The nitrate NO3- ion derives from the complete dissociation of nitric acid HNO3 or nitrates in aqueous solution, according to the following formula:
HNO3 + H2O → H3O + + NO3-
NITRATES
Nitrates are the salts of nitric acid (HNO3) and are substances in which the nitrate ion (NO3-) is present.
Being salts, they are all very soluble in water, and the most important are:
- Aluminum nitrate
- Ammonium nitrate
- Silver nitrate
- Sodium Nitrate
- Potassium nitrate
- Lead nitrate
- Strontium nitrate
- Thallium nitrate
- Zinc nitrate hexahydrate
The most common ones in nature, however, are sodium nitrate and potassium nitrate.
The nitrate ion (and some of its salts) performs many functions: it is in fact essential for plant metabolism; it is an excellent fertilizer (particularly when it is inside the ammonium nitrate NH4NO3), also acting as nourishment for the denitrifying bacteria, which have the function, starting from it, of producing molecular nitrogen N2.
The silver nitrate was used, in 1900, for the production of the first photographic cameras, and now it is instead used to evaluate the potability of tap water; moreover, it acts as a catalyst in the basic reaction of the operation of the alcohol test.
Nitrates are rapidly transformed into nitrous acid, and then into nitrites, thanks to the nitrate-reductase present in the bacterial flora of the oral cavity and intestinal lumen. This conversion negatively interferes with the functions of our organism, because the nitrites interact with the hemoglobin transforming it into methemoglobin, thus unable to carry out its function of transporting oxygen.
Furthermore, nitrites can react with amines (present in food products containing proteins), forming N-alkyl-nitrosamines: compounds classified as carcinogenic and toxic. Fortunately, this formation is contrasted by vitamin C (ie ascorbic acid) and vitamin E (tocopherol), vitamins capable of blocking the conversion of nitrites into nitrosamines, transforming the latter into nitric oxide, with an antithrombotic effect.
Nitrates are less toxic than nitrites, however at high concentrations they can cause motor and behavioral disturbances, food allergies and adverse reproductive effects. It is essential to underline that both nitrates and nitrites are present in considerable quantities in many foods, and are not always present as food additives added voluntarily, but they can also be inside foods due to fertilizers used in crops or pollution. of the water table.
Nitrates are used as food additives to increase the shelf life of foods and are used as antibacterials. On the other hand, nitrites are used in smaller quantities to enhance / preserve the color and flavor of the meat. The latter are rapidly absorbed in the intestine and little remain in the bloodstream; almost half of the nitrites are eliminated in the urine, but it is not yet known what happens to most of them; however, it was found that within 20-21 days of ingestion they disappear from the body.
It was highlighted by a group of Jordanian researchers, thanks to their study carried out on mice, that nitrites are able to predispose to carcinogenesis, and have negative effects on the immune system, considerably reducing the amount of T and B lymphocytes. , and leading to a consequent lowering of the immune defenses both at the humoral and cellular level; they also seem to reduce the weight gain of newborns and increase infant mortality.
