Name: _________________________________________Date: __________________

Unit 7: Human Health and Toxins in the Environment Webquest

Toxicology and the LD50 Bioassay

All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy. ~Paracelsus, 1590 A.D.

Background Information:

All substances, including the ones that we considered essential for life such as water or sugar, can be toxic if too much is consumed. Therefore, when introducing new chemicals into the human environment, it is essential that scientists determine the dose at which these chemicals can present a significant danger to human health. One method of determining a chemicals toxicity level is by performing a test known as the LD50 bioassay. This test determines the median lethal dose of the chemical, which is the dose at which 50% of the animals being tested do not survive. Because of ethical issues, LD50 tests are performed on mice or rats. Studies have shown that responses in these animals can be relatively easily extrapolated to humans, and therefore scientists can determine the median lethal dose of a chemical without harming humans.

When using an LD50 bioassay to assess a chemicals toxicity level, it is important to remember that a population includes individuals with different sensitivity levels. While the LD50 gives a good idea of what dose is lethal for the general population, there will always be individuals who will be affected at lower doses and some who may not be affected until higher doses.

Your Task:

In this activity, you are going to compare the toxicity of sodium cyanide and arsenic to determine which is more dangerous based on their LD50. In addition, we will look at the LD50 for a variety of substances to determine the lethal human dose.

Part I: Getting to Know Your Toxins

In this activity, we are going to prepare for conducting our LD50 simulation by getting to know the different toxins, and the different pathways of exposure that can affect human health. To accomplish this task, go to the following website.

https://science.education.nih.gov/supplements/nih2/Chemicals/activities/lessons_toc.html

Click on the names of the compounds in the list and use the periodic table to determine the elemental composition.

Compound

Elemental composition

Salt

NaCi

Chalk

CaCO3

Ammonia

NH3

Chlorophyll A

Quartz sand

SIO2

Caffeine

C8H10N4O5

Click on the tab Whats Wrong Here located below the Lesson title on the page. Watch the Inspectors video then watch each camera and decide what the primary route of exposure was and hypothesize a better method to prevent exposure.

Camera #

Primary route of exposure

Proposed method to prevent exposure

1

2

3

4

5

6

7

8

Part II: Determining the LD50

Before we analyze data for our two poisons, it is important to understand how to interpret an LD50 graph. Use the dose curve provided below to answer the questions.

The dose curve shown is for Drug X. Use the graph to determine the LD50 for Chemical X.

_____10______

A LD50 bioassay is done for Drug Y, which is found to have an LD50 level of 5 mg/kg. Would you consider this drug to be more or less dangerous than Drug X? Explain. Its lower because the lower the number the higher the ld50 level

PREDICTION: The following compounds are chemicals a person may be exposed to in their everyday life. Rank these substances 1-4 in order from least toxic to most toxic.

Nicotine _2____ Alcohol __1___ Sodium Chloride (Table Salt) __3___ Sucrose (Table Sugar) ___4__

Data Analysis

Now that you are familiar with the process of determining the LD50 level for a chemical, you will use a simulation to collect data for different toxins. To accomplish this task, click on the student activities tab at the top of the page. Click on Lesson 2: The Dose Makes the Poison. Use the simulation to collect data based on how dose affects the number of seeds that germinate. Then use this information to make a dose curve, which shows the Death Rate vs. Dose.

Click start to begin collecting data. A new window will pop up like the one shown to the right. This simulation walks you through a dose-response seed germination experiment. STARTING FROM THE BOTTOM, fill in the data table to create successively weaker solutions. Click Do ExperimentFor each concentration click on the test button, count the number of seeds NOT germinated and enter it into the provided table in the simulation.In the data table below, record the percent (%) of seeds not germinated. Do this procedure for each chemical listed: Fruit Punch Soda, Plant Fertilizer, Window Cleaner.

Percent (%) of Seeds NOT sprouted

Concentration

Fruit Punch Soda

Plant Fertilizer

Window Cleaner

0%

0

1

0

6.25%

1

9

1

12.5%

1

10

8

25%

4

10

9

50%

6

10

10

100%

10

10

10

On the graphs below, draw a line to show how the percent of seeds germinated changed with the concentration. Determine each chemicals LD50 concentration which is the dose at which 50% of the population did not germinate. See your salinization lab for an example of how to determine LD50 on a graph.

