Effects of Toxic Metals on Learning Ability and Behavior


B. Windham (Ed)

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(19,30-32,41,42,169b). Likewise infants have been found to get significant exposure to toxics, such as mercury and organochlorine compounds that their mother is exposed to, through breast-feeding(26,30-32,101,107,169b). Other toxic exposures are also extremely common as documented in Section IV.


The incidence of neurotoxic or immune reactive conditions such as autism, schizophrenia, ADD, dyslexia, learning disabilities, etc. have been increasing rapidly in recent years(2,80-82,113-115,143,144,149,169). 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, developmental neurological problems, or otherwise chronically unhealthy babies(82). There has been a similar sharp increase in developmental conditions in Canadian children(132), including increases in learning disabilities and behavioral problems, asthma and allergies, and childhood cancer. Not all children are equally affected by a given level of toxic exposures, and susceptibility factors such as immune reactivity, genetic factors affecting ability to excrete toxic metals, and other toxic exposures have major influences on toxicity effects.

A 2009 study found that inorganic mercury levels in people have been increasing rapidly in recent years(177). It used data from the U.S. Centers for Disease Control and Prevention’s National Health Nutrition Examination Survey (NHANES) finding that while inorganic mercury was detected in the blood of 2 percent of women aged 18 to 49 in the 1999-2000 NHANES survey, that level rose to 30 percent of women by 2005-2006. Surveys in all states using hair tests have found dangerous levels of mercury in an average of 22 % of the population, with over 30% in some states like Florida and New York(178).

Studies and clinical experience at treatment clinics have found consistently that gastrointestinal, immunologic and metabolic problems are found in children with ADHD, that are related to prenatal and neonatal exposure to toxic substances with much of these being related to vaccinations.(173) Lower GI dysfunction, enzyme deficiencies and impairments of hepatic detoxification pathways are very common. Many ADHD/autism patients have “leaky gut” syndrome, and inability to digest wheat gluten and milk casein, resulting in neurotoxic substances being dumped in the blood with significant adverse behavioral impacts.


Exposure to toxic chemicals or environmental factors appear to be a factor in at least 28 percent of the 4 million U.S. children born each year(6-23), with at least 1 in 6 having one of the neurological conditions previously listed according to the U.S. Census Bureau(82c). U.S. EPA estimates that over 3 million of these are related to lead or mercury toxicity, with approximately 25% of U.S. kids getting mercury exposure at dangerous levels(2,41,81,108). Evidence indicates that over 60,000 children are born each year with neurodevelopmental impairment due to methyl mercury(107,2), with even higher levels of exposure and impairment from two other sources, vaccines and mother’s amalgam dental fillings (81,169ab).


II. Extent of Exposure of Children to Toxic Metals

The U.S. Center for Disease Control ranks toxic metals as the number one environmental health threat to children, adversely affecting large numbers of children in the U.S. each year and thousands in Florida(1-4,108). According to an EPA/ATSDR assessment, the toxic metals lead, mercury, and arsenic are the top 3 toxics having the most adverse health effects on the public based on toxicity and current exposure levels in the U.S.(1), with cadmium, chromium and nickel also highly listed. According to the American Academy of Child and Adolescent Psychiatry, an estimated one out of every 6 children in the U.S. have blood levels of lead in the toxic range(87), and studies estimate that over 12 million children suffer from learning, developmental, and behavioral disabilities including ADD, autism, schizophrenia, and mental retardation(87,82,42,113,149,157). Large numbers of people have been found to have allergic conditions and immune reactive autoimmune conditions due to the toxic metals, especially inorganic mercury and nickel(28,29,59). These metals have also been found to diminish the cellular ATP energy function and be related to chronic fatigue 28,29,59,170). One of the mechanisms documented is causing intestinal dysbiosis resulting in poor vitamin and mineral absorption(112) and “leaky gut”.


