Inuence of Organic Ammonium Derivatives on the Equilibria Between of NH4+, NO2- and NO3- Ions in River Waters

The braking effect of the ammonium derivatives on the natural aquatic environment varies dramatically with the number and nature of organic radical substitutions at nitrogen atom, particularly with their structure, composition and genesis. The most common discrepancy in their toxic effect are showing the natural and synthetic amines. For instance, the values of the maximum allowable concentration (MAC) of the derivatives of the natural origin for drinking water exceed the MAC of the synthetic ones by two orders. On the other hand, it has been found out that 1- naphtylamine (1-NA) inhibitory effect is associated to its toxicity. The Diethylamine (DEA) braking impact on the nitrication process is effectively lower than that of the toxicity. Our experiments show that the carbon-radicals of organic amines act as reducing agents. It is found that DEA decomposition leads to a high NH 4+ ions (approx. 3.8 mg/L ammonium nitrogen) concentration in river water samples. By laboratory simulations two types of xations by microbial organisms have been established: 1) absorption-desorption, the hydromicrobiotic reaction to ammonium (HMBRA) at the instantaneous increase of the concentration of ammonium ion in the river water (so-called shock/stress effect); 2) nitrogen xation stimulated by a certain concentration (0.05mg/L) of a 1-NA and other amines.


Introduction
Ammonium ion from water basinsis a product largely derived from the degradation of organic matter of protein origin, which manifests a selective toxic effect (Britto et al.2001, Britto, and Konzucker, 2002, Müller et al., 2006. Similar to carbon dioxide and methane, it is a nal product of living organisms and substrates of combustion/fermentation processes. The presence of ammonium in natural water stimulates the increase of algae and heterotrophic autotrophic bacteria activities [Daum, et. al.,1998, Lin, et al., 2010, Dalton et. al., Arp, et al., 2002, Do, et al.,2008. As a result of the degradation and decarboxylation (Snider and  One should mention the toxicity ampli cation of cationic surfactants (SAS-Ct) with the increasing of water hardness (Lewis 1992). On the other hand, the increase of CaCO 3 concentration is leading to the reactivation of emerging cationic organic pollutants with a negative impact, which presence is due to discharging of the insu ciently puri ed waste water in rivers. The braking phenomenon of nitri cation in the presence of CaCO 3 is characteristic for the river sections polluted with waste water of the cities from where the cationic SAS and other emerging substances are discharged (Spataru et al. 2015, Spataru et al. 2017, Spataru et al. 2018). The starting point of our study has been dedicated to the analysis of their in uence on the concentrations of various nitrogen forms and to the behavior of a numbers of nitrogenlinked radicals. Another aspect of this study has been dedicated to the highlighting the cationic surfactants (SAS-Ct) impact on the urban sewage nitrogen forms in natural water models with and without CaCO 3 . Consequently, a previously developed model of the arrangement of SAS on the surface of calcium carbonate nanoparticles has been taken into account (Cui2010, Cui2012). The model is based on (I) the xation of the anionic part and further decomposition of the SAS-Ct • SAS-An complex, and (II) on the passage of the cationic part in solution, increasing the braking activity of ammonium derivatives (Spataru et al. 2015, Spataru et al. 2017,Spataru et al. 2018).
The investigated samples, containing SAS-Ct and SAS-An, were tested in aqueous solutions with and without CaCO 3 by the UV spectroscopy method (Spataru et al. 2017 to the in uence of the microbial enzymatic system, which, in turn, is a function of the chemical composition of natural water and, in particular, of organic matter from natural water (river, lake, sewage basin, etc.). All parameters of the models were similar (temperature, atmospheric pressure, daylight) to those of the studied aquatic objects from which the water sample was collected for the laboratory model. At the initial stage of the laboratory simulation process a small amount of NH 4 + was added. The water of the Nistru River at Vadul-lui-Voda section was used. NH 4 Cl solution was added to the river water samples, in order to achieve two concentrations of about 3 mg/L and about 6 mg/L of ammonium ions. The reference sample contained only ammonium ions, while the working samples contained also amines from chemical industry waste (1-NA, DPA) and that resulting from the decomposition of proteins plus their degradation products (DEA). Both amines used in the chemical industry and those resulting from natural processes of protein and amino acid decomposition were investigated at different concentrations: lower, permissible and higher ones. Due to the variable toxicity of the amines, a conditional reference was used as maximum admissible concentration (MAC).
Laboratory models were investigated, respecting the minimum recommended amount of water sample in glass vessels and were examined under natural lighting and temperature conditions, away from direct sunlight.

