Экологическая медицина = Ecological medicine. Учебное пособие

­contained up to 5.7 mg/kg of methylmercury, and if cats consumed that fish, they died of mercury poisoning.

–  Kashin-Beck disease (endemic deformation) is found in China (about 2 million people are ill, more than 30 million live in endemic areas), the Far East, the Amur Region, and the Chita Region. The disease usually develops in children aged 5–13, being manifested by multiple degeneration and necrosis of articular cartilage, muscular dystrophy, growth retardation, skeletal deformities.

Currently, there are several hypotheses for the development of Kash- in-Beck disease: the effect of aflatoxins; Fusarium oxysporum fungi; strontium (“strontium rickets”); increased content of humic acids in well water, combined with low concentrations of selenium; imbalance of some microand macroelements, including selenium. Therapy with selenium-contain- ing drugs reduces radiological manifestations and reduces the risk of skeletal deformities. Relocation to areas where drinking water contains normal concentrations of selenium also reduces the risk of disease development and reduces the severity of the clinical picture in sick children. Currently, the hypothesis of the link between Kashin-Beck disease and humic acids in drinking water is most confirmed by experimental and in-situ data. An important role in the mechanism of this disease is played by free-radical reactions involving oxyand hydroxy-groups of humic acids, as well as the induction of lipid peroxidation in the liver, bone tissue and blood. Adding selenium to drinking water inhibits free radical formation in the bone tissue.

–  Itai-Itai disease was discovered in 1946 in Japan (Toyama). The cause of the diseases was an increased intake of cadmium into the body with rice grown in fields irrigated from the Dzintsu River, where cadmium entered with the effluents of the upstream mine. The disease was characterised by severe pain, skeletal deformity, bone fractures, kidney damage. Cadmium is very slowly excreted from the human body, and poisoning can take a chronic form. More than 150 people died from chronic cadmium poisoning 15–30 years after the first detection of the disease. Cadmium is considered the most dangerous heavy metal. It has carcinogenic properties.

Deficiency, excess, or imbalance of trace elements entering the body from the external environment can cause a number of exogenous microelement diseases, in particular, with water (endemic fluorosis, endemic goiter, dental caries, etc.).

Endemic fluorosis, associated with excessive intake of fluoride, affects more than 20 million people in the world. Its foci are well studied in North America, Europe and some Asian countries. In India, the problem of

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fluorosis­ acquired a national importance, and the natural area of its distribution is called “fluorosis belt”. In the CIS, the highest amount of fluoride is contained in drinking water in Moldova, south-east Ukraine, the Paleozoic Basin near Moscow, the Urals, and many regions of Kazakhstan.

Small concentrations of fluoride in drinking water, which is one of the causes of mass dental caries, are noted in the North of Russia, Siberia and the Far East.

Another example is endemic arsenosis, a disease caused by excessive intake of inorganic forms of arsenic into the body with drinking water. The most well-known endemic foci of arsenazo are in Argentina (Cordova province), China, USA (Oregon), Mexico (Torreon), Japan (Niigata). Arsenic belongs to the group of unconditional carcinogens for humans: it causes lung and skin cancer. Massive cases of skin cancer are well known among residents of the province of Cordoba (Argentina) and the island of Taiwan, where the population has been using drinking water with a high arsenic content for 60 years.

Widespread foci of endemic goitre are associated with low iodine content in drinking water.

Elevated concentrations of nitrates contribute to the development of methaemoglobinaemia.

It is believed that an increased copper content in drinking water causes liver and a kidney damage, high concentrations of nickel cause a skin damage, zinc causes a kidney damage, and beryllium belongs to carcinogens.

According to a number of authors, some halogen-containing compounds formed during water chlorination have carcinogenic effect. Over the last 10 years, many reports have been published indicating that high concentrations of aluminium in water contribute to the onset of Alzheimer’s disease. But it is worth pointing out that because of the large number (tens of thousands) of chemical substances in our water it is very difficult to determine the potential risks of the overwhelming majority of them for human health, because analytical methods are used to determine only a fraction of them, and many of them are dangerous to humans even in negligible concentrations.