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

100

90

80

70

60

50

40

30

20

10

0

What is the LD50 of Fruit Punch? _________Plant Fertilizer? _________

Window Cleaner? _________

Based on your analysis, rank these chemicals in order from least dangerous to most dangerous. Explain your answer.

In the course of collecting this data, lab mice and rats have been killed. Do you consider this to be ethical research? Would you consider it more ethical to use a species that is more closely related to humans such as chimpanzees? Explain your answer.

Part III: Its All About Dose

Returning to Paracelsus remark about the toxicity of substances, anything can be dangerous to human health in excess. Substances that are more toxic simply require smaller doses to be lethal. The dose of a substance is expressed as:

From this definition, you should notice that a dose of a chemical varies from one individual to another because of differences in body mass. In this activity, you are going to calculate your lethal amount of different toxic and non-toxic substances.

Personal Lethal Dose of Common Substances

Substance

LD50 (mg/kg)

Lethal Human Amount (mg)

Lethal Human Amount (g)

Sucrose

29,700

388.235294

Ethanol

7060

92.2875

Sodium Chloride (Table Salt)

3000

392156863

Aspirin

200

2.611437908

Caffeine

192

2.509

Nicotine

50

Venom of the Austrialian Inland Taipan snake

0.025

VX Nerve Gas

0.0023

Batrachotoxin (from dart frogs)

0.0020

Polonium-210 (nuclear fission waste product)

0.00001

Determine your body mass by using the metric scale (or convert your weight in pounds to kilograms. 1 lb = 0.45 kg).

For each substance in the table, calculate your lethal dose by multiplying the LD50 level by your body mass. Convert your answers to grams and record them in the table.

Rank these substances 1-4 in order from least toxic to most toxic.

Nicotine _____ Alcohol _____ Sodium Chloride _____ Sucrose _____

How does this ranking compare to your prediction?

An 8-oz cup of coffee has approximately 148 mg of caffeine. How many cups of coffee would you need to drink to reach your lethal dose of caffeine?

Part IV: Medication Directions

When we take medications, it is important to read the instructions to make sure that you are taking the correct amount. If you dont, there can be negative impacts on your body. In this activity, we are going to investigate what happens when medication directions are misunderstood.

Read the following scenario.

According to what you read, the aunt gave Andy _______________ teaspoons every 4 hours. She gave him _________ doses of infant formula acetaminophen.

Return to the Student Activities menu. Click on Lesson 4: Individual Responses Can Be Different. Click on The Acetaminophen Mystery. Fill in the boxes with the clues you collected in the previous question.

What was the Total Dose given to Andy? ___________ mg

Look at the chart. What was the recommended total dose for infant formula? ___________ mg

Click on The Diagnosis. Watch the video or read the transcript.

What was the amount of acetaminophen found in Andys blood? ___________ mg

What amount is considered an overdose? ___________ mg per kilogram of bodyweight.

Andy weighed 12kg. Based on Andys weight, what would have been considered an overdose for him? ___________ mg

Why is infant medicine more concentrated than childrens medicine?

Part V: Pollution

Up to this point, we have been looking at compounds that for the most part are a risk because of lifestyle choices. In many cases, however, exposure to toxins is the result of pollution, which is risk imposed on the public by different sources. In this activity, we are going to look at what happens when a local community is exposed to a toxin.

Return to the Student Activities menu and click on Lesson 5: Whats The Risk? Watch the video or read the transcript of The Minamata Case Study.

What organisms showed the first signs of a problem in the village?

How were people affected?

What type of industry was causing the problem?

What were they doing to cause the problem? What specific chemical was the cause of the symptoms?

What was the route of exposure for the people and animals?

What term is used to describe how the chemical moved through the food web: bioaccumulation or biomagnification? Explain your answer.

Why do you think animals were showing symptoms before the people?

What are one pro and one con of having the factory in the small fishing village of Minamata?

How large of a fine did the company pay?

How was the site remediated?

How many years did it take for the environment and the village

Modified from James Daurays Creating LD50 Graphs for Different Substances that can be found at:

http://he.scribd.com/doc/127813617/LD50-and-Toxicity-Graph-Activity and NIHs Toxcity webquest.