1. Chapter 17 Human Health and Environmental Risks

3. Risks and Hazards
Risk = a measure of the likelihood that you will suffer harm from a hazard
We can suffer from
Physical hazards: such as fire, earthquake, volcanic eruption…
Biological hazards: from more than 1,400 pathogens.
Chemical hazards: in air, water, soil, and food, venom.

4. Biological Risks
Diseases not caused by living organisms cannot spread from one person to another (nontransmissible disease), while those caused by living organisms such as bacteria and viruses can spread from person to person (transmissible or infectious)
Infectious diseases- those caused by infectious agents, known as pathogens.
Examples: pneumonia and venereal diseases

5. Biological Risks
Chronic disease- slowly impairs the functioning of a person’s body.
Acute diseases- rapidly impair the functioning of a person’s body.

6. Disease is a major focus of environmental health
Despite our technology, disease kills most of us
Disease has a genetic and environmental basis
Cancer, heart disease, respiratory disorders
Poverty and poor hygiene foster illnesses

7. Infectious diseases kill millions
Infectious diseases kill 15 million people/year
Half of all deaths in developing countries
Money lets developed countries have access to hygiene and medicine

8. Infectious and noninfectious diseases
Lifestyles in developed nations affect diseases
Smoking, obesity, etc
Public health decreases some infectious diseases
Some (AIDS) are spreading
Some develop resistance to antibiotics

10. Diseases, the environment, and society
Our mobility spreads diseases
West Nile Virus spread from Africa to all lower 48 U.S. states in 5 years
New diseases are emerging
H5N1 avian flu, H1N1 swine flu
Climate change will expand the range of diseases
To predict and prevent diseases, experts deal with complicated interrelationships
In technology, land use, and ecology

11. Killing large #s of People
Epidemic: when a pathogen causes rapid increase in disease (exceeds what is expected based on experience)
Pandemic: when an epidemic spreads through human populations across a large region, like a continent

12. Historical Diseases
Plague
Malaria
Tuberculosis

13. Emergent Diseases HIV/AIDS-virus believed to have begun in chimps
Ebola-virus with many strains. Can be deadly
Mad Cow Disease-caused by cows being fed infected cow brain
Swine and Bird Flu-originated from bird
SARS (severe acute respiratory syndrome)
West Nile Virus-carried through mosquito

15. Chemical Risks Neurotoxins- chemicals that disrupt the nervous system
Carcinogens- chemicals that cause cancer
Mutagens-causes damage to the genetic material
Teratogens- chemicals that interfere with the normal development of embryos or fetuses
Allergens- chemicals that cause allergic reactions, affecting the immune system
Endocrine disruptors- chemicals that interfere with the normal functioning of hormones in an animal’s body

16. Indoor environmental health hazards
Radon = a highly toxic, radioactive gas that is colorless and undetectable
It can build up in basements
Asbestos = a mineral that insulates, muffles sounds, and resists fire
Asbestosis = scarred lungs that cease to function

17. Lead poisoning Lead poisoning = caused by lead, a heavy metal
Damages the brain, liver, kidney, and stomach
Causes learning problems, behavior abnormalities, and death
Exposure is from drinking water that flows through lead pipes or from lead paint
Education led to declines in poisoning, but China still used it in toy paint until recently

18. A recently recognized hazard
Polybrominated diphenyl ethers (PBDEs) = has fire-retardant properties
Used in computers, televisions, plastics, and furniture
Persist and accumulate in living tissue
Mimic hormones and affect thyroid hormones
Also affect brain and nervous system development and may cause cancer
Concentrations are rising in breast milk
Now banned in Europe, concentrations have decreased
The U.S. has not addressed the issue

19. Toxicology studies poisonous substances
Toxicology = the study of the effects of poisonous substances on humans and other organisms
Toxicity = the degree of harm a toxicant can inflict
Toxicant = any toxic substance (poison)
“The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity
Environmental toxicology = deals with toxic substances that come from or are discharged into the environment
Studies health effects on humans, other animals, and ecosystems

20. Balancing risks and rewards
There is a tradeoff between the risk and reward of most hazards
We must judge how these compare
We use bisphenol (BPA) despite its health risks
Are safer and affordable alternatives available?
Don’t forget, chemicals have given us our high standard of living
Food, medicine, conveniences

21. Toxic substances in the environment
The environment contains natural chemicals that may pose health risks
Toxins = toxic chemicals made in tissues of living organisms
But synthetic chemicals are also in our environment
Every human carries traces of industrial chemicals
The U.S. makes or imports 250 lb of chemicals for every person in the country

22. Chemicals are in the air, water, and soil
80% of U.S. streams contain 82 contaminants
Antibiotics, detergents, drugs, steroids, solvents, etc.
92% of all aquifers contain 42 volatile organic compounds (from gasoline, paints, plastics, etc.)
Less than 2% violate federal health standards for drinking water
Pesticides are present in streams and groundwater in levels high enough to affect aquatic life

