1. Human Health and the Environment
“The diseases of the present have little in common with the diseases of the past save that we die of them. ” - Agnes Repplier

2. Environmental Health
Environmental health studies aspects of the environment that can affect human health.
Includes both natural and human-caused factors.
Prior to the industrial revolution, human health was most affected by biological hazards – interactions with bacteria, viruses, insects, or parasites.

3. Miasma Theory of Disease
Prior to the 19th century, many scholars followed the miasma theory of disease, which explained that diseases were caused by a poisonous vapor or mist filled with particles from decomposed matter.
During the Black Plague, doctors wore masks containing dried flowers, herbs, spices, and a vinegar sponge to filter out bad smells.
A Plague Doctor. Source unknown.

4. Disease treatments, such as bloodletting, reflected this lack of understanding.
Many of the documented “benefits” of bloodletting were most likely due to the placebo effect.
Bloodletting in 1859, one of only three known photographs (tintype) of the procedure.

5. Germ Theory of Disease
In 1849, Dr. John Snow was studying an outbreak of cholera in London.
He developed a map of cholera cases, isolating the source to contaminated water from a public water pump.
Snow concluded that this disease was being spread by ingestion of fecal matter, not poisonous vapors.

6. In 1861, Louis Pasteur was attempting to discover what caused certain foods to ferment when left out.
Control group: A nutrient broth was boiled and left in an open-air flask.
Experimental group: A nutrient broth was boiled and left in a special flask that allowed air in, but prevented dirt and dust from entering.
Pasteur concluded that microorganisms – living things that can’t be seen with the naked eye called bacteria caused food to ferment.

7. The Medical Revolution
The discovery of microorganisms changed human understanding of disease, medicine, and sanitation.
The Germ Theory of Disease states that some diseases are caused by the growth and reproduction of bacteria, viruses, fungi, and parasites within the body.
Monster Soup commonly called Thames Water by William Heath, 1828.

8. Improved sanitation practices included:
Better separation of drinking water supplies from sewage outlets.
Tiled bathrooms instead of wood or carpet.
Porcelain toilets that flush with clean water.
Covering and refrigerating foods.
Screens on windows to keep insects out.
In the 1870s, Joseph Lister developed the first sterilization – the process of making surgical instruments free from microorganisms.
A spray of carbolic acid was applied to the patient and tools.

9. In 1928, Alexander Fleming accidentally discovered pencillin when a mold spore was introduced into a bacterial culture.
The mold was producing an antibiotic – a chemical that inhibits the growth of or destroys microorganisms.
The antibiotic was a way for the mold to reduce interspecific competition between it and the bacteria.

10. These discoveries led to a sharp decrease in the mortality rate of infectious diseases, illnesses that can be spread from person-to- person.
This increased human life expectancy and was a major contributor to the exponential growth of the population during the 20th century.

11. Causes of Infectious Disease
Bacteria are unicellular, prokaryotic microorganisms.
Prokaryotic means that the cells are very small and do not have any specialized organelles or a nucleus.
Unicellular means that each bacterium is an independent cell living on its own.

12. Protists are unicellular, eukaryotic organisms that may have characteristics similar to plants or animals.
Eukaryotic cells are larger, enclose their DNA in a nucleus, and have organelles.

13. Multicellular organisms are made of many cells working together.

14. Fungi are eukaryotic and can be either unicellular or multicellular.
Most are decomposers but some can invade living tissue.
Athlete’s foot, ringworm, yeast infection
Multicellular parasites cause disease by extracting resources from a host.
Tapeworm, trichinella (roundworms), liver flukes

15. Disease can also be caused by non-living particles.
Viruses are made of a core of genetic material surrounded by a protein coating.
Influenza, common cold, AIDS.
Prions are proteins that can induce normal, healthy proteins to misfold into an infectious shape.
The proteins accumulate, causing tissue damage and cell death.

16. Mad Cow disease is a disease of the brain caused by the spread of prions.
The disease first emerged in an outbreak in the United Kingdom in 1986, and was traced to the practice of feeding the remains of slaughtered cattle to other cattle.
The use of brain, spinal cord, intestines, eyes, and tonsils from cattle is now banned in most developed countries.

