Nitrate content is an important quality characteristic of vegetables. Nitrate is of particular importance among the various forms of Nitrogen element, due to its potential for accumulation in plant tissues. Vegetable nitrate content is of interest to governments and regulators owing to the possible implications for health and to check that controls on the content are effective. Nitrate by itself is relatively non-toxic but its metabolites and reaction products such as nitrite, nitric oxide, and nitrous compounds, have a detrimental effects on human and animal health. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis.
Excessive levels of nitrate and nitrite threaten the health of infants and children. The most important disease caused by severe nitrate toxicity is infantile methaemoglobinaemia, in which hemoglobin (ferrous iron) is converted to methemoglobin (ferric iron).
This reaction reduces the affinity of iron for oxygen and disrupts the body's ability to carry oxygen. The affinity for oxygen of ferric iron is impaired. The binding of oxygen to methemoglobin results in an increased affinity for oxygen in the remaining heme sites that are in ferrous state within the same tetrameric hemoglobin unit. This leads to an overall reduced ability of the red blood cell to release oxygen to tissues, with the associated oxygen–hemoglobin dissociation curve therefore shifted to the left. When methemoglobin concentration is elevated in red blood cells, tissue hypoxia may occur.
Therefore, due to continued consumption of vegetables or drinking water with high nitrate levels, Nitrosamine is produced in the gastrointestinal tract, which is toxic and dangerous and increases blood cancers, brain and throat tumors in adults. In livestock, the conversion of nitrate to nitrite in the digestive tract leads to nitrite toxicity in ruminants. Today, due to the inappropriate use of nitrogen fertilizers to accelerate vegetative growth, many vegetables and cucurbits, especially leafy vegetables have high concentrations of nitrate and nitrite, which in most cases these concentrations are higher than the permissible limits.
Potato, onion and cucumber account for 30, 11.7 and 24.02 percent of the total production compared to all vegetable and cucurbits products in the country, respectively. Due to the nature of nitrate as well as the challenges in its measurement methods, published reports regarding the amounts of nitrate in these products are not conclusive.
[ Investigation of nitrate status in cucumber, potato and onion produced in important cultivation areas of the country.
[ Risk assessment of Nitrate in the above products.
[ Revision of National Standard No. 16596 according to the results of studied products.