Introduction to Toxicology

Author: From ‘The Science Behind Our Food”
Original Lessons
http://science.education.nih.gov/supplements/nih2/chemicals/default.htm. (Chemicals, the Environment and You)
Editor: Stephanie Nardei

Modified for PULSE by Patricia A. Wheeler and Marti Lindsey


1 hour


10 - 15 minutes


3 400 ml Beakers
1 100 ml Beaker
Food Coloring
Various Chemicals
Presentation “Introduction to Toxicology”

Students will be introduced to the science of toxicology and the relationship between a toxic reaction (response) and amount of substance (dose).  They will observe two demonstrations illustrating the concept of dose-response

Students will be able to:

  1. Define a “toxic substance.”
  2. Define the “science of toxicology.”
  3. Differentiate between natural and manmade toxic substances.
  4. Explain the dose-response principle.
  5. Calculate chemical concentrations in water.
  6. Explain toxicological principles governing the safety of a substance.
  7. Analyze toxicological risks versus benefits of a substance based on their understanding of toxicological principles.

National Science Education Standard
Content Standard A – Science as Inquiry

  • Identify questions and concepts that guide scientific investigations
  • Formulate and revise scientific explanations and models using logic and evidence
  • Communicate and defend a scientific argument

Content Standard F- Science in Personal and Social Perspectives
Personal and community health

Arizona Science Education Standards:
Concept 1: Observations, Questions, and Hypotheses

  • PO 2. Develop questions from observations that transition into testable hypotheses.
  • PO 3. Formulate a testable hypothesis.

Concept 2: Scientific Testing (Investigating and Modeling)

  • PO 1. Demonstrate safe and ethical procedures (e.g., use and care of technology, materials, organisms) and behavior in all science inquiry.
  • PO 5. Record observations, notes, sketches, questions, and ideas using tools such as journals, charts, graphs, and computers.

Concept 3: Analysis, Conclusions, and Refinements

  • PO 2. Evaluate whether investigational data support or do not support the proposed hypothesis.

Concept 4: Communication

  • PO 2. Produce graphs that communicate data. (See MHS-S2C1-02)
  • PO 3. Communicate results clearly and logically.
  • PO 4. Support conclusions with logical scientific arguments.

Teacher Background
Hardly a week goes by without hearing that a chemical may potentially threaten our health—pesticides in the food we eat, pollutants in the air we breathe, chemicals in the water we drink, toxic dump sites near our homes. Chemicals make up everything around us. Which chemicals are really dangerous? How much does it take to cause harm? What are the effects of a particular chemical? Cancer? Nervous system damage? Birth defects? Finding scientifically sound answers to these very important questions is what toxicologists do, using the most modern molecular, genetic, and analytical techniques available. Toxicology combines the elements of many scientific disciplines to help us understand the harmful effects of chemicals on living organisms. [TAKEN FROM WIKIPEDIA.]

Related and Resource Websites
Environmental Health Resources section on Basic Toxicology of PULSE. http://pulse.pharmacy.arizona.edu/resources/toxicology/teachers.htm
See also the background section for the ‘The Science Behind Our Food” unit http://apps.caes.uga.edu/sbof/main/lessonPlan/IntroToToxicology.pdf
Dose-Response Relationships In Toxicology http://pmep.cce.cornell.edu/profiles/extoxnet/TIB/dose-response.html, an in-depth overview of dose-response
Green Facts Glossary http://www.greenfacts.org/glossary/def/dose-response-relationship-dose-response.htm, an overview of dose-response for certain chemicals and links to other toxicology terms
Health and the Environment: Food, Farming, & Pesticides http://www.nrdc.org/health/pesticides/default.asp
Questions People Ask About Animals in Research http://www.the-aps.org/pa/animals/index.htm
Write a hypothesis http://www.k12science.org/curriculum/dipproj2/en/lesson1.shtml


