Determination of nitrates in plants. Quantification of nitrates in plant products

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Introduction

Relevance:

The problem of nitrates is actively discussed by the public of our country, but not everyone fully understood what it really is, how dangerous they are.

Nitrates are salts nitric acid, which are absorbed by plants from the soil, then turning into vegetable proteins. If their content in products is very high, then they enter the body not in the form of protein, but in a “pure” form, ”even if the use of fertilizers is completely abandoned, then the presence of nitrates in vegetable fruits will remain unchanged.

Nitrates existed on earth long before the appearance of man, without them, life itself is impossible. They (nitrates) are a source of nitrogen, which has great importance in plant life. Often, they are used for the normal supply of nitrogen to plants, which increases the intensity of photosynthesis, increases the assimilation surface of the leaves and their lifespan.

In small quantities, nitrates are constantly present in the human body, as well as in plants, and do not cause negative effects, but with improper use of nitrogenous fertilizers, vegetables and fruits accumulate in themselves dangerous for human body the amount of nitrates.

But the main assistants in the fight against nitrates are vitamins.

Vitamins are active chemical compounds involved in the body's metabolism and maintaining normal homeostasis. One of the most necessary and important vitamins for human health is ascorbic acid - Vitamin C (ascorbic acid).

What beneficial features vitamin C? It participates in the processes of hematopoiesis, has a beneficial effect on the functions of the immune, nervous system, is a stimulant in the work of the endocrine glands, without its participation normal absorption of iron is impossible. Also, vitamin C has powerful antioxidant properties, fights free radicals and removes them from the body.

Target:

To identify the features of the content of nitrates in the fruits of various vegetable crops.

Tasks:

Determine the concentration of nitrates in the fruits of various vegetable crops.

Establish the safest vegetables in terms of nitrates.

Chapter 1. Literature review

1. The problem of the distribution of nitrates in nature

Nitrates and nitrites are widely distributed in the environment, mainly in soil and water. They are an element of plant nutrition, as well as a natural component of food products of plant origin. A high concentration of nitrates in the soil is absolutely not toxic to plants; on the contrary, it contributes to enhanced plant growth, more active photosynthesis, and ultimately a higher yield.

The main source of nitrogen for plants are salts of nitric acid (nitrates) and ammonium salts.

AT vivo nitrogen nutrition occurs through the consumption of NO 3 - anion and NH 4 + cation by plants, which are in the soil solution and in the state exchange-absorbed by soil colloids. The mineral forms of nitrogen that enter plants go through a complex cycle of transformation, eventually being included in the composition of organic nitrogenous compounds - amino acids, amides, and, finally, protein. Synthesis of organic nitrogenous compounds occurs through ammonia, its formation is completed and their decay.

Nitrate nitrogen cannot be directly used by plants for the synthesis of amino acids.

Nitrates in plants initially undergo a step-by-step - through nitrite, hyponitrite and hydroxylamine - enzymatic reduction to ammonia:

The reduction of nitrates occurs with the participation of enzymes containing trace elements - molybdenum, copper, iron and manganese - and requires the expenditure of energy accumulated in plants during photosynthesis and oxidation of carbohydrates. The reduction of nitrates in plants is carried out as the resulting ammonia is used for the synthesis of organic nitrogenous compounds. They are natural metabolic products of nitrogenous substances of any living organism - plant and animal, therefore, products that do not contain nitrates do not exist in nature. Even in the human body per day is formed and used in metabolic processes 100 mg or more of nitrates. Of these, daily entering the body of an adult, 70% comes from vegetables, 20% from water and 6% from meat and canned foods.

The conditions of nitrogen nutrition have a great influence on the growth and development of plants. With a sufficient supply of nitrogen to plants, the synthesis of organic nitrogenous substances is enhanced in them. Plants form powerful leaves and stems with an intense green color, grow well and bush; the formation and development of fruiting organs improves. As a result, the yield and protein content in it sharply increase. However, with a one-sided excess of nitrogen, the maturation of plants is delayed, they form a large vegetative mass, but there are few grains or tubers and root crops; in cereals and flax, excess nitrogen can cause lodging.

