Экологическая медицина = Ecological medicine. Учебное пособие

3)  substances introduced specifically for technological reasons. Foreign substances can be of different nature, both chemical and bio-

logical (Table 6.1.)

Table 6.1. Classification of foreign substances

Foreign substances

One of the most important physiological and hygienic requirements for human nutrition is the harmlessness of food.

The food consumed must be free from harmful chemicals and biological agents or contain them in quantities (concentrations) and forms that cannot negatively affect human health and the health of offspring.

Food contamination as a result of anthropogenic environmental pollution, as well as violations of sanitary and hygienic norms and rules at various stages of food movement from production facilities to their consumption can cause food poisoning of microbial nature (food toxicosis or toxicoinfection), infections (typhoid fever, paratyphis A and B and other salmonellosis dysentery, brucellosis, tuberculosis, foot-and-mouth disease, tularemia, etc.) and helminthiasis (teniidosis, trichinosis, diphyllobothriasis, opisthorchiasis, ascariasis, etc.).

An equally important indicator of food harmlessness is the degree of contamination with harmful foreign chemical substances – xenobiotics. Contamination of food by alien substances (pesticides, salts of heavy metals, radionuclides, nitrates and nitrites, nitrosamines, synthetic chemical compounds, polycyclic aromatic hydrocarbons, mycotoxins, etc.) depends

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largely on the environmental situation and, in particular, on soil quality. Food products are the main source of ingestion of xenobiotics from the environment. For example, nitrates enter the human body mainly with vegetables (about 70%), and the rest come with water; nitrites enter with meat products, radionuclides (94%) come with food of plant and animal origin. The environmentally stable pesticides enter the body with food (95%), with water (47%), with atmospheric air (only 0.3%) and very small amounts enter through the skin.

Foreign chemicals enter the body through the chain: “soil-plant-hu- man” or “soil-vegetation-animals-human”. At the same time, the main migration of xenobiotics through the food chain takes place in all biological species of terrestrial and aquatic ecosystems.

At the same time, there is a significant accumulation of xenobiotics in the aquatic food chain. This is attributed to the fact that hydrobionts (fish, mollusks, crustaceans, etc.) not only lack a mechanism that protects them from accumulation of harmful foreign chemical substances, but also accumulate them vigorously. The degree of contamination by foreign chemical substances increases with the growth of the trophic position of certain ecosystem species. For example, the concentration of xenobiotics in the tissues of predatory fish, birds, and animals is higher compared to the species they eat. All food products have substances contained in the biosphere as their initial sources. Humans are the final link in numerous food chains that have developed in the course of long evolution, where some living organisms serve as food for others.

Currently, to increase food resources and improve the quality of products in agricultural and industrial production, a variety of substances are widely used. The consequences of their exposure to humans can be the most unfavourable. Some of them are carriers of toxic, mutagenic, carcinogenic, teratogenic properties or precursors of compounds with such properties. They may also acquire these properties if the regulations for their use are violated.

Agrochemicals, which are now widely used for the intensification of agricultural production, do not represent toxic compounds that can accumulate in food and have adverse effects on the human body. However, when violating the regulations on the quantity, application periods, multiplicity, waiting periods, the resulting food raw materials can contain sufficiently high concentrations, primarily nitrogenous compounds, which include nitrates.

The presence of nitrates in plants is quite normal. But when nitrates are present in amounts exceeding the needs of organic synthesis, they begin to

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accumulate in the roots, leaves, and most importantly, in fruits of various agricultural crops, both directly consumed by humans and forage crops used for livestock feed. Their unprocessed surpluses under the influence of nitrate reductase (an enzyme contained in plant tissues) are restored into nitrites, which have an adverse effect with these compounds under the influence of microflora directly in the mouth, and then in the gastrointestinal tract. As for agricultural products, the main suppliers are potatoes and vegetables. The accumulation of nitrates in vegetable crops is largely determined by their biological characteristics. Vegetables characterised by the ability to accumulate large amounts of nitrates include the green ones such as lettuce, spinach, dill, kohlrabi cabbage, rhubarb, radish and especially garden beet. Pattissons and pumpkins are prone to this as well. Their nitrate content ranges from 1,200 to 5,000 mg/kg of wet weight. Aubergines, melons, cabbage, carrots, cucumbers, parsley, celery, garlic, and beans take the middle position, i.e., 100–1,000 mg/kg. Relatively low concentrations are found in watermelons, green peas, potatoes, onions, peppers, tomatoes (60–90 mg/kg). The concentration of nitrates in vegetables grown indoors is usually twice as high as in the open ground. Different parts of plants have different levels of nitrates. The skin and surface layers of fruits have significantly higher nitrate content. White cabbage has the most nitrates in the upper leaves and the core, beets have the highest nitrate content in the upper part and the tail, and carrots have the highest nitrate content in the central part.

