Neurotoxicants mercury

Ancient Worldwide Mercury Mine workers poisoned 1930s hat industry (the Mad Hatters) 1950s Japan, mercury in fish 1970s mercury in seed grain acceptance of mercury as a developmental neurotoxicant released from coal-fired electrical plants ongoing contamination of fish... 

Nervous System. The nervous system is also a common target of toxic metals particularly, organic metal compounds (see Chapter 16). For example, methylmercury, because it is lipid soluble, readily crosses the blood-brain barrier and enters the nervous system. By contrast, inorganic mercury compounds, which are more water soluble, are less likely to enter the nervous system and are primarily nephrotoxicants. Likewise organic lead compounds are mainly neurotoxicants, whereas the first site of inorganic lead is enzyme inhibition (e.g., enzymes involved in heme synthesis). 

Exposure to neurotoxicants or neurotoxic chemical substances causes severe adverse health effects to the nervous system, which is very sensitive to organometallic compounds and sulfide compounds. These compounds disrupt the normal functioning of the central nervous system, peripheral nerves or sensory organs, and the conduction of nerve impulses. Thus, chemical substances are considered neurotoxicants when they induce a consistent pattern of neural dysfunction. The chemical substances include but are not limited to carbon disulfide, manganese, methyl mercury, organic phosphorous insecticides, tetraethyl lead, thallium, and trialkyl tin compounds. 

The use of nonneuronal cell types may provide initial information on whether a chemical may have differential effects, or display different potencies, in neuronal versus nonneuronal cells. For example, a battery of seventeen different cell types, including cell lines and primary cells (both neuronal and glial), human and rat cells, and nervous system and nonnervous system cells, was utilized to assess the toxicity of known developmental neurotoxicants, such as methyl-mercury and polychlorinated biphenyls (PCBs).24 Endpoints were cell viability and cell proliferation, and a summary of results for methylmercury and PCB-153 is shown in Table 8.5. This simple approach would flag methylmercury as a potential neurotoxicant, as toxicity was greater in neuronal cells than in other cell types. PCB-153 would also be flagged as a potential neurotoxicant, though... 

Dental amalgam restorations leak small amounts of elemental mercury vapor into the oral cavity of the mouth. The released mercury can be taken up by the saliva and then distributed to various organs and compartments throughout the body. Daily mercury uptake rates from amalgam are estimated to range from 2 to 25 pg Hg/24 h with the worst case individual estimated to have an uptake of 70 pg Hg/24 h. Mercury is a known neurotoxicant and the off-gassing of mercury over time may cause dementia like conditions in some people. 

Recent data regarding the action of low-level mercury exposure on receptors and signal transduction pathways in peripheral lymphocytes suggest potential applications of certain surrogate markers in mechanistic studies of neurotoxicity and, possibly, in assessing early biochemical effects of neurotoxicants in humans (Manzo et al. 1995). Additional biomarkers for effects on the immune, renal,... 

Numerous neurotoxic chemicals have been identified. These include pesticides (particularly, but not limited to, organophosphates and carbamates), aliphatic and aromatic hydrocarbons, alcohols, ethers, ketones, heavy metals (including lead, mercury, manganese, and others), and mixtures of these. Hundreds of individual chemicals are established or suspected neurotoxins [132]. The EPA Guidelines for Neurotoxicity Risk Assessment [4] and the Scorecard list of neurotoxicants [5] contain partial lists of neurotoxic chemicals. The actual number of chemicals with neurotoxic potential has been estimated to range between 3% and 28% of all of the approximately 80,000 chemicals in use (2400-22,400) [1]. Clearly, the number of mixtures possible is infinite, though little attention has been devoted to the neurotoxic effects of mixtures. 

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