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Environmental Health and Toxicology

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ENVIRONMENTAL HEALTH

• 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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Environmental Health Risks

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Global Disease Burden

• Disability-adjusted life years (DALYs) - combine premature deaths and

loss of healthy life resulting from illness or disability

• Life expectancy has risen worldwide; chronic conditions are becoming a leading cause of disability and premature death. By 2020, heart disease may become

leading source of disability and disease worldwide.

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Infectious Diseases

• Greatest health threats: pathogenic organisms, accidents or

violence. Communicable diseases

- responsible for about 1/3 of all disease-related deaths.

- Majority in countries with poor nutrition, sanitation, and vaccination programs.

Malaria is a major disease in tropical areas.

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Emergent Diseases

• An emergent disease:- never known before- been absent for at least 20 years.

The spread of many diseases- is due to the speed and frequency of

modern travel Ex. SARS Ex. West Nile Virus

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Ecological Diseases

• Domestic animals and wildlife also experience sudden and widespread epidemics. Distemper in seals in

western Europe. Chronic Wasting

Disease in deer and elk in North America

http://wildlife.utah.gov/diseases/cwd/.

Sudden Oak Death Syndrome in California.

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Antibiotic and Pesticide Resistance

• The problem with antibiotics and pesticides:• 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 Use

• Why is antibiotic use a problem? 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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Antibiotic Resistance – How is it developed?

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Toxicology

• Dangerous chemicals are divided into two broad categories: Toxic - Poisonous

- Can be general or very specific. Often harmful even in dilute concentrations.

Hazardous - Dangerous - Flammable, explosive, irritant, acid,

caustic.

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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.

Sick Building Syndrome

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Toxic Chemicals

• Endocrine Disrupters Disrupt normal hormone functions

- Thyroxine Regulates cell metabolism

- Insulin regulates blood sugar levels

- Adrenalin

response to stress; stimulates autonomic nerve action - Endorphins

reduce the sensation of pain and affect emotions

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Steroid Hormone Action

Normal: Hormone carriers deliver molecules to cell surface. Intraceullur carriers deliver hormones to the nucleus; bind to and regulate expression of DNA.

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Toxic Chemicals

• Neurotoxins 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.

- Ex. Radiation• Teratogens

Specifically cause abnormalities during embryonic growth and development.

- Alcohol - Fetal Alcohol Syndrome• Carcinogens

Substances that cause cancer.- Ex. Cigarette smoke

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MOVEMENT, DISTRIBUTION, AND FATE OF TOXINS

• Solubility One of most important characteristics in

determining the movement of a toxin.• Chemicals are divided into two major groups:

- Those that dissolve more readily in water.- Those that dissolve more readily in oil.

What’s the difference in how they move?- Water soluble compounds move rapidly

through the environment, and have ready access to most human cells.

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Exposure and Susceptibility

• How and where do they affect us? Airborne toxins generally cause more ill

health than any other exposure.- Lining of lungs easily absorbs toxins.

Largest toxin exposure reported in industrial settings.

Condition of organism and timing of exposure also have strong influences on toxicity.

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Exposure Routes

Exposure routes to toxic and hazardous environmental factors

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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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Bioaccumulation and Biomagnification

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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.

- Example? (DDT)

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Chemical Interactions

• Antagonistic Reaction: One material interferes with the effects, or

stimulates the breakdown, of other chemicals.

• Additive Reaction Effects of each chemical are added to one

another.• Synergistic Reaction

One substance exacerbates the effect of the other.

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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 and Repair

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

- Urine• Tissues and organs often have mechanisms

for damage repair. Any irritating agent can be potentially

carcinogenic.

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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.

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Toxicity Ratings

• Moderate toxin takes about (1) g/kg of body weight to produce a lethal dose. Very toxic materials require about 10% of

that amount.- Extremely toxic materials require 1% of

that amount. Supertoxic chemicals can be lethal in

a dose of a few micrograms.

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Toxicity Ratings

• Many carcinogens, mutagens, and teratogens are dangerous at levels far below their direct toxic effect because abnormal cell growth exerts a form of biological amplification.

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Acute versus Chronic Doses and 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 AND ACCEPTANCE

• Risk Possibility of suffering harm or loss.

• Risk Assessment Scientific process of estimating the threat

that particular hazards pose to human health.

- Risk Identification- Dose Response Assessment- Exposure Appraisal- Risk Characterization

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Understanding Risks

• 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 / 1 million is

acceptable risk for environmental hazards.

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ESTABLISHING PUBLIC POLICY

• It is difficult to separate the effects of multiple hazards and evaluate their risks accurately, especially when exposures are near the threshold of measurement and response. May not be reasonable to mandate

protection, no matter how small the risk, from every potentially harmful contaminant in our environment.

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CERCLA and RCRA

• Remaining Slides are in reference to CERCLA and RCRA

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Hazardous Waste

• Legally, hazardous waste is any discarded liquid or solid that contains substances known to be: Fatal to humans or laboratory animals in

low doses. Toxic, carcinogenic, mutagenic, or

teratogenic to humans or other life-forms. Ignitable with a flash point less than 60o C. Explosive or highly reactive.

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Hazardous Waste Disposal

• Federal Legislation Resource Conservation and Recovery Act

(RCRA) - 1976.- Comprehensive program requiring

rigorous testing and management of toxic and hazardous substances.

Cradle to grave accounting.

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Federal Legislation

• Comprehensive Environmental Response, Compensation and Liability Act (CERCLA). Modified in 1984 by Superfund

Amendments and Reauthorization Act.- Aimed at rapid containment, cleanup, or

remediation of abandoned toxic waste sites.

Toxic Release Inventory - Requires 20,000 manufacturing facilities to report annually on releases of more than 300 toxic materials.

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Cradle to Grave

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CERCLA

• Government does not have to prove anyone violated a law, or what role they played in a superfund site. Liability under CERCLA is “strict, joint, and

several”, meaning anyone associated with a site can be held responsible for the entire clean-up cost.

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Superfund Sites

• EPA estimates 36,000 seriously contaminated sites in the U.S.. By 1997, 1,400 sites had been placed on

the National Priority List for cleanup with with Superfund financing.

- Superfund is a revolving pool designed to: Provide immediate response to

emergency situations posing imminent hazards.

Clean-up abandoned or inactive sites.

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Summary

• Environmental Health Infectious and Emergent Diseases Antibiotics and Pesticide Resistance

• Toxicology• Movement, Distribution, and Fate of Toxins• Minimizing Toxic Effects• Measuring Toxicity• Risk Assessment• Establishing Public Policy

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