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World Resources 1996-97 (A joint publication by The World Resource Institute, The United Nations Environment Programme, The United Nations Development Programme, and the World Bank) (Data edited by Dr. Róbinson Rojas)
2. Urban Environment and Human Health THE URBAN PHYSICAL ENVIRONMENT AND HEALTH
A century and a half ago, average urban mortality rates in European cities were often far higher than those in the surrounding rural areas (56). Bad sanitation, which then referred to a range of poorly understood environmental health hazards rather than just disposal of excreta, was increasingly seen as being responsible for this urban disadvantage. Prominent scientists studied sanitary conditions and health, and reformers in urban centers around the world discussed both the technical and the moral aspects of urban sanitary reform.
In many ways, the so-called sanitary revolution that resulted from these reforms was the environmental movement of the 19th Century. As in environmental discussions today, one of the most heated debates was about the appropriate role for government and whether attempts to impose sanitary improvements constituted an infringement on what would now be called the private sector. Eventually, the reformers won. One reason is that, although the health problems were far worse in poor areas, the wealthy were also at risk. Politicians even worried that the military strength of their nations was being undermined by urban health problems (57). The politically powerful gradually accepted the fact that the threat from these unhealthful urban conditions was indeed public and required a public response.
The environmental concerns of the world's wealthy have moved on, and international attention has followed suit. Now, comparisons of average urban and rural mortality rates do not display the same urban disadvantage, even in countries where urban sanitation is poor. However, as illustrated in the previous section, averages hide gross disparities in the health status of urban dwellers. Many city residents face environmental conditions roughly comparable to those that shocked the bourgeoisie in the 19th Century. Although the environmental health burden for the urban poor, now mostly in the developing countries, may not be as high as it once was, in poor neighborhoods inadequacies in the physical environment remain the most important causes of urban ill health globally (58).
Most of the following discussion centers on the physical environmental conditions that pose a large risk to health and also on the question of who bears the burden. In poor cities, and particularly poor neighborhoods, the most threatening environmental problems are usually those in the household or neighborhood as opposed to the broader city (59). Inadequate household water supplies are typically more damaging than polluted waterways to the health of urban residents. Exposure to air pollution may be higher in smoky kitchens than outdoors. Uncollected waste in neighborhoods poses more of a threat than waste at the city dump. (See Box 2.2.)
The wealthy, by contrast, can avoid some of these local threats by buying better houses in safer neighborhoods or buying water from safer sources. However, many environmental problems, such as air pollution and lead contamination, are spread over large areas, and it is difficult for households or individuals to buy their way out.
In one of the few attempts to compare systematically the environmental health risks in low-income neighborhoods with those of a city as a whole, a recent study of Quito, Ecuador, found that all inhabitants faced a high risk from microbial food contamination and outdoor air pollution, whereas the inhabitants of low-income neighborhoods also faced a high risk from bad water and sanitation, indoor air pollution, and occupational hazards (60). Roughly, the better-off citizens of Quito could do little to avoid buying locally marketed foods or breathing the air outdoors.
Although the aggregate health effects of such citywide problems are typically less than those associated with poor sanitation or other problems affecting poor households, the more articulate and politically influential members of the public often perceive them as the more important health threat. The result is that resources are often devoted disproportionately to addressing these problems relative to their public health impact.
Even in cities that have excellent water systems, relatively clean air, and most other features typically associated with environmental health, there are serious health hazards that fall heavily on the poor. As described below, many of these involve more social than physical threats to health: stress, depression, chemical dependency, and violence. Others, however, such as crowding, clearly have a physical aspect.
The following discussion distinguishes environmental health problems both by their scale of impact (for instance, at the household and neighborhood levels or the city and regional levels)and by the principal environmental medium through which people are affected (air, water, food, and pests)or proximate cause (e.g., traffic accidents). However, there is no truly satisfactory way to classify environmental health hazards, which do not respect boundaries, either physical or conceptual. That, in part, defines the challenge of environmental management: it is not possible to deal with each problem in isolation.
Household and Neighborhood Problems Water and Sanitation
Various diarrheal and other diseases are spread via the fecal-oral route, and this route is far better traveled where water supplies and sanitary conditions are inadequate. Although contaminated water can carry many infectious agents, it can nonetheless be a critical tool in maintaining good hygiene. Washing, even with water that might be better not to drink, can help curb diseases spread by the fecal-oral route as well as a variety of other health problems ranging from scabies to louse-borne typhus.
