13:22 Sep 5, 2010 

Thanks, Karen. So, how do you think it should be translated in my text? And should it be (NH4), (NH4+) or (NH3)??? Many thanks in advance! Sheila

13:19 Sep 5, 2010 

Hi. NH3 (ammonia) is a gas that when in water equilibrates with it. H2O + NH3 <--> NH4+ and HO-. Ammonium ions are oxidized into nitrites then nitrate.

10:46 Sep 5, 2010 

I'm no expert either (I'm a nurse, not chemist) but I would agree with you that your text should refer to NH3 since that's the toxic one. Maybe you should wait until a chemist has a look in on this question, or check with your client?

10:32 Sep 5, 2010 

Thanks for the second link, Emma - it just confirms what I was wondering about above. In other words, should they say 'NH3' instead of NH4 or NH4+? Since it is the un-ionised NH3 that is toxic.

10:27 Sep 5, 2010 

I meant to say that I was going on what I read in this part of the article quoted by Emma:
"Ammonia is un-ionized, and has the formula NH3. Ammonium is ionized, and has the formula NH4+. The major factor that determines the proportion of ammonia or ammonium in water is water pH. The activity of ammonia also is influenced by temperature and ionic strength. This is important as the unionized NH3 is the form that can be toxic to aquatic organisms. The ionized NH4 is basically harmless to aquatic organisms."

10:26 Sep 5, 2010 

Many thanks for your answers! Emma, that's a very interesting article. However, I'm still a bit confused (sorry!). Would it not be clearer if they had said (NH3) instead of (NH4) here (and shouldn't it be (NH4+)? I mean - could you say 'ammonia in its un-ionised form (NH3)...' Because ammonium (NH4+) does not appear to be toxic to fish. Right? I hope I've understood the article correctly!