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Most people face some kind of environmental hazard every day. The hazards we face may be voluntary, as when we make a decision to smoke tobacco, or they may be involuntary, as when we are exposed to air pollution. When assessing the risk of different environmental hazards, regulatory agencies, environmental scientists, and policy makers usually follow three steps for risk analysis: risk assessment, risk acceptance, and risk management. In this module, we will examine each of the three steps.

Learning Objectives

After reading this module you should be able to

As illustrated in FIGURE 58.1, risk assessment is the first of the three steps involved in risk analysis. Risk analysis seeks to identify a potential hazard and determine the magnitude of the potential harm. There are two types of risk assessment—qualitative and quantitative. Each of us has some idea of the risk associated with different environmental hazards. For our purposes, an environmental hazard is anything in our environment that can potentially cause harm. Environmental hazards include substances such as pollutants or other chemical contaminants, human activities such as driving cars or flying in airplanes, or natural catastrophes such as volcanoes and earthquakes.

We generally make qualitative judgments in which we might categorize our decisions as having low, medium, or high risks. When we choose to slow down on a wet highway or to buy a more expensive car because we feel it is safer, we are making qualitative judgments of the relative risks of various decisions. We are making judgments that are based on our perceptions but that are not based on actual data. It would be unusual for us to consider the actual probability—that is, the statistical likelihood—of an event occurring and the probability of that event causing us harm. Because our personal risk assessments are not quantitative, they often do not match the actual risk. For example, some people find air travel very stressful because they are afraid the plane might crash. These same people often prefer riding in a car, which they perceive to be much safer. Or, a person may be very cautious about safety while walking in an area with heavy traffic but never consider the health dangers of smoking or a lack of exercise. To manage our risk effectively, we need to ask how closely our perceptions of risk match the reality of actual risk.

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In the United States, the probability of death from various hazards can be calculated from data kept by the government. By looking at the total number of people who die in a year and their causes of death, researchers are able to determine the probability that an individual will die from a particular cause. FIGURE 58.2 provides current data on causes of death in the United States. Because these risk estimates are based on real data, they are quantitative rather than qualitative. If we examine this figure, we see that the probability of dying in an automobile is far greater than the probability of dying in an airplane. Similarly, the probability of dying from heart disease is monumentally greater than the risk of dying in a pedestrian accident. These numbers underscore the fact that our perceptions of risk can often be very different from the actual risk. Because a catastrophic event, such as a nuclear plant meltdown or a plane crash, can do a great deal of harm and receives great media attention, people believe that it is very risky to use nuclear reactors or to fly in airplanes. However, as these events rarely occur, the risk of harm is low. In contrast, we tend to downplay the risk of activities that provide us with cultural, political, or economic advantages such as drinking alcohol or working in a coal mine.

Quantitative Risk Assessment

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The most common approach to conducting a quantitative risk assessment can be expressed with a simple equation:

Risk = probability of being exposed to a hazard × probability of being harmed if exposed

Using this equation, we could ask whether it is riskier in a year to fly on commercial airlines for 1,609 km (1,000 miles) per year or to eat 40 tablespoons of peanut butter, which contains tiny amounts of a carcinogenic chemical produced naturally by a fungus that sometimes occurs in peanuts that are used to make peanut butter. The risk of dying in a plane crash depends on the probability of experiencing a plane crash, which is very low, multiplied by the probability of dying if the plane does crash, which approaches 100 percent. The risk of dying of cancer from consuming peanut butter depends on your probability of eating peanut butter, which may be near 100 percent, multiplied by the probability that consuming peanut butter will cause you to develop lethal cancer, which is very low. It turns out that both behaviors produce a 1 in 1 million chance of dying. This example demonstrates a fundamental rule of risk assessment: The risk of a rare event that has a high likelihood of causing harm can be equal to the risk of a common event that has a low likelihood of causing harm.

Quantitative risk assessments bring together tremendous amounts of data. The estimates of harm can come from acute and chronic dose-response experiments, retrospective studies, and prospective studies. The estimates of which concentrations of a chemical an organism will experience in the environment incorporates the concentrations found in nature, routes of exposure, solubility, persistence, and the potential for the chemical to bioaccumulate or biomagnify. Together, these two groups of data can be used to estimate the probability of harm.

