central case study: poison in the bottle: is bisphenol a ... · cells grow uncontrollably, damaging...
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© 2014 Pearson Education, Inc.
Lecture Outlines
Chapter 14
Environmental Health
and Toxicology
Withgott/Laposata
Fifth Edition
© 2014 Pearson Education, Inc.
Central Case Study: Poison in the Bottle: Is
Bisphenol A (BPA) Safe?
BPA is linked to cancer, nerve damage, and miscarriages
In extremely low doses
Used to make hard plastic found in hundreds of products
Cans, utensils, baby bottles, laptops, toys
BPA leaches into food, water, air, and bodies
93% of Americans have it in their bodies
Negative effects occur at extremely low doses
BPA mimics estrogen, a female hormone
In lower levels than set by regulatory agencies
© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc.
Central Case Study: Poison in the Bottle: Is
Bisphenol A (BPA) Safe?
Numerous scientific panels have examined the health risk of BPA
Some have found no concern (U.S. FDA in 2008)
Other have found reason for concern (U.S. FDA’s science advisory panel in 2009)
Numerous countries had banned the use of BPA in baby bottles by 2011
Public and scientific opinion wanted BPA regulated in the United States
In 2012, the FDA rejected a proposed ban on its use
Other countries have banned BPA for some uses
Some industries are removing BPA on their own
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Environmental Health
Environmental health = field that assesses
environmental factors that influence human health
and quality of life
Including natural and human-caused factors
Practitioners seek to prevent adverse effects on
human health and ecological systems
Many environmental health hazards exist in the
world around us
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We face four types of environmental hazards
Physical hazards = hazards that occur naturally in
our environment
Exposure to ultraviolet (UV) radiation from sunlight
Earthquakes, volcanoes, fires, floods, droughts
We can’t prevent them, but we can prepare for them
We increase our vulnerability by deforesting slopes
(e.g., landslides), channelizing rivers (e.g., flooding),
etc.
We can reduce risk with better environmental choices
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We face four types of environmental hazards
Chemical hazards = synthetic chemicals such as
pharmaceuticals, disinfectants, pesticides
Harmful natural chemicals (e.g., venom) also exist
and chemicals that we take from nature and process
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We face four types of environmental hazards
Biological hazards = result from ecological
interactions
Viruses, bacteria, and other pathogens
Infectious disease = disease occurring when species
parasitize humans, fulfilling their ecological roles
Vector = an organism that transfers a pathogen
We can’t avoid risk, but we can reduce infection
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We face four types of environmental hazards
Cultural hazards = result from where we live, our
socioeconomic status, our occupation, our
behavioral choices
Smoking, drug use, diet and nutrition, crime, mode of
transportation—some we control, others we can not
Health factors (e.g., living near toxic waste) are often
correlated with poverty
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Disease is a major focus of environmental
health
Despite our technology, disease kills most of us
Disease has a genetic and environmental basis
Cancer, heart disease, respiratory disorders have
some genetic basis
Air pollution, poverty, and poor hygiene foster
illnesses
Noninfectious diseases cause over half of the
world’s deaths
Infectious diseases account for 1 in 4 deaths
15 million people/year
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Disease is a major focus of environmental
health
Where you live helps determine your disease
Infectious disease causes half of all deaths in
developing countries
Money lets developed countries have access to
hygiene and medicine to combat these diseases
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Disease is a major focus of environmental
health
Lifestyles in developed nations affect diseases
U.S. smoking dropped 42%
But obesity has more than doubled
Public health efforts decrease some infectious
diseases
But some (AIDS) are spreading
Some develop resistance to antibiotics
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Social and environmental factors can influence
the spread of infectious disease
Our mobility spreads diseases worldwide
Severe acute respiratory syndrome (SARS) in 2003
H1N1 swine flu in 2009–2010
Climate change will expand the range of diseases
New disease threats may arise
Some pathogens evolve rapidly
Humans can alter existing diseases to make them more
deadly—bioterrorism is a growing concern
To predict and prevent diseases, experts deal with
complicated interrelationships between technology, land
use, and ecology © 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
We are fighting disease with diverse
approaches
One of the best way to reduce disease is to improve
the basic living conditions of the poor
Food security, sanitation, clean drinking water
Also, provide expanded access to health care
Health clinics, immunizations, pre- and postnatal care
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We are fighting disease with diverse
approaches
Education campaigns work in rich and poor nations
Agencies, organizations, and governments work
together
The United Nations, the World Health Organization,
U.S. Agency for International Development, etc.
