Chapter 23 The Pesticide Dilemma

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Chapter 23The Pesticide Dilemma
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Defining Pests

• Organism that is oxious, destructive
• Competes with us for food, invades lawns/gardens,
  destroys houses, spreads disease
• Injurious plant or animal

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Defining Pests

• Typical Characteristics
• Reproduce rapidly
• Migrate quickly
• Pioneers in ecological succession
• Compete aggressively against more specialized
  species
• Generalists

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Defining Pests

• Categories
• Agricultural pests feed on crops or ornamental
  plants
• Arachnids spiders, ticks, flour/grain/cheese
  mites
• Crustaceans woodlice/pill bugs,
  flour/grain/cheese mites
• Pathogens bacteria, viruses, fungi
• Rodents house mouse, common rat
• Insect pest examples

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Types of Pesticides

• Pesticides (Biocides) Chemicals developed to
  kill organisms that we consider undesirable.
• 1. Insecticides - Insect-killers
• 2. Herbicides - Weed-killers
• 3. Fungicides Fungus-killers
• 4. Nematocides Roundworm-killers
• 5. Rodenticides Rat- and Mouse-killers

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Pesticide Types

• First-generation pesticides
• Sulfur used as an insecticide since 500 BC
• Arsenic (As), lead (Pb) and mercury (Hg) by the
  1400s
• Nicotine sulfate extracted from tobacco leaves
  in the 1600s
• Pyrethrum obtained from the heads of
  chrysanthemum flowers
• Rotenone from the root of the derris plant
• Resistant pest populations developed

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Types of Pesticides

• Second-generation
• Since 1950 pesticide usage has increased 50 fold
  and toxicities have increased 10 fold.
• 10X more synthetic pesticides are used on the
  average home than on croplands in the US.
• 75 of synthetic pesticides are used in the
  developed countries

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Types of Pesticides

• About 2.5 million tons of pesticides are used
  yearly, worldwide.
• In the United States, about 630 different
  biologically active (pest-killing) ingredients
  and 1,820 inert (inactive) ingredients are mixed
  to make 25,000 different pesticide products.
• DDT 1939, Entomologist Paul Mueller discovered
  that DDT (dichlorodiphenyltrichloroethane) was a
  potent insecticide. It soon became the worlds
  most-used pesticide. Awarded a Nobel Prize in
  1948.
• Broad-spectrum agents toxic to many species
• Selective-spectrum agents effective against a
  narrowly defined group of organisms.

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Types of Pesticides
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Types of Pesticides

• 1. Persistence the length of time in which
  pesticides remain deadly in the environment this
  may vary from days to years.
• 2. Biomagnification the process by which toxins
  accumulate the higher you go in the food chain
  (generally because the toxin is not water soluble
  and therefore not easily excreted).

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Pesticide Types Chemical Structure

• o Inorganic pesticides (e.g. arsenic, copper,
  lead and mercury)
• Generally highly toxic
• Remain in soil forever
• Generally neurotoxins

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Types of Pesticides

• Natural organic pesticides (botanicals)
• Extracted from plants
• Nicotine toxic to a broad spectrum of organisms
• Rotenone used to kill fish
• Turpentine and phenols effective pesticides

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Types of Pesticides

• Fumigants (e.g. carbon tetrachloride, carbon
  disulfide)
• Generally small molecules
• Gasify easily
• Penetrate rapidly into a variety of materials
• Used to sterilize soil
• Prevent decay or rodent and insect infestations
  of stored grain
• Very dangerous to workers who apply them
• Use has been curtailed or banned altogether

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Types of Pesticides

• - Chlorinated Hydrocarbons (organochlorines)
  (e.g. DDT, chlordane, aldrin)
• Inhibit nerve membrane ion transport and block
  nerve signal transmission
• Fast acting and highly toxic in sensitive
  organisms
• Highly persistent in soil
• Stored in fatty tissues of a variety of organisms
  
