Neurotoxicants, the Developing Brain, and Mental Health

Abstract

While life in urban environments may confer a number of benefits, it may also result in a variety of exposures, with toxic consequences for neurodevelopment and neuropsychological health. Neurotoxicants are any of a large number of chemicals or substances that interfere with normal function and/or compromise adaptation in the central and/or peripheral nervous system. Evidence suggests that neurotoxicant effects have a greater effect when occurring in utero and during early childhood. Recent findings exploring neural-level mechanisms provide a crucial opportunity to explore the ways in which environmental conditions may get "under the skin" to impact a number of psychological behaviors and cognitive processes, ultimately allowing for greater synergy between macro- and microlevel efforts to improve mental health in the presence of neurotoxicant exposures. In this review, we provide an overview of 3 types of neurotoxicants related to the built environment and relevant to brain development during childhood and adolescence: lead exposure, outdoor particulate matter pollution, and endocrine-disrupting chemicals. We also discuss mechanisms through which these neurotoxicants affect central nervous system function, including recent evidence from neuroimaging literature. Furthermore, we discuss neurotoxicants and mental health during development in the context of social determinants and how differences in the spatial distribution of neurotoxicant exposures result in health disparities that disproportionately affect low-income and minority populations. Multifaceted approaches incorporating social systems and their effect on neurotoxicant exposures and downstream mental health will be key to reduce societal costs and improve quality of life for children, adolescents, and adults.

Figure 1

Sources of major neurotoxicants and proposed physiological targets. Exposure to the 3 classes of neurotoxicants discussed in this article (lead, outdoor particulate matter air pollution, and endocrine-disrupting chemicals) can occur through multiple avenues, because the sources for these toxicants include broad environmental pollution from traffic, agriculture, industrial activities, etc.; local pollution in areas, such as parks and schools, where children spend time; and home pollution, where children may be exposed to household items containing neurotoxic chemicals. These pollution sources, encountered in children’s broad and local environments, may enter the body through inhalation, ingestion, and/or dermal absorption (see Table S1 for further details). Once in the bloodstream, these toxicants may cross the blood-brain barrier and directly act upon components of the central nervous system (CNS) or indirectly affect the brain by altering other systems, including air pollution–related increases in inflammation and oxidative stress or endocrine-disrupting chemicals acting to disrupt the endocrine system. A causal arrow is not drawn between the physiological diagram and the behavioral and cognitive outcomes, because no causal link has been confirmed. However, it is hypothesized that disruption of normal neurodevelopment and damage to neural and endocrine pathways may lead to changes in behavioral symptoms, cognitive development, and mental health in children.