Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture...

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

PowerPoint® Lecture prepared by Jay Withgott

Scott Brennan • Jay Withgott

7 Toxicology and environmental health


This lecture will help you understand:

• Prevalence of toxic agents in the environment

• Epidemiology, animal testing, and dose-response analysis

• Factors affecting toxicity

• Environmental health hazards

• Risk assessment and risk management

• Policy on toxicants


Central Case: Alligators and Endocrine Disruptors at Lake Apopka, Florida

• Biologist Louis Guillette found alligators with reproductive abnormalities in a Florida lake.

• The lake had been contaminated with pesticides.

• Research revealed that chemicals in the lake were disrupting the animals’ reproductive hormones.


Toxicology

The study of poisonous substances and their effects on humans and other organisms

Toxicologists assess and compare toxic agents, or toxicants, for their toxicity, the degree of harm a substance can inflict.

Environmental toxicology focuses on effects of chemical poisons released into the environment.


Synthetic chemicals are everywhere in our environment

Many thousands have been produced and released.

Some persist for long time periods or travel great distances.

2002 USGS study: 80% of U.S. streams contain up to 82 wastewater contaminants, include antibiotics, perfumes, detergents, drugs, steroids, disinfectants, etc.


Synthetic chemicals

Of the 100,000 synthetic chemicals on the market today, very few have been thoroughly tested for harmful effects.

Figure 10.1


Environmental toxicology

Studies toxicants that come from or are discharged into the environment, and:

Health effects on humansEffects on animalsEffects on ecosystems

Animals are studied:

For their own welfareAs “canaries in a coal mine” to warn of effects on humans


Frogs, people, and atrazineFrogs show reproductive abnormalities in response to small doses of the herbicide atrazine, researcher Tyrone Hayes has found.

Others suggest that atrazine may have effects on humans as well.

The fierce criticism from atrazine’s manufacturer reflects the high stakes in environmental toxicology.

Figure 10.2


Rise of synthetic chemicals

Widespread synthetic chemical production after WWII

People are largely unaware of the health risks of many toxicants.

Figure 10.3

The potent insecticide DDT was sprayed widely in public areas, even on people.


Silent Spring and Rachel Carson

Carson’s 1962 book alerted the public that DDT and other pesticides could be toxic to animals and people.

Further research led the EPA to ban DDT in 1973.

These developments were central to the modern environmental movement.


Types of toxicants

• Carcinogens: cause cancer

• Mutagens: cause mutations in DNA

• Teratogens: cause birth defects

• Allergens: cause unnecessary immune response

• Neurotoxins: damage nervous system

• Endocrine disruptors: interfere with hormones


Types of toxicants: Teratogens

The drug thalidomide, used to relieve nausea during pregnancy, turned out to be a potent teratogen, and caused thousands of birth defects before being banned in the 1960s.

“Thalidomide baby” Butch Lumpkin learned to overcome his deformed arms and fingers to become a professional tennis instructor.

Figure 10.4


Endocrine disruption

Some chemicals, once inside the bloodstream, can “mimic” hormones.

If molecules of the chemical bind to the sites intended for hormone binding, they cause an inappropriate response.

Thus these chemicals disrupt the endocrine (hormone) system.

Figure 10.5


Endocrine disruption

The hormone system is geared to working with tiny concentrations of hormones …

… so, it can respond to tiny concentrations of environmental contaminants.

Have chemicals in the environment acted as endocrine disruptors in humans?


Declining sperm counts?

A 1992 study summarized results of sperm count studies worldwide since 1938. Data showed a significant decrease in men’s sperm counts over 50 years.

Figure 10.6a


Testicular cancer

Others hypothesize that endocrine disruptors are behind the rise in testicular cancer in many nations.

Figure 10.6b


Toxicants take many routes through the environment

Figure 10.7


Toxicants concentrate in water

Surface water and groundwater can accumulate toxicants.

Runoff from large areas of land drains into water bodies, becoming concentrated.

Toxicants in groundwater or surface water reservoirs used for drinking water pose potential risks to human health.


Airborne toxicants

Volatile chemicals can travel long distances on atmospheric currents.

PCBs are carried thousands of miles from developed nations of the temperate zone up to the Arctic, where they are found in tissues of polar bears and seals.


Persistence

Some chemicals are more stable than others, persisting for longer in the environment.

DDT and PCBs are persistent.Bt toxin in GM crops is not persistent.

Temperature, moisture, sun exposure, etc., affect rate of degradation.

Most toxicants degrade into simpler breakdown products. Some of these are also toxic.

(DDT breaks down to DDE, also toxic.)


Poisons accumulate in tissues

The body may excrete, degrade, or store toxicants.

Fat-soluble ones are stored.

DDT is persistent and fat soluble,

… so builds up in tissues: bioaccumulation.

