Nitroso compounds: safety and public health

Nitrogen contamination in groundwater in an agricultural region along the New Silk Road, northwest China: distribution and factors controlling its fate

Nitrogen contamination is a global concern and has been a serious problem in agricultural areas. The present study was carried out in an intensively irrigated region of northwest China along the New Silk Road, Yinchuan Plain, where the residents depend on the groundwater as the primary source for drinking. To understand the nitrogen contamination in the aquifer system, the distribution of nitrate and ammonium and its controlling factors were studied based on hydrochemical, hydrogeological, and isotopic analyses. 11.37 and 40% of phreatic water samples are categorized as NO₃-N and NH₄-N pollution in accordance with the WHO standards. A total of 59.52% of confined water samples has high NH₄-N values, exceeding the permissible limit for drinking purpose. The results indicate NO₃-N predominates in the shallow water and NH₄-N predominates in the deep water for the single phreatic aquifer. For the multilayer structure area, NO₃-N predominates in the phreatic aquifer of the western and the southern parts of the plain; NH₄-N predominates in the phreatic aquifer of the middle and the northern parts of the plain, and in the confined aquifers where groundwater pumping had been performed. The mixture of synthetic fertilizer and manure/sewage is primarily responsible for the phreatic water based on isotopic analysis. In the confined aquifers, higher NH₄-N concentrations are mainly attributed to intensive pumping under higher pumping rates. The results of this study can be used as a scientific basis for the future research on nitrogen in the plain. They can also be used by scholars and decision makers who are interested in groundwater protection and sustainable development.

Nitrite and nitrite reductases: from molecular mechanisms to significance in human health and disease

Nitrite, previously considered physiologically irrelevant and a simple end product of endogenous nitric oxide (NO) metabolism, is now envisaged as a reservoir of NO to be activated in response to oxygen (O(2)) depletion. In the first part of this review, we summarize and compare the mechanisms of nitrite-dependent production of NO in selected bacteria and in eukaryotes. Bacterial nitrite reductases, which are copper or heme-containing enzymes, play an important role in the adaptation of pathogens to O(2) limitation and enable microrganisms to survive in the human body. In mammals, reduction of nitrite to NO under hypoxic conditions is carried out in tissues and blood by an array of metalloproteins, including heme-containing proteins and molybdenum enzymes. In humans, tissues play a more important role in nitrite reduction, not only because most tissues produce more NO than blood, but also because deoxyhemoglobin efficiently scavenges NO in blood. In the second part of the review, we outline the significance of nitrite in human health and disease and describe the recent advances and pitfalls of nitrite-based therapy, with special attention to its application in cardiovascular disorders, inflammation, and anti-bacterial defence. It can be concluded that nitrite (as well as nitrate-rich diet for long-term applications) may hold promise as therapeutic agent in vascular dysfunction and ischemic injury, as well as an effective compound able to promote angiogenesis.

Dietary nitrate in man: friend or foe?

Based on the premise that dietary nitrate is detrimental to human health, increasingly stringent regulations are being instituted to lower nitrate levels in food and water. Not only does this pose a financial challenge to water boards and a threat to vegetable production in Northern Europe, but also may be eliminating an important non-immune mechanism for host defence. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Epidemiological studies have failed to substantiate this. It has been shown that dietary nitrate undergoes enterosalivary circulation. It is recirculated in the blood, concentrated by the salivary glands, secreted in the saliva and reduced to nitrite by facultative Gram-positive anaerobes (Staphylococcus sciuri and S. intermedius) on the tongue. Salivary nitrite is swallowed into the acidic stomach where it is reduced to large quantities of NO and other oxides of N and, conceivably, also contributes to the formation of systemic S-nitrosothiols. NO and solutions of acidified nitrite, mimicking gastric conditions, have been shown to have antimicrobial activity against a wide range of organisms. In particular, acidified nitrite is bactericidal for a variety of gastrointestinal pathogens such as Yersinia and Salmonella. NO is known to have vasodilator properties and to modulate platelet function, as are S-nitrosothiols. Thus, nitrate in the diet, which determines reactive nitrogen oxide species production in the stomach (McKnight et al. 1997), is emerging as an effective host defence against gastrointestinal pathogens, as a modulator of platelet activity and possibly even of gastrointestinal motility and microcirculation. Therefore dietary nitrate may have an important therapeutic role to play, not least in the immunocompromised and in refugees who are at particular risk of contracting gastroenteritides.

Neoplasia induced in male rats fed lead acetate, ethyl urea, and sodium nitrite

Sprague-Dawley rats were exposed to 0, 26, or 2600 ppm lead as lead acetate in drinking water for 76 weeks. At 28 weeks of lead exposure, a portion of each group was exposed simultaneously to 6.36 g/kg ethyl urea (EU) and 2.0 g/kg sodium nitrite (NaNO2) for a duration of 20 weeks, and then continued an additional 28 weeks on standard diet free of EU and NaNO2. The animals were observed for incidence, latency, and distribution of tumors. Rats exposed to 2600 ppm lead alone had 81% renal tumors, while rats given 2600 ppm lead in combination with EU/NaNO2 had a 50% incidence. Renal tumors did not occur in the EU/NaNO2 only or EU/NaNO2-26 ppm lead groups. The major tumor type found in EU/NaNO2-exposed rats was lymphosarcoma. Lead did not appear to be syncarcinogenic to the activity of ethylnitrosourea, the carcinogen formed by oral exposure to EU and NaNO2. The lead-induced renal neoplasms were histologically similar to those which occur spontaneously in man and, therefore, may serve as an animal model to study human disease.

Nitrosation in vitro and in vivo by sodium nitrite, and mutagenicity of nitrogenous pesticides

37 nitrogenous pesticides, belonging to the chemical groups of amides, carbamates and ureas, were nitrosated with sodium nitrite in vitro. The nitrosated compounds were tested for mutagenic activity in the bacterial spot test with Salmonella typhimurium his G 46. Those pesticides reacting positively in this test after nitrosation were then fed to mice in combination with sodium nitrite in order to assess the formation and mutagenicity of these nitroso compounds in vivo. With the already known exception of ethylenethiourea (ETU), no pesticide produced enhanced numbers of micronuclei in mouse bone-marrow erythrocytes when fed together with nitrite. Dose-response experiments with intraperitoneal injection of N-nitroso-ETU revealed an apparent no-effect level of about 15--18 mg/kg. The findings are correlated with the pesticide residues actually present in the environment.