Selective toxicity refers
to species differences in toxicity between two species simultaneously exposed.
This is the basis for the effectiveness of pesticides and drugs. Examples are:
to species differences in toxicity between two species simultaneously exposed.
This is the basis for the effectiveness of pesticides and drugs. Examples are:
- an insecticide is lethal to insects but
relatively nontoxic to animals - antibiotics are selectively toxic to microorganisms while
virtually nontoxic to humans
Age may be important in
determining the response to toxicants. Some chemicals are more toxic to infants
or the elderly than to young adults. For example:
determining the response to toxicants. Some chemicals are more toxic to infants
or the elderly than to young adults. For example:
- parathion is more toxic to young animals
- nitrosamines are more carcinogenic to newborn or
young animals
Although uncommon, toxic
responses can vary depending on sex. Examples are:
responses can vary depending on sex. Examples are:
- male rats are 10 times more sensitive than
females to liver damage from DDT - female rats are twice as sensitive to parathion
as male rats
The ability to be absorbed is essential for systemic toxicity to occur. Some
chemicals are readily absorbed and others poorly absorbed. For example, nearly
all alcohols are readily absorbed when ingested, whereas there is virtually no
absorption for most polymers. The rates and extent of absorption may vary
greatly depending on the form of the chemical and the route of exposure. For
example:
chemicals are readily absorbed and others poorly absorbed. For example, nearly
all alcohols are readily absorbed when ingested, whereas there is virtually no
absorption for most polymers. The rates and extent of absorption may vary
greatly depending on the form of the chemical and the route of exposure. For
example:
- ethanol is readily absorbed from the
gastrointestinal tract but poorly absorbed through the skin - organic mercury is readily
absorbed from the gastrointestinal tract; inorganic lead
sulfate is not
Metabolism, also known as biotransformation, is a major factor in determining toxicity. The
products of metabolism are known as metabolites. There are two types of
metabolism – detoxification and bioactivation. Detoxification is the process by
which a xenobiotic is converted to a less toxic form. This is a natural defense
mechanism of the organism. Generally the detoxification process converts
lipid-soluble compounds to polar compounds. Bioactivation is the process by
which a xenobiotic may be converted to more reactive or toxic forms.
products of metabolism are known as metabolites. There are two types of
metabolism – detoxification and bioactivation. Detoxification is the process by
which a xenobiotic is converted to a less toxic form. This is a natural defense
mechanism of the organism. Generally the detoxification process converts
lipid-soluble compounds to polar compounds. Bioactivation is the process by
which a xenobiotic may be converted to more reactive or toxic forms.
The distribution of toxicants and toxic
metabolites throughout the body ultimately determines the sites where toxicity
occurs. A major determinant of whether or not a toxicant will damage cells is its lipid solubility.
If a toxicant is lipid-soluble it readily penetrates cell membranes. Many
toxicants are stored in the body. Fat tissue, liver, kidney, and bone
are the most common storage depots. Blood serves as the main avenue for
distribution. Lymph also distributes some materials.
metabolites throughout the body ultimately determines the sites where toxicity
occurs. A major determinant of whether or not a toxicant will damage cells is its lipid solubility.
If a toxicant is lipid-soluble it readily penetrates cell membranes. Many
toxicants are stored in the body. Fat tissue, liver, kidney, and bone
are the most common storage depots. Blood serves as the main avenue for
distribution. Lymph also distributes some materials.
The site and rate of
excretion is another major factor affecting the toxicity of a xenobiotic. The
kidney is the primary excretory organ, followed by the gastrointestinal tract,
and the lungs (for gases). Xenobiotics may also be excreted in sweat, tears,
and milk.
excretion is another major factor affecting the toxicity of a xenobiotic. The
kidney is the primary excretory organ, followed by the gastrointestinal tract,
and the lungs (for gases). Xenobiotics may also be excreted in sweat, tears,
and milk.
A large volume of blood
serum is filtered through the kidney. Lipid-soluble toxicants are reabsorbed
and concentrated in kidney cells. Impaired kidney function
causes slower elimination of toxicants and increases their toxic potential.
serum is filtered through the kidney. Lipid-soluble toxicants are reabsorbed
and concentrated in kidney cells. Impaired kidney function
causes slower elimination of toxicants and increases their toxic potential.
The presence of other chemicals may decrease toxicity (antagonism), add to toxicity
(additivity), or increase toxicity (synergism or potentiation) of some
xenobiotics. For example:
(additivity), or increase toxicity (synergism or potentiation) of some
xenobiotics. For example:
- alcohol may enhance the effect of many
antihistamines and sedatives - antidotes function by antagonizing the toxicity
of a poison (atropine counteracts
poisoning by organophosphate insecticides)
