Registration Dossier

Diss Factsheets

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

A waiver is proposed for this endpoint. Ammonia is rapidly biodegraded in aquatic systems.

The available information are reviewed by Environment Canada (1984) and WHO (1986).

The Environment Canada review concludes that, when ammonia appears in water under the normal conditions (aerobic), it is rapidly converted to nitrate by nitrification. The pH in water is increased by the presence of ammonia ion, in the form of hydroxide ions. Bacteria convert the ammonia to nitrate creating an oxygen demand (BOD) several days after the introduction of ammonia. The bacteria that oxidize ammonia to nitrate are largely of the genus Nitrosomonas. Conversion of nitrite to nitrate is carried out primarily by the genus Nitrobacter. Temperature, oxygen supply, and pH of the water are factors in determining the rate of oxidation. At high levels of total ammonia and a high pH, resulting concentrations of free ammonia are toxic to both nitrifying forms of bacteria, but especially to nitrobacters, occasionally leading to the accumulation of nitrite.

The WHO document concludes that ammonia has a critical role in the nitrogen cycle and when introduced into the aquatic environment is rapidly converted into other nitrogenous forms under aerobic conditions. When conditions are appropriate for high nitrification this may lead to low levels of dissolved oxygen as nitrification is an oxygen consuming process.

No additional studies are proposed.