Population, Environment, and Women’s Issues

Ultimately, the necessity to supply food, energy, habitat, infrastructure, and consumer goods for the ever-growing population is responsible for the demise of the environment. Remedial actions for pollution abatement, and further technological progress toward energy efficiency, development of new crops, and improvements in manufacturing processes may help to mitigate the severity of environmental deterioration. However, we can hardly hope for restoration of a clean environment, improvement in human health, and an end to poverty without arresting the continuous growth of the world population. According to the United Nations count, world population reached 6 billion in mid October 1999 (1). The rate of population growth and the fertility rates by continent, as well as in the United States and Canada, are presented in Table 14.1. It can be seen that the fastest population growth occurs in the poorest countries of the world. Despite the worldwide decrease in fertility rates between 1975–80 period and that of 1995–2000, the rate of population growth in most developing countries changed only slightly due to the demographic momentum, which means that because of the high fertility rates in the previous decades, the number of women of childbearing age had increased. Historically, the preference for large families in the developing nations was in part a result of either cultural or religious traditions. In some cases there were practical motivations, as children provided helping hands with farm chores and a security in old age. At present the situation is changing. A great majority of governments of the developing countries have recognized that no improvement of the living standard of their citizens will ever be possible without slowing the explosive population growth. By 1985, a total of 70 developing nations had either established national family planning programs, or provided support for such programs conducted by nongovernmental agencies; now only four of the world’s 170 countries limit access to family planning services. As result, 95% of the developing world population lives in countries supporting family planning. Consequently, the percentage of married couples using contraceptives increased from less than 10% in 1960 to 57% in 1997.

Water and Land Pollution

Water covers 70% of the earth’s surface. Only 3% of this is freshwater, which is indispensable in sustaining plant and animal life. The amount of freshwater is maintained constant by the hydrological cycle. This cycle involves evaporation from oceans and inland waters, transpiration from plants, precipitation, infiltration into the soil, and runoff of surface water into lakes and rivers. The infiltrated water is used for plant growth and recharges groundwater reserves. Although the global supply of available freshwater is sufficient to maintain life, the worldwide distribution of freshwater is not even. In some areas the supply is limited because of climatic conditions or cannot meet the demands of high population density. In other places, although there is no shortage of freshwater, the water supply is contaminated with industrial chemicals and is thus unfit for human use. Moreover, fish and other aquatic species living in chemically contaminated water become unfit for human consumption. Thus, water pollution deprives us and other species of two essential ingredients for survival: water and food. An example of hydrologic changes caused by urbanization is given in Figure 11.1. Conditions before and after urbanization were measured in Ontario, Canada, by the Organization for Economic Cooperation and Development (1). In the urban setting, pervious areas are replaced with impervious ones (such as streets, parking lots, and shopping centers). Groundwater replenishment is greatly reduced and runoff is considerably increased by these changes. Thus, urbanization not only contributes to water pollution; it also increases the possibility of floods. Nitrogen is an important element for sustenance of life. However, in order to be incorporated into living matter it has to be converted into an assimilative form—an oxide or ammonia. Until the beginning of the twentieth century most of the atmospheric nitrogen was converted into assimilative form by soil microorganisms and by lightning. Nitrogen compounds which were not utilized by living matter did not accumulate because the denitrifying bacteria decomposed them to elemental nitrogen which was then released back into the atmosphere. In this way the nitrogen cycle was completed.

Risk Assessment

The purpose of risk assessment is estimation of the severity of harmful effects to human health and the environment that may result from exposure to chemicals present in the environment. The Environmental Protection Agency (EPA) procedure of risk assessment, whether related to human health or to the environment, involves four steps: 1. hazard assessment 2. dose–response assessment 3. exposure assessment 4. risk characterization The quantity of chemicals in use today is staggering. According to the data compiled by Hodgson and Guthrie in 1980 (1), there were then 1500 active ingredients of pesticides, 4000 active ingredients of therapeutic drugs, 2000 drug additives to improve stability, 2500 food additives with nutritional value, 3000 food additives to promote product life, and 50,000 additional chemicals in common use. Considering the growth of the chemical and pharmaceutical industries, these amounts must now be considerably larger. Past experience has shown that some of these chemicals, although not toxic unless ingested in large quantities, may be mutagenic and carcinogenic with chronic exposure to minute doses, or may interfere with the reproductive or immune systems of humans and animals. To protect human health it is necessary to determine that compounds to which people are exposed daily or periodically in their daily lives (such as cosmetics, foods, and pesticides) will not cause harm upon long-term exposure. The discussion in this chapter will focus primarly on carcinogenicity and mutagenicity, but also endocrine disrupters will be considered. The carcinogenicity of some chemicals was established through epidemiological studies. However, because of the long latency period of cancer, epidemiological studies require many years before any conclusions can be reached. In addition, they are very expensive. Another method that could be used is bioassay in animals. Such bioassays, although quite useful in predicting human cancer hazard, may take as long as 2 years or more and require at least 600 animals per assay. This method is also too costly in terms of time and money to be considered for large-scale screening. For these reasons an inexpensive, short-term assay system is needed for preliminary evaluation of potential mutagens and carcinogens.