With a lack of nitrogen, plant growth slows down sharply, the leaves are small, pale green in color, which is associated with a violation of the synthesis of chlorophyll, turn yellow prematurely, the stems become thin and branch weakly. The formation and development of reproductive organs and pouring grain, the yield and protein content in it are greatly reduced.

An excess amount of nitrates causes an abnormal functioning of natural ecosystems and living organisms, there is a decrease biological value products and increases negative impact on humans and animals.

The formation and accumulation of nitrates in soil and water becomes an environmental factor that determines not only the plant nutrition regime, metabolism and productivity, but also the quality of crops, water and air. The content of nitrates in excessive quantities worsens the biological quality of plant products, creates a potential hazard to human and animal health. A prime example their effect on the development of harmful intestinal microflora can serve, which leads to the ingestion of toxins into the human body, i.e. toxic substances, intoxication and poisoning of the body.

Nitrates significantly reduce the concentration of vitamins, which, in turn, contribute to the body's resistance to adverse effects. external environment which slows down the body's metabolism. 4

1. The problem of nitrate content in vegetables and measures to prevent them

Nitrates (salts of nitric acid) are a necessary attribute of the nitrogen cycle in nature, main part nitrogen nutrition of plants, without which complex biological processes of protein synthesis are impossible. Nitrates themselves are reduced in plants to nitrites, which, undergoing further transformations, give ammonia (NH3), the basis of plant nutrition. .

Plants need nitrogen to build protein. If it is not enough, the plants become pale, their leaves turn yellow. They slow down or completely stop the synthesis of chlorophyll, a disease called chlorosis.

Nitrogen accumulates very slowly in the soil. Every year, when harvesting, a person receives a significant part of nitrogen compounds from the soil. They do not have time to recover there, and their content falls all the time. Get high yield without enough nitrogen in the soil is impossible.

In itself, the presence of nitrates in plants is a normal phenomenon, but their excessive increase is highly undesirable, because. they are highly toxic to humans, or rather, their reduced form is nitrites.

According to the standards of the World Health Organization (WHO), the allowable daily dose of nitrates is 5 mg per 1 kg of body weight. If taken for average weight a person weighing 75 kg, then the allowable daily dose will be 375 mg.

The accumulation of nitrates in vegetables depends not only on the doses and terms of application mineral dressings, but also on their biological and species characteristics and ability to accumulate nitrates. Among environmental factors, their content in plants is most affected by humidity, light, air and soil temperature, which, acting in combination, enhance or weaken their interaction.

Also, changes in humidity have a strong effect on the accumulation of nitrates, intensive soil moisture enhances the absorption of nitrates by the roots, which, combined with low temperatures, leads to excessive accumulation of nitrates.

In reducing their content in vegetable products, the choice of optimal timing harvesting. So, harvesting leafy vegetables should be carried out in the evening, since at this time they contain 30-40% less nitrates. 5

Exist simple ways nitrate reduction:

Thoroughly rinse vegetables and fruits - reduces by 10%;

Mechanical cleaning - by 15-20%;

Cooking vegetables, especially peeled and chopped - by 50%;

Soak greens before eating cold water 1-1.5 hours - 20-30%;

The content of nitrates decreases during fermentation, salting, pickling.

In this case, the main means of prevention is to reduce the shelf life.

All salads, and especially vegetable juices and purees for children, should be cooked or canned just before eating.

If necessary, it is better to store ready-made products in the refrigerator, and no more than a day. Sterilization (boiling) of juices, soups - killing the microflora, also inhibits the formation of nitrites.

When purchasing vegetables in a store or on the market, we do not know all the details of caring for them. Therefore, the choice of vegetables should be made competently and correctly.

1. Maximum allowable concentrations of nitrates in vegetables

Maximum permissible concentrations of nitrates in crop products

(data from the Institute of Nutrition of the Russian Academy of Medical Sciences)

1. Individual features of some vegetable crops in relation to the accumulation of nitrates.

The accumulation of nitrates is hereditarily fixed. Grain crops practically do not accumulate nitrates. Among the families of vegetable crops, Cabbage, Pumpkin, Celery are distinguished by the greatest ability to accumulate nitrates.

The largest amount of nitrates accumulate: radish, table beet, cabbage, spinach lettuce, radish, potatoes.

