Transcript File - Claremont AP Environmental

Chapter 14
Environmental Health and Toxicology
This chapter will help you
• Identify major environmental health hazards and explain the goals of
environmental health
• Describe the types, abundance, distribution, and movement of toxic
substances in the environment
• Discuss the study of hazards and their effects, including case histories,
epidemiology, animal testing, and dose-response analysis
• Evaluate risk assessment and risk management
• Compare philosophical approaches to risk
• Describe regulatory policy in the United States and internationally
Poison in a Bottle:
Is Bisphenol A Safe?
• The chemical bisphenol A (BPA for short) has been associated with
everything from neurological effects to miscarriages, yet it’s in hundreds of
products we use every day, and there’s a better than 9 in 10 chance that it
is coursing through
your body right now.
• With so many sues, bisphenol A, and
organic compound with the chemical
formula C15H16O2, has become one
of the world’s most produced
chemicals; each year w make 1
pound of BPA for each person on
the planet, and over 6 pounds per
person in the United States!
BPA continued…
• Bisphenol A leaches out of
its many products and into
our food, water, air, and
bodies.
• Fully 93% of Americans carry detectable concentrations in their urine,
according to the latest National Health and Nutritional Examination
Survey conducted by the Centers for Disease Control and Prevention
(CDC).
BPA continued…
• Over 200 studies with rats, mice, and other animals have shown many
apparent effect of BPA, including a wide range of reproductive
abnormalities.
• Scientists say this is because BPA mimics the female sex hormone
estrogen; that is, it is structurally similar to estrogen and can induce
some of its effects in animals.
Chemical structures and
uses of common endocrine
disruptors. DES, bisphenol-a
and genistein are classified
as estrogen agonists while
both of the phthalates are
androgen antagonists. DDT is
classified as both an
estrogen agonist and an
androgen antagonist.
BPA continued…
• In reaction to the burgeoning research, a
growing number of researchers, doctors,
and consumer advocates are calling on
governments to regulate Bisphenol A and
for manufacturers to stop using it.
• In 2008, Canada became the first nation to
declare bisphenol A toxic. It banned the
sale, import, and advertising of baby
products using BPA.
BPA continued…
• In the face of mounting press coverage and public concern, many
companies are choosing to voluntarily remove BPA from their
products.
Environmental Health
The study and practice of environmental health assesses environmental
factors that influence human health and quality of life.
We face four types of environmental hazards
• Physical hazards arise from processes that occur naturally in our
environment and pose risks to human life or health.
• Examples include ultraviolet (UV) radiation from sunlight, or discrete events
such as earthquakes, volcanic eruptions, fires, floods, blizzards, landslides,
hurricanes, and droughts.
• Chemical hazards include many of the synthetic chemicals that our
society produces, such as disinfectants and pesticides, and also
include chemicals produced naturally by organisms.
• Biological hazards result from ecological interactions among
organisms.
• When we become sick from a virus, bacterial infection, or other pathogen, we
are suffering parasitism by other species that are simply fulfilling their
ecological roles, and this is what we call infectious disease.
• Hazards that result from our place of residence, our socioeconomic
status, our occupation, or our behavioral choices can be thought of as
cultural hazards or lifestyle hazards.
• Choosing to smoke, poor diet, and living in proximity to toxic waste are all
cultural hazards.
Many environmental health
hazards exist indoors
• Cigarette smoke and radon are leading indoor hazards and are the top
two causes of lung cancer in developed nations.
• Another indoor hazard is asbestos causing a condition called
asbestosis.
• Lead poisoning is another indoor health hazard. When ingested, lead,
a heavy metal, can cause damage to the brain, liver, kidney, and
stomach; learning problems and behavioral abnormalities; anemia;
hearing loss; and even death.
• A recently recognized hazard is a group of chemicals known as
polybrominated diphenyl ethers (PBDEs). These chemicals appear to
be endocrine disruptors, affecting thyroid hormones in animals, and
have been banned in Europe.
Disease is a major focus of
environmental health
• Many major killers, such as cancer, heart disease, and respiratory
disorders, have genetic bases but are also influenced by
environmental factors.
