1. Toxicology What is toxicology? The study of the effects of poisons.
Poisonous substances are produced by plants, animals, or bacteria.
Phytotoxins
Zootoxins
Bacteriotoxins
Toxicant - the specific poisonous chemical.
Xenobiotic - man-made substance and/or produced by but not normally found in the body.

2. Introduction
Toxicology is arguably the oldest scientific discipline, as the earliest humans had to recognize which plants were safe to eat.
Most exposure of humans to chemicals is via naturally occurring compounds consumed from food plants.
Humans are exposed to chemicals both inadvertently and deliberately.

3. Did You Know ? 92% of all poisonings happen at home.
The household products implicated in most poisonings are: cleaning solutions, fuels, medicines, and other materials such as glue and cosmetics.
Certain animals secrete a xenobiotic poison called venom, usually injected with a bite or a sting, and others animals harbor infectious bacteria.
Some household plants are poisonous to humans and animals.

4. Swiss physician Paracelsus (1493-1541) credited with being
“the father of modern toxicology.”
“All substances are poisons: there is none which is not a poison. The right dose differentiates a poison from a remedy.”

5. Dose/Response Relationships
“Everything is poisonous, yet
nothing is poisonous”
Most substances in too great amounts
can be dangerous, but in small
amounts are harmless.
Ex: table salt, vitamins

6. Dose response curves illustrate the
relationship between concentration
and toxicity.
Trace concentrations may be very
useful, then a certain concentration
is reached where the substance
becomes toxic.

8. LD-50,ED-50,and TD-50
Individuals differ in their response
to an environmental toxin, so a way
to measure the overall toxicity is
needed.
LD-50 represents the concentration
that is lethal to 50% of the
population exposed to the toxin.

9. The lower the LD-50, the more toxic the substance.
Some LD-50’s:
Sodium Chloride mg/kg
2,4-D (weed killer) mg/kg
DDT mg/kg
Caffeine mg/kg
Nicotine mg/kg
Strychnine sulfate (rat poison) mg/kg
Botulinum toxin mg/kg

10. In toxicology testing, the most
common route of exposure is tested,
and is the basis for setting rules for
exposure to the toxins
Ex: inhalation, skin and eye exposure,
ingestion.

11. Acute vs. Chronic Toxicity Tests
Can broadly classify toxicity tests based on length of exposure
Acute Toxicity test
Drop dead testing
Time = 2 days (invertebrates) to 4 d. (fish and mice)
LD50
LC50
TLm (median tolerance dose)
EC50 (effective concentration)
Lose equilibrium, sit on bottom  “ecologically” dead
Not very ecologically relevant but quick, relatively cheap (but still ~$700-1,200 per test)

12. Acute vs chronic toxicity testing (con’t)
Growth, reproduction
More ecologically relevant data but takes longer, more expensive
Shows effect at much lower dose
Test requires much more “baby-sitting”

13. Acute Testing - theory
Population of organisms has normally distributed resistance to toxicants  acute toxicity test designed to identify mean response
Regulations allow 5% of species to be impacted
Most tests only use 2-3 species (up to 6)  not really enough to protect 95% of all species!

14. Acute Toxicity Test Organisms
Use of test species based on
Lab hardiness
Common
Known life cycle
Cheap
Short-lived

15. Normal distribution of resistance/sensitivity
Mean response
Frequency
5% allowable impact
Resistance

16. Chronic toxicity testing
Sublethal
Time = 7d. to 18 months
Endpoints are
growth
Reproduction
brood size (Ceriodaphnia dubia can have 2-3 broods in seven days)
Reproductive success
Teratogenicity studies (birth defects)

17. The ED-50 represents the amount
that is effective in 50% of the
population.
Ex: concentration of aspirin needed
to be effective in 50% of the
population

18. Toxic responses can be things such as reduced enzyme activity, lowered
The TD-50 is defined as the dose
that is toxic to 50% of the population.
Toxic responses can be things such
as reduced enzyme activity, lowered
reproduction, or onset of specific
symptoms (known to be associated
with the toxin. )

