Pesticides

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Pesticides

• Aquatic Ecotoxicology Lecture
• November 19, 2003
• Dr. Matt Moore
• USDA Agricultural Research Service
• National Sedimentation Laboratory
• Oxford, Mississippi

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Suggested Reading
Silent Spring (1962 1994) Our Stolen Future
(1996) Aquatic Dialogue Group Pesticide Risk
Assessment and Mitigation (1994) Principles and
Methods of Toxicology (1994) USGS book series on
pesticides
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• EVERYTHING IS A STIMULUS RESPONSE REACTION
• 3 Types of Stimuli
• A. Physical
• B. Biological
• C. Chemical
• What is a pesticide?
• FIFRA definition
• What are the types of pesticides?

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Types of pesticides

• Insecticides
• 1. Organochlorines
• 2. Organophosphates
• 3. Carbamates
• 4. Biological / botanical / pyrethroids
• 5. Pyrrole

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Types of pesticides

• Herbicides
• 1. Chlorphenoxy
• 2. The Quats (para- and di-)
• 3. Triazine
• 4. Acetamides
• Fungicides
• 1. Pentachlorophenol
• Rodenticides
• 1. Warfarin
• 2. Strychnine

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Types of pesticides

• Acaracides
• Molluscicides
• Etc.

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• What are some important properties of pesticides?
• Water solubility
• Photolysis, hydrolysis, volatilization
• Table 1

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Insecticides

• -Most work on nervous system
• -Toxicity mechanism of most insecticides is
  similar in mammals and insects
• -Selectivity is primarily in the dose
• -Dose vs. Exposure

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Insecticides

• ORGANOCHLORINES
• 3 general classes (focus on just 2)
• DDT and related compounds
• Chlorinated cyclodienes
• Aldrin
• Dieldrin
• Heptachlor

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Insecticides

• ORGANOCHLORINES
• Limited vapor pressure
• Very low water solubility
• High lipophilicity TROUBLE

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Insecticides

• ORGANOCHLORINES
• Limited vapor pressure
• Very low water solubility
• High lipophilicity TROUBLE

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Insecticides

• ORGANOCHLORINES
• DDT
• First synthesized in 1874
• Insecticidal properties discovered by Paul M?ller
  (Ciba-Geigy) in 1939 Nobel Prize
• Control animal pests, disease vectors (mosquito),
  ectoparasites on farm animals
• Used as emulsifiable concentrate and spray
• Started noticing problem w/ American robins while
  spraying for Dutch Elm Disease

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Insecticides

• ORGANOCHLORINES
• DDT
• MODE OF ACTION
• --within nerve cell action potential, holds
  sodium channel open longer than usual
• --result in delayed repolarization, but still
  no precise understanding
• 7. Banned in US 1972 still in use elsewhere

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Insecticides

• ORGANOCHLORINES
• Chlorinated Cyclodienes
• (Chlordane, Dieldrin, Aldrin, Endosulfan)
• As a class, they are significantly more toxic
  than DDT-type pesticides
• Endosulfan still has limited registration for use
  on food

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Insecticides

• ORGANOPHOSPHATES
• Developed in Germany during WWII as a substitute
  for nicotene to control aphids
• Inhibit acetylcholinesterase
• HOW
• WHERE
• Example in bird migration
• Produced for warfare
• Most OPs are lipophilic

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Insecticides

• ORGANOPHOSPHATES
• Less stable than organochlorines (OCs)
• Largely short-term (acute) toxicity
• More polar and water soluble than OCs
• Largely replaced OCs as pesticides of choice

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Insecticides

• ORGANOPHOSPHATES
• EXAMPLES
• Chlorpyrifos use decreased by 62 in last
  decade
• Diazinon (being phased out by EPA) termite
  fire ant
• Parathion - weak inhibitor of cholinesterase
  highly toxic in cells due to conversion to
  paraoxon promoted by CP450 in endoplasmic
  reticulum 9000X more toxic than parathion itself