• Malnutrition can foster a wide variety of illnesses, as can poverty,
poor hygiene, lifestyle choices, and lack of exercise.
• Over half the world’s deaths result from non-infections diseases, such
as cancer and hear disease, while 1 death in 11 is due to injuries.
• In developed nations like the United States, lifestyle trends are
altering the prevalence of non-infections disease in ways both good
and bad.
• Although infectious disease accounts for fewer deaths than noninfectious disease, it robs society of more years of human life because
it tends to strike people at all ages, including the very young.
Infectious disease interacts with social and
environmental influences
• Many diseases are spreading because we are so mobile in our
modern era of globalization.
• The changes we cause to our environment can also cause diseases to
spread.
• To predict and prevent infections disease, environmental health
experts assess the complicated relationships among technology, land
use, and ecology.
Health workers are fighting
disease in many ways
• Perhaps the best way to reduce disease is to improve the basic living
conditions of the world’s poor. Other than providing them food
security, this means ensuring their access to safe drinking water and
imporving sanitation by minimizing exposure to human waste,
garbage3, and wastewater.
• Another important pursuit is to expand access to health care. In
developing nations, this includes opening clinics, immunizing children
against diseases, providing prenatal and postnatal care for mothers
and babies, and making generic and inexpensive pharmaceuticals
available.
• Education campaigns play a vital role in rich and poor nations alike.
• Such efforts are being spearheaded internationally by the United
Nations, the World Health Organization, the U.S. Agency for
International Development, and by non-governmental organizations
and funding agencies.
Toxicology is the study of
poisonous substances
• Toxicology is the science that examines the effects of poisonous
substances on humans and other organisms.
• Toxicologist assess and compare substances to determine their
toxicity, the degree of harm a chemical substance can inflict.
• A toxic substance, or poison, is called a toxicant, but any chemical
substance may exert negative impacts if we ingest or expose
ourselves to enough of it.
• These trends have driven the rise of environmental toxicology, which
deals specifically with toxic substances that come from or are
discharged into the environment.
Risks must be balanced against rewards
Toxic Substances in the
Environment
Our environment contains countless natural substances that may pose
health risks. These include toxins, toxic chemicals manufactured in the
tissues of living organisms, and many synthetic (artificial, or humanmade) chemicals.
Synthetic chemicals are all around us
• Thousands of synthetic chemicals have been manufactured and many
have found their way into soil, air, and water.
Synthetic chemicals are in all of our bodies
• And a result of exposure, every one of us carries traces of numerous
industrial chemicals in our bodies.
• Not all synthetic chemicals pose health risks, and relatively few are
known with certainty to be toxic. However, very few have been
thoroughly tested.
Silent Spring began the public debate over
synthetic chemicals
• Rachel Carson was a naturalist, author, and government scientist.
• Using Scientific studies, medical case histories, and other data, she
showed that DDT and artificial pesticides in general were hazardous
to people, wild life, and the environment.
• Carson’s book was a bestseller and generated significant social
changes in views and actions toward the environment.
• The United States does not use DDT, but manufactures and exports it
to countries that still use it, especially for mosquito control. Certain
species of mosquitoes are vectors for malaria, which is considered to
be a greater risk than the toxic effects of the pesticide.
Toxicants come in different types
• Carcinogens are substances or types of radiation that cause cancer
• Mutagens are chemicals that cause mutations in the DNA of
organisms.
• Chemicals that cause harm to the unborn are called teratogens.
• Neurotoxins assault the nervous system
• Allergens over activate the immune system, causing an immune
response when one is not necessary.
• Endocrine disruptors are toxicants that interfere with the endocrine
system.
Toxicants may concentrate in water
• Water runoff often carries low amounts of toxicants from large areas
of land and concentrates them in small volumes of surface water.
• Many chemicals are soluble in water, and thus are very accessible to
organisms. This is why aquatic animals such as fish, frogs, and stream
invertebrates are especially good indicators of pollution.
Airborne substances can travel widely
• Because many chemical substances can be transported by air,
chemicals can exert impacts far from the site of their origin and use.