Private organizations donate millions of dollars
The Bill and Melinda Gates Foundation has donated
over $15 billion to global health programs since 1994
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Toxicology is the study of chemical hazards
Toxicology = the study of the effects of poisonous
substances on humans and other organisms
Toxicity = the degree of harm a toxicant can inflict
Toxicant = any toxic substance (poison)
“The dose makes the poison”: toxicity depends on the
combined effect of the chemical and its quantity
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Toxicology is the study of chemical hazards
We have been adding increased amounts and
numbers of chemicals into the environment
around us
Environmental toxicology = deals with toxic
substances that come from or are discharged into
the environment
Studies health effects on humans, other animals, and
ecosystems
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Many environmental health hazards exist
indoors
Americans spend roughly 90% of their lives indoors
Indoor spaces can be rife with hazards
Radon = a highly toxic, radioactive gas that is colorless
and undetectable
Can build up in basements
Found in areas with certain types of bedrock
Asbestos = a mineral that insulates, muffles sounds, and
resists fire
Asbestosis = disorder that occurs when inhaled crystals of
asbestos cause scarred lungs that cease to function
Can lead to lung cancer
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Many environmental health hazards exist
indoors
Lead poisoning = caused by lead, a heavy metal
Damages the brain, liver, kidney, and stomach
Causes learning problems, behavior abnormalities, and
death
Exposure is from drinking water that flows through lead
pipes or from lead paint
Efforts in the United States have led to declines in
poisoning, but China still used lead paint in toys until
recently
In 2012, the Centers for Disease Control (CDC) cut the
danger threshold for lead in children’s blood from 10 to 5
micrograms/deciliter
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Many environmental health hazards exist
indoors
Polybrominated diphenyl ethers (PBDEs) = a group of chemicals with fire-retardant properties
Used in computers, televisions, plastics, and furniture
Persist and accumulate in living tissue
Mimic hormones and affect thyroid hormones
Also affect brain and nervous system development and may cause cancer
Concentrations are rising in breast milk
Now that they’re banned in Europe, concentrations have decreased
The United States has not addressed the issue © 2014 Pearson Education, Inc.
Risks must be balanced against rewards
As with most hazards, there is a tradeoff between
the risk of harm and reward
We must judge how these compare
We use bisphenol A despite its health risks
Are safer and affordable alternatives available?
Chemicals have given us our high standard of living
Food, medicine, conveniences
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Toxic Substances and Their Effects on
Organisms
The environment contains natural chemicals that
may pose health risks
Toxins = toxic chemicals made in tissues of living
organisms
Chemicals plants use to defend themselves
But synthetic chemicals are also in our environment
Many thousands of different chemicals have been
manufactured
The United States makes or imports 113 kg (250 lb) of
chemicals for every person in the country each year
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Synthetic chemicals are all around
us—and in us
A 2002 study found that 80% of U.S. streams
contain 82 contaminants
Antibiotics, detergents, drugs, steroids, solvents, etc.
A 2006 study of groundwater found 18% of wells and
92% of all aquifers contain 42 volatile organic
compounds (from gasoline, paints, plastics, etc.)
Less than 2% violate federal health standards for
drinking water
Pesticides are present in streams and groundwater
in levels not high enough to affect human health
But high enough to affect aquatic life © 2014 Pearson Education, Inc.