Chemical Carcinogenesis and Mutagenesis

Cancer is a common name for about 200 diseases characterized by abnormal cell growth. According to Kundson (1), the causes of cancer may be classified into the following groups: 1. genetic predisposition 2. environmental factors 3. environmental factors superimposed on genetic predisposition 4. unknown factors Typical examples of the first group are childhood cancers such as retinoblastoma (a genetically predisposed malignancy of the retina), neuroblastoma (a malignancy of the brain), and Wilms’ tumor (a malignancy of the kidney). In adults, an example is polyposis of the colon, a genetic condition that frequently leads to colon cancer. The third group is represented by xeroderma pigmentosum, a genetic condition characterized by a deficient DNA excision repair mechanism (see the discussion later in this chapter). Individuals so predisposed develop skin cancer when exposed to ultraviolet light. The variable susceptibility of the population to the carcinogenic effects of cigarette smoke may also reflect genetic predisposition. Very little can be said about the fourth group because the causes of this group of cancers are not known. Groups 2 and 3 combined (i.e., cancer attributable to environmental causes, with or without genetic predisposition) probably account for 60– 90% of all cancers (2). The environment, in this context, involves not only air, water, and soil, but also food, drink, living habits, occupational exposure, drugs, and practically all aspects of human interaction with the surroundings. This definition implies that a great majority of cancers could be prevented by avoiding exposure to potential carcinogens and by changing living habits. It is therefore not surprising that the study of chemical carcinogenesis represents a major aspect of environmental toxicology. Table 5.1 gives an overview of estimated environmentally associated cancer mortality or incidence in the United States. The data presented in this table have to be considered as rough estimates only. There are great variations in the estimates, depending on the investigators and their methods of collecting the pertinent statistics. The Office of Technology Assessment report on cancer risk offers a more in-depth treatment of this subject.

Regulatory Policies and International Treaties

The purpose of the National Environmental Policy Act (NEPA) is to ensure that all federally administered or assisted programs are conducted so as to take the environmental impact of their activity into consideration. The scope of NEPA includes privately financed and conducted projects for which federal licensing is required. The law also establishes a presidential advisory group called the Council on Environmental Quality (CEQ). The crucial section of the act (U.S. Code, Title 102, Pt. 2c), which concerns the environmental impact statement (EIS), states, in part, that The Congress authorizes and directs that, to the fullest extent possible . . . all agencies of the Federal Government shall . . . include in every recommendation or report on proposal for legislation and other major Federal actions significantly affecting the quality of the human environment, a detailed statement by the responsible official on: •The environmental impact of the proposed action, • Any adverse environmental effects which cannot be avoided should the proposal be implemented, • Alternatives to the proposed action, • The relationship between local, short-term uses of man’s environment and maintenance and enhancement of long-term productivity, and • Any irreversible and irretrievable commitments of resources which would be involved in the proposed action should it be implemented. Environment in this context refers not only to wilderness, water, air, and other natural resources. It has a broader meaning that includes health, aesthetics, and pleasing surroundings. Although the law requires an EIS, it does not say anything about what conditions would be required in order to carry out the project. Moreover, NEPA does not give more weight to environmental considerations than it gives to other national goals. Thus the decision about implementation of a program is left to the courts. In practice, few projects have ever been halted by a court decision under NEPA. However, some projects have been abandoned or modified, before being challenged in court, because of NEPA. Figure 15.1 shows the framework of the federal environmental regulatory structure. Four federal agencies cover the environmental aspects of the national policy.