Results And Discussions
The ammonia and its derivative environmental amines are physiological products, which are released The analysis of the NH 4 + concentration difference (in mg/L) for various number of days was performed.
Four sets of values of concentrations were considered: 1) the difference between the values of the initial concentration (C0) and that obtained after one day (C1), i.e. (C1 -C0); 2) the difference between the values obtained after two days of experience and the initial ones, (C2 -C0); 3) the difference between the values obtained after two days of experience (C2) and those after one day of experience (C1), (C2 -C1); as well the difference of the values (C3 -C1). Figure 3 depicts the differences in ammonium ion concentrations between the starting day (C0), of the laboratory simulations and the next few days, 1) (C1 -C0); 2) (C2 -C0); 3) (C2 -C1) 4) (C3 -C0), as a function of the 1-NA concentrations when the initial ammonium ion concentration was 3 mg/L. Fig.3. The difference of ammonium ion concentrations: One can observe from Fig. 3 and Table 1 that the total soluble mineral forms of nitrogen is increasing during the period of nitrogen xation (starting on second day and continuing on third day). Thus, the increase of ammonium nitrogen is not due to other soluble nitrogen species sources of the river water. A similar growth in the ammonium ion concentration was detected in the river water experiment within laboratory models with the initial concentration of 2 mg/L NH 4 + for the same 0.05 mg/L concentration of Simultaneously, beside the stimulation of nitrogen xation, the consumption/oxidation of ammonium ions is less signi cant during the third day comparing to the second day. The decreasing of nitrogen of ammonium ion xation and the increasing of the redox process is more signi cant after the day third of the experiment (Fig. 1), leading to a permanent decreasing of ammonium ions concentration for all the samples. On the sixth day, the rate of the NH 4 + oxidation/consumption process exceeds that of nitrogen xation. The ammonium ion concentration dynamics as a function of the 1-NA concentration ( Fig. 3 and Fig. 4) do point out to the fact that the nitrogen xation process is still continuing.
The analysis of the natural water model behavior as a function of 1-NA concentration at initial concentration of 6 mg/L NH 4 + was performed. Three sets of model experiments were selected: 1) the difference between the values of the initial concentrations (C0) and those obtained after one day (C1) of laboratory simulations, (C1 -C0); 2) the difference between the values obtained after two days of experience (C2) and those after one day (C1), (C2 -C1); 3) the difference between the values after two days of experience and initial values; (C2 -C0) (Fig. 4). One can observe that in the rst two days at the concentration of 6 mg/L NH 4 + , the 1-NA concentration has a well-de ned impact. The sharp peak of NH 4 + concentration (Fig. 3), due to the signi cant effect of nitrogen xation at 0.05 mg/L of 1-NA concentration, is not characteristic in the case for the samples with the initial concentration of 6 mg/L NH 4 + (Fig. 4). In the rst two days the nitrogen xation/adsorption and then desorption take place.
One can observe from the Fig. 4 that the curves 1, 2, and 3, showing the difference between initial, rst and second days of the NH 4 + ions concentration, should asymptotically intersect by the increasing of the 1-NA concentration. By extrapolating the curves 1, 2 and 3 of Fig.4, the concentration of 1-NA at which the modi cation of NH 4 + concentration will no longer take place, was obtained. The three curves intersect at the point with the value of 1-naphthylamine concentration of0.70 (±0.035) mg/L. Therefore, the value of 1-NA concentration, at which it is supposed to stop completely the processes connected to the biochemical production and adsorption of the NH 4 + , due to its toxicity, is equal to about 0.70 mg/L. One can conclude that the process of decreasing of ammonium concentration on the rst day after the initiation of laboratory simulations, and its increasing on the second day, caused by aquatic microorganisms, could be called the hydro-micro-biotic reaction to ammonium (HMBRA). It is worth to compare the total mineral nitrogen in samples with the initial concentration of 3mg/L and 6mg/L NH 4 + ( Table 1) (Table 1). Therefore, the increase of the NH 4 + initial concentration from 3 to 6 mg/L leads to the suppression of nitrogen xation processes. The increase of C1-C0, C2-C1 and C2-C0 parameters and the concentration of total mineral nitrogen in water (Fig. 3) for 3 mg/L NH 4 + , contrary to the case of 6 mg/LNH 4 + (Fig.4) The study of the behavior of nitrogen species equilibria in natural waters in the presence of diethylamine (DEA) is relevant not only because of its presence in the industrial waste, but also because DEA is assimilated by aquatic microorganisms. Comparing with above presented data, our simulations show a completely different picture of the bio-chemical and redox equilibria in the presence of DEA (Fig. 6aand  6b). First of all, it should be mentioned the large difference between the MAC values of the DEA samples, compared to 1-NA ones (almost larger by two orders).Samples with a relatively low concentration of 1-NA (between 0.025 and 0.5 mg/L) and those containing large amounts of DEA (between 2.0 and 20.0 mg/L) correspond to the same MAC values (between 0.5 and 10 respectively).
