1. Chapter 14 Topics: Environmental health and environmental hazards
Toxic substances in the environment
Hazards and their effects
Risk assessment and risk management
Philosophical and policy approaches to risk

2. Environmental health
Environmental health assesses natural and human-caused environmental factors that influence human health and quality of life

3. Types of environmental hazards
There are four types of environmental hazards
Physical
Chemical
Biological
Cultural

4. Physical hazards Occur naturally in our environment
Earthquakes, volcanoes, fires, floods, droughts, exposure to UV light, temperature extremes
We increase our risk by deforesting slopes (landslides), channelizing rivers (flooding), etc.

5. Chemical hazards Synthetic chemicals Natural chemicals Pharmaceuticals
Disinfectants
Pesticides
Solvents
Natural chemicals
Venom
Plant poisons

6. Biological hazards Result from ecological interactions
Infectious disease = viruses, bacteria, and other pathogens parasitize humans
Vectors = organisms that transfers pathogens to a host

7. Cultural hazards Result from our lifestyles
Where we live, our socioeconomic status, our occupation, our behavioral choices
Smoking, drug use, diet and nutrition, crime, mode of transportation

8. Some hazards are indoors
Radon = a highly toxic, radioactive gas
Colorless, odorless, and difficult to detect
Can build up in basements
Asbestos = a fibrous mineral
Used for insulation, sound-deadening, and resistance to fire
Asbestosis = scarred lungs that cease to function

9. Other indoor hazards Lead poisoning = caused by ingestion of lead
Damages the brain, liver, kidney, and stomach
Causes learning problems, behavior abnormalities, and death
Exposure from lead paint or from drinking water that flows through lead pipes
Polybrominated diphenyl ethers (PBDEs) a fire- retardant chemical
Used in computers, plastics, and furniture
Mimics hormones
Also affects brain and nervous system development
May cause cancer

10. Disease – a major focus
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

11. Infectious disease Infectious diseases kill 15 million people/year
Half of all deaths in developing countries
Public health efforts are having an effect
But some diseases (AIDS) are still spreading
And others develop resistance to antibiotics

12. Disease, society, the environment
Lifestyles in developed nations increase the rate of non-infectious disease (diabetes, cardiovascular)
Our mobility spreads diseases
West Nile Virus spread from Africa to all of the 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

13. The best first step The best way to reduce disease?
Improve the basic living conditions of the poor
Food security, sanitation, clean drinking water

14. Other public health actions
Expanded access to health care
Health clinics, immunizations
Pre- and postnatal care
Education campaigns work in rich and poor nations
Public service and governments give advice
Packaging and ads advise us on smoking, etc.
Sex and reproductive health education slows population growth and spread of HIV/AIDS

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

16. 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 in their bodies

17. They are all around us
In 2002 study, 80% of U.S. streams contained trace amounts of 82 contaminants
In 2006 study, 42 volatile organic compounds (VOCs) in 92% of aquifers tested
Pesticides are present in streams and groundwater at levels high enough to be harmful to aquatic and human life

18. Perspective
Rachel Carson’s Silent Spring (1962) showed DDT’s risks to people, wildlife, and ecosystems
Prior to that, untested pesticides were sprayed over public areas with assumption they would do no harm
But here is a tradeoff between the risks and rewards of most hazards
Synthetic chemicals have helped to give us our high standard of living

19. Types of toxicants
Carcinogens = cause cancer – can be hard to identify (long time between exposure and onset)
Mutagens = cause DNA mutations
Teratogens = cause birth defects in embryos
Neurotoxins = assault the nervous system
Allergens = over-activate the immune system
Endocrine disruptors = affect the endocrine (hormone) system

20. Endocrine disruptors Hormones Endocrine disruptors
Normally present at very low concentrations
Stimulate growth, development, and sexual maturity
Endocrine disruptors
Block natural hormones from performing their function
Mimic hormones, misdirecting the body’s response
Bisphenol A (BPA) binds to estrogen receptors
Phthalates, used to soften plastics and enhance fragrances, are a widely used endocrine disruptor

