public health and public policy chapter 8: environmental health and toxicology
TRANSCRIPT
Unit 5
Public Health and Public Policy
Chapter 8: Environmental Health and Toxicology
Human Health Risk Factors
Include physical risks Exposure to UV
radiation
Include chemical risks Exposure to pesticides
Include biological risks Pathogens and
diseases
Include cultural risks Smoking, poor diet
Infectious Diseases
Are caused by pathogens
Can be chronic Act slowly over a long
period of time Heart disease
Can be acute Act quickly over a
short period of time Ebola
Historical Infectious Diseases
Plague Caused by bacterium Yersinia
pestis Transmitted by fleas
Malaria Caused by parasitic protist
Plasmodium Transmitted by mosquitoes
Tuberculosis (consumption) Caused by bacterium
Mycobacterium tuberculosis Transmitted by human breath
Can be treated with antibiotics or other drugs Can become resistant to drugs
Emergent Infectious Diseases
Are diseases that are new to medicine
Effective treatments do not exist
Are frequently zoonoses Diseases that reside in
animal populations and can infect humans
HIV/AIDS
Human Immunodeficiency Virus (HIV) Crossed species from apes to
humans Transmissible in body fluids Attacks the immune system Antiviral drugs can reduce viral load
Human AutoImmune Deficiency Syndrome (AIDS) Significantly weakened immune
system Death results from infection by other
pathogens
Ebola and other Hemorrhagic Fevers
Also crossed species from apes to humans Unlike AIDS it kills its
primate hosts Natural host is unknown
Cause massive bleeding and organ failure Death rate is 60-90%
Bovine Spongiform Encephalopathy (Mad Cow Disease)
Called Creutzfeldt-Jakob Disease in humans
Caused by mutated proteins called prions Not destroyed by cooking
Damages the brain and nervous system Destroys motor coordination
Can be transmitted from infected meat Spread in cow population from
adding ground-up remains from meat processing
Bird/Swine Flu (H1N1 and H5N1 Viruses)
Crossed species from birds to humans
Similar to virus that caused 1918 worldwide pandemic
Could mutate and become far easier to transmit Could cause another
pandemic
West Nile Virus
Is transmitted by mosquitoes Aggressive mosquito
control has limited the virus in the US
Causes brain inflammation
Vaccination
Provides “herd immunity” Provides protection for
those who don’t have immunity by preventing the spread of infectious disease
Due to lack of immunization, measles, whooping cough and other illnesses are on the rise
Eradicated Diseases
Smallpox Killed more people than any other
disease in history Caused by the Variola virus Spreads through contact with
bodily fluids or items an infected person has touched
The most intense infection causes fever and scarring blisters in the mouth, throat, skin, and corneas
Last case was in 1978 Extensive vaccination prevented
transmission of the virus Last public vaccinations were in
1982
Eradicated Diseases
Polio Caused by the Poliovirus Can cause destruction of
nerves and paralysis of muscle groups
Transmitted by contamination with feces that contains Poliovirus
Has been eradicated in all developed countries
When it is eradicated in Nigeria, Pakistan, and Afghanistan, it will be the second human disease to be completely controlled
Toxicology
Is the study of harmful chemicals (toxicants)
Includes Neurotoxins Mutagens and
carcinogens Teratogens Allergens Endocrine disruptors
Neurotoxins
Harm the nervous system
Include lead, mercury, insecticides, and chemical weapons
Mercury (Hg)
Is added to the atmosphere by mining and burning fossil fuels
Can also come from industrial processes and medical waste
Gets into water through leaching or precipitation
Converts to methylmercury Can bioaccumulate in fish Can cause nervous system
damage in humans (Minamata disease)
Mutagens and Carcinogens
Are chemicals that mutate DNA
Can cause cancer Include asbestos, radon,
benzene, formaldehyde, and polycyclic aromatic compounds (PAHs) from smoke
Can also include radiation
Teratogens
Are chemicals that interfere with normal embryonic development
Include thalidomide, alcohol, and tetrahydrocannabinol (THC)
Allergens
Can cause an extreme reaction from the immune system that can lead to death
Include dust, pollen, nuts, milk, eggs, wheat, soy, penicillin, and codeine
Endocrine Disruptors
Are chemicals that interfere with normal hormonal function Prevent normal hormonal
bonding to cell surfaces and disrupt cell signaling
Can interfere with gender and developmental hormone pathways
Found in plastics and health and beauty products
Epidemiology
Is the study of the causes and duration of disease in animals, especially humans
Looks for levels at which toxicants cause disease
Establishes safe levels of exposure in the environment and in tissues
