Lesson 6. Bioaccumulation and Biomagnification

Estimated Time: 1 period

Objectives

  1. Students will describe bioaccumulation and biomagnification.
  2. Students will explain the impact that bioaccumulation can have on consumers
  3. Students will model how levels of contaminants change throughout a food web.

EQ: What happens to pollution when it enters food chains?

Bridge

  1. Students are chosen to be part of a Lake Ontario food chain. The organisms can be changed to fit any aquatic system you choose. There are 5 labeled cards, one for each student: phytoplankton (6), mysid(5), smelt(4), lake trout (2) and herring gull (1). It may be helpful to have sketches or pictures of the Organisms on the card. You can have one student represent all of the above organisms or one student for each of them, making sure they kind of group together for the web purposes. It is important to include the numbers as they will use this to premise designing their experiment. You can add create costumes for the participants to heighten interest.
  2. You choose another student in the class, give him/her string and ask the student to physically create a food chain with the organisms (students). This is a good time to review basic ecology with the class. Ask the student to describe the direction of energy flow, what creature is the primary consumer, etc. Correct any misconceptions before moving on.

Mini- Lesson

Graphically illustrate that the nearby lake (in this case, Lake Ontario) has been contaminated with a toxin. This can be done in many ways. One way is to present a large glass beaker or tank full of water and pour in an “unknown toxin”. This can be a bottle labeled poison that filled with a mix of food colorings and water. Add some scary music and screams to heighten the fun. The toxin should represent a real pollutant found in the water source. In the case of Lake Ontario, there are many to choose from (Mercury, DDT, PCB, sewage, carbon tetrachloride, lead, etc), or maybe you want to include a bunch of them and have different colors represent them. Ask students to write down their observations. Once you have placed in the pollutants, announce that you are now going to place “life” into the ecosystem, and drop come cotton balls into the water (phytoplankton or a plant). Pull out the cotton balls after a minute or so and show the class. Write down more observations.

Pose the following questions to the students: What is the relationship between toxin level and trophic level? Predict/hypothesize.

Give the expectations for the work time: Using the provided materials, design an experiment in which you can model how pollutants that have entered our water cycle effect the life living there.

Work Period

Experimental design…. Design and perform your experiment to create a model for biomagnifications.

Materials: Organism tags (several of the producer, and reduce the numbers up to the tertiary consumer only being 1), tokens/bingo chips (represents a unit of toxin), cups (represents the stomach of the organism)

Summary

  1. Introduce the concepts bioaccumulation and biomagnifications. Through questioning steer the students into generating 2 solid definitions that are written in their note books.
  1. Bioaccumulation: increase in concentration of a pollutant from the environment to the first organism in a food chain.
  2. Biomagnification: increase in concentration of a pollutant from one link in a food chain to another.
  1. Answer the EQ.

Closing

Ask students to describe how biomagnifications will be represented in their debate.

Independent Practice

Case Study on Bioaccumulation

Optional Activity for next day: Since each of the lessons was based on having 1 period once a day with students and the reality is that we SHOULD have lab time built into our schedules, here is an optional lab, pending time, that you can do with the students. The bioassay is very worthwhile and a true implementation of environmental concerns, something many teachers seem to overlook going into this curriculum (mostly based on running out of time at the end of the year)

This can be done 2 ways:

There is a great lab activity through wards to show this with….. WARDS LC-50: How much is too much? If you have the funds and the money. Make sure you get the cultures ordered ahead of time.

36 V 6080 / WARD’S LC50: How Much is Too Much? Lab Activity
Special promotions and discounts do not apply to this item. / $94.99

A second option is using a salt water assay. I prefer the salt water assay only because it is a more inquiry approach and much cheaper, but the LC50 is so much cooler to look at. You could actually do the LC50 as a demo while the students do the salt water assay.

SPED and ELL Modifications:

  1. Allow lower level students to work with a partner and talk through their responses to gain a better understanding
  2. Show a visual model of bioaccumulation and magnification (some are listed below in the internet activities) before asking the students who are lower level to create their own
  3. Use iPads to create models using Power Strip App orEducreation App:
  4. Ask guiding questions as they work through their experimental design
  5. Pre-record the case study using the Voice Memo feature on the iPads

Apps and Internet Activities:

  1. These are some good visual examples of biomagnification and bioaccumulation:

a)

b)

c)

  1. Helpful short videos to demonstrate the idea of bioaccumulation and biomagnification:

**(The students could easily create some of these same videos using the Video Camera on the iPad and the Educreation App or Drawing Box App)**

Optional Lesson Plan, Bioassay of Unknown

Duration: 1 45 minute period

Objectives

  1. Conduct an experiment using Daphnia magna to test the toxicity of an unknown compound and to understand the dose-response relationship.
  2. Perform serial dilutions to become familiar with the concepts of chemical concentrations and dilutions, and to prepare solutions they can use with dose-response experiments.
  3. Work collaboratively to implement experiments, interpret results, and analyze data and conclusions.
  4. Write a laboratory report which includes: problem and purpose, hypothesis, experimental methods, results, analysis, and conclusion.
  5. Students will provide constructive criticism on fellow students’ data, analysis, interpretation, and conclusions.

EQ: What is the LD50 of the unknown CSX chemical?

