Developmental lead exposure induces tactile defensiveness in rhesus monkeys (Macaca mulatta)

Elevated lead levels from e-waste exposure are linked to sensory integration difficulties in preschool children

Exposure to lead is associated with adverse effects on neurodevelopment. However, studies of the effects of lead on sensory integration are few. The purpose of this research is to investigate the effect of lead exposure on child sensory integration by correlating the blood lead levels of children with sensory processing measures. A total of 574 children, from 3 to 6 years of age, 358 from an electronic waste (e-waste) recycling town named Guiyu, and 216 from Haojiang, a nearby town with no e-waste recycling activity, were recruited in this study. The median blood lead level in Guiyu children was 4.88 μg/dL, higher than the 3.47 μg/dL blood lead level in Haojiang children (P <  0.001). 47.2% of Guiyu children had blood lead levels exceeding 5 μg/dL. The median concentration of serum cortisol, an HPA-axis biomarker, in Guiyu children was significantly lower than in Haojiang, and was negatively correlated with blood lead levels. All subscale scores and the total score of the Sensory Processing Measure (Hong Kong Chinese version, SPM-HKC) in Guiyu children were higher than Haojiang children, indicating greater difficulties, especially for touch, body awareness, balance and motion, and total sensory systems. Sensory processing scores were positively correlated with blood lead, except for touch, which was negatively correlated with serum cortisol levels. Simultaneously, all subscale scores and the total SPM-HKC scores for children with high blood lead levels (blood lead > 5 μg/dL) were higher than those in the low blood lead level group (blood lead < 5 μg/dL), especially for hearing, touch, body awareness, balance and motion, and total sensory systems. Our findings suggest that lead exposure in e-waste recycling areas may result in a decrease in serum cortisol levels and an increase in child sensory integration difficulties. Cortisol may be involved in touch-related sensory integration difficulties.

Cross-species coherence in effects and modes of action in support of causality determinations in the U.S. Environmental Protection Agency's Integrated Science Assessment for Lead

The peer-reviewed literature on the health and ecological effects of lead (Pb) indicates common effects and underlying modes of action across multiple organisms for several endpoints. Based on such observations, the United States (U.S.) Environmental Protection Agency (EPA) applied a cross-species approach in the 2013 Integrated Science Assessment (ISA) for Lead for evaluating the causality of relationships between Pb exposure and specific endpoints that are shared by humans, laboratory animals, and ecological receptors (i.e., hematological effects, reproductive and developmental effects, and nervous system effects). Other effects of Pb (i.e., cardiovascular, renal, and inflammatory responses) are less commonly assessed in aquatic and terrestrial wildlife limiting the application of cross-species comparisons. Determinations of causality in ISAs are guided by a framework for classifying the weight of evidence across scientific disciplines and across related effects by considering aspects such as biological plausibility and coherence. As illustrated for effects of Pb where evidence across species exists, the integration of coherent effects and common underlying modes of action can serve as a means to substantiate conclusions regarding the causal nature of the health and ecological effects of environmental toxicants.

Early lead exposure (<3 years old) prospectively predicts fourth grade school suspension in Milwaukee, Wisconsin (USA)

School suspensions are associated with negative student outcomes. Environmental lead exposure increases hyperactivity and sensory defensiveness, two traits likely to increase classroom misbehavior and subsequent discipline. Childhood Blood Lead Level (BLL) test results categorized urban fourth graders as exposed (2687; lifetime max BLL 10-20 µg/dL) or unexposed (1076; no lifetime BLL ≥5 µg/dL). Exposed children were over twice as likely as unexposed children to be suspended (OR=2.66, 95% CI=[2.12, 3.32]), controlling for covariates. African American children were more likely to be suspended than white children, but lead exposure explained 23% of the racial discipline gap. These results suggest that different rates of environmental lead exposure may contribute to the racial discipline gap.

Lead exposure and educational proficiency: moderate lead exposure and educational proficiency on end-of-grade examinations

PURPOSE

To investigate and quantify the impact of moderate lead exposure on students' ability to score at the "proficient" level on end-of-grade standardized tests.

METHODS

We compared the scores of 3757 fourth grade students from Milwaukee, Wisconsin, on the Wisconsin Knowledge and Concepts Exam (WKCE). The sample consisted of children with a blood lead test before age 3 years that was either unquantifiable at the time of testing (<5 μg/dL) or in the range of moderate exposure (10-19 μg/dL).

RESULTS

After controlling for gender, poverty, English language learner status, race/ethnicity, school disciplinary actions, and attendance percentage, results showed a significant negative effect of moderate lead exposure on academic achievement for all 5 subtests of the WKCE. Test score deficits owing to lead exposure were equal to 22% of the interval between student categorization at the "proficient" or "basic" levels in Reading, and 42% of the interval in Mathematics.

CONCLUSIONS

Children exposed to amounts of lead before age 3 years that are insufficient to trigger intervention under current policies in many states are nonetheless at a considerable educational disadvantage compared with their unexposed peers 7 to 8 years later. Exposed students are at greater risk of scoring below the proficient level, an outcome with serious negative consequences for both the student and the school.

The protean toxicities of lead: new chapters in a familiar story

Many times in the history of lead toxicology the view that "the problem" has been solved and is no longer a major health concern has prevailed, only to have further research demonstrate the prematurity of this judgment. In the last decade, an extraordinary amount of new research on lead has illustrated, all too clearly, that "the problem" has not disappeared, and that, in fact, it has dimensions never before considered. Recent risk assessments have concluded that research has yet to identify a threshold level below which lead can be considered "safe." Although children's intelligence has traditionally been considered to be the most sensitive endpoint, and used as the basis for risk assessment and standard setting, increased lead exposure has been associated with a wide variety of other morbidities both in children and adults, in some cases at biomarker levels comparable to those associated with IQ deficits in children. In adults, these endpoints include all-cause mortality and dysfunctions in the renal, cardiovascular, reproductive, central nervous systems. In children, IQ deficits are observed at blood lead levels well below 10 μg/dL, and the dose-effect relationship appears to be supra-linear. Other health endpoints associated with greater early-life lead exposure in children include ADHD, conduct disorder, aggression and delinquency, impaired dental health, and delayed sexual maturation. Studies employing neuroimaging modalities such as volumetric, diffusion tensor, and functional MRI are providing insights into the neural bases of the cognitive impairments associated with greater lead exposure.

Timing of moderate level prenatal alcohol exposure influences gene expression of sensory processing behavior in rhesus monkeys

Sensory processing disorder, characterized by over- or under-responsivity to non-noxious environmental stimuli, is a common but poorly understood disorder. We examined the role of prenatal alcohol exposure, serotonin transporter gene polymorphic region variation (rh5-HTTLPR), and striatal dopamine (DA) function on behavioral measures of sensory responsivity to repeated non-noxious sensory stimuli in macaque monkeys. Results indicated that early gestation alcohol exposure induced behavioral under-responsivity to environmental stimuli in monkeys carrying the short (s) rh5-HTTLPR allele compared to both early-exposed monkeys homozygous for the long (l) allele and monkeys from middle-to-late exposed pregnancies and controls, regardless of genotype. Moreover, prenatal timing of alcohol exposure altered the relationship between sensory scores and DA D₂R availability. In early-exposed monkeys, a positive relationship was shown between sensory scores and DA D₂R availability, with low or blunted DA function associated with under-responsive sensory function. The opposite pattern was found for the middle-to-late gestation alcohol-exposed group. These findings raise questions about how the timing of prenatal perturbation and genotype contributes to effects on neural processing and possibly alters neural connections.