exposure. Testing may be improved by collaboration between pediatricians and public health practitioners.

Neurotoxic effects and biomarkers of lead exposure: a review

Lead, a systemic toxicant affecting virtually every organ system, primarily affects the central nervous system, particularly the developing brain. Consequently, children are at a greater risk than adults of suffering from the neurotoxic effects of lead. To date, no safe lead-exposure threshold has been identified. The ability of lead to pass through the blood-brain barrier is due in large part to its ability to substitute for calcium ions. Within the brain, lead-induced damage in the prefrontal cerebral cortex, hippocampus, and cerebellum can lead to a variety of neurologic disorders. At the molecular level, lead interferes with the regulatory action of calcium on cell functions and disrupts many intracellular biological activities. Experimental studies have also shown that lead exposure may have genotoxic effects, especially in the brain, bone marrow, liver, and lung cells. Knowledge of the neurotoxicology of lead has advanced in recent decades due to new information on its toxic mechanisms and cellular specificity. This paper presents an overview, updated to January 2009, of the neurotoxic effects of lead with regard to children, adults, and experimental animals at both cellular and molecular levels, and discusses the biomarkers of lead exposure that are useful for risk assessment in the field of environmental health.

Comments on the Article “The Toxicology of Mercury and Its Chemical Compounds” by Clarkson and Magos (2006)

Clarkson and Magos (2006) provide their perspectives on the toxicology of mercury vapor and dental amalgam. As scientists who are involved in preparing a German federal guideline regarding dental amalgam, we welcome additional scientific data on this issue. However, Clarkson and Magos do not present all the relevant studies in their review. The additional data provided here show that: (a) Dental amalgam is the main source of human total mercury body burden, because individuals with amalgam have 2-12 times more mercury in their body tissues compared to individuals without amalgam; (b) there is not necessarily a correlation between mercury levels in blood, urine, or hair and in body tissues, and none of the parameters correlate with severity of symptoms; (c) the half-life of mercury deposits in brain and bone tissues could last from several years to decades, and thus mercury accumulates over time of exposure; (d) mercury, in particular mercury vapor, is known to be the most toxic nonradioactive element, and is toxic even in very low doses, and (e) some studies which conclude that amalgam fillings are safe for human beings have important methodogical flaws. Therefore, they have no value for assessing the safety of amalgam.

Estimated burden of blood lead levels 5 microg/dl in 1999-2002 and declines from 1988 to 1994

In light of recent data suggesting adverse health effects at blood lead levels (PbB) <10 microg/dl, lowering the current definition of elevated blood lead (>or=10 microg/dl) has been recommended. To ascertain the population level impact of such a change, we calculated the prevalence of PbB >or=5 microg/dl in 1-21-year-old population in the United States. Furthermore, we characterized changes in PbB between 1988-1994 and 1999-2002. We analyzed data from the National Health and Nutrition Examination Survey (NHANES) III (n=10,755) and NHANES 1999-2002 (n=8013). In 1999-2002, about 91.7% of study children had detectable levels of lead in the blood. Among them, 7.3%, 2.8%, and 1.0% children and adolescents aged 1-5, 6-11, and 12-21 years, respectively, had PbB between 5 and 9.9 microg/dl. This number translates to approximately 2.4 million individuals. Between 1988-1994 and 1999-2002, the geometric mean PbB declined from 2.88 to 1.94 microg/dl in children 1-5 years, 1.80 to 1.36 microg/dl in children 6-11 years, and 1.24-1.02 microg/dl in children and adolescents 12-21 years of age. Also, the prevalence of PbB >or=5 microg/dl declined from 25.7% to 8.8%, 12.8% to 3.0%, and 7.5% to 1.2% in these age groups, respectively.A substantial proportion of children may be at risk for adverse health effects from lead exposure below 10 microg/dl and a large number of children will be classified as having elevated PbB if 5 microg/dl is considered the threshold. Significant public health resources will have to be mobilized for intervention, screening, and case management of these children.

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.

DC Water and Sewer Authority and lead in drinking water: a case study in environmental health risk management

In 2001, following a change in disinfection agent in anticipation of the Environment Protection Agency Disinfection Byproduct Rule, lead levels began rising in drinking water in Washington, District of Columbia, and in 2002, the DC Water and Sewer Authority was found to have exceeded the Environment Protection Agency lead action level, requiring compliance with a series of measures under the Lead and Copper Rule. In 2004, the issue became a public concern, drawing considerable media attention. The problem was eventually resolved through the application of orthophosphate but while it played out, the utility was forced to respond to a novel public health issue with few risk management options. This case study examines the lessons learned.