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Insecticides

• ORGANOPHOSPHATES
• EXAMPLES
• Malathion degrades to non-toxic OP by mammalian
  carboxyesterases used in boll weevil eradication
• Methyl parathion 50X more toxic to mammals than
  malathion use has increased 86 over the last
  decade

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Insecticides

• CARBAMATES
• Derivatives of carbamic acid
• Developed more recently than OCs and Ops
• Acetylcholinesterase inhibitors
• EXAMPLE Aldicarb (systemic insecticide)

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Insecticides

• BIOLOGICAL / BOTANICAL
• Nicotine
• Isolated from leaves of tobacco plant
• Uses recorded at least 200 years ago
• Rotenone
• Derived from roots of Derris, Lonchocarpus,
  Tephrosia
• Commercial insecticides in 1930s
• Flavonoid derivative strongly inhibits
  mitochondrial respiration
• Highly toxic to fish
• Can be used in smaller amounts to paralyze fish
  for consumption
• Relatively non-toxic in humans
• Exempt from requirement of an EPA tolerance when
  applied to growing crops

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Insecticides

• BIOLOGICAL / BOTANICAL
• Pyrethroids
• 1. Originally derived from chrysanthemum
  plants
• 2. Significant insecticidal properties
• 3. Led to derivation of synthetic pyrethroids
  which have better photostability and are
  generally more active than their
  natural counterparts
• 4. Potential benefits?
• 5. Potential problems?
• EXAMPLES Permethrin, Cypermethrin,
  Deltamethrin, Fenvalerate, Esfenvalerate,
  Lambda-cyhalothrin, bifenthrin

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Insecticides

• BIOLOGICAL / BOTANICAL
• Biological
• Bt (Bacillus thuringiensis)
• --endotoxin
• --when ingested by insects, toxin causes
  paralysis of the gut
• --or may kill by bacterial growth if endospore
  germinates

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Herbicides

• Comprise 70 of currently applied pesticides
• Many different classes, but we will focus on 5
  briefly
• Typically characterized as very water soluble,
  with little no effects on non-targets
  (especially vertebrates / invertebrates)

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Herbicides

• CHLORPHENOXY
• One of most important groups of herbicides
• 2,4-D
• Disturb growth processes by interfering with
  transport of nutrients similar to natural growth
  regulator indole acetic acid
• Selectively toxic between monocots and dicots
• Mainly used to weed out dicots in monocot crops
• TCDD (dioxin) Agent Orange (2,4-D 2,4,5-T)

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Herbicides

• THE QUATS (Bipyridyls)
• Formerly most applied herbicide in global market
• Primarily two herbicides Paraquat and Diquat
• Diquat registered for aquatic uses
• Paraquat (and diquat) are quick acting widely
  used
• Target anything green (chlorophyll)
• Use in cotton for defoliation
• Hazardous to humans (lungs)

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Herbicides

• ACETAMIDES
• Main example PROPANIL
• Formerly most applied rice herbicide 63
  decrease in usage over last decade
• Lack of acylamidase enzymes in target plants
  (e.g. barnyard grass) causes plant death
• Fairly low toxicity to non-target organisms (when
  compared to expected environmental concentrations
  EECs)

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Herbicides

• GLYPHOSATE
• Use increased 93 in last decade
• Round-Up
• Monsanto Round-Up ready soybeans corn
• Genetic engineering debate

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Herbicides

• TRIAZINES
• Atrazine is most popular type of triazine applied
• Commonly found in Midwest groundwater wells
• Relatively non-toxic to MOST non-target
  vertebrate and invertebrates
• Recent arguments..