Radioactive Pollution

Radiation that, on passage through matter, produces ions by knocking electrons out of their orbits is called ionizing radiation. This radiation is produced through decomposition of unstable, naturally occurring or synthetic elements referred to as radionuclides. The four types of radiation are ∝-particles, β-particles, γ-rays, and neutrons. The ∝-particles have a mass of two protons and two neutrons and a charge of +2; β -particles are electrons with a mass of 0.00055 atomic mass unit (amu) and a charge of –1; γ -rays and X-rays are high-frequency electromagnetic waves with no mass and no charge. The difference between γ -rays and X-rays is that γ -rays occur naturally, whereas X-rays are generated. In addition, γ -rays are of higher frequency than X-rays. Release of an ∝ -particle leads to the formation of a daughter element with an atomic number 2 units lower and an atomic weight 4 units lower than that of the parent nuclide. Similarly, release of a β -particle from the nucleus causes conversion of a neutron to a proton, producing a daughter element with the same atomic weight as the parent nuclide but with its atomic number increased by 1 unit. Neutron radiation does not occur naturally and is released only from synthetic radionuclides. Neutrons, which have no charge, are formed from protons. This conversion is accompanied by the release of an orbital electron from the atom. Neutrons produce ions indirectly, by collisions with hydrogen atoms. The impact knocks out protons, which in turn produce ions on passage through matter. Capture of a neutron forms an isotope of the parent nuclide with its atomic weight increased by 1 unit. The mode of action of particles (∝ and β ) varies from that of photons (γ - and X-rays). When ∝- or β -particles travel through matter, their electric charges (positive or negative) cause ionization of the atoms in the matter. This is called a direct effect. Whereas the track of ∝- particles is short and straight, β -particles scatter, frequently producing a wavy track. Gamma- and X-rays act indirectly.

Air Pollution

It is somewhat artificial to consider air, water, and soil pollution separately because their effects are interchangeable. Chemicals emitted into the air eventually combine with rain or snow and settle down to become water and land pollutants. On the other hand, volatile chemicals from soil or those that enter lakes and rivers evaporate to become air pollutants. Pesticides sprayed on land are carried by the wind to become transient air pollutants that eventually settle somewhere on land or water. For discussion purposes, however, some systematic division appears to be advisable. Although the problems of air pollution have been recognized for many decades, they were once considered to be only of local significance, restricted to industrial urban areas. With the current recognition of the destruction of stratospheric ozone, the greenhouse effect, worldwide forest destruction, and the acidification of lakes and coastal waters, air pollution assumes global significance. The sources of urban air pollution are . power generation . transportation . industry, manufacturing, and processing . residential heating . waste incineration Except for waste incineration, all of these pollution sources depend on fossil fuel and, to a lesser degree, on fuel from renewable resources such as plant material. Therefore, all of them produce essentially the same pollutants, although the quantity of each substance may vary from source to source. The principal incineration-generated pollutants are carbon monoxide (CO), sulfur dioxide (SO2), a mixture of nitrogen oxides (NOx), a mixture of hydrocarbons, referred to as volatile organic compounds (VOCs), suspended particulate matter (SPM) of varying sizes, and metals, mostly bound to particles. Waste incineration, in addition, produces some chlorinated dioxins and furans that are formed on combustion of chlorine-containing organic substances Most of these air pollutants originate from geophysical, biological, and atmospheric sources. Their contribution to total air pollution is globally significant. This fact should not lead us into complacency about anthropogenic air pollution. In nature, a steady state has been established between emission and disposition of biogenic pollutants. Life on earth developed in harmony with these external influences.

Occupational Toxicology

Industrial workers make up the segment of the population that is most vulnerable to chemical injury. To protect them from occupation-related harm, the American Conference of Governmental and Industrial Hygienists publishes annually revised threshold limit values (TLVs) (1), guidelines for permissible chemical exposure at the work place. TLV refers to concentrations of substances in parts per million or milligrams per cubic meter in the air to which most workers can be exposed on a daily basis without harm. These values apply to the work place only. They are not intended as guidelines for ambient air quality standards for the population at large. Obviously, genetic variations and diverse lifestyles (such as smoking, alcohol use, medication, and drug use) must be considered. Hypersensitive individuals may be adversely affected by exposure to certain chemicals even within the limits of the TLV. Thus, TLVs should be treated as guidelines only and not as fixed standards. The recommended goal is to minimize chemical exposure in the work place as much as possible. TLVs are expressed in three ways: 1. Time-weighted average (TLV–TWA) designates the average concentration of a chemical to which workers may safely be exposed for 8 h per day and 5 days per week. 2. Short-term exposure limit (TLV–STEL) designates permissible exposure for no more than 15 min, and no more than four times per day, with at least 60-min intervals between exposures. 3. Ceiling concentrations (TLV–C) are concentrations that should not be exceeded at any time. How protective the TLVs are is being questioned. The 1990 report that analyzed the scientific underpinnings of the TLVs revealed that at the exposure at or below the TLV, only few cases showed no adverse effect (2). In some cases even 100% of those exposed were affected. On the other hand, there was a good correlation between the TLVs and the measured exposure occurring in the work place. Thus, it appears that the TLVs represent levels of contaminants that may be encountered in the work place, rather than protective thresholds. Biological exposure indices (BEIs) provide another way of looking at exposure to chemicals.

Review of Pharmacologic Concepts

Early scientific knowledge recognized two basic types of substances: beneficial ones (such as foods and medicines), and harmful ones (those that cause sickness or death). The latter were designated as poisons. Modern science acknowledges that such a strict division is not justified. As early as the sixteenth century, Paracelsus recognized that ‘‘the right dose differentiates a poison and a remedy.’’ Many chemical substances or mixtures exert a whole spectrum of activities, ranging from beneficial to neutral to lethal. Their effect depends not only on the quantity of the substance to which an organism is exposed, but also on the species and size of the organism, its nutritional status, the method of exposure, and several related factors. Alcohol is a good example. Taken in small quantities, alcohol may be harmless and sometimes even medically recommended. However, an overdose causes intoxication and, in extreme cases, death. Similarly, vitamin A is required for the normal functioning of most higher organisms, yet an overdose of it is highly toxic. If the biological effect of a chemical is related to its dose, there must be a measurable range between concentrations that produce no effect and those that produce the maximum effect. The observation of an effect, whether beneficial or harmful, is complicated by the fact that apparently homogeneous systems are, in fact, heterogeneous. Even an inbred species will exhibit marked differences among individuals in response to chemicals. An effect produced in one individual will not necessarily be repeated in another one. Therefore, any meaningful estimation of the toxic potency of a compound will involve statistical methods of evaluation. To determine the toxicity of a compound for a biological system, an observable and well-defined end effect must be identified. Turbidity or acid production, reflecting the growth or growth inhibition of a culture, may be used as an end point in bacterial systems. In some cases, such as in the study of mutagenesis, colony count may be used. Similarly, measures of viable cells, cell protein, or colony count are useful end points in cell cultures.

Environment : Past and Present

Concern for the environment is not an entirely new phenomenon. In isolated instances, environmental and wildlife protection laws have been enacted in the past. Similarly, astute early physicians and scientists occasionally recognized occupationally related health problems within the general population. As early as 500 BC, a law was passed in Athens requiring refuse disposal in a designated location outside the city walls. Ancient Rome had laws prohibiting disposal of trash into the river Tiber. In seventeenth century Sweden, legislation was passed forbidding ‘‘slash and burn’’ land clearing; those who broke the law were banished to the New World. Although no laws protecting workers from occupational hazards were enacted until much later, the first observation that occupational exposure could create health hazards was made in 1775 by a London physician, Percival Pott. He observed among London chimney sweeps an unusually high rate of scrotal cancer that he associated (and rightly so) with exposure to soot. Colonial authorities in Newport, Rhode Island, recognizing a danger of game depletion, established the first closed season on deer hunting as early as 1639. Other communities became aware of the same problem; by the time of the American Revolution, 12 colonies had legislated some kind of wildlife protection. Following the example of Massachusetts, which established a game agency in 1865, every state had game and fish protection laws before the end of the nineteenth century (1). In 1885, to protect the population from waterborne diseases such as cholera and typhoid fever, New York State enacted the Water Supply Source Protection Rules and Regulations Program. These instances of environmental concern were sporadic. It was not until some time after World War II that concern for the environment and for the effects of industrial development on human health became widespread. The industrial development of the late eighteenth century, which continued throughout the nineteenth and into the twentieth century, converted the Western agricultural societies into industrialized societies. For the first time in human history, pervasive hunger in the western world ceased to be a problem. The living standard of the masses improved, and wealth was somewhat better distributed.