Экологическая медицина = Ecological medicine. Учебное пособие

Chapter 3

CHEMICAL AND BIOLOGICAL ENVIRONMENTAL

FACTORS AND HEREDITY

Motivational characteristic of the topic. Modern environmental medicine is developing in three main directions, one of which is the problem of preserving human health in a rapidly changing environment. With this in mind, knowledge and understanding of the “environment – organism” relationship becomes important and obvious. Knowledge of the mechanisms of exposure to chemical and biological factors and mechanisms of protection from their adverse effects will make it possible to implement a set of measures to prevent violations of women’s reproductive health and foetal development.

The objective: to study the chemical and biological risk factors of environmentally caused pathology.

Tasks:

1.  To understand the mechanisms of the impact of environmental factors on the human body.

2.  To learn how to protect against the adverse effects of environmental factors.

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.  Microbiology, Virology, Immunology: “Environmental factors as the cause of modifications and mutations, and selection factors of modified forms of microorganisms”;

2.  General and Bioorganic Chemistry: “Distribution of chemical elements in nature. Bio-hereditary apparatus of human cells”;

3.  Medical Biology and Genetics: “The organism as a habitat. Biological and social aspects of adaptation of the population to living conditions”.

Review questions from related disciplines:

1.  Environmental factors of chemical nature. Classification.

2.  Characteristics of abiotic and biotic environmental factors. Mechanisms of the EF effect on a person.

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3.  Specific and non-specific mechanisms of protection against the adverse effects of environmental factors. EF and public health.

4.  Endocrine system effectors: concept, classification, properties, metabolism and mechanism of action.

5.  Heredity and environment. The role of genetic factors in formation of ecologically dependent human pathology. Significance of genomic instability in the emergence of human diseases.

LEARNING MATERIAL FOR THE CHAPTER

Chemical pollution poses a threat not only to people living now, but also to future generations through its toxic effects on human reproductive function. The effects of chemicals on both male and female bodies during the reproductive cycle can lead to harmful results in the foetus development. Environmental toxic substances impair reproductive function either by directly affecting conception or by affecting the maternal body and changing the secretion of hormones and therefore disrupting reproductive function. It is very difficult to evaluate the comparative prevalence of these effects because of the many factors that have to be taken into account. These include: incomplete data on the dose and duration of action of substances; unknown interactions between different factors; difficulty in obtaining samples; inaccuracy of analytical methods; a large number of possible causes of abortions; variability of individual sensitivity due to differences in genotypes. The most noteworthy are those chemical agents that have an embryotropic effect at or near the LOC level. Moreover, the LOCs that have been developed for most chemical compounds have been established for the female body outside of pregnancy. At the same time, pregnancy is known to significantly change the reactivity of the female body and often increase its sensitivity to the action of adverse environmental factors.

At the histogenesis stage, harmful influences lead to microscopic structural defects and possible functional abnormalities in the foetus. Since the structural and functional maturation of many systems (immunological, nervous, etc.) and organs (liver, kidneys, and other endocrine organs) continues after birth, there is a growing consensus about possible harmful effects of environmental factors during infancy and childhood.

The pregnancy outcome after exposure to chemicals depends on the following factors:

yyexposure time; yygestational age;

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yymagnitude of exposure (amount of chemicals introduced into the body); yynature of the chemicals.

Not all exposures result in foetal death or spontaneous abortion. Teratogenesis leads to congenital foetal malformations that can be detected, including in utero. Various effects on the women’s reproductive health and possible disorders in the health of the newborn are presented in Table 3.1.

Table 3.1. Women’s reproductive disfunction and foetal development disorders from exposure to various agents

Note: SpA – spontaneous abortion; LBW – low birth weight (or weight loss after); CA – congenital anomalies; “++” – connection is clear; “+” – there is certain connection; “?” – no clear connection has been established; “–” – no connection at all.

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Possible consequences of teratogenesis can be: foetal death; spontaneous abortion; congenital deformities; growth retardation; functional disorders in foetal organs and systems. With the same duration and magnitude of exposure, the ultimate manifestation of harmful effects on the foetus depends primarily on individual sensitivity and gestational age.

The total amount of a chemical that reaches an embryo or foetus depends­ on several factors:

yydose size;

yysubstance physical state;

yyexposure routes, rate of the substance absorption by the maternal ­organism;

yyeffectiveness of homeostatic mechanisms that protect the foetus. The main function of the maternal body’s homeostatic mechanisms is

to reduce the concentration of toxic substances in the blood so that the number of molecules of these substances passing through the placenta is minimised. Due to the detoxification process, the embryo or foetus receives a threshold (acceptable) dose of most toxic substances.

However, even small levels of a particular exposure to which the maternal body has been exposed are sometimes sufficient for embryotoxic or teratogenic effects. Because of the high individual sensitivity of the embryo or foetus, embryotoxic effects can be observed in the absence of symptoms of maternal poisoning by a teratogenic compound.

