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TOXICOLOGY

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Why study Toxic Risk? Make decisions about the safety of your food. ... More on your Research. Do your answers lead to new questions? You should: ... – PowerPoint PPT presentation

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Title: TOXICOLOGY


1
TOXICOLOGY
  • ENVIRONMENTAL RESEARCH

2
Why study Toxic Risk?
  • Make decisions about the safety of your food.
  • Help you make informed public policy decisions.
  • Be able to separate real risks from imaginary
    ones.
  • Learn some basic research techniques.

3
Questions for your own Research.
  • What does Toxic mean?
  • What is Safe food and water?
  • How can you improve or change an experiment to
    answer new questions?

4
More on your Research
  • Do your answers lead to new questions?
  • You should
  • Discuss your ideas with classmates.
  • Exchange feed back.
  • Make constructive criticisms.
  • Collaborate on joint projects.

5
The Dose Makes the Poison.
  • Definition Toxicity How poisonous a substance
    is to organisms.
  • All substances are poison there is none which
    is not a poison. The right dose differentiates a
    poison from a remedy.
  • Philippus Paracelsus (early 1500s)

6
Any Chemical Can Be Toxic
  • Which is more poisonous caffeine or
    trichloroethylene (dry cleaning fluid)?
  • Caffeine 50 times normal daily dose can be
    fatal
  • Vitamins A and D can also kill you in high enough
    doses.
  • To learn about trichloroethylene go to
    www.sciLINKS.org type in codeATR02

7
Are Natural Chemicals Safer?
  • That depends.
  • Lots of organisms make toxins for defense or to
    help get food.
  • Lots of synthetic chemicals are safe.
  • Anything can be a poisonous in high enough doses.

8
How much is too much?
  • A chemicals short-term toxicity is measured with
    a dose/response study.
  • Definitions
  • Dose The total amount of a chemical that an
    individual eats, breathes, or absorbs through the
    skin.
  • Exposure - Coming in contact with a chemical
    through food, water, air, or other sources.

9
  • Response- changes in organisms caused by
    exposure to a toxin.
  • Usually the higher the exposure the greater the
    response.
  • Dose/Response experiments are called bioassays.
  • Assay means test.

10
Dose/Response Bioassays
  • Bioassays use organisms to measure a chemicals
    toxicity.
  • Example
  • Lab rats each get just one dose of a chemical
  • Doses range from very low to very high.
  • At the end of 14 days any deaths or other health
    responses are recorded.

11
Dose/Response Bioassays
  • There should also be a control group.
  • In a well designed experiment, some but not all
    rats should survive.
  • You then get a number called LD50
  • The LD50 is the Lethal dose for 50 of the
    treated organisms.
  • i.e. Half the rats that got the LD50 dose were
    dead after 14 days.
  • LD50 is in milligrams of the chemical per
    kilogram of body weight (mg/kg).

12
Dose/Response Bioassays
  • Remember usually some individuals will die at
    lower doses and some will be able to take very
    high doses with little or no harm.
  • For bioassays
  • www.sciLINKS.org Code ATR02

13
A Typical Dose/Response Curve
14
Comparing Chemical Toxicities
  • 14 day bioassay does not consider long term
    effects.
  • LD50 doses can vary a lot from one species to
    another.
  • WHY?
  • Animals vary in metabolism.
  • Differences in absorption, storage and excretion
    of chemicals.

15
Comparing Chemical Toxicities
  • Animal Experiments
  • Go to www.sciLINKS.org Code ATR03
  • Sometimes toxicology studies are now done on
    single cells or blood samples.
  • These have limits

16
Lethal Doses of some Common Compounds
17
Toxicity Categories Used for Human Poisons
18
Long-Term vs. Short-Term Toxicity
  • Definitions
  • Acute effects are caused by exposure to a single
    dose.
  • Chronic effects develop slowly due to long term
    exposure.

19
Long-Term vs. Short-Term Toxicity
  • LD50 bioassays concern only acute effects.
  • Our body can get rid of many chemicals so long
    term exposure is no problem.
  • Other chemicals can build up slowly even with low
    doses and cause health problems.

20
Long-Term vs. Short-Term Toxicity
  • Some things can cause one kind of acute problem
    with one time, high doses.
  • Other problems with long-term chronic lower
    doses.
  • Example

21
Testing Chronic Toxicity
  • Feed lab animals relatively low doses each day
    for long periods of time.
  • Look for negative effects not death rates
    (examples)
  • Lower growth rates
  • Behavior changes
  • Lower immunity to disease
  • Reproduction problems
  • Shorter life span

22
Why?
  • Acute and Chronic Bioassays are the basis for
    gov. regulations about food, water, drugs,
    cosmetics, etc.
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