Bioaccumulated chemicals may be passed on to animals that eat the organism—up the food chain…


Poisons move up the food chain

At each trophic level, chemical concentration increases: biomagnification.

DDT concentrations increase from plankton to fish to fish-eating birds.

Figure 10.9


All toxicants are not synthetic

Although toxicology tends to focus on man-made chemicals, it’s important to keep in mind that there are plenty of natural toxicants.

Many are toxins produced by animals or plants for protection against predators and pathogens.


Studying effects of toxicants

Toxicologists study effects in several major ways:

• Wildlife toxicology studies

• Human epidemiological studies

• Dose-response studies in the lab


Wildlife toxicology

Determine causes of mortality in die-off events

or

Test animals in the lab for response to toxicants

or

Correlate chemical presence and animal presence in the field

Problems in wildlife can act as a warning for people.


Human epidemiology

Long-term, large-scale comparisons of different groups of people

Contrast group exposed to substance or risk factor with group not exposed

Follow them for health effects or mortality later in life

Statistically analyze results to look for differences between groups


Human epidemiology

Advantages: Realistic

All real-life factors included

Disadvantages: Statistically correlational only; does not prove causation

Takes many years to get results


Mixing toxicology with anthropology

Children were tested for pesticide effects.

From The Science behind the Stories

Drawings by nonexposed children

Drawings by exposed children


Dose-response analysis

Method of determining toxicity of a substance by measuring response to different doses

Lab animals are used.

Mice and rats breed quickly, and give data relevant to humans because they share mammal physiology with us.

Responses to doses are plotted on a dose-response curve.


Dose-response curve

LD50 = dose lethal to 50% of test animals

Figure 10.10

Threshold = dose at which response begins


Dose-response curve

Dose-response curves allow us to predict effects of higher doses.

By extrapolating the curve out to higher values, we can predict how toxic a substance may be to humans at various concentrations.

In most curves, response increases with dose.But this is not always the case; the increase may not be linear.

With endocrine disruption, it may decrease.


Factors affecting toxicity

Not all people are equal. Sensitivity to toxicant can vary with sex, age, weight, etc.

Babies, older people, or those in poor health are more sensitive.

Type of exposure:

acute = high exposure in short period of time

chronic = lower amounts over long period of time


Mixtures of toxicants

Substances may interact when combined together.

Mixes of toxicants may cause effects greater than the sum of their individual effects.

These are called synergistic effects.

A challenging problem for toxicology: There is no way to test all possible combinations!

(And the environment contains complex mixtures of many toxicants.)


Environmental health

Environmental health:

Assesses environmental factors that influence human health and quality of life.

Seeks to prevent adverse effects on human health and ecological systems.

Contains environmental toxicology within its scope.


Infectious disease

In communicable or transmissable disease,a pathogen attacks a host,

either directly or through a vector(e.g., mosquito that transfers a malaria parasite to hosts)

… and the pathogen can be transmitted from one host to another.

Infectious disease causes 25% of deaths in the world and nearly half of deaths in developing nations.


Infectious disease

Figure 10.11

2nd-leading cause of death worldwide

6 diseases account for 90% of infectious disease deaths


Environmental health hazards

Synthetic and natural toxicants are only one type of environmental health threat. Others are:

• Physical or climatic hazards (floods, blizzards, landslides, radon, UV exposure…)

• Biological hazards (viruses, bacterial pathogens…)

• Cultural or lifestyle hazards (drinking, smoking, bad diet, crime in neighborhood…)


Environmental health hazards


Many health hazards exist indoors

Substances in plastics and consumer products

Lead in paint and pipes

Radon

Asbestos

PBDE fire retardants

Figure 10.12


Risk

Risk = the mathematical probability that some harmful outcome will result from a given action, event, or substance

Harmful outcome could be defined as injury, death, environmental damage, economic loss, etc.


Perception different from reality

Our perception of risks tends not to match statistical reality.

Figure 10.13

smoking

plane crash


Risk assessment

Analyzes risks quantitatively

Measures and compares risks involved in different activities or substances

Helps identify and prioritize serious risks

Helps determine threats posed to humans, wildlife, ecosystems


Risk assessment

Involves:

• Dose-response analysis or other tests of toxicity

• Assessing likely exposure to the hazard (concentration, time, frequency)

Figure 10.14


Risk management

Consider risk assessments in light of social, economic, and political needs and values.

Weigh costs and benefits, given both scientific and nonscientific concerns.

Decide whether or not to reduce or eliminate risk.

Figure 10.14


Risk assessment and risk management inform policy

Following risk management, policy decisions are made.

Figure 10.14


Federal agencies and risk management

In the U.S., most risk management is conducted by federal and state agencies.