Tomatoes, sweet peppers, eggplant, garlic, peas - have a low content of nitrates - 20-300 mg / kg.

In a number of vegetable and gourds varietal specificity of nitrate accumulation was revealed.

Species and varietal differences in the accumulation of nitrates are due to the genetically fixed capabilities of the reducing system of plants, in particular, the level of nitrate reductase activity, as well as different reactions on conditions environment and mode mineral nutrition.

Species differences in the accumulation of nitrates are often due to the localization of nitrates in individual plant organs, which, in turn, is associated with physiological specialization and morphological features individual organs, type and arrangement of leaves, size leaf petioles and veins, the diameter of the central cylinder in root crops.

Nitrates are practically absent in the grain of cereals and are concentrated, in this case, in the leaves and stems. Green crops accumulate a large number of nitrates in stems and petioles. This is due to the fact that stems and petioles are pathways for the transport of nitrates to other plant organs.

The accumulation of nitrates varies depending on the type of plant organ. In potato tubers, a low level of nitrate content was found in the pulp of the tuber, while in the peel and core, their content was 1-1.3 times higher than in the middle part.

The core, tip and top of the table beet differ from the rest of the root high content nitrates.

AT white cabbage the highest concentration of nitrates is observed in the upper part of the stem. top leaves contain twice as much nitrates, more than internal ones. The content of nitrates is especially high in leaf petioles.

In carrots, a high content of nitrates is observed at the top and at the end of the root crop, as well as in the core, and the nitrate content decreases from the tip to the top.

Chapter 2 Objects and methods of research

2.1. Express method for the determination of nitrates in fruits of vegetable crops

The most optimal method is the measurement of nitrates with devices designed for this purpose. But it is also possible to select vegetables without special devices.

How to choose vegetables that do not contain nitrates without auxiliary devices?

Since the allowable daily dose of nitrates for an adult is 325 mg per day, in order to meet these tolerances (300 - 325 milligrams of nitrates per day), it is not at all necessary to have your own expensive devices for determining nitrates or go shopping with indicator papers. Rely on state control, which, of course, is not without difficulties, but is gradually improving everywhere, and use our advice.

The first sign the presence of nitrates is a "chemical" Colour- too bright, artificial. Try to eat vegetables with a natural color.

Second sign -the size. They differ primarily in size: the minimum content of nitrates is more often found in medium-sized vegetables. Most small fruits are mostly young plants, which are characterized by an excess of nitrates, as a reserve for the future. unusual large fruits- often the result overnutrition, including nitrogen. After that, the nitrate content should be assessed with indicator papers.

In terms of the amount of nitrates, vegetables vary greatly both within the same batch and in different batches. Therefore, you can always choose low-nitrate vegetables, especially during the period of mass harvesting.

Third sign chemical content in vegetables and fruits - it's a smell. Most vegetables and fruits do not smell. They are filled with nitrates and other chemicals.

Fourth sign - taste. Fruits with a bitter taste or generally tasteless are also not worth buying.

Thus, we can slightly control the content of nitrates in consumer products, but we should remember that along with nitrates, vitamins are also eliminated.

Introduce berries and fruits into your diet, which are hanging fruits, they are low in nitrates.

Drinking green tea can neutralize nitrates that have already entered the body. 10

Chapter 3 Pilot study

3.1 Features of the content of nitrates in the fruits of various vegetable crops

To measure nitrates in vegetables, the SOEKS Nitrate Tester was used. The amount of nitrates in vegetables was measured in mg/kg. The results of the study are entered in the table.

Maximum permissible concentrations of nitrates in crop products (see point 1.3)

Findings:

The results of our study showed that the highest concentration of nitrates is found in sweet peppers, potatoes and radishes, while these crops are characterized by a high content of nitrates. Pepper sweet variety Swallow (at MPC 200 mg / kg) - 167.4 mg / kg; potato variety Nevsky (at MPC 250 mg/kg) - 165.2 mg/kg; radish variety Celeste (at MPC 1500 mg/kg) - 160.4 mg/kg (see Appendix 1)

The highest excess of MPC for nitrates was noted by us in onion of the Zolotisty variety by 31.8 mg/kg (see Appendix 1)

