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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The toxicities of many metals, such as mercury and lead, are known to man since the dawn of civilization. Organic compounds of some heavy metals are known to have a particular toxic impact on the central nervous system. Organomercury, particularly alkyl-mercuric compounds (e.g. methylmercury), has a selective effect on the granule cells of the cerebellum, the nerve cells of the calcarine cortex, and the sensory neurons in the dorsal root ganglia. The well known Minamata Bay disease is the result of a massive epidemic episode of human exposure to alkylmercury contaminated food sources. Mental retardation and other developmental defects are also known to be a consequence of exposure to this toxic metal. Organic lead compounds have been employed as gasoline additives and in other industrial purposes. Unlike its inorganic counterpart, organolead compounds have a more prominent impact on the central nervous system. Pathological changes of the brain stem neurons have been described. Organotin compounds have been used in plastic industries and as agricultural chemicals. Both trimethyl and triethyl tin compounds are found to be extremely neurotoxic. Despite the similarity of their chemical structures, trimethyl and triethyl tins have a diversely different toxic property and effects. While triethyl tin is myelinotoxic, producing edematous and vacuolar changes in the central myelin, trimethyl tin is neurotoxic, producing prominent toxic changes in the neurons of the limbic system (hippocampus, entorhinal cortex, etc.). The factors which determine the specificity and selectivity of the neurotoxic impacts by various organometals are still unknown. In view that most of the organometals are still widely employed by many countries for industrial and for agricultural purposes, caution must be made for their proper handling and disposure to avoid undesirable exposures to workers and environmental contamination of water sources and food-chain for the common public. Since organometals are difficult to eliminate from the central nervous system, injuries usually lead to permanent neurological deficits, such tragedies are frequently long lasting and create not only a medical problem, but also a social economical problem for the society.
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PMID:The neurotoxicology and pathology of organomercury, organolead, and organotin. 210 Mar 18

There are differences between young and adult organisms regarding toxokinetic aspects and clinical manifestations of heavy metal intoxications. Chronically, toxic Cd intake causes a microcytotic hypochromic anemia in young rats at lower exposure levels and after shorter exposure periods than in adult animals. Cd absorption is increased by co-administration of milk and in conjunction with iron deficiency. After long exposure periods toxic Cd concentrations accumulate in the kidney cortex; this process starts very early in life. In 3-year-old children Cd concentrations in the kidney can reach up to one-third of those found in adults. Hg++ and methyl-Hg can cause Hg encephalopathia, and frequently cause mental retardation in adults. Correspondingly, Hg++ accumulation in the brains of suckling rats is approx. 10 times higher than in grown animals. Milk increases the bioavailability of Hg++. In suckling rats Hg is bound to a greater extent to ligands in the erythrocytes. Methyl-Hg concentrations in breast milk reach 5% of those in maternal plasma and that is a severe hazard for breastfed children of exposed mothers. Toxic Pb concentrations can lead to Pb encephalopathia. A high percentage of surviving children have seizures and show signs of mental retardation. Anemia and reduced intelligence scores were recently observed in children after exposure to very low levels of Pb. Pb absorption is increased in children and after co-administration of milk. There are no definite proofs for carcinogenesis or mutagenesis after oral exposure to Cd, Hg, and Pb in man. Heavy metal concentrations were found in the same order of magnitude in commercial infant formulas and in breast milk. When infant formulas are reconstituted with contaminated tap water, however, Pb and Cd concentrations can be much higher. The average heavy metal uptake from such diets exceeds the provisional tolerable weekly intake levels set by the WHO for adults, calculated on the basis of an average food intake and a downscaled body weight. These considerations do not even provide for differences in absorption and distribution or for the increased sensitivity of children to heavy metal exposure. However, dilution effects for essential heavy metals were observed in fast-growing young children; this effect might be extrapolated to toxic metals. These theoretical considerations are compared with epidemiological evidence. A health statistic from Baltimore shows a decline of Pb intoxications in infants. This observation correlates with a simultaneous decline in exposure to Pb which was due, for example, to decreased use of lead dyes in house paints and the abolition of tin cans for infant food.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:[The toxicological estimation of the heavy metal content (Cd, Hg, Pb) in food for infants and small children]. 218