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Other Pesticides
FUNGICIDES Pentachlorophenol --used as
fungicide and wood preservative since the
1930s --35 million lbs / year produced in US
(1985) --uncouples oxidative phosphorylation
by inhibition of Na and K ATPase
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Other Pesticides
RODENTICIDES 1. Warfarin --Vitamin K
antagonist (required for blood clotting) --lo
w water solubility --lipophilic --Second
generation of warfarins Super Warfarins are
200x more potent than original warfarin
Half-life is 60x longer
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Other Pesticides
RODENTICIDES 2. Strychnine --kills birds,
rodents, moles, predatory animals --human
effects similar to animals --blocks neuronal
excitability, sensory stimuli produce
exaggerated reflex actions --Treatment
DIAZEPAM (anti-depressant)
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Pesticide Regulation
National pesticide control first attempted
by Insecticide Act of 1910 Targeted more to
prevention of fraudulent products rather than
misuse of poisons 2 Principle Laws of
Pesticides 1. Federal Insecticide, Fungicide,
and Rodenticide Act (FIFRA) 2. Federal
Food Drug and Cosmetic Act (FFDCA)
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Pesticide Regulation
FIFRA --First enacted in 1947 amended in 1959
1961 --Emphasized consumer protection product
efficacy --Must be registered before being sold
or distributed in interstate commerce --Amended
again in 1964 thanks to Silent Spring
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Pesticide Regulation
FIFRA --Prior to 1970, USDA controlled approval
under FIFRA --Passed responsibility onto US
EPA --Major FIFRA overhaul in 1972 a.
Registration was more restrictive b. Burden of
proof was on manufacturer
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Pesticide Regulation
FIFRA --1978 further amendments a.
Streamline registration w/ generic
reregistration reviews b. Added authority to
grant conditional
registration c. Resolve data issues of
propriety and compensation
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Pesticide Regulation
FIFRA --1988 amendments a. Require expedited
reregistration of existing pesticides to
ensure that registration are
supported by adequate data
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Pesticide Regulation
FIFRA Registration --Older pesticides which
were registered before the implementation of
current regulations and testing guidelines have
data base reviewed by EPA --If found
unsatisfactory for current requirements, data
must be repeated according to current
guidelines --After this, EPA issues a
Registration Standard --If deficiencies
exist, manufacturer may repeat studies or must
cancel registration
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Pesticide Regulation
FIFRA General ecotoxicology and environmental
testing 1. Ecotoxicity tests 2.
Environmental fate testing 3. Ecological risk
assessments Tiered ecological
testing ACUTE ? CHRONIC ? SIMULATED /OR FIELD
STUDY
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Pesticide Regulation
FIFRA Minimum tests to support registration of
outdoor-use 1. Avian single-dose oral toxicity
test 2. Avian dietary toxicity test w/ upland
game bird 3. Avian dietary toxicity test w/
waterfowl species 4. Freshwater fish acute
toxicity test w/ warmwater species 5.
Freshwater fish acute toxicity test w/ coldwater
species 6. Aquatic invertebrate acute toxicity
test w/ immature life stage (Other info may be
requiredestuarine, beneficials, etc.)
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Pesticide Regulation
FIFRA Initial toxicity data used for the
following Define acute toxicity of a.i. to
different aquatic and terrestrial
species Compare initial acute toxicity with
actual or EEC to assess potential
impact Provide data to determine whether or not
need for precautionary label Indicate need for
further laboratory /or field studies
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Pesticide Regulation
FIFRA Environmental Fate Testing 1. Significant
degradation routes 2. Primary degradates 3.
Degradation / metabolic pathway 4. Potential ½
life and persistence in environment 5. Dissipatio
n / mobility of chemical, potential
EEC Ecological Risk Assessments
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Pesticide Regulation
FFDCA Food Drug Administration (FDA) enforces
tolerances (residue limits) for pesticides on
food crops Delaney Clause (1958) in the Food
Additives Amendment states there shall be NO
measurable concentration of cancer-causing
substance (no matter the true risk) Compare
analytical chemistry in 1958 (LOD 20-100 ppm) to
analytical chemistry in 2003 (LOD ????)