Thus, we have established the lowest concentration of nitrate characteristic of carrots of the Losinoostrovskaya variety (46.8 mg/kg) and eggplant of the Almaz variety (66.8 mg/kg), therefore, all the studied varieties of samples can be considered environmentally safe in this regard, with the exception of onion varieties Golden, where we noted an excess of nitrates, at a rate of 80 mg / kg, by more than 30 mg / kg, which can be explained as individual features of this variety in relation to the accumulation of nitrates, and the soil and climatic conditions of its cultivation (see Appendix 1)

Appendix 1

Bibliography

Ivanova I.V. "The harmful effects of nitrates and nitrites on the human body"

Tivo P.F, Saskevich L.A. "Nitrates. Rumors and Reality"

Paguzhe G.V. "Chemistry and everyday life human"

Kharkovskaya N.L., Lyashchenko L.F., Baryshova N.V. "Beware of nitrates!"

Varkoshkina N.M. "Nitrates in Plants"

Likholat T.V. “Reducing nitrates in crop production. School and production»

Sokolov O. Nitrates - under strict control. Science and life

Agricultural dictionary-reference book. - Moscow - Leningrad: State publishing house of collective and state farm literature "Selkhozgiz". Chief Editor: A. I. Gaister. 1934.

In itself, the presence of nitrates in plants is a normal phenomenon, because. they are sources of nitrogen in these organisms, but their excessive increase is highly undesirable, because. they (as we already know) are highly toxic to humans and farm animals.

Nitrates mainly accumulate in roots, root crops, stems, petioles and large leaf veins, much less in fruits.

Nitrates are also higher in green fruits than in ripe ones. Of the various agricultural plants, the most nitrates are found in lettuce (especially in a greenhouse), radish, parsley, radish, table beet, cabbage, carrots, dill:

• · in beets and carrots there are more nitrates in the upper part of the root crop, and in carrots also in its core.
• In cabbage - in the stalk, in thick leaf petioles and in the upper leaves.

It has also been found that all vegetables and fruits contain the most nitrates in their skins.

According to the ability to accumulate nitrates, vegetables, fruits and fruits are divided into 3 groups (2):

• 1. with a high content (up to 5000 mg / kg wet weight): lettuce, spinach, beets, dill, collards, radishes, green onion, melons, watermelons.
• 2. with an average content (300-600mg): cauliflower, zucchini, pumpkins, turnips, radishes, white cabbage, horseradish, carrots, cucumbers.
• 3. low content (10-80mg): Brussels sprouts, peas, sorrel, beans, potatoes, tomatoes, onion, fruits and berries.

From a physiological point of view, the amount of nitrate nitrogen in plants is determined by the ratio:

• absorption processes;
• transport;
• · assimilation;
• its distribution in different organs and parts of the plant.

And all these processes are due to a combination of soil and environmental conditions, agrotechnical and genetic factors.

Thus, the accumulation of nitrates in plants depends on a complex of many reasons:

• 1. from biological features plants and their varieties. It was found that the highest concentration of nitrates is found in the radish of the “Red Giant” variety compared to its other varieties (“pink with a white tip”, “heat”, etc.). The content of nitrates also depends on the age of the plants: there are more of them in young organs (except for spinach and oats). Less accumulated nitrates in hybrid plants. Nitrates are higher in early vegetables than in late ones.
• 2. from the regime of mineral nutrition of plants. So, trace elements (especially molybdenum) reduce the content of nitrates in radish, radish and cauliflower; zinc and lithium - in potatoes, cucumbers and corn. The content of nitrates in plants decreases and as a result of the replacement mineral fertilizers into organic (manure, peat, etc.), which gradually decompose and are absorbed by plants. organic fertilizers have a positive effect on cabbage, carrots, beets, parsley, potatoes, spinach. Irrational, negligent use chemical fertilizers, excessive doses of them lead to a strong accumulation of nitrates, especially in table root crops. The content of nitrates increases more strongly when using nitrate fertilizers ( KNO3, NaNO3, Ca(NO3)2 ) than with the use of ammonium. Behind last years(according to the head of the laboratory of food toxicology of the Institute of Nutrition T.S. Khotimchenko) there was a significant decrease in nitrates in domestic crop products due to less use of chemical fertilizers due to their high cost. If in 1988-89 MPC for nitrates exceeded 15% for vegetables, now it is no more than 3%.
• 3. The accumulation of nitrates also depends on environmental factors (temperature, air humidity, soil, intensity and duration of light illumination):
• 4. the longer the daylight hours, the less nitrates in plants;
• 5. During the wet and cold summer (1985), the amount of nitrates increased 2.5 times.
• 6. When the temperature was raised to 20°C, the amount of nitrates decreased in table beets by 3 times. Normal lighting of plants reduces the content of nitrates, so there are more nitrates in greenhouse plants (10)

