Download Life in the Dead Zone

Chapter 7
Human Health and Environmental
Toxicology
Overview of Chapter 7
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Human Health
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Environmental Pollution and Disease
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Health issues in developed countries
Health issues in developing countries
Environmental Contaminants
Endocrine Disrupters
Determining Health Effects of Pollutants
Ecotoxicology
Risk Assessment
Human Health
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Two indicators of human health in a given
country are:
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Life expectancy- how long people are expected to
live
Infant mortality- how many children die before age
of 1 year
Vary greatly
between countries
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Developed countries
Developing countries
Health Issues in
Highly Developed Countries
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By many measures- health is good in these
countries
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Average life expectancy
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Great sanitation
Few childhood diseases
Men = 75 years
Women = 80 years
Leading causes of death in US:
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Cardiovascular disease
Cancer
Chronic Obstructive Pulmonary Disease (of the lungs)
Health Issue in
Highly Developed Countries
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Premature deaths caused by individual lifestyle
decisions
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Poor diet
Lack of exercise
Smoking
Obesity is big problem
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Body Mass Index (BMI)
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(Weight X 740)/ (height (in))2
If your BMI is less than 18.5, you are underweight
If your BMI is 18.5-24.9, you are at a healthy weight
If your BMI is 25-29, you are overweight
A BMI of greater than 30 is obese
Health Issues in Developing Countries
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Biggest problems
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Malnutrition, unsafe water, poor sanitation
Life Expectancy
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Overall is 65 years
Very poorest developing countries = 45 years
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Most of these countries have high AIDS epidemics
Childhood mortality is high (18% of deaths)
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Diarrheal diseases
Malnutrition
Malaria
AIDS/HIV
Emerging and Reemerging Diseases
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Emerging Disease - not
previously observed in
humans
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Usually jumps from animal
host
Ex: AIDS, lyme disease,
West Nile Virus, SWINE
FLU!!!!!
Reemerging Disease- existed in the past
and are recently increasing in incidence
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Ex: tuberculosis, yellow fever, malaria
Reasons for Emergence/Reemergence
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Evolution of disease so it can move to human
host
Evolution of antibiotic resistance in disease
Urbanization and overcrowding
Increased pop. of elderly- susceptible to
disease
Pollution and environmental degradation
Growth in international travel and commerce
Poverty and social inequality
Environmental Pollution and Disease
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Often difficult to
link pollutants to
their effects on
people
Three ways to
analyze toxic
effects of
pollutants:
1.
2.
3.
Persistence
Bioaccumulation
Biomagnification
1. Persistence
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A characteristic of certain chemicals that are
extremely stable and may take many years to be
broken down into simpler forms by natural
processes
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Synthetic chemicals (those not found in nature)
Ex: DDT
Natural decomposers (bacteria) have not
evolved a way to break it down
Bioaccumulation
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The buildup of a persistent toxic substance in
an organism’s body, often in fatty tissues
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Synthetic chemical do not metabolize well
They remain in the body for extended periods of
time
Biomagnification
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The increased
concentration of
toxic chemicals in
the tissues of
organisms that are
at higher levels in
food webs
Diagram is
example of
biomagnification
of DDT
Endocrine Disrupters
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A chemical that mimics or interferes with the
actions of the endocrine system in humans and
wildlife
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Examples include:
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i.e. It effects the ability of the hormones in the
organisms to function properly
PCBs, Dioxins
Heavy metals – lead and mercury
DDT
Animals exposed to these chemicals have altered
reproductive development and are often sterile
Endocrine Disrupters
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Case Study: 1980 chemical spill into Lake
Apopka, FL
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Male alligators began to exhibit low testosterone
levels and high estrogen levels
Endocrine Disrupters and Humans
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Infertility and hormonally related cancers
are increasing
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Phthalates have been implicated as
potential endocrine disrupters
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Breast cancer and testicular cancer
Common ingredient in: cosmetics, fragrances,
nail polish, medication, toys, food packaging
Cannot make a link between endocrine
disrupters and human illness
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Too few studies have been performed
Determining Health Effects of Pollutants
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Toxicology is the study of the effect of
toxicants on the human body
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Acute toxicity
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Toxicant- chemical with adverse human health
effects
Adverse effects occur within a short period
after exposure to toxin
Chronic toxicity
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Adverse effects occur some time after
exposure, or after prolonged exposure to toxin
Symptoms often mimic other diseases- hard to
assess source
Toxicity
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Toxicity measured by dose and response
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Dose: amount that enters the body of an exposed
organism
Response: the amount of damage caused by a specific
dose
Dose – Response Curve
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Typically the dose is plotted against the percentage
of the population of test organisms showing the
response…on logarithmic graph paper
Toxicity
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Dose-Response Curve
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Illustrates the effect of different doses on a population
Threshold Level
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Threshold
Level
Maximum dose with no measurable effects
Toxicity: Dose-Response Curves
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ED50 = Effective Dose
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The dose that causes 50% of the population to
exhibit whatever effect is under study (effective
dose)
LD50 = Lethal Dose
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The dose that is lethal to 50% of the test organisms
Smaller the LD50, the more lethal the chemical
Determined for all new synthetic chemicals
ED50
ED50
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This dose-response
curve demonstrates
two assumptions of
classical toxicology.