The same subgroup should include diseases promoted by low or high mineralisation of drinking water. It is now recognised that long-term (for years) usage of “soft” water (containing insufficient amount of calcium and magnesium) causes high incidence of cardiovascular diseases, and “hard” (highly mineralised) water contributes to urolithiasis.

Water chlorination is a factor of an increased danger to public health. There is information about 19 substances-products of chlorination that are

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potentially dangerous to public health. These are trihalomethanes, chlorophenols, chloroform and other halogen-containing compounds (HCC) that have carcinogenic effects. A number of HCCs are also dangerous due to their pronounced cumulative properties (e.g., carbon tetrachloride).

Dioxin intoxication. The main sources of dioxide formation and release into the environment are the herbicide production, pulp and paper industry, chemical production (i.e., the production of chlorine and chlo- rine-containing compounds), food (up to 90%).

The connection between chlorination of drinking water and formation of chlorinated dioxins remains controversial. With dioxin intoxication in the body, the disruption of reproductive function, decrease immunity, teratogenic effect, embryotropic effect, cancer development, violation of behavioural reactions, etc., are possible.

Ecological and hygienic assessment of drinking water quality. One of the main tasks of the eco-hygiene in the field of the hydrosphere is to assess the quality of water intended for drinking, cooking, and meeting the needs of people. When solving this task, it is necessary to adhere to a certain plan. Firstly, one should have a clear idea of the requirements for water for a particular purpose. Due to the fact that the quality of water is determined not only by its properties at the moment, but also by the possibility of preserving these properties during the entire operation of the water source, that is, its reliability, it is necessary to find out the sanitary and technical condition of the water source, the conditions of the sanitary and topographic location and the sanitary and epidemiological situation. Such information can be obtained on the basis of studying relevant documents and conducting surveys. And finally, it is necessary to have data on the chemical composition of water and its microbial contamination. Following this information, a conclusion is made about the quality of water and whether it can be consumed without treatment or after certain treatment.

Drinking water quality criteria:

1)  water must have favourable organoleptic properties, i.e., it should be transparent, colourless, tasteless, odourless, contain no visible impurities, sediment;

2)  must be harmless in chemical composition, i.e., it should not contain carcinogenic, radioactive and other toxic substances (compounds);

3)  it must be safe in epidemic and radiation terms, i.e., it should not contain pathogenic bacteria, viruses, protozoa, helminth eggs; it should correspond to the indicators of α and β-activity of the normative values.

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Ways to reduce the content of xenobiotics in drinking water. The main way to supply the population with clean drinking water is a system of state measures aimed at reducing the content of toxic contaminants in water. For this purpose, standards and documents regulating the content of various substances in water have been developed and are in force in each country.

Meanwhile, other methods of drinking water purification are known and have long been used at the household level.

1.  Boiling. When boiling water or cooking, some components largely evaporate or precipitate.

2.  The most effective way to reduce the amount of radon in water is to filter water using various filters: activated carbon, ceramics, etc.

3.  A good way to obtain clean drinking water is to use filters using the principle of reverse osmosis.

PRACTICE

Task 1. Describe environmentally hazardous anthropogenic pollutants, analyse their transformations under the influence of various factors. Create a table “Harmful substances and their effects on the body”, showing the relationship between pollutants present in the environment (water) and diseases.

Task 2. Show the existence of a relationship between the nature and degree of environmental pollution (water) and the morbidity of the population; assess the carcinogenic risk. Evaluate the carcinogenic risk to public health when drinking water containing substances with carcinogenic effects (solving situational problems).

Sample solutions to cause problems / studies. Risk assessment for substances with carcinogenic effect is performed according to the formula:

CR = ADAD × PICR (POCR) × α,

where, СR – additional carcinogenic risk, i.e., the risk of an adverse effect, defined as the probability of this effect occurring under given conditions; ADAD – average daily absorbed dose; PICR (POCR) – values of potential inhalation (or oral) carcinogenic risks, i.e., risk units defined as the proportion of risk increase depending on the value of the active concentration

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(dose) in (mg/kg)–1 or (µg/m3)–1, i.e., inverse units of exposure respectively; α = 1 = 70 / 70 is a value reflecting the number of years an individual is exposed, assuming that he or she lives continuously in the study area (70 years), divided by the total number of years of life expectancy (70 years).