Sensitivity to teratogens depends on two main factors: the genotype of the foetus and its stage of development at the moment of exposure. The term “genotype” is applied to an individual’s unique set of genes. Variations in the genotype of individuals are manifested by differences in their biochemical and morphological structure. It is these differences that explain the difference in the reactions of people to individual toxic substances. These differences affect the maternal absorption, processing and removal of the toxic substance, the rate at which the toxic substance penetrates the placental membrane, and the type of interaction between the toxic substance and the foetal tissue.

Numerous experimental studies and clinical observations indicate embryotoxicity of manganese, cadmium, mercury, lead, arsenic, fluorine, antimony, aluminium, lithium and some other metals. The most extensive data are available on the teratogenicity of mercury and lead.

Embryo exposure during the first trimester of pregnancy to antineoplastic drugs such as cyclophosphamide, doxorubicin and vincristine leads to an increased rate of foetal death. Drugs with confirmed embryotoxic and

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teratogenic effects on humans include thalidomide, androgens, aminopterin, warfarin and coumarin derivatives. As early as 1935, embryotoxic properties of benzene, caused by its direct impact on the foetus, were established. Female workers exposed to benzene and benzene vapours had spontaneous miscarriages, premature births and stillbirths. Cases of congenital hypotrophy in newborns whose mothers were exposed to benzene during pregnancy were described. Certain homologues of benzene have a similar effect. The properties of some phenols during organoand foetogenesis of the foetus are of interest: various deformities and retarded skeletal ossification were observed in the foetuses. Teratogenic activity was found in formaldehyde as well. Prolonged industrial contact with carbon disulphide may cause foetal death as a result of intrauterine intoxication. Furan nitro compounds penetrate the placental barrier and can have a general toxic effect on the foetus. In Taiwan, more than 2,000 people were exposed to cooking fats contaminated with polychlorinated biphenyls (PCBs) and dibenzols. Mothers who had previously used this cooking fat had babies with gum, skin, teeth, and lung abnormalities for more than 6 years.

At present, more than 30 pesticides have been found to have embryotoxic effects. In experiments on pregnant rats previously inoculated for a long time with DDT (0.02 mg/kg) and HSH (0.5 mg/kg), embryotoxic effects of organochlorine pesticides under study were found, resulting in increased foetal death and decreased viability of the offspring. Chlorophos is of great concern. The most sensitive to the action of chlorophos is the embryonic bone system. Even relatively low concentrations of chlorophos in the air led to spinal curvature and incomplete ossification of limb bones in the foetus. At higher concentrations, various anomalies of internal organs appeared: undeveloped brain, dilated carotid artery, haemorrhages of different localisation. Special sensitivity of embryos to the action of mer- cury-containing pesticides was noted during organogenesis. Thus, severe intoxication with granosan leads to the development of meningoencephalitis with encephalomalacia phenomena in the foetus.

Environmental pollutants of different nature can have a negative effect on humans during the period of intrauterine development. The teratogenic effect, which is the most specific consequence of the direct action of a damaging agent on early embryogenesis, is relatively rare and occurs only when high doses or concentrations of chemicals are used. Foetal developmental impairment for most factors of chemical nature is not specific and depends on the gestational age at the time of exposure to the damaging agent and its concentration in the body.

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A decrease in physiological adaptive mechanisms during pregnancy leads to an increased risk of infection. In this case, not only the pregnant woman can be infected, but also the transmission of infectious agents to the newborn child is possible. The risk of infecting the foetus depends on the infecting microorganism, route of transmission, potential for placental barrier passage, time of exposure, and maternal / foetal immune status. Infections with pathogens that can cross the placenta and directly affect the foetus include the following (Table 3.2):

Table 3.2. Infectious agents penetrating the placenta

The impact of maternal infection on the foetus is manifested through direct exposure to toxins or microorganisms or through indirect contact as a result of placental or uterine dysfunction. When an infectious disease occurs in a woman during pregnancy, not only the germs affect the embryo and foetus, but also their decay products.

Early gestational infection often results in severe foetal malformations incompatible with life; pregnancy often ends in spontaneous miscarriage. If infected after 8–12 weeks of gestation, the defects may be compatible with life in utero, but before birth a number of changes occur in the foetus which may result in stillbirth, serious illness of the newborn, or death in the neonatal period (up to 1 month of life). If the foetus becomes infected in the second and third trimesters of pregnancy, both signs of infectious damage to individual foetal organs (hepatitis, myocarditis, meningitis, chorioretinitis) and symptoms of a generalised infection can be detected.

The outcomes of the harmful infections on the foetus can be as follows: 1)  abortion or stillbirth;

2)  congenital malformations;

3)  acute illness or lethality in the neonatal period;

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Chapter 4

MEDICAL AND ECOLOGICAL CONSEQUENCES

OF ATMOSPHERIC POLLUTION

Motivational characteristic of the topic. One of the main human habitats is the atmosphere, which constantly, directly or indirectly, affects the human body. Changes in the chemical composition and physical properties of atmospheric air lead to human health disorders and various negative consequences in environmental objects.

