Environmental toxins can predispose children before or after birth to severe learning and health problems. Most of the over 80,000 chemicals in pesticides, herbicides, drugs, cosmetics, food additives, fertilizers, and industrial substances have not been tested for their neurotoxic effects. To date, occupational standards have been set for only about 600 chemicals. Of these, about one-third are known to have negative effects on the central nervous system. Educators need to be aware of these hazards and help children and families avoid exposures that may deter learning.
Prenatal Toxic Effects
The brain in utero generates neurons at the rate of 250,000 per minute. Yet the fetus has neither a placental barrier against toxic substances nor the capacity to detoxify them. Consequently, prenatal toxic exposures can have significant effects on later health and cognitive status. Mercury exposure, for example, arrests the division of neurons, cadmium can cause brain hemorrhages, and inhalant anesthetics can interfere with cell proliferation. Lead, a long-known offender, affects the brain's blood vessels and reduces the number of neurons and dendrite connections. Low-dose prenatal lead exposure can result in preterm delivery, and higher doses can lead to spontaneous abortions. Prenatal polychlorinated biphenyl (PCB) exposure is related to IQ and attention deficits, hyperactivity, and learning disabilities years later.
Recreational drugs such as marijuana and cocaine also have known adverse prenatal effects. Maternal marijuana smoking increases the risk for premature delivery and subsequent learning problems. Cocaine causes malformation of the brain because of oxygen deprivation, intrauterine growth retardation, increased rate of preterm delivery, and genitourinary tract abnormalities. The 1,000 "crack babies" born each day in the United States face an increased risk of seizures, strokes, abnormal reflexes, poor or absent visual and auditory orientation, marked hyperactivity, irritability, distractability, delayed language and fine- motor development, and poor interactive ability later on. As infants, they are easily overstimulated. They are most calm and alert when left alone—not a very good way to encourage cognitive development.
Maternal cigarette smoking has been associated with attention deficits and hyperactivity, and mild intellectual, language, and academic delays in children. Excessive maternal alcohol consumption may lead to neurological and physical abnormalities, significant cognitive delays, hyperactivity, attention and memory problems, fine- and gross-motor delays, language deficits, difficulty with organization and problem solving, and emotional problems. As little as one drink a day during pregnancy can be harmful.
The harmful effects of the toxins mentioned are evident in both mothers and their babies. Other toxins affect the developing fetus but not the mother. These include the sleeping pill thalidomide (babies are born with missing limbs), the acne medicine Accutane (babies have severe heart deformities, abnormally small heads and eyes, and absent ears), and the antimiscarriage drug diethylstilbestrol, or DES (adult daughters have greater rates of premature birth, miscarriage, and vaginal cancer).
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