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Synthetic chemicals are in all of our bodies
Every one of us carries traces of hundreds of
industrial chemicals in our bodies
Including toxic persistent organic pollutants restricted
by international treaties
Babies are born “pre-polluted”—232 chemicals were
in umbilical cords of babies tested
Nine out of 10 umbilical cords contained BPA
Not all synthetic chemicals pose health risks
But very few of the 100,000 chemicals on the market
have been thoroughly tested
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Silent Spring began the public debate over
synthetic chemicals
Rachel Carson’s Silent Spring (1962) showed DDT’s risks to people, wildlife, and ecosystems
Gathered and presented scientific studies, medical cases, and other data
Chemical companies challenged the book
Attacked Carson’s science and personal reputation
DDT was banned in the United States in 1973
But is still made in the United States and exported
Used to control disease vectors in developing countries (reward is greater than risk)
New technologies may stop disease without DDT
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Not all toxicants are synthetic, and not all
synthetic chemicals are toxic
Toxic chemicals also exist naturally and in our food
It would be a mistake to assume natural chemicals
are all healthy and synthetic ones are all harmful
Plants produce toxic chemicals to defend
themselves
Most crop plants have had the level of toxic chemicals
reduced by artificial selection, but not eliminated
Eating animals may expose us to the plant chemicals
they ate
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Toxic substances come in different types
Carcinogens = substances that cause cancer
Cells grow uncontrollably, damaging the body
Prevalence of environmentally induced cancer has been underestimated
Hard to identify because of the long time between exposure and onset of cancer and because not everyone exposed gets cancer
Mutagens = substances that cause DNA mutations
Most mutations have no effect, but some can cause cancer
If they occur in sperm or eggs, can impact offspring
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Toxic substances come in different types
Teratogens = chemicals that cause birth defects in
embryos
Thalidomide caused birth defects in the 1960s
Neurotoxins = toxicants that assault the nervous
system
Animal venoms, heavy metals, pesticides, and
chemical weapons
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Toxic substances come in different types
Allergens = toxicants that overactivate the immune
system
Cause an immune response when one is not needed
Increase in asthma in recent years may be due to
increased prevalence of allergenic chemicals
Not universally considered toxicants since they only
affect some people and not others
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Toxic substances come in different types
Pathway inhibitors = toxicants that interrupt vital
biochemical processes by blocking one or more
steps in pathway
The herbicide atrazine blocks steps in photosynthesis
Endocrine disruptors = toxicants that affect the
endocrine (hormone) system = chemical messenger
system
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Toxic substances come in different types
Hormones stimulate growth, development, sexual
maturity
Work with extremely small concentrations
Synthetic chemicals interfere with normal signals
Block hormones, preventing signals from working
Mimic hormones, causing a change
Many mimic female sex hormones
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Organisms have natural defenses against toxic
substances
Organisms were exposed to toxic substances before humans
starting producing them
Heavy metals occur naturally; plants and animals produce toxic
chemicals
Exposure has driven selection for organisms that can tolerate
these toxins
Barriers (skin, scales, feathers) prevent uptake
Biochemical pathways break down toxicants or are changed for
easier excretion
Some toxicants can not be broken down and are instead
stored in fatty tissue (DDT)
Defenses only work at low levels of toxicants
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Individuals vary in their responses to hazards
Different people respond differently to hazards
Affected by genetics, surroundings, etc.
People in poor health are more sensitive
Sensitivity also varies with sex, age, and weight
Fetuses, infants, and young children are more
sensitive
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Individuals vary in their responses to hazards
The Environmental Protection Agency (EPA) sets
standards for responses based on adult responses
Extrapolate adult responses to smaller size for
children, infants
Scientists argue that standards are not low enough to
protect babies
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The type of exposure affects the response
Acute exposure = high exposure to a hazard for short periods of time
Easy to recognize
Stems from discrete events: ingestion, oil spills, nuclear accident, etc.
