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Introduction to Toxicology. Larry Johnson Partnership for Environmental Education and Rural health (PEER) Texas A & M University. Toxicology. What is toxicology ? The study of the effects of poisons. Poisonous substances are produced by plants, animals, or bacteria. Phytotoxins

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Introduction to Toxicology

Larry Johnson

Partnership for Environmental Educationand Rural health (PEER)

Texas A & M University


What is toxicology? The study of the effects of poisons.

Poisonous substances are produced by plants, animals, or bacteria.




Toxicant - the specific poisonous chemical.

Xenobiotic - man-made substance and/or produced by but not normally found in the body.


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.

you know
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 xenobioticpoison 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.


2700 B.C. - Chinese journals: plant and

fish poisons

1900-1200 B.C. - Egyptian documents that had directions for collection, preparation, and administration of more than 800 medicinal and poisonous recipes.

800 B.C. - India - Hindu medicine includes

notes on poisons and antidotes.

50-100 A.D. - Greek physicians classified over

600 plant, animal, and mineral poisons.


50- 400 A.D. - Romans used poisons for

executions and assassinations.

The philosopher, Socrates, was executed using hemlock for teaching radical

ideas to youths.

Avicenna (A.D. 980-1036) Islamic authority on poisons and antidotes.

1200 A.D. - Spanish rabbi Maimonides writes

first-aid book for poisonings,

Poisons and Their Antidotes


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.”


The Dose Makes the Poison

An apparently nontoxic chemical can be toxic at high doses. (Too much of a good thing can be bad).

Highly toxic chemicals can be life saving when given in appropriate doses. (Poisons are not harmful at a sufficiently low dose).

lethal doses

Approximate Lethal Doses of Common Chemicals(Calculated for a 160 lb. human from data on rats)

Chemical Lethal Dose

Sugar (sucrose) 3 quarts

Alcohol (ethyl alcohol) 3 quarts

Salt (sodium chloride) 1 quart

Herbicide (2, 4-D) one half cup

Arsenic (arsenic acid) 1-2 teaspoons

Nicotine one half teaspoon

Food poison (botulism) microscopic

Lethal Doses

Source: Marczewski, A.E., and Kamrin, M. Toxicology for the citizen, Retrieved August 17, 2000 from the World Wide Web:


HistoryItalian physicianRamazzini (1713) published“De Morbis Artificum” (Diseases of Workers)

describing "asthma" in bakers, miners, farmers, gilders, tinsmiths, glass-workers, tanners, millers, grain-sifters, stonecutters, ragmen, runners, riders, porters, and professors. Ramazzini outlined health hazards of the dusts, fumes, or gases that such workers inhaled. The bakers and horse riders described by Ramazzini would today probably be diagnosed as suffering from allergen-induced asthma. The lung diseases suffered by most of the other workers would now be classified as "pneumoconiosis," a group of dust-related chronic diseases.



Spanish physician Orfila (1815) established toxicology as

a distinct scientific discipline.



20th Century

Paul Ehrlich –developed staining procedures to observe cell and tissues and pioneered the understanding of how toxicants influence living organisms.



20th Century

Rachel Carson - alarmed public about dangers of pesticides in the environment.

occupational and environmental toxicology
Occupational and Environmental Toxicology

Environmental toxicants (air

and water pollutants) are

substances harmful to the

environment and to humans.

Environmental toxicants are both natural and

man made.

Public perception that man-made ones are more serious than natural ones - Reality: both

are serious.

5,000,000 yearly deaths worldwide due

to bacterial toxicants (Salmonella, E. coli)

occupational and environmental toxicology15
Occupational and Environmental Toxicology

Many examples of diseases associated with specific occupations were recorded in antiquity, but they were not considered serious because the health of the workers was not a societal concern.

- Paracelsus - Miner’s Disease (1533)

- Hill & Pott (1761 &1775)

- Radium dial painters, “aniline dye” workers (1900)

- Shoe salesmen (1950s)

- Industrial chemical workers (1940-present)

occupational and environmental toxicology16
Occupational and Environmental Toxicology

- Paracelsus - Miner’s Disease (1533) came from inhaling metal vapors, foundation for the field of chemotherapy.

- Hill (1761) linked tobacco (snuff) to cancer.

- Pott (1775) linked scrotal cancer

and soot (benzo(a)pyrene) in


occupational and environmental toxicology17
Occupational and Environmental Toxicology
  • Radium dial painters,

“aniline dye” workers (1900)

painters licked their brushes

to pull it to a point.

  • Shoe salesmen (1950s)

shoe-fitting fluoroscopes:

radiation of feet in shoes of children and repeated

exposure for salesmen.