Notes to teacher:

  1. Purchase Daphnia magna. Approximately 105 individual Daphnia are required for a class for each student group. Although you may use mixed age populations for bioassays, it is better to use only young individuals in order to minimize biological differences among the test organisms. Because the appearance of resting eggs indicates a poor culture environment, do not use Daphnia with resting eggs. To obtain a good supply of young Daphnia, begin 24 hours in advance by removing females bearing embryos from the stock culture and placing them in 400-mL beakers containing 300 mL of spring or stream water and the appropriate amount of food. Five beakers, each containing 10 adults, usually will supply enough young individuals for one toxicity test. When you are ready to begin your bioassay, choose young (small) Daphnia from these cultures. Prior to conducting the bioassay, check the Daphnia to ensure the culture is healthy.
  2. Prepare another 0.2M NaCl solution or “concentrated salt solution” from which students will make their serial dilutions. Measure 12.0 grams of table salt and add enough distilled water to make 1 liter of the concentrated salt solution. Stir solution until all of the salt is dissolved. This time add food coloring to make the toxic effect (green?). Decant the concentrated salt solution into smaller beakers for student use.

Materials per Group

-22 beakers or transparent cups

-1 x 20 mL graduated cylinder

-1 pipette with 5 mm diameter opening (a disposable 1 mL pipette with eh tip trimmed off with scissors works well).

-Daphnia magna culture (at least 105 individuals)

-100 mL of distilled water (for rinsing)

-60 mL of each of the following test solution you created when you performed the serial dilution: 100%, 10%, 1%, 0.1%, 0.01% and 0.001%.

-60 mL of spring water (used as the control).

Teacher Background on Daphnia

Daphnia, popularly known as water fleas, are small crustaceans that live in fresh water such as ponds, lakes, and streams. They serve as an important source of food for fish and other aquatic organisms. Daphnia are excellent organisms to use in bioassays because they are sensitive to changes in water chemistry and are simple and inexpensive to rise in an aquarium. They mature in just a few days, so it does not take long to grow a culture of test organisms.

Because Daphnia are transparent, it is possible to conduct bioassays using endpoints other than death. For example, through a microscope you can measure their heart rate or observe whether they have been eating. (Both of these signs are used to measure stress). If you are worried about killing Daphnia in your experiments, you could choose to measure one of these other endpoints instead. It is worth keeping in mind, though, that even under the best conditions these organisms live only a month or two, and in nature most of them get eaten within their first few days or weeks of life.

Possible Procedure (use this to guide the students into creating something similar…. Don’t just give them the procedure but this will help develop guiding questions for the students with where they should be headed).

  1. Prior to starting the bioassay, check the Daphnia to ensure the culture is healthy. Most of the individuals should be hopping around in the water, not lying motionless or doing somersaults at the bottom of the culture container.
  2. Using a pipette with a 5mm tip (cut off tip) collect small, young Daphnia from your cultures and transfer them into a beaker, pouring off extra water to make a concentrated collection of organisms for use in the bioassay. Be sure to collect only Daphnia that are small and don’t contain visible eggs or young in their blood chamber.
  3. Label three beakers or cups with each of the solution concentrations from your serial dilution, and fill each container with 20 mL of the appropriate solution. The final three beakers should be labeled “control” and filled with 20 mL of spring water.
  4. Transfer five Daphnia into each beaker (cup) being careful to minimize the amount of culture water you add to the test solutions. Be sure to release the young below the surface of each solution to avoid exposing them to the air. Rinse the pipette between solutions to avoid cross-contamination.
  5. Create a data table and record the total number of Daphnia that are dead at each time interval for each concentration. For example, the data table can list 1 hour, 24 hours, and 48 hours as the time intervals, but you can change this if you schedule or teacher requires different timing. Use close to one hour as possible, but before the end of the period, record the number of dead at each concentration. It may look confusing because Daphnia shed their shells as they grow, and these shells can look like dead organisms. Therefore, you may find it easier to count the number of surviving Daphnia and use that number to figure out how many have died.
  6. When the results are complete, graph your mean (average) number of Daphnia that have dies after 48 hours in each concentration. Then analyze and create a conclusion.

Bridge

Read the following scenario with the class. You may want to provide a copy of the scenario for the students.

‘Over the weekend, there was a terrible train crash that occurred near Charlotte Beach. The train had very few passengers and luckily no one was killed. However the train crashed into the Genesee River possibly containing several unknown chemicals. CSX, a train company responsible for the crash and owner of the train system, when contacted did not comment on what was dumped in the river. CSX however did send their own investigators to collect samples from the water. It is suspected by several environmental firms that the CSX train that crashed was carrying large quantities of one or more hazardous chemicals. The big concern is for the fish, wildlife and surrounding communities that use the Genesee River. The river empties next to Charlotte beech and is a stone throw to Duran beach”.

Mini Lesson

  1. Present the research question: What is the LD50 of the unknown CSX chemical?
  2. Give each group the “Toxin” and have them design an experiment to answer the research question.
  3. Since not all kids do homework (I know you are in shock!) provide each group with one copy of the article provided for homework the previous night to use as a guide.

Work Period

Groups conduct their serial dilutions and bioassays. Ensure data is documented by each group through a full laboratory report.

Summary

Answer the EQ

Closure

How will this fit in with your debate topic?