23. Synthetic chemicals are in all of us
Every one of us carries traces of hundreds of industrial chemicals in our bodies
Including toxic persistent organic pollutants restricted by international treaties
Babies are born “pre-polluted” – 232 chemicals were in umbilical cords of babies tested
Not all synthetic chemicals pose health risks
But very few of the 100,000 chemicals on the market have been tested

24. Dose-response analysis
Dose-response analysis = measures the effect a toxicant produces or the number of animals affected
At different doses
Dose = amount of substance the test animal receives
Response = the type or magnitude of negative effects
Dose-response curve = the dose plotted against the response

25. Dose-Response Studies
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

26. The type of exposure affects the response
Acute exposure = high exposure to a hazard for short periods of time
Easy to recognize
Stem from discrete events: ingestion, oil spills, nuclear accident, etc.
Chronic exposure = low exposure for long periods of time
More common but harder to detect and diagnose
Affects organs gradually: lung cancer, liver damage
Cause and effect may not be easily apparent

27. Dose Response Studies
Dose-response studies: expose animals or plants to different amounts of a chemical and observe a variety of responses
Acute studies: short duration experiments
Chronic studies: longer duration of experiments, goal is to examine long-term effects of chemicals including effects on survival and impact

28. LD50 Studies
To determine the dose of a chemical that causes a 50% death rate, scientists expose animals to different doses to determine what proportion will die at each dose

29. Very sensitive Very insensitive
Number of individuals affected
Very sensitive
Majority of population
Very insensitive
Dose (hypothetical units)
Fig , p. 430

30. Retrospective vs Prospective
Retrospective study: a study on people who have been exposed to chemicals sometime in their past
Prospective study: a study on people might be exposed to harmful chemicals in the future
Participants may be asked to track tobacco, food or alcohol intake to track future health problems

31. Human studies Case history approach = studies individual patients
Autopsies tell us about lethal doses
Don’t tell about rare, new, or low-concentration toxins
Don’t tell about probability and risk
Epidemiological studies = large-scale comparisons between exposed and unexposed groups
Studies can last for years
Yield accurate predictions about risk
Measure an association between a health hazard and an effect – but not necessarily the cause of the effect

32. Mixes may be more than the sum of their parts
We can’t determine the impact of mixed hazards
They may act in ways that cannot be predicted from the effects of each in isolation
Mixed toxicants can sum, cancel out, or multiply each other’s effects
Synergistic effects = interactive impacts that are greater than the sum of their constituent effects
New impacts may arise from mixing toxicants
DDE may cause or inhibit sex reversal, depending on the presence of other chemicals (DDE results from breakdown of DDT)

33. Routes of Exposure

34. Some toxicants persist
Toxins can degrade quickly and become harmless
Or they may remain unaltered and persist for decades
Rates of degradation depend on the substance, temperature, moisture, and sun exposure
Breakdown products = simpler products that toxicants degrade into
May be more or less harmful than the original substance
DDT degrades into DDE, which is also highly persistent and toxic

35. Bioaccumulation
bioaccumulation- an increased concentration of a chemical within an organism over time. Occurs when an organism absorbs the toxic substance at a greater rate than the substance is lost or broken down.
Properties of substances that bioaccumulate
Long lived
Mobile
Typically fat soluble

36. Bioaccumulation
The longer the half life of the substance leads to greater risk of chronic poisoning, even if levels of the toxin are not very high
A classic example: DDT (dichloro- diphyny-trichloroethane. It has a half- life of 15 years.
Can lead to biomagnification

37. Silent Spring began the debate over chemicals
In the 1960s, untested pesticides were sprayed over public areas, with assumption they would do no harm
Rachel Carson’s Silent Spring (1962) showed DDT’s risks to people, wildlife, and ecosystems
Chemical companies challenged the book
Discrediting Carson’s personal reputation
DDT was banned in the U.S. in 1973
But is still made in the U.S. and exported

38. DDT has rather low toxicity to humans
But
high toxicity to insects
If accidentally swallowed in large amounts, it can cause a person to become excitable, have tremors and seizures
In animals, harmful effects in reproduction and in the nervous system
Causes shell-thinning in birds, in particular carnivorous birds (raptors) such as ospreys and bald eagles

39. Biomagnification
Biomagnification- the increase in a chemical concentration in animal tissues as the chemical moves up the food chain.