To calculate the risk, multiply the ADAD by the potential oral carcinogenic risk (POCR) or potential inhalation carcinogenic risk (PICR) and by the duration of exposure (for permanent residence, this value is equal to one). The result of this calculation is the number of cancer cases (expressed as the nearest whole number) per specific population. The inverse value of this value gives the probability value for this pathology.

The reverse sequence of operations, based on a particular value of acceptable risk, will make it possible to calculate the value of the ADAD, which is able to provide the necessary value of risk.

For example, it is necessary to calculate the carcinogenic risk for arsenic in drinking water at 0.0005 mg/l. The risk is calculated based on the daily consumption of this water throughout a person’s life. For the same period, the standard for calculating the risk is also defined. The average amount of water consumed daily is (V) 3 litres, the average human weight (m) is 70 kg.

Thus, every day under these conditions, a person consumes arsenic with drinking water at a dose of:

Using the POCR value for arsenic equal to 1.5 mg/kg (see appendix), the risk value will be:

CR = 0.000021 × 1.5 × 1 = 0.000032.

This is equivalent to 32 additional cases of cancer per million people (i.e., CR multiplied by the desired number of people) who constantly consume such water or the occurrence of one case of cancer out of 31,250 observed individuals (calculated as 1/CR).

Case Problems

1.  What additional number of cases of oncological diseases (per 10 thousand people) can occur with the constant consumption of drinking water containing 2 µg/l of aldrin?

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Chapter 6

MEDICAL AND ECOLOGICAL CONSEQUENCES

OF LITHOSPHERE POLLUTION

Motivational characteristic of the topic. The lithosphere as the outer sphere of the “solid” Earth, including the Earth’s crust and part of the upper mantle, is one of the components of the ecological system that determines the conditions of human habitation. It is a huge natural laboratory for a variety of complex processes of destruction and synthesis of inorganic and organic substances and photochemical reactions. The quality and safety of agricultural raw materials and food products depends on its properties, the content of various substances of chemical and biological nature. The knowledge of the quality of soil, conditions of transition including harmful substances in food products, influence of these substances on the human body largely determines the measures on prevention of adverse effects on the health of the population.

Food can fully meet the requirements for a rational diet if the food products used in the diet are harmless. This means that they will be free from harmful chemical and biological agents, or contain them in quantities (concentrations) and forms that are unable to negatively affect the human health and the health of offspring.

Awareness of the rational nutrition laws, mechanisms of pathology occurrence in connection with their violation is essential for making a diagnosis, determining the right treatment tactics, and most importantly – for preventing numerous painful conditions.

The objective:

1.  To consider the role of the lithosphere in the formation of the human habitat.

2.  To study the mechanisms of detoxification of xenobiotics in the body and the participation of various nutrients in these processes.

3.  To ascertain the significance of developing and implementing measures aimed at preventing harmful substances from soil to food in order to reduce the health consequences of consuming contaminated products.

Tasks:

1.  To get acquainted with the main features of soils that are important for their ecological characteristic.

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2.  To gain an understanding of the main groups of harmful substances coming through “food chains” from the soil to the human body.

3.  To study the problem of endemic diseases associated with the content of various chemical elements in soils.

4.  To become aware of xenobiotics metabolism, their detoxification, the participation of various food substances in these processes.

5.  To make sure that measures are necessary to prevent anthropogenic soil pollution in order to prevent related diseases.

Requirements for students’ initial knowledge level. To fully master the topic of the chapter, a student should revise the relevant material from the following disciplines:

1.  Medical Biology and Genetics: “General patterns of life development and nutritional conditions”, “Human adaptation to living conditions”.

2.  General Chemistry: “Chemical reactions in the interaction of elements”, “Metals and their compounds”, “Nitrogen and its compounds”.

