• Understand the major ways in which environmental pollutants such as industrial chemicals make their way into humans
  
• Learn appropriate methods of personal drinking water treatment and sanitation for traveling and living in the developing world
  
• Learn to recognize health problems caused by contaminated drinking water or inadequate wastewater treatment and the benefits enjoyed by populations with good drinking water and sanitation
  
• Gain a basic understanding of appropriate methods of treating community drinking water and wastewater in the developing world
  
• Understand the magnitude of, health effects associated with, air pollution

Environmental factors profoundly influence human health. A 2006 report by the World Health Organization (WHO) estimated that 24% of the world’s burden of disease, and about a third of the burden in children, is due to preventable environmental factors.1 By preventable, it is meant that these risks can be altered or mitigated. This burden of avoidable disease is disproportionately felt by the residents of poor countries, with attributable disease burdens often 10-fold higher or more than that seen in wealthier nations.2 Reasons for the disproportionate effects felt in developing countries include a lack of modern technology, weak protective environmental laws and regulations, a lack of awareness, and poverty.3 Nonetheless, residents of wealthy countries are also affected by air pollution, poorly designed urban environments, flooding, and lead poisoning, among other risks, and thus environmental health is truly of global concern.

Unclean water and poor sanitation remain the most potent environmental causes of illness worldwide. Industrial chemical contaminants affect health everywhere. Of the more than 30,000 chemicals commonly used today, fewer than 1% have been studied in detail as to their health effects and toxicity,4 and our understanding of the effects of simultaneous low-level exposure to hundreds or thousands of chemicals is rudimentary at best. Air pollution has been found to be a top-ranked problem in nearly every country undergoing economic transition. This chapter outlines a number of the global environmental challenges to health.

Environmental hazards include biologic, physical, and chemical ones, along with the human behaviors that promote or allow exposure. Some environmental contaminants are difficult to avoid (the breathing of polluted air, the drinking of chemically contaminated public drinking water, noise in open public spaces); in these circumstances, exposure is largely involuntary. Amelioration or elimination of these factors may require societal action, such as public awareness and public health measures. In many countries, the fact that some environmental hazards are difficult to avoid at the individual level is felt to be more morally egregious than those hazards that can be avoided. Having no choice but to drink water contaminated with very high levels of arsenic, as is the situation in Bangladesh, or being forced to passively inhale tobacco smoke in restaurants, outrages people more than the personal choice of whether an individual smokes tobacco. These factors are important when one considers how change (risk reduction) happens.

It should be noted that environmental health hazards often affect political elites as well as the poor in many countries. Although there are usually higher risks for the poor than the rich, principally because the rich enjoy improved disinfection of drinking water and sanitation, other hazards, such as air pollution or chemical and heavy metal contamination of foodstuffs, can affect all sectors of society, assisting in the development of a political consensus for change.

Some environmental hazards are associated with specific individual human behaviors, which in principle can be changed. In the absence of clean water and sanitation, simple handwashing with soap has been shown to dramatically decrease the rates of infectious diseases such as diarrhea, pneumonia, and impetigo.5 Occupational exposures to pesticides, fertilizers, and microbial pathogens can be minimized by the use of protective gear, careful application techniques, and the provision of water and soap for decontamination. Irrigation not only improves crop production but also provides a conducive environment for the expansion and transmission of waterborne diseases such as schistosomiasis. In this case, reducing body contact with water will decrease rates of disease.

The handling of environmental hazards to human health must be tailored to the contaminant(s) and to the associated behaviors. It usually involves an assessment of the health burden, the routes of exposure, and identification of the stakeholders. Economic factors are often critical. Because the burden of disease may fall on people who do not share in the economic or social benefits of an environmental hazard, community action or political negotiations are often involved in the amelioration of environmental risks.

Biologic Hazards

The term biologic hazards usually refers to diseases caused by pathogens such as viruses, bacteria, prions, fungi, and parasites. It should be noted that the product of an infection can cause disease as well as the live pathogen. For example, in Ghana and other countries where foodstuffs may be stored in a damp state, fungal infections of tubers or maize (corn) produce aflatoxins, proteins that are potent carcinogens that especially affect the liver.