The content of nitrates in plants also depends on the properties of the soil. The richer the soil in humus and total nitrogen, the more nitrates accumulate in carrot roots. The storage conditions of plants also affect the content of nitrates. It has been established that when vegetables are stored in open containers along with rotten vegetables, the nitrate content in them increases, and carrot roots or tomato fruits damaged by rot should not be processed. It is better to use vegetables of the season, i.e. when the vegetables grew open sky and not in a greenhouse in winter. Vegetables rich in nitrates should be stored for a short time and preferably in a cool and dark place. Do not store broken, damaged vegetables. Vegetables are best harvested from the garden in the evening.

When eating fruits, we must carefully monitor their quality. To keep apples longer, they are covered with an emulsion coating and saturated with preservatives. Such apples are outwardly very attractive, but sometimes they have no taste, no smell, no lively juiciness, and the preservatives in them kill its beneficial microflora in the human intestine. The same preservatives are used to store other products ( vegetable oil, sausages, sausages). Therefore, one must be vigilant about the certificates of imported products.

The issue of the accumulation of nitrates in the plants of our region began to be studied by the SakhNII Agricultural Institute since 1989, whose employees found out that on Sakhalin, due to special agrometeorological conditions, the content of nitrates in plants increases:

• 1. a large number of days, frequent fogs;
• 2. low solar radiation;
• 3. more low temperatures air and soil;
• 4. strong winds.

Ways to reduce the harm of nitrates in plants on the human body.

It is very important not only to know which plants, in which organs and parts of them contain mainly nitrates, but it is equally important to know how to reduce the content of these toxic substances for the body, so a number of valuable tips are offered:

• 5. The amount of nitrates decreases with heat treatment vegetables (13) (washing, boiling, frying, stewing and blanching). So, when soaking - by 20-30%, and when cooking by 60-80%.
• § in cabbage - by 58%;
• § in table beets - by 20%;
• § in potatoes - by 40%.

At the same time, it should be remembered that with increased washing and blanching (scalding with boiling water) of vegetables, not only nitrates go into the water, but also valuable substances: vitamins, mineral salts, etc.

• 4. To reduce the amount of nitrates in old potato tubers, its tubers should be poured with 1% sodium chloride solution.
• 5. Pattisons, zucchini and eggplant must be cut upper part, which is adjacent to the stem.
• 6. Because there are more nitrates in the peel of vegetables and fruits, then they (especially cucumbers and zucchini) must be peeled, and in herbs discard their stems and use only the leaves.
• 7. In cucumbers, beets, radishes, besides, both ends must be cut off, because. here the highest concentration of nitrates.
• 8. Keep vegetables and fruits in the refrigerator, because. at a temperature of + 2 ° C, it is impossible to convert nitrates into more toxic substances - nitrites.
• 9. To reduce the content of nitrites in the human body, it is necessary to use vitamin in food in sufficient quantities. With(ascorbic acid) and vitamin E, because they reduce the harmful effects of nitrates and nitrites (4).
• 10. It was found that when canning, the content of nitrates in vegetables decreases by 20-25%, especially when canning cucumbers, cabbage, because. nitrates go into the brine and marinade, which therefore must be poured out when eating canned vegetables.
• 11. Salads should be prepared immediately before their use and eaten immediately, leaving no sweat.

Nitrogen- is one of the most important chemical elements in plant life, because it is necessary for the synthesis of amino acids from which proteins are formed. Nitrogen is received by the plant from the soil in the form of mineral nitrogen salts (nitrate and ammonia).

Nitrogen undergoes complex transformations in plants.

