Chapter 8: Environmental Health and Toxicology This set of slides and text is for Chapter Eight for ESRM100/ENVIR110 (Environmental Science), Environmental Health and Toxicology. Hong Kong residents concerned about SARS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter Eight Topics Environmental Health Toxicology Movement, Distribution, and Fate of Toxins Mechanisms for Minimizing Toxic Effects Measuring Toxicity Risk Assessment and Acceptance Establishing Public Policy Chapter Eight includes: a consideration of types and different kinds of environmental health hazards; what toxins are and their movement, distribution and fate in the environment; mechanisms for minimizing the effects of environmental toxins; measuring the toxicity of environmental toxins; the concept of risk assessment and getting the public to accept it; and, establishing public policy regarding the fate and health hazards associated with environmental toxins.

Part 1: Environmental Health There are many types of environmental health hazards and many ways in which they can affect humans. Environmental health hazards involve the introduction of pollutants into our water, air, soil and food. Air pollution is one environmental health hazard that has received lots of attention, study and legislation due to its huge negative impact on human health. In the US, we now have the Clean Air Act , which has actually done a pretty good job of cleaning up the air in many parts of the US. In some parts of Eastern Europe and the former USSR, up to 90 % of all children suffer from environmentally linked diseases.

What is Health? The World Health Organization (WHO) defines health as a state of complete physical, mental, and social well-being. Disease - a deleterious change in the body's condition in response to an environmental factor Morbidity - illness Mortality - death In order to really understand and logically talk about what an environmental health hazard is, we probably ought to start with the concept of what health is. The World Health Organization, or WHO, defines health as a state of complete physical, mental and social well-being. In other words, physically you are in good shape, your body is functioning correctly, with all the biology and chemistry and mechanics working fine. Mentally, you are in a relatively relaxed but active state. You are able to work through problems. You are able to interact with people in a positive way, with social health that includes being part of an active, successfully functioning social system. WHO defines disease as a change in the body's condition such that it cannot deal with some environmental factors. These could include things such as chemical and physical factors that could adversely affect the body. For instance, you might catch a disease and be unable to fight it off. Morbidity is the presence of illness in a population, and mortality is the occurrence of death within a population. So, diseased populations definitely have a high incidence of morbidity and also have a higher incidence of mortality compared to a healthy population.

The table above shows the leading causes of mortality worldwide and how they are changing. In many cases, some of these diseases don't affect all populations equally and don't affect young and older people equally. In particular, cardiovascular disease (the failure of the heart to adequately move blood through the body) is the number one cause of death worldwide. Cancers of various kinds have emerged as increasingly important causes of death. Other diseases such as AIDS, malaria, and diarrhea among infants, in particular, are quantifiable in terms of their death toll. The leading causes of death worldwide have been reduced over the years. In general, people do live longer, but the impacts of disease are not distributed equally throughout the world. We could say. for instance. that cancer and cardiovascular disease adversely impact older people. They tend to kill people eventually, if people they live long enough. Diarrhea adversely impacts younger people, particularly infants. Malaria affects only people in certain parts of the world, and most people don't die immediately from it, but it saps human energy and causes people to die from other diseases. A very important area of study is the distribution of disease in different parts of the world and in different parts of the populations.

At any given time, about 2 billion people suffer from As a Peace Corps volunteer in Tanzania, whenever I met other Europeans or other colleagues, our conversations always started with topics such as, "Have we had diarrhea" or "had we encountered any other nasty parasite problems (things that get under your skin and built a nest there)." These were morbid but necessary conversations. Whenever we get back together we still talk about these things. It is fascinating how so many organisms find ways to exploit the human body. For instance, the disease elephantiasis is caused by a parasite. Its effect is devastating--it causes the organs to distend. This slide shows some women suffering from the disease. It is rarely fatal, but it certainly takes away the energy from these women and lowers their ability to work. Something on the order of 2 billion people are suffering from parasites such as the one that causes elephantiasis. In Tanzania, in particular, children unable to get medical care were typically the ones most affected. I was not trained as a medical person, but since I had a first aid kit, I became the town doctor. Children would come to me with insect eggs that had been laid in their feet and resulted in grubs living in their bodies. I had to learn to remove these in a way that would not cause an infection because the infection could be fatal. I actually treated anyone who came to me, because a trained doctor was not available. At any given time, about 2 billion people suffer from worms, protozoans, and other internal parasites.

West Nile Virus 2001 West Nile virus, for instance, has only been prevalent in the US for a few years…this is the incidence of reporting of infected birds in US counties in 2001

West Nile Virus 2002 And in 2002. Note that it was seen in birds in King County in Washington State.

