A toxicity test determines if water is toxic using an animal called a Ceriodaphnia dubia, commonly referred to as a "water flea."
Ceriodaphnia dubia is a small crustacean found in vernal pools and in freshwater ponds and lakes throughout the world. Ceriodaphnia is very sensitive to pesticides, heavy metals, and other toxic substances used by humans discharged into surface waters as well as many naturally occurring substances and conditions. These properties make Ceriodaphnia a good organism for testing the toxicity of freshwater. Natural waters can become poisonous to the organisms that live in these waters when pollutants enter the water in too high a concentration. In a toxicity test, the Ceriodaphnia is placed in the water being tested and in an amount of clean water called the "control." If the organisms in the control live and the organisms in the test sample die, we know that they were initially healthy and something which is present in the sample (but not in the control) had caused their mortality. The study does not, however, differentiate between naturally occurring toxins or conditions, and man-made toxins or conditions. Each water quality test is carried out using special instruments and water samples are taken from the river, storm drain, or street at each drain spot by the different teams. Each team will also observe physical changes around their sites.
Toxicology workshops are occasionally offered to storm drain detective students, with Pacific EcoRisk facilitating these training sessions.