Nitrates are absorbed mainly in the stomach. Up to 90% of the nitrates ingested are excreted in the urine within 8 hours. When large amounts of nitrates are ingested, eating foods containing 800–1,300 mg/kg of nitrate ions (mashed beets, spinach, other non-fresh vegetables) can lead to acute poisoning. Clinical signs of poisoning occur 1–6 hours after their ingestion and are characterised by dyspeptic disorders in combination with enlarged liver, its painfulness on palpation, sclera sub-ectericity. There may also be symptoms from the nervous system such as general weakness, dizziness, darkening of the eyes, impaired coordination of movements. Vasodilating effect of nitrates leads to decreased blood pressure, sinus arrhythmia, chest pain, shortness of breath.

Nitrates themselves are not methaemoglobin-forming compounds. However, some nitrates are converted to more toxic compounds – nitrites – resulting in nitrite methaemoglobinaemia when the food itself is improperly stored, when microflora develops in the food and in the digestive tract. Low gastric acidity in infants can contribute to this process.

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Nitrites can enter the body directly with products of food raw materials of animal origin, in particular with meat products and cheeses.

Sodium nitrite is used when producing sausages and ham products as part of the technology for preserving the pink colour of meat products and partly as a preservative. Nitrite is used for the same purpose in cheese production.

The maximum level of methaemoglobin in the blood is observed 1 hour after the intake of increased doses of nitrates. Asymptomatic cyanosis may occur at 8–10%, and symptoms of acute hypoxia (shortness of breath, tachycardia, brownish-gray cyanosis, hypotension, weakness, headache) can be observed when its content is 30% or higher.

But the most dangerous of nitrogenous compounds are nitrosamines. These compounds can be formed both directly in foods and in the body at high concentrations of nitrites in the stomach. A prerequisite is also the presence of free amine groups in the protein. The main danger of nitrosamines is that they have carcinogenic, mutagenic, teratogenic and embryotoxic properties, with the carcinogenic effect being the most critical. N-nitrosamines are found in almost all meat, dairy and fish products, as well as beer malt.

Currently, when producing agricultural products of both plant and animal­ origin, a wide variety of chemical compounds, combined in a group called pesticides, are widely used. Pesticides are substances of chemical and biological origin intended for chemical protection of plants and animals. The use of pesticides still has significant environmental and health risks. Environmental hazards are associated with the inevitable contamination of not only cultivated areas, but also the global distribution of pesticides in the biosphere and in the lithosphere in particular. Once in the soil and then in crop and livestock products, they are in wide contact with a large part of the population, including children, pregnant and lactating women.

Nowadays different classifications of pesticides are used: industrial, chemical, hygienic.

The production classification of pesticides is based on the purpose and direction of their use:

yyinsecticides and acaricides – for killing insect pests; yymolluscicides – for killing slugs;

yynematicides – for destroying nematodes (worms); yyrodenticides – against rodents;

yyrepellents – for repelling rodents; yyfungicides – for destroying moulds and fungi; yyherbicides – for destroying weeds;

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yydefoliants and desiccants – for pre-harvest removal of leaves from cultivated plants;

yypheromones – for controlling insects by trapping; yyentomophages – for controlling insect populations.

Based on the chemical structure, there are organochlorine, organophosphorus, mercury-containing, arsenic-containing, carbamic acid derivatives, urea and guanidine derivatives, heterocyclic compounds and others.