17. Disease Transmission
Airborne diseases are transmitted through the air due to coughing, sneezing, toilet flushing, etc.
Common cold, influenza.
Waterborne diseases are spread through the ingestion of water infected by bacteria or parasites.
Dysentery, cholera

18. Foodborne diseases are spread through the ingestion of contaminated food.
Food poisoning, botulism
Vectorborne diseases are spread through the bite of arthropods, such as ticks, lice, flies, and mosquitoes.
Malaria is a protist that is spread through the saliva of the Anopheles mosquito.
Anopheles mosquito
Replicated Plasmodium bursting from two red blood cells.

19. Deadliest Diseases
Mortality rate is a measurement of the percentage of people who die of a disease when they contract it.

20. Global death rate measures the total number of people that die each year from specific diseases.

21. Emergent Diseases
Many of the deadliest diseases are emergent diseases that were previously unknown or have a rapidly increasing range.
Most emergent diseases are viruses, because they…
Can mutate to a new strain that people don’t have immunity for.
Can mutate and cross the species barrier.
Are not easily treatable (antibiotics are ineffective).
Are smaller than cells and can quickly be spread through the air and water.

22. Modern of emergent diseases:
AIDS – A mutated virus that originated in chimpanzees.
West Nile Virus – Virus of unknown origin; most likely originated in birds.
H5N1 avian influenza – Mutated virus that originated in birds.
Marburg virus – Unknown origin; most likely from an African primate.
H1N1 swine flu – Mutated virus from a swine farm.
Spanish flu – Mutated virus from either a swine or bird species.
Cryptosporidosis – Protist that can infect the digestive tract of multiple species through contaminated water.

23. Preventing and Treating Disease
The strategy used to deal with infectious disease depends on the agent causing it, and how it is spread.
A good example is the efforts used by the United States up through 1951 to eradicate Malaria.

24. The protozoan parasite that causes malaria can only thrive where it can access both its mosquito and human hosts.
The Anopheles mosquitos that are malaria vectors thrive in humid, tropical climates with many areas of standing water.

25. Three strategies were applied:
Applying massive amounts of pesticides to kill mosquitoes.
Treating infected individuals with antimalarial drugs to kill the protozoan parasite.
Draining wetland areas where mosquitos breed.

26. This is a 1943 film produced by Disney, promoting these strategies.
How do these strategies reflect the era before modern environmentalism?

27. Resistance
Many medications and pesticides become less effective over time due to resistance – the ability of an organism to withstand exposure to a toxin.
Resistance is more likely to occur when:
The target organism is genetically simple.
The target organism reproduces rapidly.
The toxin is used too frequently.
Spraying DDT at Jones Beach, Long Island, NY

28. Due to their small size and ability to reproduce so quickly, bacteria can evolve resistance more quickly than insects and protozoa.
Bacterial growth on a petri dish. The colony shows resistance to antibiotic 4. Disk 2 is a control.

29. Chemical Hazards
A chemical that can cause temporary or permanent harm or death to a living organism is considered toxic.
Toxins are classified based on the effects they cause to the body.
Mutagens damage DNA within cells, increasing the frequency of mutations.
Ultraviolet light, X-rays, radioactive material.

30. Teratogens are chemicals that cause birth defects in an unborn fetus.
Most mutations have little or no effect, but can lead to severe problems:
Carcinogens are chemicals, forms of radiation, or viruses that cause cancer.
Radioactive material
Cigarette smoke
Alcohol
Processed meat
Teratogens are chemicals that cause birth defects in an unborn fetus.

31. Neurotoxins disrupt the function of the brain, spinal cord, and other nerves.
Heavy metals, such as lead and mercury.

32. Pathway inhibitors block one or more steps in a biological pathway.
Allergens overactivate the immune system, causing an immune response when one is not necessary.
Dust mites, pollen
Pathway inhibitors block one or more steps in a biological pathway.
Cyanide (blocks cell respiration in mitochondria).
Microscopic image of dust: skin cells, clothing fibers, pine pollen, and a dust mite.

33. Endocrine hormone disruptors interfere with the function of chemical messengers in the body called hormones.
Hormone mimics have similar shapes to natural hormones and amply their effects.
Hormone blockers prevent natural hormones from attaching to their target organ.

34. Significant Environmental Toxins
Tobacco smoke is a mixture of multiple toxic substances:
Carcinogens: Polycyclic aromatic hydrocarbons (PAHs), formaldehyde
Neurotoxins: Carbon monoxide
Pathway inhibitors: Hydrogen cyanide
Radon is a radioactive gas that is naturally present in some underground areas and can accumulate in basements, crawl spaces, and ground water.
Radon is a carcinogen that is linked to lung cancer.