A Case Study in Risk Assessment

As we saw in our discussion of water pollution in Chapter 14, from the 1940s to the 1970s some companies manufacturing electrical components dumped PCBs (polychlorinated biphenyls) into rivers. Beginning in the 1960s, there was increasing evidence that PCBs might have harmful health effects on organisms that came into contact with them, including liver damage in animals and impaired learning in human infants.

Once the EPA identified PCBs as a potential hazard, it began a risk assessment. The agency brought together a range of data. First, scientists had to determine which concentrations of PCBs might cause cancer. To accomplish this objective, they examined dose-response studies on laboratory rats exposed to different concentrations of PCBs. They also examined retrospective studies of cancer cases in workers employed by industries that used PCBs. Next, they had to determine what concentrations people might experience. To accomplish this, scientists examined data on current concentrations in the air, soil, and water and considered the half-life of the chemical. Because PCBs were found throughout the environment and because they are very persistent, the probability of coming into contact with PCBs was considered relatively high. They also considered the potential routes of exposure: eating contaminated fish, drinking contaminated water, and breathing contaminated air.

The final result of the risk assessment on PCBs showed that the risk from eating contaminated fish is higher than the risk from drinking contaminated water and much higher than breathing contaminated air. As a result, signs were posted on the Hudson River and at Silver Lake instructing anglers not to consume any fish they caught (FIGURE 58.3). With limited fish consumption, the EPA concluded that the absolute risk of an individual developing cancer from PCB exposure was low. However, the risk was high enough to cause the EPA to recommend a dredging of the Hudson River to remove a large fraction of the PCBs that had settled at the bottom of the river (see Chapter 14).

Once the risk assessment is completed, the second step in risk analysis is to determine risk acceptance—the level of risk that can be tolerated. Risk acceptance may be the most difficult of the three steps in the risk-analysis process. No amount of information on the extent of the risk will overcome the conflict between those who are willing to live with some amount of risk and those who are not. Even among those people who are willing to accept some risk, the precise amount of acceptable risk is open to heated disagreement. For example, according to the EPA, a risk of 1 in 1 million is acceptable for most environmental hazards. Some people believe this is too high. Others feel that a risk such as a 1 in 1 million chance of death from radiation leaks is a small price to pay for the electricity generated by nuclear energy. While personal preferences will always complicate the determination of risk acceptance, environmental scientists, economists, and others can help us weigh the options as objectively as possible by providing accurate estimates of the costs and benefits of activities that affect us and the environment.

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Risk management, the third step of the risk-analysis process, seeks to balance possible harm against other considerations. Risk management integrates the scientific data on risk assessment and the analysis of acceptable levels of risk with a number of additional factors including economic, social, ethical, and political issues. Whereas risk assessment is the job of environmental scientists, risk management is a regulatory activity that is typically carried out by local, national, or international government agencies.

The regulation of arsenic in drinking water provides an excellent example of the difference between risk assessment and risk management. As we saw in Chapter 14, despite the fact that scientists knew that 50 ppb of arsenic could cause cancer in people, from 1942 to 1999 the federal government set the acceptable concentration of arsenic at 50 ppb. In 1999, the EPA announced it was lowering the maximum concentration of arsenic in drinking water to 10 ppb, which matched the standards set by the European Union and the World Health Organization. This regulation threatened to place a large financial burden on mining companies that produced arsenic as a by-product of mining, and an economic burden on several municipalities in western states with naturally high concentrations of arsenic in their drinking water. Both groups lobbied hard against the lower arsenic limits. In 2001, weeks before the new lower limits were to go into effect, the EPA announced that it would return to the 50 ppb. The agency argued that further risk assessments needed to be conducted and any risk assessment had to be balanced by economic interests. Later in 2001, the National Academy of Sciences concluded that the acceptable amount of arsenic was a mere 5 ppb, which was lower than some previous estimates. This new risk assessment played a key role in striking a balance between the scientific data and economic interests and the EPA revised its ruling, ultimately setting the safe arsenic concentration at 10 ppb.

