1. Chapter 17 Human Health and Environmental Risks

3. Biological Risks
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.
Heart disease and cancer
Acute diseases- rapidly impair the functioning of a person’s body.
Ebola hemorrhagic fever

4. Risk Factors for Chronic Diseases in Humans
In low-income countries, the top 10 risk factors leading to chronic disease are associated with poverty, including unsafe drinking water, poor sanitation, and malnutrition.
Nearly half of the children under the age of 5 who die from pneumonia succumb to the disease because they suffer from poor nutrition – simultaneously malnourished
High-income countries – people can afford better nutrition and proper sanitation – fewer young people die from diseases such as pneumonia and diarrhea
Risk factors – increased tobacco use, less active lifestyles, poor nutrition, overeating – leads to high blood pressure and obesity

6. Infectious Diseases Have Killed Large Numbers of People
Epidemic – When a pathogen causes a rapid increase in disease
Pandemic – When an epidemic occurs over a large geographic region such as an entire continent

7. Historical Diseases Plague – Bubonic Plague – Black Death
Caused by an infection from a bacterium (Yersinia pestis) that is carried by fleas
Fleas attached to rodents, such as rats and mice, giving them mobility
When humans live in close contact with rats and mice, the bacterium is transmitted either by flea bites or by handling the rodents
Infected individuals – swollen glands, black spots on skin, extreme pain
Killed hundreds of thousands of people – nearly one-fourth of the European population in the 1300s
Last major plague – Asia – early 1900s
Today – small outbreaks throughout the world – modern antibiotics highly effective at killing the bacterium and preventing human death

8. Historical Diseases Malaria
An infection from any one of the several species of protists in the genus Plasmodium.
Parasite spends one stage of its life inside a mosquito and another stage inside a human
Infection – flulike symptoms
Each year, 350 – 500 million people contract the disease and 1 million people (mostly children under the age of 5), die from it.
Sub-Saharan Africa, Asia, the Middle East, Central and South America
Since 1951 – Malaria parasite eradicated from the US by mosquito eradication programs
1,000 cases of malaria diagnosed in US each year – found in people who have returned from regions in the world where the malaria parasite lives.

9. Historical Diseases Tuberculosis
A highly contagious disease caused by a bacterium (Mycobacterium tuberculosis) that primarily infects the lungs.
Spread when a person coughs and expels bacteria into the air – bacteria can persist for several hours and infect a person who inhales them
Symptoms – weakness, night sweats, coughing up blood
Each year 9 million people develop the disease and 2 million die
Most easily treated by taking antibiotics for a year
US – antibiotics readily available – dramatic fall in number of new cases and the number of deaths
Developing countries – medicines not readily available or they do not take dose for full duration of time
Patient stops taking antibiotics before last bacteria is killed
Pathogen quickly rebuilds its population inside the person’s body
Last few bacteria generally the most drug-resistant
Drug-resistant strains becoming a major concern – Africa and Russia – 20% infected people carry drug-resistant strain

11. Emergent Diseases
Emergent Infectious Disease – infectious diseases that were previously not described or have not been common for at least the prior 20 years.
HIV/AIDS Radiolab – Patient Zero
In late 1970s, rare types of pneumonia and cancer began appearing in individuals with weak immune systems – condition names Acquired Immune Deficiency Syndrome (AIDS)
1983 – scientists discovered the weak immune system caused by a previously unknown virus they named Human Immunodeficiency Virus (HIV).
Virus spread through sexual contact and by intravenous drug users.
Origin remained a mystery until 2006 – researchers found a genetically similar virus in a wild population of chimpanzees living the Cameroon, Africa
Researchers hypothesized that local hunters were exposed to the virus when butchering or eating the chimps – exposure allowed new host (humans) to become infected
Today – more than 33 million people in the world are infected with HIV and 25 million people have died from AIDS related illnesses
New antiviral drugs maintain low HIV populations inside the human body – substantially extend life.

12. Emergent Diseases Ebola
1976 – researchers first discovered Ebola hemorrhagic fever – caused by the Ebola virus
First discovered in the Democratic Republic of Congo near the Ebola River
Infections of humans are sporadic and have not reached epidemic proportions – a concern because it kills a large percentage of those infected
Infected – fever, vomiting, internal and external bleeding, death within 2 weeks
No drugs available to fight the virus – natural source of Ebola remains unknown
Virus also kills other primates at a high rate, leaving no primate hosts for the virus – primates not likely the long-term source of the virus.

