Environmental Health
Focuses on factors that cause disease
Natural—biological agents
Cultural—social and cultural practices and attitudes
Technological—physical and chemical agents
Environmental Health
Infectious Disease
Toxicology
Disease
Abnormal change in structure/function
Morbidity—illness
Mortality—death
Morbidity and Mortality Weekly Report published by CDC
Acute/chronic illness
Causes of Illness
Morbidity—too vague
Disability-adjusted life years—DALYs
Includes premature deaths and loss of healthy life from illness, disability
Attempts to define total costs
Young vs. old; death vs. disability
Perception vs. reality
Hazard Categories
Cultural: unsafe work places, smoking, diet, drug use, assault, sex practices
Physical: ionizing radiation, fire, weather, earthquakes, volcanoes
Chemical: air, water, soil, food
Biological: pathogens, allergens, animals
Biological Hazards
Communicable & noncommunicable disease, contagious
Transmissable & nontransmissable
Nontransmissable—caused by something not living & doesn’t spread from person to person
Transmissable—caused by living organism,spread from person to person
Infectious Disease
Pathogens--disease causing agents (living organisms, viruses, prions)
Vectors—pathways through which a disease spreads
Animate: alive—insects, worms
Inanimate: air, water, food
Infectious Disease
Reservoir: where the pathogen is found all the time
Epidemiology—study of disease in populations
Infectious Disease
Acute—short incubation, sudden appearance of symptoms—colds, flu, smallpox, polio, Ebola, anthrax
Chronic—longer (?) incubation, no dramatic onset, long term—chronic fatigue, tb, malaria
Emerging Diseases
New to humans, not around for period of time or resistant to antibiotics, chemical treatment
No defenses, no immediate treatment
Depending on virulence and transmissibility—real problems
Emerging Disease
HIV—25 years ago
SARS (severe acute respiratory syndrome)
Avian flu—accurate reporting lacking, Chinese government, peasants, farmers live with animals
Ebola
Pathogens
Prions—infectious proteins
Cause proteins to change their spatial orientation
Proteins no longer functional—inactive enzymes
Neurodegenerative disease—Creutzfeldt-Jakob disease: human variant of mad cow disease
Prions
Spread vertically—from one trophic level to another
Prions found in nervous system
Passed in cows when infected NS tissue is ground into livestock feed
Cows are infected, takes time for BSE to develop, slaughtered, eaten
Prions
Not destroyed by heat or acid
Control by transmission
USDA—can’t use CNS tissues or downer cattle
???--Peripheral NS, what if infected but not manifested, infected imported cattle or meat
Periodic scares
Viruses
Genetic information and associated proteins
Attach to membrane-bound receptors, inject genetic material, commandeer cell functions
Produce new viruses, viruses released and cell destroyed
Viruses
Acute—measles, colds, flu, isolated or world-wide (flu pandemic in 1918), polio, smallpox
Chronic--Hepatitis B, C, …--different viruses, different modes of transfer, HIV
Bacteria
One-celled, microscopic, forms clones, (some genetic exchange)
Acute and chronic diseases
Tuberculosis, cholera, plague—bubonic and pneumonic
Bacteria
Treat with antibiotic
Problems—antibiotic resistance
Over-prescribed
Misused
Introduced into livestock feed—residues found in meats and milk, gradually phased out
Protozoans
One celled organisms (more complex cellular architecture)
Malaria—kills more people than AIDS
Amoebic dysentery
Worms
Multicellular
Tapeworms
Liver flukes
Intestinal parasite
Etc.
Why Still a Problem?
Poor nutrition
Poor infrastructure
Crowded living conditions
Contact with reservoir—Ebola
Food production and processing
Problem (cont’d)
Change in demographics
Travel
Increase in urban centers
Work place
Toxicology
Study of toxins (poisons) and their affects
Hazardous
Chemical
Physical—radiation
Hazard assessment
Hazard Assessment
What—not all things are hazardous
How much--dose
How often—frequency
Who—age, health, sex, detoxification systems, genetic makeup
Factors
Solubility
Persistence
Bioaccumulation
Biomagnification
Chemical interactions
Toxicity
Solubility
Water soluble—inorganic compounds (often) move through ecosystem, water supply, water everywhere, incl. body
Exposure route—drinking, bathing, eating
Fat (oil)-soluble—penetrate cell membranes, accumulate in tissues
Exposure route—food, dermal application
Toxicity
Persistence—resistance to chemical breakdown
Heat
Light
Stay active for long time—good and bad
Bioaccumulation
Molecules absorbed and stored in tissues or organs
Higher amounts than normal
Low level in environment can build up in living systems to harmful levels
Biomagnification
Levels of toxins are increased or magnified as they pass from one trophic level to next
Lower trophic levels—ingest small amounts
Next level up—eats more
At each higher level, more and more of toxin is ingested
Biomagnification
Long-lived, persistent chemicals
Fat-soluble
Bioaccumulate
Persistent organic pollutants (POPS)
Biomagnification
DDT—raptors (eagles, falcons) and pelicans
PCBs
PBDE—flame retardants
MDBE—gas additives
Stain-resistant chemicals—PFOS, PFOA or C8
Pthalates & plasticizers
Strontium-90—not a POP, radiation
Biomagnification
Once released, hard to remove
Stop release
Remove
Leave in place, encapsulate or allow sediments to cover deposits
Encapsulation/sedimentation prevents re-release
Chemical Interactions
Increase or decrease effect
Synergistic—multiplies effects
Antagonistic—reduce effects
Toxicology Assessment
Test effects on animals
Determine lethal dose
Median lethal dose—LD50
Amount received in one dose that kills 50% of test animals within 14 days
Toxicology Assessment
Does the dose make the poison?
Yes, but differently for different people
Repair mechanisms
Trace levels may or may not be toxic
depends
Determine Toxicity
Case reports
Epidemiological studies: experimental group and control group
Animal testing—controversial
Develop dose-response curve
Dose-Response Curve
Controlled experiment
Test group: exposed to chemical
Control group: identical to test group, but not exposed to chemical
Both groups: identical age, health, genetic makeup, same environmental conditions
Dose-Response
High dosages
Mathematical models extrapolate results
Estimate LD50 values: 50% mortality
2 models
Nonthreshold
threshold
LD50
Vary
Single dose at low value
Impossible to get lethal dose into body
5 most toxic:
Arsenic
Lead
Mercury
Vinyl chloride
Polychlorinated biphenyls
Nonthreshold Dose Response
Any dose causes harm
Damage increases with dosage
Linear response
Nonlinear response
Threshold Response
Threshold dosage must reached before harm occurs
Difficult to assess at low doses
Coping Mechanisms
Metabolic degradation
Metabolic excretion
Genetic repair mechanisms
Exposure to environmental chemicals & high cell turnover
Controversies
Validity of extrapolating data
Usually exposed to more than one chemical
Age of exposure important
Nonthreshold is usually used to be on safe side
EPA—assume that children’s risk of getting cancer is 10x the exposure rate of adults
Asserted that it should be 100x
Danger is everywhere?
New analytical methods now detect where nothing had been before