Occupational and Environmental Toxicology

  • Industrial chemical workers


Workers typically are exposed to

a greater number of carcinogens

for longer periods of time.

Occupations with high risk of cancer :

Health care workers, pharmaceutical and laboratory workers, refinery workers, rubber workers, furniture makers, and pesticide workers.

modern toxicology
Modern Toxicology

1961 - Society of Toxicology

1970s - EPA, FDA, and NIOSH


Toxicology Terms

Toxicity - The adverse effects

that a chemical

may produce.

Dose - The amount of a

chemical that gains

access to the body.


Toxicology Terms

Exposure–Contact providing

opportunity of

obtaining a

poisonous dose.

Hazard – The likelihood that the

toxicity will be



Threshold Effects for Dose


Is there such a thing as a ‘safe’ dose??

Agent A

Agent B


“NOEL”(No Observable Effect Level)


fundamental rules of toxicology
Fundamental Rules of Toxicology

Exposure must first occur for the chemical to present a risk.

The magnitude of risk is proportional to both the potency of the chemical and the extent of exposure.

“The dose makes the poison” (amount of chemical at the target site determines toxicity).

exposure concepts
Exposure Concepts

Different toxic responses may arise from different:

  • Routes of exposure.
  • Frequencies of exposure.
  • Duration of exposure (acute vs. chronic).

Routes of Environmental Exposure

Ingestion (water and food)

Absorption (through skin)

Injection (bite, puncture, or cut)

Inhalation (air)

chemicals chemicals everywhere
Chemicals, Chemicals Everywhere

Everything in the environment is made of chemicals. Both naturally occurring and synthetic substances are chemical in nature.

People are exposed to chemicals by eating or swallowing them,breathing them, or absorbing them through the skin or mucosa.

People can protect themselves by blocking these routes of exposure.

duration frequency of exposure
Duration & Frequency of Exposure

Duration and frequency are also important components of exposure and contribute to dose.

Acute exposure - less than 24 hours; usually entails a single exposure

Repeated exposures are classified as:

  • Subacute - repeated for up to 30 days
  • Subchronic - repeated for 30-90 days
  • Chronic -repeated for over 90 days
exposure concepts28
Exposure Concepts

Exposure to chemicals may come from many sources:

  • Environmental
  • Occupational
  • Therapeutic
  • Dietary
  • Accidental
  • Deliberate
individual responses can be different
Individual Responses Can Be Different

The variety of responses among organisms that get the same dose of chemical is due to individual susceptibility.

Dose and individual susceptibility play roles in all situations involving chemicals, including those making medicine and caffeine.

introduction to xenobiotics
Introduction to Xenobiotics

*Recall: Foreign chemicals are synthesized within the body are termed xenobiotics (Gr.Xenos meaning “strange”)*

  • Xenobiotics may be naturally occurring chemicals produced by plants, microorganisms, or animals(including humans).
  • Xenobiotics may also be synthetic chemicals produced by humans.

Poisons are xenobiotics, but not all xenobiotics are poisonous.


How Does the Body Prevent the Actions of Xenobiotics ?

1) Redistribution

2) Excretion – (primarily water soluble compounds) - kidney and liver

3)Metabolism – the major mechanism for terminating xenobiotic activity, and is frequently the single most important determinant of the duration and intensity of toxic responses to a xenobiotic. - LIVER, kidney, lung, GI, and others

Note: 1) and 2) are highly dependent upon 3)


Xenobiotics at Work





General Scheme of Xenobiotic Metabolism

Lipophilic Hydrophilic(parent compound) (metabolite)


  • Decrease biological activity2) Increase excretability

Phase I Phase II(oxidative) (synthetic)



sizeionizationwater solubility

Increase excretability




how xenobiotics cause toxicity
How Xenobiotics Cause Toxicity

Some xenobiotics cause toxicity by disrupting normal cell functions:

  • Bind and damage proteins (structural, enzymes)
  • Bind and damage DNA (mutations)
  • Bind and damage lipids
  • React in the cell with oxygen to form

“free radicals” which damage lipid, protein,

and DNA

types of toxic effects
Types of Toxic Effects

Death - arsenic, cyanide

Organ Damage - ozone, lead

Mutagenesis - UV light

Carcinogenesis - benzene, asbestos

Teratogenesis - thalidomide

target organ toxicity
Target Organ Toxicity

Central Nervous System – lead

Immune System - isocyanates

Liver - ethanol, acetaminophen

Respiratory Tract - tobacco smoke, asbestos, ozone

Eye - UV light (sunlight)

Kidney - metals

Skin - UV light, gold, nickel

Reproductive System –


mechanistic toxicology
Mechanistic Toxicology

How do chemicals cause their toxic effects?

what do toxicologists do
What Do Toxicologists Do?