Hygienic classification provides for division of pesticides according to toxicity, cumulation ability, magnification, resistance in the external environment (decomposition time into non-toxic elements), presence of longterm effects, effect on the foetus and allergenicity. By the parameters of hygienic classification, they are subdivided into 4 classes. Most pesticides belong to Hazard Classes 2 and 3. At present, there are about 600 pesticides based on 300 active substances.

Violation of hygienic norms of storage, transportation, and application regulations of pesticides leads to their accumulation in forage, food raw materials and food products. Once in the human body, they have a versatile toxic effect, depending on the features of the chemical structure and the entry dose.

The effects of pesticides are particularly dangerous due to their longterm consequences and effect on the foetus. Each of them may have one or more of the following effects: carcinogenicity, mutagenicity, teratogenicity, embryotoxicity, gonadotropicity, allergenicity.

Most pesticides are not relatively harmless and are either highly toxic (organophosphorus, mercury-containing, arsenic-containing) or highly cumulative and persistent (organochlorine, carbamates). They can also cause long-term effects. When pesticides enter the body, depending on the dose, they can cause acute, sub-acute and chronic intoxications. At the same time, all pesticides are xenobiotic and cause adaptive changes in the body.

The mechanisms of biological (toxic) action of low doses are based on violations of antioxidant protection, stability of structural and functional parameters of biomembranes, leading to disorganisation of cell structure and function. All this eventually leads to changes in various systems of the body, violation of protective-adaptation mechanisms to the development of secondary immunodeficiencies.

Pesticide poisoning develops in stages and undergoes:

yylatent period (from the moment of entering the body until the first manifestations of intoxication – from several hours for acute poisonings to several days for subacute ones);

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yyperiod of precursors, characterised by non-specific, similar to many chemical compounds’ manifestations (nausea, vomiting, general weakness, headache);

yyperiod of severe intoxication, when specific signs of poison influence on the organism are manifested along with the changes common for many chemical substances.

Subacute poisonings are characterised by less violent reactions than during acute poisonings and by a longer pathological process.

Chronic poisoning develops with prolonged ingestion of small doses of pesticides and cumulation in tropic organs.

Importantly, children, adolescents, the sick and weakened individuals are particularly susceptible to pesticides.

They are especially dangerous for pregnant and breastfeeding women. Many pesticides penetrate through the placental barrier and can have a toxic effect on the foetus, causing embryotoxic and teratogenic consequences. If the pesticides get into the infant’s body with the mother’s milk, they can also cause intoxication of the infant.

Monitoring results of recent years show an increase in the total content of pesticides in products of plant and animal origin, including fish. This is especially true for products such as potatoes, onions, cabbage, tomatoes, cucumbers, carrots, beets, apples, grapes, wheat, barley, fish from ponds and reservoirs, and milk. They detect a wide range of pesticides.

Chemical elements are well distributed in nature in various ways, primarily they can get from soil to agricultural raw materials and through food to the human body.

Most chemical elements, including metals, are vital for humans. While the role of certain elements in the body is already known, others have yet to be defined. It is necessary to take into account that macroand microelements exhibit biological and physiological effects only in certain quantities. In large quantities, they already have a toxic effect on the body. Sources of food contamination with chemical elements are wastes of industrial enterprises, exhaust gases of transport vehicles, mining. The list of the most serious toxic elements includes 8 chemical substances: mercury, cadmium, lead, copper, zinc, iron, strontium, arsenic.

At present, there is no tendency to reduce the pollution of food products with xenobiotics, including salts of heavy metals. This is related to technogenic pollution of natural environment, violation of acting norms and rules during product manufacturing.

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In terms of hygiene, the priority metals are mercury, lead and cadmium, as well as arsenic (traditionally considered in combination). These elements, besides high toxicity, have the ability to accumulate in the body at prolonged intake even in small doses and cause long-term consequences – mutagenic and carcinogenic (for arsenic and lead). Other heavy metals can enter products during their manufacturing.

Tin and chromium occur in canned products when they are packed in prefabricated tin and chrome-plated containers; nickel enters products with hydrogenated fat (margarine, cooking and confectionery fats); iron and copper occur in long-stored fat products; zinc appears in pectin.

