Toxicity Testing Activity


Michigan Environmental Education Curriculum
Water Quality - Pollutant Sources and Impacts

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Test organisms are placed in glass or plastic bottles containing the water to be tested and left there for 2-4 days. Bottles are set up for pure effluent, several dilutions of that effluent and a control water (where no more than 10% of the organisms should die). The percentage of organisms surviving exposure in each bottle is determined and the toxicity of the effluent is expressed as the effluent dilution which is lethal to 50% (LC50) of the population. An acute toxicity unit is defined as 100/LC50. The State of Michigan limits discharges to 1 acute toxic unit. If the effluent contains more than that, the treatment plant must add new processes to reduce the toxicity of their discharge.

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