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Environmental Health and Toxicology

Chapter 22

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Outline:• 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

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ENVIRONMENTAL HEALTH HAZARDS

• Health - 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.– Diet and nutrition, infectious agents, toxic

chemicals, physical factors, and psychological stress all play roles in morbidity (illness) and mortality (death).

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Infectious Organisms• For most of human history, the greatest

health threats have been pathogenic organisms.– Infectious diseases are still responsible for about

33% of all disease-related deaths.• Majority of deaths in poorer countries with poor

nutrition, sanitation, and vaccination programs.

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Morbidity and Quality of Life

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

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Disability-Adjusted Life Year

• WHO reports communicable diseases are responsible for nearly half of all 1.2 billion DALY’s lost each year.– About 90% of all DALY losses occur in

developing world where one-tenth of all health care dollars are spent.

• Malnutrition exacerbates many diseases.

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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

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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)

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In the News….

• http://www.npr.org/templates/story/story.php?storyId=4586823&sourceCode=RSS

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Infectious Disease Outbreaks

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Antibiotic and Pesticide Resistance

• Protozoan parasite that causes malaria is now resistant to most antibiotics, while the mosquitoes that transmit it have developed resistance to many insecticides.– Short life spans.

• Speeds up natural selection and evolution.

– Human tendency to overuse pesticides and antibiotics.

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Antibiotic and Pesticide Resistance

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Antibiotic Use

• At least half of the 100 million antibiotic doses prescribed in the US every year are unnecessary or are the wrong drug.

• Many people do not finish full-course.

• More than half of all antibiotics manufactured in the US are routinely fed to farm animals to stimulate weight gain.

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Vivian Vermillion

• Vivian picked up a strain of antibiotic resistant E. coli at the Vet Hospital

• This strain is resistant to six antibiotics!!!

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Antibacterial Mustard Introduced by French’s

• ROCHESTER, NY—In response to increasing American demand for tangier, more hygienic meals, condiment giant French's has introduced a new antibacterial mustard.

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Toxic Chemicals

• Dangerous chemicals are divided into two broad categories:– Hazardous - Dangerous

• Flammable, explosive, irritant, sensitizer, acid, caustic.

– Toxic - Poisonous• Can be general or very specific. Often harmful

even in dilute concentrations.

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Toxic Chemicals

• Allergens - Substances that activate the immune system.– Antigens - Allergens that are recognized as

foreign by white blood cells and stimulate the production of specific antibodies.

• Other allergens act indirectly by binding to other materials so they become antigenic.

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Toxic Chemicals

• Sick Building Syndrome– Headaches, allergies, and chronic fatigue

caused by poorly ventilated indoor air contaminated by molds, carbon monoxide, nitrogen oxides, and other toxic chemicals.

• Worker absenteeism and reduced productivity.– EPA estimates $60 billion annual loss.

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Toxic Chemicals• Neurotoxins - Special class of metabolic

poisons that specifically attack nerve cells.– Different types act in different ways.

• Heavy Metals kill nerve cells.• Anesthetics and Chlorinated Hydrocarbons disrupt

nerve cell membranes.• Organophosphates and Carbamates inhibit signal

transmission between nerve cells.

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Toxic Chemicals• Mutagens - Agents that damage or alter

genetic material.– Radiation

• Teratogens - Specifically cause abnormalities during embryonic growth and development.– Alcohol - Fetal Alcohol Syndrome

• Carcinogens - Substances that cause cancer.– Cigarette smoke

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US Age-Adjusted Cancer Death Rates

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Endocrine Hormone Disrupters

• Chemicals that disrupt normal endocrine hormone functions.– Hormones are chemicals released in blood by

glands to regulate development and function of tissues and organs elsewhere in the body.

• Environmental Estrogens and Androgens

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Diet

• Strong correlation between cardiovascular disease and the amount of salt and animal fat in an individual’s diet.– Highly-processed foods, fat, and smoke-

cured, high nitrate meats appear to be associated with cancer.

– Nearly 2/3 of all Americans are considered overweight.

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DISTRIBUTION AND FATE OF TOXINS

• Solubility - Chemicals are divided into two major groups:

• Dissolve more readily in water.• Dissolve more readily in oil.

– Water-soluble compounds move rapidly through the environment, and have ready access to most human cells.

– Oil-soluble molecules generally need a carrier to move through the environment.

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Bioaccumulation and Biomagnification

• Cells have special mechanisms for Bioaccumulation - Selective absorption and storage.– Dilute toxins in the environment can build to

dangerous levels inside cells and tissues.

• Biomagnification - Toxic burden of a large number of organisms at a lower trophic level is accumulated and concentrated by a predator at a higher trophic level.

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Sensitivity and Developmental Stage

• Many factors help determine reaction of an individual to a given dose.– Age– Sex– Body Weight– Nutritional / Immunological Status– Repair Mechanisms

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Persistence

• Some chemical compounds are very unstable and degrade rapidly under most conditions, thus their concentrations decline quickly after release.

• Others are more persistent. – Stability can cause problems as toxic effects

may be stored for long period of time and spread to unintended victims.

• (DDT)

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Bioaccumulation

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Chemical Interactions

• Antagonistic Reaction - One material interferes with the effects, or stimulates the breakdown, of other chemicals.

• Aluminum and phosphate ions form solid• Additive Reaction - Effects of each chemical

are added to one another.• Xenoestrogens + estrogens• Synergistic Reaction - One substance

multiplies the effect of the other.• Nitrate ion and phosphate ion

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MECHANISMS FOR MINIMIZING

TOXIC EFFECTS• Every material can be poisonous under

certain conditions.– Most chemicals have a safe threshold under

which their effects are insignificant.

• Metabolic Degradation– In mammals, the liver is the primary site of

detoxification of both natural and introduced poisons.

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Excretion

• Effects of waste products and environmental toxins reduced by eliminating via excretion.– Breathing– Kidneys

• Urine

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MEASURING TOXICITY

• Animal Testing– Most commonly used and widely accepted

toxicity test is to expose a population of laboratory animals to measured doses of specific toxins.

• Sensitivity differences pose a problem.– Dose Response Curves– LD50 - Dose at which 50% of the test population is

sensitive (dies).

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LD50

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Population Sensitivity Variations

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Acute vs. Chronic Effects

• Acute Effects - Caused by a single exposure and result in an immediate health problem.

• Chronic Effects - Long-lasting. Can be result of single large dose or repeated smaller doses.– Very difficult to assess specific health effects

due to other factors.

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RISK ASSESSMENT

• Factors influencing risk perception:– Rating risks based on agendas.– Most people have trouble with statistics.– Personal experiences can be misleading.– We have an exaggerated view of our abilities

to control our fate.– News media sensationalizes rare events.– Irrational fears lead to overestimation of

certain dangers.• Fear of the unknown.

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Accepting Risks

• Most people will tolerate a higher probability of occurrence of an event if the harm caused by that event is low.– Harm of greater severity is acceptable only at

low levels of frequency.• EPA generally assumes 1 in 1 million is acceptable

risk for environmental hazards.

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ESTABLISHING PUBLIC POLICY

• Biggest problem in making regulatory decisions is that we are usually exposed to many sources of harm, often unwillingly.

• May not be reasonable to demand protection from every potentially harmful contaminant in our environment, no matter how small the risk.

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ESTABLISHING PUBLIC POLICY

• In setting standards for environmental toxins, need to consider:– Combined effects of different exposures.– Individual sensitivities within population.– Effects of chronic and acute exposures.

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Food for Thought

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From the Star - Tribune

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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

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