Each of us has at least once in a lifetime encountered the unpleasant consequences of consuming nitrate products. For some, such a meeting continued with a slight intestinal upset, while someone managed to get to the hospital and for a long time looked with apprehension at any fruits and vegetables bought on the market. The near-scientific approach and lack of awareness make a monster of nitrate capable of even killing, but it is worth getting to know these concepts better.
Nitrates and nitrites
Nitrites are salts of nitric acid that look like crystals. They dissolve well in water, especially in hot. On an industrial scale, they are obtained by the absorption of nitrous gas. Used to obtain dyes, as an oxidizing agent in the textile and metalworking industries, as a preservative.
Nitrates are salts of nitric acid, previously called nitrate. They are obtained after exposure to metals of nitric acid, and in themselves they are very strong oxidizing agents. Well soluble in water. The decomposition of nitrates occurs at temperatures above three hundred degrees Celsius. The main field of application of nitrates is agriculture, but some compounds use pyrotechnics as explosives, as well as components of rocket fuel.
The role of nitrates in plant life
One of the four main elements that make up a living organism is nitrogen. It is necessary for the synthesis of protein molecules. Nitrates are salt molecules that contain the amount of nitrogen a plant needs. Absorbed by the cell, salts are reduced to nitrites. The latter, in turn, along the chain of chemical transformations reach ammonia. And he, in turn, is necessary for the formation of chlorophyll.
Natural sources of nitrates
The main source of nitrates in nature is the soil itself. When the organic substances that it contains are mineralized, nitrates are formed. The speed of this process depends on the nature of land use, weather and the type of soil. The earth does not contain much nitrogen, so ecologists are not worried about the formation of a significant amount of nitrates. Moreover, agricultural work (harrowing, disking, constant use of mineral fertilizers) reduces the amount of organic nitrogen.
Therefore, natural sources cannot be considered a factor in the pollution of groundwater and the accumulation of nitrates in plants.
Anthropogenic sources
Conventionally, anthropogenic sources can be divided into agricultural, industrial and municipal. Fertilizers and livestock waste belong to the first category, industrial wastewater and industrial waste to the second. Their effect on environmental pollution is not the same and depends on the specifics of each particular region.
The determination of nitrates in organic materials gave the following results:
- more than 50 percent is the result of a harvesting campaign;
- about 20 percent - manure;
- municipal waste is approaching 18 percent;
- everything else is industrial waste.
The most serious damage is caused by nitrogen fertilizers, which are introduced into the soil to increase the yield. The decomposition of nitrates in the soil and plants forms a sufficient amount of nitrite for food poisoning. Agricultural intensification only exacerbates this problem. The highest level of nitrates is noticed in the main drains, which collect water after irrigation.
Effects on the human body
Nitrates and nitrites first compromised themselves in the mid-seventies. Then in Central Asia, doctors recorded an outbreak of watermelon poisoning. During the investigation, it was found that the fruit was treated with ammonium nitrate and, apparently, a little overdone. After this incident, chemists and biologists closely engaged in the study of the interaction of nitrates with living organisms, in particular man.
- In the blood, nitrates interact with hemoglobin and oxidize the iron in its composition. This forms methemoglobin, which cannot carry oxygen. This leads to disruption of cellular respiration and oxidation of the internal environment of the body.
- By disrupting homeostasis, nitrates contribute to the growth of harmful microflora in the intestine.
- In plants, nitrates reduce the content of vitamins.
- An overdose of nitrates can lead to termination of pregnancy or to impaired sexual function.
- In chronic nitrate poisoning, a decrease in the amount of iodine and a compensatory increase in the thyroid gland are observed.
- Nitrates are a trigger factor for the development of tumors of the digestive system.
- A large dose of nitrates at the same time can lead to collapse due to a sharp expansion of small vessels.
Nitrate metabolism in the body
Nitrates are derivatives of ammonia, which, getting into a living organism, are built into the metabolism and change it. In small quantities, they do not cause concern. With food and water, nitrates are absorbed in the intestines, pass through the liver through the blood stream and are excreted from the body by the kidneys. In addition, in nursing mothers, nitrates pass into breast milk.