• Become concentrated through food chains

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Types of Pesticides

• Organophosphates (e.g. parathion, malathion)
• Inhibit cholinesterase which is an enzyme
  essential for removing excess neurotransmitter
  from synapses in peripheral nervous system
• Extremely toxic to mammals, birds, and fish
• Less persistent in environment than
  organochlorines

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Types of Pesticides

• Carbamates (e.g. carbaryl, aldicarb)
• Share many organophosphate properties
• Extremely toxic to bees

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Types of Pesticides

• Microbial agents and biological controls
• Living organisms or toxins derived from them
  used in place of pesticides
• Some species of bacteria kill caterpillars or
  beetles by releasing a toxin that ruptures that
  digestive tract.
• Some parasitic wasps attack moth and caterpillar
  eggs

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Benefits of Pesticides

• Benefit Disease control
• Fleas, lice and mosquitoes carry disease

• Malaria- mosquito born
• 2.7 million people die each year
• Few drugs available, so focus is on killing
  mosquitoes
• DDT

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Benefits of Pesticides

• Disease Control
• Insects and ticks serve as vectors in the
  transmission of a number of disease-causing
  pathogens and parasites
• Diseases spread by biting insects
• o Malaria
• o Yellow fever
• o Encephalitis
• o Sleeping sickness
• Diseases can be reduced by judicious use of
  pesticides.

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Benefits

• Crop Protection
• Plant diseases, insect and bird predation, and
  competition by weeds reduce crop yields worldwide
  by at least 1/3.
• Without modern chemical pesticides, losses might
  be much higher.
• Farmers may save 3 to 5 for every 1 spent on
  pesticides.
• o Lower costs and generally better quality for
  consumers
• Cosmetic damage can greatly reduce the economic
  value of crops

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Pesticide Problems

• Effects on Nontarget Species
• Estimated that up to 90 of the pesticides we use
  never reach their intended targets.
• Many beneficial organisms are poisoned
  unintentionally as a result
• o Sometimes effects are immediate
• o Sometimes effects are not immediate and thus
  difficult to pin down
• A 1999 study linked insecticide (4-nonylphenol)
  spraying on Canadian forests with dramatic
  declines in Atlantic salmon

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Pesticide Problems

• Pesticide Resistance and Pest Resurgence
• Pesticides almost never kill 100 of a target
  species even under the most ideal conditions
• The most resistant members of a population
  survive pesticide treatment and produce more
  offspring like themselves with genes that enable
  them to withstand further chemical treatment.
• Pest resurgence because most pests propagate
  rapidly and produce many offspring, the
  population will quickly rebound with pesticide
  resistant individuals.
• Pesticide treadmill due to pesticide resistance,
  it takes constantly increasing doses to get the
  same effect

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Pesticide Problems

• Creation of New Pests
• Broadcast pesticide spraying may kill beneficial
  predators that previously kept a number of pests
  under control
• Higher trophic levels are more likely to be
  knocked out than lower ones.

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Pesticide Problems

• Persistence and Mobility in the Environment
• The qualities that make DDT and other chlorinated
  hydrocarbons so effective (stability, high
  solubility, and high toxicity), also make them
  environmental nightmares.
• o Some of the compounds have been discovered far
  from any possible source and long after they were
  used.
• o Can accumulate in polar regions through a
  series of evaporation, condensation, and
  precipitation events.
• o Have a high affinity for fat

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Pesticide Problems

• Breakdown by-products may still be present in the
  environment.
• In a 1999 study, breakdown by-product of DDT,
  p,p'-DDE , is found in the amniotic fluid of 30
  of a sample of pregnant women in Los Angeles, CA.
  
• o Atrazine and alochlor are widely used
  herbicides
• 30 of all community wells and as much as 60 of
  all private wells in the mid-western corn belt
  are contaminated with atrazine and alochlor.
• o Because of the ubiquity of these persistent
  organic pollutants (POPs), there is a widespread
  movement to ban them.

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Human Health Problems

• Pesticide effects on human health can be divided
  into 2 categories
• Short-term effects, including acute poisoning
  and illnesses caused by relatively high doses and
  accidental exposures.
• Long-term effects suspected to include cancer,
  birth defects, and immunological problems, and
  other chronic degenerative diseases.