Factors Contributing to the Spread of Contagious Diseases High population densities Settlers pushing into remote areas Human-caused environmental change Speed and frequency of modern travel Contact with water or food contaminated with human waste It has been documented that a number of factors are related to the spread of contagious diseases. Having high population densities at today's scale is a relatively new occurrence. Having humans closer to one another enhances the ability of a disease organism to move from one human to another. Another factor is that some groups of humans have been isolated for long periods of time. In many cases, they have adapted to local conditions and have not developed resistance to diseases present elsewhere in the world. So, when Europeans settled in the New World, the Native Americans that were here typically were not resistant to diseases brought by the Europeans, and fell victim to such things as small pox. These new diseases killed Native Americans on a very large scale. For instance, when De Soto moved though Florida and the American Southeast he described enormous populations of Native Americans with highly sophisticated societies. A few decades later, no such populations were seen. Many assumed De Soto lied in his journals. Today archaeologists have discovered things like Moundville in Alabama and other signs that indicate how extensive these populations were. In the case of environmental change, global warming could change the impact of contagious diseases. Anything that stresses the body decreases its resistance to disease. Today, humans move around the world very fast. It is believed that one reason AIDS spread so quickly throughout the world was because a very mobile airline employee who was infected was also very promiscuous and created infection points on several continents among hundreds of people. In addition, it is increasingly difficult for many people in the world to find uncontaminated food and water.

Part 2: Toxicology Toxicology: The study of toxins (poisons) and their effects on living systems. What does toxic mean? Environmental Wisdom…visit http://www.dhmo.org What does Toxic mean

Antibiotic and Pesticide Resistance Indiscriminate use of antibiotics and pesticides - perfect recipe for natural selection Protozoan that causes malaria now resistant to most antibiotics, and mosquitoes have developed resistance to many insecticides Drug resistance: TB, Staph A, flesh-eating bacteria Some of the miracle drugs created over the last 50 or so years that have been very important in reducing the incidence of disease worldwide are starting to lose their effect. In particular, antibiotics that can cure disease directly (for example, penicillin) don't work as well as they initially did. Some varieties of Staphylococcus, a disease causing bacterium, have developed a resistance to all but one antibiotic. The same phenomenon has occurred with pesticides that were once effective in eliminating or reducing pests that spread disease (for instance, mosquitoes that carry malaria). The insects that carry the disease develop resistance to pesticides. Some disease-causing protozoa are now resistant to most antibiotics. Disease-resistant organisms impact the incidence of disease and our ability to treat sick people.

Fig. 8.6 Since their discovery antibiotics have been applied on a massive scale. Many diseases and infections that were formerly lethal were suddenly curable. Soon, however, antibiotics were used so extensively that bacteria evolved resistance to antibiotics. As a result, many antibiotics no longer are effective. Here, two mechanisms of acquiring resistance are portrayed. In example (b) a donor bacterium actually transfers genetic material conferring resistance to a recipient cell. Often this transfer involves a circular strand of DNA called a plasmid.

Hazardous and Toxic Chemicals Allergens - formaldehyde Immune system depressants - PCBs? Neurotoxins - lead, DDT Mutagens Teratogens - alcohol Carcinogens Also, we are producing thousands of new chemicals every year that people can be exposed to. Many of these chemicals are created to kill certain organisms such as like insects or weeds. Some people have allergic reactions to chemicals (allergic reactions are unreasonable responses on the part of the human body to the presence of a chemical) . The chemical makes the body think it is being attacked by a disease and the body responds by producing histamines, or poisons, to kill the disease it thinks it has. Allergens are substances that cause allergic reactions. Allergens are something that you can use to study a human and see no response but if the persons are allergic they might have extreme responses. Chemicals that affect the immune system (such as some PCBs) reduce the immune system's ability to fight off diseases. Some toxins affect the nervous system and reduce the ability of the brain to function. Certain hazardous chemicals cause mutations, which adversely affect the developing fetus. These substances are called teratogens. For instance, fetal alcohol syndrome is a major societal problem and babies born of alcoholic mothers typically have less ability to fight off diseases. Carcinogens are substances that actually can cause or aggravate the incidence of cancer. There is no way we can actively study all the potentially damaging products we produce, but many of them are probably causing problems with human health.

Following is a list of the top 20 toxic and hazardous substances in the US. They include substances that Americans commonly use. For example, I use lead shot as weights in my fishing lures. Some of these chemicals are known to have adverse effects on human health, yet we use them in large amounts. In many cases, they are absolutely necessary. For instance, I remember handling chloroform when I was working on my Ph.D. Breathing large amounts of chloroform had an interesting effect, kind of like drinking. The moral of this story is that it is impossible to know everything about each potential chemical toxin in the environment. So, it is important to research each new chemical you encounter that might be dangerous.

