However, the National Academy of Science recommends, and many European nations have adopted, a drinking water standard of 0.5 mg/L. Initially, the ammonium concentration was 2.0 mg/L, but after 1-2 hour in contact with each of the respective macrophytes, the ammonium concentration decreased to around 1.0-1.5 mg/L. As time increased, the ammonium was absorbed by the macrophyte roots through the process of phytoaccumulation, and eventually decreased to 0 mg/L after 24 hours. This is crucial as ammonia is toxic and detrimental to most fish and other aquatic organisms at concentrations above 1 mg/L in water. Similarly, long-term ingestion of water containing more than 1 mg/L may damage the internal organ systems and even cause severe burns and scarring to humans (Oregon Department of Human Services, 2000).