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This lecture will help you understand:
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Environmental health hazards
Environmental health goals
Synthetic and natural toxicants
Study of hazards and their effects
Risk assessment and risk management
Policy and regulation
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.
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.
Environmental health hazards
Synthetic and natural toxicants are only one type of environmental health
threat. Others are:
• Physical hazards (floods, blizzards, landslides, radon, UV
exposure)
• Chemical hazards (disinfectants, pesticides)
• Biological hazards (viruses, bacterial infections)
• Cultural or lifestyle hazards (drinking, smoking, bad diet, crime in
neighborhood)
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.
West Nile Virus
Many health hazards exist indoors
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Substances in plastics and consumer products
Lead in paint and pipes
Radon
Asbestos
PBDE fire retardants
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.
• Analagous to a pathogenicity or virulence of the biological hazards that
spread infectious disease.
• Environmental toxicology focuses on effects of chemical poisons
released into the environment.
Environmental toxicology
• Studies toxicants that come from or are discharged into the environment,
and:
• Health effects on humans
• Effects on animals
• Effects on ecosystems
• Animals are studied:
• For their own welfare
• As “canaries in a coal mine” to warn of effects
on humans
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.
Rise of synthetic chemicals
• Widespread synthetic chemical production after WWII
• People are largely unaware of the health risks of many toxicants.
Types of toxicants
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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.
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.
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?
Frogs, people, and atrazine
Frogs 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.
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.
Testicular cancer
Others hypothesize that endocrine disruptors are behind the rise in testicular
cancer in many nations.
Toxicants take many routes through the environment
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.
Transport to the Arctic: “Global distillation”
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.
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 hazards
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 (e.g., toxoplasma)
or
• Test animals in the lab for response to toxicants
or
• Correlate chemical presence and animal presence in the field
Human epidemiology
Human studies rely on:
• Case history = observation and analysis of individual patients
• Epidemiological studies = long-term, large-scale comparisons of
different groups of people
• Animal testing
Human epidemiology
• Advantages:
Realistic
All real-life factors included
• Disadvantages: Statistically correlational only;
does not prove causation
Takes many years to get results
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
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.)
Risk
• Risk = the mathematical probability that some harmful outcome will
result from a given action, event, or substance
• Probability = a quantitative description of the likelihood of a certain
outcome
• 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.
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)
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.
Risk assessment and risk management inform policy
Following risk management, policy decisions are made.
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
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
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: Pesticides
• Pesticides to be introduced to market in the U.S. need to be registered
with the EPA.
• Registration involves risk assessment and risk management.
• EPA assesses research from the manufacturer along with any outside
research.
• EPA can set restrictions on use, or even ban a product.
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.
Conclusion
• International agreements are a hopeful sign that governments will prevent
environmental hazards.
• But solutions can come more easily when they do not arise from
government regulation alone.
• Consumer choice can influence industry if consumers have scientific
information.
• But we will never attain complete knowledge of risks.
• A safer future depends on knowing risks, phasing out harmful substances,
and replacing them with safer ones.