11' Agricultural Pollution: Pesticides

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11. Agricultural Pollution Pesticides

• Textbook Chapters 10.1 -10.3 16.6

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Pesticides

• Insecticides
• Herbicides
• Fungicides
• Rodenticides
• Fumigants
• Soil
• Grain
• Fruit
• Wood preservatives

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Pesticide use in the US, millions of pounds, Fig
16.9
Other includes pool chemicals wood treatment,
rodenticides, etc
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Inorganic pesticides

• Before the advent of modern organic chemistry, of
  the few pesticides available, many were
  inorganic.
• E.g.
• Insecticides
• Arsenic grasshopper bait
• Boric acid
• Sulfur dust

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Inorganic pesticides (cont.)

• Fungicides
• Bordeaux spray (CuSO4)
• NaCl
• Some of these chemicals like As and Cu are not
  very mobile and do not degrade in soils.

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Natural organic pesticides

• insecticides
• Rotenone - root extract.
• Pyrethrum - flower extract.
• Herbicide
• Petroleum oil.

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Synthetic organic pesticides

• Contact
• Kill on contact.
• Systemic
• Must be translocated to target organs
• E.g. 2-4 D a herbicide that is translocated to
  the roots.

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Information on pesticide structure and properties

• EXTOXNET pesticide information profiles
• http//ace.orst.edu/info/extoxnet/
• Pesticide information profile
• http//extoxnet.orst.edu/pips/ghindex.html
• Chem ID plus
• http//chem.sis.nlm.nih.gov/chemidplus
• TOXNET

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Some types of synthetic insecticides

• Chlorinated hydrocarbons
• Many of the early synthetic insecticides like
  lindane and DDT were highly chlorinated
  compounds.
• Many are very persistent.
• Half-life for DDT is greater than 150 years.
• DDT not high in toxicity for humans but severe
  problem for birds and other organisms.

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Lindane, still used in some products like lice
shampoo, persistent.
Cl
Cl
Cl
Cl
Cl
Cl
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DDT
Cl
Cl
Cl
Cl
Cl
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Some types of synthetic insecticides (cont.)

• Organic phosphate derivatives
• Cholinesterase inhibitors
• Some are very toxic
• E.g. parathion
• Some are less toxic
• malathion

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Parathion
O

N
O
S
O
P
O
O
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Malathion
O
P
O
S
S
O
O
E
t
O
E
t
O
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Some types of synthetic insecticides (cont.)

• Carbamates
• Carbofuran (Furdan)
• Bacterial insecticides.
• Bacillus thurengensis

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Carbofuran, a carbamate
O
O
O
N
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Herbicides

• Some classes of compounds.
• Chlorinated
• Trazines
• Phenoxy compounds
• Amides
• Nitroananilines
• Substitudes ureas
• Some have estrogen type activity

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2,4 - D not very persistent in soil
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Atrazine, a triazine
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Trifluralin, a nitroaniline
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Soil Fumigants

• Ethylene dibromide (EDB)C2 H4 Br2
• Used in nurseries etc. as a soil sterilent.
  Kills weed seeds and soil borne disease organisms
• Is being phased out because it is involved in
  destruction of the ozone layer

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WHO POPs lisiting

• World health Organization (UN) lists the dirty
  dozen Persistent Organic Chemicals
• USEPA POPs page
• http//www.epa.gov/international/toxics/pop.htm
• See dirty dozen.
• All chlorinated compounds

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Concern for pesticide toxicity to humans and
other animals

• Types of response to exposure
• Acute
• Chronic
• Intermittent
• Carcinigenesis
• Mutagenesis
• E.g. The insecticide methyl parathion, and
  herbicides alachlor (Lasso) and atrazine.

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Look up properties of methyl parathion and
aldicarb

• Pesticide Information Profile (PIP) in EXTOXNET
• http//extoxnet.orst.edu/pips/ghindex.html
• New Terms.
• ADI - acceptable daily intake (like NOAEL)
• HA - health advisory
• PEL - Permissible Exposure Limit (OSHA) air
  quality limit.
• TLV - Threshold Limit Value (worker)

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• Agency for Toxic Substances and Disease Registry
  (ATSDR)
• FAQs(limited list of chemicals)
• http//www.atsdr.cdc.gov/toxfaq.html
• TOXNET
• http//toxnet.nlm.nih.gov/

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Limits of pesticides in drinking water

• USEPA National primary drinking water standards.
• Sets Maximum Contaminant Limits, MCLG and TT
  values. http//www.epa.gov/safewater/contaminants/
  index.html and Table 10.2
• TT
• Lead and copper are regulated by a Treatment
  Technique that requires systems to control the
  corrosiveness of their water. If more than 10 of
  tap water samples exceed the action level, water
  systems must take additional steps. For copper,
  the action level is 1.3 mg/L, and for lead is
  0.015 mg/L.
• Secondary standards for nuisance chemicals

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Some SRV Limits
Source, I IRIS
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Environmental fate of organic pesticides

• Persistence
• Usually decay is first order.
• Half-life is useful
• Mobility
• Some are weak bases (amines, like trifluralin)
  and form cation at lower pH which affects
  solubility and binding to soils (behavior is pH
  dependent).

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Environmental fate of organic pesticides (cont.)

