In the last issue of The Volunteer Monitor , I described a bioassay using lettuce seeds as the test organism. Here I will describe another very simple bioassay procedure that uses the common duckweed. Duckweeds are ideal for aquatic toxicity testing because they are easy to collect and culture.
Duckweeds are very small aquatic plants that are usually found floating on the water surface.
They are very common on quiet water bodies like lakes and ponds, especially those suffering from eutrophication. Although duckweeds are flowering plants, they seldom flower. Many factors, including pollutants like metals or herbicides and environmental factors like light or temperature, can cause a reduction in the number of fronds. This forms the basis of the duckweed bioassay, in which the number of new fronds on plants exposed to the test water is compared to the number of new fronds on control plants. Below is a brief description of the procedure.