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