Low-level prenatal and postnatal blood lead exposure and adrenocortical responses to acute stress in children

BACKGROUND

A few recent studies have demonstrated heightened hypothalamic-pituitary-adrenal (HPA) axis reactivity to acute stress in animals exposed to heavy metal contaminants, particularly lead. However, Pb-induced dysregulation of the HPA axis has not yet been studied in humans.

OBJECTIVE

In this study, we examined children's cortisol response to acute stress (the glucocorticoid product of HPA activation) in relation to low-level prenatal and postnatal Pb exposure.

METHODS

Children's prenatal blood Pb levels were determined from cord blood specimens, and postnatal lead levels were abstracted from pediatrician and state records. Children's adrenocortical responses to an acute stressor were measured using assays of salivary cortisol before and after administration of a standard cold pressor task.

RESULTS

Pb exposure was not associated with initial salivary cortisol levels. After an acute stressor, however, increasing prenatal and postnatal blood Pb levels were independently associated with significantly heightened salivary cortisol responses.

CONCLUSIONS

Our results suggest that relatively low prenatal and postnatal blood lead levels--notably those below the 10 microg/dL blood lead level identified by the Centers for Disease Control and Prevention for public health purposes--can alter children's adrenocortical responses to acute stress. The behavioral and health consequences of this Pb-induced HPA dysregulation in children have yet to be determined.

Blood lead concentrations < 10 microg/dL and child intelligence at 6 years of age

BACKGROUND

Few studies provide data directly relevant to the question of whether blood lead concentrations < 10 microg/dL adversely affect children's cognitive function.

OBJECTIVE

We examined the association between blood lead concentrations assessed throughout early childhood and children's IQ at 6 years of age.

METHODS

Children were followed from 6 months to 6 years of age, with determination of blood lead concentrations at 6, 12, 18, and 24 months, and 3, 4, 5, and 6 years of age. At 6 years of age, intelligence was assessed in 194 children using the Wechsler Preschool and Primary Scale of Intelligence-Revised. We used general linear and semiparametic models to estimate and test the association between blood lead concentration and IQ.

RESULTS

After adjustment for maternal IQ, HOME scale scores, and other potential confounding factors, lifetime average blood lead concentration (mean = 7.2 microg/dL; median = 6.2 microg/dL) was inversely associated with Full-Scale IQ (p = 0.006) and Performance IQ scores (p = 0.002). Compared with children who had lifetime average blood lead concentrations < 5 microg/dL, children with lifetime average concentrations between 5 and 9.9 microg/dL scored 4.9 points lower on Full-Scale IQ (91.3 vs. 86.4, p = 0.03). Nonlinear modeling of the peak blood lead concentration revealed an inverse association (p = 0.003) between peak blood lead levels and Full-Scale IQ down to 2.1 microg/dL, the lowest observed peak blood lead concentration in our study.

CONCLUSIONS

Evidence from this cohort indicates that children's intellectual functioning at 6 years of age is impaired by blood lead concentrations well below 10 microg/dL, the Centers for Disease Control and Prevention definition of an elevated blood lead level.

Immigration and risk of childhood lead poisoning: findings from a case control study of New York City children

OBJECTIVES

We investigated whether foreign birthplace and residence were associated with an increased risk of childhood lead poisoning.

METHODS

We conducted a matched case-control study among New York City children (mean age=3 years) tested for lead poisoning in 2002 (n=203 pairs). Children were matched on age, date of test, and residential area. Blood lead and housing data were supplemented by a telephone survey administered to parents or guardians. Conditional logistic regression analysis was used to examine the relationship of lead poisoning status to foreign birthplace and time elapsed since most recent foreign residence after adjustment for housing and behavioral risk factors.

RESULTS

Both foreign birthplace and time since most recent foreign residence had strong adjusted associations with lead poisoning status, with children who had lived in a foreign country less than 6 months before their blood test showing a particularly elevated risk of lead poisoning relative to US-born children with no foreign residential history before their blood test (odds ratio [OR]=10.9; 95% confidence interval [CI]=3.3, 36.5).

CONCLUSIONS

Our findings demonstrate an increased risk of lead poisoning among immigrant children.

