Introduction, environmental medicine

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Introduction
01 Cancer
02 Ozone
03 Urban air
04 Air pollutants
05 Blue-green algae
06 Water mutagens
07 Contamination
08 Chernobyl
09 Radon
10 Medical geology
11 Renal hazards
12 Organohalogens
13 Estrogens
14 Food hazards
15 Mycotoxins
16 Poisoning
17 Genetics
18 Risk

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(Full text of Introduction)

The book you are holding in your hand focuses on environmental medicine. This sector of science and research is broad in comparison with other areas of medicine and the environmental sciences. The reason is that environmental medicine deals with the interaction between risk factors in the environment and human health.

When we visit a doctor or a hospital, our purpose is usually to find out what type of disease we have and to cure that disease. Environmental medicine does not focus on how to cure the disease, but rather on explaining the cause of disease in an environmental context.

A simple answer to the cause of disease consists of inheritance and environmental risk factors, but these are very complex issues to deal with. Most diseases are to some degree related to inheritance and/or risk factors in the environment, and environmental medicine therefore involves many different diseases and exposures.

The human environment involves exposure to many different physical, biological and chemical agents. This exposure can be divided into different categories. General environmental exposure such as air pollution is something we are all exposed to and, as individuals, do not have the possibility to change. Other general exposures can be avoided or, at least, the risk (the exposure) can be reduced, as in the case of UV-irradiation from the sun.

Certain environmental exposures are easy to avoid if one possesses the knowledge. Toxic mushrooms are one example. Chemicals that have a low acute toxicity and occur as contaminants in food products are extremely difficult for the individual to avoid. Persistent halogenated aromatic hydrocarbons such as chlorinated dioxins are an example. Often, qualified research is needed in order to become aware of the problem. In addition to this there are socially accepted toxins - individuals do not choose to avoid the exposure even with good knowledge of the potential consequences. It is also common to either under or overestimate a certain risk due to gender, age or cultural, educational and other factors.

Although environmental medicine may be defined simply as the interaction between risk factors and human health, this definition includes a wide variety of risk factors, a wide variety of diseases and a wide variety of genetic predispositions for disease.

The aim of research in environmental medicine is not to cure disease, but rather to prevent it. With knowledge of the exposure to a risk factor, knowledge of the mechanisms of the adverse effects in the different tissues and the health consequences, assessments can be performed. Such assessments provide the basis for safety limits, control of potentially dangerous substances or removal of unnecessary risks.

How are we exposed to environmental agents?

The environment is not something that exists parallel to human life. By definition, we all live in the environment and the environment interacts with the human body in many ways. All agents (chemical, biological or physical) in the environment are in chemical equilibrium with the organisms, with the consequence that all individuals are to some extent exposed to what is found in the environment. This is the reason why animals in the sea and forests, etc., may be used as indicators of environmental change and the existence of risk factors, since some species are highly exposed to certain agents that will also affect humans sooner or later.

Air pollutants are inhaled. Larger particles end up in the upper respiratory tract and are eventually swallowed into the gastro-intestinal tract. Minor particles find their way down to the sensitive small alveoli of the lung where the exchange of oxygen and carbon dioxide takes place. Particles normally have an organic layer, i.e. toxic substances are absorbed on the surface of the particles. This layer and/or the particle itself can initiate lesions in the different cells of the lung. Gases are inhaled and, to a large extent also exhaled, but there is potential for reactions to occur. For instance, nitrogen dioxide can react with water in the mucous membranes and form nitric acid which can result in different lung reactions. Many air pollutants, especially particles and metals, precipitate on soil and can contaminate vegetables and grass and thereby reach humans via the food chain.

Water pollutants originate in many cases from sewage water from urban areas and industrial plants. The contaminants are either released into the sewage water or are subsequently formed in the aqueous recipient. An indirect consequence is consumption of oxygen, when the organic material is metabolized by microorganisms, with severe consequences on life in general. Many substances precipitate on the bottom where organisms are contaminated and eaten by other organisms. Finally, the contaminants accumulate in the upper part of the food chain and are eaten by man. Other types of water pollutants are formed in the water after disinfection (chlorination), growth of algae, chemical reactions or leakages from dump sites, storage places and agricultural areas. The recipient can be rivers, lakes, oceans or ground water. Ground water is the most sensitive recipient, since the turnover time is very long and the biological activity is limited. Another factor as regards ground water is that it is a very important and finite source of drinking water. Water pollutants are also generated from air pollutants when dissolved in the atmospheric water particles that precipitate as rain. An example of this is acid rain. Acidification is a serious environmental problem that inhibits reproduction of aquatic organisms, induces the release of chemically bound metals and nutrients, and affects the growth of forests.

Soil pollution may come from many different sources. Examples include mines, dump sites, former industrial areas and areas close to main roads and airports. In many cases this type of pollution is related to metals, pesticides or coal/tar/oil products. Soil can be contaminated by direct exposure or indirectly via precipitation of particles. The main routes for exposure to soil contaminants are via wind-spread dust, leaching into water, exposure to fruit/vegetables in agriculture areas or children eating contaminated soil/sand.