40. Biomagnification
Biomagnification causes accumulation of toxins in the food chain.
Predators eat contaminated prey
Pollutions accumulates at each stage of the food chain
Top consumers, including humans, are most affected

41. Biomagnification of Other Pollutants
Substance
Use & Problems
PCB’s
insulators in transformers
Fire retardant
Impairs reproduction
Widespread in aquatic systems
Heavy Metals
Mercury, Copper, Cadmium, Chromium, Lead, Nickel, Zinc, Tin
Mercury from gold mining
Many from metal processing
May affect nervous system
May affect reproduction
Cyanide
Used in leaching of gold
Used in fishing
Toxic

42. Persistence
Persistence- how long a chemical remains in the environment

43. We express risk in terms of probability
Exposure to health threats doesn’t automatically produce an effect
Rather, it causes some probability (likelihood) of harm
A substance’s threat depends on its identity and strength
Chance and frequency of an encounter
An organism’s exposure and sensitivity to the threat
Risk = the probability that some harmful outcome will result from a given action, event, or substance
Probability = describes the likelihood of a certain outcome

44. Perceptions of risk may not match reality
We try to minimize risk
But perception may not match reality
Flying versus driving
We feel more at risk when we do not control a situation
We fear nuclear power and toxic waste
But not smoking or overeating
Everything we do involves some risk

45. Risk Analysis
Environmental Hazard- anything in our environment that can potentially cause harm.
Environmental substances include substances such as pollutants or other chemical contaminants, draining swamps, logging forests, or volcanoes and earthquakes.
Hazards that are voluntary include smoking, tobacco…
Hazards that are involuntary include pollution

47. 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

48. Quantitative Risk Assessment
Risk assessment = the quantitative measurement of risk
Compares risks involved in different activities or substances
It identifies and outlines problems
Risk assessment has several steps:
The scientific study of toxicity
Assessing an individual or population’s exposure to the substance (frequency, concentrations, length)
Teams of scientific experts review hundreds of studies
Regulators and the public benefit from informed summaries

49. Risky Business
Risk acceptance determines how much risk can be tolerated
Risk management balances potential harms against other factors

50. Risk management
Risk management = decisions and strategies to minimize risk
Federal agencies manage risk
The U.S. has the Centers for Disease Control (CDC), the EPA, the Food and Drug Administration (FDA)
Scientific assessments are considered with economic, social, and political needs and values
Comparing costs and benefits is hard
Benefits are economic and easy to calculate
Health risks (costs) are hard-to-measure probabilities of a few people suffering and lots of people not

52. Worldwide Standards of Risk
Currently about 80,000 regulated chemicals in the world but they are not regulated the same way around the world
Innocent-until-proven-guilty principle assumes a substance is harmless
Helps technological innovation and economic advancement
But it allows dangerous substances to be used
Precautionary principle assumes a substance is harmful until it is shown to be harmless
Identifies troublesome toxicants before being released
May impede the pace of technology and economic advance

53. Who should have to prove a product is safe: the manufacturers or government/citizens?

54. Assessing Chemical Hazards
Federal and state governments do not regulate about 99.5% of the commercially used chemicals in the U.S.
Estimating a chemical’s toxicity is difficult, uncertain, and expensive.
Manufacturers contend that wide-spread application of the precautionary principle would make it too expensive to introduce new chemicals and technologies.

55. Philosophy affects policy
Different nations use different policies for regulating synthetic substances
Europe incorporates the precautionary principle
The U.S. uses the innocent-until-proven-guilty approach
Federal agencies involved in tracking and regulating synthetic chemicals include:
The FDA: monitors food, food additives, cosmetics, drugs, medical devices
The EPA: regulates pesticides and chemicals not covered by other laws

56. EPA regulation is only partly effective
The Toxic Substances Control Act (1976) = the EPA monitors chemicals made in or imported into the U.S.
The EPA can ban substances that pose excessive risk
Many health advocates think the TSCA is too weak
Of 83,000 chemicals, only five have been restricted
To push for more testing, toxicity must already be proven, but testing is minimal
Only 10% of chemicals have been tested for toxicity
Fewer than 1% are regulated
Almost none have been tested for endocrine, nervous, or immune system damage

57. FIFRA (1974) The Federal Insecticide, Fungicide, and Rodenticide Act
Charges the EPA with “registering” new pesticides manufacturers want to market
The EPA asks the manufacturer to provide information on safety assessments
The EPA examines ingredients, use, etc. to determine risks to people, other organisms, water, or air
It approves, denies, or sets limits on the chemical’s sale and use and approves language used on the label
Hazardous chemicals are approved if economic benefits outweigh hazards

58. Europe’s REACH program
The EU’s REACH program (Registration, Evaluation, Authorization, and Restriction of Chemicals) shifts the burden of proof for safety to industry
Helps industries research and develop safer products
Chemicals will be approved, deemed unsafe, or tested further
1,500 chemicals will be replaced with safer ones
REACH will cost industry $3.8–7 billion over 11 years
Health benefits will be $67 billion over 30 years

59. Stockholm Convention on Persistent Organic Pollutants (POPs)
In 2001, a group of 127 nations gathered in Stockholm, Sweden, to reach an agreement on restricting the global use of some chemicals
12 most dangerous POPs (known as the “dirty dozen”)were to be banned, phased out, or reduced. In 2013, 11 more were added to the list
These include DDT, PCBs, and certain chemicals that are by-products of manufacturing processes.