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Health Problems

• The World Health Organization (WHO) estimates
  that between 2.5 and 5million people suffer from
  acute pesticide poisoning.
• o At least 2/3 of this illness and death results
  from occupational exposures in developing
  countries
• Long-term health effects difficult to document
  conclusively, however, links have been
  established.
• o Significant learning and attention problems in
  children whose mothers at Lake Michigan fish
  regularly
• o Children from farming communities where
  pesticide use is high had diminished growth and
  development as compared to children with minimal
  pesticide exposure

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Alternatives

• In many cases, improved management programs can
  cut pesticide use between 50 and 90 with
  reducing crop production or creating new diseases
  

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Alternatives

• Behavioral
• Crop rotation (growing a different crop in a
  field each year in a 2-to6-year cycle) keeps pest
  populations from increasing.
• Mechanical cultivation can substitute for
  herbicide treatment, but can increase erosion
• Flooding fields before planting can suppress
  both weeds and insect pests.
• Burning crop residues and replanting with cover
  crop can suppress weeds and insect pests.

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Alternatives

• Behavioral
• Habitat diversification
• Growing crops where pests are absent
• Adjusting planting times can avoid pest
  outbreaks
• Switching from monoculture to mixed polyculture
  
• Tillage at certain times

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Alternatives

• Biological predators or pathogens that can
  control many pests more cheaply and safely than
  broad-spectrum, synthetic chemicals
• o Bacteria can be sprayed on crops to control
  pests.
• o Ducks, chickens, and gees can rid fields of
  both insects and weeds.
• o Insects including mantises and ladybugs protect
  against a multitude of pests.

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Alternatives

• Biological
• Plants with insect-repelling properties such as
  garlic and marigolds.
• Herbivorous insects can be used to control
  weeds.
• Genetics and bioengineering
• Breeding livestock that tolerate pests well
• Hormones can be used to upset development or as
  sex attractants to bait traps containing toxic
  pesticides.

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Integrated Pest Management

• Integrated pest management (IPM) flexible,
  ecologically based pest-control strategy that
  uses a combination of techniques applied at
  specific times, aimed at specific crops and
  pests.
• Does not give up pest controls entirely.
• Enhances growth and diversity of beneficial
  organisms.
• Enhance plant defenses

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Systems Approach- Integrated Pest Management (IPM)

• IPM
• Combination of pest control methods that keeps
  pest population low without economic loss
• Conventional pesticides are used sparingly when
  other methods fail

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Systems Approach- Integrated Pest Management (IPM)

• Rice Production in Indonesia

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Benefits and Problems with Pesticides

• Problem Mobility in the Environment
• Do not stay where they are applied
• Move through soil, water and air

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Risk of Pesticides to Human Health

• Short-term Effects of Pesticides
• Handling food with pesticide residue

• Mild case nausea, vomiting, headaches
• Severe case damage to nervous system,

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Risk of Pesticides to Human Health

• Long-term Effects of Pesticides
• Cancer- lymphoma
• Breast cancer
• Sterility
• Miscarriage
• Birth defects
• Decreases bodys ability to fight infection
• Potential connection to Parkinsons disease

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Alternatives to Pesticides

• Irradiating Food
• Harvested food is expose to ionizing radiation,
  which kills many microorganisms
• Predominantly used on meats
• Somewhat controversial due to potential for free
  radicals

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Laws Controlling Pesticide Use

• Food, Drug, and Cosmetics Act (1938)
• Pesticide Chemicals Amendment (1954)
• Delaney Cause (1958)
• Federal Insecticide, Fungicide, and Rodenticide
  Act (1947)
• Food Quality Protection Act (1996)

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Manufacture and Use of Banned Pesticides

• Some US companies still make banned or seriously
  restricted pesticides
• Product is exported
• May lead to the importation of food tainted with
  banned pesticides
• Global ban of persistent organic pollutants
• Stockholm Convention on Persistent Organic
  Pollutants (2004)

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Manufacture and Use of Banned Pesticides