Physical agents are common environmental pollutants. The most well-known of these is radioactivity, which can be divided into cosmic, ground and water radiation. In addition to this there are anthropogenic sources of radioactivity such as medical treatments, production and use of nuclear weapons and nuclear power. Another well-known physical agent is UV-irradiation from the sun, which is very intense if the protective ozone-layer is affected by other types of pollution.

Biological contamination is a severe problem best illustrated by fungal infection of crops, especially in humid and warm conditions. These fungi produce certain toxins (mycotoxins) that are potential risk factors for humans.

Life style factors such as drug use/abuse, alcohol, tobacco, certain eating habits, chemicals used at home, pesticides etc., can also be included in the list of risk factors in the human environment.

Inheritance and behavior in environmental medicine

Inheritance is an important factor in how the body respond to risk factors in the environment. Many genes are involved in this response and we are only beginning to understand the very complex nature of this. One example is that one smoker may smoke his whole life without any severe diseases, while another individual, only exposed to side-stream smoke dies from lung cancer at a young age. Predisposition can be found to contribute to most types of lesions or disease, albeit to different extents. One person might easily break her leg, but is careful and avoids dangerous situations - and therefore does not break the leg. Another person with the same predisposition can be involved in demanding physical activities like ice-hockey, rugby or mountain climbing with an increased risk of broken legs. The same applies to other lesions or diseases. The stronger the predisposition is and the greater the number of risk-factors which a person is exposed to, the higher the risk of developing a certain disease is. In the case of cancer, inheritance is probably the predominant factor in only a few per cent of all cases. Likewise, in only a small fraction of cancer cases is one specific environmental risk factor enough to generate the disease. In most cases, a combination of a number of inherited predispositions and complex exposure to a large variety of environmental risk factors is involved.

Human behavior is very complex. One person might consider a certain activity to be very dangerous (high risk) while another person would do anything to take part in the same activity (a chance). On the basis of on education, cultural behavior, age, sex and many other factors we all interpret a certain risk very differently. Other factors, such as the time between exposure and health effect, have a major influence on whether we consider something to be dangerous or not. If, for instance, all the people who die in smoking- related diseases were to die when they smoked their first cigarette, cigarettes would be considered extremely dangerous and would be banned in all societies. No one would be allowed to even touch a cigarette without very strict safety measurements. But since there is a time delay of decades from the start of smoking and the occurrence of lung cancer it is very hard to see the connection.

Two people in the same place could be exposed very differently due to behavior. Small children eating the sand/soil of parks in central areas of cities which are commonly polluted with metals provide an example. The parents, who are at the same place, do not get the same exposure.

Human behavior has a strong bearing on exposure to different risk factors. This also means that we can avoid risk factors if we have the knowledge.

What subjects are discussed in this book?

As indicated above there are many exposures, diseases and genetic factors that can be discussed. This book deals with a number of examples in order to increase the understanding of how complex our lives are in terms of environmental risk factors. These examples are presented in the 18 chapters of this book.

Water quality is discussed in two chapters which deal with algae toxins and substances formed by chlorination of drinking water. Contamination of soil is considered from the perspective of dump sites for waste. Air pollution involves many exposures and different sources and are discussed as exposure (urban air pollution) and health effects (lung). Physical agents such as UV-irradiation and radioactivity are discussed in three chapters which include the example of the severe accident at Chernobyl in the Ukraine. Acute intoxication and chronic effects are very different in terms of time frame. These aspects are presented in two chapters. Specific exposures are discussed in six separate chapters; persistent chlorinated organic chemicals, metals and mycotoxins, food preparation and hormone-like contamination. Two chapters focus on genetic inheritance and risk perception. In addition to this, there is a section on recommended reading.

Who are the authors?

The authors of this book are all scientists and/or physicians who work with research and health care. They represent a variety of research institutions in several countries. Karolinska Institutet, Stockholm, Sweden, is represented by the authors of the majority of the chapters. Karolinska Institutet is the Medical University of Stockholm. There are also two other authors from Swedish universities, the University of Lund in the south of Sweden and the Swedish University of Agricultural Sciences in Uppsala, just north of Stockholm. One author is from the Swedish Geological Survey, a Swedish governmental agency.

From the US, there are authors representing three universities. These are the Massachusetts Institute of Technology (MIT) in Boston, the University of California in Riverside, California and Harvard Medical School in Boston. The US Environmental Protection Agency is represented by one author from the Health Effect Research Laboratories, Research Triangle Park, North Carolina. The US National Cancer Institute (NCI), a part of the US National Institute of Health, is represented by one author. One of the authors from the US, Professor Mario Molina, was the first (together with his colleagues) to receive the Nobel Prize for an environmentally related area of research, the discovery of the mechanism behind the destruction of the ozone-layer.

Canada and South Africa are represented by Carleton University, Ottawa and the Medical Research Council, Cape Town, respectively.

All these authors have a common desire to share their knowledge in their areas of expertise. They have not written these chapters for other scientists, but for readers who want to gain more knowledge than can be found in newspapers and magazines, but in a more easily digested form than that of highly specialized scientific papers.

Lennart Möller
editor
Karolinska Institutet