The level of exposure in most infants to mercury thimerosal has been found to be many times higher than the federal limits for mercury exposure (81,122,169). The largest increase in neurological problems has been in infants(2,80-82), with an increase in autism cases to over 500,000 (2,80-82,169), an over 500% increase to a level of almost 1 per 300 infants in the last decade(80), making it the 3rd most common chronic childhood condition, along with similar increases in ADD (2,41,83,88,143,149,169a, 172). According to the American Academy of Pediatrics between 4 to 12 % of all school age children are affected by ADHD(144) and a similar number have some degree of dyslexia(41). However large surveys of elementary level student records finds much higher levels- with over 20% of elementary school boys in some areas being treated for ADD(143). Similar levels of children have been found to have mood or anxiety disorders. At least 4% of adults have also been found to have ADHD symptoms(176). Studies have found that long term use of stimulant drugs commonly are not effective in the long run and causes significant adverse neurological and health effects(145, 172), There are more effective options available to deal with such conditions without such adverse effects including dealing with the underlying causes (172,173,175,176) and diet, exercise, and supplement options that deal with underlying deficiencies(172).



The heavy metals(lead,mercury,cadmium,nickel) tend to concentrate in the air and in the food chain along with other toxic metals like and aluminum, facilitating metal poisoning which is the most widespread environmental disorder in the U.S(1-4,34). Mercury and cadmium from combustion emissions are also accumulating in coastal estuaries and inland water body sediments, and are widespread in shellfish and other org anisms (34-36). Mercury and cadmium are extremely toxic at very low levels and have serious impacts on the organisms in water bodies that accumulate them(34,2). These heavy metals have also been found to be endocrine system disrupting chemicals and have been found to be having effects on the endocrine and reproductive systems of fish, animals, and people, similar to the reproductive and developmental effects of organochlorine chemicals (30,33,155,170). Estrogenic chemicals like mercury have been found in Florida wildlife at levels that feminized males to the extent of not being able to reproduce, and also had adverse effects on the female reproductive systems(33,36). Similar effects have also been documented in humans (33,37,155,170).



III. Developmental Effects of Toxic Metals on Cognitive Ability and Behavior.


Studies have found that heavy metals such as mercury, cadmium, lead, aluminum, and tin affect chemical synaptic transmission in the brain and the peripheral and central nervous system (19,24,25,37-40,57,154,169,170). They also have been found to disrupt brain and cellular calcium levels that significantly affect many body functions: such as (a) calcium levels in the brain affecting cognitive development and degenerative CNS diseases(5,28,170,74) (b) calcium-dependent neurotransmitter release which results in depressed levels of serotonin, norepinephrine, and acetylcholine(5,19,28,44-47,83, 110,170) – related to mood and motivation; (c)cellular calcium-sodium ATP pump processes affecting cellular nutrition and energy production processes (5,28,170); (d) calcium levels in bones causing skeletal osteodystery(5,74). Toxic metals have also been found to affect cellular transfer and levels of other important minerals and nutrients that have significant neurological and health effects such as magnesium, lithium, zinc, iron, Vitamins B-6 & B1-12(5,27,46, 68,75,83,104,160-163,170,170). Based on thousands of hair tests, at least 20 % of Americans are deficient in magnesium and lithium(5,68,76,83), with zinc deficiencies also common(123,160,163) and iron deficiencies(162). The resulting deficiency of such essential nutrients has been shown to increase toxic metal neurological damage (5,74,75,83,160,170). Cerebrospinal magnesium was found to be significantly lower in both depression and adjustment disorder and in those who have attempted suicide(166).

Much of the developmental effects of mercury(and other toxic metals) are due to prenatal and neonatal exposures damage to the developing endocrine(hormonal) system(155,169,32c). A recent study found that prenatal Hg exposure is correlated with lower scores in neurodevelopmental screening, but more so in the linguistic pathway(32c). Prenatal and neonatal toxic metal exposure to mercury, lead, arsenic, cadmium, nickel, and aluminum have been documented in medical publications and medical texts to cause common and widespread neurological and psychological effects including depression, anxiety, obsessive compulsive disorders, social deficits, other mood disorders, schizophrenia, anorexia, cognitive impairments, ADHD, autism, seizures, etc. (48,113-115,153-155, 157,169,170). Children with autism had significantly ( 2.1-fold) higher levels of mercury in baby teeth, but similar levels of lead and similar levels of zinc. Children with autism also had significantly higher usage of oral antibiotics during their first 12 mo of life. Baby teeth are a good measure of cumulative exposure to toxic metals during fetal development and early infancy(168).


