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Environmental Health and Toxicology

Chapter 8

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Outline:

• Environmental Health Hazards Global Disease Burden Emergent and Infectious Diseases Antibiotics and Pesticide Resistance Toxicology

• 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 - An abnormal change in the body’s condition that impairs important physical or psychological functions-. 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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Global Disease Burden

• Health agencies calculate disability-adjusted life years (DALYs) as a measure of disease burden. Chronic diseases now account for nearly

60% of the 56.5 million total deaths worldwide each year.

- Progress in eliminating communicable diseases such as smallpox, polio, and malaria, is allowing people to live longer.

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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 and Infectious Diseases

• An emergent disease is one not previously known or that has been absent for at least 20 years. An important factor in the spread of many

diseases is speed and frequency of modern travel.

Malaria is one of the most prevalent remaining infectious diseases.

- SARS and Avian Flu- HIV/AIDS has the largest death toll from

an emergent disease.

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Ecological Diseases

• Domestic animals and wildlife also experience sudden and widespread epidemics. Distemper Virus (Seals) Chronic Wasting Disease (Deer and Elk)

- Transmissible Spongiform Encephalopathies

Black-Band Disease (Coral)

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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 U.S 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 U.S. are routinely fed to farm animals to stimulate weight gain.

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Toxicology

• 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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Toxicology Cont’d

• 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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Toxicology Cont’d

• 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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Toxicology Cont’d

• 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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Toxicology Cont’d

• 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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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 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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Biomagnification

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DDT• DDT is a synthetic chemical compound once used widely in the United States and throughout

the world as a pesticide (a chemical substance used to kill weeds, insects, rodents, or other pests). It is probably best known for its dual nature: although remarkably effective in destroying certain living things that are harmful to plants and animals, it can also be extremely dangerous to humans and the environment.

• The abbreviation DDT stands for dichlorodiphenyltrichloroethane. DDT was first produced in the laboratory in 1873. For more than half a century, it was little more than a laboratory curiosity—a complicated synthetic (produced by scientists) compound with no apparent use.

• Then, in 1939, Swiss chemist Paul Hermann Müller (1899–1965) discovered that DDT was highly poisonous to insects. The discovery was very important because of its potential for use in killing insects that cause disease and eat agricultural crops. For his work, Müller was awarded the Nobel Prize in medicine in 1948.

• DDT's environmental problems arise because of two important properties: persistence and lipid-solubility. The term persistence refers to the fact that DDT does not break down very easily.

• Once the pesticide has been used in an area, it is likely to remain there for many years. In addition, DDT does not dissolve in water, although it does dissolve in fatty or oily liquids. (The term lipid-solubility is used because fats and oils are members of the organic family known as lipids.)

• Since DDT is not soluble in water, it is not washed away by the rain, adding to its persistence in the environment. But since DDT is lipid-soluble, it tends to concentrate in the body fat of animals.

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Before the dangers of DDT were known, crops and people alike were sprayed with the chemical to protect against bothersome insects.

DDT is used today in such African nations as Zimbabwe and Ethiopia to control mosquitoes and the tsetse fly. These two insects cause serious diseases, such as malaria and sleeping sickness. DDT saves lives when used on the tsetse fly in Lake Kariba in Zimbabwe. But once sprayed on the lake, DDT does not disappear very quickly. Instead, it is taken up by plants and animals that live in the lake. Studies have shown that the concentration of DDT in the lake itself is only 0.002 parts per billion. But algae in the lake have a concentration of 2.5 parts per million.

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Clutch of mallard eggs contaminated by DDT. The accumulation of DDT in many birds causes reproductive difficulties. Eggs have thinner

shells that break easily, and some eggs may not hatch at all

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DDT & The American Bald Eagle

• The bald eagle (Haliaeetus leucocephalus) is currently listed as a federally threatened species in Washington.  In July 1999, the U.S. Fish and Wildlife Service published a proposal to delist the bald eagle under the Endangered Species Act. 

• At the time the species was listed, environmental contaminants were cited as the primary reason for its decline.  Beginning in the 1940's, dichloro diphenyl trichloroethane (DDT) and other organochlorine pesticides became widely used as insecticides. 

• In the late 1960's and early 1970's, it was determined that dichlorophenyl-dichloroethylene (DDE), the principal breakdown product of DDT, accumulated in the fatty tissues of adult female bald eagles and resulted in thin shells and reproductive failure (Wiemeyer et al. 1972, 1984; Grier 1982). 

• Due to the bioaccumulative and persistent nature of DDT and the adverse reproductive effects elicited by DDT, particularly on birds, its use was banned in the United States in 1972.

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Agent Orange• During the Vietnam War, US military forces sprayed nearly 19 million gallons of herbicide on

about 3.6 million acres of land in Vietnam and Laos to remove forest cover, destroy crops, and clear vegetation from the perimeters of US bases. This effort, known as Operation Ranch Hand, lasted from 1962 to 1971.

• • Various herbicidal (plant-killing) formulations were used, but most were mixtures of 2 herbicides

known as phenoxy herbicides because of their chemical structures: • 2,4-dichlorophenoxyacetic acid (2,4-D) • 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)

• Each formulation was shipped in a chemical drum marked with an identifying colored stripe. The most widely used mixture contained equal parts 2,4-D and 2,4,5-T. Because this herbicide came in drums with orange stripes, it was called Agent Orange. Today, Agent Orange is used to refer generally to all the phenoxy herbicides sprayed at the time.

• The 2,4,5-T was contaminated with small amounts of dioxins, which were created unintentionally during the manufacturing process.

• Dioxins are a family of biologically active compounds formed during the manufacturing of paper and some other industrial processes. Because they can remain in the environment for years, they form part of a group of chemicals known as "persistent organic pollutants."

• The particular dioxin present in Agent Orange, 2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD, is unusually toxic.

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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 because

these materials persist in the environment and have unexpected effects far from their original use.

- PBDE (flame-retardants in textiles)

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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 multiplies 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

• 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.

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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 unknowingly.

• 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 CONT’D

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