Better sanitation can lead to less contact with fecal material at defecation sites and less indirect exposure via water, insects, food, or human carriers. Given the number of illnesses and deaths attributed globally to diarrhea, it seems fair to say that human feces remain one of the world's most hazardous pollutants and that related water and sanitation inadequacies still constitute one of the world's most serious health problems.
In many poor urban neighborhoods in the developing world, other hazards contribute to the burden of diseases spread by the fecal- oral route as well. Indeed, the boundaries between water, sanitation, food contamination, insects, and solid waste problems are blurred. Although it is difficult to determine which routes are the most important, the most common technological interventions involve providing new facilities both for supplying water and for sanitation. Epidemiological studies have consistently shown that improving access to such facilities can reduce the incidence of diarrheal disease substantially--more than 20 percent, according to a recent review (61).
In the developed world, these problems were solved, or were at least displaced, by providing indoor piped water and flush toilets to virtually all urban residents. The same is true for the wealthy in developing countries. For the poor majority, however, comprehensive technological solutions like these are unrealistic. Neither low-income residents nor their financially strapped governments can afford anything like complete coverage with indoor plumbing.
In cities of the developing world, households without indoor piping often obtain their water from a number of sources, such as overcrowded or distant communal standpipes, expensive private water vendors, or heavily polluted wells or open waterways. Those without flush toilets may end up using pit latrines, pan latrines, or latrines located over ponds, streams, drains, or open sewers--all of which demand far more rigorous hygiene behavior than is required for the more standardized technologies of the wealthy.
Technical improvements are an important part of the solution, and there has been some success with relatively simple but more hygienic latrines (62). For example, the "ventilated improved pit" latrine developed in Zimbabwe is designed to eliminate flies and odors while providing a more hygienic and comfortable facility. Overcrowding, however, combined with poor maintenance, can and often does defeat such design improvements. Public latrines are difficult to manage and, when overused, can become public health hazards--less hy-gienic and convenient for the user than defecation in the open. Even when private latrines are available, sharing them among several families seems to increase sanitation problems (63).
Poorly treated or untreated wastes released into open waterways can also have health impacts on water users downstream. Although the overall burden on health is relatively small, it can be quite severe locally. During a cholera epidemic, for example, the ingestion of seafood contaminated by sewage can be an important transmission route.
The quality of housing is a significant factor affecting health. Case studies in many larger cities in the developing world show that as much as 30 to 60 percent of the urban population lives in substandard housing, although this percentage may be less in smaller cities (64). Housing quality extends beyond the availability of water or sanitation facilities. Overcrowding, dampness, inadequate insulation from the extremes of heat and cold, pest infestation, noise, dust, inadequate drainage, and insufficient ventilation all contribute to the health risks associated with substandard housing. Women and children, many of whom spend considerable time in the house, are especially subject to these hazards (65).
Overcrowding is particularly common among poor urban residents, many of whom live in cheap boarding houses or tenements. In Delhi, India, a case study of a typical two-story tenement found 518 people (constituting 106 separate households)living in 49 rooms, allowing approximately 1.5 square meters per person (66). Overcrowding can aid the transmission of a variety of infectious diseases, particularly airborne respiratory diseases such as colds, pneumonia, and tuberculosis (67). Overcrowded conditions, where privacy is an unaccustomed luxury, can also be detrimental to mental health, adding stress and contributing to depression and other psychosocial disorders (68).
Also contributing to the psychological burden of inadequate housing for many is insecure tenure. Fear of eviction is a common worry among most low-income tenants or residents in illegal settlements and causes considerable stress (69).
Food, like water, can transmit infectious diseases and harmful chemicals. Infectious bacteria can multiply in food, and some of the bacteria and fungi that grow on food produce toxins. The major health burden arising from food contamination is almost certainly its contribution to the diarrhea and dysentery that figure so highly in the illness and premature death of children in the developing world.
However, the extent to which food contamination is involved in the spread of these diseases is poorly understood. Epidemiological studies give little indication of the relative importance of food contamination, and one of the few attempts to estimate indirectly the share of diarrhea involving food contamination gives a strikingly wide range of 15 to 70 percent (70). Even so, it is safe to say that microbial food contamination is a health problem that is more severe in poor countries than in wealthy ones, although some kinds of contamination, such as salmonella, may be more common in the latter.
