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Polychlorinated biphenyls and the developing nervous system: cross-species comparisons
H A Tilson1, J L Jacobson, W J Rogan
1Laboratory of Molecular and Integrative Neurosciences, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709.
Neurotoxicology and Teratology
|May 1, 1990
Summary
Polychlorinated biphenyls (PCBs) are toxic industrial compounds that harm fetal development. Exposure can lead to developmental impairments in children, even at low levels, highlighting the need for accurate risk assessment.
Area of Science:
- Environmental Toxicology
- Developmental Neurotoxicology
- Reproductive Health
Background:
- Polychlorinated biphenyls (PCBs) are persistent, lipophilic industrial compounds found globally in human tissues, wildlife, and sediments.
- PCBs are known teratogens and neurotoxicants, capable of crossing the placenta and affecting fetal development.
- Documented human exposures, such as outbreaks in Asia, have resulted in developmental deficits in children born to exposed mothers.
Purpose of the Study:
- To evaluate the neurodevelopmental effects of polychlorinated biphenyl (PCB) exposure in humans and animal models.
- To compare the consistency of PCB-induced neurodevelopmental effects across different species.
- To assess the discrepancies in current risk assessment methods for PCBs based on neurotoxicological data.
Main Methods:
- Review of human epidemiological data from PCB poisoning outbreaks.
- Analysis of laboratory studies involving rhesus monkeys and rodents assessing neural and developmental outcomes.
- Comparison of neurodevelopmental effects observed in humans and animal models following transplacental PCB exposure.
- Evaluation of current methodologies for calculating allowable or reference doses for PCBs.
Main Results:
- Transplacental PCB exposure in humans is associated with birth hypotonia, hyporeflexia, psychomotor developmental delays, and impaired visual recognition memory.
- Animal studies (rhesus monkeys, rodents) demonstrate similar neurodevelopmental effects, including altered activity levels, learning deficits, and delayed reflex maturation.
- Despite species similarities, current risk assessment methods for PCBs yield results with discrepancies up to four orders of magnitude apart.
- The lowest reference dose levels are derived from human neurotoxicology data.
Conclusions:
- PCBs pose significant neurodevelopmental risks to fetuses and children, with effects observed across human and animal studies.
- Existing methods for determining safe PCB exposure levels are highly variable and require refinement.
- Human neurotoxicological data provides the most sensitive basis for establishing protective reference doses for PCBs.