13. Emergent Diseases Mad Cow Disease
1980s – neurological disease in which a pathogen slowly damages a cow’s nervous system
Cow loses coordination of its body (cow goes “mad”) and then dies
Small, beneficial proteins in the brain, called prions, occasionally mutate into deadly proteins that act as pathogens.
Prions – not well understood – represent new category of pathogen
1996 – Great Britain announced mad cow disease, also known as Bovine Spongiform Encephalopathy (BSE), could be transmitted to humans who ate the meat
Prions difficult to destroy by cooking
Variant Creutzfeldt-Jakob disease (vCJD) – infected humans who suffer a fate similar to the infected cow.
Transmission requires an uninfected cow to consume the nervous system of an infected cow. Cannot be spread through cattle grazing on the same pasture.
1980s – Europe commonly included ground-up remains of cattle as a source of additional protein – spread throughout cattle population
Infected humans who ate the beef
Britain – Total of 180,000 cattle were infected and 166 people had died as of 2009
Estimated that several thousand people currently infected – prions exist in the human body for many years before they begin to cause symptoms of the disease
New rules forbid the feeding of animal remains to cattle and as a result, the current risk of mad cow disease has been greatly reduced.

14. Emergent Diseases Bird Flu – caused by the H1N1 virus
Normally infects only birds – rarely deadly to wild birds but can frequently cause domesticated birds such as ducks, chickens, and turkeys to become sick and die
2006 – reports emerged from Asia that a related virus, H5N1, jumped from birds to people, primarily people who were in close contact with birds
Humans always have contact with flu viruses – evolutionarily, no contact with the H5N1 and therefore, have little defense against it.
As of 2009, more than 400 people have become infected by H5N1 and more than half have died.
Currently not easily passed among people, but if a future mutation makes transmission easier, scientists estimate it has the potential to kill 150 million people.

15. Emergent Diseases West Nile Virus
Lives in hundreds of species of birds and is transmitted among birds by mosquitos.
Highly lethal to blue jays, American crows, and American robins
1937 – first human case was identified in the West Nile region of Uganda
In humans - causes an inflammation of the brain leading to illness and sometimes death
1999 – appeared in the US and quickly spread throughout much of the US
Highest number of infections occurred in 2002 and 2003
Increased efforts to combat mosquito populations and protect against mosquito bites are causing a decline in the disease.

16. Types of Harmful Chemicals
Neurotoxins- chemicals that disrupt the nervous systems of animals.
Many insecticides – interfere with an insect’s ability to control its nerve transmissions.
Insects and other invertebrates are highly sensitive to neurotoxin insecticides – can become completely paralyzed, cannot obtain oxygen, and quickly die
Lead and mercury – harmful heavy metals that can damage a person’s kidneys, brain, and nervous system
Carcinogens- chemicals that cause cancer
Cause cell damage and lead to uncontrolled growth of cells either by interfering with the normal metabolic processes of the cell of by damaging the genetic material of the cell
Mutagens – carcinogens that cause damage to the genetic material of the cell
Well known carcinogens – asbestos, radon, formaldehyde, and chemicals found in tobacco.

17. Types of Harmful Chemicals
Teratogens- chemicals that interfere with the normal development of embryos or fetuses
Thalidomide – infamous teratogen prescribed to pregnant women during the late 1950s and early 1960s to combat morning sickness
Tens of thousands of mothers around the world gave birth to children with birth defects before the drug was taken off the market in 1961.
Most common modern teratogen – alcohol
Excessive alcohol consumption reduces the growth of the fetus and damages the brain and nervous system – fetal alcohol syndrome

18. Types of Harmful Chemicals
Allergens- chemicals that cause allergic reactions
Not pathogens but could cause an abnormally high response from the immune system
Breathing difficulties and death
Peanuts and milk and several drugs including penicillin and codeine
Endocrine disruptors- chemicals that interfere with the normal functioning of hormones in an animal’s body
Hormones normally manufactured in the endocrine system and released into the bloodstream in low concentrations
As the hormones move through the body they bind to specific cells stimulating the cell to respond in a way that regulates the functioning of the body
Wastewater containing hormones from human birth control and animal rearing facilities found in waterways – scientists finding male fish, amphibians, and reptiles are becoming feminized – possessing testes with low sperm counts and testes that produce both sperm and eggs.
Occurs because males normally convert the female hormone estrogen into the male chemical testosterone. If endocrine disruptors interfere with the production of testosterone , males will have higher concentrations of estrogen and lower concentrations of testosterone in their bodies.
Low sperm count in men and increased risk of breast cancer in women

20. 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 and reproduction.
Most only last from 1-4 days – called acute studies because of their short duration.
Commonly measure mortality as a response – at the end, scientists count how many individuals die after exposure to each concentration.
Graphed data generally follows an S-shaped curve.
Threshold – the dose at which an effect can be detected
As dose is further increased, many individuals die – at highest concentration, all individuals die