Food handling and storage practices are critical factors in food contamination, and the dangers of contamination are heightened where water and sanitation are inadequate. Washing hands before food preparation and avoiding contact between food and flies are two obvious examples of preventive measures in the home. They are also practices that are easier, although less important, in homes with good water and sanitation facilities.
Contamination can also occur during transport or processing, before the food is purchased, which is difficult for the consumer to monitor. Finally, urban con sumption patterns can contribute to food contamination problems. In a study of Monrovia, Liberia, it was found that most poor urban households stored cooked food, and 63 percent of the stored food samples were heavily contaminated with enterobacteria (81 percent for baby foods) (71). On the other hand, rural households were less inclined to store cooked food, and only 39 percent of their food samples were contaminated (72).
In wealthy countries, complex regulations and inspection procedures help to control food-handling practices at the point of sale in restaurants and markets. However, in poor countries, such regulations are often too costly to enforce. Informal means of avoiding bad food provide an important alternative to regulation. For example, the economic lure of future sales and the psychology of personal contact can induce a vendor to avoid selling contaminated food to regular customers. However, such informal mechanisms are generally less effective in an urban context. In any case, measures that help to prevent food spoilage are likely to be far more effective than measures that attempt to stop spoiled food from being sold.
Rats, fleas, and the bubonic plague firmly established pests in the annals of urban environmental health. Even today, a minor outbreak of plague can quickly make international headlines. (See Box 2.3.)However, for most wealthy urbanites of the developed world, diseases transmitted by pests are no longer a major concern. And in urban areas in the developing world, mosquitos and flies are far more important health threats than rats or fleas.
Neither mosquitos nor flies are particularly urban. Indeed, there is a far greater variety of habitats and species of these insects in rural areas. In addition, the opportunities for controlling such disease vectors are generally greater in urban areas. However, some types of disease-bearing mosquitos and flies have adapted well to particular urban habitats and find themselves relatively free of competition (73).
The Aedes aegypti mosquito breeds in small containers, such as flower vases and water drums, and has been carried from its East African home to every tropical continent, often following the used tire trade. Its Asian relative, Aedes albopictus , is now using the same trick and has recently invaded North and South America, the Mediterranean, and West Africa. Both of these species transmit dengue, a disease of increasing importance in Latin America and Southeast Asia.
In African and Indian cities, malaria is the most prevalent mosquito-borne disease and is often a prime cause of hospital admissions and deaths, particularly among children. In Accra, for instance, malaria accounted for more than 40 percent of reported illnesses at outpatient facilities from 1987 to 1990 (74). In both regions, urbanization has created important new breeding sites. In India, for instance, the Anopheles stephensi mosquito breeds in overhead water storage tanks.
Just as urban mosquito problems are intimately linked to water, urban fly problems are linked to waste. Various families of flies have adapted to the opportunities of urban ecology. The most obvious health risk is that they provide a shortcut on the fecal- oral route, although the extent of their contribution is still not clear. The housefly, along with several other species, is a filth feeder and breeder. Given poor sanitation, some flies are likely to be in contact with human feces and later land on human food, drink, or skin. Piles of garbage increase fly populations. Open food preparation and food storage areas provide opportunities for flies to land on food.
Some diseases are transmitted by mites, face flies, or other pests that thrive in dwellings or neighborhoods (75). Chagas' disease is carried by triatomine bugs, leishmaniasis by sand flies, schistosomiasis by snails, scabies by mites, and yaws by face flies. Globally, these diseases are less serious urban health problems than those spread by mosquitos or the fecal-oral route diseases transmitted by flies. In many locations, however, they can be critical problems.
Some of the measures used to control insects and other pests indoors create their own environmental health threats. Mosquito coils and other substances burned to repel insects cause air pollution. Indoor spraying with aerosols and pump sprays exposes residents to potentially damaging pesticides. There may well be cases in which the health damage caused by using such measures outweighs their sometimes minimal effect on the spread of pest- borne disease.
Air Pollution from Domestic Sources
For much of the 20th Century, air pollution has been identified with urban smog or smoke spewing forth from factory chimneys. In wealthy countries, these images can seem outdated amid discussions of invisible pollutants. In the developing world, however, smoky household fires probably constitute the largest air-pollution health hazard, with women and children being the principal victims.