35. Atrazine is a pesticide that acts as an estrogen mimic in frogs.
It has been shown to feminize male frogs enough that they can produce viable eggs.
BPA is a plastic additive that has also been shown to be an estrogen mimic, leading to many companies removing it from their products.

36. Asbestos is a substance that was used in the past as insulation in building construction.
Carcinogen: Linked to lung cancer.
Physically scars the lining of the lungs.
Lead is a heavy metal that was in leaded gasoline up through the 1970s, paint, and some water pipes.
Neurotoxin: Linked to lower IQ levels, especially in children.

37. Polybrominated diphenyl ethers (PBDEs) are used as fire retardants in electronics, plastics, furniture, and certain types of baby clothing.
Mutagen: Damage DNA
Neurotoxin: Linked to increased hyperactivity and lowered IQ.
Endocrine disruptor: Interfere with thyroid hormones.
Snug-fitting pajamas do not legally have to contain PBDEs.

38. Evaluating Toxins
We are exposed to carcinogens, hormone disruptors, allergens, and neurotoxins nearly every day, yet rarely experience symptoms.
Toxicity is the measure of how harmful a substance is to the health of living organisms.
Dose is the amount of the toxin an individual is exposed to.
Any synthetic or natural chemical has the potential to cause harm if the level of exposure is high enough.
“The dose makes the poison.”
Paracelsus, German scientist,

39. Factors Influencing Toxicity
The solubility of a substance is whether it can dissolve in oil or water.
Water-soluble toxins tend to be passed through the body via the kidneys fairly easily.
Oil-soluble toxins, once ingested, pass directly into cells and tissues, allowing them to accumulate.

40. Vitamin supplements reflect this, as doses of fat soluble vitamins (A, D, E, and K) are measured in International Units (IU), which are much smaller than milligrams (mg).
400IU of Vitamin D = mg.

41. The toxicity of a chemical also depends on what kind of exposure a person has:
Acute exposures are high doses that occur for short periods of time.
Chronic exposures are low doses that occur for long periods of time.

42. Persistent chemicals are more likely to:
Chemicals with a high level of persistence do not degrade easily in the environment or in living organisms.
Persistent chemicals are more likely to:
Bioaccumulate: Build up into higher and higher levels in the body over time.
Biomagnify: Become more concentrated at higher levels of a food chain.

43. Two chemicals, although now banned, are still widely present in the environment due to their persistence and biomagnification:
Polychlorinated Biphenyls (PCBs) are chemicals that were used for electronics, paints, oils, and other industrial applications.
DDT is a synthetic pesticide that was used to treat areas for mosquitoes.

44. Dose-Response Analysis
To determine the toxicity of a substance, scientists will perform a dose-response analysis to determine the level of exposure needed to elicit specific symptoms in a test animal.

45. The threshold dose is the minimum dose required to achieve a response.
If the response is death, the point at which half of the tested animals are killed is called the LD50.

46. Lower LD50 values are indicative of substances that are more highly toxic.
LD50 (mg/kg)
Table sugar
29,700
Monosodium Glutamate (MSG)
16,600
Vitamin C
11,900
Alcohol (Ethanol)
7,060
Table salt
3,000
Aspirin
200
Caffeine
192
Nicotine 50
Capsaicin
47.2
Poison Dart Frog Toxin
0.002
Polonium-210 (Nuclear Waste)

47. Risk Assessment
Risk Assessment is estimating the likeliness or severity of a specific hazard to human health.
Hazards could include injury or death as a result of diet, infectious disease, or toxic chemicals.
Individual risk assessment tends to be biased, due to:
Rare events are sensationalized by the media and politicians.
Misunderstanding of statistics.
Having a personal experience with a specific hazard or toxin.
Fear of the unknown.

48. Assessing risk involves three steps:
Identifying whether a substance has any toxic effects at all.
Performing a dose-response analysis.
Assessing an individual or population’s level of exposure.

49. Example Risk Assessment
A soft drink contains brominated vegetable oil (BVO) at a level of about 8mg per liter.
The following threshold doses have been identified:
6.4mg/kgBW/day risks cardiac degeneration
25.7mg/kgBW/day risks digestive illness
The LD50 is 3000mg/kgBW/day.
How much would you have to consume to risk acute toxicity? Is death a likely outcome from consuming these soft drinks?

50. Public policy decisions should be made based on risk assessment and promoting the best health possible in the population.

51. What policies would help alleviate these hazards the most?
Source: Miller Environmental Science

52. These are examples of proposed changes in response to identified human health hazards.