Chronic exposure = low exposure for long periods of time
More common but harder to detect and diagnose
Affects organs gradually: lung cancer, liver damage
Cause and effect may not be easily apparent due to
time between onset of exposure and symptoms
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Toxic Substances and Their Effects on
Ecosystems
Toxicants concentrated in the environment can harm
the health of many individuals of a species
Population size decreases
If the species is a predator, their prey may see
population growth
If the species is prey, its predator population may
suffer
Cascading impacts can cause changes in the
composition of biological communities
Can threaten ecosystem functioning
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Airborne substances can travel widely
Chemicals can travel by air
Their effects can occur far from the site of use
Synthetic chemicals are found globally
Pristine lakes in the Canadian wilderness are
contaminated with industrial toxicants
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Airborne substances can travel widely
Because of global air patterns, the poles are
particularly contaminated with industrial toxicants
Found in tissues of Arctic polar bears, Antarctic
penguins, and people in Greenland
Effects can occur over shorter distances
Pesticide drift is the airborne transport of pesticides to
land near agricultural fields
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Toxic substances may concentrate in water
Toxic substances are not evenly distributed in the
environment
Move in specific ways
Runoff carries toxins from land to surface water
Chemicals in the soil can leach into groundwater,
contaminating drinking water
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Toxic substances may concentrate in water
Chemicals enter organisms through drinking or
absorption
Aquatic organisms (fish, frogs, etc.) are good pollution
indicators, giving early warnings of contamination
Contaminants in streams and rivers enter drinking
water and travel through the air
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Some toxicants persist in the environment
Toxins can degrade quickly and become harmless,
or they may remain unaltered and persist for
decades
Rates of degradation depend on the substance,
temperature, moisture, and sun exposure
Many persistent chemicals are designed to last in
the environment (paints, plastics)
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Some toxicants persist in the environment
Breakdown products = simpler products that
toxicants degrade into
May be more or less harmful than the original
substance
DDT degrades into DDE, which is also highly
persistent and toxic
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Toxicants may accumulate and move up the
food chain
Toxicants in the body can be excreted, degraded, or
stored
Fat-soluble toxicants are stored in fatty tissues
Bioaccumulation = process of toxicants building up
in animal tissues to greater concentration than in the
environment
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Toxicants may accumulate and move up the
food chain
Biomagnification = process that occurs when
concentrations of toxicants become magnified in
higher levels of the food chain
Each individual consumes multiple individuals from
lower trophic levels, getting the toxicants from each
Caused the near extinction of peregrine falcons and
bald eagles from the 1950s to 1970s
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Toxic substances can threaten ecosystem
services
Toxicants can alter the composition of ecosystems
and species interactions
Can threaten ecosystem services
Pesticide exposure has been implicated in in
declines of honeybee populations
Honeybees pollinate over 100 economically important
crops
Decomposers and detritivores break down organic
matter and improve soil
Pesticides and antifungal agents may disrupt nutrient
cycling
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Wildlife studies integrate work in the field and
lab
Wild animals can serve as an early warning system
for human health threats of toxicants in the
environment
Museum collections provide data from times before
synthetic chemicals were used
Can be used to assess changes seen today
Measurements from animals in the wild can be
compared to controlled experiments in the lab
Work on alligators and frogs shows reproductive
abnormalities due to endocrine disruption from
pesticides and the herbicide atrazine © 2014 Pearson Education, Inc.