Part 3: Movement, Distribution, and Fate of Toxins Humans can be exposed to toxins through a variety of pathways. For instance, humans can encounter exposure by drinking water that contains a toxin, by breathing polluted air, by eating contaminated food, by taking recreational or medicinal drugs, or by putting things on the skin (accidentally, as when changing the oil in a car, or intentionally, as when applying of cosmetics). Exposure can be inadvertent (for example, toxins settling on the skin from the air). The study of toxins and how they might harm humans or other organisms is called risk assessment.

Bioaccumulation and Biomagnification Bioaccumulation - dilute toxins in the environment can reach dangerous levels inside cells and tissue Biomagnification - the effects of toxins are magnified through food webs Here we consider the phenomenon of biomagnification. Biomagnification occurs when toxins that are in relatively small concentrations in the environment increase in concentration when they move up through the food chain. For instance, if the water concentration of a toxin is very low, but zooplankton and phytoplankton are absorbing the toxin from the water, they will often have tissue concentrations higher than the water. When these plankton are consumed by primary consumers such as small fish, the concentration of the toxin can increase further. As we move further and further up through the food chain, we find the concentration of the toxin will increase more and more. Ultimately, the concentration of the toxin in the highest level consumers can become a serious problem, such as with the pesticide DDT in the American bald eagle.

"DDT - Powerful Insecticide, Harmless to Humans" I particularly like this slide because it shows you an awful lot about how much we don't know. Yet government agencies often say, assume, and act as if we do. In this case, DDT is being sprayed directly on people. The level of toxicity of substances is measured by a factor called the LD 50. LD stands for lethal dose, and the LD 50 is the dose that kills 50% of a test population of organisms such as mice. The LD 50 for DDT is 50mg/kg, so we know that there will not be an immediate lethal impact on people here at the beach; however, we now know that humans do incur health problems with DDT and similar insecticides. These facts eventually come out, partly because people like the ones in this slide were involuntary guinea pigs.

Part 4: Minimizing Toxic Effects Every material can be poisonous under some conditions. Taken in small doses, most toxins can be broken down or excreted before they do much harm. Liver - primary site of detoxification Tissues and organs - high cellular reproduction rates replace injured cells - down side: tumors, cancers possible Although most people might not realize it, humans are well adapted to exposure of many substances that are very toxic to other organisms. For example, if you were to give a dog Tylenol, you would almost certainly kill it. Certain plants that humans utilize in their diets are loaded with toxins. For instance, broccoli is composed of almost 80% toxic substances. Humans have developed the capability of detoxifying many substances, though certainly not all of them. Every material can be poisonous under certain conditions. There are two classes of toxins, those that are toxic at low levels and those that are toxic at some threshold below which they have no effect. If the dose of a toxin is low enough, it can often be broken down and/or passed through the organism without harming the organism. In humans, the liver is the primary site where toxins are broken down before being excreted. Toxins that aren't broken down can affect tissues and organs, disrupting their growth and possibly causing cancer.

Part 5: Measuring Toxicity Animal Testing Most commonly used and widely accepted Expensive - hundreds of thousands of dollars to test one toxin at low doses Time consuming Often very inhumane Difficult to compare toxicity of unlike chemicals or different species of organisms In order to understand the toxicity of a substance, we need to know the levels at which it is toxic. For instance, if we look at a toxin as it moves up through the food chain or as it is absorbed from the environment, we need to know the concentrations at which it starts to become a problem. The typical way in which we measure toxicity of new substances such as a new cosmetic or food additive is to use animals. Sometimes, animal testing is quite inhumane. It can also be time consuming, because toxicity effects often show up after long periods of time. In many cases (with lab rats, for example), it may be unreasonable to compare the toxicity of a chemical to an animal with the toxicity to a human. Also, because there are thousands and thousands of chemicals and all of them can't be tested, we often assume similar chemicals behave the same in animals as in humans, and this may or may not be true.

A Typical Dose/Response Curve This image shows the typical response of a population of organisms (say humans) to a dose of a chemical. The dose would be in hypothetical units, but usually it is expressed as milligrams of substance per kilogram of body weight. The axis on the left shows the number of organisms responding. So, we start with a zero dose that should have no impact, and we set this as the baseline to measure effect. As we increase the dose a little, a few individuals that are very sensitive show a negative response (they may get a rash or be slightly ill sick). As the dose increases more, a majority of the individuals experience negative effects. With higher concentrations, a few individuals would have no response – they are insensitive to the material. This graph is called a dose/response curve and it is used to evaluate the impact of a toxin on a population. We would typically want to protect that population at a arbitrary level (negative responses from only one in a thousand, one in a million, or even one in a billion).