There is a particularly high probability of heavy metal salts entering food raw materials obtained in areas of geochemical anomalies with their high content in the soil, in areas where metallurgical, machine-building, chemical industry enterprises are located, as well as near major highways and industrial cities.

A number of conditions influence the accumulation of xenobiotics in agricultural products. On the one hand, this is the level of soil contamination and, on the other hand, biological characteristics of plants. Selective toxicity of salts of heavy metals and arsenic is mainly concentrated in the epithelium of the kidneys, the liver and the intestines, the erythrocytes and the nerve cells; therefore, nephropathy, toxic liver dystrophy, severe neurological symptoms, and hemolysis often prevail in the clinic of these poisonings.

For example, lead toxicity primarily affects the haematopoietic organs (anaemia), the nervous system (encephalopathy and neuropathy), and the kidneys (nephropathy). The early stages of chronic lead intoxication are characterised by a decrease in the body’s adaptive abilities and resistance to toxic infectious and other pathological agents. A variety of symptoms may follow, including general weakness, headaches, dizziness, bad taste in the mouth, loss of appetite, limb tremors, weight loss, constipation, abdominal pain, and signs of anaemia.

Cadmium, being a highly poisonous substance, in acute intoxication causes nausea, vomiting, diarrhoea, abdominal cramps, and in severe cases it leads to shock. Chronic poisoning attacks bones (osteoporosis), kidneys, develops hypertension, anaemia. The nervous system is affected by tremor, dizziness, headache, dermographism.

As a result of chronic mercury lesions, the central nervous system, liver, and excretory organs such as the kidneys and the intestines are affected, leading to headaches, rapid fatigability, weakened memory, anxiety, apathy, diminished appetite, and weight loss. In severe cases, skin sensitivity to the

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extremities is reduced, paresthesia around the lips appears, visual fields are narrowed, and the emotional sphere is disordered. Mercury has gonadoand embryotoxic, teratogenic and mutagenic effects.

There are similar clinical manifestations of poisoning caused by other metals. In contrast, in chronic arsenic poisoning, the clinical picture is very polymorphic. After such initial symptoms as loss of appetite, nausea, vomiting, dyspeptic phenomena, there appears symmetrical warty keratosis of palms and soles, melanosis combined with areas of skin depigmentation, atrophy, and fragility of nails (Mayo lines – transverse white stripes on nails are of diagnostic value), hair loss. There are a number of neurological symptoms that manifest themselves, such as intellectual and speech difficulties, depression, polyneuritis, followed by paresthesia and subsequent muscle atrophy, as well as taste and smell disorders. Power plant emissions, industrial effluents, and arsenic-containing pesticides are powerful sources of arsenic pollution in the environment. It enters the body through animal products, including fish and seafood.

Xenobiotics of anthropogenic origin also include polychlorinated biphenyls, including dioxin and furan. They get into the environment as a result of the activities of various industries related to waste recycling, as a result of combustion of various fuels, production of a number of enterprises of petrochemical, pulp and paper and metallurgical products, synthetic materials. The peculiarity of these substances is that despite their inability to be destroyed in the external environment, they accumulate in different environments, especially in water and bottom sediments, and progressively concentrate along the food chain.

The main way they enter the body is alimentary. Polychlorinated biphenyls are carcinogenic substances. Sensitising, hepatotoxic effects and the ability to cause secondary immunodeficiency have been noted. People chronically exposed to these substances have been found to suffer from increased cancerous diseases, endocrine diseases (diabetes mellitus), cardiovascular diseases, and hereditary and reproductive disorders. These substances can accumulate and enter the body with almost any products of animal origin, concentrating in the higher-fat products and their components. Fish and seafood are the most dangerous products in this regard. But these substances may be present in dangerous concentrations in meat and dairy products. Their ability to accumulate in milk, where their content can be 40–200 times higher than in animal tissues, has been noted. The permissible daily dose of these substances for humans, according to the WHO recommendations, is 10 ng/kg.