Widespread environmental pollution leads to the destruction of biological resources, which are the carrier of genetic material. The recent spread of such phenomena as acid precipitation, destruction of the ozone layer, the greenhouse effect, etc. has an adverse effect not only on nature, but also on human health. Diseases associated with the biosphere trouble are particularly alarming: upper respiratory tract diseases and allergic diseases associated with xenobiotics entering the body.

Establishing causal relationships between the quality of the air environment and the state of health is necessary for the medical professional to justify a set of preventive measures to preserve the health of the population.

The objective: to consider the environmental consequences of atmospheric pollution, to show the presence of environmentally dependent morbidity of the population.

Tasks:

1.  To explain simple methods of analysing pollutants in the atmosphere.

2.  To be able to give an environmental-hygienic assessment of atmospheric air pollution effect on public health.

3.  To realise the importance of preserving a life-friendly habitat by carrying out a complex of ecological and hygienic measures for the atmospheric air protection.

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.  Microbiology, Virology, Immunology: “Ecological environment of microorganisms. Air microflora”.

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2.  General Chemistry: “Toxic effect of lead, mercury, copper compounds on organism. Biogenic elements as environmental factors”.

3.  Medical Biology and Genetics: “Organism as a habitat. Parasite and host interaction at individual and population levels”.

4.  General Hygiene: “Hygiene of atmospheric air. Measures to protect atmospheric air”.

Review questions from the related disciplines:

1.  What is the role of the air microflora in spreading infectious diseases? What infectious and parasitic diseases can be transmitted through the air?

2.  What is the role of biogenic elements as environmental factors? 3.  List the physical properties of air.

4.  What is the role of the air in the occurrence of human non-commu- nicable diseases?

5.  What hygiene measures on atmospheric air protection do you know?

Questions related to the topic of the chapter:

1.  The concept of the atmosphere, its structure and composition. 2.  Sources of atmospheric air pollution.

3.  Main air pollutants and their brief characteristics.

4.  The influence of anthropogenic human activity on the atmosphere gas composition.

5.  Chemical transformations of pollutants in the air and their consequences.

6.  The influence of atmospheric air pollution on human health and sanitary living conditions.

7.  Pollution and protection of atmospheric air as an environmental problem in the conditions of scientific and technological progress.

LEARNING MATERIAL FOR THE CHAPTER

The atmosphere, as one of the main human habitats, affects the human body as a physical body (pressure, temperature, humidity, air speed, electrical state) as well as by its chemical composition. A human can survive food deprivation up to 70 days, without water – up to 3–7 days, but without air – only minutes.

The atmosphere constantly affects people, and at the same time, changes itself under human influence. These changes can have an impact on human health. According to the famous hygienist F.F. Erisman, air is the most common medium, with which a person comes into contact. Changing the chemical composition of physical properties can easily upset the harmonic equilibrium of our body, i.e., health.

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Structure, composition of the atmosphere and its ecological and hygienic significance. The atmosphere is the gas envelope of the Earth. Its mass is about 5.9×1015 tons. It has a complicated structure and consists of several spheres, between which there are transitional layers, i.e., pauses.

The air densest layer, adjacent to the Earth’s surface, is the troposphere. Above the troposphere, there is the stratosphere. In the stratosphere, under the influence of cosmic rays and the short-wave part of the sun ultraviolet rays, air molecules are ionised, resulting in the ozone formation. The ozone layer is at an altitude of 25–40 km.

Next comes the mesosphere and the thermosphere, where gases are very sparse, the temperature reaches 200 °C at an altitude of 150 km.

The hygienic value of the atmosphere in general and the air in particular is primarily a supply of oxygen. In addition, changes in the physical and chemical properties of the air can have a negative impact on the body. And finally, the air can be a carrier of toxic and infectious origin. It is known that the surface of pulmonary alveoli is more than 100 m2, and more than 95% of all occupational poisonings are inhalation.

In this regard, the main problems of environmental medicine are the conditions of air supply to the population, its quality and opportunities to improve it.

Air quality is a set of properties that determine human existence in the air environment as a habitat. These properties are: chemical composition, temperature, pressure, velocity, electrical state and ionisation.

The chemical composition and physical properties of the air should ensure the existence of a person without straining compensatory physiological mechanisms and, moreover, without pathological shifts in health.

Physical properties and air quality can vary depending on the altitude above sea level, as well as the intensity of economic and industrial activity of people.

Sources of air pollution. There are two main sources of atmospheric pollution: natural and anthropogenic.

The first one is cosmic dust, which is formed from the remains of burnt meteorites as they pass through the atmosphere. Every year 2–5 million tons fall on the Earth. Natural dust is a constant component of the Earth’s atmosphere, which is of organic and inorganic origin.

Atmospheric dust promotes the condensation of water vapour, and consequently the formation of precipitation. Moreover, it absorbs direct solar radiation and protects the body from solar radiation. Academician V.I. Vernadsky noted that atmospheric dust plays a huge role in the chemistry of the planet.

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