Chapter 22
The Pesticide Dilemma
http://smccd.net/accounts/snitovsky/bio215/Labs/bioins.html
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Pesticides
• Pesticides: toxic chemicals used to control
pests (weeds, rodents, insects, bacteria,
fungi…)
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Herbicides  weeds
Rodenticides  rats, mice, moles, voles
Insecticides  insects, arachnids
Fungicides  fungi, molds, yeasts
http://www.epa.gov/ebtpages/pollchemicals.html
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Narrow-Spectrum
• These pesticides would kill only the target
organism.
• It would biodegrade into C, H, & O.
• It also would not move throughout the
environment.
• However this “perfect pesticide” does not exist.
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Broad-Spectrum
• These pesticides kill a wide variety of organisms,
including beneficial ones.
• They do not readily break down but they turn
into secondary pollutants.
• They also move easily through ecosystems &
biomes (mobile).
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Pesticides
• 1st Generation Pesticides: produced prior to 1940
(before synthetics) & include inorganics,
organics, & botanicals.
• Botanicals are plant derived pesticides that are
produced as a natural plant defense.
• Ex: nicotine (tobacco), pyrethrin
(chrysanthemum), rotenone (Derris plant)
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Pesticides
2nd Generation Pesticides: synthetic (man-made)
pesticides mostly used after the 1940’s.
Ex: DDT dichloro-diphenyl-trichloroethane was
the first of the 2nd generation pesticides (1939).
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http://www.epa.gov/pesticides/about/types.htm
Major Groups of Insecticides
• Chlorinated hydrocarbons: Organic compounds
that contain Cl.
• These are mostly broad-spectrum pesticides.
Slow degradation & remain in the environment
& within organisms.
• Still in use; endosulfan, lindane, & methoxychlor.
• 1963 author Rachel Carson brought pesticides to
the public attention in Silent Spring.
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Major Groups of Insecticides
• Organophosphates: These contain phosphates &
were developed based upon nerve gas..; These are
more poisonous than other insecticides. They are
toxic to birds, bees, & aquatic organisms.
• These don’t persist in the environment as long as
the Hydrocarbons. Have replaced commercial use
of hydrocarbons.
• Ex: Methamidophos, dimethoate, & malathion.
http://www.crisny.org/not-for-profit/nycap/mosquitopaper.htm
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Major Groups of Insecticides
Carbamates: derived from carbamic acid. Are
broad-spectrum pesticides. Not as toxic to
mammals as organophosphates.
Ex: carbaryl & aldicarb
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Major Groups of Herbicides
• Nonselective: Kill all vegetation.
• Selective herbicides: kill only certain types.
A) Broad-leaf herbicides: Kill broad-leafed plant
but no grasses.
B) Grass Herbicides: kill grass but safe for most
other plants.
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Use of Herbicides in Vietnam
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Use of Herbicides in Vietnam
• 12 million gallons of herbicides to expose hiding
places & destroy crops of Vietcong.
Agent White, Agent Blue, and Agent Orange.
• Agent Orange is made of:
(2,4,-D) 2,4 dichlorophenooxyacetic acid &
(2,4,5-T) 2,4,5 trichlorophenooxyacetic acid
as well as dioxins.
Birth defects, stillbirths, cancer in Vietnam
Agent orange Syndrome in Vietnam Vets.
Benefits of Pesticides
• Disease control (malaria, west Nile)
• Crop protection (increase yields)
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Problems with Pesticides
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Genetic resistance
Imbalance in the ecosystem
Persistence of pesticides
Bioaccumulation in organisms
Biological magnification in food web
Mobility in the environment
Risks to human health (short-term & long-term)
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Problems with Pesticides
• Genetic resistance: inherited characteristics
(natural selection) that decrease the effect
of the pesticide on the pest.
• Resistance Management: a technique
employed to delay the evolution of genetic
resistance in a population to maximize the
effectiveness of a pesticide.
Methicillin-Resistant Staphylococcus aureus Infections
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5233a4.htm
Problems with Pesticides
• Imbalance in the ecosystem
http://www.indiana.edu/~bradwood/eagles/ddt2.htm
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Problems with Pesticides
DDE (dichlorodiphenyldichloroethylene) and
DDD (dichlorodiphenyldichloroethane) are chemicals
similar to DDT that contaminate commercial DDT
preparations.
