2. Toxicology is the scientific field that measures the degree of harm a hazardous agent can cause. Scientists measure toxicity based on dosage, solubility, persistence, bioaccumulation, biomagnification, and chemical interactions.
3. Chemical hazards include agents that are flammable or explosive, damage or irritate lungs or skin, interrupt oxygen uptake, and cause allergies. Chemical hazards are defined by their toxicity, the person’s acute and chronic reactions to it, and its pervasiveness in the environment.
4. The types of disease threatening people in developing countries are primarily infectious diseases of childhood, while those threatening people in developed countries tend to be chronic diseases of adults, such as heart disease, stroke, cancer, and respiratory conditions.
5. Risks can be estimated, managed, and reduced by identifying hazards, evaluating related risks (risk assessment), ranking risks (comparative risk analysis), determining alternative solutions, making decisions about reducing risks (risk management), and informing decision-makers about risk (risk communication).
Key Questions and Concepts
17-1 What major health hazards do we face?
A. A risk is a measure of your likelihood of suffering harm from a hazard. Hazards may cause injury, disease, economic loss, or environmental damage. Risk assessment is projected as a probability: a mathematical statement about how likely it is that harm will result from a hazard. It gives the estimate of an event’s actually happening. Risk management involves deciding whether or how to reduce a particular risk to a certain level and at what cost.
B. There are four major types of hazards.
1. Biological hazards come from more than 1400 pathogens (bacteria, viruses, parasites, protozoa, and fungi) that can infect humans.
2. Chemical hazards from harmful chemicals in air, water, soil and food.
3. Physical hazards such as fire, earthquake, volcanic eruption, flood, tornado, and hurricane.
4. Cultural hazards such as smoking, unsafe working conditions, poor diet, drugs, drinking, driving, criminal assault, unsafe sex, and poverty.
17-2 What types of biological hazards do we face?
A. Diseases not caused by living organisms do not spread from one person to another, while those caused by living organisms such as bacteria and viruses can spread from person to person.
1. Non-transmissible diseases tend to develop slowly, have multiple causes, are not caused by living organisms, and do not spread from one person to another. Examples are cancer, diabetes, asthma, malnutrition, and blood vessel disorders.
2. Transmissible disease is caused by a living organism and can spread from one to another. Infectious agents/pathogens are spread in air, water, food, body fluids, by some insects, and by vectors.
B. The World Health Organization estimates that each year the world’s seven deadliest infectious diseases kill 13.6 million people—most of them poor people in developing countries. This amounts to about 37,000 mostly preventable deaths every day.
SCIENCE FOCUS: Rapidly producing infectious bacteria are becoming genetically resistant to widely used antibiotics. The bacteria can transfer this resistance to nonresistant bacteria. Resistance to antibiotics has increased because of antibiotics being over-prescribed, added to household products (e.g., soaps) and used in livestock and dairy animals to control disease and promote growth.
D. Tuberculosis kills 1.7 million people per year and could kill 25 million more people by 2020. Tuberculosis is a silent global epidemic since many people do not know that they have been infected.
E. Flu, HIV, and hepatitis B viruses infect and kill many more people each year than the highly-publicized West Nile and SARS viruses. The influenza or flu virus is the biggest killer. It is responsible for the deaths of about 1 million people a year. CORE CASE STUDY: The second biggest killer is HIV, transmitted in a variety of ways. Globally, it infects about 4.9 million new people a year. The resulting complications from AIDS kill about 3 million people annually.
CASE STUDY: Malaria kills about 2 million people per year and has probably killed more people than all of the wars ever fought. Malaria is caused by a parasite that is spread by the bites of certain mosquitoes. It is caused by four species of protozoan parasites in the genus Plasmodium and the parasite circulates from mosquito to human and back to mosquito.
F. There are a number of ways to reduce the incidence of infectious diseases if the world is willing to provide the necessary funds and assistance. Global death rate dropped by about 2/3rds between 1970 and 2000. The number of children immunized between 1971 and 2000 went from 10% to 84% and saved an estimated 10 million lives a year. Only about 10% of global medical research and development money is spent on preventing infectious diseases in developing countries, even though more people worldwide suffer and die from these diseases than all other diseases combined.
G. Mostly because of human activities, infectious diseases are moving at increasing rates from one animal species to another and from one animal species to humans. SCIENCE FOCUS: Infectious diseases that are transmitted from wild and domesticated animals to humans include avian flu, SARS, West Nile virus, Hantavirus, and Lyme disease. The clearing and fragmentation of forests has played a major role in exposing humans to new types of infectious disease. Understanding the connections between human activities and ecosystem functioning is a key to preventing or slowing the spread of infectious organisms from wild and domesticated animals to humans.