Studies of personal exposure and indoor air pollution levels indicate that although there is considerable variation, many users of smoky fuels are exposed to disturbingly high levels of particulates and other pollutants (76). Rough data suggest that, on average, indoor air pollution tends to be a problem that is worse in rural environments than in urban environments. However, in the homes of the urban poor, especially those in small towns, particulate concentrations are likely to be higher than urban averages and to exceed those of rural households.
Three major health risks have been associated with the domestic use of polluting fuels (77). First, by irritating the respiratory passages and perhaps through other means, pollution from domestic fuels may facilitate the spread of acute respiratory infection, a major killer of children under age 5 in poor countries (78). Second, long-term exposure may contribute to chronic lung diseases such as chronic bronchitis, emphysema, and asthma, which are significant health problems among adult women. Third, long-term exposure is a risk factor for cancer.
As with inadequate water supplies and sanitation, the extent of ill health actually caused by exposure to domestic smoke is difficult to determine. Cancer and chronic respiratory problems are likely to be the consequence of long-term or past exposures, which are hard to assess. There are many other risk factors for respiratory infection--crowding, poor ventilation, malnutrition, poor sanitation, and lack of immunization--and they tend to be interrelated (79). Other sources of domestic air pollution may relate to respiratory illness as well, such as mosquito coils, waste burning, and tobacco smoking. Generally, the women and children who are more exposed to air pollution from domestic fires are also likely to be more exposed to other environmental hazards, which could also account for ill health.
Household fuel choice in the developing world is often described as an energy ladder, with dirty fuels such as crop residues and firewood at the bottom. These are followed by charcoal, kerosene, liquid propane gas, and finally, electricity (80). Generally, the higher up the ladder, the less polluting the fuel. The cleaner and more convenient fuels such as kerosene, liquid propane, and electricity are usually favored by wealthy households.
Although wood and crop wastes are less common in cities, charcoal and coal are fairly common. Charcoal is widely used by poor and even middle-class households in African towns and cities and, to a lesser extent, households in Asian and Latin American urban areas. In terms of respirable particulates, which probably represent the major health risk of these fuels, charcoal is considerably less polluting than wood, although carbon monoxide exposure may be higher (81). Coal emissions are heavily dependent on the type of coal, but they can be relatively high in both particulates and carbon monoxide (82). Studies of coal use in China have produced some of the most convincing evidence of a link between domestic fuel use and cancer (83).
Some indoor air pollution problems are specifically urban. A large number of domestic users of smoky fuels can create a neighborhood air pollution problem and can even contribute to citywide air pollution problems, as has happened in Beijing. Studies in South Africa indicate that whether the neighborhood is electrified, and perhaps even whether the school is located in an electrified neighborhood, can make a significant difference in the level of children's exposure to particulates (84). Exposure to pollution from domestic fires therefore seems to be yet another factor that cannot be easily controlled by individual households in an urban setting.
Although smoke and other combustion products are perhaps the most damaging of indoor air pollution, they are not the only source. Formaldehyde, chloroform, and other organic chemicals emitted by building materials or furnishings, asbestos fibers from insulation materials, and radon are other significant pollutants. These may be of particular concern in office buildings or other urban institutional settings that have restricted or closed-loop ventilation systems, giving rise to the so-called sick building syndrome (85) (86).
Most domestic solid waste is not a direct threat to health, although it is safer to avoid it. Compared with industrial waste, it contains few hazardous chemicals. However, fecal matter is often mixed with domestic waste, especially where disposable diapers are used or sanitary facilities are scarce. If solid waste is kept in closed containers and removed regularly, as is usually the case in wealthy neighborhoods in developing and developed countries, the health risks to local residents are minimal.
Problems of waste disposal are most severe in poor cities in developing countries. Door-to-door waste collection is too expensive for many households or municipalities to afford, and in any case, the streets of many poor neighborhoods are too narrow for vehicles. Collection points can easily become small garbage dumps, especially when collection is intermittent. In many poor countries, public budgets have been under great pressure in recent years, and waste collection is often among the services to suffer most (87) (88). Solid waste often creates one of the most visible environmental problems in low-income communities.
The two groups most directly exposed to solid waste are children and wastepickers in low-income neighborhoods in cities in developing countries. Accumulated garbage, however, can also contribute indirectly to neighborhood environmental health problems by providing food or breeding sites for flies and other pests.
Although the environmental threats people are exposed to in their homes and neighborhoods tend to pose the greatest health risks, some citywide problems pose significant risks as well. These include occupational exposures, ambient air pollution, traffic accidents, and exposure to lead. Box 2.4 explores which types of problems tend to be most severe--household or citywide--by wealth and city size.