22. Dose-Response Studies
LD50- lethal dose that kills 50% of the individuals
Important for assessing the relative toxicity of a chemical
By quantifying LD50 for a new chemical, scientists can compare the value to thousands of previous tests.
Determine if the chemical is lethal
Conducting LD50 studies on humans is considered unethical so studies are conducted on animals such as mice and rats and the results are extrapolated to humans.
ED50- effective dose that causes 50% of the animals to display the harmful but nonlethal effect
Sublethal effects – when scientists are interested in other harmful effects that a chemical might have, including its acting as a teratogen, carcinogen, or neurotoxin that could alter the behavior of an individual

23. Dose-Response Studies – Testing Standards
In US – effects of chemicals on humans and wildlife are regulated by the EPA
Toxic Substances Control Act of 1976 – gives the EPA the authority to regulate many chemicals, excluding food, cosmetics, and pesticides
Federal Insecticide, Fungicide, and Rodenticide Act of 1996 – regulates pesticides. A manufacturer must demonstrate that a pesticide “will not generally cause reasonable adverse effects on the environment.”
10 million species on Earth – every species cannot be tested
Scientists test the most sensitive in four animal groups – bird, mammal, fish, and invertebrate
Using LD50 and ED50 values regulatory agencies can determine concentrations in the environment that should cause no harm
Most animals – a safe concentration is obtained by taking the LD50 (causes 50% to die) and dividing it by % of the LD50 value should cause few or no animals to die
LD50 and ED50 values obtained from rats and mice are divided by to set safe values for humans

24. Dose-Response Studies – Chronic Studies
Chronic Studies – experiments of longer duration
Will often last from the time an organism is young to when it is old enough to reproduce.
Fish – could take several months
Goal – examine the long-term effects of chemicals, including their effects on survival and their impacts on reproduction.

25. Retrospective vs. Prospective Studies
An alternative to dose-response experiments examines large populations of humans or animals who are exposed to chemicals in their everyday lives and then determines whether these exposures are associated with any health problems.
Epidemiology – a field of science that strives to understand the causes of illness and disease in human and wildlife populations.
Two ways of conducting research: retrospective and prospective studies

26. Retrospective vs. Prospective Studies
Retrospective Studies – monitor people who have been exposed to a chemical at some time in the past.
Scientists identify a group of people who have been exposed to a harmful chemical and a second group who have not been exposed
Both groups monitored to see if the exposed group has greater health problems
1984 – accidental release of methyl isocyanate gas from a Union Carbide pesticide factory in Bhopal, India
More than 36,000 kg of hazardous gas spread throughout the city of 500,000 inhabitants
An estimated 2,000 people died that night and another 15,000 died later from the effects
Scientists have been monitoring citizens of Bhopal for more than two decades – found that nearly 100,000 people are still suffering illness from the accident

27. Retrospective vs. Prospective Studies
Prospective Studies – monitor people who might become exposed to harmful chemicals in the future
Scientists might select a group of 1,000 participants and ask them to keep track of the food they eat, the tobacco they use, and the alcohol they drink for the next 40 years.
Could be challenging because a participant’s habits, such as tobacco use, can be associated with many other risk factors including socioeconomic status
Particular Concern - Synergistic interactions- when two risks come together and cause more harm that one would.
For example, the health impact of a carcinogen such as asbestos can be much higher if an individual also smokes tobacco.

28. Routes of Exposure
Routes of Exposure – the ways in which an individual comes into contact with a chemical
For any particular chemical, the major routes are usually limited to just a few of the many possible routes
Bisphenol A – chemical used in the manufacturing of hard plastic items such as toys, food containers, and baby bottles.
Recent research – bisphenol A may be responsible for early puberty and increased rates of cancer – these effects are being debated and investigated
Scientists can then determine the chemical’s solubility and its potential for bioaccumulation

29. Bioaccumulation
Solubility – the movement of a chemical in the environment depends in part on how well the chemical can dissolve in a liquid
Some readily soluble in water whereas others more soluble in fats and oils.
Water-soluble chemicals – widespread in groundwater and surface water
Fat and Oil-soluble – found in higher concentrations in soils
Oil-soluble – readily stored in the fat tissues of animals
Continued exposure to oil-soluble chemicals can cause bioaccumulation
Bioaccumulation- an increased concentration of a chemical within an organism over time
Begins when an individual incorporates small amounts of a chemical from the environment into its body. As the chemical continually accumulates over time, often in fat tissues, the concentration inside the organism increases.

30. Biomagnification
Biomagnification- the increase in a chemical concentration in animal tissues as the chemical moves up the food chain.
Primary consumer – obtain an oil- soluble chemical from the environment and the chemical accumulates in fat tissue
Secondary consumer – consume primary consumers – bioaccumulate the chemical they have ingested by consuming the chemical that is stored in the fat tissues of the primary consumers
As we continue to move up the food chain, each trophic level is exposed to higher concentrations of chemicals from the food it consumes.
The original concentration is magnified to occur at a much higher concentration in the top predator of the community.