21. Toxicants move in water
Runoff carries toxins from land to surface water
Chemicals in the soil can leach into groundwater, contaminating drinking water
Chemicals enter organisms through drinking or absorption
Aquatic organisms (fish, frogs, etc.) are good pollution indicators

22. Toxicants move in the air
As simple as pesticide drift where sprayed pesticides are carried downwind into adjacent fields
As complex as the long- distance transport of chemicals to polar regions where synthetic chemicals are found in the middle of wilderness areas

23. Environmental fate of toxicants
Persistence
Some degrade quickly and become harmless
Others remain unaltered and persist for decades
Rates of degradation depend on the substance, temperature, moisture, and sun exposure
Breakdown products
Simpler chemicals formed when toxicants degrade
May be more or less harmful than the original substance
DDT degrades into DDE, which is also highly persistent and toxic

24. Fate of toxicants in organisms
Toxicants in the body can be excreted, degraded, or stored
Bioaccumulation = toxicants build up in animal tissues
Biomagnification = concentrations of toxicants become magnified up the food chain

26. Studying toxic effects
Wildlife studies integrate field and lab work
Museum collections provide data from times before synthetic chemicals were used
Measurements from animals in the wild can be compared to controlled experiments in the lab

27. 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

28. Laboratory studies Manipulative experiments show causation
Animals are used as test subjects
Mammals share evolutionary history
Substances that harm rats and mice probably harm us
Some people object to animal tests
New techniques may replace some live- animal testing

29. Dose-response
Dose-response analysis = measures the strength of the effect a toxicant produces or the number of animals affected at different doses
Dose = the amount of substance the test animal receives
Response = the type or magnitude of negative effects

30. Dose-response curves
Dose-response curve = the dose plotted against the response
LD50/ED50= the amount of toxicant required to kill 50% of the subjects
Threshold dose = the level where observable responses begin to occur

31. Unusual dose-response curves
Sometimes a response decreases as a dose increases, creating an inverted J- or U-shape dose- response curve
Counterintuitive curves occur with endocrine disruptors because the hormone system is geared to respond to very low levels

32. Variation in response
Different people respond differently to toxicants
Sensitivity is affected by
Genetics
Surrounding environmental conditions
General health conditions
Sex, age, and weight
Exposure route (inhalation, ingestion, dermal contact)
Fetuses, infants, and young children are more sensitive

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

34. Nature is messy In the real world, toxicants do not exist in isolation
Difficult to 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

35. Evaluating hazards from toxicants
Given all the variables connecting a toxicant to an actual health effect, a probability-based approach must be used to quantify such hazards
Risk = the probability that some harmful outcome will result from a given action, event, or substance
Everything we do involves some risk
We try to minimize risk but perception is not reality
We feel more at risk when we do not control a situation

36. Risk Assessment The quantitative determination of risk
Risk assessment has several steps:
Scientific study of the toxicity effects of substances
Development of “exposure scenarios” for a population’s exposure to the substances in question (frequency, duration, concentrations, exposure routes)
Calculation of risks posed by combining toxicity and exposure information

37. Risk management Risk management = decisions/policies to minimize risk
Several Federal agencies manage environmental risk U.S. EPA, the Centers for Disease Control (CDC), 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

38. Risk management visualized

39. Philosophies of risk management
Innocent-until-proven-guilty: assumes a substance is harmless until it is shown to be harmful
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

40. Philosophy affects policy
Different nations use different policies
Europe use the precautionary principle
The U.S. uses innocent- until-proven-guilty
Who should have to prove a product is safe: the manufacturers or government/citizens?

41. Major U.S. laws - TSCA
The Toxic Substances Control Act (TSCA, 1976) charges EPA with monitoring chemicals made in or imported into the U.S.
Many health advocates think the TSCA is too weak
83,000 chemicals are “grandfathered”
Catch-22 – to get detailed meaningful testing, toxicity must already be proven
Only 10% of have been thoroughly tested for toxicity
Only 2% tested for carcinogenicity, mutagenicity, etc.
Almost none have been tested for endocrine, nervous, or immune system damage

42. Major U.S. laws - FIFRA
The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA, 1974) charges EPA with “registering” new pesticides
Manufacturers provide toxicity & safety information
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