Studies have also found heavy metals to deplete glutathione and bind to protein-bound sulfhydryl SH groups, resulting in inhibiting SH-containing enzymes and production of reactive oxygen species such as superoxide ion, hydrogen peroxide, and hydroxyl radical(39,41,45-47,101,105,139,169, 170). In addition to forming strong bonds with SH and other groups like OH,NH2, and Cl in amino acids which interfere with basic enzymatic processes, toxic metals exert part of their toxic effects by replacing essential metals such as zinc at their sites in enzymes. An example of this is mercury’s disabling of the metallothionein protein, which is necessary for the transport and detoxification of metals. Mercury inhibits sulfur ligands in MT and in the case of intestinal cell membranes inactivates MT that normally bind cuprous ions (125,141), thus allowing buildup of copper to toxic levels in many and malfunction of the Zn/Cu SOD function. Another large study(114) found a high percentage of autistic and PDD children are especially susceptible to metals due to the improper functioning of their metallothionein detoxification process, and that with proper treatment most recover. Mercury has also been found to play a part in neuronal problems through blockage of the P‑450 enzymatic process (141). Mercury induced reactive oxygen species and lipid peroxidation has been found to be a major factor in mercury’s neurotoxicity, along with leading to decreased levels of glutathione peroxidation and superoxide dismustase(SOD) (39). This has been found to be a major factor in neurological and immune damage caused by the heavy metals, including damage to mitochondria and DNA(37-40,170), as well as chronic autoimmune conditions and diseases(29). Turmeric(curcumin) has strong antioxidant effects and has been shown to counteract lipid peroxidation and toxicity effects of metals and to reduce the toxic effects of metals such as copper, lead, cadmium, etc. (171).

The effects on DNA are a factor in several of the toxic metals such as arsenic, beryllium, cadmium, chromium, and nickel being known carcinogens(147), but chronic exposure to other toxic metals such as mercury are also known to promote cancer through their DNA effects and suppression of the immune system(170).

Metals by binding to SH radicals in proteins and other such groups can cause autoimmunity by modifying proteins which via T-cells activate B-cells that target the altered proteins inducing autoimmunity as well as causing aberrant MHC II expression on altered target cells(136). Studies have also found mercury and lead cause autoantibodies to neuronal proteins, neurofilaments, and myelin basic protein (137,155,45); and immune mechanisms are a major factor in neurotoxicity of metals seen in conditions such as autism and ADD(98b,169)

Although vaccinations appear to be the largest source of mercury in infants, mercury has been found to be transmitted from the mother to the fetus through the placenta and accumulate in the fetus to higher levels than in the mother’s blood (30,169b). Breast milk of women who have amalgam fillings is the second largest source of mercury in infants and young children(169b,69), but eating a lot of fish has also been found to be a significant source of methyl mercury(101). Milk increases the bioavailability and retention of mercury by as much as double(169b,131,31) and mercury is often stored in breast milk and the fetus at much higher levels than that in the mother’s tissues (169b,31). Mercury is transferred mainly by binding to casein(131,92). The level of mercury in breast milk was found to be significantly correlated with the number of amalgam fillings(31,169b), with milk from mothers with 7 or more fillings having levels in milk approx. 10 times that of amalgam-free mothers. The mercury in milk sampled ranged from 0.2 to 6.9 ug/L. Prenatal mercury exposure can also developmentally damage the metals detox system of the liver which can lead to accumulation and toxicity of later metals exposure(169b).


High lead, copper, manganese, or mercury levels have been found to be associated with attention deficit hyperactivity disorder(ADHD), memory deficits, impulsivity, anger, aggression, inability to inhibit inappropriate responding, juvenile delinquency, and criminality (19,20a,21,61,62,83,122,133,134,145,150-155,159,169). Mercury has been found to be a factor in anger, aggressive behavior, depression, obsessive compulsive behavior(OCD), ADD, autism, schizophrenia, suicidal behaviors, learning disabilities, anxiety , mood disorders, and memory problems (135,133,149,150,153-155,157,169,170,15,113-115). It has been found that excess levels of copper can cause violent behavior in children(124,115,15,114). A study that investigated the effects of zinc and copper on the behavior of schizophrenic patients by comparing blood zinc and copper levels in criminal and noncriminal schizophrenic patients found criminal subjects have significantly lower zinc levels and signif. higher copper levels than non-criminal subjects(165).