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Human studies rely on case histories,
epidemiology, and animal testing
Case histories = studies of individual patients; e.g.,
autopsies tell us about lethal doses
Don’t tell about rare, new, or low-concentration toxins
Don’t tell about probability and risk
Epidemiological studies = large-scale comparisons
between exposed and unexposed groups
Can last for years
Yield accurate predictions about risk
Measure an association between a health hazard and an
effect—but not necessarily the cause of the effect
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Human studies rely on case histories,
epidemiology, and animal testing
Since epidemiological studies can not establish causation, manipulative experiments are needed
Animals are used as test subjects
Mammals share evolutionary history
Substances that harm rats and mice probably harm us
Some people object to animal tests
Medical advances would be far more difficult without them
New techniques may replace some live-animal testing
Human cell cultures, bacteria, etc.
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Dose-response analysis is a mainstay of
toxicology
Dose-response analysis = testing method that
measures the effect a toxicant produces or the number
of animals affected at different doses
Dose = amount of substance the test animal receives
Response = the type or magnitude of negative effects
Dose-response curve = the dose plotted against the
response
LD50/ED50 = the amount of toxicant required to kill (lethal
dose) or show symptoms in (effective dose) 50% of the
test subjects
A high number indicates low toxicity
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Dose-response analysis is a mainstay of
toxicology
Threshold dose = the level of toxicant where certain
responses start to occur
Organs can metabolize or excrete low doses of a
toxicant; DNA damage can be repaired slowly
Sometimes a response decreases as a dose increases
U- or J-shaped or inverted-U curves
Counterintuitive curves occur with endocrine disruptors
The hormone system is geared to respond to minute
concentrations (e.g., hormones)
Scientists give large doses in animal studies and
extrapolate downward to estimate the effect on humans
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Mixes may be more than the sum of their parts
Determining the impact of mixed hazards is difficult
They may act in ways that cannot be predicted from the
effects of each in isolation
Mixed toxicants can sum, cancel out, or multiply each
other’s effects
New types of impacts may result from mixtures
Synergistic effects = interactive impacts that are greater
than the sum of their constituent effects
New impacts may arise from mixing toxicants
DDE may cause or inhibit sex reversal, depending on the
presence of other chemicals
The interactive effects of most chemicals are unknown
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Endocrine disruption pose challenges for
toxicology
Unconventional dose-response curves are hard to study or use to set safety standards for toxic substances
Theo Colburn’s Our Stolen Future (1996) describes how
synthetic chemicals may be altering hormones
Thousands of studies linked endocrine disruptors to
effects on reproduction, development, immune functions,
nervous systems, etc.
Evidence is strongest in non-human animals
Evidence in humans is growing
Uncertainty in studying endocrine disruptors exists
Negative findings pose economic threats to manufacturers
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We express risk in terms of probability
Exposure to health threats doesn’t automatically
produce an effect
Rather, it causes some probability (likelihood) of harm
A substance’s threat depends on its identity and
strength, the chance and frequency of an encounter,
and an organism’s exposure and sensitivity to the
threat
Probability = description of the likelihood of a certain
outcome
Risk = the probability that some harmful outcome
will result from a given action, event, or substance
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Our perceptions of risk may not match reality
Every action involves some element of risk
We try to behave in ways that minimize risk, but
perception may not match reality
People worry about negligibly small risks while engaging
in high-risk activities
Flying is perceived as riskier than driving
The chance of dying from an automobile accident is 73
times higher than in an airplane crash
We feel more at risk when we do not control a situation
We fear nuclear power and toxic waste
But not smoking or overeating
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Risk assessment analyzes risk quantitatively
Risk assessment = the quantitative measurement of risk
Compares risks involved in different activities or
substances
Identifies and outlines problems
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Risk assessment analyzes risk quantitatively
Risk assessment has several steps. If assessing a chemical
substance:
Conduct a scientific study of toxicity
Assess an individual or population’s exposure to the
substance (frequency, concentrations, length)
Teams of scientific experts review hundreds of studies
Regulators and the public benefit from informed
summaries
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Risk assessment analyzes risk quantitatively
Endocrine disruptors pose regulatory problems in
relation to their risk assessment
Scientific panels were convened to review research on
BPA
A government panel initially found that BPA posed an
intermediate health risk
Panel used mix of research with 70% coming from
academic laboratories
Industry protested that academic labs did not use the
correct lab procedures
Panel removed many academic studies and found no
evidence of health impact © 2014 Pearson Education, Inc.