Nitrogen metabolism in plants- This difficult process, and nitrates occupy an intermediate position in it:

HNO 3 - HNO 2 - (HNO) 2 - NH 2 OH + NH 3

(Nitrate) (Nitrite) (Hyponitrite) (Hydroxylamine) (Ammonia)

Nitrates in plants are reduced to nitrites. Various metals (molybdenum, iron, copper, manganese) are involved in this process, and at the same time, an intensive waste of carbohydrates occurs, because. energy is spent on recovery, the source of which is carbohydrates. Nitrites can accumulate in plants and inhibit their growth. But the main part of the nitrites, undergoing further transformations, gives ammonia (NH3).

In itself, the presence of nitrates in plants is a normal phenomenon, because. they are sources of nitrogen in these organisms, but their excessive increase is highly undesirable, because. they are highly toxic to humans and farm animals.

Nitrates mainly accumulate in roots, root crops, stems, petioles and large leaf veins, much less in fruits.

According to the ability to accumulate nitrates, vegetables, fruits and fruits are divided into 3 groups:

1)high content(up to 5000mg/kg wet weight): lettuce, spinach, beets, dill, collards, radishes, green onions, melons, watermelons.

2) with an average content(300-600mg): cauliflower, zucchini, pumpkins, turnips, radish, white cabbage, horseradish, carrots, cucumbers.

3) low content(10-80mg): Brussels sprouts, peas, sorrel, beans, potatoes, tomatoes, onions, fruits and berries.

Nitrates and water quality

A large amount of nitrates is contained in the collector and drainage waters draining agricultural areas where nitrogen fertilizers and manure are used. The concentration of nitrates in these waters can exceed 120 mg/l. Under natural (natural) conditions, their number does not exceed 9 mg / l. The largest amount (over 200 mg/l) of nitrates is found in domestic wastewater and in the effluents of livestock complexes.

Ground waters contain, as a rule, less nitrates than surface waters, since the soil serves as a kind of “filter” along the path of nitrate nitrogen movement. The deeper the groundwater lies, the less nitrates it contains.

The most rational way to reduce the concentration of nitrates in the surface and groundwater is to reduce the release of nitrogen and its oxides from natural and anthropogenic sources and limit their migration in agricultural landscapes. In areas of intensive use nitrogen fertilizers it is necessary to create protection zones to prevent the entry of mobile nitrogen compounds into water bodies, the water of which is used as drinking water.

The norms of nitrogen fertilizers should be environmentally safe, the timing and methods of their application are determined by taking into account the soil and ecological conditions of the agrolandscape and the biological characteristics of the plant's response to the nitrogen nutrition regime. For example, the system of application of nitrogen fertilizers in rice cultivation based on the local application of fertilizers to the soil, which reduces the flow of nitrates into the above-ground layer of water and eliminates the need for top dressing during the growing season from the aircraft. The last way application of nitrogen fertilizers poses the greatest threat to the quality of surface waters.

When disposing Wastewater animal husbandry is recommended to limit their use in undiluted form. The most acceptable and expedient is the mandatory dilution of effluents with water by 1.5 times with the mandatory introduction of phosphorus and potash fertilizers in doses necessary to fully provide plants with phosphorus and potassium and balanced to the amount of nitrogen used in wastewater.

In order to prevent excessive accumulation of nitrates in natural waters, to preserve and predict changes in water quality, it is necessary to establish regional and local control over their content in both natural and waste waters, while setting scientifically based standards for maximum permissible concentrations in all types of waters.

The harmful effects of nitrates on the human body

It is well known that the intake of nitrates is harmful to humans and farm animals. At the same time, it should be remembered that it is not nitrates themselves that are especially toxic to the body, but nitrites, into which they turn under certain conditions:

1) Nitrates under the influence of the enzyme nitrate reductase are reduced to nitrates, which interact with blood hemoglobin and oxidize 2-valent iron in it into 3-valent iron. As a result, the substance methemoglobin is formed, which is no longer able to carry oxygen. Therefore, the normal respiration of the cells and tissues of the body is disrupted (tissue hypoxia), as a result of which lactic acid and cholesterol accumulate, and the amount of protein drops sharply.