Manganese toxicity has long been known to be associated with impulsive and violent behavior (37,61a,134,151). Lead also has been the subject of extensive research documenting its relation to all of these conditions(19-21,61,etc.). Based on a national sample of children, there is a significant assoc. of lead body burden with aggressive behavior, crime, juvenile delinquency, behavioral problems(62b). By the government’s latest count, 2.2 percent of children ages 1 to 5 in the United States – 300,000 children – have a blood lead level that is greater than or equal to 10 micrograms per deciliter of blood, a level that studies have shown to be associated with adverse effects. In a recent study after adjustment for covariates and interactions and removal of noninfluential covariates, adjudicated delinquents were four times more likely to have bone lead concentrations >25 ppm than controls(21a).

High aluminum levels have been found to be related to encephalopathies and dementia (49,15). Scores for tension, depression, anger, fatigue and confusion in workers exposed to aluminum for more than ten years were significantly more than those in non-exposed controls(49). ” Recent studies suggest that aluminum contributes to neurological disorders such as Alzheimer’s disease, Parkinson’s disease, senile and presenile dementia, clumsiness of movements, staggering when walking, and inability to pronounce words properly”. Arsenic, like most of the other metals has been found in studies to be associated with neurologic, vascular, dermatologic, and carcinogenic effects, along with reproductive effects(100,15c). Long-term exposure to ingested arsenic has been documented to induce peripheral vascular disease, cartoid arteriosclerosis, ischemic heart disease, and cerebral infarction in a dose-response relationship. A comparison of areas with higher levels of arsenic in the water supply found higher fetal and infant mortality in areas with higher arsenic levels and higher cancer rates. Cadmium is also a known carcinogen(100c,d). Some of the developmental effects documented to be caused by low level toxic metal exposure include developmental delays, growth problems, slower reaction times, diminished intellectual ability, behavior problems, poor balance and motor function, hearing loss, attention deficit disorder, etc.(19,159,169,170,etc.)

Many individuals have been found to be more sensitive to toxic metals depending on genetic sensitivity and past exposure to toxic substances(28,29).Nickel exposure is common and nickel exposure has been found to be significantly related to perinatal unthriftiness and mortality in animal studies. Large numbers of people affected by allergic conditions such as eczema and psoriasis vulgaris(59) and serious autoimmune conditions such as lupus and CFS have been found to be immune reactive to nickel or mercury(28,29,59,43a,170)



Other agents including mercury are known to accumulate in endocrine system organs such as the pituitary gland, thyroid, and hypothalamus and to alter hormone levels and endocrine system development during crucial periods of development (33,37,27,109,111,155,170). Such effects are usually permanent and affect the individual throughout their life. Pregnant women who suffer from hypothyroidism (underactive thyroid) have a four-times greater risk for miscarriage during the second trimester than those who don’t, and women with untreated thyroid deficiency were four-times more likely to have a child with a developmental disabilities and lower IQ(111) . Some of the documented effects of exposure to toxic metals include significant learning and behavioral disabilities, mental retardation, autism, etc. But even some of the relatively subtle effects that have been found to occur such as small decreases in IQ, attention span, and connections to delinquency and violence, if they occur in relatively large numbers over a lifetime can have potentially serious consequences for individuals as well as for society (21,26,37,41,42,113-115,155).

The incidence of neurological conditions in children such as autism has increased over 500% in the last decade(80,143,149,169), along with similar increases in ADD and other pervasive developmental diseases(PDD). Autism is a condition that was unknown prior to the 1940s but whose incidence has increased so rapidly that it is currently the 3rd leading childhood neurological conditions and the current incidence in approximately 1 in 300, and 1 in 150 in some communities surveyed in Maryland(80). Millions of kids are currently afflicted with PDD conditions. Mercury and other toxic metals have been found to be a factor in most of those tested(81,99,153,169). Vaccinations that use mercury thimerosal as a preservative appear to be a common and causative factor in these conditions as well as SIDS(81,83,99,122,149,169). A study at the U.S. CDC and followup studies found “statistically significant associations” between certain neurologic developmental disorders such as attention deficit disorder(ADD) and autism with exposure to mercury from thimerosal‑containing vaccines before the age of 6 months(122,149,169). (READ MORE)

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