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Topics in Toxicology
Independent Assignments
Toxicology Enrichment Materials
Teacher's Notes
These questions will require students to
perform independent research. Information can be gathered from
encyclopedias, other reference books and periodicals. Increasingly,
information on these and other toxicology topics can be found
at various internet Web sites. The questions range from factual
to interpretive to evaluative. The goal is for students to gain
enough information on a particular topic to be able to form an
opinion about it. What follows is a brief description of each
of the topics and suggestions for use.
Students could be assigned a short
report, using the questions as a guide.
Students could work on these research
projects individually or in groups.
The topics could be covered individually
in class, emphasizing different aspects of the topic as they are
covered in the course curriculum.
Gulf War Syndrome
This assignment
may be useful as a current event or "in the news" topic. It also
illustrates complex problem solving. The syndrome symptoms would
fit into a study of the nervous system.
This
has been a 'hot' topic in the news and continues to receive attention.
Complaints from Gulf War veterans include memory problems, sleep
problems, confusion, dizziness, muscle pains and fatigue. Causes
under investigation include chemical exposure, stress and infectious
disease. Chemicals under consideration include insecticides, anti-nerve
gas agents and chemical weapons. Some combination of these or
other causes are also possible factors.
Thalidomide
This assignment would fit into the study
of reproduction, birth or development. Also, it exemplifies issues
related to epidemiology and animal testing. The drug is lipophillic
and crosses the placenta by simple diffusion, thus would fit into
the study of membranes.
Thalidomide
is a sedative and hypnotic commonly prescribed in Europe in the
late 1950's to pregnant women to decrease vomiting and nausea
and as a sleeping aid. In 1960, an epidemic of newborns with rare
limb deformities was identified in West Germany and other parts
of the world. Thalidomide is a teratogen which, when exposed during
fetal development, causes missing and malformed limbs, as well
as other malformations and even death. In 1961, thalidomide was
identified as the causative agent of the epidemic and it was withdrawn
from the market. By 1962, the epidemic had subsided. Approximately
7000-8000 children were affected. The drug was tested in the mouse
and rat, both of which are resistant to the effects of the drug.
Dichlorodiphenyltrichloroethane (DDT)
This topic would fit into the study
of enzymes, ecology, populations and the food chain.
DDT
was discovered over 100 years ago, and its use as an insecticide
began in 1939 by a Swiss chemist. In World War II it was used
to dust soldiers for prevention of insect bites and diseases passed
on by insects. This chemical was considered ideal because it was
persistent, highly toxic to invertebrates and had low toxicity
toward vertebrates. However, when it was used in agriculture,
problems quickly developed. Both a spatial and temporal correlation
were made between its use and to the decline in populations of
several bird species. DDT bioaccumulates, thus its effects were
primarily seen at the top of the food chain. Fish-eating birds
affected included bald eagles, pelicans, osprey, heron and gulls.
Bird-eating birds included falcons and hawks. DDT caused a decrease
in egg shell thickness and an increase in egg breaking in the
falcons. Subsequent research revealed that DDT inhibits an enzyme
(Ca ATPase) that transports calcium from the blood to the oviduct
where the egg shell is formed. Once DDT was banned, the falcon
population and others bounced back.
Aflatoxin
This assignment should illustrate the
point that not all dangerous chemicals are human-made. It also
demonstrates differences in susceptibility between animal species.
Aflatoxins and other toxicants that interfere with DNA can be
incorporated into the study of molecular genetics. The biotransformation
of aflatoxin should be interesting to chemistry students in their
study of functional groups.
Aflatoxin
is a natural toxin produced by the fungus Aspergillus flavus
that contaminates corn, peanuts and other grains. Because it is
produced by a fungus, aflatoxin is a "mycotoxin." This compound
is very potent as a hepatotoxin and hepatocarcinogen, meaning
it is toxic and causes cancer of the liver. Aflatoxin will cause
50% lethality due to liver toxicity at 0.5 mg/kg in ducklings
to 60 mg/kg in mice. The compound is biotransformed and subsequently
causes cancer by binding to DNA.
Lead
The study of lead is appropriate within
the context of the nervous system, development and behavior. It
is also frequently in the news, most recently regarding laws regulating
the removal and disposal of lead-based paint.
Humans
are exposed to this heavy metal in food, in lead-based paint in
older dwellings, in air from combustion of lead-containing auto
exhausts or industrial emissions and lead-glazed earthenware.
The major risk is toxicity to the nervous system, though other
forms of toxicity have been reported, especially in adults with
high occupational exposure. The most susceptible populations are
children, particularly toddlers and infants in the neonatal period,
and the unborn fetus. Neurological, neurobehavioral and developmental
effects have been described in children. A variety of tests are
used to evaluate the effects of lead in children including impact
on behavior, intelligence (IQ) and other psychological skills.
Testing is also done in laboratory animals. Clinically overt signs
of lead toxicity can be seen in children with blood levels of
80 µg/dl. Children with levels between 50-70 µg/dl may have decreased
cognitive function as measured by IQ.
Domoic Acid
Outbreaks of domoic acid poisoning occur
periodically. The study of domoic acid is appropriate within the
context of the nervous system, especially in terms of neuron structure
and nerve impulses. A discussion of domoic acid would also be
appropriate in the context of the food chain, protozoa and/or
invertebrate animals. Finally, domoic acid is an amino acid (an
unusual one) and could be discussed in relation to protein chemistry.
Domoic
acid is an "excitotoxin." It is a neurotoxin that causes overstimulation
of a particular type of nerve cell receptor (glutamate receptors).
Upon initial exposure, people exhibit gastrointestinal distress.
Within 48 hours, these symptoms are followed by neurological symptoms
including convulsions, agitation, memory impairment and/or coma.
The toxin has proved to be fatal in some cases. The toxin is produced
by a species of plankton that serves as a food source for shellfish,
including mussels. In 1987, an outbreak of domoic acid poisoning
occurred in Canada. The cause was traced to blue mussels and over
100 cases were documented. The most severe cases occurred in those
aged 60 or over and lead to studies to correlate glutamate receptors
with the aging of the nervous system.
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