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Pollution and Human Health

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Patricia Adams

on 16 May 2011

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Transcript of Pollution and Human Health

~ List five pollutants, their sources, and their possible effects on human health. ~ Explain how scientists use toxicology and epidemiology. ~ Explain how pollution can come from both natural sources and human activities. ~ Describe the relationship between waste, pollution, and human health. Pollution and Human Health Pollution of air, water, and soil is frequently in the news. Because people in the US are so concerned about pollution, our country enjoys a relatively clean environment. But this situation is also due to the efforts of scientists who have studied the relationship between pollution and human health. Scientists are also beginning to understand the broader relationships between health and the environment. Environmental Effects on Health Pollution causes illness in two main ways. First, it may cause illness directly by poisoning us, as in the cases of lead poisoning and lung cancer. Second, pollution may cause illness indirectly because many infectious diseases spread in polluted environments. Examples of these diseases include cholera and river blindness, diseases caused by organisms found in polluted water. The World Health Organization (WHO) has begun to collect data on how the environment affects human health. Poor health is measured by the estimated number of days of healthy life lost to death and disease. The main factor behind poor health is the enormous role of infectious diseases, such as tuberculosis and cholera, which are more common in crowded areas with poor sanitation. Toxicology The word toxic means poisonous. Toxicology is the study of the harmful effects of substances on organisms. We are exposed to small amounts of chemicals every day, in food, in the air we breathe, and sometimes in the water we drink. Almost any chemical can be harmful if taken in, or ingested, in large enough amounts. The question is whether the concentration of any particular chemical in the environment is high enough to be harmful. To determine the effect of a pollutant on health, we need to know several things. We need to know how much of the pollutant is in the environment and how much gets into the body. Then we need to determine what concentration of the toxin damages the body. The amount of a harmful chemical to which a person is exposed is called the dose of that chemical. The damage to health that results from exposure to a given dose is called the response. Whether a chemical has a toxic effect depends in part on the dose. The response also depends on the number of times a person is exposed, the person’s size, and how well the person’ body breaks down the chemical. A persistent chemical is a chemical that breaks down slowly in the environment. The pesticide DDT is an example of a persistent chemical. Persistent chemicals are dangerous because more people are likely to come into contact with them, and these chemicals are more likely to remain in the body. Dose-Response Curves! The toxicity of a chemical can be expressed by a dose-response curve. A dose-response curve shows the relative effect of various doses of a drug or chemical on an organism or organisms as determined by experiments. Sometimes, we find that there is a threshold dose. Exposure to any amount of chemicals less than the threshold dose has no adverse effect on health. Exposure to levels above the threshold dose usually leads to worse effects. Epidemiology When an epidemic occurs, such as a widespread flu infection, health officials use their knowledge of epidemiology to take action. Epidemiology is the study of the spread of diseases. Epidemiologists collect data from health workers on when and where cases of the disease have occurred. Then scientists trace the disease to try to find its origin and how to prevent it from spreading. For example, in a case of mercury poisoning, health officials may ask questions such as: What did the people with mercury poisoning have in common? Were they all exposed to the same chemicals? Risk Assessment! In order to safeguard the public, health officials determine the risk posed by particular pollutants. Recall that risk is the probability of a negative outcome. In the case of human health, risk is the probability of suffering a disease, injury, or death. Scientists and health officials work together on risk assessments for pollutants. A risk assessment is an estimate of the risk posed by an action or substance. During the process of risk assessment, scientists first compile and evaluate existing information on the substance. Then they determine how people might be exposed to it. The third step is determining the toxicity of the substance. Finally, scientists characterize the risk that the substance poses to the public. Risk assessments may lead to government regulations on how and where the substance can be used. In the US, the EPA formulates these regulations. Pollution from Natural Sources You may think of pollution as being entirely caused by people, but some pollutants occur naturally in the environment. Naturally occurring pollutants usually become hazardous to health when they are concentrated above their normal levels in the environment. Particulates! The most common pollutants from natural sources are dust, soot, and other particulates. Particulates are particles in the air that are small enough to breathe into the lungs. These particles become trapped in the tiny air sacs in our lungs and cause irritation. This irritation can