Transcript Chapter 3 Environmental Toxicants and

Chapter 3
Environmental Toxicants and
Neurocognitive Development
Overview
• Vulnerable periods in the neurocognitive development of
children
• List and discuss several known neurotoxicants
• Possible mechanisms of action of neurotoxicants
• Current limitations on protecting children from
neurotoxins and other hazardous chemicals
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
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Sample Case Study: Thalidomide
• Morning-sickness drug marketed over the counter in Europe,
Canada, and Japan in the 1950s and early 1960s
• Caused ~10,000 infants to be born with birth defects due to
first-trimester exposure
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Effects of Neurotoxicants
1. Fetal death
2. Death at an older age related to early or recent exposure
3. Malformations related to in utero exposure
4. Growth retardation related to in utero or later exposure
5. Developmental disabilities, including intellectual disability,
learning disabilities, and cerebral palsy
6. Subclinical outcomes, such as statistically significant
decrements in IQ, executive functioning, and/or adaptive
skills
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Scope of the Issue
• 3% of all neurobehavioral disorders in children directly caused
by exposure to environmental contaminants
• 25% of all neurobehavioral disorders in children caused by
interactions among environmental factors
• 13% of all neuropsychiatric diseases caused by environmental
factors
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Susceptible Periods of Development
• Before conception, by influencing the sperm or ova
• During pregnancy
• After birth
• For the first two decades of life
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
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Toxicants
• Lead:
• Found in lead-based paint
• Peripheral neuropathy in adults, CNS damage in children
• Attention deficit, decreased adult gray matter, decreased
brain volume, and impaired language function
• Mercury:
• Found in thermometers, barometers, and fluorescent
lighting and as MeHg in contaminated fish or shellfish
• Severe brain damage with microcephaly, seizures, severe
cognitive delay, and motor deficits with prenatal exposure
to high doses
• Cognitive and motor deficits with childhood exposure to
acute doses
• Minimal effects in exposed adults
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Toxicants (continued)
• Arsenic:
• Found in contaminated drinking water or industrial sites
• Problems with learning, short-term memory, decreased IQ,
and concentration
• Alcohol:
• Fetal alcohol spectrum disorder (FASD) from maternal
ingestion during pregnancy
• Range of physical, behavioral, and cognitive problems
• More severe cases: fetal alcohol syndrome (FAS)
• Milder cases: partial fetal alcohol syndrome (pFAS)
• FAS: microcephaly, behavior problems, attentiondeficit/hyperactivity disorder (ADHD), executive function
deficits, learning problems, decreased brain volume, and
brain abnormalities
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Toxicants (continued)
• Polychlorinated biphenyls (PCBs):
• In electronics, plastics, paint, and pesticides, fish, and farmraised salmon
• Cross the placenta and are found in breast milk
• High-dose contamination: cognitive delays, behavior
disorders, and growth retardation
• Low-dose contamination: deficits in neuromotor development and IQ; problems with attention and impulse control
• Pesticides:
• Over 1,300 registered chemicals
• Dichlorodiphenyltrichloroethane (DDT): crosses the
placenta; found in breast milk; has variable effects
• Chlorpyrifos: increased risk of developmental delay,
ADHD, and autism at age 3
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Toxicants (continued)
• Endocrine disrupting chemicals:
• Phthalates, PCBs, brominated flame retardants, DDT,
bisphenol A, and others
• Interferes with homeostatic, reproductive, and
developmental hormones
• Estrogenic, antiestrogenic, antiandrogenic, antithyroid, or
antiprogestin effects
• Decreased IQ and other neurodevelopmental abnormalities
• Mixed toxicants:
• Difficult to replicate in lab settings or determine outcome
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Toxicants (continued)
• Environmental tobacco smoke:
• Over 4,000 chemicals
• Occurs prenatally through maternal smoking or exposure
• Reductions in cortical gray matter, alteration in white matter
development, and deficits in speech and language skills,
visual/spatial abilities, behavior, and IQ
• Dietary exposures and ADHD:
• Not conclusively linked by the U.S. Food and Drug
Administration
• Small subset of children with ADHD have worsening
behavior due to certain foods
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Public Policy Implications
• Certain infant bottles, toys, and cookware a concern
• No U.S.-required testing for nonpharmaceutical and
nonpesticide chemicals
• No commercial incentives to conduct safety studies
• Pending legislation to remediate this
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.
Summary
• Over 1,000 chemicals are neurotoxicants
• Similar effects in humans as in animals with same exposure
time
• Exposure to same toxicant at different times = different effects
• Most damage caused by toxicants is irreversible; focus is on
prevention
Chapter 3 slides in Children with Disabilities, Seventh Edition, Online Companion Materials.
Copyright © 2013 Paul H. Brookes Publishing Co., Inc. All rights reserved.