There are currently about 80,000 regulated chemicals in the world but they are not regulated the same way around the globe. A key factor determining the type of chemical regulation is whether the regulations are guided by the innocent-until-proven-guilty principle or the precautionary principle, both illustrated in FIGURE 58.4. The innocent-until-proven-guilty principle is based on the belief that a potential hazard should not be considered a real hazard until the scientific data definitively demonstrates that it actually causes harm. This strategy allows beneficial chemicals to be sold sooner. The downside is that harmful chemicals can affect humans or wildlife for decades before sufficient scientific evidence accumulates to confirm that they are harmful.

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In contrast, the precautionary principle is based on the belief that when a hazard is plausible but not yet certain, we should take actions to reduce or remove the hazard. The plausibility of the risk cannot be speculation; it must have a scientific basis. In addition, the intervention should be in proportion to the potential harm that might be caused by the hazard. This approach allows fewer harmful chemicals to enter the environment. However, if the initial assessment indicates a plausible risk and the chemical ultimately proves harmless but beneficial, its introduction can be delayed for many years. Moreover, the slower pace of approval can reduce the financial motivation of manufacturers to invest in research for new chemicals. In short, there is a trade-off between greater safety with slower introduction of beneficial chemicals versus greater potential risk with a greater rate of discovery of helpful chemicals. Use of the precautionary principle has been growing throughout many parts of the world and was instituted by the European Union in 2000. The United States, however, continues to use the innocent-until-proven-guilty principle.

The benefit of the precautionary principle can be illustrated using the case of asbestos. Asbestos is a white, fibrous mineral that is very resistant to burning. This made asbestos a popular building material throughout much of the twentieth century. It is now widely accepted that dust from asbestos can cause a number of deadly diseases including asbestosis (a painful inflammation of the lungs) and several types of cancer. When asbestos was first mined in 1879, there was no evidence that it harmed humans. The first report of deaths in humans was in 1906 and the first experiment showing harmful effects in rats was conducted in 1911. In 1930, it was reported that 66 percent of workers in an asbestos factory suffered from asbestosis. In 1955, researchers found that asbestos workers had a higher risk of lung cancer than other groups. In 1965, a study linked a rare form of cancer with workers who were exposed to asbestos dust. Despite all of the growing scientific evidence that asbestos was harming human health, little was done to reduce the exposure of workers and the public. Indeed, it was not until 1998 that the European Union banned asbestos. Today, workers go to great lengths not to be exposed to asbestos dust such as by wearing protective suits and using respirators (FIGURE 58.5). A study in the Netherlands estimated that had asbestos been banned in 1965 when the harm to health became clear, the country would have had 34,000 fewer deaths from asbestos and would have saved approximately $25 billion in cleanup and compensation costs. Because the effects of asbestos can take several decades to harm a person’s health, the European Union estimates that from 2005 to 2040 it will have 250,000 to 400,000 additional people die as a result of past exposures to asbestos. Had the European Union been using the precautionary principle decades earlier, the number of deaths would have been considerably less.

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International Agreements on Hazardous Chemicals

In 2001 a group of 127 nations gathered in Stockholm, Sweden, to reach an agreement on restricting the global use of some chemicals. The agreement, known as the Stockholm Convention, produced a list of 12 chemicals to be banned, phased out, or reduced. These 12 chemicals came to be known as the “dirty dozen” and included pesticides such as DDT, industrial chemicals such as PCBs, and certain chemicals that are by-products of manufacturing processes. All of the chemicals were known to be endocrine disruptors, and a number of them had already been banned or were experiencing declining use in many countries. However, bringing countries together in a forum to discuss controlling the most harmful chemicals was the great achievement of the Stockholm Convention. By 2013, an additional 11 chemicals were added to the original list of 12; several more have been suggested for future listing.

In 2007, the 27 nations of the European Union put into effect an agreement on how chemicals should be regulated within the European Union. Known as REACH, an acronym for registration, evaluation, authorization, and restriction of chemicals, the agreement embraces the precautionary principle by putting more responsibility on chemical manufacturers to confirm that chemicals used in the environment pose no risk to people or the environment. This regulation was enacted because many chemicals used for decades in the European Union had not been subjected to rigorous risk analyses. The new regulations are being phased in over 11 years to permit sufficient time for chemical manufacturers to complete the required testing.