An astounding 94% of the disability-adjusted life years (DALYs) of disease burden due to diarrhea, principally caused by viruses and bacteria, is environmental in origin.1 Approximately 1.5 million deaths a year, mostly in young children, are caused by poor sanitation, contaminated water, and lack of hygiene (a complex behavioral and socioeconomic component). When feces and urine are not disposed of carefully, and when hygiene (the ability to wash hands with soap) is absent, human pathogens contaminate food, surface and groundwater, and hands. Lifespan in the United States increased in the period from 1900 to 2000 by more than 3 decades, and a good two thirds of this increase has been attributed to clean water, clean food, and sanitation.6 One reason that some countries with limited budgets for health, such as Cuba and Costa Rica, have recently achieved major increases in lifespan and major decreases in childhood mortality and adult morbidity is that they have focused on water and sanitation risks.7 If you take a single point away from this chapter, it is the crucial importance of keeping human and animal feces out of water and food.

Pathogens found in human feces are exquisitely adapted to causing human disease, and it should be obvious that breaking the cycle of transmission through basic sanitation and the provision of clean water should be an extraordinarily high societal priority.8 The major pathogens causing illness and death through these transmission pathways include rotavirus, enteroviruses (a group that includes polio), Salmonella, Shigella, Escherichia coli, Cryptosporidium, Campylobacter, and hepatitis A and E viruses. Some of these are shared with domestic or peridomestic animals of economic importance, such as Salmonella, Campylobacter, E. coli, and Cryptosporidium. Typhoid (Salmonella typhi), in contrast to most of these pathogens, is a disease only of humans, and one way to judge the adequacy of water treatment and sanitation is to look at decreases in typhoid incidence.

Water Supply

The issues of water supply and sanitation in the developing world are of great importance. As the saying goes, “An ounce of prevention is worth a pound of cure.” More to the point is the fact that public health engineers have saved many more lives than doctors over the course of human history. Safe, clean drinking water and adequate sanitation are critical needs for the developing world. However, projects to improve these conditions must include appropriate technology, cultural sensitivity, and long-term management procedures or they will quickly fail.

Water supply starts at the source, either surface water or groundwater. Surface water (i.e., streams, lakes, rivers, or ponds) is easily found and used. Large rivers and lakes provide year-round sources of water, whereas small streams and ponds may fail in dry seasons. Impoundments (dams) may be used to store stream flow from the wet season to supply community needs during the dry season. However, all surface water sources are unprotected. That is, they are very susceptible to pollution and should not be used without treatment.

Groundwater falls into two sources, shallow and deep. Shallow groundwater comes from water infiltrating the soil and trickling down until it is caught on top of the bedrock. This upper aquifer, or water table, fluctuates in depth depending on the season, dropping in dry seasons and rising in wet weather. Although the soil can filter out many pollutants, shallow groundwater is susceptible to pollution and should be used with care.

Shallow groundwater is tapped through wells or springs. Shallow wells are typically hand dug down to the water table and use a hand pump or bucket to bring water up. Springs are natural points where the water table meets the ground surface and water seeps out. Typically these occur at the toes of slopes or on hillsides.

Shallow wells and springs are very common water sources for developing countries. Although they are not pristine sources of water, the method of getting water from them can add considerable pollution to the water, and the solutions are usually easy and inexpensive to use. For wells, a small wall around the top of the well made of stone, brick, or concrete serves to keep animals and small children from falling in and diverts rainwater runoff from entering the well. A cover also serves to protect the well from trash and pollution; providing a bucket and rope, with a windlass to gather the rope when out of use, solely for the well helps keep these items clean and keeps dirt out of the well (Figure 6-1).

Hand pumps provide the best protection for a shallow well because the well remains covered while the water is withdrawn. Further, using a bucket and rope will introduce some contamination because buckets are frequently set on the ground, and ropes pass through the unwashed hands of the users. Many types of hand pumps are available in developing countries, and their use is limited only by cost. They typically cost more than submersible electric pumps in the United States but have the advantage of working without power (Figure 6-2).

