The acute toxicity limit test challenges a group of fish with a single high dose of material for 96 hours to determine whether toxicity can be observed at that concentration. Substances that pass the test criteria may be considered “non-toxic” to the organisms at that and lower concentrations. PRINCIPLE OF THE TEST METHOD Acute toxicity is the discernible adverse effect induced in an organism within a short time (days) of exposure to a substance. A limit test may be performed at 100 mg per litre in order to demonstrate that the LC50 is greater than this concentration. The fish are exposed to the test substance added to water at a range of concentration (100 mg per litre in water) for a period of 96 hours. Mortalities are recorded at least at 24-hour intervals. A limit test is designed to determine whether or not mortality or toxic effects are observable at 100 mg/L.