LD50 - the dose of a toxin that is lethal to half the test population The most extreme response to a toxin is death. As explained previously, the lethal dose, or LD50 (the concentration of a toxic substance at which 50% of the population dies) is commonly used to describe the level of toxicity of a substance. The concentration is usually expressed as mg of toxic substance per kg of body weight. One point to note about the LD50 is that some of the organisms die before this 50% level is reached. At another point, all of the organisms in a population would die. Another point is that the LD50 does not describe how healthy the 50% of the population is that survives.

Acute Versus Chronic Doses and Effects Acute effect - immediate health effect caused by a single exposure to a toxin (can be reversible) Chronic effect - long lasting or permanent health effect caused by (1) a single exposure to a very toxic substance or (2) continuous or repeated sub lethal exposure to a toxin We divide toxic impacts into acute and chronic effects. Acute effects are those we can immediately recognize after a person has had a single exposure. Acute effects can be reversible. An example of an acute effect is the symptoms you would have if you swallowed some rat poison. You would become immediately sick, you might start throwing up, you might have a fever, and you might even die. On the other hand, an acute effect might be completely reversible, and you would get well quickly after your body got rid of the poison. Chronic effects are long lasting, and are caused by either a single exposure or by repeated exposures. A chronic effect might not show up for years after the exposure, and might continue over a long period of time. Chronic effects are much more difficult to diagnose. The symptoms might not be as obvious as those of an acute effect, particularly if the symptoms come on slowly. Your body might adjust and you might overlook symptoms such as pain and constant fatigue. Chronic effects are probably more widespread and less likely to be treated because they are less likely to be noticed or thought to be serious.

Part 6: Risk Assessment and Acceptance Risk - the probability of harm times the probability of exposure A number of factors influence how we perceive relative risks associated with different situations. Accepting risks - we go to great lengths to avoid some dangers, while gladly accepting others We have to recognize that the very act of living involves risks. The concept of risk assessment and acceptance is important when we consider potentially toxic substances in the environment. For instance, the biggest risk we take every day (that is if we don't smoke or over eat) is driving. Driving involves high risks of accidents and the potential for fatality. The perception of risk and exactly how we are confronted with risks is often very important in whether or not we are willing to accept them. I work with the potential risk that comes with the application of organic amendments (biosolids) and I have talked at many meetings and pointed out how small these risks were. I remember in particular a woman with a child who came to me and started yelling at me about how biosolids would put her children at risk; yet while she talked she was smoking, thereby exposing her children to a definite risk. This woman, if she continues to smoke, will lower her children's lives by several years. Biosolids effects are relatively small and unknown. Her actions will have a big impact on her children, yet she was willing to ignore this well-known high level of risk, but was not willing to accept the small risk imposed on her by the City of Seattle's application programs. So, there is a very different perception of risk here in terms of what constitutes risk and whether or not it is acceptable.

It is important to put risk in perspective It is important to put risk in perspective. For instance, certain activities such as smoking, drinking or working in hazardous occupations carry very high risk. One of the things about some of the toxins mentioned on the slide is that they probably have a threshold level and also some of these are activities. Living in the very polluted cities of Boston and New York increases your chances of dying over the average. Living a particularly long life increases your chance of dying from diseases that eventually finish everyone off like heart disease. Car driving is dangerous and listed because we do it so much, but actually bicycling off the Burke Gilman trail is more dangerous per mile than riding in a car. Flying by jets is relatively safe when compared to driving a car, but we hear more about airplane wrecks than car wrecks, so many people perceive o flying as being more dangerous than driving.

Part 7: Establishing Public Policy In setting standards for environmental toxins, we need to consider: Combined effects of exposure to many different sources of damage Different sensitivities of members of the population Effects of chronic as well as acute exposures In terms of establishing policy with regard to environmental toxins, there are several factors we need to consider. First of all, there are many potential exposures to potential toxins and many types of impact these exposures can have. Members of a society or population have very different sensitivities, so if you do a study on just a few individuals, or a particular economic group or gender, the result probably don't carry over to the population in general. It is important also to consider chronic effects because certain effects can be debilitating. For instance, back pain, which can result from hazardous activities, doesn't kill people, but it reduces people's productivity and greatly reduces the quality of life for those who have it.

Regulatory Decisions This diagram shows how risk assessment is used to determine the potential risk associated with a particular toxin and then how socioeconomic, technical, scientific, and political factors affect regulatory decisions. For instance, there are terms relating to the acceptance of things like the location of a jail or the application of bio-solids in a particular area. The term NIMBY means "Not in My Back Yard," which is a social decision by people who think they are being negatively impacted by a policy decision. Then there is NIMTO, which means "Not in My Term of Office." We hear this often from politicians who might say, "Oh yes, that would really be a good thing for my constituents, but I just can't accept that happening while I'm in office because it is a bad political decision for me to let it happen." Biased decisions can affect acceptance of policies such as location of a jail or a landfill or a land application of organic waste material.