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