Particularly:

Environmental Protection Agency

and

Food and Drug Administration


Philosophical approaches

“Innocent until proven guilty”:Assume harmless until shown to be harmful

Precautionary principle: Assume harmful until shown to be harmless


Implications for product testing

“Innocent until proven guilty”:Industry can introduce any products it wants.

Government bears the burden of proof to show if products are dangerous.

Precautionary principle:Industry cannot introduce a product until it is very thoroughly tested and shown convincingly to be harmless.


Implications for product testing

Industry has pressured government to take an “innocent-till-proven-guilty” approach.

Environmental advocates have pressured government to follow the precautionary principle.

Figure 10.15


Viewpoints: Industry or government?

Warren Porter

Marian Stanley

“Given the inherent inadequacies of the testing process and the uncertainty of the economic impacts, both government and industry should share the responsibility of testing to ensure public safety.”

“Manufacturers often voluntarily conduct new studies to support the continued safe use of their chemicals. … It is important that the EPA and manufacturers work together in evaluating chemicals.”

From Viewpoints


Policy on toxicants

Key agencies and products they regulate:

Food and Drug Administration (FDA)food, additives, cosmetics, drugs, medical devices

Environmental Protection Agency (EPA)pesticides, industrial chemicals, and any synthetic

chemicals not covered by other agencies

Occupational Health and Safety Administration (OSHA)workplace hazards


EPA regulation: Industrial chemicals

EPA is charged with monitoring 75,000 industrial chemicals.

Too many chemicals, too little time, people, resources

Only 10% of chemicals on the market are thoroughly tested.

Only 2% are screened for carcinogens, mutagens, teratogens.

<1% are government regulated.

~0% are tested for endocrine, nervous, or immune effects.


International policy on toxicants

Little or no effective regulation in most developing nations.

Europe follows a policy closer to the precautionary principle than does the U.S.The EU is now considering a still-tougher policy.

Stockholm Convention, 2001: international treaty to phase out 12 persistent organic pollutants (POPs), “the dirty dozen”


“The dirty dozen” POPs


Conclusions: Challenges

Synthetic chemicals are ubiquitous in our environment.

Very few chemicals on the market are thoroughly tested.

Our understanding of endocrine disruption and certain other effects is still in its infancy.

Regulatory agencies are caught between pressure from industry and environmental advocates.

People disagree over the roles of government and industry in testing new chemical products.


Conclusions: Solutions

Monitoring, public education, and regulation of industry could together decrease our exposure to toxicants.

Endocrine disruption and other novel threats are being actively researched.

EPA and other regulatory agencies do their best to continue assessing chemicals accurately and fairly.

Greater public participation in the risk management process would promote regulatory decisions that favor citizens.


QUESTION: Review

Which causes birth defects?

a. Allergen

b. Mutagen

c. Carcinogen

d. Teratogen

e. Endocrine disruptor


QUESTION: Review

Which statement is NOT correct regarding the insecticide DDT?

a. It was criticized in the book Silent Spring.

b. It helps fight malaria.

c. It is persistent and bioaccumulates.

d. It has no toxic breakdown products.

e. Its use was banned by the EPA.


QUESTION: Review

Epidemiological studies… ?

a. Can prove a certain toxicant causes a certain effect.

b. Search for statistical association between hazard and effect.

c. Are rapidly completed.

d. Take place with lab animals.


QUESTION: Review

Which statement is FALSE?

a. Babies are more sensitive to toxicants than people aged 30.

b. Synergistic effects can occur with mixtures of chemicals.

c. Chronic exposure occurs over a short period of time.

d. Some doses may elicit no measurable response.


QUESTION: Weighing the IssuesDDT is banned in the U.S. to protect human health and the

environment, but U.S. companies produce and sell DDT to developing nations to use against malaria-carrying mosquitoes. How do you feel about this?

a. It is hypocritical for the U.S. to protect its own citizens against DDT but to sell it abroad.

b. It is fine, because every nation has the right to pass its own laws regarding pesticides.

c. It is good, because malaria is a bigger health hazard in some developing nations than are risks from DDT.


QUESTION: Interpreting Graphs and Data

For the red curve with the threshold, the LD50 value is … ?

a. A higher dose than the LD50 of the blue curve.

b. A lower dose than the LD50 of the blue curve.

c. There is no LD50 value for the red curve.

Figure 10.10


QUESTION: Interpreting Graphs and Data

Which hazard involves the greatest risk?

a. Car crash

b. Plane crash

c. Murder

d. Being overweight

Figure 10.13


QUESTION: Viewpoints

In testing new synthetic chemicals, should we follow the “innocent-till-proven-guilty” approach, or the precautionary principle?

a. “Innocent-till-proven-guilty” approach

b. Precautionary principle

c. A hybrid of both approaches

Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture...

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