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The diversity of landscapes and natural zones determines the peculiarities of the circulation and accumulation of atoms of these or other chemical elements in the soil. Proceeding from this, A.P. Vinogradov substantiated the doctrine of bio-geochemical provinces, i.e., uneven distribution of chemical elements on the globe in accordance with peculiarities of geological and soil-forming factors. As a result, in some areas the soil and agricultural products contain some trace elements in a small amount, while in other areas they are more abundant. Deficiency, excess, or imbalance of microelements can lead to the development of specific diseases, known as geochemical endemics.

There are certain regularities in iodine distribution in the atmosphere, water, and soil. The most of it is concentrated in seawater, air, and soil in coastal areas. There is also the highest iodine content in plant foods such as grains, vegetables, fruits, and foods of animal origin such as meat, milk, eggs. A lot of iodine is found in sea fish, algae, and other seafood.

The dependence of iodine content in the environment on the content of organic matter in the soil has been noted, which is of great importance for the emergence of geographical areas with insufficient iodine content in the environment, including the soil and, as a consequence, food products.

Insufficient intake of iodine in the body leads to the emergence of such a disease as goitre, which is characterised by visible enlargement of the thyroid gland. Areas in which a large part of the population has clinical manifestations of the disease are considered endemic. Endemic goitre occurs both in mountainous areas (the Alps, the Altai, the Himalayas, the Karpaty etc.) and in lowland areas (Western Ukraine, upper Volga, some regions of Transbaikalia and the Far East, Polesie and others). These areas include most of the territory of Belarus.

As a result of iodine deficiency in children’s diet, a symptom-complex is formed, characterised by mental and physical retardation, up to stunting and cretinism. In adults, iodine deficiency is characterised by the development of endemic goitre, resulting in reduced thyroid function.

The presence in the diet and the environment of the so-called strumogenic substances (zobogens) is of considerable importance. Their action is based on the ability to block the stages of iodine metabolism in the thyroid gland, resulting in a decrease in its total amount, which affects the thyroid gland. Zobogens include mercury, arsenic, and antimony, which combine with iodine and convert it to an inactive state. Negative effect on the occurrence of thyroid gland lesions also has an incomplete monotonous diet with a deficit of protein and vitamins. Insufficient intake of bromine, zinc,

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cobalt, copper, molybdenum, as well as an incorrect ratio of trace elements (excess fluorine, manganese, chromium) is of paramount importance in the development of goitre endemia.

In areas contaminated with halogen-organic compounds, the same conditions can be created as in the foci of goitre endemia and iodine deficiency. High concentrations of nitrates in drinking water are also an aggravating factor in the aetiology of endemic goitre on the background of even mild insufficiency.

The factors mentioned above may simultaneously intensify iodine deficiency in organisms and decrease the outcome of dietary supplementary iodine, as well as affect the efficacy of iodine prophylaxis programs and complex treatment of diseases requiring iodine.

As a rule, state programs implemented in this context consist of information exchange, improvement of the iodized salt provision system and production of food products containing additional iodine, development of a monitoring system for assessment of efficiency of measures taken. The Republic of Belarus has also adopted a number of documents at the governmental level aimed at elimination of iodine deficiency syndrome among the population, including provision of iodized salt to the population.

In some parts of Europe, including Belarus, there is a lack of selenium in the soil. Residents experience an endemic deficiency of selenium in food, resulting in cardiopathy and Keshan’s disease.

At high levels of selenium in the soil, people may have selenium toxicosis. The most typical symptoms are nail damage and hair loss, jaundice, peeling of the epidermis, dermatitis, damage to dental enamel, anaemia, and nervous disorders.

In countries with a deficit of this element, several measures are taken to prevent related diseases. They use both tablet selenium forms and food enrichment. Selenium enrichment of yeast eliminates its loss in the environment, which is the most effective method. Selenium-enriched yeast also has chemopreventive activity against human cancers. As a way to prevent selenium-deficiency conditions, mass consumption of selenium-en- riched food products can also be developed.

A prerequisite for the effective implementation of all programs for the elimination of deficiencies in the intake of necessary elements for the body is the organisation of effective medical monitoring of their implementation.

The human body needs various nutrients, which can only come from food. Food is a complex multi-component system, consisting of hundreds of chemical compounds. Modern human beings consume about 800 grams

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