In the process of metabolism, nitrates turn into nitrites, oxidize the iron molecules in hemoglobin and disrupt the respiratory chain. In order for twenty grams of methemoglobin to form, just one milligram of sodium nitrite is enough . Normally, the concentration of methemoglobin in the blood plasma should not exceed a couple of percent. If this indicator rises above thirty, poisoning is observed, if above fifty - it is almost always fatal.
To control the level of methemoglobin in the body there is methemoglobin reductase. This is a liver enzyme that is produced in the body starting from three months of life.
Permissible nitrate rate
Of course, the ideal option for humans is to avoid the ingress of nitrates and nitrites into the body, but this does not happen in real life. Therefore, the doctors of the sanitary-epidemiological station established the norms of these substances, which can not harm the body.
For an adult with a weight of more than seventy kilograms, a dose of 5 milligrams per kilogram of weight is considered acceptable. Without serious health consequences, an adult can swallow up to half a gram of nitrate. In children, this indicator is more averaged - 50 milligrams, regardless of weight and age. At the same time, a fifth of this dose will be enough for a baby to be poisoned.
Penetration paths
You can get nitrate poisoning alimentarily, that is, through food, water and even medications (if they include nitrate salts). More than half the daily dose of nitrates enters a person with fresh vegetables and canned goods. The remaining dose comes from baking, dairy products and water. In addition, an insignificant part of nitrates is a metabolic product and is formed endogenously.
Nitrates in water is an occasion for a separate conversation. It is a universal solvent, therefore, it contains not only useful minerals and trace elements necessary for normal human life, but also toxins, poisons, bacteria, helminths, which are causative agents of dangerous diseases. According to the World Health Organization, about two billion people fall ill due to poor-quality water each year, and more than three million die of them.
Chemical fertilizers containing ammonium salts seep through the soil and enter underground lakes. This leads to the accumulation of nitrates, and sometimes their amount reaches two hundred milligrams per liter. Artesian water is cleaner, as it is extracted from the deeper layers, but toxins can also get into it. Residents of rural areas along with well water daily receive eighty milligrams of nitrates from each liter of drinking water.
In addition, the nitrate content in tobacco is high enough to cause chronic poisoning among smokers with long experience. This is another argument in favor of combating addiction.
Nitrates in products
During the culinary processing of products, the amount of nitrates in them is significantly reduced, but at the same time, violation of storage rules can lead to the opposite effect. Nitrites, the most toxic substances for humans, are formed at temperatures from ten to thirty-five degrees, especially if the food storage location is poorly ventilated, and the vegetables are damaged or they begin to rot. Nitrites are also formed in thawed vegetables; on the other hand, deep freezing prevents the formation of nitrites and nitrates.
Under optimal storage conditions, you can reduce the amount of saltpeter in foods up to fifty percent.
Nitrate poisoning
Signs of nitrate poisoning :
- blue lips, face, nails;
- nausea and vomiting, there may be abdominal pain;
- yellowness of eye proteins, stool with blood;
- headache and drowsiness;
- noticeable shortness of breath, palpitations and even loss of consciousness.
Sensitivity to this poison is more pronounced in conditions of hypoxia, for example, high in the mountains or with carbon monoxide poisoning or heavy alcohol intoxication. Nitrates enter the intestines, where the natural microflora metabolizes them to nitrites. Nitrites are absorbed into the systemic circulation and affect hemoglobin. The first signs of poisoning can be replaced after an hour with a large initial dose or after six hours if the amount of nitrates was small.
It should be remembered that acute nitrate poisoning in its manifestations is similar to alcohol intoxication.
It is impossible to separate our life from nitrates, because it will affect all areas of human life: from nutrition to production. However, you can try to protect yourself from excessive consumption by observing simple rules:
- wash vegetables and fruits before eating;
- store food in refrigerators or in specially equipped rooms;
- drink purified water.