Pediatrics November 1999;104:e59

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      Effects of Toxic Metals on Learning Ability and Behavior

      I. Mechanisms of Developmental Damage by Toxic Metals.

      The human brain forms and develops over a long period of time compared to other organs, with neuron proliferation and migration continuing in the postnatal period. The blood-brain barrier is not  fully developed until the middle of the first year of life. Similarly there is postnatal activity in the development of neuronal receptors  and transmitter systems, as well as in the production of myelin. The fetus has been found to get significant exposure to toxic substances  through maternal blood and across the placenta, with fetal levels of toxic metals often being higher than that of maternal blood(19,30- 32,41-43). Likewise infants have been found to get significant exposure to toxics, such as mercury that their mother is exposed to, through breast-feeding(26,43,101,107).    The incidence of neurotoxic or immune reactive conditions such  as autism, schizophrenia, ADD, dyslexia, learning disabilities, etc. have been increasing rapidly in recent years(2,80-82). A recent  report by the National Research Council found that 50% of all  pregnancies in the U.S. are now resulting in prenatal or postnatal mortality, significant birth defects, or otherwise chronically  unhealthy babies(82). Exposure to toxic chemicals or environmental factors appear to be a factor in as much as 28 percent.