If an event occurs to contaminate a well, perhaps an animal drowning in the bottom, it is possible to “shock” the well to cleanse it. This will remove the existing pollution but will not guard against recontamination. The procedure is to add chlorine, typically in the form of bleach, to the well and then draw out all of the chlorinated water and dispose of it. This prevents people from drinking overchlorinated, and dangerous water, and removes the source of contamination. The bleach should be added to a bucket of water, mixed well, and then lowered into the well to mix with all of the water at the bottom. It is necessary to get an idea of how much water is in the bottom of the well so that the proper amount can be withdrawn. Without too much math, the volume is the area of the well times the water depth. A typical circular well, 1 meter in diameter (3.28 feet) with a water depth of 2 meters (6.56 feet), holds

  h × (π d2/4)

  2 × (3.14 × 12/4) = 1.6 cubic meters or 1,600 liters (410 gallons)

For a spring, a spring box or house helps gather the water from the ground and stores it in a protected place until needed. Typically, a pipe drains the box and allows users to fill their buckets under the pipe, keeping buckets and dirt out of the spring. Also, washing and bathing activities then take place downstream of the spring and do not affect the water quality at the source.

Deep wells, or boreholes, tap a water source (aquifer) that is much deeper and more protected than shallow wells. These deeper aquifers are contained in water-bearing rock layers under layers of impermeable rock. Thus their waters are safe from most forms of pollution but are also more of a finite resource because they are so hard to recharge.

Reaching these deep aquifers can be quite a challenge. They need to be drilled or bored into the rock with specialized machinery. Further, the hole has to be cased through the upper soil levels to keep potentially dirty waters out of the well. Finally, an electric submersible pump is extended into the hole to access the deep waters, thus requiring modern machinery and electricity for use.

A final source of drinking water is collecting rainwater. This is most commonly done on the roofs of houses, with gutters to collect and carry the rain to a storage basin, the prototypical American rain barrel. Gutters are fairly easy to install, but sizing the storage basin can be a problem. Ideally, it would be large enough to store all the water needed by the inhabitants of the building from one rainfall until the next. The difficulty arises because so many locations on earth have wet seasons and dry seasons, and the time between rainfalls may last weeks or even months. Storing enough rainfall from a rainy season to last through a dry season requires large and expensive storage tanks (Figure 6-3).

The other aspect of rainwater collection is that roofs are typically quite dirty, with leaves, sticks, and bird droppings. There are two solutions to the problem of a dirty roof: foul flush tanks and filters. The foul flush tank diverts and stores the initial rainfall, which is assumed to rinse the roof clean. After a short time, the rest of the rain is collected in the main storage tank. Filters are usually sand columns placed on top of the storage tank to remove contamination. Filtration is discussed in more detail later in the chapter.

Water Delivery

Once the water source has been identified and developed, some thought must be given to getting it to the users. The most common and low-tech method is to have users come to the water source and carry their daily supply home in buckets or jars. This requires a lot of human effort and also serves to reduce daily consumption. People are not inclined to take long baths or to waste water when they have to tote it a long way. In these cases, water use is usually restricted to cooking, cleaning, drinking, and occasionally bathing. Washing clothes and bathing may take place nearer to the source. This reduces the need for transporting water but usually leads to further contamination of the source water unless protective steps are taken as outlined previously.

Another method of water delivery is the commercial water cart. Here, larger supplies of water are brought to homes by cart, and the water is sold to the homeowner. Carts can vary from small pushcarts carrying 50 gallons or so to animal-drawn carts with a few hundred gallons, or to tanker trucks capable of delivering thousands of gallons.

The “modern,” or preferred, method of water delivery is through pipes. Laying pipes in the ground is an expensive investment in community infrastructure, which is the main drawback to its universal adoption. When using pipes, it is also necessary to provide pressure to force the water through them. This is typically done by pumps, which require a power source. Water towers are usually included in the system because the demand for water varies through the day and can exceed the pumping rate. Thus towers store water at night, when demand is low, and assist the pumps in the morning and evening, when demand is highest. In some places pressure may be provided by gravity, if the water source is sufficiently elevated above the users. When relying on gravity, storage tanks are sometimes required to maintain a sufficient supply of water.

A commonly adopted system is to pipe water into a community center from a remote source and then require users to carry their daily supply from the tap to their homes. This reduces individual treks to find water from miles of walking to more reasonable distances, but it also saves money on laying pipes throughout the community to every home.