2) Nitrates are especially dangerous for infants, because their enzyme base is imperfect and the reduction of methemoglobin to hemoglobin is slow.

3) Nitrates contribute to the development of pathogenic (harmful) intestinal microflora, which releases toxic substances into the human body, toxins, resulting in toxication, i.e. body poisoning. The main signs of nitrate poisoning in humans are:

Blueness of nails, face, lips and visible mucous membranes;

Nausea, vomiting, abdominal pain;

Diarrhea, often with blood, enlargement of the liver, yellowness of the whites of the eyes;

Headaches, increased fatigue, drowsiness, decreased performance;

Shortness of breath, increased heartbeat, up to loss of consciousness;

With severe poisoning - death.

4) Nitrates reduce the content of vitamins in food, which are part of many enzymes, stimulate the action of hormones, and through them affect all types of metabolism.

5) Pregnant women have miscarriages, and men have a decrease in potency.

6) With prolonged intake of nitrates in the human body (even in small doses), the amount of iodine decreases, which leads to an increase in the thyroid gland.

7) It has been established that nitrates strongly influence the occurrence of cancerous tumors in gastrointestinal tract in a person.

8) Nitrates can cause a sharp expansion of blood vessels, resulting in lower blood pressure.

Permissible norms of nitrates for humans

Extremely for an adult allowable rate nitrates 5 mg per 1 kg of human body weight, i.e. 0.25g per person weighing 60kg. For a child, the allowable rate is not more than 50 mg.

It is relatively easy for a person to tolerate a daily dose of nitrates of 15-200 mg; 500 mg is the maximum allowable dose (600 mg is already a toxic dose for an adult). For poisoning baby 10 mg of nitrates is enough.

MPC of nitrates in water according to SanPiN 2.1.4.1175-02 " Hygiene requirements to water quality decentralized water supply. Sanitary protection of sources "is 45 mg / dm 3

Reverse osmosis and ion exchange are used to purify water from nitrates. In the first case, desalination of water should be carried out to such an extent that the concentration of nitrates will correspond to the norm. However, reverse osmosis removes all salts with little selectivity and results in demineralized water. The question of the usefulness of such water for the body and palatability is debatable. The cost of such water treatment is quite high. With a high content of nitrates, it is quite possible to use small installations reverse osmosis for the preparation of water for drinking purposes only.

Among the many reasons for the accumulation of nitrates in the plant, the following should be highlighted; species and varietal specificity of nitrate accumulation; conditions of mineral nutrition, soil-ecological factors. Often, factors contributing to the accumulation of nitrates act in combination, which complicates the prediction of the level of nitrates in products.

Plant species differences in nitrate accumulation are often due to the localization of nitrates in individual plant organs. Elucidation of the features of nitrate localization in different organs and tissues seems important both for understanding the mechanisms of redistribution and storage of nitrates during ontogenesis and for diagnosing the quality of vegetable and fodder crops.

Distribution of nitrates in plants

Knowledge of the distribution of nitrates in the marketable part of the product crop is of particular interest to the consumer, as it allows the rational use of products both for processing (boiling, juicing, fermentation, salting, canning) and for food in fresh. This, in turn, reduces the amount of nitrates entering the human body.

The distribution of nitrates is associated with the physiological specialization and morphological features of individual organs of cultivated crops, the type and arrangement of leaves, the size of leaf petioles and veins, and the diameter of the central cylinder in root crops. The distribution of nitrates is closely related to the plant species. So, nitrates are practically absent in the grain of cereal crops and are mainly concentrated in the stems and leaves. Green crops accumulate large amounts of nitrate, usually in stems and leaf petioles. The leaf blade of green crops contains 4-10 times less nitrates than the stems. The high content of nitrates in stems and petioles is due to the fact that they are the site of transport of nitrates to other plant organs, where they are assimilated to organic compounds nitrogen. The ability of tissue to accumulate nitrates is associated with a whole range of factors, both internal and external. The greatest number of them is in the lower 11th part of the sheet, the minimum - in its top.

The accumulation of nitrates varies depending on the type of plant organ. In potato tubers, a low level of nitrates was found in the pulp of the tuber, while in the peel and core, their content increased about 1.1-1.3 times. The core, tip and top of the table beet differ from the rest of its parts in a high content of nitrates. Therefore, in the table beet, it is necessary to cut off the upper and lower parts of the root crop.

