A Brief Review of Chapters
11, 12, & 13 in Silent Spring
by Rachel Carson
By Jennifer Cunningham, Katie Tang,
and Robert Rock
• Gardening is now firmly linked with the super poisons.
• In 1960 the Florida State Board of Health found it
necessary to forbid the commercial use of pesticides in
residential areas.
• Weed and bug killing chemicals are hidden under brand
names. Never suggesting that they are harmful.
• A constant stream of
new gadgets make it
easier to use poisons
on lawns and gardens,
thus creating public
water to become
contaminated.
• Excessive use of poisons
such as DDT on lawns
and crop fields can cause
illness and even death if
exposed to too much.
• Most DDT found in the
human body enters
through the food we eat.
• The existence of
chemical residues on the
food we eat is played
down by the industry.
Toxins can be
concentrated in
successive trophic
levels of food webs.
A process called
biological
magnification.
Why Aren’t We Protected?
• Food and Drug Administration only has control over
foods shipping in interstate commerce, and there are not
enough inspectors on staff.
• Toxins can not be broken down by microorganisms and
other detritivores. Meaning the toxins stay with in the
environment for years or even decades.
• The longer food remains in storage, the greater the
danger of contamination.
• The chemical industry recognizes the frequent misuse of
insecticides and the need for education of farmers,
however refuses to do anything about it.
Carson’s Suggested Solutions
• First is the elimination of tolerances on highly toxic
chemicals.
• A vigilant and aggressive Food and Drug Administration,
with a greatly increase of spectators.
• The ultimate answer is to use less toxic chemicals so that
public hazard of their misuse is greatly reduced.
• Public education on the nature of the chemicals is greatly
needed
• Explore non-chemical methods.
• Eskimos on the far Arctic shores of
Alaska were found to have no DDT or
other toxins in there system at all.
• In fact, the only sign of pesticide was
in two white owls from Point Hope that
had migrated.
Chapter 12: The Human Price
“Today we are concerned with a different kind of hazard that lurks in our environment-a
hazard we ourselves have introduced into our world as our modern way of life has evolved.”
Ecology Vs. Environmentalism
Environmentalism
• Advocating for the protection or preservation of the natural
environment.
Ecology
• Often complicated and delicate relationships between organisms and
the environment.
To address environmental problems, we need to understand ecology.
Where do pesticides fit into the picture of
environmental disease?
Contaminate:
•
•
•
Soil
Water
Food
“..they have the power to make our streams fishless and our gardens and
woodlands silent and birdless.”
Population Growth
“For the population as a whole, we must be more concerned with
the delayed effects of absorbing small amounts of the pesticides
that invisibly contaminate our world.”
•Population Ecology is the study of populations in relation to the
environment.
•The biological effects of chemicals are cumulative over long
periods of time, and the hazard to the individual may depend on the
sum of the exposures received throughout his lifetime.
•The major forces affecting population growth-birth rates and death
rates-can be measured in many populations to predict how the
populations will change in size over time.
Idealized survivorship curves: Types I, II, and III
Figure1
•
A graphic way of representing the data in a life table is to
draw a survivorship curve.
•
1.
2.
3.
Survivorship Curves can be classified into three general types:
Type1 – relatively flat at the start, reflecting low death rates during early and middle life, then drops
steeply as death rates increase among older age-groups.
Type 2- intermediate, with a constant death rate over the life span.
Type 3- drops sharply at the left of the graph, representing very high death rates for the young, but then
flattens out as death rates decline for those who have survived to a critical age.
The Problem of ecology, of interrelationships, of
interdependence
Figure2: Examples of terrestrial and marine food chains
Figure3: An antarctic marine food web
Arrows trace energy and nutrients
Energy decreases as you travel up the chain.
•Decomposers are not shown
“A change in one point, in one molecule even, may
reverberate throughout the entire system to initiate changes
in seemingly unrelated organs and tissues.”
What is DDT?
•DDT is soluble in lipids, it collects in the fatty tissues of animals, and its
concentration is magnified in higher trophic level.
•One of the first signs that DDT was a serious environmental problem was a
decline in the populations of pelicans, ospreys, and eagles, birds that feed at the
top of the food chains. The accumulation of DDT in the tissues of these birds
interfered with the deposition of calcium in their eggshells, a trend that may have
already begun because of other environmental contaminants.
Birds that feed at the top of the food chain come in contact with DDT.
Lay eggs and try to incubate them.
The weight of the parents break the shells of affected eggs.
Catastrophic declines in their reproduction rates.
Chapter 13:
Through a Narrow Window
•Life is a very complicated thing and the effects
pesticides have on living organisms can be
difficult to understand when viewed from the big
picture.
•It is not until one looks closer, at the building
blocks of life, that the effect pesticides have on
living things can be understood.
• The most basic unit of an organism that can still be called living is the cell. It is
within each individual cell that the processes of life take place.
• The foods we eat go to cells so that they can make energy for the entire body.
Proteins and carbohydrates are broken down to create immense amounts of
energy.
•
•
•
•
The creation of energy occurs in the
mitochondria of a cell.
Here the energy created is stored in the form of
ATP (adenosine triphosphate).
ATP is used for energy storage in all living
things large or small.
The reason ATP is used for energy storage is
its ability to shift one of its phosphate groups to
another substance.
• If the mitochondria were incapable of creating
ATP the energy they produce would be lost.
•The efficiency of creating and keeping the
bond for the third phosphate group is vital for
organisms to survive.
• Sadly this is exactly what pesticides
attack. Insecticides such as phenols
and chlorinated hydrocarbons break
the third phosphate bond and rob cells
of vital energy
•
Without ATP sperm cells can’t swim to fertilize egg cells and fertilized egg
cells do not have the energy to divide and develop into new born animals.
• This attack on the basics of life is what makes
pesticides so dangerous.
• Affecting a single cell wouldn’t make much of a
difference, but the fact that a process that occurs
within every cell is being affected causes the
problem to be magnified.
•
•
The most dangerous thing about pesticides is not their disruption of cellular
development.
It is their disruption of the transmission of genetic information from one generation
to the next.
• Certain pesticides can destroy
chromosomes in some plants and change
genetic codes in others.
• This affect on the genetic information of
organisms causes mutations that can
cause serious birth defects in the next
generation.
• This danger is not limited to only plants
and animals.
• Humans too can fall victim to genetic
mutation at the hands of pesticides stored
in the body.
That’s the review of
chapters 11, 12, &13.
Any questions?