Environmental Health



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

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