Nitrite

About: Nitrite is a research topic. Over the lifetime, 15425 publications have been published within this topic receiving 484581 citations.

Influence of dissolved oxygen concentration on nitrite accumulation in a biofilm airlift suspension reactor

Abstract: The biofilm airlift suspension (BAS) reactor can treat wastewater at a high volumetric loading rate combined with a low sludge loading. Two BAS reactors were operated, with an ammonium load of 5 kg N/(m3 d), in order to study the influence of biomass and oxygen concentration on the nitrification process. After start-up the nitrifying biomass in the reactors gradually increased up to 30 g VSS/L. Due to this increased biomass concentration the gas-liquid mass transfer coefficient was negatively influenced. The resulting gradual decrease in dissolved oxygen concentration (over a 2-month period) was associated with a concomitantly nitrite build-up. Short term experiments showed a similar relation between dissolved oxygen concentration (DO) and nitrite accumulation. It was possible to obtain full ammonium conversion with approximately 50% nitrate and 50% nitrite in the effluent. The facts that (i) nitrite build up occurred only when DO dropped, (ii) the nitrite formation was stable over long periods, and (iii) fully depending on DO levels in short term experiments, led to the conclusion that it was not affected by microbial adaptations but associated with intrinsic characteristics of the microbial growth system. A simple biofilm model based on the often reported difference of oxygen affinity between ammonium and nitrite oxydizers was capable of adequately describing the phenomena. Measurements of biomass density and concentration are critical for the interpretation of the results, but highly sensitive to sampling procedures. Therefore we have developed an independent method, based on the residence time of Dextran Blue, to check the experimental methods. There was a good agreement between procedures. The relation between biomass concentration, oxygen mass transfer rate and nitrification in a BAS reactor is discussed. © 1997 John Wiley & Sons, Inc.

Nitrite in soils: accumulation and role in the formation of gaseous N compounds

Abstract: Nitrite is an intermediary compound formed during nitrification as well as denitrifiication. It occasionally accumulates in soils and drainage water. The nitrite can then undergo transformations to gaseous nitrogen compounds such as NO and NO2. Soil pH controls the abiotic nitrite decomposition to a large extent. Under acidic conditions(pH <5.5), nitrous acid spontaneously decomposes preferentially to NO and NO2. Nitrite also undergoes reactions with metallic cations (especially ferrous iron) and with organic matter. As a result of these reactions gaseous compounds such as NO, NO2, N2O and CH3ONO can be formed. Through reaction of nitrite with phenolic compounds nitroand nitrosocompounds can be formed, building up organic N. With normal agricultural practices on slightly acidic soils, the nitrite instability usually does not lead to economically important N losses from soils. However, the compounds formed through its degradation or interaction with other soil constituents are linked to environmental problems such as tropospheric ozone formation, acid rain, the greenhouse effect and the destruction of the stratospheric ozone.

