لخّصلي

and prescription drugs, cosmetics, and solvents comprise
the most frequent human toxic exposures. Young children
and elderly are most likely to be accidentally exposed to
drugs or household chemicals at home. During adolescence
and young adulthood the exposures are more likely to be
intentional, either through suicide attempts or
experimentation with drugs or alcohol. More than 72.4% of
all poison exposures occur in children and adolescents less
than 17 years of age. Exposures are equally reported in
males and females. However, adult men have been reported
to be more at risk of occupational exposures than adult
woman. Route of entry of exposures reported was by mouth
in most cases: 77% were the result of ingestion, 7.0% were
transdermal, 5.9% were ophthalmic; and 5.5% were by
inhalation. Site of exposure was a residence in 91.9% of all,
followed by the workplace, schools and health facilities.
Most poison exposures do not result in clinical toxicity. In
general, nearly everyone is at risk of acute and chronic toxic
exposures to hazardous substances in the ambient
environment.
3. Toxicologic terms and definitions
A) Important toxicologic terms
 Toxin- a poison of natural origin.
 Poison (Toxicant) - a chemical that may harm or kill an
organism
Toxicity – is the ability of a chemical agent to cause injury.
It is a qualitative term which depends on the amount of
chemical absorbed, severity of the exposure, dose & others.
It can be acute (toxic event which occurs soon after acute or
limited exposure), or chronic (apply to an event which occurs
many weeks, months or years after exposure).
 Hazard – is the likelihood that injury will occur in a given
situation or setting: the conditions of use and exposure are
primary considerations.
 Risk – is defined as the expected frequency of the
occurrence of an undesirable effect arising from exposure to
a chemical or physical agent.
 Acute exposure is a single exposure – or multiple
exposures occurring over 1 or 2 days.
 Chronic exposure is multiple exposures continuing over a
longer period of time.
B) Presence of mixtures
Humans normally come in contact with several (or many)
different chemicals concurrently or sequentially. The resulting
biologic effect of combined exposure to several agents can be
characterized as synergistic, additive, Potentiation &
antagonistic
Synergism-when the effect of two chemicals is greater than the
effect of individual chemicals e .g carbontetrachloride + alcohol=
more toxic to the liver than the sum of the individual drugs
Additive effect- when the total pharmacological action of two or
more chemicals taken together is equivalent to the summation of
their individual pharmacological action.