Chapter 17 Human Health and Environmental Risks

Human health is affected by a large number of risk factors A disease is any impaired function of the body with a characteristic set of symptoms. Figure 17.1 shows the leading causes of death in the world.

Human health is affected by a large number of risk factors Three major categories of risk that can harm human health: physical biological chemical

Human health is affected by a large number of risk factors Physical Risks Physical risks include environmental factors, such as natural disasters, that can cause injury and loss of life. Physical risks also include less dramatic factors such as excessive exposure to ultraviolet radiation from the sun.

Human health is affected by a large number of risk factors Biological risks are those associated with diseases. Infectious diseases- those caused by infectious agents, known as pathogens. Examples: pneumonia and venereal diseases Chronic disease - slowly impairs the functioning of a person’s body. Acute disease - rapidly impairs the functioning of a person’s body. When a pathogen causes a rapid increase in disease, we call it an epidemic. When an epidemic occurs over a large geographic region such as an entire continent, we call it a pandemic.

Human health is affected by a large number of risk factors Figure 17.2 shows leading health risks in the world. If we consider all deaths that occur and separate them into different causes, we can examine which categories cause the highest percentage of all deaths. (a) low income countries include issues related to low nutrition and poor sanitation. (b) high income countries include issues related to tobacco, inactivity, and obesity.

Historical Diseases Plague –also known as Black Death. Plague is caused by an infection from a bacterium that is carried by fleas. Malaria – is caused by an infection from any one of several species of protists in the genus Plasmodium. The parasite spends one stage of its life inside a mosquito and another stage of its life inside a human. Tuberculosis – is a highly contagious disease caused by a bacterium that primarily infects the lungs. Tuberculosis is spread when a person coughs and expels the bacteria into the air.

Historical Diseases Figure 17.5 is an illustration of the Black Death in Europe. As depicted in Carlo Coppola’s The Marketplace in Naples During the Plague of 1656, plague pandemics repeatedly swept through Europe from the 1300s through the 1800s, and killed millions of people. Because the disease caused black sores on people’s bodies, it also had the name Black Death.

Emergent Infectious Diseases HIV/AIDS – In the late 1970s, rare types of pneumonia and cancer began appearing in individuals with weakened immune systems. The virus is spread though sexual contact and sharing needles during drug use. Ebola – first discovered in Republic of Congo near the Ebola River. The virus has infected several hundred humans and primates. It has killed a large percentage of those infected. Mad Cow Disease – a disease in which a pathogen slowly damages a cow’s nervous system. The cow loses coordination of its body and then dies.

Emergent Infectious Diseases Bird Flu - Spanish flu was an avian influenza, also known as bird flu. It is caused by the H1N1 virus. This virus is similar to a flu virus that humans normally contract, but H1N1 normally infects only birds. West Nile Virus – lives in hundreds of species of birds and is transmitted among birds by mosquitoes. Although the virus can be highly lethal to some species of birds most species of birds survive the infection.

Emergent Infectious Diseases Figure 17.7 shows a map of the emergence of new diseases around the world. Since the 1970s, new diseases, or diseases that have been rare for more than 20 years, have been appearing throughout the world at a rate of approximately one per year.

Infectious diseases have killed large numbers of people Figure 17.4 shows the many pathways of transmitting pathogens. Pathogens have evolved a wide variety of ways to infect humans.

Toxicology is the study of chemical risks Neurotoxins - chemicals that disrupt the nervous system Carcinogens - chemicals that cause cancer Teratogens - chemicals that interfere with the normal development of embryos or fetuses Allergens - chemicals that cause allergic reactions Endocrine disruptors - chemicals that interfere with the normal functioning of hormones in an animal’s body

Toxicology is the study of chemical risks Figure shows an endocrine disruption. Male animals normally make estrogen and then convert it to testosterone, an important hormone for male reproduction. Some endocrine disrupting hormones are thought to interfere with this process, causing less testosterone to be produced. As a result, these males can have low sperm counts and eggs may develop inside their testes.