Water Quantity

What options exist for poor rural people in the developing world? It must be recognized that in many places, an adequate quantity of water is more important than quality. Water may have to be carried, sometimes for miles, which consumes a huge amount of time, principally for women and children. In developed countries, the basic assumption is that each person uses 50 to 70 gallons per day (195 to 275 liters per day). Of course, this covers various uses such as watering the lawn, washing cars, laundry, automatic dishwashers, and teenagers taking long showers. The WHO suggests that the minimum amount in the developing world, where people must carry their own water, is 2.5 gallons per day (10 liters per day). An adult in the setting of drought needs at least 5 liters of water per day for basic food and hydration needs, without even considering the needs for basic hygiene (washing hands, etc.).9 Actual use will fall somewhere in this range and will tend to increase if water is piped directly into each house. Thus efforts to decrease the environmental risks of unclean water must often address both quantity and quality.

• Feces should be kept out of water supplies with the use of basic or improved pit latrines.
  
• Water can be boiled if there is sufficient fuel in the area.
  
• Simple filtration (e.g., through cloth, such as a sari) will remove some pathogens, as has been amply demonstrated in Bangladesh and India.10
  
• It is being increasingly recognized that simply letting water settle after collection will carry many pathogens down with the sediment.
  
• Relatively simple methods for treatment at the household point of use—such as chlorinating water with the use of household bleach, or storing water in translucent or transparent vessels that allow ultraviolet (sunlight) sterilization to occur—are being tested.
  
• Communities can organize themselves to build simple water distribution systems, using PVC or similar pipes, where the source water is upstream of the community and therefore unlikely to be fecally contaminated.

Water Quality

With water provided to homes, the next thought is treating it to improve the water quality and reduce incidents of sickness. Treatment may occur on many levels, from small doses for the individual, to a household system for all occupants, to communitywide treatment systems. However, the basic steps and methods of treatment are similar at all levels.

Water treatment consists of three basic steps, although not every method includes all the steps.

1. 
   

   Primary, or physical, treatment consists of settling out particles in the water.

   
   
2. 
   

   Secondary, or biologic, treatment involves filtering the water through a benign biologic layer to reduce organic contamination. The biologic layer is typically fixed or suspended in some type of filter medium, such as sand. Modern plants in the developed world sometimes use plastic shapes or grids for the same purpose.

   
   
3. 
   

   Tertiary, or chemical, treatment (also known as disinfection) is aimed at killing and removing harmful pathogens in the water. The most common chemical for disinfection is chlorine.

Personal water treatment, mostly used in travel situations, consists of either portable filters (backpacking water filters) or chemical tablets. Backpacking filters use a hand pump to force water through extremely small pores in a filter medium and remove particles, organic materials, and possibly pathogens, depending on the pore size. Tablets, either chlorine or iodine, disinfect the water, killing pathogens but not removing any silt, particles, or organic material. These tablets will not remove color or existing bad taste from the water.

Household treatment accounts for daily water use for several people. The simplest method is to store water in large covered barrels. This form of primary treatment will settle out particles in the water that lead to bad taste and color. Secondary treatment, or filtration, can be achieved with a range of commercially bought units that use porcelain candles or fabric bags to strain out contaminants. In general, the pore sizes on these filters are not small enough to remove pathogens, so a disinfection step is also required. Forcing water through a pore size small enough to remove pathogens requires pressure, and this complication would make most home-sized filters too complex (Figure 6-4).

The most accepted method of disinfection for a household is boiling. Water temperatures higher than 140°F (60°C) will kill pathogens. Of course, without a thermometer it is hard to judge 140°F, so bringing the water to boiling temperature is a nice visual indication of the proper amount of heat. Some authorities recommend boiling water for 30 minutes to ensure complete disinfection. This can be quite wasteful of fuel, however, and simply bringing the water to a rolling boil at sea level is sufficient. At higher elevations, boiling water for 5 minutes or less will typically give good results. The water should be boiled in a covered pot for protection and be allowed to cool. When sufficiently cool, it may be poured into the filter or other storage container.

Household filters can also be constructed using local materials. Typically the container is an oil drum or other large barrel. Gravel is placed at the bottom around the outlet pipe, which needs to be punched through the barrel wall. The gravel should be small enough, such as pea gravel, so that the sand does not settle into the pore spaces. Over the gravel, at least 24 inches (0.60 m) of sand should be placed. This should leave enough room at the top of the barrel for water to stay while it filters through the sand. The outlet pipe should also be equipped with a tap, so that water may be withdrawn without problem. Of course, this means the filter needs to be raised enough to get a container under the tap.

