Background lead and mercury exposures: Psychological and behavioral problems in children

Abstract

Background The potential harm from exposure to nonessential metals, particularly mercury (Hg) and lead (Pb), has been the focus of research for years. Initial interest focused on relatively high exposures; however, recent evidence suggests that even high normal exposures might have adverse consequences for child development. Identifying the extent of these consequences is now a priority. Methods We assessed blood Pb and Hg levels in a biracial sample of 9–11 year-old children (N = 203). Neurodevelopment and psychological functioning assessments included hostility, disruptive behaviors, emotion regulation, and autism spectrum disorder behaviors. Parasympathetic (vagal) responses to acute stress were indexed by heart rate variability (HRV) at rest and during stress. Results With increasing Pb levels, children exhibit higher levels of hostile distrust and oppositional defiant behaviors, were more dissatisfied and uncertain about their emotions, and had difficulties with communication. These significant associations were found within a range of blood Pb levels from 0.19 to 3.25 μg/dL, well below the “reference value” for children of >5 μg/dL. Vagal reactivity interacted with Hg such that increasing Hg was associated with increasing autism spectrum behaviors for those children with sustained vagal tone during acute stress. Conclusions This study is the first to demonstrate an association between very low-level Pb exposure and fundamental psychological mechanisms that might explain prior associations with more complex outcomes such as delinquency. Analyses of vagal reactivity yielded entirely novel associations suggesting that Hg may increase autism spectrum behaviors in children with sustained vagal tone during acute stress. The novelty of these later findings requires additional research for confirmation and the cross-sectional nature of the data caution against assumptions of causality without further research.

Blood Lead Levels and Learning Disabilities: A Cross-Sectional Study of the 2003–2004 National Health and Nutrition Examination Survey (NHANES)

“…The results observed in the current study are not only consistent with the aforementioned studies [ 1 , 2 , 3 , 4 , 9 ], but they provide additional important insights into the potential attributable population consequences of elevated blood Pb levels among the general US childhood population. The results of the present study revealed that children in the 50th to 100th percentile of blood Pb levels (1.007 µg Pb/dL to 13.50 µg Pb/dL), when compared with children in the 0 to 50th percentile of blood Pb levels (0.2 µg Pb/dL to 1.007 µg Pb/dL), were significantly more likely to have a LD (prevalence ratio = 1.71, 95% confidence interval = 1.18 to 2.49, p = 0.0007, prevalence attributable rate = 0.062).…”

“…Despite this limitation, the results observed in this study are biologically plausible, and are supported by previous studies linking increased blood Pb levels with a LD diagnosis. Furthermore, a recent study by Gump et al [ 9 ] revealed, consistent with the results observed in the present study, a significant relationship between increasing blood Pb levels and LD-associated psychological and behaviors among children of similar age (9 to 11 years-old) and similar blood Pb levels (0.19 to 3.25 µg Pb/dL) to those examined in this study. It is recommended that future studies further explore the phenomena observed in this study with other populations.…”

Assessment of Cardiac Autonomic Function in Relation to Methylmercury Neurotoxicity

“…We excluded review papers ( n = 6), case series ( n = 3), studies addressing occupational mercury exposure ( n = 2) or studies in which data for either HRV ( n = 3) or mercury biomarkers ( n = 6) were not described. Finally, included were 13 studies of methylmercury exposure and HRV: ten studies [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ] that were included in a previous systematic review by Gribble et al [ 6 ] and three new studies [ 17 , 18 , 19 ]. In all of the identified studies, the statistical significance was set at p < 0.05.…”

High affinity interactions of Pb2+with Synaptotagmin I

“…1, 2 Lead exposure is especially detrimental in young children, resulting in serious neurodevelopmental and psychological disorders. [3][4][5] The potency of Pb 2+ ([Xe]-4f 14 5d 10 6s 2 ) stems from its ability to cross the blood-brain barrier 6 and preferentially target Zn 2+ and Ca 2+ coordination sites of biological macromolecules. [7][8][9] The ability of Pb 2+ to mimic these essential divalent metal ions results in disruption of cellular signaling, ion transport, and calcium homeostasis.…”