Hazards in the workplace can be a significant addition to the health burdens that urban life imposes. These can include contact with a wide range of toxic substances and communicable diseases, unsafe machinery, unhealthful noise levels, inadequate lighting or ventilation, and extremes of heat or cold. These hazards are often made worse by a lack of protective clothing or equipment (89).
In many developing countries, the problem of occupational hazards is compounded by the lack of any sick pay or compensation for workplace injuries, as well as a lack of adequate occupational health care (90). In developing nations in Asia and Africa, less than 25 percent of the work force is thought to have access to any kind of occupational health service (91). In addition, appropriate occupational health standards have been neither universally adopted nor enforced.
Occupational exposures are thought to be widely underdiagnosed and underreported and therefore to be a greater problem than government statistics sometimes indicate (92). For example, researchers found that the number of health-impaired workers at a single Mexican steel mill was roughly twice the number officially recorded for the whole of Mexico in 1988; the researchers reported that more than 80 percent of the mill workers were exposed to extreme heat, noise, and toxic dust (93).
The most common occupational diseases include respiratory diseases caused by particulates such as asbestos, silicon, and cotton; metal poisoning from lead; pesticide poisoning; hearing loss from excessive noise; and skin diseases due to chemical exposures (94) (95). In some instances, disease rates among exposed workers can be very high. In asbestos factories in Bombay, India, one third of workers suffered from asbestos-related lung disease, according to a 1983 report (96).
Health hazards in the workplace may be exacerbated by malnutrition or the burden of chronic diseases that workers already suffer from, both of which may lower resistance to toxic insults or infectious diseases encountered at work. For example, nonalcoholic liver disease is widespread among Africans and Asians and may make workers who suffer from it less able to detoxify the poisons that they encounter in the workplace (97).
Hazards may also be intensified by climatic conditions, such as hot and humid weather, which make it more difficult to convince workers to use protective clothing such as respirators or aprons. Long working hours, frequently demanded by employers in the developing world or opted for by the workers themselves for financial reasons, can play a part in increasing exposures to chemical toxins or increasing accident rates due to fatigue (98).
Occupational hazards are a particular problem in small-scale or home-based industries. Small enterprises make up a surprisingly large percentage of the industrial base in many nations. For example, small-scale industries with fewer than 50 employees constitute more than 40 percent of all industries in Southeast Asia. However, conditions in these settings are often much worse than those in larger industries, with poorer physical facilities, less money available to buy safe machinery or safety equipment, and a lower priority given to worker protection and safe operating procedures (99) (100).
Small workshops and informal or home-based enterprises are often the worst in terms of occupational exposures, frequently making use of toxic chemicals without the proper equipment or precautions and sometimes spreading contaminants into the home environment. For example, automobile mechanics and gas vendors in many urban settings are routinely exposed to benzene, a gasoline additive, and suffer high rates of anemia and other diseases associated with benzene exposure (101). In Jamaica, workers in small enterprises that repair and recycle lead-acid batteries often suffer from lead contamination, which can also affect their customers and families (102).
Ambient Air Pollution
In those cities with high air pollution levels and a combination of geography and weather that prevents pollutants from dispersing, ambient air pollution can pose a significant health risk to rich and poor alike. That risk is compounded in cities where air pollution regulations or enforcement is weak. Worldwide, an estimated 1.1 billion urban residents are exposed to particulate or sulfur dioxide levels in excess of the guidelines set by the World Health Organization (WHO) (103).
Although air pollution traditionally has been linked to industrial emissions, motor vehicles have now become a major source of pollution in many cities. The problem is particularly pronounced in cities with large numbers of poorly maintained vehicles and widespread use of leaded gasoline, which is still common in Latin America, Asia, and Eastern Europe.
Studies confirm the ill effects of outdoor air pollution on health. Pollution at the levels typically found in the air of large cities has been implicated in both acute and chronic illnesses, such as asthma and chronic bronchitis. Those most vulnerable are children, the elderly, cigarette smokers, and those who already have respiratory difficulties. Most research has concentrated on particulate matter, sulfur dioxide, and nitrogen oxides. The most dangerous pollutants appear to be small particles under 10 microns in diameter, which can be easily breathed into the lungs (104) (105). These arise mostly from motor vehicle exhaust, coal-fired power plants and boilers, and certain manufacturing industries.