In white cabbage the largest number nitrate is located at the top of the stem (stalk). The upper leaves of the head contain 2 times more of them than the inner ones. And just like green vegetables, cabbage leaf stalks have a higher content of nitrate nitrogen than leaf blades.

In itself, the presence of nitrates in plants is a normal phenomenon, since they are sources of nitrogen in these organisms, but an excessive increase in them is highly undesirable, since they (as we already know) are highly toxic to humans and domestic animals.

Nitrates mainly accumulate in roots, root crops, stems, petioles and large leaf veins, much less in fruits.

Nitrates are also higher in green fruits than in ripe ones. Most nitrates are found in lettuce (especially in a greenhouse), in radish, parsley, radish, table beets, cabbage, carrots, dill:

beets and carrots have more nitrates in the upper part of the root, and carrots also have more nitrates in its core;

in cabbage - in the stalk, in thick petioles and in the upper leaves.

It has also been found that all vegetables and fruits contain the most nitrates in their skin.

According to the ability to accumulate nitrates, vegetables, fruits and fruits are divided into 3 groups (2):

with an average content (300 - 600 mg): cauliflower, zucchini, pumpkins, turnips, radish, white cabbage, horseradish, carrots, cucumbers;

From a physiological point of view, the amount of nitrate nitrogen in plants is determined by the ratio:

absorption processes;

transport;

assimilation;

its distribution in different organs and parts of the plant.

And all these processes are due to a combination of soil and environmental conditions, agrotechnical and genetic factors.

Thus, the accumulation of nitrates in plants depends on a complex of reasons:

on the biological characteristics of the plants themselves and their varieties. It was found that the highest concentration of nitrates is found in the radish of the “Red Giant” variety compared to its other varieties (“pink with a white tip”, “heat”, etc.).

on the age of plants: in young organs there are more of them (except for spinach and oats). Less accumulated nitrates in hybrid plants. Nitrates are higher in early vegetables than in late ones.

on the mineral nutrition of plants. So, trace elements (especially molybdenum) reduce the content of nitrates in radish, radish and cauliflower; zinc and lithium - in potatoes, cucumbers and corn. The content of nitrates in plants also decreases as a result of the replacement of mineral fertilizers with organic ones (manure, peat, etc.), which gradually decompose and are absorbed by plants. Organic fertilizers have a positive effect on cabbage, carrots, beets, parsley, potatoes, spinach. Irrational, careless use of chemical fertilizers, excessive doses of them lead to a strong accumulation of nitrates, especially in table root crops.

The content of nitrates increases more with the use of nitrate fertilizers (KNO3, NaNO3, Ca(NO3)2) than with the use of ammonium fertilizers. In recent years (according to the head of the laboratory of food toxicology of the Institute of Nutrition T.S. Khotimchenko), there has been a significant decrease in nitrates in domestic crop products due to less use of chemical fertilizers due to their high cost. If in 1988-89 MPC for nitrates exceeded 15% for vegetables, now it is no more than 3%.

on environmental factors (temperature, air humidity, soil, intensity and duration of light illumination):

the longer the daylight hours, the less nitrates in plants;

during wet and cold summers, the amount of nitrates increased by 2.5 times.

with an increase in temperature to 20 °C, the amount of nitrates decreased in table beets by 3 times. Normal illumination of plants reduces the content of nitrates, so there are more nitrates in greenhouse plants.

When eating fruits, we must carefully monitor their quality. To keep apples longer, they are covered with an emulsion coating and saturated with preservatives. Such apples are outwardly very attractive, but sometimes they have no taste, no smell, no lively juiciness, and the preservatives in them kill the beneficial microflora in the human intestine. The same preservatives are used for the storage of other products (vegetable oil, sausages, sausages). Therefore, it is necessary to carefully monitor the certificates of imported products.

The issue of the accumulation of nitrates in the plants of our region began to be studied by the SakhNII Agricultural Institute since 1989, whose employees found out that on Sakhalin, due to special agrometeorological conditions, the content of nitrates in plants increases:

a large number of days, frequent fogs;

low solar radiation;

lower air and soil temperatures;