Airborne transport of pesticides is sometimes termed pesticide drift.
• Earth’s polar regions are particularly contaminated, because patterns
of global atmospheric circulation tend to move airborne chemicals
toward the poles. Thus, although we manufacture and apply
synthetic substances mainly in temperate and tropical regions,
contaminates are strikingly concentrated in the tissues of Arctic polar
bears, Antarctic penguins, and people living in Greenland.
Some toxicants persist
• DDT and PCBs have long persistence times, while Bt toxin has a very
short persistence time.
• Toxicants remain in the environment because they are designed to
persist. Some plastics, for example, were developed because they
resist breakdown.
• Some toxicants have breakdown products that are just as toxic as the
original chemical, or more so. For example, DDT breaks down into
DDE, a highly persistent and toxic compound.
Toxic substances may accumulate
and move up the food chain
• Fat-soluble toxicants such as DDT and DDE are absorbed and stored in
fatty tissues and may build up in animals in a process called
bioaccumulation.
• Toxic substances that bioaccumulate in the tissues of one organism
may then be transferred to other organisms in the food chain, in a
process called biomagnification.
• Polar bears in arctic Norway are suffering from PCB contamination
because of biomagnification, resulting in high cub mortality, and
persistence of toxins across generations.
Not all toxicants are synthetic, and not all
synthetic chemicals are toxic
• Toxic substances exist naturally in the environment around us and in
the foods we eat.
• Scientists have actively debated just how much risk is posed by
natural toxicants.
Studying Effects of Hazards
Wildlife studies integrate work in
the field and the lab
• Scientists study the impacts of environmental hazards on wild animals
to help conserve animal populations and also to understand potential
risks to people.
• Often wildlife toxicologists work in the field to take measurements,
document patterns, and generate hypothesis, and then head to the
laboratory to run controlled manipulative experiments to test ehir
hypotheses.
Human studies rely on case histories,
epidemiology, and animal testing
• In studies of human health, we gain much knowledge by studying sickened
individuals directly. This process of observation and analysis of individual
patients is known as a case history approach.
• Epidemiological studies involve large-scale comparisons among groups of
people, usually contrasting a group known to have been exposed to some
toxicant with a group that has not.
• The advantages of epidemiological studies are their realism and ability to
enable relatively accurate predictions about risk. Drawbacks include the
length of time it takes to obtain results and the inability to address future
effects of new hazards.
• Manipulative experiments are needed to truly nail down causation.
However, this is not possible with human subjects, so other animals are
substituted.
Dose-response analysis is a
mainstay of toxicology
• The standard method of testing lab animals in toxicology is called dose-response analysis.
• The dose is the amount of toxicant the test animal receives, and the response is the type or
magnitude of negative effects the animal exhibits as a result. The response is generally quantified
by measuring the proportion of animals exhibiting negative effects.
• Once a dose-response curve is plotted, scientists can calculate a convenient shorthand gauge of a
substance’s toxicity- the amount of toxicant it takes to kill half the population of study animals
used (LD50)
• Nonlethal health effects are determined by the level of toxicant at which 50% of the population is
affected (ED50).
• Common sense suggests that the greater the dose, the stronger the response will be. However,
sometimes responses occur only above a certain dose, called the threshold dose.
• Sometimes responses decrease with dosage. Some dose-response curves are U-shaped, Jshaped, or shaped like an inverted U; these curves appear to apply to endocrine disruptors.
• Knowing the shape of the dose-response curve is important for predicting effects. For some
toxicants, such as endocrine disruptors
Endocrine disruption poses
challenges for toxicology
• Because so many novel synthetic chemicals exist in very low concentrations over
wide areas, many scientists suspect that we may have underestimated the
dangers of compounds that exert impacts at low concentrations.
• The idea that synthetic chemicals might be altering the hormones of animals was
not widely appreciated until the 1996 publication of the book Our Stolen Future,
by Theo Colburn, Dianne Dumanoski, and J.P. Myers.