Recent studies give strong evidence of the relationship between particulate air pollution and premature death (106) (107). One U.S. study that followed some 550,000 people in 151 cities over 7 years found that residents of the most polluted cities have a 15 to 17 percent higher risk of premature death from all causes than residents of the least polluted cities (108) (109). Since the late 1970s, epidemiological data from cities in the United States have consistently suggested that air pollution kills--primarily through respiratory or cardiovascular dise ase--about 30,000 to 60,000 people per year, accou nting directly for 2 to 3 percent of all deaths (110) (111).
Such results have been replicated in urban areas in other countries as well. Studies in the Czech Republic and in Poland, parts of which suffer from very high pollutant levels, suggest that, as in the United States, 2 to 3 percent of all deaths there could be attributed to air pollution (112) (113). A similar study in Jakarta, Indonesia, where concentrations of particulates are also very high, estimates that reducing airborne particulates to the level recommended by WHO could prevent 1,400 deaths, about 2 percent of annual deaths in the city (114) (115).
Although these data suggest that air-pollution-related deaths are only a modest contributor to urban mortality rates, the role of air pollution in causing ill health among urbanites is much wider. For example, in Jakarta, researchers estimated that compliance with WHO guidelines could prevent some 600,000 asthma attacks and 125,000 cases of bronchitis in children each year (116).
An estimated 885,000 people per year lose their lives in traffic accidents, according to WHO (117). The majority of traffic accidents (70 percent)occur in the low-and middle-income countries of the developing world, even though private vehicle usage is markedly lower there than in wealthier nations (118). The differences in risk per vehicle are dramatic: in several African countries, fatality rates exceed 100 per 10,000 registered vehicles, compared with fewer than 4 in Western Europe. In Kenya, 40 percent of road accidents happen in cities and 60 percent occur in rural areas.
The rate of fatal injuries per registered vehicle has climbed 300 percent since 1968 in Africa, whereas it has dropped slightly in the developed world (119). One reason for the higher fatality rate is that each incident frequently affects many people, for example, when an accident involves an overcrowded bus. Inadequate safety standards are another contributor to high fatality rates.
In developing countries, pedestrians account for about 40 percent of deaths from traffic accidents, compared with 20 percent in developed countries (120). A major reason for this is the concentration of different road users jostling for space on crowded city roads.
Exposure to Lead
Lead is ubiquitous in the urban environment. Emissions from vehicles burning leaded gasoline constitute an important source of dispersed lead in many urban areas. Industrial emissions, particularly from smelters and battery recycling plants, are also a significant source.
Humans are exposed via the inhalation of contaminated air, ingestion of contaminated water and foods, and, especially among children in North America, ingestion of lead-based paint. Contact with and ingestion of contaminated soil provide another important route of exposure, particularly among children. Serious occupational exposures occur among adults involved in metal industries, electronics industries, construction trades, and battery manufacturing.
The adverse effects of lead on health have been recognized for centuries. Lead's principal threat, other than acute lead poisoning, is neurological damage in children. A 1988 study in Mexico City, where ambient lead levels are high because of the use of leaded gasoline, found that more than one quarter of newborns had blood lead levels high enough to impair neurological and motor- physical development (121).
Studies conducted in North America, Western Europe, and Australia report that elevated levels of exposure to lead in infancy cause intellectual impairment, although quantifying this impairment is still somewhat controversial (122). Children with elevated dentine lead levels are reported to have a deficit in intelligence scores, speech, and language processing skills compared with children with low lead levels (123). A 1990 study in Bangkok, Thailand, a city heavily polluted with lead, suggested that 30,000 to 70,000 children risked a loss of four or more IQ points because of high lead levels, and many more risked lesser reductions in intelligence (124).
Moreover, it has been suggested that exposure to high lead levels in childhood may be associated with dropping out of high school, reading disability, absenteeism, and neurodevelopmental deficits later in life (125). Some studies have also linked increases in blood lead levels in adults with elevated blood pressure, although this finding has not been borne out in all studies (126) (127).
The findings of neurological impairment in children sparked the effort in the 1970s and 1980s to reduce lead levels in gasoline and other sources in the United States and Europe--an effort that has resulted in lower ambient and blood lead levels in these areas. Blood lead concentrations in the United States, for instance, have dropped substantially since the late 1970s, when the use of leaded fuel was phased out. Many countries in developing regions, however, have yet to enact such regulations, and the risk of exposure to lead remains dangerously high.