Most toxicologists work to develop a mechanistic understanding of how chemicals affect living systems:

  • Develop safer chemical products
  • Develop safer drugs
  • Determine risks for chemical exposures
  • Develop treatments for chemical


  • Teach ( e.g. other toxicologists,

graduate students, and youth)

what do toxicologists do40
What Do Toxicologists Do?

Mechanistic toxicologists study how a chemical

causes toxic effects by investigating its absorption,

distribution, and excretion. They often work in

academic settings or private industries and develop


Descriptive toxicologists evaluate the toxicity of drugs, foods, and other products. They often perform experiments in a pharmaceutical or academic setting.

Clinical toxicologists usually are physicians or

veterinarians interested in the prevention, diagnosis,

and treatment of poisoning cases. They have specialized training in emergency medicine and poison management.

what do toxicologists do41
What Do Toxicologists Do?

Forensic toxicologists study the application of toxicology to the law. They uses chemical analysis to determine the cause and circumstances of death in a postmortem investigation.

Environmental toxicologists study the

effects of pollutants on organisms, populations, ecosystems, and the biosphere.

Regulatory toxicologists use scientific data to decide how to protect humans and animals from excessive risk. Government bureaus such as the FDA and EPA employ this type of toxicologist.


regulatory toxicology
Regulatory Toxicology

Use data from descriptive and mechanistic toxicology to perform risk assessments.

Concerned with meeting requirements of

regulatory agencies.

Industry/government interactions.


Toxicologyis the science that studies the harmful effects of overexposure to drugs, environmental contaminants, and naturally occurring substances found in food, water, air, and soil.

  • Main objectives are to establish safe doses and determine mechanisms of biologic action of chemical substances.

A career in toxicology involves evaluating the harmful effects and mechanisms of action of chemicals in people, other animals, and all other living things in the environment.

  • This work may be carried out in government, private industry and consulting firms, or universities and other research settings.

Toxicologists routinely use many sophisticated tools to determine how chemicals are harmful.

(e.g.) computer simulations, computer chips, molecular biology, cultured cells, and genetically-engineered laboratory animals .

what is the risk
What Is the Risk?

People can make some choices about chemical exposure; however, some exposure is controlled at a level other than an individual one. Collective groups of people, such as communities and governments, seek to control chemical exposure on a community or global level.


Animals in Research

“Virtually every medical achievement of the last century has depended directly or indirectly on research in animals.”

U.S. Public Health Service


Toxicology is a fascinating science that

makes biology and chemistry interesting

and relevant.

Understanding HOW (i.e. mechanism)

something produces a toxic effect can lead to new ways of preventing or treating chemically-related diseases. Animal use in research is essential for medical progress.

Many diseases are the result of an interaction between our genetics (individual variability) and chemicals in our environment.

Toxicology provides an interesting and exciting way to apply science to important problems of social, environmental, and public health significance.



The science of toxicology provides a fantastic pedagogical opportunity to do true ‘interdisciplinary’ teaching, to make relevant many of the exciting biological discoveries that occur everyday.

Whether it is exploring the wonders of the biology of DNA and heredity, or the more mundane aspects of acid-base chemistry, or the ethical,legal, and social implications of genetic testing for common diseases such as cancer or Alzheimer's -



or the global ecological implications of species extinction;

or social risks and benefits of genetically modified foods -

or diagnosing the cause of the Mad Hatter’s strange behavior in Lewis Carol’s ‘Alice in Wonderland’ (mercury poisoning)-

or the fall of the Roman Empire (lead poisoning),

toxicology and environmental health

science provide an interesting

“hook” to make the subject matter

– what ever it may be –

interesting and relevant to your


your role
Your Role

NIEHS, SOT, and PEER feels the responsibility to help educate the next generation of citizens to better understand the world around them, and especially to understand how chemicals – man-made or natural – present both risks and benefits to society.

Of course, everything we eat, drink, breathe, touch, or use is made of chemicals, so the task is LARGE!

We hope to make the science of toxicology ‘less obscure’ to the public.

your role51
Your Role

Risk is a part of everyday life, and one’s decisions as to the ‘acceptability’ of a particular risk is influenced by knowledge and experience.

While we can’t do much about the ‘experience part’, we can try to increase the public’s knowledge about the risks and benefits of all things chemical.

You play a critical role in this effort, and we can’t do it without YOU.


National Institute of Environmental Health


Texas Rural Systemic Initiative

The Center for Environmental and Rural Health

Partnership for Environmental Education and Rural Health

College of Education, Texas A&M University

College of Veterinary Medicine at Texas A&M University