17-3 What types of chemical hazards do we face?
A. Toxic and hazardous chemicals can harm or kill. A toxic chemical can cause temporary or permanent harm or death to humans or animals. A hazardous chemical can harm because it is flammable or explosive, or because it irritates or damages skin or lungs or induces allergic reactions.
B There are three major types of potentially toxic agents.
1. Mutagens are chemicals or ionizing radiation that cause or increase the frequency of random mutations in the DNA molecules. It is generally accepted that there is no safe threshold for exposure to harmful mutagens.
2. Teratogens are chemicals that cause harm or birth defects to a fetus or embryo. Alcohol and thalidomide are examples of teratogens.
CASE STUDY: Mercury toxicity and food chains.
3. Carcinogens are chemicals or ionizing radiation that cause or promote cancer.
C. Long-term exposure to some chemicals at low doses may disrupt the body’s immune, nervous, and endocrine systems. There is concern that certain synthetic chemicals can mimic hormones and that low-level exposure to these hormonally active agents (HAAs) can disrupt the endocrine system.
SCIENCE FOCUS: Bisphenol A and plastics.
17-4 How can we evaluate chemical hazards?
A. Factors determining the harm caused by exposure to a chemical include the amount of exposure (dose), the frequency of exposure, the person who is exposed, the effectiveness of the body’s detoxification systems, and the exposed person’s genetic makeup. Other factors can affect the harm caused by a substance including solubility, persistence, bioaccumulation, biomagnification, and chemical interactions. CASE STUDY: children can be particularly sensitive to toxic chemicals.
B. Toxicity is usually measured using laboratory animals, but increasingly with computer simulations or cell cultures.
C. Trace amounts of chemicals in the environment or your body may or may not be harmful. Should we be concerned about trace amounts of various chemicals in air, water, food, and our bodies? The honest answer is we often do not know.
D. Under existing laws, most chemicals are considered innocent until proven guilty, and estimating their toxicity to establish guilt is difficult, uncertain, and expensive.
E. Some scientists and health officials say that preliminary but not conclusive evidence that a chemical causes significant harm should spur preventative action, but others disagree.
17-5 How do we perceive risks and how can we avoid the worst of them?
A. There are scientific ways to evaluate and compare risk, to decide how much risk is acceptable, and to find affordable ways to reduce risk. Risk assessment involves identifying hazards and evaluating their associated risks.
CASE STUDY: Avoidance of cultural hazards such as death from smoking also improves longevity of life.
B. Estimation of risk for complex technology is difficult due to unpredictability of human behavior, human error, and sabotage.
C. Most individuals are poor at evaluating the relative risks they face, mostly because of misleading information, denial, and irrational fears, but there are techniques to evaluate and reduce risk (see page 464-465).
carcinogens (p. 448)
dose (p. 454)
dose response curve (p. 455)
infectious disease (p. 440)
mutagens (p. 448)
nontransmissible disease (p. 440)
pathogen (p. 440)
response (p. 455)
risk (p. 439)
risk analysis(p. 460)
risk assessment (p. 439)
risk management (p. 439)
teratogens (p. 448)
toxic chemical (p. 448)
toxicity (p. 453)
toxicology (p. 453)
transmissible disease (p. 440)
ABC News Videos
Water Pollution Threatens Millions; Biology in the Headlines, 2007, DVD ISBN: 0495385689
Cloned Food Approved; Biology in the Headlines, 2007, DVD ISBN: 0495385689
Food Allergy Increase; Biology in the Headlines, 2006, DVD ISBN: 0495016020
Fat Man Walking; Biology in the Headlines, 2006, DVD ISBN: 0495016020
AIDS Conference in Brazil; Environmental Science in the Headlines, 2005, DVD ISBN: 0534404804
Bird Flu; Environmental Science in the Headlines, 2005, DVD ISBN: 0534404804
Pollution and Women’s Health; Environmental Science in the Headlines, 2007, DVD ISBN: 0495385433
Additional Video resources
We all Live Downstream (Documentary, 1991)
A look at pollution in the Mississippi River and the effects on human health.
NOVA: Can Buildings Make You Sick?
NOVA/Frontline: Harvest of Fear (Video series, PBS, 2001)
A Civil Action (movie, 1999)
The families of children who died sue two companies for dumping toxic waste.