CH 8 - Environmental Health & Toxicology

In some parts of Eastern Europe and the former USSR, upto 90% of all children suffer from environmentally linked diseases.

What is Health?

• The World Health Organization defines health: state of complete physical, mental, & social well-being –

not just absence of disease.

• Disease - a deleterious change in the body’s condition in response to an environmental factor (nutrition, chemicals, biological agents, etc)

• Morbidity – illness or disease

• Mortality – death rate

Eg: Tuberculosis

Deforestation causes insect vectors to move to cities

Morbidity and Quality of Life

• Death rates do not tell everything about burden of disease.

• What is the total social burden of diseases?– Total economic and social consequences of

diseases are difficult to obtain.• Disability-Adjusted Life Year (DALY) combines

premature deaths and loss of healthy life resulting from illness or disability.

Disruption to quality of life & economic productivity caused by premature deaths & loss of healthy life caused by illness/disability.

• Problems occurring when people live in crowded conditions--eg, developing countries (90% DALY losses), poverty)

• New global mega-cities where managing human generated wastes is poor

Morbidity and Quality of Life in Poor Households

(Disability-Adjusted Life

Years)

At any given time, about 2 billion people suffer fromworms, protozoans, and other internal parasites.

Elephantiasis – caused by parasitic worm

Emergent Diseases

• An emergent disease is one never known before, OR has been absent for at least 20 years.– An important factor in the spread of many

diseases is speed and frequency of modern travel.• Foot and Mouth Disease• Ebola

Recent outbreaks of lethal infectious diseases

At least 30 new infectious diseases have appeared in the past two decades while many well-known have reappeared in more virulent, drug-resistant forms.

Factors Contributing to the Spread of Contagious Diseases

• High population densities• Settlers pushing into remote areas• Human-caused environmental change

(elimination of predators increasing rodents, use of fertilizers, pesticides etc)

• Speed and frequency of modern travel• Contact with water or food contaminated

with human waste

Emerging Ecological Diseases

• Domestic animals and wildlife also experience sudden and widespread epidemics.– Distemper (Seals)

– Chronic Wasting Disease (Deer and Elk)• Transmissible Spongiform Encephalopathies

– Black Band Disease (Coral)

Antibiotic and Pesticide Resistance

• Indiscriminate use of antibiotics and pesticides - perfect recipe for natural selection– Protozoan that causes malaria now resistant

to most antibiotics, and mosquitoes have developed resistance to many insecticides

– Drug resistance: TB, Staph A, flesh-eating bacteria

Toxic Chemicals• Hazardous chemicals – dangerous (eg, flammables,

explosives, irritants, acids, etc)• Toxins – poisonous, kills cells• Allergens – activate the immune system• Mutagens – chemicals or radiation that damage/alter

genetic material (DNA)• Teratogens - chemicals or other factors that cause

abnormalities during embryonic growth & development

• Carcinogens – substances that cause cancer (out of control cell growth)

Toxins: Movement, Distribution, Fate

Movement, fate of chemicals in the environment (processes that modify, remove or sequester compounds)

(Brennan & Withgott 2005)

Many routes of synthetic chemicals traveling through the environment

Toxins: Movement, Distribution, Fate

Routes by which chemicals enter body determine toxicity

Movement via

Solubility

- water

- oil

Bioaccumulation and Biomagnification

• Bioaccumulation – selective absorption & storage of molecules; dilute toxins in the environment can reach dangerous levels inside cells and tissue

• Biomagnification - the effects of toxins are magnified through food webs

“DDT - Powerful Insecticide, Harmless to Humans” common statement in the 1950s

???????

Pesticides and Child Development in Mexico’s Yaqui Valley• Elizabeth Guillette (anthropologist) – 1994

• Valley farmers used pesticides but foothill farmers continued traditional farming

•Valley children were far behind foothill children developmentally in:

CoordinationPhysical enduranceLong-term memoryFine-motor skills (Brennan & Withgott 2005)

Peregrine falcons disappeared from the eastern US in 1960s due to excess pesticide use

Minimizing Toxic Effects• Every material can be poisonous under some

conditions• Taken in small doses, most toxins can be

broken down or excreted before they do much harm – belief in 1800s, arsenic (Napoleon)

• Liver - primary site of detoxification• Tissues and organs - high cellular

reproduction rates replace injured cells - down side: tumors, cancers possible

Measuring Toxicity

• Most commonly used and widely accepted

• Expensive - hundreds of thousands of dollars to test one toxin at low doses

• Time consuming

• Often very inhumane

• Difficult to compare toxicity of unlike chemicals or different species of organisms

Animal Testing

A Typical Dose/Response Curve

LD50 - the doseof a toxin that is lethal to half the test population

It is useful to group materials according to their relative toxicity.

mouse

rat

Acute Lethal Doses for Some Toxic Organic Chemicals

Acute Versus Chronic Doses and Effects

• Acute effect - immediate health effect caused by a single exposure to a toxin (can be reversible)

• Chronic effect - long lasting (or permanent) health effect caused by:– a single exposure to a very toxic substance,

OR – continuous or repeated sublethal exposure to

a toxin

Risk Assessment and Acceptance

• Risk probability of harm X probability of exposure

• A number of factors influence how we perceive relative risks associated with different situations (interests as industrialist vs environmentalist, understanding probability, personal experience, our abilities to control our fate, news media biases, fear of technology).

• Accepting risks - we go to great lengths to avoid some dangers, while gladly accepting others

McKinney & Schoch

Establishing Public Policy

• Combined effects of exposure to many different sources of damage (synergistic effects of different toxins, eg smoking & asbestos effects on lung cancer rates)

• Different sensitivities of members of the population

• Effects of chronic as well as acute exposures

In setting standards for environmental toxins, we need to consider:

Regulatory Decisions – EPA framework

The Science Specific to the Problem

Other Factors Not Specific to the Problem

Summary:• Environmental Health Hazards

– Infectious Organisms– Emergent Diseases– Antibiotics and Pesticide Resistance– Toxic Chemicals

• Distribution and Fate of Toxins

• Minimizing Toxic Effects

• Measuring Toxicity

• Risk Assessment

• Public Policy