Dose-Response Studies
Expose organisms to toxicants and observe any changes
Can be measured in concentration of chemical exposed
Can also be measured in the dose an organism ingests
Include the LD50 and ED50
Dose-Response Studies
LD50 Are studies that measure the
lethal dose that kills 50% of the test subjects
ED50 Are studies that measure the
effective dose that causes nonlethal but harmful effects in 50% of test subjects
Results from these studies can be used to set safe levels and exposures Invertebrates, fish, birds,
mammals
Union Carbide Pesticide Factory Leak Occurred in Bhopal, India in
1984 Released methyl isocyanate
gas Worst industrial accident ever 2,000 people died in first 24
hours 15,000 more died in the
weeks to follow As many as 500,000 injured
Acute and Chronic Studies
Acute studies examine the effects of toxicants over short periods of time LD50, ED50 Occur over hours to days
Chronic studies examine the effects of toxicants over long periods of time Often follow test subjects for
years
Retrospective and Prospective Studies Retrospective studies monitor
organisms that have been exposed to a toxicant
Prospective studies monitor organisms that may be exposed to a toxicant
Must compare group that is exposed to a non-exposed group
Need to take into account socioeconomic factors, and exposure to multiple toxicants
Synergistic effects can occur from exposure to multiple toxicants
Routes of Exposure for Toxicants
Are the same as those for infectious diseases
Can have multiple toxicants from multiple sources Can be difficult to distinguish which
toxicant is causing which symptoms
Are affected by a toxicant’s solubility Soluble toxicants have a greater
likelihood of becoming part of a food chain
Bioaccumulation and biomagnification
Persistence
Is how long a toxicant remains in the environment
Depends on temperature, humidity, pH, solubility, radiation, and whether it can be broken down by bacteria
May be different for the same toxicant in water or in soil
Can be measured in half-lives Pesticide DDT has a half-life in
soil of 30 years
Risk Assessment
Identifies hazards and determines their potential harm Can be qualitative
Based on perceptions or personal values
Can be quantitative Based on data Risk = proability of being exposed to a hazard X probability
of being harmed if exposed
Perceived risk can be different than actual risk
Risk Acceptance
Is the level of risk that can be tolerated
Some individuals can tolerate more risk than others
EPA risk acceptance is usually set at 1 in 1 million
Case Study: PCBs PCBs in the Hudson River System
were high enough to ban fishing Fish were thought to be the main
vector for humans to acquire PCBs Swimming and drinking water were
discouraged but not banned EPA recommended dredging river
bottom to remove PCBs
Rick Management
Strikes a balance between possible harm and other interests
Case Study: Arsenic EPA allowed levels of 50 μg/L
in water for many years even though the safe level was 10 μg/l
It was too expensive for some municipalities to remove that much arsenic
Finally reduced levels to 10 μg/L when new research showed that 5 μg/L was the true safe limit
Principles of Risk
Innocent-until-proven-guilty principle Substances must be shown to be
harmful before they are treated as toxicants
Precautionary principle All potentially harmful substances are
assumed to be toxicants
Case Study: Asbestos Use would have been regulated far
sooner and more lives would have been saved under the precautionary principle
International Standards
Stockholm Convention Established a list of 12
Persistent Organic Pollutants (POPs) to be banned outright or their use reduced
127 nations signed an agreement to ban these chemicals, phase out their use, or severely restrict their use
Additional meetings have added new chemicals to the list each year since 2001
Name Use
Aldrin Pesticide
Chlordane Pesticide
Dichlorodiphenyl trichloroethane (DDT)
Pesticide
Dieldrin Pesticide
Endrin
Heptachlor Pesticide
Hexachlorobenzene Pesticide
Mirex Pesticide
Toxaphene Pesticide
Polychlorinated biphenyls (PCBs)
Industrial emissions
Polychlorinated dibenzofurans
Industrial emissions
Dioxins Industrial emissions
International Standards
REACH Registration, Evaluation,
Authorization and restriction of CHemicals
Puts the precautionary principle into action
Requires risk analysis of all chemicals before they are used industry or consumer products
Is the how the European Union regulates toxicants
Public Health in Developing Nations
Is often compromised because of Inadequate funding Lack of services environmental
regulation Higher pollution rates Corporations taking
advantage of less punitive laws
Superstition and distrust of medical staff