Heavy metal in children's tooth enamel: related to autism and disruptive behaviors?

To examine possible links between neurotoxicant exposure and neuropsychological disorders and child behavior, relative concentrations of lead, mercury, and manganese were examined in prenatal and postnatal enamel regions of deciduous teeth from children with Autism Spectrum Disorders (ASDs), high levels of disruptive behavior (HDB), and typically developing (TD) children. Using laser ablation inductively coupled plasma mass spectrometry, we found no significant differences in levels of these neurotoxicants for children with ASDs compared with TD children, but there was marginal significance indicating that children with ASDs have lower manganese levels. No significant differences emerged between children with HDB and TD children. The current findings challenge the notion that perinatal heavy metal exposure is a major contributor to the development of ASDs and HDB.

Prenatal manganese levels linked to childhood behavioral disinhibition.

Although manganese (Mn) is an essential mineral, high concentrations of the metal can result in a neurotoxic syndrome affecting dopamine balance and behavior control. We report an exploratory study showing an association between Mn deposits in tooth enamel, dating to the 20th and 62-64th gestational weeks, and childhood behavioral outcomes. In a sample of 27 children, 20th week Mn level was significantly and positively correlated with measures of behavioral disinhibition, specifically, play with a forbidden toy (36 months), impulsive errors on a continuous performance and a children's Stroop test (54 months), parents' and teachers' ratings of externalizing and attention problems on the Child Behavior Checklist (1st and 3rd grades), and teacher ratings on the Disruptive Behavior Disorders Scale (3rd grade). By way of contrast, Mn level in tooth enamel formed at the 62-64th gestational week was correlated only with teachers' reports of externalizing behavior in 1st and 3rd grades. Although the source(s) of Mn exposure in this sample are unknown, one hypothesis, overabsorption of Mn secondary to gestational iron-deficiency anemia, is discussed.

Hierarchical sampling of multiple strata: an innovative technique in exposure characterization.

Sampling of multiple strata, or hierarchical sampling of various exposure sources and activity areas, has been tested and is suggested as a method to sample (or to locate) areas with a high prevalence of elevated blood lead in children. Hierarchical sampling was devised to supplement traditional soil lead sampling of a single stratum, either residential or fixed point source, using a multistep strategy. Blood lead (n=1141) and soil lead (n=378) data collected under the USEPA/UCI Tijuana Lead Project (1996-1999) were analyzed to evaluate the usefulness of sampling soil lead from background sites, schools and parks, point sources, and residences. Results revealed that industrial emissions have been a contributing factor to soil lead contamination in Tijuana. At the regional level, point source soil lead was associated with mean blood lead levels and concurrent high background, and point source soil lead levels were predictive of a high percentage of subjects with blood lead equal to or greater than 10 micro g/dL (pe 10). Significant relationships were observed between mean blood lead level and fixed point source soil lead (r=0.93; P<0.05; R(2)=0.72 using a quadratic model) and between residential soil lead and fixed point source soil lead (r=0.90; P<0.05; R(2)=0.86 using a cubic model). This study suggests that point sources alone are not sufficient for predicting the relative risk of exposure to lead in the urban environment. These findings will be useful in defining regions for targeted or universal soil lead sampling by site type. Point sources have been observed to be predictive of mean blood lead at the regional level; however, this relationship alone was not sufficient to predict pe 10. It is concluded that when apparently undisturbed sites reveal high soil lead levels in addition to local point sources, dispersion of lead is widespread and will be associated with a high prevalence of elevated blood lead in children. Multiple strata sampling was shown to be useful in differentiating among sources by site-specific association to mean blood lead and the prevalence of elevated blood lead at the regional level.

Tijuana childhood lead risk assessment revisited: validating a GIS model with environmental data.

The objective of this research was to determine the spatial distributions of childhood lead poisoning and soil lead contamination in urban Tijuana. The Bocco-Sanchez model of point-source emissions was evaluated in terms of validity and reliability. We compared the model's predicted vulnerable populations with observed cases of childhood lead poisoning in Tijuana, identified fixed point sources in the field, and analyzed 76 soil samples from 14 sites. The soil lead results were compared to the blood lead analyses performed on Tijuana children whose blood lead levels were > or =10 microg/dL, who reported that they did not use lead-glazed ceramics for cooking or storing food (n = 63). Using GIS, predicted vs observed risk areas were assessed by examining spatial patterns, including the distribution of cases per designated risk area. Chi-square analysis of expected vs observed values did not differ significantly at the p = 0.02 level, showing that the model was strikingly accurate in predicting the distribution of subjects with elevated blood lead. Results reveal that while point sources are significant, other sources of lead exposure are also important. The relative public health risk from exposure to lead in an urban setting may be assessed by distinguishing among sources of exposure and associating concentrations to blood lead levels. The results represent an iterative approach in environmental health research by linking environmental and human biomarker lead concentrations and using these results to validate an environmental model of risk to lead exposure.