Risk management combines science and other
socil factors
Risk management = decisions and strategies to
minimize risk; encorporates results of risk assessment
Federal agencies manage risk
The United States has the Centers for Disease Control
and Prevention (CDC), the EPA, the FDA
Scientific assessments are considered with economic,
social, and political needs and values
Comparing costs and benefits is hard
Benefits are economic and easy to calculate
Health risks (costs) are hard-to-measure probabilities of a
few people suffering and lots of people not
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Two approaches exist for determining safety
We can not know a substance’s toxicity until it is tested
Two philosophies exist about determining safety
The “innocent-until-proven-guilty” approach assumes a
substance is harmless until shown to be harmful
Helps technological innovation and economic
advancement by limiting initial testing
But allows dangerous substances to be used
The precautionary principle approach assumes a substance
is harmful until it is shown to be harmless
Identifies troublesome toxicants before being released
May impede the pace of technology and economic
advance
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Philosophical approaches are reflected in
policy
Different nations use different policies for regulating synthetic substances
Europe incorporates the precautionary principle
The United States uses the innocent-until-proven-guilty approach
But for some uses the precautionary principle is used
Federal agencies involved in tracking and regulating synthetic chemicals include:
The FDA: monitors food, food additives, cosmetics, drugs,
medical devices
The EPA: regulates pesticides and chemicals not covered
by other laws
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EPA regulation is only partly effective
The Toxic Substances Control Act (1976) directs the
EPA to monitor thousands of chemicals made in or
imported into the United States
The EPA can ban substances that pose excessive risk
Many health advocates think the TSCA is too weak
Of 83,000 chemicals, only five have been restricted
To push for more testing, toxicity must already be proven,
but the EPA can not do testing to show this
Only 10% of chemicals have been tested for toxicity
Fewer than 1% are regulated
Almost none have been tested for endocrine, nervous, or
immune system damage
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EPA regulation is only partly effective
The Federal Insecticide, Fungicide, and Rodenticide Act
(FIFRA) charges the EPA with “registering” new
pesticides manufacturers want to market
The EPA asks the manufacturer to provide information
on safety assessments
The EPA examines ingredients, use, etc. to determine
risks to people, other organisms, water, or air
It approves, denies, or sets limits on the chemical’s sale
and use and approves language used on the label
Hazardous chemicals can be approved if economic
benefits outweigh hazards
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Toxicants are regulated internationally
The EU’s REACH program (Registration, Evaluation,
Authorization, and Restriction of Chemicals) shifts the burden
of proof for safety to industry
Precautionary principle
Chemicals produced in amounts over 1 metric ton must be
registered
Helps industries research and develop safer products
Chemicals will be approved, deemed unsafe, or tested
further
Estimated that 30,000 substances will be registered
REACH will cost industry $3.8–7 billion over 11 years
Health benefits will be $67 billion over 30 years
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Toxicants are regulated internationally
The Stockholm Convention on Persistent Organic
Pollutants (POPs) was enacted in 2004 and ratified
by over 150 nations
POPs = toxic, persistent chemicals that
bioaccumulate and biomagnify and can travel long
distances
The Stockholm Convention sets guidelines for
phasing out the “dirty dozen” = the 12 most
dangerous POPs
Encouraging transition to safer alternatives
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Conclusion
International agreements show that governments are
working to protect society, wildlife, and ecosystems from
toxic chemicals and environmental hazards
But solutions need more than government regulations
Consumer choice affects industries
Once scientific results are in, society’s approach to risk
management determines what policies are enacted
A safe and happy future depends on knowing the risks
some hazards pose and then replacing those substances
with safer ones