DDE has no commercial use. DDT  Eagles  DDE
DDD was also used to kill pests, but its use has also been
banned. One form of DDD has been used medically to treat
cancer of the adrenal gland.
Imbalance in the ecosystem
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Problems with Pesticides
http://www.epa.gov/pbt/pubs/accomp99.htm
• Persistence: resistance to degradation
into less toxic forms.
Biological magnification
Bioaccumulation
Problems with Pesticides
• Bioaccumulation: the build up of a persistent
chemical (pesticide)within an organism.
• Biological magnification: an increase in the
chemical (pesticide) concentration of a pollutant
as it passes through successive trophic levels of a
food web.
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Problems with Pesticides
• Mobility in the environment
Pesticide Mobility in the environment
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Problems with Pesticides
Risks to human health 
Short-term:
Poisoning & irritation
Long-term:
Cancers
Endocrine disruption
Mental/physical retardation
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Solutions to the Pesticide Dilemma
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Using cultivation to control pests
Biological controls
Pheromones & hormones
Genetic controls
Bt & its potential & problems
Quarantine
Integrated Pest Management
Irradiating Foods
Solutions to the Pesticide Dilemma
• Using cultivation to control pests
Aphid infestation of Wheat & Barley
•Infestation was stopped by a local
resistant variety of these plants (not
a monoculture.)
Solutions to the Pesticide Dilemma
• Biological controls: utilizes naturally
occurring disease organisms, parasites,,
or predators to control pests.
• Sterile Male technique: reduces
population by “tricking” the females into
thinking their eggs have been fertilized
(sterile male can’t)
biological controls
• Aphids and Ladybeetles
www.ces.ncsu.edu/.../notes/ Fruits/NoteS-1.html
www.eap.mcgill.ca/Publications/ EAP53.htm
biological controls
Solutions to the Pesticide Dilemma
• Hormones: chemical
messengers produced by
organisms.
• Pheromones:
reproductive hormones
used to lure in the
opposite sex.
• Both are used to lure
pests into traps or to
confuse pests to prevent
mating.
Solutions to the Pesticide Dilemma
Scientists will use pheromones to
kill sea lamprey
Solutions to the Pesticide Dilemma
• Genetic controls: using genetic variation to
produce species that are resistant to pests.
• Selective breeding (genetic diversity)
Or
• Genetic engineering: the ability to take one
gene from an organism & place it into an
unrelated organism where it is expressed.
Solutions to the Pesticide Dilemma
• Case in Point: Bt, Its Potential & Problems
http://www.bt.ucsd.edu/crop_refuge.html
Solutions to the Pesticide Dilemma
• Quarantine: restricting the importation of
exotic plant & animal material that might
harbor pests.
Solutions to the
Pesticide Dilemma
• Integrated Pest
Management
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Solutions to the Pesticide Dilemma
• Irradiating Foods:
http://www.storewars.org/flash/index.html
Irradiating Foods
www.ext.vt.edu/pubs/foods/ 458-300/458-300.html
Pesticide Dilemma: Laws, Laws, Laws
• FDCA Food, Drug, and Cosmetics Act:
enacted in 1938 it recognized the need to regulate pesticides in
food (no means for regulation)
The Miller Amendment: passed in 1954, required
standards for levels of pesticides in food (acceptable
& unacceptable) Who decides? Criteria?
The Delaney Clause: 1958, no known carcinogens (lab
animals or humans) would be permitted in processed
foods. (based upon 1978 standards) Prior?
Pesticide Dilemma: Laws, Laws, Laws
• FIFRA: Federal Insecticide, Fungicide, &
Rodenticide Act:
1947, required testing & registration of the active
ingredients of pesticides. 1988 version targeted
older pesticides and new for ED50 and LD50
testing.
Pesticide Dilemma: Laws, Laws, Laws
• The Food quality Protection Act:
1996, amended both the FDCA and the FIFRA.
Set pesticide residue limits.
Revised The Delaney Clause to include raw &
processed foods.
Pesticide Dilemma: Laws, Laws, Laws
• Stockholm Convention on Persistent Organic
Pollutants: eliminate the production and use of
P.O.P’s (persistent organic pesticides).
• DDT falls into this category but will still be used
BY SOME.
External
External
Internal
Gene Splicing
GENE for
Nicotine
production
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Biotechnology
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Biotechnology
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Biotechnology
Each bacterial cell can now make nicotine.
Each bacterial cell has the gene for making
nicotine.
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