• Today, thousands of studies have linked hundreds of substance to effects on
reproduction, development, immune function, brain and nervous system
function, and other hormone-driven processes in animals. Many studies also
suggest impacts on people.
• Much of the research into hormone disruption has brought about strident
debate, partly because a great deal of scientific uncertainty is inherent in any
young and developing field, and that negative findings about chemicals pose an
economic threat to the manufacturers of those chemicals.
Individuals vary considerably in their
response to hazards
The type of exposure can affect the response
• The toxicity of many substances varies according to whether the
exposure is in high amounts for short periods of time –acute
exposure- or in lower amounts over long periods of time-chronic
exposure.
• Acute exposure is easier to recognize but chronic exposure is more
common, and is more difficult to detect and diagnose.
Mixes may be more than the
sum of their parts
• Traditionally, environmental health has tackled the effects of single
hazards one at a time, and single-substance tests have revieved
priority. This is changing, but scientists will never be able to test all
possible combinations.
Risk Assessment and Risk
Management
We express risk in terms of probability
• Risk can be measured in terms of probability, a quantitative
description of the likelihood of a certain outcome, The probability
that some harmful outcome (for instance, injury, death,
environmental damage, or economic loss) will result from a given
action, event, or substance expresses the risk posed by that
phenomenon.
Our perception of risk may not match reality
Risk assessment analyzes risk quantitatively
• The quantitative measurement of risk and the comparison of risks
involved in different activities or substances together are termed risk
assessment.
• Assessing risk for a chemical substance entails several steps:
• The first steps involve the scientific study of toxicity we examined abovedetermining whether a substance has toxic effects and, through doseresponse analysis, measuring how effects vary with the degree of exposure.
• Subsequent steps involve assessing the individual’s or population’s likely
extent of exposure to the substance, including the frequency of contact, the
concentrations likely encountered, and the length of encounter.
Risk management combines science and
other social factors
• Accurate risk assessment is a vital step toward effective risk
management, which consists of decisions and strategies to minimize
risk.
• In most developed nations, risk management is handled largely by
federal agencies.
Philosophical and Policy
Approaches
Two approaches exist for determining safety
• One approach is to assume that
substances are harmless until
shown to be harmful- the
innocent-until-proven-guilty
approach.
• This approach encouraged
technological innovation but may
put some dangerous substances
into wide use.
• The other approach, called the
precautionary principle, is to
assume hat substances are
harmful until shown to be
harmless.
• This enables us to identify
toxicants before they are released
into the environment, but may
also impede technological and
economic advances.
Philosophical approaches are
reflected in policy
• Most nations follow a blend of the two approaches.
• At present, European nations follow the precautionary principle.
• The U.S. largely follows the innocent-until-proven-guilty approach.
• In the U.S., the tracking and regulation of synthetic chemicals is
shared among several federal agencies.
EPA regulation is only partly effective
• The EPA also regulates diverse chemicals under the Toxic Substances
Control Act (TSCA).
• Many public health and environmental advocates view TSCA as being too
weak.
• The registration process involves risk assessment and risk management.
• Because the registration process takes economic considerations into account,
critics say it allows hazardous chemicals to be approved if the economic
benefits are judged to outweigh the hazards.
Toxicants are regulated internationally
• In 2007, the European Union’s REACH (registration, evaluation,
authorization and restriction of chemicals) program went into effect.
The burden of proof for chemical safety shifted from governments to
industry. REACH will also test previously authorized chemicals for
toxicity; 1,500 chemicals should become restricted.
• These new regulations are expected to cost as much as $7 billion, but
the benefits to public health are estimated to be $67 billion.
• In 2004, an international treaty, the Stockholm Convention, was
ratified by over 140 nations. The convention aims first to end the use
and release of 12 persistent organic pollutants (POPs) called the “dirty
dozen”. It appears to be on its way to ratification.
Conclusion
• International agreements such as the Stockholm Convention
represent a hopeful sign that governments will act to protect the
world’s people, wildlife, and ecosystems from harm by toxic chemicals
and other environmental hazards.
• A society’s philosophical approach to risk management will determine
what policy decisions it makes.