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Toxicity to microorganisms

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Description of key information

Ammonia is used as a source of nitrogen by microorganisms and is also produced by bacteria from other nitrogenous compounds.  A waiver is therefore proposed for this endpoint as testing is not relevant.

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Additional information

Ammonia is generated as a product of metabolism by bacteria present in STPs from other sources including nitrogenous waste. STPs will therefore contain ammonia generated by bacteria from other sources at potentially much higher levels. Ammonium is readily converted by bacterial species to nitrate, via the process of nitrification. The primary stage of nitrification, the oxidation of ammonium to nitrite (NO2-) is performed by Nitrosomonas (among other) species. Other bacterial species (including Nitrobacter) are responsible for the subsequent oxidation of nitrite to nitrate (NO3-).