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The biological response
increases as the dose is
increased
There is a “safe” dose
below which there is no
response (the
threshold level)
Results of Toxicology Testing
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Dose response
curves for 2
hypothetical
toxicants, A and B
Toxicant A has a
lower Effective
Dose than toxicant
B
Toxicant B,
however, is MORE
toxic at lower doses!
Results of Toxicology Testing
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Hormesis = occurs
when a toxin is
healthy at low doses
(necessary) but
harmful at high
doses (cadmium,
vitamin D, etc)
Aka the “hormetic
effect”!
Children and Chemical Exposure
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Children more susceptible
to chemicals
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Weigh less than adults
Bodies are still developing
Play on floors and lawns
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Exposed to cleaning products
and pesticides
Put things into their mouths
Diagram
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Children in foothills not
exposed to pesticides
Children in valley were
exposed
Identifying Cancer Causing Substances
(Carcinogens)
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Toxicologists
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Dose rats with varying levels of chemicals to see if
they develop cancer
Difficult to extrapolate results to humans
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Both mammals, but very different body size, metabolic
rates, diet, etc. Humans may respond the same as rats,
or very differently for a given toxin!
Doses given to animals are usually much larger than the
typical doses humans are exposed to!
Lab animals only live about 2 years…humans 75-80!
Human exposure is much more sporadic…and involves
multiple chemicals and exposure pathways
Toxicology vs. Epidemiology…
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Epidemiologists
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Look at historical exposure of groups of humans
See if exposed group have increased cancer rate
Make generalizations about risk based upon
likelihood of exposure and effects.
A very uncertain science!
Chemical Mixtures
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Most studies look at one chemical, but humans tend to
be exposed to chemical mixtures
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Chemical Mixtures interact by
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Ex: automobile exhaust
Additivity = exactly what one would expect, the combined
effect of two toxins is the sum of the two toxins
Synergy = when the effect of two toxins has a greater
combined effect than the sum of the two individual toxins
Antagonism = when the combined effect of two toxins is less
than the sum of the two individual toxins
Toxicity studies are expensive and take a while to
complete
Chemical Testing
Ecotoxicology
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Dilution Paradigm is not valid
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Boomerang Paradigm is accepted
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“Dilution is the solution to pollution”
“What you throw away can come back and hurt
you”
Ecotoxicology
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The study of contaminants in the biosphere
and their harmful effects on ecosystems
Helps policy makers determine costs and
benefits of industrial and technological
“advances”
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And how they often adversely effect ecosystems
Case Study: The Ocean
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Land based nutrient and
pollution runoff into ocean
is affecting
microorganisms
Ex: Red Tide
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Red pigmented poisonous
algal blooms
Toxins kill off fish and
make humans sick
Red Tides…. (Diatoms)
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Algal bloom = a sudden
increase in the diatom
population in shallow coastal
waters
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“Brown tides” on Long Island
were a sudden diatom bloom
that occurred in the
1980’s…and devastated the
scallop industry….no known
cause for this!
Harmful Algal Blooms
(HAB’s) are now monitored
by NOAA
Harmful Algal Blooms Bulletin…
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See a HAB bulletin from
January 2008 for NE
Florida
Gulf of Mexico
“The Dead Zone”…
Can you tell the difference?
The Dead Zone
• The dead zone is a large area of the Gulf of
Mexico, where the Mississippi River drains and
deposits sediment into the delta
• Hypoxia = an oxygen-free condition; this is why
the area is “dead”
– this occurs in the Gulf of Mexico due to excess
nutrient loading from the Mississippi River
watershed
D.O. contours show the extent…
Hypoxia:
• Every summer, this environmental phenomenon
occurs off the coast of Louisiana, covering over 7,000
square miles of the Gulf of Mexico at times.