3.  Organic Chemistry: “Biogenic elements as environmental factors”, “Food substances and their significance for the organism”.

Review questions from the related disciplines:

1.  Define “nutrients”. Explain their significance for the body.

2.  The importance of nutrition for ensuring the vital activity of the body.

3.  The effect of harmful substances on the body.

4.  Properties of harmful substances that determine their adverse effect on the body.

Questions related to the topic of the chapter:

1.  The main indicators that are important for the ecological and hygienic characteristics of soils.

2.  Features of the soils of the Republic of Belarus.

3.  Sources of harmful substances entering the soil, their characteristics. 4.  Classification of xenobiotics contained in food products.

5.  Nitrates, nitrites, nitrosamines. The sources of their intake into food, the mechanism of pathological action. Preventive measures.

6.  Pesticides. Classification. Properties of pesticides, which have hygienic value. Action mechanism of various pesticides and medical consequences of consumption of food products containing different amounts of pesticides.

7.  Biogeochemical provinces, definition, main characteristics. Endemic diseases in the Republic of Belarus.

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8.  Peculiarities of xenobiotics ingestion into various products of plant and animal origin.

9.  Requirements to food harmlessness. Main sources of food contamination.

10.  Criteria for assessing the quality and safety of food products. 11.  Metabolism of xenobiotics in the human body.

12.  Prevention of possible intake of xenobiotics with food.

13.  Nutritional habits of the population living in conditions of ecological disadvantage.

LEARNING MATERIAL FOR THE CHAPTER

The lithosphere is the outer sphere of the “solid” Earth, including the Earth’s crust and part of the upper mantle. The Earth’s mantle is the shell located between the Earth’s crust and the core. Soil, or earth, is a natural formation located between the atmosphere and the underlying rocks. The thickness of soil ranges from a few centimetres to two metres or more. Soil as an integral part of the ecological system is the most important component of human and animal habitat.

Soil types differ by certain combinations of soil horizons. Depending on the ratio of sand and clay, all soils are divided into sandy, sandy loam, clay, sod podzolic and loamy. There are various types of soils on the territory of the Republic of Belarus, but sod podzolic soils predominate. Such soils are more common in the Gomel region.

The soil chemical composition is very complex; it contains mineral (inorganic) and organic substances. Mineral compounds (90–99%) include salts of calcium, silicon, magnesium, aluminium, etc. The mineral composition of soil includes almost all elements of the Periodic system of D.I. Mendeleev in smaller or larger amounts.

Depending on the behaviour in living systems, 9 trace elements (iron, iodine, copper, chromium, cobalt, molybdenum, manganese, zinc, selenium) are considered essential (vital). With a lack of these elements, functional disorders occur in the body. Conditionally essential trace elements include fluorine, nickel, vanadium, arsenic, silicon, lithium, boron, and bromine.

The group of toxic elements includes aluminium, cadmium, lead, mercury, beryllium, barium, bismuth, thallium, etc. Pathogenic bacteria, viruses, protozoa, and helminth eggs live and die in the soil. It is one of the main ways of transmission of infectious and non-communicable diseases. Deficiency or excess of trace elements in the soil can lead to the occurrence of endemic diseases.

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The presence of certain elements in agricultural products, both plant and animal origin, their quality, usefulness, and safety are closely related to the soil.

Recently, anthropogenic pollution of the soil has become particularly important, i.e., the occurrence of chemical compounds that are not its natural component and are not typical for this type of soil.

The introduction of chemical and organic fertilisers, pesticides, industrial waste, sewage of different origin, adsorption of toxic substances from the atmospheric air, including the exhaust gases of vehicles, lead to increasing pollution of the soil. Numerous studies indicate the toxic significance of soil pollution, from which these harmful substances enter the human body through the so-called food chains, that is, through products of vegetable and animal origin, having an adverse effect. The most significant of them are xenobiotics.

Classification of extraneous food contaminants

FOOD

Xenobiotics, or foreign harmful substances that can enter the human body with food, are roughly divided into three main groups:

1)  natural food components with harmful effects;

2)  environmental substances that have a harmful effect (contaminants);

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