Carcinogenicity of nitrate, nitrite, and cyanobacterial peptide toxins

Abstract: In June, 2006, 19 scientists from eight countries met at the International Agency for Research on Cancer (IARC) in Lyon, France, to assess the carcinogenicity of ingested nitrate and nitrite, and the cyanobacterial peptide toxins microcystin-LR and nodularins. These agents are linked environmentally through the runoff of agricultural fertilisers that increase nitrogen concentrations in surface water and groundwater, and that could contribute to cyanobacterial growth in surface water. The assessments will be published as volume 94 of the IARC Monographs. Nitrate and nitrite are naturallyoccurring ions. In the past century, the global nitrogen cycle has been increasingly aff ected by nitrogen fi xation for agricultural activities, which now exceeds the amount that occurs naturally. Both groundwater and surface water can be contaminated by excess nitrate as a result of agricultural activities. Human exposure to nitrate and nitrite is mainly from the ingestion of food. Important sources include vegetables, cereal products, and cured meat. Drinking-water is generally not the main source of nitrate, unless concentrations exceed the WHO guideline of 50 mg/L, which is especially found in contaminated groundwater. Ingested nitrate (NO3) is excreted in the saliva and reduced to nitrite (NO 2) mainly by oral bacteria. Under acidic conditions in the stomach, nitrite then reacts readily with nitrosatable compounds, especially sec ondary amines and alkyl amides, to generate N-nitroso compounds. Several N-nitroso compounds are potential human carcinogens. The nitrosation reactions can be inhibited by the presence of vitamin C or other antioxidants. Some epidemiological studies assessed the risk of cancer in people who had high intake of nitrite or nitrate and low intake of vitamin C, a dietary pattern that could result in increased endogenous formation of N-nitroso compounds. The Working Group weighted these studies more heavily than studies without this information. From the epidemiological studies of nitrate in food, no increased risk of cancer was seen. For nitrate in drinkingwater, epidemiological studies were few, exposure levels were low, and endogenous nitrosation was not often considered. For ingested nitrite, the risk for stomach cancer was investigated in seven well-designed case-control studies. Six of these showed consistent, positive associations, four of which were signifi cant. Two studies looked at eff ect modifi cation, and the risk was most pronounced in people who had high nitrite and low vitamin C intake. Neither of the two cohort studies reported a clear positive association. No study accounted for potential confounding or eff ect modifi cation by Helicobacter pylori, an important risk factor for stomach cancer. For oesophageal cancer, two well-designed case-control studies investigated an association with nitrite intake. Both reported a positive association for nitrite intake overall; for people with high nitrite and low vitamin C intake, these associations were signifi cant. For brain tumours, two of fi ve casecontrol studies in children showed positive associations with nitrite intake. In one study, children born to mothers with the highest intake of nitrite from cured meat during pregnancy had a three-fold increased risk for brain tumours. The other study reported an increased risk for astroglial brain tumours in the children of mothers whose drinking-water had high nitrite concentrations. For adult brain cancer, no clear pattern emerged from seven case-control studies. The Working Group concluded that there is “limited evidence of carcinogenicity” for nitrite in food based on the association with stomach cancer. For nitrate in food and nitrate or nitrite in drinking-water, the studies provide “inadequate evidence of carcinogenicity”. No increased incidence of tumours was recorded in mice and rats if nitrate alone was added to the drinking-water or to the diet, providing inadequate evidence of carcinogenicity. Mice given nitrite in drinking-water showed a signifi cant trend in the incidence of forestomach papillomas and carcinomas combined. Rats exposed to nitrite in utero and throughout life had an increased incidence of lymphoreticular tumours, and mice with similar exposure had raised incidences of lymphoma and lung tumours. These results provide limited evidence of carcinogenicity for nitrite alone. Many studies of mice and rats tested nitrite in combination with specifi c secondary or tertiary amines or amides, added to the diet or drinkingwater, or by gastric intubation. Most combinations resulted in increased incidences of benign and malignant tumours at many organ sites. The Working Group concluded that these results provided “suffi cient evidence of carcinogenicity” for nitrite in combination with amines or amides. The combination of positive and negative results from epidemiological Upcoming meetings

Studies of nitrate reductase in marine phytoplankton1

Abstract: Certain marine phytoplankton contain the enzyme nitrate reductase when growing on nitrate, but only low levels of enzyme were found during growth with ammonium or when the nitrogen source was depleted. Netted samples of oceanic phytoplankton contained the enzyme when taken from waters with nitrate concentrations 2–10 µm. Ammonium was assimilated in preference to nitrate in phytoplankton cultures supplied with both forms of nitrogen at 5–15 µm. Enzyme synthesis and nitrate use began when ammonium was depleted to 0.5–1.0 µm. Nitrate reductase assay of phytoplankton samples is a useful tool in that a positive result indicates utilization of nitrate and a negative one implies growth on ammonium, nitrogen depletion, or, improbably, growth with other N-sources such as nitrite, urea, or amino acids. The enzyme assay seems especially useful for studying the timecourse of phytoplankton blooms because it provides a sensitive measure of the initiation and cessation of nitrate assimilation.