Another good household disinfection method is using clay filters treated with colloidal silver, such as those made by Potters for Peace.11 These filters, which can be made locally in almost any village, are inexpensive and do a fair job of destroying pathogens. The silver impregnation lasts for about a year of normal use before replacement is needed.

Of all these household treatment methods, the single most important is boiling because this does an effective job of removing pathogens, and every household has a way of heating water. Thus teaching villagers to boil water is the single most effective way of getting them to improve their water quality. It can be difficult to convince them of the need, however, because the fuel cost of boiling all drinking water can be excessive. However, this simple step can reduce the incidence of sickness dramatically, especially for infants, young children, and the aged.

Community water treatment is generally an extension of the procedures just mentioned. Settling basins are used to remove solid particles suspended in the water. Filters are then used to further purify the water, and then it is disinfected and stored.

Historically, the first community filters were slow sand filters. These were large beds of sand through which water slowly percolated. The slow rate of application kept the sand from getting clogged too often. When the sand had trapped enough contamination to clog the filter and reduce the percolation, the filter was cleaned by manually raking the sand and removing the top layer. As demand for water in cities grew, these slow filters soon became too large, and rapid sand filters were introduced. As the name implies, the water is applied much more quickly to a rapid sand filter, and the filter tends to clog much sooner. The cleaning method is to apply a backwash periodically to the filter. Backwashing means forcing water through the filter in the reverse direction, which expands the sand, cleans out the clogging material, and readies the filter for continued operation. In developing countries with available land, especially for small communities, slow sand filters are preferred for their low cost and easily understood maintenance. Where land is not available, rapid sand filters should be considered.

For disinfection, the most commonly used chemical is chlorine. It comes in three forms: gas, liquid, and solid tablet. The gas form can be somewhat tricky, so for small systems, a liquid drip is the preferred method. This drip is introduced by a small feed pump into the water line so that the concentration of chlorine in the water is roughly constant. Chlorine is a dangerous chemical, both for the operator and for the end user if the concentration is too high. However, it is well understood, relatively inexpensive, and leaves a residual in the water line that continues to protect the quality of the water throughout transmission.

People living in the developed world as well as the developing world have the need to maintain rigorous water treatment and sanitation practices. The methods used for water treatment—halogenation, usually with chlorine or chloramines, and then filtration—were devised over a century ago, and although effective when optimally implemented, they suffer the deficiencies of old technology. Chlorination is highly effective against bacterial and viral infections, and when first instituted it uniformly leads to major decreases in the burden of disease due to these infections. However, it is ineffective against a number of emerging pathogens that are chlorine resistant. Many of these resistant pathogens are most active where especially susceptible populations exist, such as people with acquired immunodeficiency syndrome (AIDS) or pregnant women.

An epidemic of waterborne toxoplasmosis was detected in Vancouver, Canada, stemming from the use of water from a reservoir that was chlorinated but not filtered. Astute clinicians noted an increase in the number of cases of in utero (congenital) Toxoplasma infections, as well as retinal disease in the general population. An epidemiologic investigation revealed that cougar feces in the watershed contained Toxoplasma oocysts. Presumably, the infectious oocysts were washed by rainfall into the reservoir and (unaffected by the chlorination) then directly entered the drinking water supply.12 To globalize this incident, one only needs to reflect on the absence of filtration in many countries where basic chlorination is provided. Estimates from Central America and Africa suggest that most cases of toxoplasmosis are the result of infection with the oocyst form of the parasite, which is only excreted by felines. In the United States and Europe, most toxoplasmosis is the result of eating undercooked meat that contains Toxoplasma cysts.13 The addition of filtration to water treatment, even simple sand filtration, is believed to decrease the risk of infection from pathogens such as Giardia, Cryptosporidium (and, one supposes, Toxoplasma) by about 100-fold.14

Filtration is not a perfect defense, even though it may remove the vast majority of pathogens (99.00% to 99.99% of pathogens is typical for modern conventional treatment plants).14 Unfortunately, the infectious dose needed to infect 50% of people for Cryptosporidium is under 10 oocysts for some strains,15

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