Dose-Response Studies Dose-response studies expose animals or plants to different amounts of a chemical and then observe a variety of possible responses including mortality or changes in behavior or reproduction. Acute studies are of a short duration, while chronic studies are a longer duration. LD50 - lethal dose that kills 50% of the individuals ED50 - effective dose that causes 50% of the animals to display the harmful but nonlethal effect

Dose-Response Studies Figure shows an LD50 graph. To determine the dose of a chemical that causes a 50 percent death rate, scientists expose animals to different doses of a chemical and determine what proportion of the animals die at each dose. Such an experiment typically produces an S-shaped curve.

Retrospective versus Prospective Studies Epidemiology is a field of science that strives to understand the causes of illness and disease in human and wildlife populations. Retrospective studies monitor people who have been exposed to a chemical at some time in the past. Prospective studies monitor people who might become exposed to harmful chemicals in the future. Synergistic interactions- when two risks come together and cause more harm than one would. For example, the health impact of a carcinogen such as asbestos can be much higher if an individual also smokes tobacco.

Retrospective versus Prospective Studies Figure discusses the chemical disaster in Bhopal, India. (a) In 1984, a massive release of methyl isocyanate gas killed and injured thousands of people. (b) Retrospective studies that have followed the survivors of the accident have identified a large number of longer-term health effects from the accident.

Factors That Determine Concentrations of Chemicals Organisms Experience Figure shows routes of exposure when dealing with chemicals. Despite a multitude of potential routes of exposure to chemicals, most chemicals have a limited number of major routes.

Factors That Determine Concentrations of Chemicals Organisms Experience Solubility – how well a chemical can dissolve in a liquid. Biomagnification –is the increase in chemical concentration in animal tissues as the chemical moves up the food chain. Persistence of a chemical refers to how long the chemical remains in the environment.

Factors That Determine Concentrations of Chemicals Organisms Experience Figure The biomagnification of DDT. The initial exposure is primarily in a low trophic group such as the plankton in a lake. Consumption causes the upward movement of the chemical where it is accumulated in the bodies at each trophic level and upward movement by consumption allows the concentration to magnify.

Persistence Table 17.2 shows how scientists often measure persistence by observing the time needed for a chemical to degrade to half its original concentration, or the half life of the chemical.

Risk analysis helps us assess, accept, and manage risk Table shows the process of risk analysis. Risk analysis involves risk assessment, risk acceptance, and risk management.

Risk analysis helps us assess, accept, and manage risk Table show probabilities of death in the United States. Some factors that people perceive as having high risks of death, such as dying in an airplane crash, actually are quite low. In contrast, some factors that people rate as low risk such as dying from heart disease, actually pose the greatest risk.

Qualitative Risk Assessment Making a judgment of the relative risks of various decisions Probability- the statistical likelihood of an event occurring and the probability of that event causing harm

Quantitative Risk Assessment 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 X probability of being harmed if exposed

Risk Management 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.

Worldwide Standards of Risk The innocent-until-proven-guilty principle is based on the philosophy that a potential hazard should not be considered a hazard until the scientific data can definitively demonstrate that a potential hazard actually causes harm. The precautionary principle is based on the philosophy that when a hazard is plausible but not yet certain, we should take actions to reduce or remove the hazard.

Worldwide Standards of Risk Figure shows two different philosophies for managing risk. The innocent-until-proven-guilty principle requires that researches prove harm before the chemical is restricted or banned. The precautionary principle requires that when there is scientific evidence that demonstrates a plausible risk, the chemical must then be further tested.

International Agreements on Hazardous Chemicals Stockholm Convention In 2001, a group of 127 nations gathered in Stockholm, Sweden, to reach an agreement on restricting the global use of some chemicals 12 chemicals were to be banned, phased out, or reduced These include DDT, PCBs, and certain chemicals that are by-products of manufacturing processes.