Cheap & Easy Environmental Science Lab: Using Bread and Food Colouring to Model Ground Pollution!

How can students see what happens underground? Understanding and visualizing ground pollution is something that many students find challenging. After teaching AP Environmental Science, IBDP Environmental Systems & Societies as well as a couple of other general high school environmental science courses I have lots of experience in the struggle to help students really "get" ground pollution and finally, this year I stumbled upon the perfect and super easy model... slices of bread!

What makes bread such a useful tool is the fact that it comes with a crust layer and then a more porous "soil" layer already, as well as the fact that food colouring readily shows up on slices of bread... you can see and measure the "pollution" quite easily. I recommend using a darker colour like red, blue or green food colouring rather than yellow, but with white bread most colours will show up clearly. To run this lab you will need the following materials:

• Slices of bread (I used 9 slices of white bread per group to allow for 3 trials of each type)

• Bottles of dark food colouring (1 bottle per group)

• A tray or container for each group to reduce the mess (see the takeout containers we used above)

• A beaker or cup for water per group

• A pipette or eye dropper for each group

• A ruler for each group

The lab I chose to do with my students was to investigate how different amounts of precipitation after a pollution event would affect the subterranean spread of the pollutants. In order to investigate this students placed a single drop of food colouring on the center piece of the crust of their bread and then made it "rain" by dripping a specific amount of tap water onto the pollution (see the video below). The amount of precipitation was our independent variable and changed in every three trials, while the surface spread and depth of the pollution spread was the dependent variable. It worked really well, but definitely took an entire class period to collect all of the data.

If you would like to run this lab here are some tips and tricks to make sure it goes smoothly:

• Use the same type of bread for each group and/or trial to keep results comparable

• Ensure that students keep the bread upright as it dries to recreate the flow of pollution downwards due to gravity

• My students used extra beakers to lean the bread against as it dried

• Spend some time talking about the importance of constants in this lab, it is a great one for reviewing constants as they are very intuitive... such as the same type of bread, same amount of "pollution/food colouring" and same force of rainfall

• This lab readily fits into any unit on pollution, but is particularly effective once students have learned a bit more about porosity and permeability of different soil types

• You can choose to extend it by using different bread types to represent different soil types - whole grain bread being much more porous than white bread etc.

If you would like to do this lab, but don't have the time or energy to make your own lab sheet, I have one for sale in my TPT shop, you can find it here. The resource includes three different versions, one for IBDP ESS, one for any environmental science course or unit and one for an open inquiry lab. Whichever way you choose to do this lab have fun with it!

Thanks for reading teachers, travelers and curious souls of all kinds.

The Roaming Scientist