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Chapter 8: Environmental Health and Toxicology

Hong Kong residents concerned about SARSCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Chapter Eight Topics

• Environmental Health• Toxicology• Movement, Distribution, and Fate of Toxins• Mechanisms for Minimizing Toxic Effects• Measuring Toxicity• Risk Assessment and Acceptance• Establishing Public Policy

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Part 1: Environmental Health

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

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

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West Nile Virus 2001

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What is Health?• The World Health Organization

(WHO) defines health as a state of complete physical, mental, and social well-being.

• Disease - a deleterious change in the body's condition in response to an environmental factor

• Morbidity - illness• Mortality - death

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West Nile Virus 2002

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Factors Contributing to the Spread of Contagious Diseases

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

habitat for organisms)• Speed and frequency of modern travel• Contact with water or food contaminated with

human waste• Climate change• Increased consumption of wild species

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Part 2: Toxicology

Toxicology: The study of toxins (poisons) and their effects on living systems.

What does toxic mean?

Environmental Wisdom…visit

http://www.dhmo.org

What does Toxic mean

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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

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Fig. 8.6

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Hazardous and Toxic Chemicals• Allergens -

formaldehyde

• Immune system depressants

• Neurotoxins - lead, DDT

• Mutagens

• Teratogens - alcohol

• Carcinogens

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Part 3: Movement, Distribution, and Fate of Toxins

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Clorox

• Kills Flu Virus• Vapors may irritate, harmful if swallowed, do not get in the eye or

clothes, avoid prolonged breathing of vapors, use in highly ventilated areas, not recommended for use by people that have heart problems, or breathing problems.

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Factors to consider

• Solubility and mobility (organic Vs inorganic)

• Exposure and susceptibility

• Bioaccumulation and biomagnification

• Persistence

• Chemical interactions (antagonistic Vs synergistic)

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Bioaccumulation and Biomagnification

• Bioaccumulation - dilute toxins in the environment can reach dangerous levels inside cells and tissue

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

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"DDT - Powerful Insecticide, Harmless to Humans"

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Part 4: 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.

• Liver - primary site of detoxification

• Tissues and organs - high cellular reproduction rates replace injured cells - down side: tumors, cancers possible

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Part 5: 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

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A Typical Dose/Response Curve

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

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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 (1) a single exposure to a very toxic substance or (2) continuous or repeated sub lethal exposure to a toxin

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Fig. 8.15

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Part 6: Risk Assessment and Acceptance

• Risk - the probability of harm times the probability of exposure

• A number of factors influence how we perceive relative risks associated with different situations.

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

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Part 7: Establishing Public Policy

• Combined effects of exposure to many different sources of damage

• 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:

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Regulatory Decisions