20. All toxicity tests try to determine level of toxicant which will or will not cause an effect
NOEC – No Observable Effect Concentration
Highest conc not signficantly different from control
LOEC – Lowest Observable Effect Concentration
Lowest test concentration that is significantly different from control
MATC – Maximum Allowable Toxicant Concentration
Geometric mean of NOEC and LOEC
Often called the “chronic value”

21. MATC
MATC = √NOEC + LOEC

22. Sources of Pollution Point Source vs. Non-Point Sources:
-Point source polluters are single
sources of pollution, such as pipes,
smokestacks, or spills
Non-Point sources (also Area Sources)
are spread over the land, and do not
have a single outflow of pollution.
Ex: runoff from polluted land areas,
automobile exhaust

23. Categories of Pollutants
Infectious agents: diseases, spread
through interactions of environment and
man.
EX: Salmonella, a food poisoning bacteria spread
via water or food.
Giardiasis, a protozoan infection spread via water,
or person-to-person contact.

24. 2) Toxic Heavy Metals: -metals with high atomic weight
-Pose health hazards to humans and ecosystems
-mercury,lead,cadmium,arsenic,gold
chromium, vanadium, thallium
-most of these metals are by-products
of a modern industrialized society

25. Body Burden of Heavy Metals
-Body Burden is defined as the amount
of heavy metals contained within an
organisms tissue.
-heavy metals are accumulated over
an organisms lifetime, and biomagnify
in the food chain.
Human averages: 13 mg mercury, 150mg lead
30mg cadmium.

26. Biomagnification is the accumulation of
a substance up the food chain by transfer
of residues of the substance in smaller
organisms that are food for larger
organisms in the chain.
Biomagnification can result in higher
concentrations of the substance than
would be expected if water were the only
exposure mechanism.

28. Let's look at our food chain to see how biomagnification works
Let's look at our food chain to see how biomagnification works. Let's say for example that each piece of plant material has one microscopic drop of methylmercury. One insect eats 25 pieces of plant material, that would mean that each insect would have __________ microscopic drops of methylmercury in its body.
One small fish needs 10 insects to live, if each insect has 25 microscopic drops
of methylmercury in its body, then one fish would have __________
microscopic drops of methylmercury.
One big fish eats 5 small fish to live. Each small fish has __________
microscopic drops of methylmercury in its body, therefore, one big fish would
collect a total of __________ microscopic drops of methylmercury in its body.
What about you and me? Lets say we eat 1 big fish a day for 3 days. If each
big fish has __________ drops of methylmercury in its body then we would
collect a total of __________ drops of methylmercury in our body over the 3
days.

29. 3) Organic Compounds:
-produced naturally, or synthetically
by humans.
-compounds containing carbon as an
element.
-many synthetic organic compounds
are used in industrial processes, food
additives, pesticides, and drugs.

30. -Some synthetic organics are called “persistent organic pollutants” or
POP’s
POP’s have several characteristics that
make them particularly bad for the
environment.
They are carbon-based, and often contain
chlorine,which is highly reactive (and toxic) in the
environment.

31. 2) They are synthetic
3) They are long-lived in the environment
4) They are very toxic to a variety of organisms
5) They are soluble in fat, so they accumulate
within the fatty tissue of organisms
6) They occur in forms which allow them to be
transported in a large variety of ways (wind,
water, sediment)

32. Some Organic Pollutants
-Aldrin (1949) :Insecticide
-Dieldrin (1948) :Insecticide
-DDT (1942): Insecticide
-PCB’s (1929) : Electrical Insulators
-Dioxins (1920’s) :by-product of
herbicide production

33. 4)Particulate pollution
-small particles of dust, released
into the atmosphere by many
human activities.
Ex: construction, exhaust
-Particulates are also released
Into the atmosphere by natural
processes as well.
Ex: volcanoes, wind erosion

34. Particulates can cause many
respiratory problems, from asthma
to cancer.
Particulate pollution has been
declining in the U.S., mostly due
to pollution limits on coal fired
power plants.