• Some are weak acids that form anions at higher pH
  values (e.g. in neutral or alkaline soils, like
  2,4-D
• Most of the binding is to soil organic matter.

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Fate of Gylphosate (Roundup) Fig. 16.10
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Mobility in and losses from soil

• Vapor losses
• Some pesticides have relatively high vapor
  pressure.
• Use Henrys Law
• Leaching in soils and mobility in aquifers.
• Use KD (for some this pH dependent)
• S KD Cw
• or
• Cw S/KD

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KOC

• Because most organic compounds are retained
  almost solely by organic matter use a KD 
  calculated in terms of organic C.
• KD KOCfOC
• Where foc is the fraction of organic C

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Estimate retardation factor

• ? is the soil bulk density and theta is the
  volumetric water content.

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Koc and half-life(mL/g L/Kg)
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Koc and half-life
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In class exercise

• Compare the retardation coefficients for
  glyphosate (Roundup) and atrazine in a soil with
  4 OM in a saturated soil. Make reasonable
  estimates for porosity and water content.

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Answer

• Koc- glyphosate - 10,000
• atrazine - 163
• Assume the OM 50 C, 2 C. COM 0.02
• KD glyphosate (10,000)(.02) 200
• KD atrazine (163)(.02) 3.2
• Assume soil is 50 water by volume and bulk
  density of 1.3
• R (1 2.6KD)
• Glyphosate - R 520
• Atrazine - R 9.3

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Mobility and persistence of some pesticides (Fig.
16.10)
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Persistence in the environment

• Biological decay
• Volatile losses
• Photodegradation
• On soil surface and in the air

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Vapor losses

• Atrazine- not volatile
• vapor pressure 2.89 X 10-7 mm Hg _at_ 25 oC
• Henry's Law constant 2.96 X1 0-9 atm-cu m/mol
  _at_ 25 deg C
• Pendimethalin (EPTC) - volatile
• vapor pressure 3 X10-5 mm Hg at 25 deg oC
• 8.6 X10-7 atm-cu m/mol _at_ 25 deg C

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In Class Exercise

• Calculate the vapor pressure of atrazine and
  pendimethalin in atm units.

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Answer

• 1.0 atm 760 mm Hg
• For Atrazine pressure (3x10-7)/760
• 4 x10-10 atm
• For EPTC pressure (3x10-5)/760
• 4 x10-8 atm

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First order biological decay rate

• A0 initial concentration
• t time
• A concentration at time t
• k rate constant

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In class exercise

• In adjacent plots 4 kg/ha of atrazine or
  alachlor are added to a soil. What is the
  approximate quantity remaining after 48 days
  assuming no leaching.

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Answer

• Half life - atrazine 48 d, alachlor 7 days
• Atrazine 2 kg/ha
• Alachlor - about 7 half lives-- 0.035 kg/ha

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Fate of atrazine

• Atrazine is commonly found in ground water and
  surface water.
• May be banned

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Changes due to Biotechnology

• B.T. Corn
• Bacillus thuringensis gene inserted in corn
• Roundup ready soybeans
• Genetically modified to be resistant to
  glyphosate a broad spectrum herbicide.

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Endocrine mimicking compounds and endocrine
disrupters

• DDT, Diethylstibersterol etc. mimic endocrine
  hormones.
• Feminization of fish alligators etc.
• Act at very low concentrations. See Environmental
  Estrogens and Other Hormones http//e.hormone.tula
  ne.edu/

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Suspected and Proven Environmental Estrogens

• Pesticides
• Insecticides such as o,p'-DDT, endosulfan,
  dieldrin, methoxychlor, kepone, dicofol,
  toxaphene, chlordane
• Herbicides such as alachlor, atrazine and
  nitrofen
• Fungicides such as benomyl, mancozeb and tributyl
  tin
• Nematocides such as aldicarb and
  dibromochloropropane)
• Products associated with plastics
• Plasticizers bisphenol A, phthalates

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• Pharmaceuticals
• Drug estrogens and birth control pills, DES,
  cimetidine.
• Ordinary household products
• Breakdowns products of detergents and associated
  surfactants, including nonylphenol and
  octylphenol.
• Industrial chemicals
• polychlorinated biphenyls (PCBs), dioxin and
  benzo(a)pyrene (a PAH)
• Heavy metals
• lead, mercury, and cadmium.

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Chemicals in household products

• National Library of Medicine website
• http//householdproducts.nlm.nih.gov/index.htm

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Summary

• A great number of synthetic organic pesticides
  have been developed
• Many more persistent and environmentally
  problematic compounds have been banned.
• The fate in soils and water is dependent on
  Henrys Law constant, Koc, and half life.

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Daily assignment

• Endrin and related compounds (aldrin and
  dieldrin) are tematicides that were used in
  abundance on the former Clark Air Force Base in
  the Philippines. Relatively large quantities of
  these pesticide were spilled at the Entomology
  Unit. Assume 50 kg was in the soil 20 years
  ago. How much do you expect now.
• Do you expect much leaching?
• Endrin is listed by WHO as one of the Persistent
  Organic Pollutants (POPs).

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• Chronic Toxicity of Endrin
• Pregnant women, particularly those whose diets
  contain large amounts of fish, are considered a
  special group at risk. Evidence that endrin may
  cause chromosomal damage in germinal tissue
  suggests that men and women of child-bearing age
  may also be a special risk group.

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