Lead in pharmaceutical products and dietary supplements

The objective of this study is to determine lead concentrations in a variety of widely used pharmaceutical products, and to assess the risk of lead exposure from using these products. Lead concentrations of 45 products were measured with inductively-coupled plasma mass spectrometry. Six products had lead concentrations greater than 100 parts per billion (ppb), and the highest measured concentration was 500 ppb. The average mass of lead delivered to consumers by all products examined in this study when taken as directed was 0.22 micrograms per day, which is expected to increase the blood lead level of an adult by less than 1%. Five products were found to deliver more than 1 microg of lead per day when used as directed. Current tolerable lead limits in pharmaceutical substances vary widely, and in some cases exceed 10,000 ppb. The products examined in this study have lead concentrations far below these levels. However, in light of recent research demonstrating adverse effects in both children and adults from low level lead exposure, current lead limits for pharmaceutical substances are unacceptably high. Uniform lead limits that reflect current manufacturing capabilities are needed to insure the lowest achievable exposure to lead from these products.

Elevated lead in drinking water in Washington, DC, 2003-2004: the public health response

BACKGROUND

In 2003, residents of the District of Columbia (DC) experienced an abrupt rise in lead levels in drinking water, which followed a change in water-disinfection treatment in 2001 and which was attributed to consequent changes in water chemistry and corrosivity.

OBJECTIVES

To evaluate the public health implications of the exceedance, the DC Department of Health expanded the scope of its monitoring programs for blood lead levels in children.

METHODS

From 3 February 2004 to 31 July 2004, 6,834 DC residents were screened to determine their blood lead levels.

RESULTS

Children from 6 months to 6 years of age constituted 2,342 of those tested; 65 had blood lead levels > 10 microg/dL (the "level of concern" defined by the Centers for Disease Control and Prevention), the highest with a level of 68 microg/dL. Investigation of their homes identified environmental sources of lead exposure other than tap water as the source, when the source was identified. Most of the children with elevated blood lead levels (n = 46; 70.8%) lived in homes without lead drinking-water service lines, which is the principal source of lead in drinking water in older cities. Although residents of houses with lead service lines had higher blood lead levels on average than those in houses that did not, this relationship is confounded. Older houses that retain lead service lines usually have not been rehabilitated and are more likely to be associated with other sources of exposure, particularly lead paint. None of 96 pregnant women tested showed blood lead levels > 10 microg/dL, but two nursing mothers had blood lead levels > 10 microg/dL. Among two data sets of 107 and 71 children for whom paired blood and water lead levels could be obtained, there was no correlation (r(2) = -0.03142 for the 107).

CONCLUSIONS

The expanded screening program developed in response to increased lead levels in water uncovered the true dimensions of a continuing problem with sources of lead in homes, specifically lead paint. This study cannot be used to correlate lead in drinking water with blood lead levels directly because it is based on an ecologic rather than individualized exposure assessment; the protocol for measuring lead was based on regulatory requirements rather than estimating individual intake; numerous interventions were introduced to mitigate the effect; exposure from drinking water is confounded with other sources of lead in older houses; and the period of potential exposure was limited and variable.

Blood lead levels and specific attention effects in young children

The detrimental effects of early exposure to lead are credible and persistent, but there is presently no agreement on a safe threshold for circulating lead levels. Although several research groups have found significantly poorer cognitive performance in children who have whole blood levels as low as 5 microg/dL, most government agencies, including the EPA and the CDC, continue to use 10 microg/dL as the criterion for concern in public health advisories. Prior research has consistently indicated a negative relation between lead levels and attention. Similarly, the results of the present study show a relation between blood lead level and neurobehavioral outcome in 7-year-old children (N=506). Higher lead levels were associated significantly with decreased scores on measures of intelligence (i.e., overall, performance and verbal IQ), lengthened reaction time, hyperactivity, and social and delinquent behavior problems. Importantly, the present study documents a significant negative impact of blood lead levels on attention, but not impulsivity, in early elementary age children, further delineating the specific aspects of attention related to blood lead concentrations. Analyses were also conducted to identify a "safe" blood lead level threshold. Visual inspection of non-parametric regression plots suggested a gradual linear dose-response relationship for each endpoint. None of the neurobehavioral outcomes assessed showed evidence of a threshold under which lead levels appear to "safe". In light of the consistency of these findings with those of several other groups, it is advisable to consider whether the threshold for an acceptable blood lead level should be reduced.