produce pneumoconiosis. Many dusts, of organic origin such as those arising from
cotton or wood can cause pathology of the lungs and/or alterations in lung function.
e. Systemic Poisons. In this category are materials that cause damage to
internal organs such as the liver, the kidney, and the nervous system. Carbon
tetrachloroethane is probably the most toxic of the chlorinated hydrocarbons and
produces atrophy of the liver; that is why it is no longer used as a solvent. Other
chlorinated hydrocarbons are chloroform and a certain group of pesticides. Some
halogenated hydrocarbons are chloral hydrate, trichloroethane, and chloroform. Some
halogenated hydrocarbons produce damage to the kidney as well as the liver if
excessive, acute, or chronic exposure to these compounds occurs. Some metals such
as manganese, mercury, and thallium cause damage to the nervous system. Organic
phosphorus pesticides inhibit the production of cholinesterase, which is an enzyme
necessary for the proper function of the nervous system. Some other examples are
benzene, uranium, lead, and mercury.
f. Carcinogens. These materials have demonstrated that they cause cancer in
humans or suspected of causing cancer based on animal studies. The classic example
is cancer of the scrotum from coal tar pitch volatiles. Other substances of proven
carcinogenic potential in humans are asbestos, chromium (VI), vinyl chloride, and
naphthylamine. The list of substances suspected of causing cancer is lengthy and is
growing nearly every day. It includes benzene, beryllium, carbon tetrachloride,
chloroform, ethylene oxide, formaldehyde, and methyl iodide.
NOTE: Some substances may fit in two or more categories. Many variables determine
the effect of hazardous substances with the most important consideration is the dose
response relationship. Dose involves two variable concentration and duration of
exposure. For certain chemicals, a high concentration for a short period of time would
produce the same effects as a low concentration for a long period of time. Safe limits
are set so that the combination of concentration and time are below levels, which will
produce injury or illness, the "response." A sufficiently small amount of most chemicals
do nothing injurious. This means that there is a threshold of effect of a "no response"
FACTORS AFFECTING TOXICITY
a. The toxicity (poisonous effect) of a chemical agent may be affected by a
variety of factors based on the characteristics of the contaminant itself, such as: