Each year, air pollutants adversely affect the health of 4-5 billion people worldwide (World Bank 1992, Leslie and Haraprasad 1993, WHO/UNEP 1993). Air pollution is increasing because of the activities of the expanding world population: the burning of fossil fuels, the increased emissions of industrial chemicals, and the increased use of automobiles. In particular, automobile numbers are growing approximately three times faster than the world population (WHO/UNEP 1993). Although governmental efforts since the 1950s have led to significant improvements in urban air quality in many developed nations, overall emissions continue to rise with the expanding human population. Because developing and East European nations have negligible pollutant emission controls, living conditions are becoming especially hazardous in their growing urban areas.
By 1993, air pollution levels in all 20 of the world's largest cities exceeded World Health Organization guidelines (WHO/UNEP 1993). For example, during the winter months, particulate concentrations in Santiago, Chile, were among the highest observed in world urban areas {300-400 ug/m3). Los Angeles has the highest density of automobiles per person in the world, so it is not surprising that EPA standards for ozone levels were exceeded at all city monitoring stations in 1990. Moreover, the average exposure to carcinogens from automobiles in Los Angeles is as much as 5000 times greater than the level considered acceptable by the EPA (Mann 1991, Wilken 1995).
Air pollution is also rampant in China, where less than 1% of 500 Chinese cities surveyed have clean air (Zimmerman et al. 1996). From 1955 to 1984, the prevalence of respiratory diseases in China rose by 50%. Respiratory diseases occur at a rate five times higher in China than in the United States; indeed, they are the leading cause of death in China (Zimmerman et al. 1996).
Compounding this public health problem is a nearly fivefold increase in cigarette use in China over the past few decades, from approximately 360 to nearly 1800 cigarettes per person each year (World Bank 1992). Although Chinese males smoke 98% of the cigarettes, mortality due to lung cancer is approximately equal in males and females (Leslie and Haraprasad 1993).
The problem of respiratory diseases is not limited to China. Worldwide, the incidence of respiratory disease is increasing along with cigarette use. In fact, the two major underlying causes of premature death in the world are the significant increases in tobacco use and HIV. Exhaled tobacco smoke contains more than 3800 chemicals, including numerous carcinogens (Hulka 1990). Smoking causes approximately 3 million deaths annually, 2 million in developed countries and 1 million in developing countries (WHO 1995, Murray and Lopez 1996). In industrialized nations as a whole, the prevalence of lung cancer increased approximately threefold from 1950 to 1986. US death rates from lung cancer alone increased nearly fourfold between 1950 and 1990 (WHO 1994). In 1990, nearly 419,000 US deaths were attributed to smoking (WHO 1994). By 2020, predictions are that tobacco will cause 10 million deaths per year worldwide (Murray and Lopez 1996).
Globally, but especially in developing nations where people cook with fuelwood and coal over open fires, approximately 4 billion humans suffer continuous exposure to smoke (WHO 1992, World Bank 1992, Leslie and Haraprasad 1993, WHO/UNEP 1993). This smoke, which contains large quantities of particulate matter (Leslie and Haraprasad 1993) and over 200 chemicals, including several carcinogens (Godish 1991), results in pollution levels that are considerably above those considered acceptable by the World Health Organization (WHO 1992, World Bank 1992, Leslie and Haraprasad 1993, WHO/UNEP 1993). Fuelwood cooking smoke is estimated to cause the death of 4 million children each year worldwide (World Bank 1992). In India, where people cook with fuelwood and dung, particulate concentrations in houses are reported to range from 8300 to 15,000 ug/m3, greatly exceeding the 75 ug/m3 maximum standard for indoor particulate matter in the United States (Christiani 1993).
Radon radiation from the earth, another indoor air pollution hazard, is a growing problem, in part because of the modern construction of airtight houses. During the past 30 years there has been a four- to five-fold increase in radon concentration in houses in Sweden (Lindvail 1992). In the United States, radon radiation is considered to be a significant cause of lung cancer, causing approximately 14,000 deaths per year (CEQ 1996).
In general, air pollutants exacerbate asthma, which ultimately can become severe enough to cause death. Worldwide, the incidence of asthma has increased nearly 50%, from 1.3 cases per 100,000 people in 1980 to 1.9casesper 100,000in 1989 (WHO 1993a). Deaths of children younger than 5 years of age from acute respiratory infections more than doubled, from 2.2 million worldwide in 1985 (USBC 1996) to the current level of approximately 5 million per year (WHO 1995). In addition, 400 million cases of acute lower respiratory infections are reported each year, of which an estimated 4.4 million are fatal (WHO 1996f).
Atmospheric pollution also adversely affects the stratospheric ozone layer, which protects organisms from heavy doses of ultraviolet radiation (McMichael 1993). Before October 1980 at the South Pole, which is the site of the greatest ozone depletion, the measures ranged between 250 and 325 DU (Dobson Units). These values have declined to dangerous levels -- between 125 and 175 DU. The acceptance of the 1987 Montreal Protocol has helped to reduce the worldwide production, use, and release of ozone-destroying chlorofluorocarbons (McMichael 1993). However, the ozone layer continues to be depleted, in part from the release of pollutants from increased burning of wood and from the worldwide use of the methyl-bromide fumigant (Coleman et al. 1993).
Estimates are that every 1% decrease in the ozone layer increases cancer-inducing UV-B radiation by 1.4% (McMichael 1993). Exposure to sunlight, including UV-B radiation, accounts for 70% of skin cancers in the United States (McMichael 1993). At present, skin cancer prevalence is increasing between 30% and 50% every 5 years in many North American Caucasian populations (Coleman et al. 1993). For example, in the United States, the prevalence of new cases of skin cancer increased from approximately 10,000 cases in 1975 to 40,000 in 1996, while the number of deaths from skin cancer rose from approximately 4000 to 9490 (Schultz 1997).
Although the use of lead in US gasoline has declined since 1985, yearly emissions of lead into the atmosphere from other sources remain near 2 billion kg and continue to threaten public health (O ECD 1985). Lead poisoning causes anemia, kidney problems, and brain damage. Children exposed to lead are particularly at risk of brain damage and reduced learning capabilities (Ittenbach et al. 1995, Renner 1995). Even now, an estimated 1.7 million children in the United States are exposed to hazardous levels of lead and have blood levels above the acceptable level of 10 ug/dL (CEQ 1996).
Benzene, a carcinogen that causes leukemia even from exposure to low dosages (1-30 ppm), is a common component of gasoline and is therefore released into the atmosphere (Krstic 1994, UKDE 1996). From 1950 to 1980, US benzene production increased from 0.7 billion kg to 4.6 billion kg, and production is currently approximately 7.4 billion kg/yr (WR11994). Although the general use of benzene as a solvent has decreased as its negative effects have become better known (Krstic 1994, UKDE 1996), benzene use needs to be further reduced to lessen current public health problems.
Pesticide pollution and disease
Since the first use of DDT for crop protection in 1945, the global use of pesticides in agriculture continues to expand. From approximately 50 million kg of pesticides in 1945, global usage has since risen 50-fold, to approximately 2.5 billion kg/yr worldwide (Pimentel 1995). In the United States, the use of synthetic pesticides has grown 33-fold since 1945, to approximately 0.5 billion kg/yr (Pimentel 1995). The increase in related hazards is greater than the increase in applied amounts because most modern pesticides are more than 10 times as toxic to organisms than those used in the early 1950s (Pimentel 1995).
In 1945, when synthetic pesticides were first used, few human pesticide poisonings were reported. But by the late 1960s, when pesticide use and toxicity had increased dramatically, the number of human pesticide poisonings also rose (Pimentel 1995). In California, the use of pesticides increased from 68 million kg in 1950 to 269 million kg in 1988, while the number of reported human poisonings rose from 115 to 903 cases per year (Maddy et al. 1990). The total number of pesticide poisonings in the United States increased from 67,000 in 1989 to the current level of 110,000 per year (Litovitz et al. 1990, Benbrook et al. 1996). This trend continues today.
By 1973, when global pesticide use was approximately 1.3 billion kg/yr, the number of human pesticide poisonings reached an estimated 500,000, with approximately 6000 deaths (Labonte 1989). Two decades later, Pimentel (1995) reported that worldwide pesticide use had risen to approximately 2.5 billion kg. By 1992, approximately 3 million human pesticide poisonings were reported each year, with approximately 220,000 fatalities and 750,000 cases of chronic illnesses (WHO 1992).
Available US data indicate that 18% of all pesticides and approximately 90% of all fungicides are carcinogenic and pose a hazard to human health (NAS 1987). Several other studies substantiate the adverse effects of pesticides on the human respiratory system. For example, among a group of professional pesticide applicators, 15% suffered asthma, chronic sinusitis, or chronic bronchitis, compared with only 2% for people who used pesticides infrequently (Weiner 1972).
In addition, pesticides, especially the organophosphate and carbamate classes, adversely affect the nervous system by inhibiting cholinesterase. This problem is particularly critical for children because their brains are more than five times larger in proportion to body weight than the brains of adults. In California, 40% of the children working in agricultural fields have blood cholinesterase levels below normal, a strong indication of organophosphate and carbamate pesticide poisoning (Repetto and Baliga 1996).
The effect of land degradation on disease incidence
Soil is easily contaminated by a wide array of chemicals and pathogens. Humans may acquire chemical pollutants and pathogens directly from the soil (i.e., by contact with it) or indirectly, through food and water. At times, soil particles themselves may be pollutants, entering the eyes, nose, and mouth and acting as irritants or allergens.
Cleared and exposed soil is highly susceptible to wind and water erosion. Wind erosion can cause serious health problems by blowing soil particles and microbes into the air. These windborne particles irritate the respiratory tract and eyes while aggravating allergies and asthma. Erosion also disperses toxic chemicals, such as heavy metals and pesticides, leading to contaminated food and water. Furthermore, erosion strips soil of its nutrients and thus lowers food crop productivity and ultimately reduces human nutrition.
As people invade natural ecosystems and land is cleared of trees, soil is exposed and the chances increase of humans becoming infected by helminths, such as hookworms, and microbes, such as pathogenic Escherichia coli (WHO 1992). Such increases were observed in 1984 in Nepal, a mountainous country that is experiencing serious soil erosion and severe disease problems: 87% of the population was infected with helminths (Suguri et al. 1985, Metz 1991). Children suffer greater morbidity from helminthic infections than adults because children need more protein than adults per kilogram of body weight; under severe parasitic infections, they may be unable to utilize protein efficiently enough to remain healthy.
In addition, many helminth species that infect humans are found in soil contaminated by human feces, thereby exacerbating the cycle of exposure. Worldwide, approximately 2 billion people are estimated to be infected with one or more helminth species, either by direct penetration or by consumption of contaminated food or water (Hotez et al. 1996). The most prevalent helminths are hookworms (Necator americanus and Ancylostoma duodenale), Strongyloides (Strongyloides stercoralis), and Ascarids (Ascaris lumbricoides). In locations in which sanitation is poor and people are overcrowded, as in parts of urban Africa, up to 90% of the population may be infected with one or more helminth species (Stephen-son 1994).
Food contamination, disease, and malnutrition
Worldwide, reported cases of food-borne diseases are as high as 240 million per year (WHO 1990). In the United States, approximately 6.5 million foodborne disease cases occur each year, causing approximately 9000 deaths (Todd 1996).
Poultry, hogs, cattle, and other animals are easily contaminated with Salmonella enteritidis and various E. coli microbes, especially when they are crowded together in husbandry facilities with inadequate waste disposal systems (Lederberg et al. 1992). Further microbial contamination can be caused by unsanitary conditions during slaughtering, processing, and handling. In the United States, hen eggs have been identified as the main source of S. enteritidis, which can cause severe gastrointestinal illnesses and sometimes death in humans, especially among children and the infirm (Altekruse and Swerdlow 1996). Worldwide, between 1979 and 1987, S. enteritidis infections increased significantly in 24 of the 35 countries reporting to the World Health Organization (Altekruse and Swerdlow 1996).
Malnutrition, which includes inadequate intake of calories, protein, and numerous essential vitamins and minerals, is a major disease related to environmental degradation. Malnutrition prevails in regions in which the overall food supply is inadequate, where populations lack economic resources to purchase food, and where political unrest and instability interrupt food supplies. In addition, rapidly expanding human populations intensify the food-supply problems by diminishing the per capita availability of cropland (Pimentel and Pimentel 1996).
In 1950, 500 million people (20% of the world population) were considered malnourished (Grigg 1993). Today more than 3 billion people (one-half of the world population) suffer from malnutrition (WHO 1996e), the largest number and the highest rate in history. Each year, between 6 and 14 million people die from malnutrition (Murray and Lopez 1996). Malnutrition problems are also on the increase in the United States, especially among the poor.
In many parts of the world, especially in developing countries, severe shortages of vitamin A cause blindness and death. For example, in the Sahelian region, as well as in west and east Africa, per capita consumption of vitamin A has been declining during the past 10-20 years, while associated serious eye problems have been increasing (ACC/SCN 1992). Worldwide, approximately 258 million children are vitamin A deficient (WHO 1996e). Each year, vitamin A deficiency causes approximately 2 million deaths and 3 million serious eye problems, including blindness (Murray and Lopez 1996).
Similarly, iron intake per person has been declining during the past 10-30 years, especially in sub-Saharan Africa, south Asia, China, and South America, because of inadequate nutrition resulting from overall shortages of food (ACC/SCN 1992). Globally, more than 2 billion people are iron deficient, and the problem is severe enough that 2 billion people suffer from anemia (WHO 1996e). Worldwide, an estimated 20% of malnutrition deaths can be attributed to anemia (Murray and Lopez 1996). In addition, approximately 1.6 billion people live in iodine-deficient environments and suffer from iodine-deficiency disease (WHO 1996e).
Malnutrition, complicated by parasitic infections, is frequently found in poverty-stricken areas with inadequate sanitation. Malnourished individuals, especially children, are seriously affected by parasitic infections because these infections can reduce nutrient availability. The presence of intestinal parasites frequently diminishes appetite and food intake. Their presence also increases the loss of nutrients by causing diarrhea and dysentery. Hookworms, for instance, can suck as much as 30 mL of blood from an infected person each day, gradually weakening individuals and lowering their resistance to other diseases (Hotez and Pritchard 1995). Because an estimated 5-20% of an individual's daily food intake is used to offset the effects of parasitic illnesses, the overall nutritional status of a parasite-infected person is greatly diminished over time (Pimentel and Pimentel 1996).
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