Ammonia, originated from the decomposition of organic matter, being the richest natural substance in nitrogen,
with the exception of that molecule, is non-toxic for a wide range of bacteria at the level of a few mol/L, unlike
animal and plant cells. In this paper, the difference in the impact of amines of natural origin (diethylamine, DEA)
and synthetic origin (1-naphtylamine, 1-NA and diphenylamine, DFA) on the processes of ammonia oxidation has
been investigated. 1-NA significantly inhibited nitrification by a mixed population of Nitrobacter and Nitrosomonas
species isolated from activated sludge; a concentration of 15 mg/L gave a 50% inhibition. Maximum admissible
concentrations (MAC) for 1-NA and DEA differs by two orderd. The laboratory simulations have been carried out in
water of the Nistru River (in the section of the Vadul-lui-Voda town). To river water samples of water, the NH4Cl
solution has been added, in order to achiieve concentrations of ~ 3.2 mg/L and ~ 6.4 mg/L of ammonium, which
are characteristic for rain water and a series of contaminated objects. Both DEA and 1-NA influence in the redox
processes generated by bacterial enzyme activity even within the MAC values. In the case of 1-NA the braking
effect is related to the toxic effect, while for DEA this effect is doubled (due to the toxic effect and also that related
to the aminic carbon). It has been shown that the aminic nitrogen exhibits more pronounced toxic effects in
comparison with ammonia. Typically, the amines, originated from the decomposition of organic materials of natural
origin, have less toxicity and lower MACs by about ten times higher than those of synthetic origin. Here, it is
important to mention that laboratory models are sensitive even at concentrations below MAC.