31. Persistence
Persistence- how long a chemical remains in the environment
Depends on temperature, pH, whether the chemical is in water or soil, whether it can be degraded by sunlight, and whether it can be broken down by microbes.
Scientists often measure persistence by observing the time needed for the chemical to degrade to half its original concentration – half-life of the chemical

32. Risk Analysis
Environmental Hazard – anything in our environment that can potentially cause harm.
When assessing the risk of different environmental hazards, regulatory agencies, environmental scientists, and policy makers usually follow the three steps listed above.

33. Qualitative Risk Assessment
Making a judgment of the relative risks of various decisions
Choosing to drive slowly on a wet highway or buying a more expensive car because it is safer
Probability- the statistical likelihood of an event occurring and the probability of that event causing harm
Because our personal risk assessments are not quantitative, they often do not match the actual risk
Perceived Risk vs. Actual Risk
Some people might be afraid to fly and prefer riding in a car even though the probability of dying in an automobile (1 in 84) is far greater than the probability of dying in an airplane (1 in 5,051).
Because plane crashes so a lot of harm and receive a great deal of media attention, people believe that it is risky to fly in airplanes.
In contrast, we downplay activities that provide us with cultural, political, or economic advantages
Drinking alcohol

34. Quantitative Risk Assessment
The approach to conducting a quantitative risk assessment is:
Risk= probability of being exposed to a hazard x probability of being harmed if exposed
Can calculate whether it’s riskier to fly on a commercial airline for 1,000 miles per year or to eat 40 tablespoons of peanut butter per year (contains tiny amounts of a carcinogenic chemical produced naturally by a fungus that sometimes occurs in peanut butter).
Both behaviors produce a 1 in 1 million chance of dying.
Bring together large amounts of data- from acute and chronic dose-response experiments, retrospective studies, and prospective studies.
Estimate the probability of harm

36. Risk Acceptance
Once the risk assessment is completed, the second step is determining risk acceptance – the level of risk that can be tolerated.
Most difficult of the three steps
Conflict between those who are willing to live with some amount of risk and those who are not.
According to EPA, a 1 in 1 million risk is acceptable for most environmental hazards – some people believe this is too high
Others feel a 1 in 1 million chance of death from radiation leaks is a small price to pay for electricity generated from nuclear energy

37. Risk Management
Third part of the risk-analysis process – seeks to balance possible harm against other considerations
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.
This step is a regulatory activity that is typically carried out by local, national, or international government agencies.
– federal government set acceptable concentration of arsenic at 50µg/L in drinking water, even though scientists knew that concentration could cause cancer
1999 – EPA announced it was lowering the acceptable concentration to 10µg/L.
New regulation threatened to place economic burden on mining companies and several municipalities in western states with naturally high concentrations of arsenic
Both groups lobbied hard against the changes
2001 – weeks before new change was to be placed into effect – EPA announced it would remain at 50µg/L
Agency argued further risk assessments needed to be conducted and had to be balanced by economic interests
Later in 2001 – National Academy of Sciences concluded the acceptable amount was actually 5µg/L
EPA revised ruling – setting the concentration at 10µg/L.

38. Worldwide Standards of Risk
Currently about 80,000 registered chemicals in the world but they are not regulated in the same way around the globe
Innocent-until-proven-guilty principle – based on the philosophy that a potential hazard should not be considered a hazard until the scientific data can definitely demonstrate that a potential hazard actually causes harm.
Allows introduction of beneficial chemicals more quickly
Downside – harmful chemicals can affect humans or wildlife for decades before sufficient scientific evidence accumulates to confirm they are harmful
Precautionary Principle – based on the philosophy that when a hazard is plausible but not yet certain, we should take actions to reduce or remove the hazard.
Must have scientific basis
Benefit – fewer harmful chemicals will enter the environment
Beneficial chemical introduction could be delayed for year if initial assessment shows plausible risk
Slower pace – reduces financial motivation of manufacturers to invest in research
Trade off between greater safety with slower introduction of beneficial chemicals vs. greater potential risk with a greater rate of discovery of helpful chemicals.
Precautionary Principle growing throughout the world and instituted by European Union in 2000.
United States, however, continues to use the Innocent-Until-Proven-Guilty Principle.
Potential benefit of Precautionary Principle – asbestos
First mined in 1879 – first report of human deaths 1906 – Multiple studies linking asbestos to cancer – despite evidence, little was done to prevent exposure
Not banned in EU until 1965

39. 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.
2007 – 27 nations of the EU put into effect an agreement on how chemicals should be regulated within the EU
Called REACH – acronym for registration, evaluation, authorization, and restriction of chemicals
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 to the environment.