The content of the nitrogen amine is much larger in DEA samples than in 1-naphthylamine ones. DEA is an aliphatic amine of natural origin and 1-NA is an aromatic amine of synthetic origin. Therefore, the decomposition, oxidation, and assimilation of DEA occurs naturally much easier (see Fig. 5 and 6) than those of 1-NA, which impact on generated redox processes is in uenced by lower activity of bacterial enzymes and/or microbial populations. For 1-NA, the NH 4 + oxidation is delayed during the rst days of experiments (Figs. 5 and 6) comparing with the reference sample, even if after this time theNO 2 concentration in analyzed models is larger compared to the reference one. One can expect that this oxidation delay comes merely from the effect of braking NO 2 oxidation. In the case of DEA, (Fig. 6) (Fig. 6). It is possible that in these samples the oxidation of organic carbon takes place by the participation of oxygen from nitrite and nitrate ions due to a relative oxygen de cit in aquatic samples. Here, there is a de nite shortage of oxygen, as evidenced by decreasing the amount of NO 2 and NO 3 in the rst ten days of experiments. However, after 10 days, the NO 3 concentration has an increasing tendency, up to 50 days after simulation. Interestingly, the NO 2 concentrations in the samples, for both 3 mg/L and 6 mg/L of NH 4 + initial concentration with 20.0 mg/L of DEA, becomes moderately high even after 50 days of the experiment (Fig. 6a and 6b).
The industrial waste product in natural waters is often diphenylamine (DPA). Figs 7 and 8 display the braking effect on the NH 4 + to NO 2 oxidation in water containing both 0.05 mg/L and 0.5 mg/L DPA in initial models. In contrast to 1-NA models of river water samples, the models of DPA manifest a low in uence of its concentration on the NH 4 + oxidation process. In the sample containing 0.5 mg/L DPA (curve 2 in Fig. 7), the oxidation of NH 4 + is somehow slower than that in the samples with 0.05 mg/L DPA (curve 3 of Fig. 7).
For natural water models with 3mg/L of the initial concentration of NH 4 + , the difference between the sample with 0.05 mg/L and 0.5 mg/L DPA is completely surprising due to the increase in the NH 4 + concentration on the day 16 th . Presumably, the shift from 0.05 mg/L to 0.5 mg/L of DPA leads to the reversal of the oxidation time of NH 4 + for these two samples. The con rmation of this phenomenon is detailed in  (Fig. 7, curves 3 and 5, and Table 2).
The concentration of total soluble nitrogen (TSN) on the day 16 th exceeds by about 1 mg/L this quantity for the other days (14, 15 and 19). This difference is similar to the increase of NH 4 + concentration compared with the previous days (14,15). Table2 Soluble mineral nitrogen in river water models within 14-19 th days

Conclusion
Natural water model experiments show that ammonium derivatives have a brake impact on redox processes of stable soluble nitrogen forms at concentrations below MAC. By increasing their concentration in river waters, the effect becomes more obvious. By laboratory simulations, two types of xations by microbial organisms have been distinguished: 1) Ammonium absorption-desorption, e.g.
HMBRA, at the instantaneous increase in the NH 4 + concentration in the river waters(so-called shock/stress effect); 2) Nitrogen xation stimulated by a certain concentration (0.05mg/L) of 1-NA and other analyzed amines. These modi cations constitute a sensitive reaction of aquatic microorganisms to environmental changes. A noticeable effect of the attenuation of nitri cation processes caused by the toxicity of ammonium derivatives has been evidenced. All at once, the models with diethylamine reveal an increase in NH 4 + concentration due to its decomposition (approx. 3.5-3.8 mg/L nitrogen ofNH 4 + ).Slightly degradable organic carbon in uences the transformation of nitrogen species into ammonia, leading to a decrease in nitrite concentrations over a su ciently long period of time.
Diethylamine, being easily degradable, causes an increase in the concentration of ammonium ions due to the transformation of its amino nitrogen and the reduction of nitrites and nitrates through its organic carbon. Authors' contributions PS is the only author of this manuscript.PS has designed the study, collected data, carried out eldwork and experiments and interpreted the results of the manuscript. PS has contributed to whole bibliographic, reviewing, and editorial works.
Availability of data and materials All data are included in the manuscript.
Ethics approval and consent to participate Not applicable.