Day One

  1. Pose questions such as: “What is a chemical? What are some examples of chemicals?  Where would I find chemicals in nature?  When is a chemical toxic?”  Have students respond to these questions in a science journal.  As a class, discuss their responses by listing them on the board or butcher paper and individually on Post-it® notes.  Have students determine a system that classifies substances as synthetic, natural, toxic, nontoxic.  Allow 10 – 15 minutes for this introduction.
  1. Now play a game similar to “Twenty Questions”, using the Post-it® notes generated before with names of one chemical on each.  Stick a Post-it® on individual student’s backs.  Keep the list of the possible chemicals visible to the students as a guide for their thinking.  The students would then have to go around the room asking other students questions about their chemical to gain clues.  The questions should be “yes” or “no” questions (similar to the game “Twenty Questions”.  Suggested questions for clues might be:
        • “Is it found in nature?”
        • “Is it synthetic?”
        • “Is it toxic?”
        • “Is it reactive with…?” 
  1. Introduce the science of toxicology and the concept of dose-response, using the presentation provided. Have students take notes in their science notebooks as you present the information on the presentation provided. Feel free to add to the presentation as you desire. Allow about 10 – 15 minutes. 

Details for Presentation:

  • Living organisms, including humans, are exposed to chemicals through ingestion, inhalation or absorption.  A chemical is toxic when it interrupts the natural chemical processes of cells.
  • All chemicals, natural and synthetic, have the capacity to be toxic.  The father of modern toxicology, Paracelsus, stated: “The dose makes the poison.”  The science of toxicology is based on the principle there is a relationship between an organism’s toxic reaction (response) and the amount (the dose) ingested, inhaled or absorbed.  The job of a toxicologist is to research the “safe dose” of a given chemical.  For example, the amount of Ibuprofen a person can be exposed to before it becomes harmful.   
  • A chemical’s effect (beneficial or harmful) depends on the dose (amount that enters the body), resulting concentration (amount of chemical relative to body size/volume), the length of exposure, and the route of exposure (ingestion, inhalation or absorption). 
  • Draw a dose-response graph on the board or overhead.  Be sure to explain to students these can be either qualitative or quantitative.  Explain the “S-shape”. 
    • The first point along the graph where a response above zero is reached is referred to as the threshold-dose. 
    • Desired effects of medical or recreational drugs are usually slightly greater than the threshold dose. 
    • As the dose increases, side effects appear and grow stronger as the dose increases. 
    • The stronger the substance the steeper the curve.

Response curve


  1. Now that the students have some background on the concept of dose-response, they are ready for a demonstration that illustrates the phenomenon.  Food coloring in water is an effective way to create a visualization of dose-response.  Fill three 400 ml beakers approximately ¾ full and put them in a line where all the students can see them.  Place a white paper behind the beakers to help with the visualization.  Tell the students the beakers serve as a model of the human body because we are about ¾ water.  Add only one drop of food coloring to one beaker, five to the second beaker, and 15 or more to the third beaker.  Stir with a stirring rod and discuss how the change in color is a response to dose.  Correlate the outcome this demonstration to a common chemical people consume, such as caffeine, to further illustrate how a chemical distributes throughout the human body.  You could also have the students make qualitative graphs in their notebooks of the dose-response they observed and/or what they know about their personal dose-response to caffeine.  Allow 5 – 10 minutes for this demonstration.
  2. Follow the “dose demonstration” with a “size demonstration”.  Fill a 400 ml beaker and a 100 ml beaker ¾ with water.  Tell students you are going to add two drops to each beaker.  Ask students to hypothesize whether or not there will be a difference in color as a response to dose.  Ask students the differing amounts of water in each container model (adult and child).  Conduct the demonstration, being sure to discuss the importance of size or weight of the organism/human.  Students should infer children are more severely affected than adults by the same dose.  Caffeine is an example.  You can have students qualitatively graph the difference, but it may require discussion on how this would be accomplished (labeling two different lines on the same graph) since the variable of size has been added.  Allow 5 – 10 minutes for this demonstration.

If applicable. 

Embedded Assessment
Assess students’ ability to address the toxicity of chemicals and to ask questions related to the presentation.





PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

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