Pesticides and the Environment

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Pesticides and the Environment
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Pesticides

• Fast acting
• Effective
• Emergency measure
• - - - Environmental effects

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Fate of applied insecticides and other pesticides

• Some insecticide applied lands on target pests
  but some lands on
• Natural enemies, pollinators
• Plant (residue issues if a food crop)
• On soil or washed off plants into soil

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Pesticide Resistance

• Frequent use of toxic materials can select for
  pests resistant to them (more common with insects
  and plant pathogens) minimize by
• Rotating chemicals
• Tolerating lower kills (less selection pressure)
  less frequent application, lower rates

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Non-Target Effects of Pesticides

• 1. Residues in crops or food (tolerance limits,
  regulated)
• 2. Selection for pesticide resistance
• 3. Direct kill of beneficial organisms (insect
  predators, pollinators, etc.)
• 4. Enter environment
• Air (volatilization, drift, e.g., methyl bromide)
• Soil
• Water (runoff or leaching)

Systemic materials !
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Non-Target Effects of Pesticides

• 1. Residues in crops or food (tolerance limits,
  regulated)
• 2. Selection for pesticide resistance
• 3. Direct kill of beneficial organisms (insect
  predators, pollinators, etc.)
• 4. Enter environment
• Air (volatilization, drift, e.g., methyl bromide)
• Soil
• Water (runoff or leaching)

Note many different kinds of nontarget effects
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Pesticides in the Environment
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Several different ways to classify pesticides

• Target pest (fungicides, insecticides,
  herbicides, nematicides, acaracides,
  rodenticides, etc.)
• Origin (natural vs synthetic product)
• Mode of action (growth regulator, systemic,
  contact, etc.)
• Formulation (dust, fumigant, water soluble, etc.)
• Chemical composition

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Environmental Effects Depend on Chemistry
When compounds break down, released elements like
N, P, C can be recycled
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Metal elements not further broken down, persist
in environment
Also As arsenic
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Potential for Breakdown/Persistence Depends on
Chemical Composition

• 1. Inorganic
• 2. Organohalides
• 3. Other organic compounds

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Potential for Breakdown/Persistence Depends on
Chemical Composition

• 1. Inorganic
• Pre-World War II
• often have persistent metals, e.g., CuSO4, Hg, Pb
  and As compounds.
• metal ions don't break down in environment

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Potential for Breakdown/Persistence Depends on
Chemical Composition

• 2. Organohalides
• contain Cl, Br
• most used from World War II -1970s
• large molecule breaks down (but often very
  slowly) and Cl, Br don't break down further in
  environment.

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Potential for Breakdown/Persistence Depends on
Chemical Composition

• 3. Other organic compounds (organophosphates,
  carbamates, insect growth regulators, etc.)
• mostly newer materials
• break down into common elements (e.g., C, N, O,
  S, P) that are nontoxic and recycled in
  environment.

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Environmental Effects Depend on Chemistry
When compounds break down, released elements like
N, P, C can be recycled
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Pesticides in Soil and Groundwater

• 1. General pathway for degradation
• Organic compounds
• ?
• Hydrolysis
• ?
• Some intermediate products still
• toxic and provide control
• ?
• Degradation by soil microflora
• ?
• Movement through soil
• (into water table)

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Pesticides in Soil and Groundwater

• 1. General pathway for degradation
• Organic compounds
• ?
• Hydrolysis
• ?
• Some intermediate products still
• toxic and provide control
• ?
• Degradation by soil microflora
• ?
• Movement through soil
• (into water table)

Depends on how long material remains in soil vs
moves through water
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Pesticides in Soil and Groundwater

• 2. Rate of movement through soil into
  groundwater depends on
• a) Solubility
• b) Half life (persistence of material)
• c) Soil depth (shallow vs. deep groundwater)
• d) Soil type and other soil properties
• Rao et al. (1985) - Table ranking solubilities
  and half lives of some common pesticides.

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Solubilities (S) and Half-lives of Pesticides
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Solubilities and Half Lives of Pesticides
High Solubility !
Rao et al., 1985
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Solubilities and Half Lives of Pesticides
Half Life
S
High solubility means high chance for groundwater
contamination
Rao et al., 1985
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Solubilities and Half Lives of Pesticides
Long Half Lives !
Rao et al., 1985
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Solubilities and Half Lives of Pesticides
Half Life
S
Long half lives typical of organohalides
Rao et al., 1985
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Biodegradation

• Breakdown of pesticides by soil microflora
• A normal process in soil
• Recycles pesticide residues to harmless and
  useful elements like N, P, S, etc.

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Accelerated or Enhanced Biodegradation

• Breakdown of pesticides by soil microflora
  proceeds too quickly.
• Noted in mid-1970s in corn growing area of US
• Standard management for corn rootworms at that
  time was carbofuran placed in soil at planting.
• In mid-1970s efficacy in protecting roots from
  damage was reduced.
• Insects were still susceptible to carbofuran.

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Accelerated or Enhanced Biodegradation

• Breakdown of pesticides by soil microflora
  proceeds too quickly.
• Noted in mid-1970s in corn growing area.
• Standard management for corn rootworms at that
  time was carbofuran placed in soil at planting.
• In mid-1970s efficacy in protecting roots from
  damage was reduced.
• Insects were still susceptible to carbofuran.
• Soil levels of carbofuran in certain areas were
  very low.
• Several bacteria in these areas were found to use
  carbofuran as a food source ( accelerated or
  enhanced biodegradation).

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Accelerated Biodegradation

• Can affect efficacy of soil pesticides in some
  cases
• heavy, frequent use selects for microflora
  capable of breaking down specific chemical
  products.
• breakdown may be so rapid that product is
  ineffective, especially if targets are soilborne
  pests, like soil insects or nematodes.
• note difference from pesticide resistance.
• examples (1970s-1980s) - decline in efficacy of
  soil insecticides in U.S. corn belt (Felsot,
  1989).

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Accelerated Biodegradation

• 3. Remedies for accelerated biodegradation
  (Felsot, 1989)
• a) Adhere to IPM ? use only when needed.
• b) Proper calibration avoid overdose.
• c) Rotate chemicals and classes of chemicals
  used.
• d) Use alternative (non-chemical) methods when
  possible and effective.

Some have tried antibiotics !
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Bioaccumulation

• Cumulative buildup of toxic elements or
  compounds in the body of an organism.
• Organohalides very soluble in fat tissues of
  organisms, good candidates for bioaccumulation.

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Biomagnification Increase in concentration of
toxic products in higher consumers in food chains
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Biomagnification

• Most often seen as a problem in raptors and in
  higher aquatic predators.
• A particular problem with persistent elements
  like Cl, Br, metals, and persistent compounds
  like organohalides.
• Can be a problem in aquatic systems, far removed
  from agricultural sites.
• Results from bioaccumulation but note difference
  from bioaccumulation.

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With Bioaccumulation and Biomagnification, some
toxic effects reach beyond agricultural system
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Heavy Metals

• Persistent, can remain in site years after
  pesticide with metal was used
• Pesticides with metals not used much anymore
• Main source of metals in ag today is some
  amendments, especially municipal solid wastes,
  sludges, etc.
• Even if metal amount in amendment application is
  low, total amount accumulates on site over time

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References

• Text pp. 216-219 (intro to pesticides), pp.
  256-262 (pesticides in environment)
• Carroll et al. 1990. Ch.
• Felsot, 1989. Ann. Rev. Entomol. 34453-476.
• Rao et al. 1985. Soil Crop Sci. Soc. Fla. Proc.
  441-8.