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Risk and Toxicology
Chapter 19
The Ebola virus causes a form of
hemorrhagic fever, and was first
recognized in Africa in 1976. The
virus is transmitted through direct
person-to-person contact and is one
of the most virulent viruses known,
with a mortality rate usually over
90%. TEM.
TOXICITY AND HEALTH
A toxin is any substance that is inhaled, ingested, or absorbed at sufficient
dosages that it damages a living organism, and the toxicity of a toxin is
the degree to which it is biologically harmful. Almost any substance that is
inhaled, ingested or absorbed by a living organism can be harmful when it
is present in large enough quantities—even water. In order for a substance
to be harmful, all of the following must be considered:
Dosage amount over a period of time
Number of times of exposure
Size and/or age of the organism that is exposed
Ability of the body to detoxify that substance
Organism's sensitivity to that substance (due, for example, to genetic
predisposition, or previous exposure)
Synergistic effect
more than one substance combines to cause a toxic effect that's greater than any one
component
Five major factors can affect the harm caused by a
substance.
a. Solubility. Water-soluble toxins can move throughout the environment.
Oil- or fat-soluble toxins (generally organic compounds) can penetrate
the membranes surrounding an organism’s cells and accumulate in
the body.
b. Persistence of a substance is also important. Some substances resist
breakdown and remain in the environment a long time and can have
long-lasting harmful effects.
c. Bioaccumulation is a third factor. Molecules are absorbed and stored
in the body at higher than normal levels.
d. Biomagnification is where toxins accumulate at greater levels as they
are moved up from one trophic level to the next higher one.
e. Chemical interactions can decrease or multiply the harmful effects of a
toxin. An antagonistic interaction reduces the harmful effect, while a
synergistic interaction multiplies the harmful effects
Bioaccumulation within species
Biomagnification within the food chain
What is Toxicity? How is it Measured?
Substances are usually tested for
toxicity using a dose-response
analysis. In a dose-response
analysis, an organism is exposed to
a toxin at different concentrations,
and the dosage that causes the
death of the organism is recorded.
The information from a set of organisms
is graphed and the resulting curve
referred to as a dose-response
curve. The dosage of toxin it takes to
kill 50 percent of the test animals is
termed LD50, and this value can be
determined from the graph.
A high LD50 indicates that a substance
has a low toxicity, while and a low
one indicates high toxicity. A poison
is any substance that has an LD50
of 50 mg or less per kg of body
weight.
Dose-Response Curve
Types of dose-response curves
The dosage at which a negative effect occurs is referred to as the threshold
dose. Two more terms you should know for the test are acute effect and
chronic effect. An acute effect is an effect caused by a short exposure to a
high level of toxin; a snake bite, for example, causes an acute effect. A chronic
effect is that which results from long-term exposure to low levels of toxin; an
example of this would be long-term exposure to lead paint in a house.
What have we been exposed to?
Industrial Chemicals
Impact of Pesticides - Development
Everyday chemicals – Smoking,
asbestos, indoor air pollution “SickBuilding Syndrome”
Examples from the Big Screen:
Civil Action & Erin Brockovich
There are three major types of potentially toxic agents.
a. Mutagens are chemicals or ionizing radiation that cause or increase the
frequency of random mutations in the DNA molecules. It is generally
accepted that there is no safe threshold for exposure to harmful mutagens.
b. Teratogens are chemicals that cause harm or birth defects to a fetus or
embryo. Alcohol and thalidomide are examples of teratogens.
c. Carcinogens are chemicals or ionizing radiation that cause or promote
cancer.
Major Pollution Events (Disasters):
Bhopal
Times Beach (dioxin)
Love Canal
Exxon Valdez (Alaska) , BP Gulf Oil Spill
Chernobyl, Japan's Nuclear Reactor Disaster after 2011 Quake
More Recent:
Amazon Crude (Chevron) – 60 seconds – Politics of Pollution
China’s cost of growth
Table 9-1 Toxicity Ratings and Average Lethal Doses for Humans
Toxicity Rating
LD50 (milligrams per
kg of body weight)*
Average Lethal Dose†
Examples
Supertoxic
Less than 0.01
Less than 1 drop
Extremely toxic
Less than 5
Less than 7 drops
Nerve gases, botulism toxin,
mushroom toxins, dioxin (TCDD)
Very toxic
5–50
7 drops to 1 teaspoon
Toxic
50–500
1 teaspoon to 1 ounce
Moderately toxic
500–5,000
Slightly toxic
5,000–15,000
1 pint to 1 quart
Essentially nontoxic
15,000 or greater
More than 1 quart
1 ounce to 1 pint
Potassium cyanide, heroin, atropine,
parathion, nicotine
Mercury salts, morphine, codeine
Lead salts, DDT, sodium hydroxide,
sodium fluoride, sulfuric acid, caffeine,
carbon tetrachloride
Methyl (wood) alcohol, ether,
phenobarbital, amphetamines (speed),
kerosene, aspirin
Ethyl alcohol, Lysol, soaps
Water, glycerin, table sugar
*Dosage that kills 50% of individuals exposed
†Amounts of substances in liquid form at room temperature that are lethal when given to a 70.4-kg (155-pound) human
Pathogens
An infection is the result of a pathogen invading our body, and disease occurs when
the infection causes a change in the state of health. For example, HIV, the virus that
causes the disease AIDS, infects the body and typically has a long residence time
before it causes a change in the state of health; in the form of the disease called
AIDS.
There are five main categories of pathogens.
• Viruses (and other subcellular infectious particles, such as prions)
• Bacteria - Anthrax
• Fungi
• Protozoa – Malaria -Lifecycle
• Parasitic worms – Examples
Top Ten Killer Germs
Pathogens are bacteria, virus, or other microorganisms that can cause disease.
Pathogens can attack directly or via a carrier organism (called a vector). One
example of a pathogen that relies on a vector is the bacteria that causes Rocky
Mountain spotted fever; it is within the bodies of ticks, and when ticks bite humans,
the bacteria is injected and causes the disease.
Hot Zones
Bioterrorism & antibiotic resistant disease
The degree of likelihood that a person will
become ill after exposure to a toxin or
pathogen is called risk. Many
environmental, medical, and public
health decisions are based on
potential risk.
Calculating risk is referred to as risk
assessment, and risk management
uses strategies to reduce the amount
of risk. The public health department
is an organization that makes use of
risk assessment and management; for
example, they decide who can receive
the flu shot each year.
If the risk of getting the flu is high for a
particular year, most of the population
is encouraged to have the shot;
however, if the risk seems small or the
predicted flu stains are mild, only
older people and the
immunocompromised are advised to
have the flu shot.