Environmental factors associated with a spectrum of neurodevelopmental deficits.
A number of environmental agents have been shown to demonstrate neurotoxic effects either in human or laboratory animal studies. Critical windows of vulnerability to the effects of these agents occur both pre- and postnatally. The nervous system is relatively unique in that different parts are responsible for different functional domains, and these develop at different times (e.g., motor control, sensory, intelligence and attention). In addition, the many cell types in the brain have different windows of vulnerability with varying sensitivities to environmental agents. This review focuses on two environmental agents, lead and methylmercury, to illustrate the neurobehavioral and cognitive effects that can result from early life exposures. Special attention is paid to distinguishing between the effects detected following episodes of poisoning and those detected following lower dose exposures. Perinatal and childhood exposure to high doses of lead results in encephalopathy and convulsions. Lower-dose lead exposures have been associated with impairment in intellectual function and attention. At high levels of prenatal exposure, methylmercury produces mental retardation, cerebral palsy and visual and auditory deficits in children of exposed mothers. At lower levels of methylmercury exposure, the effects in children have been more subtle. Other environmental neurotoxicants that have been shown to produce developmental neurotoxicity include polychlorinated biphenyls (PCBs), dioxins, pesticides, ionizing radiation, environmental tobacco smoke, and maternal use of alcohol, tobacco, marijuana and cocaine. Exposure to environmental agents with neurotoxic effects can result in a spectrum of adverse outcomes from severe mental retardation and disability to more subtle changes in function depending on the timing and dose of the chemical agent.
Mendola
Pauline
P
National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA. Mendola.Pauline@epa.gov
Selevan
Sherry G
SG
Gutter
Suzanne
S
Rice
Deborah
D
D000293:Adolescent; D000328:Adult; D000428:Alcohol Drinking / Q000009:adverse effects; D000818:Animals; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D002658:Developmental Disabilities / Q000139:chemically induced / Q000453:epidemiology*; D004147:Dioxins / Q000009:adverse effects; D004781:Environmental Exposure; D004785:Environmental Pollutants / Q000009:adverse effects* / Q000506:poisoning; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D007854:Lead / Q000009:adverse effects; D020263:Lead Poisoning, Nervous System / Q000453:epidemiology*; D008297:Male; D018811:Maternal Exposure / Q000009:adverse effects; D020262:Mercury Poisoning, Nervous System / Q000453:epidemiology*; D008767:Methylmercury Compounds / Q000009:adverse effects / Q000506:poisoning; D008800:Mexico / Q000453:epidemiology; D009420:Nervous System / Q000187:drug effects; D020258:Neurotoxicity Syndromes / Q000453:epidemiology*; D010575:Pesticides / Q000009:adverse effects; D011078:Polychlorinated Biphenyls / Q000009:adverse effects; D011839:Radiation, Ionizing; D014028:Tobacco Smoke Pollution / Q000009:adverse effects; D014481:United States / Q000453:epidemiology
D004147:Dioxins; D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D010575:Pesticides; D014028:Tobacco Smoke Pollution; D007854:Lead; D011078:Polychlorinated Biphenyls