make lung conditions, such as chronic bronchitis and emphysema, worse. Wildfires also produce large amounts of particulates. Heavy Metals Another important type of pollution from natural sources are the so-called heavy metals. Dangerous heavy metals include the elements arsenic, cadmium, lead, and mercury. These metals occur naturally in rocks and soil. Most of these elements cause nerve damage when they are ingested beyond their threshold dose. Selenium, also found naturally in many soils, is actually a beneficial element when taken in very small quantities. But larger doses pose health risks to humans. Pollution from Human Activities Human activities release thousands of types of chemicals into the environment, but we know surprisingly little about the health effects of most of them. Only about 10% of commercial chemicals have been tested for their toxicity, and about 1,000 new chemicals are introduced every year. Recent Improvements In the US, regulations have helped reduce our exposure to pollutants. Most vehicles and factories now have pollution-control devices. As a result, people living in the US contain lower levels of some toxic chemicals in their bodies, on average, than they did in the recent past. In 2001, the US CDC released a study on chemical residues in 3,800 people. Levels of nicotine (from smoking), lead, and several other toxic chemicals were considerably lower in these peoples’ tissues than they had been 10 years earlier. Burning Fuels Despite the very real advances in public health resulting from pollution control, air pollution is still a major health problem. Burning fuels in vehicles, home furnaces, power plants, and factories introduces enormous amounts of pollutants into the air. These pollutants include the gas carbon monoxide and many kinds of particulates. Gasoline and coal burning contribute to the many premature deaths each year from asthma, heart disease, and lung disorders. In fact, it may be possible to predict an area’s death rate based on the amount of pollution. A recent study found that long-term exposure to air contaminated with soot particles raises a person’s risk of dying from lung cancer or other lung and heart diseases. Pesticides are chemicals designed to kill unwanted organisms such as insects, fungi, or weeds. Pesticides are beneficial in that they allow us to grow more food by reducing pest damage. Many of the increases in food production in the past 60 years are partly due to the development and use of more effective pesticides. But because pesticides are designed to kill organisms, they are often dangerous to humans in large enough doses. Although we are exposed to pesticide residues on fruits and vegetables, the amounts consumed by most people pose little danger. Most modern pesticides, such as those used in the US, break down quickly in the environment into harmless substances. Widely used organophosphate pesticides have replaced more persistent pesticides, such as DDT. But organophosphates are very toxic, causing nerve damage and perhaps cancer. In 1999, US poison centers reported more than 13,000 cases of organophosphate poisoning. Most cases of pesticide poisoning affect the people applying the chemicals. Persistent chemicals are still used in many developing countries. Such pesticides pose the greatest risk to children, whose internal organs are still developing and who eat and drink more in relation to their body weight than adults do. Industrial Chemicals Railroad tankers carrying industrial solvents overturned near Rochester, New York, in 2002. Two solvents reacted to cause a fire that destroyed several houses. Several people were treated for breathing the fumes. We are exposed to low levels of industrial chemicals every day, particularly inside new buildings that have new furnishings. Toxic chemicals are used to make building materials, carpets, cleaning fluids, and furniture. Older buildings were often painted using lead-based paint. Lead is directly linked to brain damage and learning disabilities. Often, industrial chemicals are not known to be toxic until they have been used for many years. For example, polychlorinated biphenyls (PCBs) are oily fluids that have been used for years as insulation in electrical transformers. PCBs do not break down in the environment. In 1996, studies showed that children exposed to PCBs in the womb can develop learning problems and IQ deficits. The waters of the Great Lakes are polluted by PCBs, and doctors warn pregnant women not to eat fish from these lakes. Studies have shown that adults with high concentrations of PCBs in their tissues have more memory problems than adults who do not. Waste Disposal Much of the pollution in our environment is a byproduct of inadequate waste disposal. Wastewater from cities can carry oil and dozens of toxic chemicals into our waterways. Waste incineration plants can emit toxic products into the air, and mining can release toxic contaminates into streams and rivers. One of the reasons that our air and water is less polluted in many areas than it was 50 years ago is that methods of disposing of waste have improved. However, problems remain. Many old landfills are leaking. And many communities still have sewage treatment plants that release raw sewage into a river or the ocean after heavy rains. In addition, laws regulating waste disposal are not always enforced. The US government has not decided how it will dispose of radioactive waste from nuclear power plants. Meanwhile, the waste remains in barrels at or near the plants, and small quantities of radioactive iodine, cesium, and other elements leak into nearby waterways.
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