Central Nervous System - Microsoft Word Toxicology and Exposure Guidelines doc

Central Nervous System. Neurons (nerve cells) have a high metabolic rate but little capacity for
anaerobic metabolism. Subsequently, inadequate oxygen flow (anoxia) to the brain kills cells
within minutes. Some may die before oxygen or glucose transport stops completely.
Because of their need for oxygen, nerve cells are readily affected by both simple asphyxiants and
chemical asphyxiants. Also, their ability to receive adequate oxygen is affected by compounds
that reduce respiration and thus reduce oxygen content of the blood (barbiturates, narcotics).
Other examples are compounds such as arsine, nickel, ethylene chlorohydrin, tetraethyl lead,
aniline, and benzene that reduce blood pressure or flow due to cardiac arrest, extreme
hypotension, hemorrhaging, or thrombosis.
Some compounds damage neurons or inhibit their function through specific action on parts of the
cell. The major symptoms from such damage include: dullness, restlessness, muscle tremor,
convulsions, loss of memory, epilepsy, idiocy, loss of muscle coordination, and abnormal
sensations. Examples are:
• Fluoroacetate: Rodenticide.
(Created 12/02)
UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
• Triethyltin: Ingredient of insecticides and fungicides.
• Hexachlorophene: Antibacterial agent.
• Lead: Gasoline additive and paint ingredient.
• Thallium: Sulfate used as a pesticide and oxide or carbonate used in manufacture of
optical glass and artificial gems.
• Tellurium: Pigment in glass and porcelain.
• Organomercury compounds: Methyl mercury used as a fungicide; is also a product of
microbial action on mercury ions. Organomercury compounds are especially hazardous
because of their volatility and their ability to permeate tissue barriers.
Some chemicals are noted for producing weakness of the lower extremities and abnormal
sensations (along with previously mentioned symptoms):
• Acrylamide: Soil stabilizer, waterproofer.
• Carbon disulfide: Solvent in rayon and rubber industries.
• n-Hexane: Used as a cleaning fluid and solvent. Its metabolic product, hexanedione,
causes the effects.
• Organophosphorus compounds: Often used as flame retardants (triorthocresyl phosphate)
and pesticides (Leptofor and Mipafox).
Agents that prevent the nerves from producing proper muscle contraction and may result in death
from respiratory paralysis are DDT, lead, botulinum toxin, and allethrin (a synthetic insecticide).
DDT, mercury, manganese, and monosodium glutamate also produce personality disorders and
madness.
Liver. Liver injury induced by chemicals has been known as a toxicologic problem for hundreds
of years. It was recognized early that liver injury is not a simple entity, but that the type of lesion
depends on the chemical and duration of exposure. Three types of response to hepatotoxins can
be identified:
• Acute. Cell death from:
• carbon tetrachloride: Solvent, degreaser.
• chloroform: Used in refrigerant manufacture solvent.
• trichloroethylene: Solvent, dry cleaning fluid, degreaser.
• tetrachloroethane: Paint and varnish remover, dry cleaning fluid.
• bromobenzene: Solvent, motor oil additive.
• tannic acid: Ink manufacture, beer and wine clarifier.
• kepone: Pesticide.
• Chronic. Examples include:
• cirrhosis: a progressive fibrotic disease of the liver associated with liver
dysfunction and jaundice. Among agents implicated in cirrhosis cases are carbon
tetrachloride, alcohol, and aflatoxin.
• carcinomas: malignant, growing tissue. For example, vinyl chloride (used in
polyvinyl chloride production) and arsenic (used in pesticides and paints) are
associated with cancers.
(Created 12/02)
UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
• Biotransformation of toxicants. The liver is the principal organ that chemically alters
all compounds entering the body. For example:
ethanol---> acetaldehyde---> acetic acid---> water + carbon dioxide
This metabolic action by the liver can be affected by diet, hormone activity, and
alcohol consumption. Biotransformation in the liver can also lead to toxic
metabolities. For example:
carbon tetrachloride---> chloroform
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