Together with pupils, identify different kinds of pollution and pollutants:
Write on the blackboard different types of pollution (with nutrients, bacteria and other pathogen microorganisms, toxic substances); Identify the types of pollutants with the following questions: Which substances can we find in sewage? Think for a moment what kind of things you pour down the drain at home. What happens on a farm or different industrial units?
After you have identified the pollutants, categorize them according to the type of pollution: (1) with nutrients, (2) bacteria and other harmful microorganisms, (3) toxic (hazardous) substances.
Preparing an experiment:
Together with pupils, prepare in jars equal amounts of water taken from a stream or a river (1 liter) and mark them with the following labels: clean water, liquid soap, vinegar, mineral fertilizer for flowers, toilet cleaner, food remains.
In plastic glasses, prepare pollutants that we will mix with the water in the glass jars. Let pupils help with measuring out the amounts, mixing them, and to marking plastic glasses. Pour water from a stream to five plastic glasses and fill approximately ¼ of each:
Do not add anything to the first glass.
Mix half of a teaspoon of mineral fertilizer for flowers in the second glass.
Add a small spoon of vinegar to the third glass.
Mix half of a teaspoon of toilet cleaner (toxic for bacteria) in the fourth glass (2 -3 ml).
Mix food remains in the fifth glass. (Warning: avoid meat remains for this mix, because the mixture will smell very bad in a short time.)
Add liquid soap in the sixth glass.
Pollutants in plastic glasses should be mixed Add them to the water in glass jars. Do not cover the jars: just protect them with a piece of fabric so that air (oxygen) will have free access, but not insects.
The mixture with chemical fertilizer from the second glass represents pollution with mineral nutrients. The solution with vinegar represents pollution with acid waste used in industry (vinegar changes the pH of water – microorganisms adapted to low pH can develop after some days).
Toxic substances are represented by toilet cleaner that kills bacteria. Mix with food remains represents biodegradable organic pollution, and bacteria will decompose it quickly.
Let pupils try to predict what will happen with the polluted water in each of the jars.
We should leave the samples of polluted water to stand approximately ten days. Pupils should check the samples water every day and write down their observations about noticeable changes. We should talk to them about their observations.
Sample with added clean water will stay unchanged.
In the sample with toxic substances, there may not be any perceptible change.
We notice a green color, which is an indicator of the growth of green plants (algae), in the sample with nutrients.
The glass with food remains must smell bad (bacteria used up oxygen and now anoxic decay goes on. Oxic processes do not smell bad while unpleasant smelling gases occur with anoxic decay).
Materials and Worksheets
five glass jars
6 l of water from a stream or river located nearby