• The Gulf of Mexico "Dead Zone", or hypoxic zone, is
an expanse of oxygen-depleted waters that cannot
sustain most marine life.
• This hypoxic zone is caused by excessive amounts of
nitrogen pollution delivered to the Gulf by the
Mississippi River, and the subsequent eutrophication
process (dead algae eaten by bacteria)
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The Dead Zone….
• The Dead Zone has become a serious threat to
commercial fishing, shrimping and recreation
industries.
• The livelihoods of many thousands of people and
their communities are at risk, as is the large marine
ecosystem on which they depend.
• The vast size of the Dead Zone and the severity of its
impact are largely a consequence of human activity —
such as river course and landscape alterations,
industry, municipal waste treatment and agriculture —
throughout the Mississippi River Basin.
The Dead Zone….
• Human activity has resulted in enormous
increases in the amount of dissolved inorganic
nitrogen delivered to the Gulf by the Mississippi
River.
• Current estimates suggest that three times as
much nitrogen is being carried into the Gulf
today compared with levels 30 years ago or at
any previous time on record.
Life in the Dead Zone
• During the summer months of low oxygen, while fish
and other mobile animals can escape the developing
Dead Zone, bottom dwellers that are attached to the
ocean floor are doomed as the normal bottom
ecosystem collapses.
• Significantly, when the autumn mixing brings oxygen
levels back to normal, the bottom communities do not
have the chance to revive. Instead, the area tends to
be re-colonized by only a few short-lived species
(such as polychaete worms) that can establish
themselves in the aftermath of the Dead Zone.
Life in the Dead Zone
• Larger, longer-lived species (such as
gastropods, bivalves, starfish, brittle stars and
sea anemones) vanished from this part of the
Gulf 30-40 years ago.
• These new bottom communities fall far short of
the normal ecosystems in diversity, abundance
or biomass.
• Ken Teague of the U.S. Environmental
Protection Agency says “In the Dead Zone, the
original bottom communities were lost a long
time ago.”
Risk Assessment
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Risk- probability that a particular adverse effect will
result from some exposure or condition
Risk Assessment = the use of statistical methods to
quantify the risks of a particular action so they can
be compared or contrasted with other risks
We assess risk daily with four steps
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2.
3.
4.
Hazard identification
Dose response assessment
Exposure assessment
Risk characterization
Risk Assessment
Risk Assessment
Using Risk Assessment
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Risk assessment is used in several ways for
environmental regulation
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Government may establish a “maximum risk” (one in
one million chance, for example) standard for a
toxin, or a “Maximum Contaminant Level” (actual
dosage) that people should not be exposed to
MCL is what is “feasible” considering cost and
available technology
MCLG is the dosage “goal” that the EPA is striving
for to protect health better
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Example: TCE (Tri-chloro-ethylene) has an MCL of 0.005
mg/L and a MCLG of 0.000 mg/L
NOTE: mg/L is the same as ppm
Ecological Risk Assessment
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Difficult to assess because effects occur
at wide range of scales
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Human-induced environmental stressors
also range greatly
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Individual plants and animals
Ecological communities over wide regions
Good to bad
Acceptable to unacceptable
There is a need to quantify risks to the
environment
Case Study on Ecological Risk Assessment
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Snake River Ecosystem in Southern Idaho
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River provides hydroelectric power and water for
irrigation
Human use causes reduced flow, elevated water
temperature and nutrient enrichment
Results in decrease
in fish, algal blooms
Ecol. Risk
Assessment
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Used to help
government and
locals set priorities
to manage and
protect ecosystem
Addressing Environmental Problems
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Case in Point: Lake Washington
•Scientific
assessment (U. of
Washington)
•Public education
and involvement
•Political action
(Washington
Pollution Control
Commission)
Addressing Environmental Problems
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Case in Point: Lake Washington
Evaluation
Addressing Environmental Problems
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Case in Point: Lake Washington
Evaluation
Precautionary Principle!
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“An ounce of prevention is worth a pound of
cure”…
When a new technology or chemical product is
suspected of threatening health or the
environment, precautionary measures should be
taken, even if there is uncertainty about the
scope of danger.
Puts the burden of proof on the developers of
the new technology or substance
Critics of this principle often cite the extensive
cost of “proving” safety of a
substance/technology, and a negative economic
impact.