Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Environmental Health and Toxicology Chapter 9.

Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

Environmental Health and Toxicology

Chapter 9


Outline:

• Environmental Health Hazards Infectious Organisms Antibiotics and Pesticide Resistance Toxic Chemicals

• Movement and Fate of Toxins• Minimizing Toxic Effects• Measuring Toxicity• Risk Assessment


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).


Infectious Organisms

• For most of human history, the greatest health threats have been pathogenic organisms and accidents or violence. Infectious diseases are still responsible for

about 24% of all disease-related deaths.- Majority of these deaths in poorer

countries with poor nutrition, sanitation, and vaccination programs.

AIDS now largest single cause of communicable death in the world.


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.


Disability-Adjusted Life Year

• WHO reports communicable diseases are responsible for nearly half of all 1.4 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.


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 the speed and frequency of modern travel.

- Foot and Mouth Disease


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.


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.


Toxic Chemicals

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

- Flammable, explosive, irritant, acid, caustic.

Toxic - Poisonous- Can be general or very specific. Often

harmful even in dilute concentrations.


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.


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.


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


US Age-Adjusted Cancer Death Rates


Natural and Synthetic Toxins

• Many natural chemicals are very dangerous while many synthetic chemicals are relatively harmless. Both plants and animals produce

chemicals similar to neurotransmitters, hormones, and regulatory molecules.

- Arsenic and cyanide are both natural.


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.

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


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.


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)


Bioaccumulation


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.


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.


Excretion

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

- Urine


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.


Population Sensitivity Variations


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.


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.


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.



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.


Summary:

• Environmental Health Hazards Infectious Organisms Antibiotics and Pesticide Resistance Toxic Chemicals

• Movement and Fate of Toxins• Minimizing Toxic Effects• Measuring Toxicity• Risk Assessment


Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Environmental Health and Toxicology Chapter 9.

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